The following was the script for the “Amber 101” episode for Fossil Bonanza.
Hello, my name is Andy Connolly and welcome back to another episode of Fossil Bonanza. This is a podcast where I look at fantastic fossil sites found across the world, called Fossil-Lagerstätten, and gush why these sites are so fantastic, what they can tell us about the ancient world, and how their fossils became preserved. This is a special episode for us as this is the first episode focused on amber! Amber! Yes, the almost fantastical substance who has played strong roles in both our cultural and scientific history. Not only has it been a part of our history for thousands of years, it continues to astound us to this day for the fossils they contain.
Fossils in amber, called inclusions, are among the best preserved fossils in the world. Amber’s unique properties are so amazing in halting decay that it seems the trapped insects are in stasis, ready to be woken again. The entombification of these creatures is so precise that you can find mummified insect organs, and even pollen and bacteria. Other, more “traditional” ways of fossilization can’t even approach the level of life-like quality that amber inclusions have obtained. Even in older times, many people were appreciative of these inclusions and a stanza I particularly like by 18th century, English poet, Alexander Pope goes
“Pretty! In amber to observe the forms Of hairs, or straws, or dirt, or grubs, or worms! The things, we know, are neither rich nor rare, But wonder how the devil they got there.”
Wonder indeed! But we’ll learn in this episode how the devil the insects got into the amber and why they are in amazing condition. And for our first amber episode we’ll dive into the Dominican Amber and appreciate the animals locked in its golden tombs. We’ll see crawling spiders, terrifying parasites, and ants, ants, ants! Ladies and gentlemen…(in the voice of John Hammond)…welcome to Fossil Bonanza!
All amber is formed from resin, a viscous substance used by trees to patch open wounds. Whenever a tree may experience damage from high winds or an insect invasion, it exudes the resin to patch these wounds and ensure that no further damage or invaders take place. The resin works very well as an insecticide as not only can the chemicals be deadly but they suffocate any would be intruders from getting into the tree. The resin then hardens and acts as scab for the wounded tree. (Grimaldi 1996, Nudds and Selden 2008)
Immediately, we begin to understand why amber is an excellent way to preserve fossils. Not only is there a high opportunity for insects (invasive or not) to be entombed, but the resin’s solidifying properties means it can survive transport and burial.
It should be pointed out, before we go any further, that resin and sap are technically different from each other even though they both come from trees. Sap is a watery substance that is full of sugars. Trees use sap to deliver nutrients and sugars, produced in the leaves, throughout its body. Maple syrup is derived from the sap of maple trees. Resin on the other hand is made from a tree’s bark and is much thicker. In fact, if you ever go hiking through a conifer forest, it’s highly likely you have stumbled upon resin and even felt its highly sticky, pine-like aroma on the tree’s bark. The resin is made of terpene chemicals which give it its unique properties.
It actually takes awhile for the viscous resin to transform into an amber gem. The transformation immediately begins once the resin has left the tree and is exposed to the air. Many of the resin’s chemicals will slowly evaporate over time while the rest will begin to link together in a process known as polymerization. This polymerization is what hardens the resin into amber. (Grimaldi 1996, Nudds and Selden 2008)
Before the resin can fully become amber, it reaches a stage called copal which is sort of like a proto-amber. Copal is very similar to amber in that it’s hard and can contain inclusions but there are a few critical differences. For one thing, it’s still undergoing polymerization and as such can be melted at lower temperatures than amber. It also isn’t as hard as amber and it can be dissolved in many kinds of acids. Many people have been fooled into thinking they have an amber which in fact it’s just a disguised copal. Copal isn’t as useful for paleontologists because they are relatively young, usually less than 50,000 years old or so. Real amber takes much longer to form and although there isn’t a hard date of when the transformation is complete. When transformed, the amber is harder and can withstand higher temperatures and is more resistant to acids. (Grimaldi 1996, Nudds and Selden 2008)
However, if the resin is exposed to air for too long during polymerization it can degrade and crack. The resin needs to be safely transported and buried somewhere to continue its transformation. That is why a lot of amber sites have been found in delta and lagoon deposits. As the resin drips off the tree or falls down with a broken branch, it can be carried by a fast moving current to a river where it will eventually be buried by the sand and mud. The burying mud is air-sealed and allows the water-proof resin to continue its amberfication. (Grimaldi 1996)
There’s also another problem with amber that we need to take into account. The trees that produce it. You see, not every tree can produce resin and even the ones that do may not produce a lot of it. The trees that DO produce a lot of resin are usually found in tropical areas possibly due to the high amount of invasive insects and fungi and the prominence of tropical storms that can break branches. (Martínez-Delclòs et al. 2004)
As such, we are seeing very specific circumstances for our Amber-Lagerstätten to happen. There needs to be an abundance of trees that can produce a high amount of resin who live near a delta or a river which can quickly transport and bury the resin so it can become amber. These are very rare circumstances which seems fitting given these are among the best fossils in the entire world. We’ll briefly mention a few global amber sites that satisfy these conditions but I want to talk about one more important piece to our Lagerstätte puzzle and that’s our inclusions, the poor critters who got stuck in the resin.
So one of the running themes on this show is fossilization bias, that not every type of animal or plant in an ecosystem will get preserved. Fossilization usually favors animals with hard parts located near areas that can bury them. Even our previous Lagerstätten demonstrated some form of bias despite their amazing fossils. The underwater mudslide in Beecher’s Trilobite Bed only buried the animals living on the sea floor while the Posidonia Shale only fossilized creatures who could swim or float in the open waters. The same thing is true for our amber fossils.
Obviously, size is going to be the first factor here that eliminates who can become an amber inclusion. If you’re big enough, you can easily escape the resin if you find yourself semi-trapped by it. An absolutely huge proportion of animal inclusions are less than an inch long so it’s no wonder a lot of them are arthropods like insects, spiders, and millipedes. It’s very rare to find vertebrate inclusions and when you do it’s just a portion of them like a body part of a feather or scales.
Also, as mentioned before, the trees that are likely to produce amber are found in tropical rainforests. So you’re eliminating animals and plants that can be found in other habitats like grasslands even if the two habitats are nearby. Even then, the many micro-habitats that reside in tropical rainforests are outstanding. Animals may specialize to live in just the trees, solely on the ground, IN the ground itself, and anywhere in between. I encourage you all next time you’re in a park or in your own backyard to observe a tree for a few minutes and then observe the ground nearby and see how animals and plants differ even when they’re fifteen feet apart.
The Dominican Republic amber is a fantastic example of this. Even though there are over 800 species of butterflies and is the third most species-rich insect on modern Hispaniola, only 7 species are known from amber. This is probably because they just don’t regularly interact with the resin trees. Meanwhile, ants make up 26% of all the amber inclusions due to their frequent crawling up and down the tree. (Penney 2010)
Then you have to take into account geologic time. Although resin has been found dated to about 300 million years old, it didn’t become abundant until about 120 mya during the age of dinosaurs. Why the sudden rise? Although there is some discussion on the matter, it may have been tied to the evolution of wood-boring insects. More resin means less intruders! (Martínez-Delclòs et al. 2004)
All of this means we have a very, very focused lens on our inclusions. Yes, the animals and plants may not wholly represent the world they lived in but danget are they not the most wonderful fossils out there. Let’s dive into what it takes for an insect to be immortalized in amber.
In general, one of the best ways for an organism to become a fossil is to remove it from the environment as fast as you can. You want to minimize the time between an animal’s death to its burial so you can preserve as much of it as you can. For many burying environments, this can take several days to hundreds of years before the animal remains are submerged. Resin can do this in minutes. As an insect, say an ant, is crawling on a tree, it walks across the resin and almost immediately becomes stuck in the viscous substance. While struggling in its gooey deathbed, another wave of resin buries it completely and submerges it. The ant dies through either suffocation or dehydration and exhaustion if it’s only partially submerged. Immediately, the resin begins it amberfication and the ant begins its fossilization.
Resin is incredibly good for decay prevention. I already mentioned before that resin is waterproof but some resin have anti-fungal or anti-bacterial properties that prevent tiny microbes from infiltrating and growing in its golden walls. Not all resin have this though as I came across an example of fungi growing off of an insect inside of the amber! It’s likely that the fungi was already leeching on the insect by the time the resin submerged it. The fungi then immediately grew off of its now dead host before it succumbed to its oxygen-deprived, resinic environment. Very cool! (Martínez-Delclòs et al. 2004)
However, in some cases, resin may be too good at its entombification. If an insect is quickly submerged, it can go through a process known as autolysis. The insect’s own cells and bacteria begin to break down the internal cells and tissues. When the resin seeps into the insect, it reacts with the internal soupy fluids and creates a bubbly sphere around the insect. The resulting process leaves a 3-dimensional, hollow cast of its inclusion. (Martínez-Delclòs et al. 2004)
Fortunately, there is a way nature can prevent autolysis from happening. If the insect is only partially submerged and dies before another wave of resin buries it, it can dehydrate to the surrounding environment. The lack of water halts any kind of bacteria activity that may destroy the internal organs. Once the resin submerges it, the insect will be mummified with its internal organs still in place. (Martínez-Delclòs et al. 2004)
This is when amber’s astonishing potential of fossilization occurs. If the tissue compounds are relatively stable we can detect the likes of organs like a spider’s book lungs, liver, or spinning glands. We can even identify cell organelles like mitochondria, ribosomes, and cell nuclei which is absolutely insaaaaaaaane (Nudds and Selden 2008).
Which leads me to the T-Rex in the room, the million dollar question, can amber preserve DNA?! To give an unsatisfying answer…it likely does not. DNA is highly unstable and even in the best of best conditions it’s rare to find DNA that’s over 100,000 years old. In the 90’s, during the Jurassic Park hey-day, there were a number of publications saying scientists were able to extract DNA from insects millions of years old but these results have since not been replicated and were likely due to lab error. The history behind the DNA Holy Grail is quite complex but fascinating so I’ll leave it to a future amber episode to tell that story. (Austin et al. 1997, Martínez-Delclòs et al. 2004)
In fact, DNA, and other organic compounds like proteins, in general do not have a stable shelf life, even in the comforts of an amber home. The body constantly needs to update, fix, and mend broken and degraded molecules to keep itself functional. Many of those compounds just break down over time while others, like the hard exoskeleton of insects, remain strong and relatively unchanged for millions of years. So even amber, despite its near perfect conditions of delaying decomposition, can only do so much for its imprisoned inclusions. (Martínez-Delclòs et al. 2004)
As we have seen, amber deposits just go all in on having high quality fossils. They’re the definition of a Konservat-Lagerstätten or a fossil site with excellently preserved fossils. The trade off being that A. only certain kinds of organisms can become fossils and B. there are relatively few amber sites found throughout the world. Even profitable amber sites struggle to produce inclusions as a majority of the amber stones have nothing in them. (Martínez-Delclòs et al. 2004)
One source I’ve read dating from the 90s said there are hundreds of known global sites that produce amber but only in trace quantities. About 20 of them have an abundance of mined amber. Even then, these 20 or so, from what I can tell, are overshadowed by four sites that dominate the amber literature. They are known as the Lebanon, Burmese, Baltic, and Dominican Amber sites. These big four sites again and again are praised for their scientific significance and their amber abundance. The Dominican and Burmese sites in particular have seen a rush of new species identified every year and keeping up with them is almost impossible. The fossils all four of these sites contain are magnificent and give a critical look into our world’s evolutionary history. Their importance cannot be understated. (Grimaldi 1996)
In another time, we will look at the Lebanon, Burmese, and Baltic sites but for now we’re going to end the episode here and resume next time for the Dominican Amber! Hope to see you then.
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-Austin, Jeremy J., et al. “Problems of reproducibility–does geologically ancient DNA survive in amber–preserved insects?.” Proceedings of the Royal Society of London. Series B: Biological Sciences 264.1381 (1997): 467-474. -Grimaldi, David A. “Amber: window to the past.” (1996). -Martı́nez-Delclòs, Xavier, Derek EG Briggs, and Enrique Peñalver. “Taphonomy of insects in carbonates and amber.” Palaeogeography, Palaeoclimatology, Palaeoecology 203.1-2 (2004): 19-64. -Penney, David, ed. Biodiversity of fossils in amber from the major world deposits. Siri Scientific Press, 2010. -Selden, Paul, and John Nudds. Fossil ecosystems of North America: a guide to the sites and their extraordinary biotas. CRC Press, 2008.
Hello and welcome back to our third episode of Fossil Bonanza. This is a podcast focused on amazing fossil sites found across the world called Fossil-Lagerstätten. Each episode we look at one of these Lagerstätten and learn why it’s special, how the fossils became preserved and the animals and plants found there. In the previous episode we looked at Beecher’s Trilobite Bed and its golden trilobites. And while that site was focused on a very select group of fossils that were excellently preserved, today’s Lagerstätte casts a much wider net and preserves an ecosystem of organisms. As such, we will be looking at a variety of animals and plants with our prehistoric creature of the episode being the ichthyosaurs!
Today’s Lagerstätte hails from Germany near the small town of Holzmaden. The fossils are excavated from the Posidonia Shale which itself is spread throughout Europe. Although the Posidonia Shale contains a multitude of fossils, it’s the Holzmaden locality that is the most well known within the paleontology community.
The Posidonia Shale was deposited during the Jurassic Period, about 185 million years ago over a period of about ½ million years. Back then, the ancient Tethys Sea separated the super continents of northern Laurasia and southern Gondwanaland. During this time, much of western Europe was submerged under the Tethys forming epicontinental seas that were rich with coral reefs. (Selden and Nudds 2012)
Reptiles like crocodiles and took advantage of this oceanic paradise and exploded with diversity and abundance. Other reptiles, like the notable plesiosaurs and ichthyosaurs found so much success that they became the top predators of their food chains. Fish of all kinds swam the seas such as sharks and even coelacanths. The invertebrates were numerous as well like the plant-like crinoids, spiral-shelled ammonites, and wondrous squids.
These creatures, including flying reptiles, and dead dinosaurs or plants that floated out to sea, are preserved in amazing detail at this fossil site. Their skin outline and body tissue are unmistakable. The detail is so remarkable that even squids can have their ink sacs and tentacles reproduced within the rocks. Very neat.
What was the cause of the extraordinary quality and quantity of fossils? And why is it that the Holzmaden quarry is most recognized for its fossils when the Posidonia Shale itself is spread throughout Europe?
Let me just say, before I go any further, that the literature on the Posidonia Shale is deeeeeeense. After all this rock formation has been researched and mined for hundreds of years. So I’m going to summarize the Posidonia Shale in a few paragraphs but I encourage my stratigrapher fans to read up on this as it’s complex but fascinating.
The Posidonia Shale is made up of organic shales broken up by limestone. The shale is incredibly dark due to the pyrites and the high concentration of organic material which can be mined for oil. The Shale is one of six major Jurassic stratigraphic units in Southern Germany. Each of the six units are designated with Greek letters with the Shale’s letter being “epsilon.” The Shale itself is further divided into three divisions labeled Epislon I through III with the I being the lowest layer and the III being the highest layer. Epislon II is the layer most recognized for its fantastic fossils. (Etter et al. 2002)
It may surprise you that despite the richness of life preserved in this specific layer of rocks, these rocks were formed in an inhospitable environment. The sea bottom was anoxic, meaning it lacked oxygen, and as such nothing could survive down there. One of the most telling signs of this is the rarity of fossilized organisms that lived on the seafloor like reefs. Despite the very occasional event where oxygen enriched the area, this was a dead zone. (Etter et al. 2002, Selden and Nudds 2012)
This dead zone gave us the foundation for these amazing fossils. When the marine animals die and fall to the seafloor, nothing would disturb them. There was no aerobic bacteria to eat away the skin and tissue and there were no scavengers to rip apart the animals and scatter their limbs. So these animals would just sit there, for thousands of years as they were slowly buried by sediment that would “rain” from above. Because of the delicate nature of this preservation, the fossils would be perfectly recreated in rock form, their skin and muscle carbonized, and their skeleton permineralized with pyrite and phosphate down to the tip of their tails. (Etter et al. 2002, Selden and Nudds 2012)
This is what makes the Posidonia Shale special and one of the most famous Lagerstätten in the world. Their fossils can be found in European museums and across the world. Whole walls and murals are filled with its incredible animals. And documentaries and TV specials, like “Walking with Dinosaurs” praise this wonderful formation. Its historical influence cannot be understated…
But why Holzmaden? After all the Shale covered a large swath of land! Does it have to do with geological exposure or is Holzmaden just extra special???
Actually, the answer to this question emerges from a combination of social happenstance, geological uniqueness, and the influence of one man and his descendents.
So, Posidonia Shale quarries have been active for at least several hundred years across different parts of modern day France and Germany and were mined for building material. The Holzmaden site itself was a relative latecomer. However, Holzmaden is lucky as the Shale only has 30 cm of overburden on top of it making it easy to access. The local Shale also had a layer of rock, called the “Fleins layer,” that was fantastic to use as oven bases, flooring, window sills, and even laboratory tables. This made it very profitable to mine. The constant mining would even spark fires due to the high amount of kerogen which could last for years! (pers comm. Maxwell)
So naturally, as people were quarrying for these money-making shales they would discover the amazing fossils which caught the interest of the nearby Tübingen University. The university had a strong geology and paleontology program and would regularly pay for these amazing fossils. The workers were thus incentivized to prepare these fossils carefully and sell the best ones to the university. One of these workers was a man named Bernhard Hauff who would become the most influential paleontologist in Holzmaden history. (pers comm. Maxwell)
Ever since he was a child, Bernhard Hauff, born 1866, was encouraged by his mother to look for fossils in his father’s quarry which was located near present day Holzmaden, Germany. Although the quarry’s purpose was to extract oil it also yielded a bevy of well preserved fossils that excited the inquisitive boy. These fossils were covered by shale and dirt which had to be carefully removed through careful preparation. Thankfully, Bernhard’s enthusiasm was matched by his gifted patience and focus (a trait I wish I had!) and he set to work preparing and cleaning the darkened fossils. (Selden and Nudds 2012)
His meticulous nature paid off and in 1892, the true potential of the Holzmaden shales was realized. When he was 26 years old, Bernhard prepared the first fossil of an ichthyosaur complete with a perfect outline of its skin. It was called Stenopterygius and at that time, the 1.2 meter long specimen became the most fantastic ichthyosaur fossil in the entire world. (Urwelt Museum Website)
Contemporary Paleontologist Dr. Eberhard Fraas of the State Museum of Natural History Stuttgart described this finding in the following opening sentence of his 1892 paper “I take the liberty of informing you all of a unique Ichthyosaurus which is capable of considerably expanding and transforming our knowledge of this strange group of animals, especially in relation to their outer appearance…”
Unmatched and unrivaled by its completion, it’s splendor, and its importance, this ichthyosaur, and the thousands that would follow afterward, would become the Holzmaden’s Shale most recognizable mascot and would put it on the map as a fantastic Lagerstatte.
For Bernhard Hauff, his passion, combined with his exquisite fossils, led to a once-in-a-lifetime success. He became so successful that he abandoned his oil endeavors and pursued fossil preparation full time. His work led to him publishing his opus, “Study of the Fossil Finds from Holzmaden in the Posidonia Shale of the Upper Lias of Württemberg” in 1921. And for his research and work on the ichthyosaurs, the University of Tübingen awarded him an honorary doctorate. (Urwelt Museum Website)
To this day the Hauff name continues to influence the Holzmaden fossils. In 1937, Bernhard Hauff and his son, Dr. Bernhard Hauff Jr built the first Hauff museum. Junior would take over as the curator in 1950 after his dad passed away and reconstructs the Hauff museum in 1971. Junior and HIS son, Dr. Rolf Bernhard Hauff would continue to publish new fossil literature and Rolf would take over as the new curator in 1990 after his dad passed away where he still curates today. To this day, the Hauff family continues to positively influence the community by not only excavating and preparing fossils but allowing the public to come in and look for fossils with a fee. It is wonderful to think that Holzmaden to this day contains a multigenerational tradition of enthusiasm, excitement, and passion for fossils. (Urwelt Museum Website)
Ichthyosaurs-blubbery, colorful, and motherly
Let us now ask the important question, what is an ichthyosaur? This is such a big question as this is one of the most iconic ancient animals ever discovered. The influence that these swimming reptiles had on the advancement of paleontology in its toddler days should not be underappreciated and deserves an episode all to itself.
In short, an ichthyosaur is a marine reptile that swam in the oceans during the age of dinosaurs. Although it was contemporaneous with dinosaurs, and has that notable “-saur” suffix, it was not a dinosaur rather an offshoot reptile that evolved alongside the dinosaurs. It looks remarkably like a dolphin as it had a torpedo-shaped body, a pointy nose, and a powerful fluked tail. The comparisons are so striking that many introductory biological textbooks frequently compare the ichthyosaur with that of a dolphin and a swordfish as an example of convergent evolution, that species independently adopt similar and successful body plans for the purposes of survival. Even ichthyosaur’s name denotes this similarity, “fish-lizard,” a reflection of the then debated classification that arose from its discovery.
The earliest known ichthyosaurs arose in the early Triassic, about 20 million years before the first dinosaurs. Already, they were adapted for marine life with their dolphin-shaped forms, long nose and tails, and limbs modified into fins. After the devastating Permian extinction, the ichthyosaur ancestors quickly took to the seas and shed their terrestrial adaptations. Overnight they became successful reaching cosmopolitan levels of distribution and occupying various niches including apex predator status. Although they found fantastic levels of success in the Triassic and Jurassic. They became extinct during the Cretaceous Period, due to competition from other marine reptiles and a mini extinction event that stressed their way of life. (Lomax 2018)
Perhaps one of the more distinguishing traits of the ichthyosaur are their eyes. Both absolute and relative to body size, ichthyosaurs had the largest eyes out of any animal! The largest was recorded at about 26 cm or just over 10 inches long. Which is absolutely insane. By comparison the largest eye from a living animal is the blue whale clocking in at 15 cm which is quite a bit smaller. Paleontologists infer that ichthyosaurs were probably deep divers and used their eyes to see low-light conditions. (Motani 1999)
What made Hauff’s 1892 specimen so unique and influential was its exceedingly excellent preservation. It was so perfect that it confirmed the existence of a fluked tail. You see, relatively decent ichthyosaur fossils would usually have a little “kink” on the end of its tail pointing downward. Some scientists equated this to simple rigor mortis and would even “correct” this bend to make it straight! Early artistic interpretations of ichthyosaur would even have them with this straight tail. With the skin outline preserved, not only do we see a fluke tail but a dorsal fin as well! Very cool. (Lomax 2018)
The fluked tail was one of many things we learned about ichthyosaurs thanks to the Posidonia shale. To put it bluntly, the Holzmaden ichthyosaurs changed the name of the fish-lizard game. It was as if the Holzmaden Quarry pushed the turbo button of advancement and we took off without a second thought. The Shale has taught us so many things about ichthyosaurs including their diets, life cycle, and even their color!
So first, many of the Stenopterygius specimens, amazingly, were preserved with their lunch. Inside them you can find belemnite hooks and fish scales; leftovers of the ichthyosaur’s lunch . For those of you who are unfamiliar with belemnites, they were cephalopods related to squids. Although extinct now, they were quite numerous during the age of dinosaurs. In fact, other marine animals, like plesiosaurs, also had belemnite hooks in their body. The fossilized hooks were on the belmnite’s tentacles and were used to grab and hold small prey. Since the hooks were harder than the softer body, the hooks were easily preserved within the ichthyosaur. (Selden and Nudds 2012)
Amazingly, Holzmaden also tells us that ichthyosaurs were more similar to dolphins than we originally realize! A 2018 multi-disciplinary study titled “Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur” revealed that ichthyosaurs had blubber based on chemical and structural analysis of fossilized tissue. This is amazing because this supports a homeothermy (or warmblooded) lifestyle for ichthyosaurs! Blubber is great for marine animals as it acts as an insulator against cold waters and can be used to metabolize energy for energetic activity. Ichthyosaurs likely used blubber additionally to streamline their bodies and make them more torpedo shape similar to dolphins. (Also, when I was doing research for this episode, I found out that leatherback turtles also had blubber so that’s pretty neat!)
This same study additionally concluded ichthyosaurs likely had a lighter colored belly and a darker colored back based on the presence of fossilized cells called melanophores. Melanophores are specialized pigment cells which can cause color change in an animal’s body; it’s useful in camouflage, body temperature regulation, and ultraviolet radiation-filtration. It’s likely ichthyosaurs could change color in response to their environment.
The skin tissue also revealed that ichthyosaurs lost their trademark reptilian scaly skin. Instead they had very smooth and slick skin, great for reducing drag in the water (the leatherback sea turtle does this as well).
Perhaps the most spectacular finds for the Holzmaden Quarry though are the ichthyosaurs preserved with embryos. And I’m not talking about ichthyosaurs fossilized near baby ichthyosaurs, I’m talking actual fossils of ichthyosaur embryos inside their mother.
This is insane.
And it’s not just one fossil, there are dozens upon dozens of mother ichthyosaur specimens with embryos still inside of them. A single mother could even have up to 11 embryos at once stored in their uterus. Sometimes, the embryos would be in perfect, articulated precision like their moms and sometimes they would be shattered, disconnected, and lay alongside their mother like a jumbled puzzle. (Botcher 1990)
Traditionally, the Holzmaden site has been viewed as a Stenopterygius’ nursery site. Of course the main evidence of this is the high amount of expecting mothers and juveniles but we can look at other pieces of evidence as well. Since the fossils are in great condition and don’t show any sign of stress before death we can propose that the ichthyosaurs died very near their burial site and not violently carried off from a storm. We also see periodic accumulations of mothers over time suggesting they may have returned here when expecting. (Massare 1988). This hasn’t been rigorously investigated though and may need further research to shed light on this.
With these incredible finds, it may not surprise you that some paleontologists initially thought the embryos were cannibalized young swallowed whole by the adult Stenopterygius. We can easily put these to rest based on the anatomical position of the embryos AND the belemnite hooks that I talked about earlier. Paleontologist Ronald Botcher published a study translated “New information on the reproductive biology of ichthyosaurs (Reptilia)” in 1990 where he tackled this question and concluded after studying 46 mothers that not only were the young Stenopterygius embryos, but there was no way the adults could swallow the babies because their throat and stomach were way too small.
In fact research suggests that not only did the Stenopterygius refrain fromcannibalization but the adults and the children weren’t even eating the same foods. Based on tooth morphology and stomach contents, young Stenopterygius would mainly eat small fish. But once full grown they would only eat squids and other cephalopods. This is an incredible adaptation and ensures healthy offspring growth by limiting competition from the same species. I should stress how amazing this find is because it’s incredibly hard to get diet data in the fossil record and we got it here not only for the adults but for kids as well! It’s incredible. (Dick et al. 2016)
What’s interesting though is that based on the embryos positioning, they were likely born tail first into the ocean. Many of the fossils have the embryos arranged with their head pointed towards the mother head. And guess what?? Dolphins ALSO birth their young tail first although there are exceptions. This is done to minimize drowning for the air-breathing animals.
In fact there are a few fossilized Stenopterygius which show the moment of birth. One example of these incredible fossils is a mother, displayed out neatly on the black shale. Her flipper digits still connected, her ribs arranged in parallel arcs, and her vertebrae sweeping outward to a thin tail that turns downward forming the lower fluke. Her baby is displayed in similar perfection with the biggest flaw being its tail which slightly twists around in an awkward angle. The baby’s body is out except for its tiny mouth, whose long jaw still resides within the mother. This is called viviparity or live birth as opposed to oviparity which is egg hatching. Although there is debate how much of these “fossilized births” are actual births as opposed to decaying discharge, there is no doubt that ichthyosaurs gave live birth. And it may surprise you that live birth was probably one of the most important adaptations for ichthyosaurs.
Fossil evidence suggests that ichthyosaurs evolved live birth relatively early in their history, even before they took to the sea. There’s even a very primitive ichthyosaur from the Early Triassic that was also preserved with live birth! Only in this case the embryo was coming out head-first (like a land animal) and not tail-first (like a marine animal). Why is this important? Well, think of a sea turtle. Sea turtles have to crawl onto land to lay their eggs. That means sea turtles have to be able to both swim and be able to move on land. But for ichthyosaurs, they could forgo land altogether! Nothing’s holding them back! Because they could already give live birth, they quickly evolved their fish-like features and soon became dominant animals in the water. All because of live birth. (Motani et al. 2014, Lomax 2018)
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The Stenopterygius fossils are among the most amazing and awe-inducing fossils in the world. Their beauty can be appreciated by anyone, and you can take away a deep sense of appreciation of them. As I reflect on these wonderful fossils, I can’t help but compare Hauff’s ichthyosaurs with Beecher’s trilobites from the previous episode. Two Lagerstätten, although vastly different in time period, location, and animals preserved, are united by their significance. They reveal crucial information like their animal’s appearance, their diet and digestive system, and their life cycle. Their findings pushed the field of paleontology forward leaps and bounds breaking down old ideas and building new ones in their place. And finally, their importance was fully realized in the 1890s led by a passionate scientist with a steady hand and a lot of patience. It just brings a smile to my face just thinking about these amazing fossil sites…
The Animals of the Jurassic Tethys Sea
With my appreciation and gushing of ichthyosaurs satisfied I want to turn now to the other animals that lived alongside the fish-lizards in our ancient, European seas. Because of the Posidonia Shale’s unique conditions, we are seeing a bit of a bias in who gets fossilized and who doesn’t. Remember, the prevailing hypothesis of the Posidonia Shale is the anoxic sea bottom which led to a fantastic preservation of fossils. However, that means we’re seeing a lot of animals who may have swum above the ocean floor, like our ichthyosaurs, and not as much as animals who may have lived on the bottom, like clams, who would’ve found the conditions too intolerable. True, there have been a few fossilized animals that likely lived on the seafloor but they are few and far between compared to those who live near the surface.
Before I get into the animals I want to introduce new vocabulary that paleontologists frequently use to describe oceanic creatures and their ecological niches. Broadly speaking, we can divide an oceanic creatures’ lifestyle into one of three categories; plankton, nekton, and the benthic zone.
Planktonic organisms are those who freely float in the water, like dust particles in the air. They don’t have full control of their movement but that’s not necessary for them to survive. They can consume other floating microparticles and some of them get their energy from sunlight. Organisms like algae, bacteria, and jellyfish are examples of this group.
Nektonic organisms are those who can freely swim in the various oceanic depths. Their movement is not defined by oceanic currents. The classic fish, whales, and sea turtles easily fit this category.
Finally, the benthic zone encompasses animals that live at the bottom of a seafloor but can also include lake and river bottoms. Epifaunal benthos are organisms who live on the sediment surface while infaunal benthos are those that live beneath the sediment. A whole host of organisms include this group such as coral, sponges, crabs, clams, starfish, and etc.
As you can tell, you don’t have to be closely related to each other to be in a certain niche. In fact, many animals transition from one niche to another as they grow older. Remember the trilobites in the last episode? The baby Triarthrus would have a planktonic lifestyle as they float in the water but as they grew older they would slowly settle to the seafloor and move around as a benthos creature.
So in our case, for this episode, we’re seeing favoritism towards nektonic and planktonic animals due to their independence from the sea floor. As such, we can reconstruct some of this ancient ecosystem to get an idea what this Jurassic community looked like.
First, what few benthic creatures we have include bottom feeding fish, burrowing bivalves like clams, as well as very small snails, sea urchins and brittle stars. These fossils are few and far between though and only need a passing mention for the purpose of this episode. (Selden and Nudds 2012)
More numerous and interesting are our hitchhiking invertebrates! We see a number of brachiopods (which look like clams but are a completely different group of animal), bivalves, and crinoids who latch themselves onto floating logs or debris and just float on the water’s surface. As this weird, organic flotsam carries on, they feed off of the rich plankton life, grow, and release floating larvae who begin the hitchhiking process all over again. Some paleontologists even argue that bivalves latch onto living ammonite shells and get a free ride as the ammonite swims around! (Selden and Nudds 2012)
Before I go any further I want to dive briefly into crinoids. In a future episode, I will cover this amazing group of animals in more detail similar to the ichthyosaur but for now I want to give a special shout out to them. Long story short, crinoids are animals related to starfish but look more like an underwater flower. In fact, they’re commonly referred to as “sea lilies.” Typically, they have a long stalk attached to the ground, a bulbous head where the mouth and anus is, and long feathery tentacles that extend from its “head.” They use their feathery tentacles to eat by suspension feeding by capturing small particles of food in the water. Although crinoids are still alive today, they were nowhere near as dominant as they once were millions of years ago.
Normally, when a crinoid dies its soft tentacles rot away while oceanic currents disrupt the more durable stalk into many disk-like pieces called columnals. The columnals are usually the only crinoid fossil you’ll find and even then the jumbled mess makes it near impossible to reconstruct the original crinoid. But the Holzmaden fossils have none of that and preserve the entire crinoid in all its feathery glory. In all honesty, if it wasn’t for the numerous and jaw-dropping ichthyosaurs, Holzmaden would have likely been known for its crinoids. But alas, the crinoid has to play second fiddle and that’s not right! So let’s talk about them and what makes them so special here.
There are two species of Holzmaden crinoids Seirocrinus and Pentacrinus; of the two, the Seirocrinus is the most common so we’ll be focusing mainly on them. I really want to stress how incredible these fossils are. Huge, I’m talking huge slabs of rocks have been found displaying these fossils. The Hauff museum has the largest slab measuring 18 by 6 m with a 12 m long driftwood covered in bivalves and roughly 280 crinoids! The whole slab took 18 years to prepare before it was finally displayed in the Hauff museum when it reopened in 1970. (Hess 1999)
These huge slabs take up walls in their respective museums and are so large that it’s hard to take photographs encompassing the whole thing and reproduce them in journals or articles. I highly encourage you to look at a photo of one of them, which I will provide on my website or you can google it, as it’s incredible. A mass of crinoids just erupts from the engulfed driftwood, and creates a mural of stalks that intertwines and spreads outward from the dense center. And the crinoids in general can be incredibly long. The longest one recorded was about 20 meters! Fantastic.
With these incredible dense clusters of bivalves and crinoids, some paleontologists question the floating log hypothesis and wonder if the crinoids instead grew off of a sunken log on the seafloor. There are actually many pieces of strong evidence that support a floating log hypothesis and not a seafloor hypothesis. First, the crinoid size is proportional to the log size meaning larger logs will have larger crinoids. This means the large logs are able to support larger crinoids. Additionally, the crinoids themselves are incredibly light compared to their dense bivalve roommates so even massive crinoids would only have a small effect on the log’s floating capabilities. Next, modern relatives of the fossilized driftwood have been observed floating a minimum of a couple of years and could theoretically stay afloat up to 10 years. This may not seem like enough time but the Seirocrinus crinoid likely rapidly matured within their first year of birth as indicated by their huge spacing of growth lines (kind of like the growth lines of a tree). Finally, one of the most compelling pieces of evidence, I think, is that many of the logs are discovered on top of the crinoids. And if they had grown off of the logs on the sea floor then the crinoids should’ve been buried on top of them instead. This means when the log eventually sank, they fell on top of some of the crinoids.
The previous information came from an article written by Dr. Michael Simms in 1986 and it’s one of my favorite articles I have read for this episode. He looked at the argument of a plankton life vs a benthic life and systematically argues for the plankton hypothesis by using evidence from taphonomy, structural morphology, ontogeny, and geology to make his case. I did not include all of his points but I do recommend you guys to check out the article which I shall provide a link to on the website.
When the ancient driftwood did eventually sink, by succumbing to water loggedness or just too many hitchhiked clams, the log would fall quickly downwards and drag the crinoids with it. The crinoids would then flip upwards and act as underwater parachutes. The crinoids would become entangled with each other and the log as they eventually land on the seafloor. Unable to support themselves upward, the heavy crinoid heads would flop downwards and lay undisturbed for thousands of years in the anoxic waters until they were eventually buried and fossilized. (Hess 1999)
The crinoids weren’t the only invertebrates in our Tethy’s sea, we also have the nekton based (or free-swimming) cephalopods like squids, belemnites, and the iconic ammonites. Molluscs in general make up the most common animal fossil in the Posidonia Shale so you can get some real nice specimens. One of my favorites are fossils of the squid-like Clarkeiteuthis still in the process of attacking their prey! Four separate fossils have been found with fish still enwrapped in the predators’ tentacles. And what’s really cool is that these ancient squids attacked their prey like some modern squids. They bring their prey close to their mouth and cut into the fish’s spine with its sharp beak, paralyzing it. However, through either inactive movement of the squid or the deflation of the fish’s swim bladder, the two sank to the bottom of the ocean where the squid died from the oxygen-deprived conditions. The two would lay buried still entangled in their life and death struggle. So awesome. (Jenny et al. 2019)
And now we come to the vertebrates, our last group of nekton animals. Obviously, fish are incredibly common and come in many varieties with over 20 species documented. They range from a few cm to several meters across with the biggest ones being the sturgeons. As mentioned before many of their scales have been documented in the stomachs of ichthyosaurs and as regurgitate which is quite fascinating. One notable absence are bottom dwelling fish which makes sense given the inhospitable conditions at the seabottom. We also find shark fossils which is quite impressive. The shark’s cartilage body normally rots away but here we see a nice black outline of them which gives us an idea what they looked like and how big they were. (Selden and Nudds 2012)
Then there’s our marine reptiles. We already tackled one of them, the ichthyosaurs, but there are other reptiles here as well. Plesiosaurs and marine crocodiles compete with the ichthyosaurs for resources. However, their presence is much rarer. Plesiosaurs were among the top predators of these oceans and likely ate fish, squids, and ichthyosaurs depending on the species. The largest of which was Rhomaleosaurus which could grow up to 23 feet long. (Selden and Nudds 2012)
Of particular note are the crocodiles where some of them have the amphibious lifestyle of modern crocs and others have adapted to a fully marine life. The most common crocodile is the Steneosaurus which had a long and narrow snout like a gavial and likely caught fish by ambushing them and quickly trapping them in their toothy jaws. So impressive are the Steneosaurus fossils that they serve as a mascot of sorts for the Urwelt Museum Hauff as seen on their website, museum logos, and street signs. (Selden and Nudds 2012)
Finally, we conclude our episode with the non-marine animals. There was only one dinosaur found in the Posidonia Shale and that was a tibia belonging to a long neck dinosaur called Ohmdenosaurus which was named after the nearby village it was found. More interesting are the two species of flying reptiles, Dorygnathus and Campylognathoides which are only known from a few specimens but are preserved quite amazingly well. It’s likely they quickly sank after they drowned in the ocean as they’re found with their bones mostly intact and in amazing flashy, dance-like poses! I’m hoping that we’ll continue to find more of these flying critters and learn more about their airborne lives. (Selden and Nudds 2012)
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The Posidonia Shale continues to deliver new insight into the life and times of these ancient Jurassic creatures. Even now, over a hundred years after their discovery we’re still learning new things about the fossils and tinkering our current perspective. Within the last ten years we have seen newly described species of plesiosaurs, squids with fish still in their tentacles, and ichthyosaurs with blubber! It just floors me. The quality and quantity of these fossils has allowed us to reconstruct almost every aspect of their life; a feat that few fossil sites can achieve. Who knows what new information awaits for us? Perhaps we’ll learn new things about the life of a plesiosaur. Maybe we’ll discover a new species of crocodile. Or maybe we’ll find a crinoid that is over 50 yards long!! That would be crazy! Whatever the case I’ll be looking forward to it.
I hope you enjoyed this episode of Fossil Bonanza. These episodes take a lot of time to research, write, and produce so if you liked this episode and want to see more please subscribe, leave a comment, and heck, tell me of a time you went fossil collecting! I would love to hear that and I can read it as well at the end of the next episode. I want to give a very special thank you to Dr. Maxwell and Dr. Massare who gave me insight on the ichthyosaurs and the Holzmaden site which helped me greatly for this episode’s research.
Also, I’ll be releasing a transcript of this episode next week on my website Fossilbonanza.com so if you want to read it or know somebody who would benefit from a transcript then check it out. I’ll also be releasing a few, short articles on the Posidonia Shale this month on Fossilbonanza.com that will cover some other interesting stuff on this Lagerstätte. Finally, I’ll leave a list of references I used for this episode on my website. If I can, I’ll even provide a link to the actual research paper provided it’s legally available to the public.
Thanks again and see you next time where we cover the Dominican Amber, our first amber episode. Should be great!
For eight years, William Valiant, a one-armed carpenter and fossil enthusiast had been looking for the find of a lifetime. He and his half-brother, Sidney Mitchell, would spend their days off in the countryside, near their home of Rome, New York, looking for a particular fossil. It started from a chance find, when William found an odd fossil at Six Mile Creek in 1884. It was a golden leg of a trilobite, an ancient sea creature that looked like a squashed centipede. Up until then, no one knew what a trilobite’s leg looked like. This leg was amazingly preserved, unlike what William had ever seen before, and he was enamored by its design. He knew that if he could find the rest of the fossil, he might find something even more remarkable, their antennae. Paleontologists, up until then, had thought trilobites had antennae but the lack of fossilized evidence meant that this was mere postulating. William knew that if he found the trilobite, antennae, legs and all, he would be making history.
So for eight years he and his brother would search for these fossils. Again and again, nothing. Finally, he found the fossils; they were buried deep along a hillside and nestled within a layer of shale just 4 cm thick that was practically indistinguishable from the meters of rock that surrounded it. Yet within these 4 cm of rock were some of the most amazing fossils found by that date. These trilobites were golden as if touched by Midas himself. They were preserved in stunning detail with their many legs in neat rows and their original 3-dimensional body only slightly squashed by the layers of rock above it. And there, in miraculous detail, were the thin antennae arching like a whip. He had finally found his white whale, or in this case, his golden trilobite. Few other trilobite fossils can match the level of stunning quality and detail of these golden trilobites. But how did this happen? Why are the trilobites preserved so perfectly?
In this episode of Fossil Bonanza, we will answer these pertinent questions and dive into the wonderful Lagerstatte of Beecher’s Trilobite Bed. Let’s take a look!
<Music intro> History of Beecher’s Trilobite Bed
Hello and welcome to Fossil Bonanza! My name is Andy Connolly and this is a podcast where we look at unusual fossil sites around the world called Fossil-Lagerstätten. In our first episode, we talked about the history of paleontology, how it can be very hard for a critter to become a fossil, and the different types of Fossil-Lagerstätten. This is our second episode and the first to focus on a particular fossil site. For our first episode, I wanted to focus on something that was small but impressive and I thought Beecher’s Trilobite Bed fit the bill.
If you were to step back to upstate New York about 445 mya, you would not be strolling through a cool, temperate forest but swimming in a sub tropical sea. It is the late Ordovician Period and the world is very different than it is today. Dinosaurs, reptiles, mammals, or amphibians haven’t evolved yet. In fact, life on land is restricted to just a few small colonizers of bugs and moss. The sea in New York hosts a variety of weird and wonderful creatures who thrive in this world. One of which are the trilobites; a very successful ancient group of bug-like animals who could be found in every sea across the world. And on one fateful day, these trilobites and their ecological partners, would be preserved in a freak accident that would make them one of the best fossil sites in North America.
Beecher’s Trilobite Bed, found within the Frankfort Shale of the Utica Formation, is a Konservat-Lagerstätten, a Lagerstätte with very high quality fossils. There’s not a lot of fossils here but dang are they not just outstanding! The fossils are made of pyrite which gives them a most luxurious sheen compared to the more drab and dull-looking fossils you may see in museums. This gives the golden fossils a very sharp image contrasting the surrounding shale which is a dark gray, almost black color.
You may be thinking that Beecher was the scientist who discovered the these pyritic fossils. Well, although Charles Beecher was instrumental in the site’s history, he wasn’t the first to discover it.
Like a lot of famous fossil finds, Beecher’s Trilobite Bed was found by luck, persistence, and an amateur. As introduced in this episode, the fossils were found by William Valiant of Rome, New York. While walking along Six Mile Creek, he found a chip of shale with trilobite appendages on it and immediately recognized its importance. As we’ll get into later, trilobite legs are rarely preserved in the rocks. Even rarer were fossilized antennae which paleontologists hypothesized trilobites had but lacked crucial evidence to support it. Valiant recognized the importance of his lucky find and vowed to locate the site that entombs these creatures. It took him eight years but he and his brother found the trilobite bed in 1892. Antennae, appendages, and all.
Finding these golden critters was like hitting the paleontological jackpot and Valiant was excited! He wrote to several regional paleontologists and sent them fossil samples of his instrumental find. One of them was WD Matthew who recognized their significance and proclaimed in 1893 using the samples as examples that trilobites had antennae. Valiant also wrote to the famous Professor Marsh at Yale. Marsh referred this information to a man he thought would take a great interest in the pyritic trilobites, a younger colleague named Charles Beecher. Beecher was Yale’s first invertebrate paleontologist and was Curator of Geology beginning in 1891 (as a side note, an invertebrate is an animal that doesn’t have a backbone like we do such as insects, corals, clams, and worms). The excited Beecher wasted no time; he took a lease on the land in 1893 and started excavating the fossils that same year. When Beecher found the trilobites he excitedly wrote to Marsh “I feel quite well satisfied now with the results of this trip, and think we can nearly control the antennae business. I look forward with pleasure to working up the collection.” You see? I wasn’t kidding about the antennae, it was like the paleontological equivalent of seeing dollar signs.
Upon fossil extraction, Beecher prepared the 4 cm long trilobites by experimenting with different tools. When it was quite apparent that a simple chisel and hammer weren’t going to cut it, he tried acid which ended up dissolving both the stone and the fossil. Dental tools worked well but couldn’t uncover the delicate legs very well. But finally, Beecher found that an eraser with a soft rubber was the best tool as he could rub away the soft shale without damaging the fossil. It was so refined he could even clean out the spaces inbetween the trilobite legs. He was so good at it that William Dall of the Smithsonian wrote “aided by his remarkable manual dexterity, mechanical skill, and untiring patience, [he] worked out the structure of antennae, legs, and other ventral appendages with a minuteness which had previously been impossible.”
Beecher’s meticulous preparation, research, and publications on the trilobites is the reason why the quarry is named after him. He gave detailed analysis of the trilobites’ anatomy and described larval stages of key trilobite species using the specimens. His artistic reconstructions of a trilobite were so incredible that his artwork was reproduced many, many times in textbooks and brought fame to his quarry. In fact, before he published photographs as proof, some scientists regarded his drawings as so outlandish that they were unreliable. They were that game breaking. Unfortunately, before Beecher could publish more papers on the triobite’s anatomy and family relationships, he passed away at just 47 in 1904. Thankfully, his student Percy Raymond completed his work in 1920 when he became a professor at Harvard University and Beecher’s work is still available today for all to read.
Beecher believed his quarry, and another quarry that was located just upstream, was completely excavated but attempts have been made decades after his death to confirm it. This proved difficult as many people had trouble trying to find it. But in the 1980s the bed was rediscovered by two fossil collectors after carefully studying old photographs of Beecher’s site. The site has since been further excavated by paleontologists from the Smithsonian, American Museum of Natural History, and the Yale Peabody Museum and continues to be a treasure trove of fossils to this day.
Trilobites and their Fossilization
So, it may not come as a great shock to you that most of the discovered fossils of Beecher’s Trilobite Bed are trilobites with just a few creatures from other animal groups. So…what is a trilobite exactly?
The trilobite is probably the most iconic fossil just behind the ammonites (the spiral shaped fossil). It’s more than likely you have seen one before and there’s a good chance that if you have a fossil collection you have a trilobite. Trilobites kind of look like pill bugs but a bit wider, a more prominent head, and generally larger. The name “trilobite” means “three lobe” in reference to their general body plan. They have an axial lobe, which runs centrally from their head to tail, and is flanked by two pleural lobes that make up their sides. Despite the great difference in size and shape among trilobites, they all have these three lobes.
Trilobites are in the arthropod group of animals which contains critters like insects, spiders, crabs, and basically anything that has a hard exoskeleton and jointed legs. A lot of people like to compare trilobites to the modern horseshoe crab which I’m a bit uneasy at. True, horseshoe crabs are marine and they’re arthropods but they’re not descendents of them; they are as closely related to them as they are to spiders.
In fact, trilobites are basically their own group of arthropods! Broadly speaking, there are five groups of arthropods; the crustaceans (which include lobsters and crabs), the myriapods (centipedes and millipedes), the chelicerates (spiders, scorpions, and horseshoe crabs), the insects, and finally the trilobites. I have read estimates that over 20,000 species have been named so far which is incredible. By comparison there are just over 5,000 species of modern mammals. Indeed, trilobites were a very successful group of animals.
You may have noticed that among the five arthropod groups only trilobites aren’t alive today. Trilobites, unfortunately, are currently extinct. They evolved very early about 521 million years ago and rapidly flourished. However, as time went on they began to die off and their numbers were greatly reduced following many extinction events. The greatest extinction of all time, the Permian Extinction, was the one that wiped them out 252 million years ago. So they lived for about 270 million years which is a fantastic achievement. (As a frame of reference, dinosaurs, who appeared after trilobites went extinct, lived for about 165 million years.)
Okay, so since trilobites are a very common fossil, why do paleontologists make a big deal about Beecher’s Trilobite Bed? This…is where the story gets interesting!
One of the reasons why arthropods are the most dominant lifeform on the planet is their exoskeleton. Their exoskeleton is made of mostly chitin which is a rather tough and resilient material. In trilobites, crabs, and lobsters, the shells are further reinforced by the hard mineral calcium carbonate. The exoskeleton is the main source of strength and speed for arthropods. With it, they’re able to exploit environments and fill in roles that may otherwise be left open.
The biggest drawback of the exoskeleton is its rigidity. Unlike our bones or a shell of a tortoise, an arthropod’s exoskeleton does not grow with the animal as it ages from larva to adult. Every time it gets too big for its exoskeleton, it sheds it, crawls out of it like some sort of freaky body bag, and allows its new exoskeleton to expand and harden. This process is called “ecdysis” and the discarded old exoskeleton is called an “exuviae.” A well known example of this are cicadas who, after they crawl out of the ground like cute zombies, will shed their old skin, unfurl their wings, and begin their wonderful life above ground. You’ll see their exuviae everywhere, especially when a group of them come out of the ground at the end of their 17 year cycle.
Trilobites go through ecdysis as well! Paleontologists hypothesize that trilobites start its ecdysis by latching its tail to the bottom of the ocean and wiggling back and forth. The sides of their head, called a cephalon, would then split wide open and allow the trilobite to escape. Their exuviae, now completely discarded, could be easily buried by sand and mud and eventually fossilize. Given that trilobites can sometimes be a foot long, they likely shed their skin at least several times a year. This means (ready for the mind blowing part?) that a single trilobite can leave multiple fossils of itself! In fact, most trilobite fossils found in the world are just their exuviae! Whole species and genera are described from their discarded exoskeleton alone. It’s honestly quite rare to find the actual trilobite body.
Now remember what I said a moment ago that trilobites use calcium carbonate to reinforce their shells? That shell’s durability gives it strength to fossilize properly. HOWEVER, a trilobite’s legs and antennae do NOT have that mineral! That means they are much softer AND are more likely to rot away before being preserved! It’s very much like a bird’s feather or a mammal’s hair, if you find a trilobite’s antennae, you found something good.
Now it falls into place. Why our amateur fossil collector, Valiant, was so keen in finding those trilobite fossils. When he stumbled upon that shale chip of a fossilized trilobite leg, he knew how valuable it was and why he had to find the rest of it. Why he had to spend eight years of his life looking for that bed. To find trilobites that were not just their exuviae but of their legs, and antennae, and anything else that could be preserved in those black layers of shale.
That is the significance of Beecher’s Trilobite Bed. Not just because they’re golden or preserved in pyrite but because they store the memory of the trilobite itself, body and all. We know exactly what trilobites look like thanks to those 4 cm layers of rock. This is why Beecher’s Trilobite Bed is a Konservat-Lagerstätten.
How the Trilobites got Preserved
So how did these trilobites gets preserved? And why did pyritized trilobites only happen in this very specific, 4cm layer of rock when the surrounding shale layers only have bits and pieces of fossils?
Organisms can become fossils in several different ways but one of the most prominent methods is called “permineralization.” This occurs when pores inside an animal or plant’s cells are filled with mineralized water; this water can come oceans, lakes, or even rain. As the water evaporates or moves out of the pores, it leaves behind minerals that were dissolved in the water. The minerals will crystalize and reconstruct the tissue shape of the organism and can even preserve the original organic material. Petrified wood and bones commonly go through permineralization to become a fossil. As we progress on Fossil Bonanza, we will return to permineralization again and again and how it affected our Lagerstätten.
So, permineralization can use different minerals to preserve the organism. Silica is a really common mineral in permineralization and can be frequently seen petrified wood. If the animal is preserved fast enough, some minerals work very well to protect soft tissues like carbonate or phosphate. For Beecher’s Trilobite Bed, the presence of sulfur changes the trilobite into pyrite which is called pyritization.
Pyrite, also known as Fool’s Gold, has a simple chemical formula of iron disulfide and is a very common Earth mineral especially in marine sediment (if you ever go to gem and mineral shows you’ll see these minerals on sale relatively cheap). I really like pyrite because they’ll grow into these beautiful golden cubes. Sometimes they’ll have cubes upon cubes and create a stunning geometric shape to them! They’re very wonderful. (and as a side note, I love teaching rocks and minerals to my students because they’ll get to see pyrite and debate if they pyrite cube is gold or not which is quite amusing.)
A source for pyrite’s commonality are humble organisms with an intense name; anaerobic sulfate-reducing bacteria. There’s a lot to unpack here! Anaerobic sulfate-reducing bacteria. Let’s break that down. First, bacteria are single-celled microorganisms that are smaller than our animal cells and can live in all sorts of crazy environments like the hot springs of Yellowstone. In fact, many bacteria don’t need oxygen to survive. These bacteria are called “anaerobic” while those who do need oxygen are called “aerobic.” Aerobic organisms use oxygen to breathe while anaerobic organisms use other molecules instead. What’s wild is that many anaerobic bacteria find oxygen toxic and can even die from oxygen poisoning! Okay, so if they don’t need oxygen, what do they use?
Anaerobic organisms can use such molecules as sulfate, nitrate, or iron to produce energy and quote-unquote “breathe.” For sulfate-reducing bacteria, they use sulfate (which is made of one sulfur and four oxygen atoms) and reduce it to hydrogen sulfide as an end product. You may have experienced sulfate-reducing bacteria in real life as they’re the source of rotten egg smell or the sulfurous smells from salt marshes. The hydrogen sulfide is important to us as when it reacts to the sediment’s iron minerals they form pyrite! (this, btw, is a simplified look at the process and is about as in-depth as we’ll get for our fossil podcast).
Despite the commonality of these bacteria along with sulfur and iron, the process to turn animals into pyrite is actually pretty rare. Even then, when pyritization does happen it’s only the animal’s hard parts that are preserved and nothing else. Only in very specific circumstances can soft-part preservation happen. So what was it that led to the trilobite preservation?
Before the trilobites came, the sulfate-reducing bacteria were living in an ocean floor with a severe lack of organic food. We know this because many of the surrounding rock layers had a plethora of fossilized burying organism but that 4 cm layer of rock had nothing, it was an underwater desert. This was a time when the bacteria were starving. But what the layer DID have was iron and lots of it. All of this iron and all of these starving bacteria were primed to make our Lagerstatte happen. It just needed one more key ingredient.
That key ingredient came in a flash. Based on the fossils and the sediment patterns, we can infer that the trilobites were dumped into their current position from somewhere upshore by a turbidity current (basically an underwater avalanche). We know this for several reasons and the first of which are the trilobites which are arranged roughly parallel to each other. This indicates that a strong unidirectional-moving current carried the trilobites all at once before burial. This also means that the trilobites were already dead by the time they got buried because otherwise they would have attempted to escape and disrupt their alignment. Furthermore, the sediment patterns in Beecher’s Trilobite Bed match modern turbidity currents which is quite a smoking gun. You can see evidence of this in the rock layers as it starts with a heavily eroded base followed by a gradual decrease of sediment size upward due to a weakening current.
As such, we now have all our pieces to reconstruct the scene of the crime. First, a turbidity current was triggered by some unknown force and swept across the ocean floor. It picked up the trilobites and buried them further downwards. The shock of the deeper water’s cold temperatures likely killed the trilobites quickly which kept them in place. Now buried, the trilobites were protected from any scavengers who may tear apart the soft limbs.
The influx of this fresh meat triggered the sulfate-reducing bacteria who immediately went to town on the trilobites’ shells, antennae, and legs. The bacteria produced hydrogen sulfide which was trapped by the overlying sediment. The water, rich with iron, seeped in through the trilobites’ pores and reacted with the hydrogen sulfide. Pyrite precipitated out of the water and replaced the trilobite’s original body, reconstructing it with the golden mineral. Since the sediment was still loose and non-compacted, the trilobite bodies’ original 3-dimensional form was replaced by the pyrite recreating even their soft tissues and structures. In a matter of months the reactions ceased and the trilobites laid undisturbed for over 400 million years, waiting patiently to be discovered by William Valiant.
The Trilobites in Beecher’s Bed
Now that we understand how our trilobites got preserved let’s focus on the animals themselves. What have we found in these rock layers and what can we infer from the fossils?
Although trilobites dominate the fossil assemblage, both in abundance and in notoriety, we see other animals that are typical of the Ordovician period. These mainly include the clam-like brachiopods and the colony-oriented graptolites. As these animals make up a small percentage of the fossils, and aren’t particularly special, we will put them aside for now. Perhaps in a future episode I will talk more about them and their global commonality but for now they’ll just be a footnote for us.
Even among our trilobites there is one species that dominates the rest called Triarthrus. It’s so abundant it makes up about 85% of the fauna recovered from the bed! Growing up to 4 cm long, Triarthrus is probably one of the most recognizable species of trilobites in the world thanks to Beecher’s Trilobite Bed. The original drawings of Triarthrus by Beecher were quickly favored in paleontology textbooks and research papers and they were recreated again and again. The clean visuals, the many spindly legs, and the long and flowing antennae were easy on the eyes and mind. If you ever see a recreation of a trilobite, it’s a good chance it’s a Triarthrus.
The plethora of Triarthrus that make up our death assemblage means we can gleam some juicy information that may otherwise be lost with just the one individual. For instance, the amazingly preserved legs and gills give us an idea how Triarthrus moved and fed along the ocean floor. We also have an idea of their overall shape given their 3-dimensional burial with minimal squashing. However, one of the more incredible things about these fossils are their preserved guts! Since the pyrite recreated the original structure of the trilobites’ internal organs, we can peak inside them using X-rays and see what they look like. It’s preserved so well that we can determine a trilobite’s gut is very similar to a crab or spider’s gut. Isn’t that wild???
These detailed anatomical recreations of Triarthrus are quite useful in reconstructing the overall arthropodal family tree. Thanks to these remarkable trilobites along with other fossilized evidence, paleontologists infer that trilobites’ closest living relatives are the crustaceans and the chelicerates (who again include the horseshoe crab, spiders, and scorpions).
The abundance of Triarthrus fossils also means we can think about their life cycle. Adult Triarthrus are very common in Beecher’s Trilobite Bed but what’s notably absent are the juveniles. Although you can find fossils of juvenile exuviae, just like any other trilobite fossil, their actual bodies are completely absent. This is also interesting given that only a small percentage of trilobites reach adulthood. So why is Beecher’s Trilobite Bed so adult-heavy?
Well, based on Beecher’s Trilobite Bed and other Triarthrus fossils found elsewhere, we have a pretty good idea what their lifecycle was like. After hatching from eggs less than a millimeter long, the baby trilobites would float in the water for a month or so as a suspension feeder. As they grow older and shed their exoskeletons, they gradually transitioned to a seabed-only lifestyle where they scavenged on carcusses and hunt any small critters they dig up. Based on their exuviae, it’s likely they lived to about four years of age and probably had an annual breeding season like modern crustaceans.
Given this context, it makes sense why the adults were preserved and not the juveniles in Beecher’s Trilobite Bed. When the turbidity current came it only affected the adults and not the kids as they were having a good time up in the water column, relaxing, and taking it easy. Meanwhile, the adults were swept away by the underwater avalanche and died for simply being too old. This also explains why there’s a notable absence of other sea dwellers as they were above the disaster zone. Very cool.
There are a few other trilobite species found here but they are quite rare. One of the more interesting species is Cryptolithus which, unlike Triarthrus lacked eyes! They had these sensory pits instead which helped them observe the low-light world of the ocean floor. We also find mainly baby specimens of Stenoblepharum andit’s likely they spent their time on the sea floor before moving up to the water column (basically the complete opposite scenario of Triarthrus). But like I said, both of these species are quite rare and really, a more accurate name for Beecher’s Trilobite Bed should be Beecher’s Triarthrus Bed! Hm, probably for the best that we stick to the original; it’s a lot more brand friendly!
So as we close our first Lagerstätte-themed episode I want to reflect on the importance of Beecher’s Trilobite Bed. I think Beecher’s Trilobite Bed is a great example of a Konservat-Lagerstätte because of those amazing trilobites. The fact that we can preserve the legs, antennae, and even their gut, preserved in multiple specimens is amazing! We can recreate their life cycle, their feeding habits, and their way-of-life from these precious fossils. We can also learn more about how Triarthrus, and in general trilobites, fit in the overall tree of life, how they relate to modern animals and, on the flip side, how we can use modern animals to infer about their lifestyle. And to this day, we see Beecher’s drawings of trilobites as they fill our textbooks and minds of these once bygone creatures. It’s all just very remarkable and poetic.
As we progress in this series, I have a feeling we will be seeing the influence of Fossil-Lagerstatten, whether subtle or not, come again and again. The gaps in our Earth’s history are so wide and so thin that any remarkable fossil will give a peak into a world that is otherwise lost. Their fossils fill museum displays, painted into murals, and make up so many iconic ancient animals that we see on TV and in the movies.
When I teach my students geology, I sometimes get asked how much money the pyrite is worth. And my response? It’s not the financial value that makes it important, it’s what we can learn from the object. And though the trilobites’ pyritic makeup does make them amazing to behold, what we can learn from them, I would argue, makes them many times more special. William Valiant knew this as well and it’s what made his eight years of searching for the golden trilobites worth it.If you liked this episode and would like to hear more please subscribe and check out my Fossil Bonanza blog where I post articles and more podcast episodes. If you have any thoughts or what you would like to learn more og let me know in the comments! If you also want to read more about Beecher’s Trilobite Bed I’ll include research papers that are free for the public as well as Beecher’s original papers. One thing that I didn’t mention were the Sulfur isotopes that were influential in the pyritization process. I’d figured I already went technical enough as is in this episode so I kept it on the lighter side. And check out the books Fossil Ecosystems of North America by Nudds and Selden and Exceptional Fossil Preservation by Bottjer, Etter, Hagadorgn, and Tang. These books talk about Beecher’s Trilobite Bed along with other unusual fossil sites. Also check out Richard Conniff’s House of Lost Worlds which provided some good insight into the trilobite bed. Thanks again for watching and I hope to see you again next time!
Hey everyone! Excited news. I’ll be premiering my upcoming podcast, “Fossil Bonanza,” on October 14th, National Fossil Day! It’s been a long time coming and after working months of researching, writing, recording, and editing, I’ll finally premiere the podcast. I’m very, very excited! I’m very satisfied with the end result.
So far, barring any major surprises, this is what the schedule will look like: October 14th: Episode 1-Introduction and Episode 2-Beecher’s Trilobite Bed October 28th: Episode 3-Posidonia Shale November 11th: Episode 4-Amber Introduction November 25th: Episode 5-Dominican Amber December 9th: Episode 6-Jehol Biota Part 1 December 23rd: Episode 7-Jehol Biota Part 2 January 6th: Episode 8-Naracoorte Caves
The first five episodes are already finished and the last three just need to be recorded and edited. Depending on how well Season 1 does I will work on Season 2 but that will take awhile. Thankfully, since I have experience with this and know how to produce these I somewhat expect the process to be a little faster? But we’ll see.
I’ll post a link to the feed on my website and I’ll post rough transcripts of the episodes the day they premiere. Looking forward to it!
Who: Maple Seed Lagerstätte: Florissant Formation at Florissant Fossil Beds National Monument in Colorado What: This is a maple seed preserved in shale at Florssiant Fossil Beds NM. The park is well known for its amazingly preserved insects and plants which are usually quite rare in the fossil record. It dates to the Eocene about 34 million years ago. Plant fossils like redwoods, hickory, elms, and rubber trees indicate that the area was once warm and humid; a far difference from its modern cold and drier climate. These plants were preserve in a lake which had occasional algal blooms. When plants or insects landed on the algal mat, they get entrapped and then fall to the lake’s bottom. The algae holds the leaves together and delicately buries them leaving a thin carbon film.
Who:Pumiliornis tessellatus Lagerstätte: Messel Pit in Germany What: Pumiliornis is the oldest known flower-visiting bird in the fossil record at 47 million years old (Eocene Epoch). This is based on preserved pollen grains in its stomach! This strongly supports nectar-eating behavior further compounded by its beak which was long and likely flexible similar to hummingbirds. Fish and seeds have been found in birds stomach before, like the Jehol Biota in China, but pollen-finds are rarer and usually nectar-visiting behavior has to be inferred based on the fossil’s anatomy which can be difficult. Pumiliornis is not closely related to any known modern pollinators.