Who: Triarthruseatoni Lagerstätte: Beecher’s Trilobite Bed (Ordovician, New York) What: These trilobites are preserved through pyritization which gives them a golden hue. An underwater avalanche, called a turbidity current, carried the trilobites into deep waters and buried them. The shock of the cold water killed them. Anaerobic bacteria within the soil reacted to the influx of sudden food and began to feed on them. As they feed, they released hydrogen sulfide which reacted with the soil’s iron and produced pyrite. The pyrite replaced the organic tissues preserving the legs, antennae, and internal organs. This makes these trilobites highly valuable in understanding what they looked like as most trilobite fossils do not have these soft body parts.
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!