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Season 1 Transcript

“Posidonia Shale” Transcript and References

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.

Posidonia Shale - Alchetron, The Free Social Encyclopedia

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)

Bernhard Hauff im Schieferbruch_klein
Image from https://www.urweltmuseum.de/bernhard-hauff-am-04-juli-1866-vor-150-jahren-in-holzmaden-geboren/

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) 

Stenopterygius quadricissus SMF 457 (Senckenberg Museum), approximately 2.3 m long, showing a large dorsal fin and high-aspect-ratio caudal fin, reminiscent of the thunniform white shark, Carcharodon carcharias 
Image from https://www.researchgate.net/figure/Stenopterygius-quadricissus-SMF-457-Senckenberg-Museum-approximately-23-m-long_fig1_6772952

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.

Fossil blubber shows ichthyosaurs were warm blooded reptiles | New Scientist
Image by John Sibbick / Science Photo Library

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)

List of belemnite genera - Wikipedia
An interpretation of Belemnites. Image via https://www.wikidata.org/wiki/Q39957193

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.

Polycotylus - The Good Mother Plesiosaur? | WIRED

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.

An illustration of the ichthyosaur
Image by N.Tamura/University of Manchester

In fact research suggests that not only did the Stenopterygius refrain from cannibalization 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)

<begin soft music leading to break>

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.  

3 Groups of Ocean Animals - Welcome to Mr. Gulka's 5th Grade

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.

Holzmaden Pentacrinites Crinoid 1 – Indiana9 Fossils
Crinoid from Holzmaden

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)

John Nudds on Twitter: "The famous 18 m long specimen of the crinoid  Seirocrinus from the Holzmaden Shale. Urwelt Museum Hauff, Holzmaden.  Attached to a floating log ! #crinoids #Seirocrinus…  https://t.co/73hfAWBjKm"
The slab of crinoid fossils on a large driftwood

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.

Artist rendition of the Crinoid Raft. Image from https://royalsocietypublishing.org/doi/10.1098/rsos.200142

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)

figure1
Fossil of Belemnite attacking a fish. Image from 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)

Sven Sachs on Twitter: "Skeleton of Hybodus hauffianus, a shark from the  Lower Jurassic Posidonia Shale of Holzmaden (Germany), containing  belemnites as stomach content. On display at the Urweltmuseum Hauff in  Holzmaden. #
Fossil of the shark Hybodus hauffianus

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)

Dorygnathus banthensis (cast) at Göteborgs Naturhistoriska Museum 9000.jpg
Fossil of Dorygnathus, image by Gunnar Creutz.

<ending, soft music begins>

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!

References
-Boettcher, R. “New information on the reproductive biology of Ichthyosaurs (Reptilia).” Stuttgarter Beitraege zur Naturkunde Serie B (Geologie und Palaeontologie) (1990): 1-51.
Dick, Daniel G., Günter Schweigert, and Erin E. Maxwell. “Trophic niche ontogeny and palaeoecology of early Toarcian Stenopterygius (Reptilia: Ichthyosauria).” Palaeontology 59.3 (2016): 423-431.
-Etter, Walter, et al. “Posidonia shale: Germany’s Jurassic marine park.” Exceptional fossil preservation (2002): 265-291.
Hess, Hans. “Lower Jurassic Posidonia Shale of Southern Germany.” Fossil crinoids (1999): 183-196.
Jenny, Dominique, et al. “Predatory behaviour and taphonomy of a Jurassic belemnoid coleoid (Diplobelida, Cephalopoda).” Scientific reports 9.1 (2019): 7944.
Lindgren, Johan, et al. “Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur.” Nature 564.7736 (2018): 359-365.
Lomax D (2018) The Evolutionary History of Ichthyosaurs Capeia: 20181015.014
-Massare, J. A., and J. M. Callaway. “Live birth in ichthyosaurs: Evidence and implications.” Journal of Vertebrate Paleontology 8.Suppl. 3 (1988): 21A.
Motani, Ryosuke, Bruce M. Rothschild, and William Wahl. “Large eyeballs in diving ichthyosaurs.” Nature 402.6763 (1999): 747-747.
-Selden, Paul, and John Nudds. Evolution of fossil ecosystems. Elsevier, 2012.
Urwelt Museum Hauff Website
Simms, Michael J. “Contrasting lifestyles in Lower Jurassic crinoids: a comparison of benthic and pseudopelagic Isocrinida.” Palaeontology 29.3 (1986): 475-493.

By Andy

I'm a museum science educator with a passion for all things geek and natural science related!

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