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Vertebrate Paleontology

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Mesozoic Monthly: Champsosaurus

Good news everyone: it’s September! We’ve made it to month nine of 12! Sometimes it feels like this year will never end. I take comfort in the idea that if life can survive the traumatic Cretaceous-Paleogene (K-Pg) extinction that killed the non-avian dinosaurs, I can make it through 2020. One of the survival champs of the K-Pg extinction was Champsosaurus, a superficially crocodile-like reptile belonging to the extinct group Choristodera.

The skeleton of Champsosaurus laramiensis looks superficially like that of a crocodilian, but this is the result of convergent evolution. Choristoderes (like Champsosaurus) and crocodilians lived contemporaneously for at least 150 million years, until the choristoderes said “after a while, crocodile!” and went extinct. Photo by Triebold Paleontology, Inc., used with permission.

The class Reptilia encompasses an incredible variety of animals: lizards, snakes, turtles, crocodilians, pterosaurs, dinosaurs, and even birds are just a few of its members. In addition to the familiar reptiles that live today, many other reptile groups thrived for millions of years before eventually going extinct. It’s easy to think of dinosaurs like Tyrannosaurus or Triceratops when we talk about extinct reptile groups, but in reality, many extinct groups of animals with no living relatives escape the public eye. Choristodera, an order within the class Reptilia, is one of these groups. Choristoderes were semi-aquatic or aquatic carnivorous reptiles that evolved during the Mesozoic Era (the Age of Dinosaurs) and died out in the Cenozoic Era (the Age of Mammals). Just because they went extinct does not mean they were unsuccessful; the group survived for at least 150 million years! Like many animals, a rapidly shifting environment was probably the source of their demise. Until that point, choristodere evolution was able to ‘keep up’ with the changing times, including the monumental global changes that came with the K-Pg extinction. The combination of a massive asteroid impact in what’s now Mexico, extensive volcanic activity in India, and worldwide climatic shifts resulted in the extinction of over 75% of all species. Research on choristodere teeth suggests that they beat the odds by adapting to new prey.

When you think of an aquatic carnivorous reptile, you probably think of a crocodilian – and that’d be right! The crocodilian body plan is a very successful build for hunting prey in the water. As another aquatic carnivorous reptile, Champsosaurus evolved similar traits. This is an example of convergent evolution, in which unrelated species develop similar characteristics to deal with comparable circumstances. (You can read about more examples of convergent evolution in the January edition of Mesozoic Monthly about the sauropodomorph dinosaur Ledumahadi.) Some of the shared features between Champsosaurus and crocodilians include long, muscular jaws for catching fish, eyes at the top of the head for peering out of the water, and a flattened tail that was paddled side-to-side for propulsion. Of course, Champsosaurus and the rest of the choristoderes had many features that set them apart as well. Unlike crocodilians, which have bony armor called osteoderms embedded in their skin, choristoderes just had skin covered with tiny scales. In addition, crocodilians have nostrils on top of their snouts so that they can breathe while lurking beneath the surface of the water; choristodere nostrils were at the end of their snouts, so that they could stick the tip of their nose out of the water like a snorkel and breathe from down below.

A right dentary (tooth-bearing lower jaw bone) of Champsosaurus sp. from the Upper Cretaceous of Wyoming in Carnegie Museum of Natural History’s Vertebrate Paleontology collection (specimen number CM 96509). The bone is facing upwards, so you’re looking down on the teeth. Check out the dark ‘stripes’ on the enamel of each tooth. These unusual enamel striations are a hallmark of neochoristoderes, the particular choristodere subgroup to which Champsosaurus belongs. Photo by Joe Sawchak.

The traits we see in the skeleton of Champsosaurus help paleontologists paint a picture of its behavior. Instead of lurking at the surface of the water, Champsosaurus would wait on the bottom of a shallow lake or stream for prey to come close, lifting the tip of its snout out of the water to breathe. When a tasty fish approached, it would spring off the bottom with its powerful legs and snatch it with its toothy jaws. Despite having strong legs, Champsosaurus was not adapted to a terrestrial lifestyle. In fact, adult males may not have been able to leave the water at all! Fossils attributed to females have more robust hips and hind limbs, allowing them to crawl onto land to lay eggs. According to this hypothesis, the less-robust males would have been restricted to an aquatic-only lifestyle.

Some of the freshwater environments that Champsosaurus inhabited were relatively cold, but that wasn’t a big deal; choristoderes may have been able to regulate their body temperature (a talent known as endothermy or ‘warm-bloodedness’). Crocodilians, by contrast, live in warm, tropical habitats because they are not capable of regulating their body temperature and rely on the sun to warm their bodies (aka ectothermy or ‘cold-bloodedness’). This would explain why choristoderes were able to live further north than crocodilians. However, it seems that crocodilians had the right idea; temperatures around the tropics change less during cooling and warming periods than those at higher latitudes. So, when the current Antarctic ice sheets began to form and the planet started cooling, the temperate choristoderes had to deal with more environmental change than the tropical crocodilians, and finally went extinct. I think the moral of the story is, we would all be handling 2020 better if we lived in the tropics!

Lindsay Kastroll is a volunteer and paleontology student working in the Section of Vertebrate Paleontology at Carnegie Museum of Natural History. Museum staff, volunteers, and interns are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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The Bromacker Fossil Project Part IX: The Dissorophoid Amphibians Tambachia, Rotaryus, and Georgenthalia, Capable Travelers

New to this series? Read The Bromacker Fossil Project Part I, Part II, Part III, Part IV, Part V, Part VI, Part VII, and Part VIII.

The Dissorophoidea are a group of ancient amphibians that were common about 290 million years ago, when the animals fossilized in the Bromacker quarry were alive. The group consists of small to medium-sized water- and land-dwelling vertebrates (animals with backbones) that ate invertebrates (e.g., dragonflies, cockroaches, and millipedes) and vertebrates smaller than themselves. Most scientists agree that modern amphibians (frogs, salamanders, and the reclusive, worm-like, subterreanean caecilians) had their origins among the dissorophoids. Three disssorophoid species are currently known from the Bromacker quarry, and at least one and possibly two more are yet to be described. Two of the described species, Tambachia trogallas and Rotaryus gothae, are members of the dissorophoid subgroup Trematopidae, and the other, Georgenthalia clavinasica, is a member of the subgroup Amphibamiformes. All of them inhabited the terrestrial realm and most likely only returned to water to breed.

Photograph (left) and reconstruction (right) of the skull of the holotype and only known specimen of Tambachia trogallas in dorsal (= top) view. Photograph by the author (2013) and reconstruction by Stuart Sumida, modified from Sumida et al. (1998).

The first trematopid discovered in the Bromacker quarry was found by Thomas Martens in 1980, and it is represented by a poorly preserved skull and skeleton. Stuart Sumida, as lead author of the scientific paper presenting it, coined the name Tambachia trogallas. Tambachia refers to the Tambach Formation, the rock unit preserving the Bromacker fossils, which in turn is named after the nearby village of Tambach, which is now merged with the adjacent town Dietharz to become Tambach-Dietharz. “Trogallas” is from the Greek “trogo,” meaning munch or nibble, and “allas,” meaning sausage, in reference to all of the bratwurst consumed during Bromacker field seasons by the authors of the Tambachia publication (Stuart, Dave Berman, and Thomas). The state where the the quarry is located, Thuringia, is famous for its bratwurst and rightly so. A hot bratwurst for lunch was always welcomed when we experienced what Thomas called “Scandanavian summers,” which were cold and rainy. The then-Bürgermeister (mayor) of Tambach-Dietharz, who also was a butcher, was so thrilled by the name that he hosted an annual bratwurst lunch featuring brats that he’d made. This tradition was carried on by subsequent Bürgermeisters, though they had to buy the featured main course.

Bratwurst lunch in the Thuringian Forest close to the Bromacker quarry. Seated are (from left to right) unknown, Rainer Samietz (then Director of the Museum der Natur Gotha, now retired), Thomas Martens, Johannes Müller (then field assistant and now Professor at Museum für Naturkunde, Berlin), the author, and Stuart Sumida. The Bürgermeister is standing behind Thomas. His bratwurst grill, which he transported in his SUV, is between the vehicles. Photo by Dave Berman (2002).

Skull and partial skeleton of Rotaryus gothae in left lateral (= side) view. Photograph by the author, 2008.

When Rotaryus gothae was found in 1998, only part of the skull was exposed, so we took out a large block expecting a complete skeleton to be preserved, as typically occurs at the Bromacker. Once I began preparing the specimen, however, I was extremely disappointed to find that only a small portion of the body of the animal was present. At least we had the skull, the most scientifically important part of the skeleton. Dave led the scientific study of Rotaryus, and he named it in honor of the Gotha Rotary Club, an organization that generously provided financial support for Bromacker fieldwork. Dave sent the head of the Gotha Rotary Club three choices for the fossil’s name, and the members voted on which one to use.

At the time that Tambachia and Rotaryus were named and described in scientific publications in 1998 and 2011, respectively, trematopids were known only from the USA. Their presence at the Bromacker added to the growing list of animals previously thought to only inhabit North America, such as Diadectes and Seymouria. In hindsight, it is not surprising that trematopids also had a more cosmopolitan distribution, because although they are amphibians, their skeletons were strong enough to support their body out of water and withstand the effects of gravity, thus enabling them to disperse to far corners of the world (though hypotheses of such dispersal assume that no physical or climatic barriers prevented movement).

I was the lucky person who discovered, in 2002, the amphibamiform Georgenthalia clavinasica. I recall lifting up a block of rock that I had loosened with a hammer and chisel and seeing two ghostly eye openings staring back at me. The rest of the skeleton was preserved with the skull, but unfortunately all bone beyond the skull was extremely eroded from groundwater and had the consistency of mashed potatoes.

Photograph (left) and reconstruction (right) of the skull of Georgenthalia clavinasica in dorsal (= top) view. Both by Jason Anderson, 2007.

After Tambachia was named, the Bürgermeister of the nearby village of Georgenthal, whose boundaries included the Bromacker quarry, approached Dave about naming a fossil after his village. Dave then asked Jason Anderson, a colleague from the University of Calgary and the project’s lead researcher, to name it Georgenthalia. Jason created clavinasica from the Latin “clavis” for key, and “nasica” for nostril, in reference to the fossil’s keyhole-shaped nostril, a unique feature that differentiates Georgenthalia from all other amphibamiforms.

Jason, as lead author of a 2008 scientific publication, concluded that the relationship of Georgenthalia to other amphibamiforms was uncertain. Computer algorithms are used to analyze relationships of organisms by tabulating the proportion of unique characteristics shared between the members of the group under study. A group of organisms that share unique characters is called a clade, and members of a clade are considered to be more closely related to each other than they are to members of other clades. These relationships are depicted in a diagram of relatedness called a cladogram.

A 2019 study by dissorophoid expert Rainer Schoch (Curator, Naturkunde Museum Stuttgart) that investigated the ancestry of modern amphibians revealed Georganthalia as a member of a clade that also includes modern amphibians (see figure below). The fossil Gerobatrachus, however, is more closely related to modern amphibians than it is to the clade consisting of Georgenthalia and Branchiosauridae (a group of aquatic amphibamiforms). This indicates that although Georgenthalia (along with Branchiosauridae) is in the clade containing modern amphibians, it is not directly ancestral to them.

Cladogram showing the relationship of Georgenthalia (far right) to modern amphibians. Cladogram modified from Schoch (2019); images of modern amphibians from Wikimedia Commons.

Stay tuned for my next post, which will feature yet another terrestrial amphibian, a fossil from a locality in Tambach-Dietharz.

If you would like to learn more about Tambachia, Rotaryus, or Georgenthalia, please follow the links below.

Tambachia

Rotaryus

Georgenthalia

Amy Henrici is Collection Manager in the Section of Vertebrate Paleontology at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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The Bromacker Fossil Project Part X: Tambaroter carrolli, an Amphibian with a Wedge-Shaped Head 

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Mesozoic Monthly: Aspidorhynchus

As we all seek out responsible ways to enjoy our summer months while the world continues to respond to COVID-19, many of us are embracing the therapeutic effects of the great outdoors. One popular activity, especially in and around the Three Rivers, is fishing. Some modern fishes look positively primeval, as if they were hooked straight out of the Age of Dinosaurs and reeled into the present day. For July’s edition of Mesozoic Monthly, our star is Aspidorhynchus, one of the weird and wonderful fishes that inhabited the oceans of the Mesozoic Era.

Let’s start with a quick lesson on fish, for context. There are two main groups of bony fishes. One group, the class Sarcopterygii, are called the lobe-finned fishes because they have fleshy, limb-like fins that they use to paddle through the water like oars. The first vertebrates to go on land were sarcopterygians, and the descendants of these adventurous fish eventually evolved into amphibians, reptiles, and mammals – including us! Despite their prolific limbed descendants, sarcopterygians make up only a small fraction of fishes today. The vast majority of fish belong to the other class: Actinopterygii, or the ray-finned fishes. These fishes have delicate ray-like bones supporting thinly webbed fins instead of the meaty fins of the sarcopterygians. Actinopterygians are so successful that they dominate both freshwater and saltwater ecosystems, thrive in a variety of habitats, and fill various ecological niches. Such diverse lifestyles mean that actinopterygians come in many shapes and sizes. Nemo (a clownfish) is an actinopterygian. So is the barracuda that ate his mother, the catfish in the Monongahela River, and the unfortunate goldfish you won at the carnival as a kid. Most fossil fishes, like Aspidorhynchus for example, are also actinopterygians.

Aspidorhynchus is an extinct member of the order Holostei, nested, in diagrams of relatedness, within the class Actinopterygii. The only members of the Holostei today are gars and bowfins. Superficially, Aspidorhynchus looks like a gar, but it is more closely related to bowfins. Its name means “shield snout,” in reference to its pointy, swordfish-like upper jaw. Unlike swordfish, which lack teeth as adults, this snout was filled with many sharp teeth. The limited flexibility of its skull restricted its diet to tiny fish, two inches (5 centimeters) in diameter at the largest. Aspidorhynchus was not very large itself, its slender body only growing to approximately two feet (60 centimeters) in length. It was covered with ganoid scales, which are hard, diamond-shaped scales made with a shiny compound called ganoin. Only a few types of modern fishes have ganoid scales, including gar, sturgeon, and paddlefish.

Jurassic feeding frenzy: the pterosaur (flying reptile) Rhamphorhynchus and the predatory fish Aspidorhynchus attack a school of smaller fish. Usually, the baitfish were the only casualties here, but once in a while, everybody lost (see below!). Art by RavePaleoArt on DeviantArt, reproduced with permission.

Although species of Aspidorhynchus lived in the Jurassic and Cretaceous periods, we know that it encountered the same struggles as some modern fish due to several remarkable fossils. Just like swordfish, the pointy snout of Aspidorhynchus frequently got it into trouble by impaling other animals! The abundance of fossil evidence for this was provided by the unique conditions of the habitat preserved in the famous Solnhofen Limestone of Germany. In the Late Jurassic, this area was an isolated series of lagoons that accumulated a bottom layer of anoxic brine, which is extra-salty, low-oxygen water where oxygen-dependent (aerobic) life cannot survive. Despite this, the surface still teemed with life: fishes and marine reptiles dominated the water, small non-avian dinosaurs scurried along the shore, and pterosaurs (flying reptiles) and archaic birds flew overhead. The fish-eating pterosaur Rhamphorhynchus seems to have been a fairly frequent victim of the snout of Aspidorhynchus, with multiple fossils documenting unfortunate collisions in which the fish’s snout pierced and became entangled in the wing membrane of the pterosaur. (For a summary of pterosaur wings, check out the March edition of Mesozoic Monthly, on Nemicolopterus.) It’s obvious from the size of the animals that neither was trying to eat the other, but somehow, they became stuck together. As the two animals struggled to survive, they slowly drifted downward into the anoxic brine, where they suffocated and settled onto the bottom of the lagoon. If any other animals had tried to eat or otherwise disturb the corpses, they would have died in the brine as well, so the fossils of the Solnhofen Limestone are typically pristine and undisturbed by scavengers.

Three views of the most famous (and probably the most beautiful) Aspidorhynchus vs. Rhamphorhynchus fossil from the Upper Jurassic Solnhofen Limestone of southern Germany. Avid fisherman Matt Lamanna, the head of Vertebrate Paleontology at Carnegie Museum of Natural History (CMNH), jokes that the Aspidorhynchus looks angry, as if it’s mad about getting its snout stuck in the Rhamphorhynchus and dooming them both. Sorry Matt, this is just a quirk of preservation – the compression of the Aspidorhynchus skull during fossilization gave it the appearance of having grouchy eyebrows that weren’t there in life. You can learn more about this specimen in a paper by Frey and Tischlinger (2012).And if you want to see real fossils of both of these animals in person (albeit preserved separately), come visit the Solnhofen case in CMNH’s Dinosaurs in Their Time exhibition.

Because Aspidorhynchus lived only during the Mesozoic, there’s no chance that a modern-day angler will ever hook one. But should you find yourself fishing in one of Pennsylvania’s rivers or lakes this summer, and manage to land a gar or bowfin, pause for a moment and reflect on the ancient legacy of these fishes – a heritage that dates to the Age of Dinosaurs.

Lindsay Kastroll is a volunteer and paleontology student working in the Section of Vertebrate Paleontology at Carnegie Museum of Natural History. Museum staff, volunteers, and interns are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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The Bromacker Fossil Project Part VIII: Martensius bromackerensis Honoring a Colleague

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The Bromacker Fossil Project Part VIII: Martensius bromackerensis, Honoring a colleague

New to this series? Read The Bromacker Fossil Project Part I, Part II, Part III, Part IV, Part V, Part VI, and Part VII. 

Adult, holotype specimen of Martensius bromackerensis. Image digitally assembled by the author from five photographs taken by Diane Scott (Preparator at University of Toronto Mississauga [UTM]), 2010–2013. The specimen was collected in several large blocks.

The formal publication of some of the Bromacker discoveries took more time to complete than others, and our most recently pubished fossil, Martensius bromackerensis, holds the record in that regard. Four nearly complete specimens of Martensius were collected from the Bromacker quarry between 1995–2006. The first, discovered by Thomas Martens and his father Max, came from a jumbled pocket of fossils. Unfortunately, muddy groundwater had penetrated cracks in the subsurface of this portion of the quarry and coated and eroded bone present along these cracks. Despite this damage and the lack of a skull, we could identify the specimen as a caseid synapsid (synapsids, also known as mammal-like reptiles, are a group of amniotes whose later-occurring members gave rise to mammals).

Drawing of 1995 Martensius bromackerensis specimen. Because the specimen was collected in numerous pieces of rock, with parts of some bones exposed on apposing rocks, Scientific Illustrator Kevin Dupuis (UTM) had to first draw the bones exposed on each piece and then assemble all of the drawings digitally. Dotted lines indicate bone impression in the rock. Arrows point to healing scars from two fractures in the last right rib. Additional healing scars can be seen in preceding ribs. This animal apparently survived a serious injury. Modified from Berman et al., 2020.

The next specimen was discovered in 1999 by Georg Sommers (Preparator, Museum der Natur, Gotha), who prepared the fossil. It consists of a vertebral column, ribs, some limb bones, and a few scattered skull elements. Unfortunately, a more complete skull was needed to allow for comparison to other caseids, some of which are based only on skull material. It wasn’t until the discovery of two more specimens in 2004 and 2006 by Stuart Sumida and Dave Berman, respectively, that the long sought-after skull was found. Preparation of these specimens took a long time due to their size and the considerable amount of rock covering the bones in some of the blocks. My promotion to Collection Manager in 2005 left me with considerably less time to prepare fossils. Other preparators were asked to help with the preparation at both Carnegie Museum of Natural History (CMNH, Dan Pickering and Tyler Schlotterbeck) and in Dr. Robert Reisz’s lab at the University of Toronto at Mississauga (Diane Scott and Nicola Wong Ken). Robert was originally slated to lead the study, but other commitments prevented him from working on it, so Dave took over.

Besides preparation, the scientific study and publication of the specimens required illustrations and photographs, most of which were done by Diane, Nicola, and Kevin. Andrew McAfee (Scientific Illustrator, CMNH) made skeletal and flesh reconstructions of the animal, as well as an illustration of two Martensius in their ancient habitat (see The Bromacker Fossil Project Part III for a link to this illustration). All of this effort was worth it, however, because besides adding to the diversity of the Bromacker vertebrate fauna, Martensius has an unusual life history.

Juvenile specimen of Martensius bromackerensis. Image digitally assembled by the author from two photographs (skull and body) taken by Diane Scott in 2013. The skull, shown in ventral aspect, is incomplete and eroded on its dorsal surface.

Caseid synapsids are a diverse, long-lived group known from the Late Pennsylvanian–Middle Permian epochs (~300–259 million years ago) of Europe, Russia, and the USA, and, with one exception, all are adapted to eating plants (herbivorous). The most advanced caseids (such as the enormous Cotylorhynchus romeri) have ridiculously small skulls when compared to those of carnivores, spatulate (spoon-shaped) teeth tipped with small tubercles (cuspules) for cropping vegetation, and huge, barrel-shaped ribcages to support a large gut for fermenting cellulose-rich plants. The exception is the earliest known (Late Pennsylvanian epoch, ~300 million years ago) caseid, Eocasea martini, represented by a single, incomplete juvenile specimen from Kansas. The teeth of Eocasea are small and conical, which indicate that it most likely ate insects. Because it’s skull and ribcage are of normal size, in contrast to juveniles of Martenius, Eocasea probably ate insects throughout its life.

Reconstruction of the skull of Martensius bromackerensis (left) from the Early Permian (~290 million years ago) Bromacker quarry, Germany, and the more advanced caseid Ennatosaurus tecton (skull, middle and skull fragment with cuspule-tipped teeth, right), from the Middle Permian (~263 million years ago) of Russia. Skull reconstruction of Martensius made by Diane Scott and modified from Berman et al., 2020. Ennatosaurus skull reconstruction and jaw fragment drawing modified from Maddin et al., 2008.

Martensius has a modestly expanded ribcage and a small skull, suggesting that it was herbivorous. Furthermore, the feet of Martensius, like those of other caseids in which the feet are known, are large, with massive, elongated, strongly recurved claws. Martensius also has a well-supported hip region that may have enabled it to rise on its hind legs to reach and tear down overhead branches to feed upon.

The upper and lower teeth of the adult Martensius differ from those of more advanced caseids in being triangular and lacking cuspules. The upper jaw teeth of the juvenile resemble those of the adult, but the lower jaw teeth are more numerous—31 in the juvenile compared to 25 in the adult—and surprisingly, they resemble those of Eocasea. Dave concluded that juveniles of Martensius had teeth adapted for eating insects, which were replaced by an adult dentition that would’ve been good for cropping plants and piercing insects. Remarkably, the juvenile Martensius apparently died while in the process of replacing its juvenile dentition with that of adults.

So why have different juvenile and adult dentitions? Modern animals that eat fibrous plant matter have micro-organisms called fermentative endosymbionts in their large guts, which break down difficult-to-digest plant matter via fermentation. It is assumed that early fossil plant-eaters with broad ribcages also had large guts housing fermentative endosymbionts. Prior to the discovery of Martensius, other scientists hypothesized that early herbivores acquired endosymbionts by eating herbivorous insects that already had these microbes in their guts. In Martensius, the introduction of endosymbionts apparently occurred during the juvenile, insectivorous stage of life, which set the stage for adults to add plants to their diet.

Flesh (top) and skeletal (bottom) reconstructions of Martensius bromackerensis. Illustrations by Andrew McAfee and modified from Berman et al., 2020.

The generic name Martensius honors Thomas Martens for his discovery of vertebrate fossils at the Bromacker quarry and his perseverance in maintaining a highly successful, long-term field operation resulting in the discovery and publication of the exceptionally preserved Bromacker fossils. Bromackerensis refers to the Bromacker quarry, the only locality from which this species is known.

Stay tuned for my next post, which will feature some terrestrial dissorophoid amphibians.

For those of you who would like to learn more about Martensius, here’s a link to the 2020 Annals of Carnegie Museum publication in which it was described.

Amy Henrici is Collection Manager in the Section of Vertebrate Paleontology at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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The Bromacker Fossil Project Part IX: The Dissorophoid Amphibians Tambachia, Rotaryus, and Georgenthalia, Capable Travelers

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The Bromacker Fossil Project Part VII: Eudibamus cursoris, the Original Two-legged Runner

New to this series? Read The Bromacker Fossil Project Part I, Part II, Part III, Part IV, Part V, and Part VI. 
Holotype specimen of Eudibamus cursoris, the most complete bolosaurid reptile known. Photo by the author, 2013.

Stuart Sumida discovered some small bones in the Bromacker quarry in 1993, the same year that the holotype skeleton of Diadectes absitus was found. Dave Berman told me that when Stuart showed them to him, he couldn’t see anything because they were so small. Upon closer examination, Dave, Stuart, and Thomas Martens identified them as those of the captorhinomorph reptile Thuringothyris mahlendorffae. Thomas’ wife Stefani, whose maiden name is Mahlendorff, discovered the first specimen in the Bromacker in 1982, and Thomas and a colleague named it in her honor in a 1991 publication.

The fossil was exposed in several pieces of rock, which Thomas shipped to Carnegie Museum of Natural History (CMNH) along with the large block of rock containing Diadectes. I didn’t prepare the specimen until several years later, as other projects, including the Diadectes, overshadowed it. Once I began working on it, though, Dave and I realized that it was not Thuringothyris. Indeed, we had no idea what type of animal it was, and our puzzlement grew as I exposed more of it. The identity wasn’t revealed until I had uncovered some very unusual, tiny teeth, which under the high magnification of the preparation microscope appeared to have a bulbous cusp towering over a basin. They looked vaguely familiar to me, but because I couldn’t immediately put a name on them, I rushed to get Dave from his office. Once Dave saw the teeth, he realized that the specimen was a new genus and species in the rare, enigmatic reptile group Bolosauridae.

Tiny teeth of a bolosaurid reptile, Bolosaurus striatus, in lateral (side; left) and occlusal (chewing surface; right) views. The specimen is in the CMNH Vertebrate Paleontology collection. Photos by Spencer Lucas (Research Associate, CMNH).

Until the discovery of Eudibamus cursoris, bolosaurids were represented in the fossil record by two genera, Bolosaurus and Belebey, which were based mainly on poorly preserved skull and fragmentary jaw fossils from Texas and Russia, respectively. Even though bolosaurids had been known since 1878, their relationship to other reptiles was not well understood. The nearly complete anatomy of Eudibamus allowed our team to determine that bolosaurids are the oldest member of the ancient group of reptiles called Parareptilia. This group has no living relatives, except possibly for turtles, a hypothesis that is highly debated by scientists.

Eudibamus cursoris fossil
Closeup of front and hind legs of Eudibamus. The hind leg, folded upon itself, is considerably longer than the front leg. Photo by the author, 2013.

When our study of the fossil began, we realized that Eudibamus was very different than other reptiles from that time. Proportions of the limbs and positions of the articulation surfaces on the upper and lower hind leg bones indicated that, in terms of posture, Eudibamus resembled a bow-legged human with a bad back instead of a typical sprawling reptile on four legs. It could stand and locomote on its hind legs in an upright posture (bipedal) with its legs held close together and in the same plane (parasagittal).

Dave was in constant phone communication with team member Dr. Robert Reisz (Professor, University of Toronto at Mississauga). One day Robert called Dave to ask if all the tail had been exposed, because he learned that modern lizards that are able to run bipedally have a long tail to help maintain their balance. The specimen was in Dave’s office and he immediately uncovered more of the tail and then let me finish the task. The tail was indeed very long and extended close to the edge of the block, which I had previously reduced in size. Additionally, we determined that the third, fourth, and fifth toes of the hind foot also were greatly elongated through lengthening of some of the individual toe bones, and that the first and second toes were extremely shortened by the reduction in size of individual toe bones. We hypothesized that when Eudibamus ran bipedally, it would rise on its toes, so that only the tips of the third, fourth, and fifth toes would contact the ground.

Drawing of the hind leg of Eudibamus cursoris (left) and the roughly contemporaneous reptile Captorhinus (right). Leg drawings are scaled to the same torso length of the whole animal. Illustrations of the animals are not to scale. Hind leg drawings are modified from Berman et al., 2000 and animal illustrations are from Wikimedia Commons.

Eudibamus occurred at least 60 million years before other bipedal, parasagittally-running reptiles appeared in the fossil record. This is reflected in its scientific name, which is derived from the Greek “eu,” meaning original or primitive, and “dibamos,” meaning on two legs. “Cursoris” is Latin, meaning runner. Examples of other reptiles using this locomotion mode are the dinosaurs Allosaurus fragilis and Tyrannosaurus rex, which you can view in CMNH’s Dinosaurs in Their Time exhibition.

So, what was the advantage of being able to run bipedally instead of running on all four legs? Lengthening the hind leg and foot would greatly increase stride length, especially if only the tips of the toes contacted the ground, which is an efficient way to increase speed. Eliminating arm to ground contact while running removes forelimbs from the path of the long-striding hind legs. The bulbous teeth and jaw structure of Eudibamusindicate that it was herbivorous. It seems likely, then, that Eudibamus used its ability to sprint to avoid becoming a tasty meal for a pursuing predator.

Eudibamus cursoris illustration
Peter Mildner (exhibit preparator at the Museum der Natur, Gotha) made a surprise visit to the Bromacker one afternoon to show us a model of Eudibamus cursoris he’d made. This image shows the model in the present day Bromacker quarry, part of the region it inhabited 290 million years ago. Photo by the author, 2006.

One of our laments is that a fossil trackway preserving Eudibamus walking quadrupedally and then switching to a bipedal gait has yet to be found.

Next time you are at CMNH, make sure you see the cast of the fossil skeleton and a model of Eudibamus that are exhibited in the Fossil Frontiers display case in CMNH’s Dinosaurs in Their Time exhibition. Stay tuned for my next post, which will feature the herbivorous mammal-like reptile Martensius bromackerensis.

For those of you who would like to learn more about Eudibamus, here is a link to the 2000 Science publication in which it was described: https://science.sciencemag.org/content/290/5493/969.

Amy Henrici is Collection Manager in the Section of Vertebrate Paleontology at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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The Bromacker Fossil Project Part VIII: Martensius bromackerensis, Honoring a Colleague

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The Bromacker Project Part VI: Seymouria sanjuanensis, the Tambach Lovers

New to this series? Read The Bromacker Fossil Project Part I, Part II, Part III, Part IV, and Part V.
Seymouria sanjuanensis fossils
Two exquisitely preserved, nearly complete adult skeletons of Seymouria sanjuanensis that were discovered in the Bromacker quarry in 1997. Photo by Dave Berman.

At lunchtime on the last day of the 1997 field season, Thomas Martens discovered the two exquiste specimens shown above, the only fossils found that year. Thomas had uncovered a piece of the hip region with some attached vertebrae that resembled, once again, those of the ancient amphibian Seymouria. Because our work time was limited, we estimated the length of the specimen and rushed to extract it from the quarry. When we flipped the block over, a few pieces of rock fell out, revealing a series of vertebrae of a second individual in the block. We were thrilled to learn that Thomas had discovered two specimens of Seymouria. We put the rock pieces back in place and quickly finished plastering the block. There was just enough time for Dave, Stuart Sumida, and I to return to our hotel, clean up, quickly pack, and meet Thomas, his family, and his fossil preparator Georg Sommer for a celebratory dinner. What a great way to end the field season.

Working in tight quarters to quickly extract the Seymouria specimens discovered at lunchtime on the last day of the field season. Clockwise from right: Georg Sommer, Dave Berman, and the author. Photo by Stuart Sumida, 1997.

Seymouria had already been known from the Bromacker quarry. Thomas had discovered and identified two skulls in 1985, fossils he brought with him when he came to Carnegie Museum of Natural History (CMNH) in 1993 to study for six months with Dave Berman under a CMNH-financed fellowship. Both skulls were of juvenile individuals. Of the two known species of Seymouria, Dave and Thomas were excited to discover that the Bromacker skulls were nearly identical to those of Seymouria sanjuanensis. The 1997 lunchtime discovery of the two complete adult specimens confirmed the identification of the Bromacker Seymouria as S. sanjuanensis.

The first discovered species of Seymouria was Seymouria baylorensis, from near Seymour, Baylor County, Texas, from which its name was derived. Seymouria sanjuanensis was first found in San Juan County, Utah, by Dave Berman and the field team he was leading as a graduate student at the University of California, Los Angeles. Dave’s advisor, Dr. Peter Vaughn, named it Seymouria sanjuanensis in reference to the county of discovery. Another discovery of five specimens of this species preserved together was made by Dave in New Mexico in 1982.

Comparison of the skulls of Seymouria baylorensis (top) and S. sanjuanensis (bottom). The individual bones of the skull are color coded. Skulls scaled to same size. Image from Wikimedia Commons.

Seymouria baylorensis is geologically younger than S. sanjuanensis and has a more robust skull, larger and fewer teeth of variable size, and a subrectangular postorbital bone compared to the chevron-shaped postorbital of S. sanjuanensis.

Seymouria is considered a terrestrial amphibian that only returned to water to breed. Its strongly built skeleton provided the support needed to move on land. With its numerous, slender, pointed teeth, S. sanjuanensis most likely ate insects and small land-living vertebrates. We know that the Bromacker Seymouria didn’t consume fish, because not a single fish fossil, scrap of fish fossil, or fish coprolite (fossil poop) has ever been found at the Bromacker quarry. Study of the rock deposits preserving the fossils at the Bromacker indicate a lack of permanent water, which would explain the absence of fish.

Growth series of skulls of Seymouria sanjuanensis from the Bromacker Quarry showing (left to right) early juvenile, late juvenile, and adult growth stages. Photos by the author, 2006.

Conditions for breeding must have been favorable in the Tambach Basin, the ancient basin where sediments preserving the Bromacker fossils accumulated, because several juvenile specimens of Seymouria are known. The smallest is a skull measuring about ¾ of an inch long. In a study led by our colleague Josef Klembara (Comenius University, Slovak Republic), we determined that the smallest individual was post-metamorphic—in other words, no longer a tadpole—based on the presence of certain ossified bones in the skull. In tadpoles, these skull elements are cartilaginous; that is, they haven’t yet turned to bone.

Seymouria sanjuanensis fossils
Five skeletons of Seymouria sanjuanensis preserved together were discovered in north central New Mexico by Dave Berman in 1982. These specimens are on display in CMNH’s Benedum Hall of Geology, in the “What is a Fossil?” case. Photo by the author, 2013.

The discovery in Germany of the same species of Seymouria previously known only from New Mexico and Utah has important implications in terms of paleobiogeography (the study of the distribution of species in space and time). At the time S. sanjuanensis was alive, the continents were merged to form the supercontinent Pangaea. The presence of S. sanjuanensis across Pangaea, north of a roughly east-west trending mountain range, indicates that climatic or physical barriers (e.g., deserts, inland seas, mountain ranges) didn’t prevent its dispersal.

Map showing the arrangements of the continents in the Early Permian. The locality where Seymouria occurs in present-day New Mexico, Texas, and Utah and the Bromacker locality in present-day Germany are indicated. Map modified from Scotese, 1987.

The two Seymouria specimens preserved together were a big hit in the local region in Germany. Museum der Natur (MNG) exhibit preparator Peter Mildner nicknamed them the “Tambacher Liebespaar” (“Tambach Lovers”) after a painting entitled “Gothaer Liebespaar” (“Gotha Lovers”) on exhibit in the Herzogliches Museum of the Stiftung Schloss Friedenstein (also the parent organization of MNG). This name caught on and is fondly used by our German friends and colleagues. Peter even made a fleshed-out model of the two Seymouria specimens in their death pose. The proprietor of the hotel in which we stayed hung a copy of the model of the Tambach Lovers and a framed collage of newspaper articles featuring the Bromacker on a wall in one of the hotel rooms, which she named the “Präparation Suite” (i.e. “Preparation Suite” in reference to the preparation of fossils). I often stayed in this room.

The painting entitled “Gothaer Liebespaar” (“Gotha Lovers”), which is on display at Herzogliches Museum of the Stiftung Schloss Friedenstein, Gotha, Germany. Image from Wikimedia Commons and provided by Thomas Martens.
Tambach Lovers postcard
Postcard showing the Tambach Lovers. The postcard was made for and sold by the Museum der Natur, Gotha. Photo of the postcard by the author, 2020.
Stuart Sumida (left) and Heike Scheffel, proprietor of the Hotel Wanderslaben where we stayed (right), with the model of the Tambach Lovers in the “Präparation Suite.” The framed collage to the right of the model holds newspaper articles featuring the Bromacker project. Photo by the author, 2003.

A cast of the Tambach Lovers specimen and a model of Seymouria sanjuanensis are exhibited in the Fossil Frontiers display case in CMNH’s Dinosaurs in Their Time exhibition. Be sure to look for them once the museum re-opens. And stay tuned for my next post, which will feature the unusual bipedal reptile Eudibamus cursoris.

For those of you who would like to learn more about Seymouria sanjuanensis, here is a link to the publication describing the 1997 specimens: https://www.tandfonline.com/doi/abs/10.1671/0272-4634(2000)020%5B0253%3AROSSSF%5D2.0.CO%3B2.

Amy Henrici is Collection Manager in the Section of Vertebrate Paleontology at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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The Bromacker Fossil Project Part VII: Eudibamus cursoris, the Original Two-legged Runner