dinosaurs in their time

September 25, 2020 by wpengine

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.

In the Field: Following the Work of a Paleontologist

Introduction by Jessica Sperdute

Edited by Matt Lamanna

With 22 million specimens housed at Carnegie Museum of Natural History (CMNH) and nearly 10,000 on display at any given time, chances are you’ve seen a dinosaur or two during your museum visits. But have you ever wondered how those dinosaurs get to the museum after they’re found? Or how we know where to dig for them in the first place?

What is a Fossil?

Fossils are the remains of animals, plants, and other ancient life that have been preserved in rock layers, or sediment. Fossils can include things such as leaves, skin, feathers, hair, footprints, and, most commonly, hard material such as wood, shells, teeth, and bones. Even poop can be fossilized! Many kinds of fossils are rare, and studying them can help us understand how the world looked tens of thousands or even millions of years before our time. Scientists who study fossils are known as paleontologists.

Looking at the Layers

Paleontologists use many tools to help them find fossils, but the key to knowing where fossils may be hidden underground lies with rocks—massive layers of rocks, called strata, are piled onto one another over time. These layers of different rocks can tell us not only what type of rock the layer is made of, but also approximately how old the layer is. The study of rock layers is called stratigraphy, and paleontologists use it to find potential fossil beds. For instance, if a paleontologist is looking specifically for fossils of dinosaurs, they would use stratigraphy to locate exposed layers of sedimentary rocks that formed at the time when dinosaurs lived and died—the Mesozoic Era. Once rocks from the Mesozoic Era are found in a location, the paleontologist goes to that location to hunt for fossils.

Big Prospects

Finding the right type of strata is only half the work of finding fossils; once paleontologists arrive at the field site, they need to physically walk around and search for clues that fossils may be around or underneath them. This is called prospecting, and the best place to prospect is usually at the base of a hill. Wind and rain will erode or gradually wear away rocks, allowing some fossils to break loose from higher sediments and roll downhill. If a fossil fragment is found, the team can then search the area to see if there may be other, more complete fossils—oftentimes higher up the hill and still embedded in rock.

Once prospecting has yielded an area where a fossil is likely to buried, the team can begin to block out the site and start digging. They use a wide variety of tools—even household items like paintbrushes, shovels, and hammers—to uncover fossils without damaging them. Records are taken of this step-by-step process to ensure all the data, from the precise location of the dig site, to the type of fossils found and their spatial relationships to one another, and even the measurements of the quarry, is kept for further study.

Safety First

The team has found a fossil, dug it up, and recorded the data. Now what? Once a fossil has been carefully excavated, it needs to be protected. Most fossils are delicate, so to transport them, especially larger ones, paleontologists use a method called plaster jacketing to protect them. First, they wrap the fossil in soft material such as paper towels, toilet paper, or aluminum foil to cover it. Then they wrap the covered fossil in strips of burlap that have been soaked in liquid plaster. This method is like using a cast on broken bones. After the plaster hardens, it acts as a shield. When the fossil has been safely transported and is ready to be studied or put on display at a place like Carnegie Museum, the paleontologist can gently cut away the plaster without damaging the fossil inside.

Paleontologist Photos

Dr. Matt Lamanna, Mary R. Dawson Associate Curator of Vertebrate Paleontology here at CMNH, has shared some of his favorite photos of his work at previous fossil dig sites. Look at the photos—do you recognize some of the locations, the tools that Dr. Lamanna is using, or the fossils that he’s digging up?

Here, Carnegie Museum of Natural History Mary R. Dawson Associate Curator of Vertebrate Paleontology Dr. Matt Lamanna is pointing at two ribs of a small—possibly baby—sauropod (long-necked plant-eating dinosaur) projecting from a rock face in the Bahariya Oasis of Egypt in 2001. He’d found this small sauropod only minutes before this photo was taken. Sometimes prospecting yields great finds! Credit: Mandi Lyon.

Dr. Matt Lamanna (right) on an expedition that found dozens of roughly 120-million-year-old fossil bird skeletons, mostly belonging to the species *Gansus yumenensis*, in the Changma Basin of Gansu Province, China in 2004. Lamanna is with collaborator Hailu You. Credit: Ken Lacovara.

In this photo, also taken in 2004 in Gansu Province, China, Dr. Lamanna poses next to the ribs of a giant sauropod—these ribs were just part of the massive skeleton that was discovered. Credit: Hailu You.

Dr. Lamanna on the expedition that found the new and gigantic titanosaur (a type of sauropod, again, a long-necked plant-eating dinosaur) *Dreadnoughtus schrani* in Santa Cruz Province, Argentina in 2005. Lamanna is shoveling loose rock out of the Dreadnoughtus quarry. Credit: Ken Lacovara.

Members of the expedition from Drexel University, the Universidad Nacional de la Patagonia San Juan Bosco, and CMNH that found the giant titanosaur *Dreadnoughtus* in Santa Cruz Province, Argentina in 2005 (left to right: Lucio Ibiricu, Chris Coughenour, Ken Lacovara, Matt Lamanna, Marcelo Luna, and Gabriel Casal). The huge femur (thigh bone) and tibia (shin bone) of *Dreadnoughtus* are visible in the foreground. Credit: Matt Lamanna.

Dr. Lamanna on the expedition that found the titanosaur *Dreadnoughtus* in Santa Cruz Province, Argentina in 2005. He’s sitting behind the 1.91 m (6 ft 3 in) femur, or thigh bone, of *Dreadnoughtus* not long after its discovery. Credit: Chris Coughenour.

Here, Dr. Lamanna is using a rock drill (one of his very favorite field tools!) to help collect the skeleton of a new armored dinosaur in Queensland, Australia in 2008. Credit: Steve Salisbury.

Dr. Lamanna (right) with collaborator Gabriel Casal making a plaster-and-burlap jacket to protect bones of the titanosaur *Sarmientosaurus musacchioi* in Chubut Province, Argentina in 2008. Credit: Mandi Lyon.

Lamanna on the day he found the only known fossil of the new, ~90-million-year-old crab *Hadrocarcinus tectilacus* on James Ross Island, Antarctica in 2009. Credit: Patrick O’Connor.

Here’s another photo of Lamanna on James Ross Island of Antarctica, this time in 2011. The team found tooth and bone fragments of the theropod—meat-eating dinosaur—*Imperobator antarcticus* at this site. Credit: Meng Jin.

During the 2011 Antarctic expedition, Lamanna and his fellow paleontologists also found lots of fossils on nearby Vega Island, especially those of approximately 70-million-year-old birds. Credit: Meng Jin.

In this photo from 2015, Lamanna is shown collecting fossils in a New Jersey quarry with a research team from Drexel University, who were uncovering marine creatures from the very end of the Mesozoic Era. Credit: Ken Lacovara.

Jessica Sperdute is a Gallery Presenter II Floor Captain and Lead Animal Husbandry Specialist in CMNH’s Lifelong Learning Department. Museum staff, volunteers, and interns are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

The Strange Saga of Spinosaurus, the Semiaquatic Dinosaurian Superpredator

I’ve been captivated by dinosaurs for as long as I can remember. My parents tell me that I told them that I wanted to be a paleontologist as early as age four. Naturally, then, I had lots and lots of books about dinosaurs when I was a boy growing up during the 1980s. One of the dinosaurs that always fascinated me the most was Spinosaurus aegyptiacus. Found in 1912 in the Bahariya Oasis of the Western Desert of Egypt (could anyplace sound more exotic to a small-town kid from upstate New York?!), Spinosaurus was originally known from a highly incomplete but also very large and extremely distinctive partial skeleton found in a middle Cretaceous-aged (roughly 95-million-year-old) rock layer in the oasis. Among the few skeletal elements known were part of a strangely shaped (for a dinosaur) lower jaw, some crocodile-like teeth, and most strikingly, several back vertebrae that each sported tall spines, some of them measuring nearly six feet. These spines clearly impressed Ernst Stromer von Reichenbach, the German paleontologist who studied the skeleton and gave the animal its name in a 1915 publication. Tragically, however, that original Spinosaurus skeleton—and all of Stromer’s other dinosaur fossils from Egypt—were destroyed during the Second World War, more specifically in a British Royal Air Force bombing of Munich on April 24, 1944. The story of Stromer’s lost dinosaurs found its way into many a children’s book, including several that I read cover-to-cover. As such, the tale took on near-legendary status for me, and, I’m sure, many other young dinosaur enthusiasts around the world. Here was an absolutely extraordinary dinosaur from a faraway land, similar in size to the gargantuan Tyrannosaurus rex, but clearly very different from all other predatory dinosaurs known at the time – and it was represented only by a few teeth and bones that had been blasted into oblivion decades ago and so now existed only as pictures in books.

A scan of my photocopy of plate I of Ernst Stromer’s original 1915 publication on *Spinosaurus aegyptiacus*, showing some of the teeth and bones preserved in the holotype (= name-bearing) partial skeleton, discovered in 1912 in Egypt’s Bahariya Oasis. Check out the long spines on the back vertebrae at lower left!

Stromer’s conception of *Spinosaurus*, as depicted in a 1936 publication and on a glass slide of his that colleagues of mine scanned during our visit to the Paläontologisches Museum München in Munich, Germany in 2001. Stromer knew this animal was big, as evidenced by the human skeleton he included for scale. Interestingly, too, he reconstructed *Spinosaurus* with unusual proportions for a carnivorous dinosaur, such as an abnormally elongate torso and short hind limbs. We’ll come back to those odd proportions a little later…

When I arrived in graduate school at the University of Pennsylvania in 1997, one of the first things I did was make a lengthy list of all the paleontological sites I was interested in exploring, ranked by their potential (in my mind, at least) to produce scientifically significant finds. The Bahariya Oasis and the search for a ‘replacement Spinosaurus’ quickly rose to the top of the list. Amazingly, no one had ever found—or at least officially reported—new dinosaur fossils in the oasis in the more than half-century since Stromer’s beasts were obliterated during that fateful airstrike. A need to keep this post to a reasonable length prevents me from describing the stars that had to align to make this happen, but in January 2000 I found myself in the Bahariya Oasis—one of the places I’d dreamed about going since I was a small child—as part of the first significant ‘dinosaur hunt’ to take place at the site since the early 20^th century. It was bittersweet, though, in the sense that we never really found that ‘replacement Spinosaurus’ I’d fantasized about – all we ever discovered of that creature were a few isolated, fragmentary teeth and bones (and, in a very different location, a couple previously unpublished photos of the original skeleton in a Munich archive). We did find and dig up a gigantic new species of long-necked, plant-eating sauropod dinosaur, Paralititan stromeri, a creature that to this day is one of the largest land animals of any kind that’s ever been found, anywhere – but that’s another story for another time.

One of the rare contributions that I personally have made to scientific knowledge of *Spinosaurus*: a glass slide showing the only known photo of the right dentary (tooth-bearing lower jaw bone) of the original, name-bearing partial skeleton from Egypt. Like all of Stromer’s Egyptian dinosaur material, this specimen (including this bone) was destroyed in a British air raid on Munich during World War II. Several colleagues and I ‘rediscovered’ this photo—which nobody apparently knew existed—in an archive at the Paläontologisches Museum München in 2001. We published it and one other previously unknown photo of the Spinosaurus type specimen in a 2006 paper in the Journal of Paleontology.

A much younger yours truly digging up the incomplete left humerus (upper arm bone) of the gigantic sauropod (long-necked herbivorous dinosaur) *Paralititan stromeri* in the Bahariya Oasis of Egypt, February 2000. *Paralititan* is one of the largest dinosaurs ever discovered – a nice ‘consolation prize’ given that we didn’t find much of *Spinosaurus* during our expeditions to Bahariya. (A cast replica of the complete right humerus of *Paralititan* is on display in *PaleoLab* at Carnegie Museum of Natural History.) Credit: Josh Smith.

Back to the matter at hand, meaning Spinosaurus. Fast-forward to 2011. I had the honor of serving as the external thesis examiner for Nizar Ibrahim, a promising doctoral student at University College Dublin in Ireland. I’d known Nizar for years, ever since he reached out to me by email while an undergraduate at the University of Bristol, England, to discuss our mutual interests in African Cretaceous dinosaurs. Nizar’s Ph.D. thesis was on dinosaurs and other middle Cretaceous-aged vertebrates from the celebrated Kem Kem beds of southeastern Morocco, a set of rocks that had yielded a fossil fauna very similar to, though seemingly more diverse than, that of the Bahariya Oasis. Among the many finds that Nizar documented in his colossal thesis were intriguing new remains of Spinosaurus. I went to Dublin to participate in his successful thesis defense, and afterward, he and I hit up some of the city’s finest public houses to celebrate (no surprise for those who know me). Over a pitcher of yummy Irish stout, he told me an exciting story – he and his team had lately discovered not just isolated bones of Spinosaurus in Morocco, but parts of a probable new skeleton. If so, this find would be the first skeleton since Stromer, and moreover would be exceedingly important given how little was known about Spinosaurus, even as recently as the early 2010s. The more parts we paleontologists have of a given fossil animal, the more we can generally learn about it, so the prospect of a new and relatively complete Spinosaurus skeleton—in other words, many bones belonging to a single individual dinosaur—was thrilling to say the least.

Again I’ll skip details for brevity’s sake, but fast-forward once again, to 2014. I was contacted by an editor of Science—one of the foremost scientific journals in the world—to peer-review a paper that had been submitted by (you guessed it!) Nizar and a long list of collaborators describing that new skeleton of Spinosaurus that he’d told me about over beers in Ireland three years before. Nizar and team had revisited the quarry and it had panned out in a big way. From this one, single individual Spinosaurus—again, the first associated skeleton of this dinosaur to have been found in roughly a century—they had bones from the skull, backbone (including a few of those famously long-spined vertebrae!), forelimb, pelvis, and hind limb. More importantly, these ‘new’ bones revealed that Spinosaurus was even more bizarre than anyone imagined! We already knew, from Stromer’s specimen and other, isolated finds made through the years, that the shapes of the skull and back were really weird for a predatory dinosaur. Now, the new skeleton showed that the bones were remarkably dense, the hind legs were oddly short, and the hind feet may have been webbed! All of this led Nizar and colleagues to propose that Spinosaurus may have been semiaquatic; in other words, that its lifestyle was much more comparable to that of a modern-day alligator or crocodile than it was to a more ‘typical’ land-living predatory dinosaur such as T. rex. Other evidence for an affinity to watery habitats had been found in Spinosaurus and closely related dinosaurs (known, perhaps unsurprisingly, as spinosaurids) before, but this was, in my mind, the most convincing case yet made that these animals spent significant amounts of their time at least partly submerged in lakes and rivers. The paper was published in Science a few months later, accompanied by a cover story in National Geographic magazine and a special on the venerable PBS TV series NOVA. Almost exactly one hundred years after it had been named, Spinosaurus had become a celebrity.

Nizar Ibrahim and colleagues’ initial conception of *Spinosaurus aegyptiacus* in the flesh, released to coincide with the publication of their *Science* paper in 2014. Two aspects stand out: as Stromer already knew (see his skeletal reconstruction above), the animal is enormous, but it was more oddly proportioned than even he had imagined. Note also the ‘regular-looking’ (for a dinosaur) tail, and read on. Credit: Davide Bonadonna.

Semiaquatic *Spinosaurus* chowing down on a tasty lungfish in what is now northern Africa some 95 million years ago. Italian paleoartist Davide Bonadonna has produced some of the most beautiful and accurate modern depictions of this extraordinary dinosaur, and I’m grateful to him for letting me reproduce his art here.

But the story didn’t end there. Some prominent paleontologists criticized Nizar and colleagues’ semiaquatic interpretation of Spinosaurus. These opinions weren’t a final judgment. Instead, this is just how science works: we scientists propose ideas, or hypotheses—in this case, that Spinosaurus lived and behaved more like a crocodile than your garden-variety carnivorous dinosaur—and then test these hypotheses by reevaluating the existing evidence and/or bringing new information to light. If a hypothesis repeatedly stands up to testing, then it gradually gets incorporated into the body of knowledge. Other paleontologists presented evidence that they claimed refuted the semiaquatic hypothesis, but Nizar and team eventually countered with new data of their own. In late 2019, another prominent scientific journal—this time it was Nature—came calling, asking me to review a second paper by Nizar et al. on Spinosaurus. What, I thought, could these researchers have to say about this dinosaur that they hadn’t already said before? Well, as it turns out, Nizar and colleagues had kept digging at their Spinosaurus skeleton site, and incredibly, they’d continued to find important new bones belonging to the same specimen. Among these post-2014 finds was the almost complete tail. When I saw what it looked like (via an illustration in their paper), I literally laughed out loud with surprise and delight. Somehow, the shape of the Spinosaurus tail Nizar’s team had discovered—the first even reasonably complete tail of this dinosaur to have ever been unearthed—was simultaneously both unexpected and predictable. It looked really dissimilar from the tails of other predatory dinosaurs, but it was nearly exactly like what one might expect for a dinosaur that used its tail to propel itself through water. In other words, the tall, fin-like tail of Spinosaurus looked more like that of a supersized alligator or newt than that of T. rex.

Nizar and team’s Nature paper on their Spinosaurus tail was published this past April 29. Is it the last word on this dinosaur and its mode of life? Most certainly not, but the evidence is now stronger than ever—in my opinion, very strong—that Spinosaurus spent more time in the water than any other non-avian (= non-bird) dinosaur that we currently know about.

The modern view of *Spinosaurus*, not as a ‘regular’ predatory dinosaur, but rather as a specialized semiaquatic hunter that spent much of its life in the water. Self-serving side note: the three smaller, spiky-looking fish are *Bawitius bartheli*, a polypterid (an archaic, still-extant group of thick-scaled ray-finned fishes) that several colleagues and I named in 2012 from fossils found in the Bahariya Oasis. The larger fish at lower left is the giant coelacanth *Axelrodichthys* (sometimes called *Mawsonia*) *libyca*. Credit: Davide Bonadonna.

Two *Spinosaurus* invite the sawfish *Onchopristis numidus* to lunch in what’s now northern Africa some 95 million years ago. Look at those fin-like *Spinosaurus* tails! Credit: Davide Bonadonna/National Geographic.

Nizar (who’s a Research Associate here at Carnegie Museum of Natural History), myself, and our many colleagues and collaborators are continuing to study the mysterious dinosaurs and other fossil vertebrates from the middle and Late Cretaceous of northern Africa. Indeed, Nizar and I have several collaborative papers in the works right now, and I’m also working with an amazing team of paleontologists at Mansoura University on multiple new Egyptian fossil finds. It’s a good bet that African Cretaceous dinosaurs even stranger than Spinosaurus are still out there, waiting to be discovered!

Further reading/watching:

Nothdurft, W. E., with J. B. Smith, M. C. Lamanna, K. J. Lacovara, J. C. Poole, and J. R. Smith. 2002. The Lost Dinosaurs of Egypt. Random House, New York, 256 pp.

Smith, J. B., M. C. Lamanna, H. Mayr, and K. J. Lacovara. 2006. New information regarding the holotype of Spinosaurus aegyptiacus Stromer, 1915. Journal of Paleontology 80:400–406.

Ibrahim, N., P. C. Sereno, C. Dal Sasso, S. Maganuco, M. Fabbri, D. M. Martill, S. Zouhri, N. Myhrvold, and D. A. Iurino. 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science 345:1613–1616.

Bigger Than T. rex (NOVA documentary): https://www.pbs.org/wgbh/nova/video/bigger-than-t-rex/

Henderson, D. M. 2018. A buoyancy, balance and stability challenge to the hypothesis of a semi-aquatic Spinosaurus Stromer, 1915 (Dinosauria: Theropoda). PeerJ 6:e5409.

Ibrahim, N., S. Maganuco, C. Dal Sasso, M. Fabbri, M. Auditore, G. Bindellini, D. M. Martill, S. Zouhri, D. A. Mattarelli, D. M. Unwin, J. Wiemann, D. Bonadonna, A. Amane, J. Jakubczak, U. Joger, G. V. Lauder, and S.E. Pierce. 2020. Tail-propelled aquatic locomotion in a theropod dinosaur. Nature 581:67–70.

Matt Lamanna is Mary R. Dawson Associate Curator and Head of 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.

Mesozoic Monthly: Gryposaurus

The Late Cretaceous-aged (~75 million-year-old) large-nosed North American hadrosaur (aka duck-billed dinosaur) *Gryposaurus* by ginjaraptor on DeviantArt.

Anyone who frequents the Pittsburgh area is familiar with ‘Pittsburghese,’ the regional dialect given full voice in what was once voted America’s ugliest accent (a fact that does not diminish our pride for it). One of my personal favorite Pittsburghese words is “nebby,” which translates to “nosy” for any non-local readers. “Nebby” can be used in a variety of contexts: the distant relative asking prying questions about your love life at Thanksgiving dinner is nebby, the pet cat trying to crawl under the bathroom door to see what you’re doing is nebby, and even the statue of Carnegie Museum of Natural History mascot Dippy the Diplodocus, silently judging your driving on Forbes Avenue, is nebby. We can assume other dinosaurs were nebby too, since so many had huge noses to stick into things. One of the biggest noses in the fossil record belongs to Gryposaurus notabilis, the star of this edition of Mesozoic Monthly.

Gryposaurus belongs to a group of dinosaurs called hadrosaurs, which are commonly referred to as duck-billed dinosaurs. Hadrosaurs were herbivores that got their nickname from the flat, toothless, somewhat duck-like beaks at the tips of their jaws. These beaks were used to bite through tough vegetation so that it could be ground up by the numerous teeth embedded in the rear half of the jaws. There are two main groups of hadrosaurs, both of which are featured in CMNH’s Dinosaurs in Their Time exhibition. Probably the more famous group is the Lambeosaurinae, known for their distinctive head crests that housed extra-long nasal passages. Virtually everyone can recognize the incredible backward-curving crest of Parasaurolophus (featured multiple times in the Jurassic Park franchise), and visitors to CMNH will also know the helmet-like crest of Corythosaurus. The second group is the Saurolophinae (traditionally known as the Hadrosaurinae), which typically lack bony crests. You can find a simulated carcass of the saurolophine Edmontosaurus (lovingly known to those of us in CMNH’s Section of Vertebrate Paleontology as “Dead Ed”) between the two imposing Tyrannosaurus skeletons in Dinosaurs in Their Time.

A gallery of hadrosaur heads. Top left: the lambeosaurine *Parasaurolophus* at the Field Museum of Natural History in Chicago (photo by the author). Top right: the lambeosaurine *Corythosaurus* at Carnegie Museum of Natural History (photo from Wikimedia Commons). Bottom left: the saurolophine *Edmontosaurus* at the Houston Museum of Natural Science (photo from Wikimedia Commons). Bottom right: the saurolophine *Gryposaurus* at the Natural History Museum of Utah in Salt Lake City (photo from Wikimedia Commons).

As a crestless hadrosaur, Gryposaurus was a saurolophine. Despite its lack of crest, its skull still had pizzazz: its nasal bone arched dramatically, giving the impression of a ‘Roman nose’ (which is very noticeable if you compare the skulls of Edmontosaurus and Gryposaurus in the image above). The name Gryposaurus notabilis means “notable hooked-nose lizard” in homage to this feature. G. notabilis is the type species of Gryposaurus; type species are typically the first ones to be named in a genus, and therefore become the reference to which all new specimens that may belong to that genus are compared. The other species (such as G. monumentensis, shown in the photo montage above) are similar enough to the type species that they can be referred to the genus Gryposaurus, but they differ in too many ways to be assigned to G. notabilis itself.

Occasionally, paleontologists will revisit a fossil species or genus and decide that it is either too similar to another to justify its own name or that certain specimens are too different to be grouped under the same name. Kritosaurus, another saurolophine with a ‘Roman nose,’ has fallen victim to both of these circumstances. It was originally considered its own genus, but was subsequently revisited by paleontologists who decided that it was so similar to Gryposaurus that the two genera were lumped together under the name Gryposaurus (when combining taxonomic groups, the first name that was published is the one that gets used). However, later paleontologists reviewed the evidence again and split a single species of Kritosaurus back out of Gryposaurus. The famous sauropod (giant long-necked herbivorous dinosaur) Brontosaurus underwent a similar series of changes over the years: originally, it and Apatosaurus were considered different animals, but after a review they were lumped together under Apatosaurus. Recently, the two were split apart again and the name Brontosaurus was revived (to the delight of fans of that name around the world).

It is not uncommon in paleontology for species to be lumped or split based on new or revisited evidence. When you consider that the decision to name new fossil species is often based on fragmentary, highly incomplete skeletons, you can see why it might be difficult to get things right the first time! These changes sometimes give people the impression that paleontologists “can’t make up their minds” or “contradict themselves,” but we must remember two things. First, that science is meant to change based on new evidence. Second, there have been thousands of paleontologists over the course of history, and every one of them is an individual person who can draw their own conclusions based on the same evidence. Although the resulting changes can disappoint fans of a specific animal or hypothesis, revision is normal and beneficial for the field as a whole. Scientists are supposed to be nebby – it’s how we make new discoveries!

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.

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

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.

Keep Reading

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

Mesozoic Monthly: Champsosaurus

Related Content

In the Field: Following the Work of a Paleontologist

What is a Fossil?

Looking at the Layers

Big Prospects

Safety First

Paleontologist Photos

Related Content

The Strange Saga of Spinosaurus, the Semiaquatic Dinosaurian Superpredator

Related Content

Mesozoic Monthly: Gryposaurus

Related Content

Mesozoic Monthly: Aspidorhynchus

Related Content

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

Keep Reading

About

Get Involved

Bring a Group

Powdermill

More Information