Saturday, May 20, 2017

Postosuchus: Beast of the Week

This week we will be checking out a beast that shows us that evolution is capable of truly amazing things and how deceiving looks can really be.  This creature also helps teach us it's okay to change our perceptions as we learn new things, especially in science.  Enter Postosuchus kirkpatricki!

Postosuchus was a pseudosuchian archosaur, more closely related to crocodilians than to dinosaurs, that lived in what is now the Southern United States, specifically New Mexico, Arizona, Texas, and as far east as North Carolina, during the Triassic Period, between 221 and 203 million years ago.  It was one of the largest animals in its environment, with adults measuring between thirteen and fifteen feet long from snout to tail, and ate meat, probably hunting many of the other Triassic animals from the area, including fellow pseudosuchians, Shuvosaurus and Desmatosuchus, and the dinosaur, Coelophysis.  The genus name, Postosuchus, translates to "Post Crocodile", in reference to Post Town, Texas, where the first Postosuchus bones were unearthed.  The species name is in honor of the Kirkpatrrick family, who helped in Postosuchus' excavation.

Postosuchus life reconstruction in watercolors by Christopher DiPiazza.
 
Postosuchus has gone through a few makeovers over the years since it was discovered.  Because the first group of specimens' bones were not always found articulated, and often times among those of other species, early Postosuchus skeletal reconstructions accidentally were partially made of bones from other kinds of animals.  An example of this would be a the pelvis, hand, and toe bones, which would later be found to have really belonged to Shuvosaurus.  Because of this, Postosuchus was often depicted as being able to walk on four or two legs when alive.  However, we now know that it was much more likely to have been an obligate biped, only able to walk on its hind legs, like most theropod dinosaurs. This is thanks to more complete remains of Postosuchus found more recently, proving that the arms and hands were actually much smaller than previously thought, and were incapable of supporting its weight even if they could reach the ground.  The pelvis was much larger than originally thought, too, meaning the animal's center of gravity was over the hips.

Postosuchus brass skeletal mount on display at the Mesalands Dinosaur Museum in Tucumcari, New Mexico.  This mount is actually outdated.  Parts of the pelvis actually belong to Shuvosaurus, and the four-legged stance is improbable.  The vertebrae, especially behind the skull, would have much shallower neural arches in reality.

Postosuchus' skull was tall overall, but narrow laterally in the front, gradually getting wider towards the back.  It had prominent ridges over the eyes, forming an overhanging shelf, perhaps to help block out sun glare in life.  The eye sockets were relatively large, and partially faced forwards, suggesting Postoscuchus may have relied on its sense of site to hunt.  Due to large hollow areas connected to the nostrils, it likely also had a good sense of smell in life.  Postosuchus' jaws were lined with relatively long, pointed teeth that were serrated, for better cutting meat.  Some of the teeth were much longer than the others in certain parts of the jaws, like the tip of the lower jaw, and the mid-section of the upper jaw.  This would have made Postosuchus' mouth act like a deadly trap if it were to bite into a still-living/struggling animal.

Brass cast of Postosuchus skull at the Mesalands Dinosaur Museum.  Note how the longest teeth are in the middle of the upper jaw, and the front of the lower jaw.

Osteoderms have also been discovered with Postosuchus.  Osteoderms are pieces of bone that grow under the skin of an animal.  Modern crocodilians are most famous for having osteoderms, which they use as armor, as well as for built-in solar panels, to better absorb heat from the sun.  The osteodersm associated with Postosuchus appear to have been growing in two rows down the back.  It is still uncertain as to what their purpose was.

Photographs of Postosuchus foot bones from Karin Peyer's 2008 paper, describing the specimen found in North Carolina.  Note how Postosuchus would have walked on four toes on the ground.  This is different from what you'd see in MOST theropods.  (Therizinosaurs walk on four toes.)

Within pseudosuchia, Postosuchus belongs to the family called rauisuchidae.  Rauisuchians all exhibited fully erect posture, and typically had large heads with sharp teeth.  Not surprisingly, they are often mistaken for meat-eating dinosaurs.  They even possessed hollow bones, a trait normally associated with dinosaurs.  However, Postosuchus, like all pseudosuchians, shows some key differences from dinosaurs that give it away as more closely related to crocodilians.  It's ankles are the biggest giveaway because they could rotate, like those of modern crocodilians, rather than the more rigid, one-way bending ankles all dinosaurs have.  It also would have walked with it's first four digits touching the ground and its outermost fifth digit, which was much shorter, out to the side.  Postosuchus was another amazing example of convergent evolution.  In this case, it evolved the same body design you would see in large meat-eating dinosaurs like Megalosaurus or Allosaurus...before large, meat-eating dinosaurs even evolved!

That is all for this week!  As always feel free to comment below or on our facebook page.

References

Chatterjee, Sankar (1985). "Postosuchus, a new Thecodontian reptile from the Triassic of Texas and the origin of Tyrannosaurs". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 309 (1139): 395–460.

Long, Robert A.; Murry, Phillip. A. (1995). "Late Triassic (Carnian and Norian) tetrapods from the southwestern United States". New Mexico Museum of Natural History and Science, Bulletin. 4: 1–254.

Nesbitt, Sterling J.; Norrell, Mark A. (2006). "Extreme convergence in the body plans of an early Suchian (Archosauria) and Ornithomimid Dinosaurs (Theropoda)"Proceedings of the Royal Society B273 (1590): 1045–1048.

Novak, Stephanie E. (2004). A new specimen of Postosuchus from the Late Triassic Coelophysis Quarry, siltstone member, Chinle Formation, Ghost Ranch, New Mexico (M.Sc. thesis). University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.

Peyer, Karin; Carter, Joseph G.; Sues, Hans-Dieter; Novak, Stephanie E.; Olsen, Paul E. (2008). "A new Suchian Archosaur from the Upper Triassic of North Carolina". Journal of Vertebrate Paleontology. 28 (2): 363–381.

Sunday, May 7, 2017

Zalmoxes: Beast of the Week

This week we will be checking out an unusual ornithopod.  Check out Zalmoxes!

Zalmoxes was a plant-eating dinosaur that lived in what is now Romania, during the Late Cretaceous, between 70 and 66 million years ago.  There are currently two named species, Zalmoxes robustus and Zalmoxes shqiperorumZ. shqiporum is deemed the "larger" species at about eight feet long from beak to tail, but Z. robustus's largest known individuals, at about six feet long, were determined to be sub-adults, so it is likely Z. robustus could have grown more than what the fossil record shows.  The genus name is in reference to Zalmoxis, a character from ancient Dacian (province in Romania) folklore.

Zalmoxes robustus life reconstruction in watercolors by Christopher DiPiazza.

Zalmoxes is considered an ornithopod dinosaur, and is currently thought to be within the iguanodontid clade on the dinosaur family tree.  This would make it a close relative of the more famous, Iguanodon, as well as Mantellisaurus, and Tenontosaurus.  However, within iguanodontidae, Zalmoxes is part of the more specific family, called rhabdontidae.  Rhabdontids were generally smaller, but robust, bipedal dinosaurs.  Despite that they are currently considered most related to iguanodontids, they have also been compared to the even smaller, and more lightly-built hypsilophodontids.

Possibly the most striking feature about Zalmoxes is its skull, which is large when compared to its overall body size.  At the tip of Zalmoxe's triangular-shaped skull, it had a short beak, that would have helped it clip vegetation.  This food would later be processed by its small teeth in the back, which were backed up by a very deep lower jaw.  This deep jaw, paired with the high ridge on the back of the skull, suggests there were large muscles attached in life, and therefore Zalmoxes would have had a very powerful bite.  Perhaps it specialized in eating a certain variety of tough plant?

Zalmoxes shqiporum skeletal mount on display in Brussels. By MWAK - Own work, Public Domain,  Note the high section on the top of the rear of the skull where muscles would have connected to the lower jaw. 

The part of the world that Zalmoxes was found in was an island during the late Cretaceous.  Some scientists have suggested Zalmoxes' smaller size, when compared to other ornithopods of its time is a result of island dwarfism.  Island dwarfism is one of several phenomenons that have been observed when animals from the mainland end up genetically isolated from the rest of their original population on an island.  Over time, this new, smaller population, can evolve smaller bodies to better adapt to their new environment.  Note that Zalmoxes lived at the very end of the Cretaceous, right be fore the mass extinction that wiped all of the dinosaurs (except birds) while the majority of other known iguanodontids flourished during the early Cretaceous.  By Zalmoxes' time, the duck-billed hadrosaurs had taken the niches iguanodontids once held.  Zalmoxes being separated from the rest of the world on an island may have been its saving grace in that it didn't have to compete with the same newer forms of dinosaurs its ancestors on the mainland did, and thus was able to persist up until the end of the Mesozoic.

That is all for this week!  As always feel free to comment below or on the facebook page!

References

Ősi, A.; Prondvai, E.; Butler, R.; Weishampel, D. B. (2012). Evans, Alistair Robert, ed. "Phylogeny, Histology and Inferred Body Size Evolution in a New Rhabdodontid Dinosaur from the Late Cretaceous of Hungary". PLoS ONE. 7 (9): e44318.

Weishampel, D.B.; Jianu, C.-M.; Csiki, Z.; Norman, D.B. "Osteology and phylogeny of Zalmoxes (n. g.), an unusual euornithopod dinosaur from the Latest Cretaceous of Romania" (PDF). Journal of Systematic Palaeontology. 1 (2): 65_123.

Tuesday, May 2, 2017

Interview with Paleontologist: Daniel Barta

Daniel Barta is a Ph.D. Candidate in Comparative Biology at the Richard Gilder Graduate School at the American Museum of Natural History. He grew up in Helena, Montana, and hold Bachelor's and Master's degrees in Earth Sciences from Montana State University. Broadly, He us interested in vertebrate reproduction, growth, and development. His research integrates fieldwork with phylogenetic, histological, and taphonomic techniques to better understand the evolution of ontogenetic trajectories, eggs, and nesting strategies of extinct animals and their living relatives. Fieldwork in the western United States, China, and Mongolia shapes my interests in the faunal evolution and biostratigraphy of the Cretaceous of Asia and North America. Currently he focuses on the post-hatching growth and development of basal theropod and ornithischian dinosaurs. The exceptional sample sizes available at the American Museum of Natural History can provide important insight into dinosaur growth rates and anatomical transformations during development, thereby establishing an essential context for understanding both individual morphological variation and the evolution of the extreme growth and metabolic rates achieved by dinosaurs’ bird descendants. He is passionate about sharing through outreach the thrill of the scientific process and our evolutionary history that it reveals.



Question 1: Let’s start from the beginning.  What was your earliest sign of interest in paleontology that you can remember?

DB: I’m from Helena, Montana, and my earliest sign of interest came from a family visit to Museum of the Rockies in Bozeman, Montana, when I was about four years old.

Question 2: Did you have any professionals or family members who served as role models when you were younger?  Do you still have any now?

DB: My family members, especially my parents, greatly encouraged my interest in the natural world and in paleontology specifically. I still look up to them, and also to so many of my mentors and colleagues who have made great contributions to the natural sciences—there truly are too many to list here!

Question 4: Was there anything you did or learned as you were on your way to your current career that you feel got you to where you are?  By this I mean any sort of field experience, a class, networking with the right people, or possibly something different or all three?

DB: I’ll highlight three experiences chronologically. The earliest was a “job shadow” experience in sixth grade, when I got to work alongside Jamie Jette, a fossil preparator at the Museum of the Rockies, and learned more about what working with fossils is actually like as a career. This helped solidify my decision to attend Montana State University for my undergraduate studies. The second was my undergraduate research experience in China with Dr. Dave Varricchio of MSU, who later became my master’s thesis advisor. And the third would be a collections visit to the American Museum of Natural History during my master’s research with Dave that introduced me to my current Ph.D. advisor, Dr. Mark Norell, for the first time.

Question 5: You do a lot of work with dinosaur eggs, particularly birdlike theropod eggs.  Did you have a prior interest in this branch of paleontology prior to starting your career? Did it choose you?

DB: It was a little of both. Growing up, I’d always been interested in dinosaur eggs and parental care from reading books and news stories about both Montana’s Egg Mountain locality and the discoveries in the Gobi Desert by AMNH and other expeditions. I thought that they were both just really interesting scientific stories. However, my desire to devote much of my studies so far to dinosaur eggs really grew out of the undergraduate research that I mentioned earlier. I found that there’s a lot of work still to be done to understand the evolution of eggshell microstructure and what fossil egg assemblages can tell us about the biology of the animals that laid them.

Question 6: What was or is your favorite project in paleontology so far?  Would you be able to tell us about some of your current projects?

DB: This is really hard to pick, as I’ve enjoyed all the projects that I’ve been involved with, but I’ll highlight two projects here. I’m really proud of the paper in Acta Palaeontologica Polonica that I co-authored with Dave Varricchio on some Mongolian Cretaceous bird eggs that we named Styloolithus sabathi. It’s not every day that you get to help describe a new type of fossil egg, and I think the paper stands as a nice tribute to the late Karol Sabath of the Polish Academy of Sciences, who made key contributions to the study of fossil eggs. The specimens in our study help to reveal the very non-avian dinosaur-like reproductive mode of early birds, and may also hold implications for why these early birds went extinct along with the non-avian dinosaurs at the end of the Cretaceous.

My other favorite project is one of my dissertation chapters that I just recently submitted for review, and though I can’t say too much about it here, it involves anatomical study of the hands and wrists of early dinosaurs. I also recently worked on a couple of egg-citing projects related to dinosaur eggshell, but again, you’ll have to wait for the papers to hear more about those!

Question 7: Where have you travelled for your career?  Do you have a favorite destination when it comes to fossils?  Why?

DB: I’ve been really fortunate to travel a lot for my career. I’ve done fieldwork in Montana, China, and Mongolia, and collections visits and conferences have taken me to Europe, Asia, and South America. Mongolia is my favorite fieldwork destination. The quality of preservation and abundance of fossils there really can’t be beat, and we have some wonderful Mongolian colleagues who are incredibly fun to work with.



Question 9: Do you ever get criticized on any of your work?  How do you handle it?

DB: The criticism of my work that I've faced has, without exception, helped to sharpen my thinking and improve the final manuscripts. I’ve been really lucky in my short career not to have encountered anything directed at me that I would consider unfair or mean-spirited. I think it’s really important for everyone in science to work to ensure a collegial academic environment.

Question 10: Jurassic Park and Land Before Time (opposite ends of the spectrum, I know) were just two of the programs I remember as a kid that helped fuel my obsession with paleontology.  Did you have favorite shows, movies, or even toys growing up that fueled your passion?

DB: Those were two important ones for me as well! I also discovered many of the older dinosaur movies, like "The Land that Time Forgot,” pretty early on and still have a real fondness for those. Another thing that helped spark my initial interest was a blue Brontosaurus toy that my parents bought for me when I was about four (around the same time as my first visit to a museum).

Question 11: One of my pet peeves is when people assume paleontology doesn’t really do any real good in the grand scheme of things and is just a “for fun” science.  Do you think paleontology has a bigger part to than this?  How?

DB: Paleontology provides us with our only direct record of past biodiversity. Many people say that the current biodiversity crisis represents a sixth mass extinction, and we wouldn’t have any context for understanding what a “mass extinction” is without studying fossils. We would know very little about our modern world and even less about how to predict its future without studying past environments and the life that inhabited them.

Question 12: Who was the first paleontologist you met?  How was that interaction?

DB: The first paleontologist I met was Dr. Jack Horner. I attended a talk that he gave at an elementary school in Helena, and I later got to interview him during my sixth grade “job shadow” experience that I mentioned. Both were tremendously inspiring experiences for me as a young student.



Question 13: Why do you think prehistoric animals are so influential to us today?

DB: Prehistoric animals are ambassadors from a succession of alien worlds ( our own Earth at different points in its past), and as such, are both tantalizingly familiar and startlingly strange. I think they provide one of the most accessible “hooks” for people of all ages to learn about the scientific process.

Question 15: What is your favorite prehistoric animal?  Was it different when you were younger?

DB: My favorite prehistoric animals now tend to be whichever ones I’ve studied scientifically, so currently the early carnivorous dinosaur Coelophysis bauri is one of my favorites. Like a lot of people, I was enamored with Tyrannosaurus rex when I was younger, and still am.

Coelophysis

Question 16: If you could use a time machine to go back and pick only one prehistoric animal to bring back from history and observe alive and in person, which would it be and why?

 DB: I think any of the whole range of extinct reptiles, mammals, amphibians, fish, and invertebrates for which we have no obvious modern analogues would be fascinating to observe, as a time machine might be the only way that we would ever be able to answer basic questions about their structures, functions, and behaviors. Among dinosaurs, I would of course love to answer my questions about Coelophysis growth in real time.

Question 17: Back to the time machine.  This time you can go back to any place and time period and have a look at what the environment was really like.  Which one would you pick and why?

DB: I would pick any time and place during the Triassic Period. One could examine not only the ecologies of the range of bizarre, extinct reptile groups, but also see how the components of the “modern” fauna were becoming established.

Question 18: Which is your favorite museum?  Why?

DB: Based on my answers above, this will probably not come as a surprise: my two favorite museums are the American Museum of Natural History and Museum of the Rockies, as they’ve both contributed immensely to the development of my ideas and interests, setting the direction of my professional life.

Question 19: What hobbies do you have?  (Don’t have to be paleo-related.)


DB: I enjoy hiking, bird-watching, spending time with family and friends, and learning about history, music, and the visual arts.