STL Science Center

STL Science Center

15 March 2020

Talk to me on Twitter!

Hello all!
You're stuck at home. You're loved ones are stuck at home. I'm stuck at home. I'll be working on lectures and moving my class (and helping colleagues move online) all week. However, if you, your friends, or those lovely students you've suddenly been locked in with are looking for dinosaur or ornithology information over the coming weeks I'd like to offer what I can.

From 9am - 12pm EST during the weekdays I'll leave my Twitter feed (@ornithanatomist) open to questions. Maybe I'll get a lot of questions, maybe I won't! If you have questions, though, ask and I'll answer, find an answer (if I can), or point you to a good source to find the answer.

Stay tuned here and on Twitter. As I'm able I may be able to work out themed question days. I may (time permitting) be able to set up live Q & A sessions as well. Stay tuned everyone.

02 February 2020

Fossil Squirrels?

Good morning! What a wonderful morning it is! Punxsutawney Phil came out and told us all that spring is right around the corner, which is a very big deal. This is a North American "tradition" that was adapted from a similar German tradition (Dachstag: "Badger day") involving the European badger. American badgers would be far less amicable to this sort of treatment I think. In Pennsylvania, Phil is kind of a big deal him(her?)self. Groundhogs (Marmota monax) make a somewhat lucrative life for themselves in the state, even being endorsed by the state lottery as a spokes... hog named Gus. It is also quite hard to walk near any wooded area of Pennsylvania without running into at least a few of these large animals scurrying about the edge of the forest. But what are they really?

Fear is an acceptable response.
The animal has a lot of common names: groundhog, woodchuck, Canada marmot, and, my personal favorite, whistlepig, are just a few. Groundhogs, by any name, are not actually pigs or hogs (they are in the same genus as marmots, so that name has some basis, though they are certainly found south of Canada), but instead, they are actually some of the larger members of the squirrel family. Specifically, as some of their common names somewhat allude to, they are ground squirrels. Groundhogs can climb, despite their name, and a groundhog in a tree is something worth seeing.

When we think of oversized anything in the animal kingdom we tend to think that the only place to look is in the fossil record. That is, after all, where we find giant sloths, oversized wolves, dinosaurs, and enormous terror birds. We know that they are fantastic digging animals and spend a lot of time, including hibernation in a burrow. Was there, then, an even more giant ground squirrel that burrowed extensively in the history of life? Fossilized burrows are known from much earlier than the current era. The first burrows belong to very early animals, but if we are looking for the recent ancestors of giant squirrels, we do not need to go that far back.

Photo of Clarkia, Idaho squirrel fossil by
Bill Richards, North Idaho College
The first squirrels in North America appear in the Late Eocene, around 41 to 33 million years ago. Any "squirrel-like" fossils from before this are not squirrels.
The first ground squirrels appear shortly after the Eocene, in the early Oligocene, at approximately 30 million years ago in Europe. As far as the marmots themselves, there is no clear consensus on when this large group of ground squirrels first appear in the fossil record. They are evident by the Late Oligocene in North America. It is acknowledged that by the time we have a good fossil record, in the Mid-Miocene, the ground squirrels, particularly prairie dogs, are already well-represented within their modern range. The fact that we recognize their fossils as highly similar to their extant morphology does not really bode well for finding the origins of Punxsutawney Phil and Gus' family though. Truly, the fact of the matter is that squirrels, as long as we have known them in the extinct and extant capacity, have looked pretty much like squirrels. One could almost say that rodents are kind of like the cockroach of the mammal family in that they have existed long enough to have "survived anything and everything" that life can throw at them. We may see if this remains true in our own lifetimes, but let us hope that we do not.

For more reading:

  • Helgen, Kristofer M.; Cole, F. Russell; Helgen, Lauren E.; Wilson, Don E. (April 2009). "Generic Revision in the Holarctic Ground Squirrel Genus Spermophilus" (PDF). Journal of Mammalogy. 90 (2): 270–305. doi:10.1644/07-MAMM-A-309.1. Archived from the original (PDF) on 2011-10-22.

  • Kryštufek, B.; B. Vohralík (2013). "Taxonomic revision of the Palaearctic rodents (Rodentia). Part 2. Sciuridae: Urocitellus, Marmota and Sciurotamias". Lynx, n. s. (Praha). 44: 27–138.

  • Steppan, Scott J.; Storz, B.L. &; Hoffmann, R.S. (2004): "Nuclear DNA phylogeny of the squirrels (Mammalia: Rodentia) and the evolution of arboreality from c-myc and RAG1". Mol. Phyl. Evol. 30(3): 703–719. doi:10.1016/S1055-7903(03)00204-5 PDF fulltext
  • 29 July 2019

    Non-crocodilian Face

    Holotype as depicted in von Baczko and Desojo, 2016
    The holotype skull of Riojasuchus is very non-crocodilian to the casual observer. Having previously been associated with a number of people interested in crocodiles this skull shapes is not very alien to me and others that have experiences like mine. This is far from the strangest of crocodilian ancestors of course and we have discussed others here before (such as Simosuchus). The ancestral variations and resulting evolutionary history of crocodilians is actually quite fascinating. Riojasuchus is somewhere in the middle of this history. It is, obviously I think, not quite a crocodile and not one of the "primitive" herbivorous crocodilian ancestors. Further separating Riojasuchus from its descendant cousins (possibly a more appropriate description than saying it is directly ancestral to crocodilians) is the tree of Butler et al. (2011) which describes Riojasuchus (and ornithsuchidae) as a lineage that ends without more descendant lineages. Regardless of whether Riojasuchus has extant descendants or not, the skull shape is decidedly non-crocodilian, which is what we wanted to look at specifically today. The teeth are more crcodilian than some other crocodile ancestors. The dorsoventrally tall skull is quite distinct from living crocodilians. The transition from skulls of this shape to the more familiar flattened skull of crocodilians is the subject of much ongoing inquiry and research. It is a long, complex story, and we are still learning quite a lot from this group of animals about how and why head shape changes, or does not, over the evolution of a group.

    Butler, R. J., Brusatte, S. L., Reich, M., Nesbitt, S. J., Schoch, R. R., & Hornung, J. J. (2011). The sail-backed reptile Ctenosauriscus from the latest Early Triassic of Germany and the timing and biogeography of the early archosaur radiation. PloS one, 6(10), e25693. doi:10.1371/journal.pone.0025693

    Nesbitt, S. J., Desojo, J. B., & Irmis, R. B. (2013). Anatomy, phylogeny and palaeobiology of early archosaurs and their kin. Geological Society, London, Special Publications, 379(1), 1-7.

    27 July 2019

    More from 1969

    More paleontological discoveries were made in 1969 than just Deinonychus, though that is certainly one of the most famous of dinosaurs. A supposed basal was also described during 1969 that turned out to be a little more unique than a basal dinosaur (of course these are unique themselves). Described by J. F. Bonaparte along with another "new reptile" (Andescynodon being the second description, but not the focus of today's discussion) of the Argentinian Triassic, Riojasuchus tenuisceps (Bonaparte 1969) is an ornithosuchid ("bird crocodile") archosaur whose line of descendants include extant alligators and crocodiles. The holotype includes a nearly complete cranium and partial postcranial elements; more than 50% of the postcranial skeleton is preserved. Four total skeletons are known. The skulls average 25 cm (9.8 in) in length. Riojasuchus actually has a similar head to total length ratio compared to its descendants despite the general appearance of having a much shorter skull than alligators and crocodiles. Ornithosuchids, including Riojasuchus' relatives are known to reach approximately 2 m (6.6 ft) in length. Two other genera (with single species) show that there was likely a fairly wide distribution, if not a global distribution, of the ornithosuchids: Venaticosuchus Bonaparte 1971 (known from Argentina also) and Ornithosuchus Newton 1894 (known from Scotland).
    ©Nobu Tamura

    19 July 2019

    Modern Dinosaurs

    Since the description of Deinonychus by John Ostrom in 1969 the "dinosaur renaissance" that was kicked off by this paper and the hypotheses it generated, in part, has radically changed how we imagine and study dinosaurs. Deinonychus, for example, was originally illustrated as a leather skinned dinosaur. Deinonychus illustrations ranged in color and from strong looking to the often emaciated appearance that many dinosaurs, especially in the 1980's, were illustrated like. These versions have the skin pulled taut over bones in a way that makes the animals appear to lack muscle and other soft tissue. However, we do not generally see these kinds of illustrations anymore. Now, Deinonychus illustrations are almost always covered in feathers and typically have some elaborate feathers on the forelimbs, tail, and/or head. Admittedly, some of my favorite illustrations are those of Emily Willoughby, who has made this ferocious nightmarish dinosaur into an almost innocent looking (though likely still murderous) ball of fluffy feathers (on Wikipedia and DeviantArt). The bird-like appearance of Deinonychus has been taken to extremes at times as well; consider Luis V. Rey's rather turkey-like version of the dromaeosaur here. Unfortunately, the feathering and bird-like appearance have not been adopted by the most mainstream representation of Deinonychus: the "Velociraptor" of Jurassic Park. Crichton's dromaeosaurs were based off of Deinonychus antirrhopus. Jurassic Park (1990) was published shortly after Gregory S. Paul's Predatory Dinosaurs of the World (1988) which assigned Deinonychus to Velociraptor. This may explain why Crichton's Jurassic Park refers to these animals as Velociraptor antirrhopus; it's a nice story either way. However, the movies have increased the size of the animals and retained their old style of integument, possibly too inspire fear. The very minor exception is Jurassic Park 3, which did show some proto-feathering on the dromaeosaurs.
    Some effort shown here, right?

    17 July 2019

    July 1969

    There are a number of events turning 50 this year. Paleontology is not left out of 50 year old events. One of the most important, in my opinion, is Bulletin 30 of the Yale Peabody Museum of Natural History. Bulletin 30 included one of the most iconic scientific illustrations of my childhood (see below), drawn by Robert Bakker, and accompanying the description by John Ostrom of an "unusual theropod" found in Montana known now as Deinonychus antirrhopus (discovered in 1964). The inspiration for Jurassic Park's Velociraptor antagonists, Deinonychus was a small to medium sized bipedal dinosaur approximately 3.4 m (11 ft) long that lived 115 - 108 million years ago. Hypotheses of Deinonychus behavior and the 172 page description of its osteology by Ostrom have fueled comparisons to birds and produced images of an intelligent, pack-hunting dinosaur. The 120 mm (4.7 in) toe claw reconstructed from YPM 5205 by Ostrom was enough to inspire nightmares even before that annoying kid spoke up in Jurassic Park. Estimated to weigh in at 100 kg (220 lbs) Deinonychus was beefy and adding strength and a giant claw to an animal that was likely rather fast for its size only adds to the nightmarish qualities of this Cretaceous predator.

    Happy 50th naming month to one of my favorite, and one of the most frightening, dinosaurs that we know of, Deinonychus antirrhopus!
    Deinonychus antirrhopus ©Robert Bakker

    12 July 2019

    Week of Moving

    When Keichousaurus came across my screen the first time I thought it was an impressive appearing nothosaur but that it had a funny little head. Then I realized everything about this aquatic reptile was small, and a little funny. Its rudimentary flippers still appear to be mostly pes and manus, rather than true flippers, and its elongate neck with a short faced head is almost somewhat comical. Most of these fossils are found as entirely complete animals. Their intriguing morphology and the completeness with which they are often found, as well as the fact that specimens are not much longer than 2.7m (and many smaller specimens are known), Keichousaurus fossils are highly sought after as attainable collector's pieces. Though their abundance makes this possible, it does not necessarily make it acceptable. The variation of known fossils is, as with any animal group, appreciable. The morphological variation that has been lost due to the sale, or simply retention by finders, of these fossils to collectors hurts population studies as well as our knowledge of the evolution of aquatic reptiles overall. However, we do know a lot about Keichousaurus, as this WizScience video shares: