STL Science Center

STL Science Center

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:


06 July 2019

Returns and New Beginnings

I am back to having the time to write a little bit here and there every day. There are many good animals to start with as we restart these (mostly) daily entries. I decided that, since this is the restart of this blog we should go back to the roots of the roots of the first project I worked on after the inception of this page. The only way that makes sense is to talk about an animal that is a member of the group that gave rise to the animals that I originally worked on. My first project was describing a set of plesiosaur vertebrae, and the animals that preceded the plesiosaurs were a group that we call the nothosaurs. One genus, Keichousaurus (consisting of K. hui Young 1958 and K. yuananensis Young 1965), was first discovered in China in 1958 by Hu Chengzhi and described by C. C. Young. This genus, like other nothosaurs, possess a long neck and tail, short head (relatively), and paddle-like hind and forelimbs; the forelimbs being more paddle-like were thought to be more important in locomotion than the hindlimbs. This locomotion was also thought to resemble that of plesiosaurs and has been described as "underwater flight", though this is still largely hypothetical at present. The holotype species (K. hui) is represented by numerous fossil animals, including pregnant individuals indicating live birth or ovoviviparity (hatching in the uterus and being "born" live) in Keichousaurus.

We might think these animals would be quite large, given that their plesiosaur descendants are quite large animals. However, many of these nothosaurus are extremely small, ranging from 15-30 cm (6-12 in) in length. There are individuals known to reach 2.7m. Despite the long neck and tail that we see in illustrations of Keichousaurus, that long neck is actually quite short, in respect to what we usually think of for long-necked animals (think of giraffes and long-necked dinosaurs, as examples). Of course, that neck is relatively long for these small animals!

©Nobu Tamura

09 February 2019

Fancy Pets

The "Mexican Walking Fish" (Ambystoma mexicanum) is probably one of the first non-mammalian animals that I ever interacted with (aside from actual fish) in an extended capacity. My mother was tasked with feeding the Ambystoma in one of Indiana University Bloomington's biology research labs back in the late 1980's. This is also where I first hung out (I was maybe 8 so "was tolerated" may be a better description) with graduate students and learned how to play Tetris, but those are stories for another time. We generally do not call Ambystoma Mexican Walking Fish, which is good because in the traditional nomenclature sense they are actually salamanders and not fish at all. Most know them as those strangely adorable pink aquatic pets known as Axolotl.

The story of Axolotl is amazing, endearing, and almost somewhat ridiculous; but we are not going to learn much more about Axolotl today as they are a means to an end for us here. I will share that they love uncooked beef liver. Also, I was inspired to talk about them today because a friend that works at the Boston Museum of Science shared a post about an upcoming exhibit featuring these adorable little salamanders. Salamanders in general are fairly recognizable by most, though there is sometimes confusion over names (e.g. newt vs. salamander) and appearance (think Axolotl vs. any other generic "salamander" that comes to mind). We could discuss how newts are salamanders and why Axolotl look different from Tiger Salamanders (which they are closely related to), but we are going to talk, now that we all have a picture of salamanders in our heads, about fossil salamanders from the Permian known as Apateon.

Senckenberg Museum of Frankfurt
Photo  by Ghedoghedo

Often preserved as flat impressions on slabs, these Permian temnospondyls are primitive amphibians that, like the Axolotl, are neotenic; meaning that they retain juvenile traits, such as the external gills seen in Axolotls, in their mature adult forms. This is often referred to as pedomorphosis also. Researchers have shown that these traits are retained in large numbers of these animals and they were so populous that we have a wide swath of ontogenetic or life cycle examples of animals in this genus to show that we are not just looking at odd young from many different groups. We have, of course, living examples to draw from as well. Many interesting things are known from these fossils, but probably one of the most intriguing things, to me, is the number of large group fossils and the detail in both the large group fossil assemblages and single animal fossil slabs that exist for Apateon. The genus Apateon actually consists of 7 species with Apateon pedestris von Meyer 1840 containing the holotype for the genus. As with many exquisitely preserved slab fossils, Apateon was originally discovered in Germany, a country with a rich history of excellent freshwater fossil diversity and preservation, and specimens have been dated from 295.0 to 290.1 million years ago.

Apateon pedestris Natural History Museum, Bonn University
Photo by Ghedoghedo

The skeleton of these Permian amphibians can be seen in this image from the Natural History Museum of Bonn University, which is actually quite a feat. The skeletons of Apateon are very weakly ossified, so the identifiable vertebrae, ribs, and limbs are truly exceptional and speak directly to the preservation of the fossil. Additionally, the orbits are fairly identifiable and, because we can see where the eyes would have been, we can see that the snout and the area of the skull directly caudal, or behind the eyes, are very short. We can say that Apateon had a very small head rostrocaudally (front to back) but also a very wide skull and very large eyes. If we turn our attention to those limbs we can just make out the digits. We know from more splayed out fossils of the limbs that there were four digits on the forelimb (on the "hand") and the hindlimb as well.