Fame and Mice

As we have stated this week, Mussaurus is well-known among paleontologists and it is actually fairly well-known by the public as well. This is partly because of its bogus claim of being the smallest dinosaur; granted it was the smallest known dinosaur when originally discovered and the hatchlings and juveniles are still quite small for dinosaurs. The sheer number of websites with information, images, and videos of Mussaurus attests to the dinosaur's popularity. If that was not enough, there is also an electronic toy version of the dinosaur and, back after not seeing one of these information trading cards in a long time, Mussaurus is featured below, looking very angry for some reason.

Anatomy of A Mouse Lizard

The first article that appears in a Google Scholar search for Mussaurus is Pol and Powell's 2011 paper Skull anatomy of Mussaurus patagonicus (Dinosauria: Sauropodomorpha) from the Late Triassic of Patagonia. Starting off with the cranium is the right way to go (my research is concerned with the skull, in case anyone wasn't aware). Because there are so many specimens of Mussaurus known to us, there is a lot of the skeleton that is known as well; the head is just the beginning. In fact, Pol also helped to describe some of the postcranial anatomy as well (Otero and Pol, 2013). Like Pol, Mussaurus is known from Argentina, which partially explains why he has been involved in numerous papers on the small dinosaur including Cerda et al., 2014a, Cerda et al., 2014b, and Otero et al., 2017 in addition to the two mentioned above. These studies are all largely descriptions of anatomy, generally either skeletal or joint related. This is not the limit of studies on Mussaurus of course.

Mussaurus had its own profile in the 1993 book Age of Dinosaurs by Peter Dodson which briefly discussed all the details that were known of small dinosaur at that point. Many studies not describing skeletal or joint attributes directly have also been published on Mussaurus that rely heavily on those descriptions, a prime example being Montague, 2006 which generated estimates of body size for over 600 dinosaur species, including Mussaurus. Phylogenetic analyses have been conducted using these descriptions and anatomical characters also; see Upchurch et al., 2007. Lastly, we know that the nests have been described, notably in Bonaparte and Vince, 1979, the paper initially describing Mussaurus from juvenile and infant specimens found in the nest that forms the basis of the title and bulk of the paper. This occurrence of the first Triassic nest on record is significant beyond just the naming of Mussaurus of course. Dinosaur eggs have been known since at least 1923 when the American Museum of Natural History led expedition of Mongolia discovered supposed Protoceratops nests; these led to the naming of Oviraptor and eventually it was discovered that the nest belonged to Oviraptor rather than Protoceratops (another story for another day). This nest, that of Mussaurus, is one of the earliest known dinosaur nests and an important link in the story of dinosaur evolution. Also we can all agree that dinosaur nests are pretty cool and that the earliest dinosaur nests and their tiny occupants are also very cool.

References:

Bonaparte, J.F. and Martin, V., 1979. El hallazgo del primer nido de dinosaurios triasicos,(Saurischia, Prosauropoda), Triásico superior de Patagonia, Argentina. Ameghiniana, 16(1-2), pp.173-182.

 

Cerda, I.A., Chinsamy, A. and Pol, D., 2014a. Unusual endosteally formed bone tissue in a Patagonian basal sauropodomorph dinosaur. The Anatomical Record, 297(8), pp.1385-1391.

 

Cerda, I.A., Pol, D. and Chinsamy, A., 2014b. Osteohistological insight into the early stages of growth in Mussaurus patagonicus (Dinosauria, Sauropodomorpha). Historical Biology, 26(1), pp.110-121.

 

Dodson, P., 1993. Age of Dinosaurs. Publications International Limited.

 

Montague, J.R., 2006. Estimates of Body Size and Geological Time of Origin for 612 Dinosaur Genera (Saurischia, Ornithischia). Florida Scientist, pp.243-257.

 

Otero, A., Allen, V., Pol, D. and Hutchinson, J.R., 2017. Forelimb muscle and joint actions in Archosauria: insights from Crocodylus johnstoni (Pseudosuchia) and Mussaurus patagonicus (Sauropodomorpha). PeerJ, 5, p.e3976.

 

Otero, A. and Pol, D., 2013. Postcranial anatomy and phylogenetic relationships of Mussaurus patagonicus (Dinosauria, Sauropodomorpha). Journal of Vertebrate Paleontology, 33(5), pp.1138-1168.

 

Pol, D. and Powell, J.E., 2007. Skull anatomy of Mussaurus patagonicus (Dinosauria: Sauropodomorpha) from the Late Triassic of Patagonia. Historical Biology, 19(1), pp.125-144.

 

Upchurch, P., Barrett, P.M. and Galton, P.M., 2007. A phylogenetic analysis of basal sauropodomorph relationships: implications for the origin of sauropod dinosaurs. Special Papers in Palaeontology, 77, p.57.

 

Mouse Movement

Mussaurus is not a movie star, despite it being a recognizable dinosaur for many people in and out of the paleontological profession. It has been studied and a video showing its range of movement has been posted online by John Hutchinson, author of What's in John's Freezer? and well known locomotion expert known for studying a wide range of animals, fossil and extant, among other topics (see his biographical blurb on his faculty website). Tomorrow there will be a lot more to read than there is to watch today; so do not feel like the mighty Mussaurus is under-represented yet!

Cute Titles

Mussaurus lends itself to cute titles on webpages. One such page, from Mental Floss, is title 10 Mousey Facts about Mussaurus. The facts on this site address issues like the size of the animal and the misinterpretation of the remains as well as other issues in a serious manner; not at all what one expects from a cute website title. These facts are again summarized in a WizScience video, for folks without the time to read websites right now. However, if websites are your Sunday morning or afternoon reading material, there are far more than just the Mental Floss page shared above. There are also pages on Mussaurus on Enchanted Learning, KidsDinos, Prehistoric Wildlife, and a number of other pages (though this may be enough Mussaurus for most people in a day!).

The Mouse Lizard

Reaching an estimated 3 m (10 ft) in length and 70 kg (150 lbs) in weight, the early sauropodomorph Mussaurus patagonicus was an aptly named dinosaur. The name means "Mouse Lizard" and was applied originally to the skeletons of infants, which are considerably smaller at 20 to 37 centimeters (7.9 to 14.6 in) long, because these were the only specimens known for a fairly long time. Some of the first adult specimens were found alongside or within nests of the already known juvenile and infant dinosaurs. Eggs of this species have also been found in some of these nests. The original juvenile specimens were described in 1979 and the first adult specimens were not described until 2013. The first adult specimens in this description were actually reassigned from Plateosaurus specimens that were described mistakenly in 1980. Their similarities make sense because both were early dinosaurs and both were early sauropodomorphs.

©Henrique Paes

Known but not Famous

I mentioned on Tuesday that Staurikosaurus is a much published and important dinosaur in the scientific community. Outside of the scientific community the knowledge about, and reaction to, the existence of Staurikosaurus is minimal at best. Staurikosaurus does appear in a number of popular arenas, including the The Lost World: Jurassic Park video game on the original PlayStation (see the video below at 5:39 for this version of Staurikosaurus). One place we know that people know about Staurikosaurus for sure is Brazil, where the animal was originally discovered and unearthed. Canela, a town near the discovery site, has a statue of Staurikosaurus alongside a small rhynchosaur.

Photo by Sergio Kaminski, CC BY-SA 3.0

Papers and Beyond

Staurikosaurus headlines a chapter in an older edition of the book The Dinosauria. This chapter has been replaced in newer editions of the book, but the importance of Staurikosaurus and the many papers discussing the anatomy and the phylogeny of Staurikosaurus remain in the newly re-designated chapters. These include the papers that initially described the holotype fossil (Colbert 1970) and estimates of missing elements of the skeleton (Grillo and Azevedo, 2011b) as well as those that ask questions about the origin of saurischian dinosaurs and Staurikosaurus' placement in this discussion (e.g. Galton, 2000). Staurikosaurus continues to be studied beyond the skeleton and its phylogenetic importance to the evolution of dinosaurs also. Grillo and Azevedo (2011a) studied the pelvis and hindlimb to describe the state of the musculature in these areas. These papers should be plenty for a day's reading, so enjoy learning more about the anatomy of Staurikosaurus and where this dinosaur sits in the dinosaur family tree!

References:
Colbert, E.H., Price, L.I. and White, T.E., 1970. A saurischian dinosaur from the Triassic of Brazil. American Museum novitates; no. 2405.

Galton, P.M., 2000. Are Spondylosoma and Staurikosaurus (Santa Maria Formation, Middle-Upper Triassic, Brazil) the oldest saurischian dinosaurs?. PalZ, 74(3), pp.393-423.

 

Bittencourt, J.D.S. and Kellner, A.W.A., 2009. The anatomy and phylogenetic position of the Triassic dinosaur Staurikosaurus pricei Colbert, 1970. Zootaxa, 2079(1), p.e56.

 

Grillo, O.N. and Azevedo, S.A., 2011. Pelvic and hind limb musculature of Staurikosaurus pricei (Dinosauria: Saurischia). Anais da Academia Brasileira de Ciências, 83(1), pp.73-98.

 

Grillo, O.N. and Azevedo, S.A., 2011. Recovering missing data: estimating position and size of caudal vertebrae in Staurikosaurus pricei Colbert, 1970. Anais da Academia Brasileira de Ciências, 83(1), pp.61-72.

Short Video

Staurikosaurus is not very well known, in terms of media presence and general availability of quality fact pages on the internet. There are a few notable pages, such as the NHM in London, KidsDinos, and the DinosaurFacts website. These pages are all summarized, for the most part, in the WizScience slide show/video that has been made for Staurikosaurus shown below.

Brazilian Theropod

Herrerasaurids make up some of the earliest dinosaurs and the earliest theropod dinosaurs as well. These small carnivorous bipeds are known for their agile appearances and small stature as well as their basal characteristics that laid the groundwork for their descendants, even some of the characteristics that can be found in the latest theropods like tyrannosaurids and abelisaurids. These characteristics were modified over time of course, but the changes can be traced back to these small herrerasaurid dinosaurs that have mostly be found in South America from a number of different locations. One of these locations, in Brazil, was the discovery site of an animal known as the "Southern Cross lizard", Staurikosaurus pricei. The specific epithet honors one of Brazil's first paleontologists, Llewellyn Ivor Price, who collected the fossil which was later described by Edwin H. Colbert. Staurikosaurus was Brazil's first discovered and described dinosaur, but has remained a very uncommon find, meaning that either it was not native to an area that allowed for easy fossilization (such as a forest) or was simply uncommon in its environment.

Staurikosaurus was one of the first dinosaurs and that makes its fossilized remains just as important in understanding the rise of dinosaurs as those of Herrerasaurus and other dinosaurs considered to be the first members of the dinosaur clade. Its long slender limbs appear to have been well equipped for running; forelimbs are missing from the fossil record so we do not know if was good at catching its prey. We do know that its jaw was filled with many serrated and recurved (curved toward the back of the skull) teeth, so it could have caught prey with its mouth rather than with hands. These teeth were also able to slice into its prey. As far as predators of the Late Triassic are concerned, Staurikosaurus was likely a fearsome foe for many smaller reptiles and mammals that it lived with.

©Nobu Tamura

Socketed Teeth

Thecodontosaurus was named for its teeth. Thecodont teeth are situated so that the base is completely enclosed in a bony socket, like our teeth and the teeth of other mammals, crocodilians, and dinosaurs. To help visualize this refer to the image below.

The specific epithet refers to the ancient age of the animal. John Morris, the English geologist who provided the specific epithet in 1843, simply appended the name antiquus to Thecodontosaurus, attributing the name to Henry Riley, the surgeon who helped with the excavation, without any explanation. Therefore we do not know what Morris was referencing with the name T. antiquus. It could be either the fact that it was a fossil animal or that it came from Triassic rock. We may not know any time soon.

Over 245 fragmentary specimens of Thecodontosaurus are known, all attributed to this single species; not for a lack of trying though as 14 other species have been named only to be reassigned to other genera or re-folded into the single valid species. A second species was speculated in 2000 by Benton et al., 2000 when observing more robust specimens of Thecodontosaurus. In the same paper the authors stated that the more robust morphology was equally as likely a result of sexual dimorphism as it was a potential additional species. Regardless of the findings of the paper as regards sexual dimorphism or secondary species, two morphologies are acknowledged simply as gracile and robust.

A Short Short

Thecodontosaurus is not very famous in terms of on film presence (for many dinosaurs this translates simply into "not very famous" at all). However, the University of Bristol started a program in 2000 to engage and educate the public using the research and expertise of university faculty in conjunction with local (and global) fossils and the research that has gone into them. Thecodontosaurus is a dinosaur that was featured heavily in the Bristol Dinosaur Project because it was a very local (read found near, around, and in Bristol) dinosaur that made for an engaging animal in the initial stages of the growth of the Bristol Dinosaur Project; the project originally centered around the recovery and preparation of Thecodontosaurus specimens in addition to the outreach components conducted by the faculty. In fact, the mission statement is still mostly concerned with laboratory work on Thecodontosaurus specimens, but the outreach component appears to continue to be a very valuable portion of the work. The website is a little outdated and other news sources only cover up to the funding cycle for 2013, though the Bristol Zoo (which partnered with the university for some time) last mentions their dinosaur exhibit during the summer of 2017, so there is hope. Anyone that knows more about the project's current state is encouraged to share more with us, but we can only hope that a wide-reaching scientific and educational project like this is still in effect.

A Learning Video

WizScience with a summary video of facts for you to learn some more general information about Thecodontosaurus on this wonderful Sunday:

Additionally, there are a number of pages that have fact files, many different visual interpretations, and a fair bit of discussion about the dinosaur and what we know about it.

Thecodontosaurs

An early socket-toothed sauropod, Thecodontosaurus antiquus Morris, 1843, was discovered in Southern England from Late Triassic (227-205 million years ago) soils around 1834. As many of these stories go, the people that found the remains were academics that could have been called doctors, naturalists, or scientists, depending on the definition they decided to use. A surgeon, Henry Riley, and the curator of the Bristol Institution for the Advancement of Science, Literature, and the Arts, Samuel Stutchbury conducted an expedition in a Bristol quarry where "saurian remains" were reported. Most of a skull was recovered, leading to descriptions of the teeth and name of the animal: Thecodontosaurus meaning "socket-toothed lizard", referencing the way in which the teeth were socketed in the jaws. 

Other fragments of the fossils represented various portions of the entire skeleton including the neck and "body" (ribcage and vertebrae), forelimbs, and legs led the initial description to identify Thecodontosaurus as a dinosaur; the fifth known and named dinosaur in fact. This diagnosis has not changed (some dinosaurs and non-dinosaurs identified in the earliest days of paleontology have been rediagnosed any number of times in the past 200 years) and has actually been supported by more material being recovered and identified. This is a good thing for many reasons, including that the holotype was destroyed in a 1940 bombing raid of Bristol by the German Luftwaffe.

Fame and the Dinosaur

Tawa hallae is a famous early theropod not only because of its coverage by the National Science Foundation or the publication of its description in Science. Tawa is also famous because it was an early theropod situated between the earliest theropod dinosaurs we know, animals like Herrerasaurus and Eoraptor, and the previously considered base of the theropod tree: Coelophysis and its family members. In a way that makes Tawa a kind of "missing link" (a term that scientists do not generally actually like using because it has been so warped). Tawa may be a link between those South American theropods and the rest of the theropod family, but that does not mean it is the only link nor that it is the most important link. The fame that its current status has given it, though, has been immortalized in books, television, online videos, and it has even become a model and toy that is loved by many children (and adults); there is even a new model for this year.

Science Descriptions

When an article appears in Science it is typically accessible forever. In terms of Tawa hallae this is very good news for us because the describing and naming paper are housed and available on the website. The paper is stored as a PDF and as html (Nesbitt et al., 2009), which is nice when you do not want to download another PDF and instead just want to read a paper on your screen. The high resolution photographs of bone and approximated skeletal drawings are available too in this format. This is not the only paper to describe Tawa or its family line though. There are a number of other descriptions of Triassic animals that call upon Tawa and other known dinosaurs for comparisons. However, the other paper linked here today is a little more inference based in that it discuss soft tissues of Tawa that are not actually preserved in the fossils. Instead, Burch 2014 uses osteological correlates of muscle attachments and inferences from extant phylogenetic brackets to reconstruct the muscles of the forelimb in Tawa. These kinds of studies are of interest to me because I have done similar things in the head, but muscle reconstruction in dinosaurs, even if one does not do this type of work themselves, is interesting and important in learning how dinosaurs lived, survived, and died in their environment.

Tawa and the National Science Foundation

The National Science Foundation (NSF) was all over the discovery and naming of Tawa hallae, with good reasons, and because of their coverage we have an entire page of videos on not only the dinosaur but also the discovery and an interview with Sterling Nesbitt, who led the paper naming the fossil. Rather than pasting all of the videos into today's entry, the NSF has been kind enough to place all of the videos on the same page, so we only have to use a single link. Also, rather than describe each video here, the NSF page has done that for us as well. There is a lot of information on this page, and it doesn't take a whole day to go over it, so enjoy the videos and information and then enjoy a Sunday outside, or watching the World Cup; whatever you enjoy!