STL Science Center

STL Science Center

13 August 2018

Living Relatives

The Chacoan peccary (Catagonus wagneri) of Paraguay, Bolivia, and Argentina numbers approximately 3,000 animals remaining in the wild. This is important for a number of reasons, but the most important reason for us today is that, as the closest remaining descendant (hypothesized) of Platygonus, it is a stand in for our fossil peccary. Though smaller than its extinct ancestor genus Platygonus, Catagonus shares an interesting part of its known history with Platygonus. The Chacoan peccary was initially described as an extinct animal of South American in 1930. It was not until 1971 that living examples of the peccary were found by non-native scientists. The native people of Argentina showed the animals, which they called tagua, to biologists that were in the area. This video shows images of the tagua or Chacoan peccary, which stands in for its ancestor Platygonus.

11 August 2018

New Week

I intended to discuss the book Unnatural Selection more than I was able to last week, but I received an email that has kept me fairly bust since last Monday or Tuesday. Instead of spending multiple weeks on the book, I thought that this week we could di○scuss a fossil ancestor of one of the animals that is highly important to discussions in the book about selective breeding. We have discussed the origins of cats and dogs a number of times here and we have also discussed more than a few early birds, their cousins, and their ancestors. The remaining group that I had mentioned from the book is that lovable farm (and table group), the pigs (a magical animal, as regards the table comment).

Suidae consists of a large group of animals, both domesticated and feral, today. At one point we tried to discuss the origin of pigs, but they are a diverse group of animals that have evolved into 17 species across 6 genera and a wide variety of sizes and diets. Also, it was a two entry week, because I was extremely busy, in which we discussed Strozzi's Pig (Sus strozzi). The story of the evolution of the domesticated pig begins with the wild boar (Sus scrofa) and Strozzi's pig is a step along the road between ancient relative and modern pigs. Part of the reason Strozzi's pig died out is actually tied to surges in the population of S. scrofa. Going farther back on the family tree is somewhat problematic, but entertaining because the clade that all pigs and boars belong to is called Artiofabula which welcomes its own puns. Despite all we know about living pigs and boars and having a general idea about their familial relationships, there is not that much known about the origins of Suiidae itself. However, because we had a brief discussion about S. scrofa and domestication before, we are going to talk this week about an ancestor of the peccaries, rather than the wild boar.

Peccaries of the family Tayassuidae in the group of Suidae are the only pigs native to the Americas. Historically measuring approximately 90 and 130 cm (3.0 and 4.3 ft) in length and about 20 to 40 kg (44 to 88 lb), peccaries are smaller than boars and domesticated pigs. Wild pigs and boars in the United States, for instance, are not peccaries but feral versions of the domesticated pigs that came over with European settlers. One of the most well-known wild suids in the United States, the javelina, is a peccary though. Confusion between feral domesticated pigs and peccaries is very common. Regardless, peccaries have their own rich history in North America. One of the extinct members of the family, Platygonus, consists of 18 described species of ranging from Canada to Mexico and California to Pennsylvania throughout the Pliocene and into the Pleistocene. Platygonus was rather large for a peccary at 1 m (3.3 ft) long. Long legs made it capable of running at a fair speed and tusks allowed it to defend itself from predators. It is thought that these peccaries lived in herds as well, making them a bit more well protected than solitary pig and peccary species.

©Charles R. Knight, Platygonus leptorhinus

05 August 2018

Classy Introductions

In order to name something, you need to be able to define the parameters of that thing — to know categorically when it ceases to be one thing and becomes another.
- Page 8, Unnatural Selection 

Every science text that aims to cross over to popular nonfiction work needs to have a very good introduction that not only grabs the reader's attention but also explains the basic tenets of the book's context in a way in which non-scientist readers can follow along and apply the fundamentals of these ideas. Application can be either within the text or outside of the book. Most authors that care about teaching their audience (we hope all authors, of course) spend a great deal of time explaining these basic principles of their text to make this process easier. The first few chapters of Unnatural Selection outline some of the basic principles of evolutionary science including basic lessons in phylogenetics, speciation, and a basic understanding of plasticity.

I did not mention this yesterday, however, Unnatural Selection is a book that focuses primarily on the phenomenon of dometication in its various forms, that is from the development of livestock to pigeon fanciering and from dog breeding to the very complex nature of swine domestication and hybridization. To sum it up more succinctly, the book is about selective breeding, and the basic principles of how we name animals, how they are related, and how this breeding process has worked over time are very important to understanding the later chapters of the book. Therefore, the first section of the book, in which these principles are taught to the reader, are very important. They are, fortunately, very well written.

As an example, the sometimes difficult to explain concept of organismal plasticity is written such that it is fairly easy to follow as well. In the scope of the book (that is in its use in describing selective breeding), a slightly different definition is used than that of the strict biological definition of the word. In that strict biological sense of the word we are looking at a phenotypic plasticity or the adaptability of an organism to changes in its environment. Unnatural Selection approaches plasticity in terms of the potential for changes over generations, rather than in a single generation. We could say the difference is that between an animal that experiences an environmental change over its life (for a myriad list of reasons hypothetical or otherwise) compared to the changes of a dog (cat, pig, pigeon, parakeet) breed over successive generations (see below for change over time in Bullterrier skulls). That breed can change in many different ways for a variety of reasons including, as van Grouw says, "fashions might simply change." Additionally, because these animals are all interbreeding subspecies, those plastic changes can flip, flop, and twist in amazingly interesting ways over the years because of the breeding of mutts and mixes of purebreeds that become fashionable (think of things like Labradoodles).

©Katrina van Grouw

04 August 2018

Skeletons and Popular Literature

A few years ago a book was written called The Unfeathered Bird that was focused on the anatomy of birds, showing birds as they are not often seen in popular literature. The illustrations for the book were hand-drawn skeletal, muscle, and even some feathered images of a wide array of birds, highlighting differences and similarities across a wide range of birds; hitting every bird in this manner would be a life's work and well beyond the scope of a single book. A follow-up work by the author and illustrator Katrina van Grouw was recently published titled Unnatural Selection. Though not a follow-up in the sense of focusing on birds, Unnatural Selection does continue as an investigation of evolution, anatomy, and high quality illustration of a wide range of animals. Over the next week I am going to go over some of the chapters of the book. We will also get to see some of the illustrations that grace the pages of the book.

We can get back to fossil animals next week.

26 July 2018

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.

24 July 2018

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.
 

23 July 2018

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!