Your Daily Fossil

Hybodus

Fossil specimen from the Museum für Naturkunde in Berlin, Germany

Model by Dan Erickson and on display at the American Museum of Natural History

When: Permian to Cretaceous (260 to 80 million years ago)

Where: World Wide

What: Hybodus is a very wide spread, both temporally and geographically, fossil shark. I will be upfront here and say that I may be grossly over representing its temporal range, the literature is rather confusing and there have been a number of species going in and out of Hybodus over the years. So you may want to consider this an article on hybodontiform sharks in general, rather than just the one genus. Shark fossils are fairly rare in the fossil record when compared to other fish because sharks do not ossified their skeleton. However, Hybodus and its kin can be identified from fragmentary remains by their distintive teeth (two kinds in their jaws, both flat and pointy) and their ossified dorsal spines. These spines can be easily seen on both the fossil and the model above, they were most likely involved with stabilization of Hybodus as it swam.  The relatively few full body specimens preserved complete the picture, showing us that Hybodus was a streamlined shark  with a very heavy ribcage compared to most sharks, and that the males had not only ventral claspers, as seen in modern sharks, but also a series of spines on the side of the head - which are depicted above. 

Hybodontiform sharks were the dominate group of sharks in the Jurassic period, and were even very common in the late Cretaceous after modern sharks had originated and diversified. Studies of this archaic shark clade have shown they were most likely over all slow swimmers, but they could enjoy brief bursts of speed if needed. The diverse teeth forms of hybodont sharks imply they did not just eat fish, but also were able to prey on hard shelled invertebrates. In the shark family tree Hybodontiformes is the first group outside of Neoselachii - the clade that contains all living sharks and rays. 

Rutiodon

Mounted specimen on display at the American Museum of Natural History, NYC

Model on display at Dinosaur State Park, Connecticut

When: Late Triassic (~ 230 to 204 million years ago)

Where: North America 

What: Rutiodon is a phytosaur. We have looked at another phytosaur before, Redondasaurus, which was one of the biggest and most derived of the phytosaurs. Rutiodon falls on the other end of the phytosaur family tree. Rutidon was about half (~25 feet/7.5 meters) as long as Redondasaurus, but as it was built so much more slenderly, it is more accurate to say it is only 1/3rd or even 1/4th the size of its gigantic relative. This different body construction naturally translated into a different mode of life in Rutidon. Notice how slender and long its snout is? Some modern crocodiles have this same style of snout and they are predominately fish eaters, thus it is likely that Rutidon was as well, and it did not prey on terrestrial vertebrates. 

Phytosaurs strongly resemble modern crocodiles in other ways, and Rutiodon looks even more like a crocodile than many others of its kin. But this animal is most assuradly a phytosaur, /not/ a crocodile. One easy way to tell is if you look at the front end of its snout, look how the upper jaw is bent? That is a clear phytosaur feature. Another thing to look for is the position of the nose holes. Rutiodon has the phytosaur position of back near the top of its skull - whereas crocodiles have them in the more typically place at the end of the snout. 

Minor side trivia about this particular specimen of Rutiodon. It is number FR:AMNH 1, this means it was the first specimen to be catalogue into the fossil reptile collection. This specimen comes from a coal mine in Chatham County, North Carolina, and was collected by the famous paleontologist William Diller Matthew in 1895. 

Plesiadapis

Mounted specimen on display at the American Museum of Natural History, NYC

Reconstruction by Jay Matternes

When: Late Paleocene to Early Eocene (~ 61 - 55 millon years ago)

Where: North America and Europe

What: Plesiadapis is a small tree-dwelling mammal that was fairly comment in the late Paleocene of North America and Europe. This ancient mammalian taxon was about the size of a house cat, and though it may look very reminiscent of a squirrel it is a member of the primate family, as part of the larger group Plesiadapiformes. The latest research has shown that Plesiadapis was actually atypical for its namesake clade; this genus tended to be much larger than the average plesiadapiform and was not as well adapted for climbing as its smaller relatives, lacking a hand specially adapted for grasping. Plesiadapis could climb trees, but it would have been an arboreal quadruped, like the living squirrels, rather than a grasping locmotion as seen in most primates today. Another features reminiscent of rodents in Plesiadapis (and this is found in most of its kin) is its enlarged front teeth and the reduction or loss of teeth between these massive incisors and the grinding cheek teeth. Plesiadapis has been reconstructed as a frugivore - meaning its diet was primarily comprised of fruit. As much of North America and Europe was covered with lush sub-tropical forests during its range, Plesiadapis would have had quite a large selection of fruits to feed on. 

The placement of Plesiadapiformes has been somewhat controversial in the past decade or so. There is uniform agreement that these animals fall somewhere near the group Euarchonta within placental mammals, but exactly where has been much debated. Euarchonta contains not only primates, but also the Scandentia (tree shrews) and Dermoptera (flying lemurs). Some early studies placed plesiadapiforms closer to the dermopterans than primates, but more recent studies tend to find this clade as either the first branches to spring off the primate lineage or just outside of Euarchonta itself, as stem taxa to all three orders. One last point to make things even more confusing! The group Plesiadapiformes? It is probably not a monophyletic (natural) group in reality. It is looking more and more like that some taxa previously grouped within Plesiadapiformes fall closer to living primates than to other taxa within  the group. 

To sum up that confusing mess, Plesiadapiformes are very important in understanding primate evolution, as at least some members of this assemblage of taxa are the first animals on the primate lineage. As this lineage includes me and you there is a lot of study focused on this group right now! Nice to see animals that are primarily paleocene taxa finally getting some attention.

Today I spent the morning working in Mammalogy here. I snapped a couple of quick pictures of one of my favorite things that lurk in the hallways.

The pygmy dog! 

I included the first picture for a sense of scale, this thing is tiny! Supposedly it was a fully grown adult dog. Is it real? Nobody really knows. This is one of those objects that just have been in the museum forever and its original history is unknown. But either way it is adorable. Look at those tiny claws! 

Where I was today instead of writing an entry for you! ;) 

This is the CT scanner at the American Museum of Natural History. It is a fickle beast. Hence the dunce cap upon the top of the machine. Putting specimens in here and bombarding them with X-rays gives us a digital image of the object, such as the elephant skull I linked yesterday. 

The close up view shows a specimen in the midst of being scanned. 

Busy busy busy! 

Hello my dear followers! I have missed you!! I am only quasi-back right now, unfortunately! Plans have changed such that I will be traveling more than I thought, with several days with no internet. I don’t want to start up with entries again only to have to quickly stop. But I said I would post again today, and so instead over the next few days I will be posting some different things that I hope you will like. 

First up is a mystery object! I was inspired by the amazing umzoology  tumblr. if you do not follow that tumblr you really really should, so get to it. 

Can you guys guess what the specimen above is? 

Here are some hints!

It is not a fossil itself, but it does represent the anatomy of an extinct animal. 

I have not yet done an entry on the animal represented by this object, but I have hit several species in its group, including one very very closely related to it. 

As indicated on the images it is about a foot long. Just in case you do not the anatomical terms I used above, the views shown are: lateral - from the side, dorsal - from the top, and ventral - from the bottom. The arrow indicates that anterior - the front of the animal - is to the right in all images. 

you can reblog with your guesses or just answer this post thanks to this question mark! ?