Your Daily Fossil

Koskinonodon formerly known as Buettneria

Mounted specimen on display at the American Museum of Natural History

Reconstruction by Matt Celeskey

When: Triassic (~228 - 216 million years ago)

Where: North America

What: Koskinonodonis one of the later surviving of the giant amphibians. This beast could read up to 10 feet (~ 3 meters) long and was very common in the ancient American southwest. Koskinonodon  was known by the name Buettneria for over 80 years, until a long standing nomenclature problem was resovled. See, the name Buettneria was applied to this animal in honor of W. H. Buettner, a fossil collector in the first part of the 20th century.  This was in 1922, however, a living species of katydid was given the genus name of Buettneria decades earlier in 1889. Thus the name was not actually availble to be used for this giant amphibian. The name Koskinonodon was applied in 2007. This name was used because a specimen that was named Koskinonodon  in 1929 was later determined to belong to the same genus as the previously known specimens that were then called Buettneria. When a genus is renamed this is typically how it is done, you comb though the past literature and use the oldest available name that has ever been used for any species (or specimens!) now housed in that genus. Sadly sometimes you end up using names that are just not as cool as the original. Sorry W. H. Buettner. At least your namesake fossil lives on in outdated museum exhibits. ;)

Koskinonodon is closely related to another large amphibian I have posted, Metoposaurus. It is likely that these two animals occupied the same habitates in life. What differentiates them? At just the general morphology level Koskinonodon has a much longer skull, a longer tail, and less robust limbs. It is common that when a paleo environment is reconstructed just one example of each ‘type’ of animal is used, but this is not really realistic. Think about the average North American forest today. Multiple species of all sorts of ‘types’ of animals are found there, multiple squirrels, deers, and birds that resemble each other very closely but are distinct species. This is how it was in the Mesozoic world as well! 

Dinodontosaurus

Mounted specimen on display at the Harvard Museum of Natural History

Reconstruction by Dmitry Bogdanov

When: Triassic (242 - 230 million years ago)

Where: Worldwide 

What: Dinodontosaurus is a synapsid, or ‘mammal like reptile’. It was one of the most common large herbivorous animals in the mid Triassic. These beasts reached lengths of 8 feet (2.4 meters) and are estimated to have weighed hundres of pounds. They fall within the clade Dicynodontia, so named for their two large front teeth. A fossil find in Brazil of over 10 Dinodontosaurus, including juveniles, shows these animals lived in herds and cared for their young. 

Synapsids were extremtly common in the Permian, but were hit hard by the end Permian extinction. Some groups, such as the Dicynodonts exemplified by Dinodontosaurus, however, made it though the extinction just fine. The extinction at the end of the Triassic period, however, was brutal to this clade, wiping out the vast majority of species. Some dicynodonts made it though this extinction, but the clade continued to dwindle throughout the rest of the Mesozoic, with the last dicynodont vanishing in the mid Cretaceous. In the synapsid family tree dicynodonts are fairly far up there, falling far closer to gorgonopsids than to the basal “pelycosaurs”. 

Gemuendina 

Fossil and model both on display at the American Museum of Natural History, NYC

Model created by Louis Ferraglio

When: Early Devonian (~410 to 392 million years ago)

Where: Germany 

What: Gemuendina is an odd little placoderm fish. It is known only from the early Devonian of Germany, from deposits that have been reconstructed to represent areas with anoxic bottom waters. Anoxic means ‘lack of oxygen’, so there was no oxygen in the sediments where the dead or dying fish fell, and thus scavengers and decomposing organisms could not disturb the remains. Specimens of Gemuendina  have only been preserved in such conditions because their armor was not a solid shield, as seen in some other placoderms, but rather a series of unfused relatively thin bony plates. This placoderm bears a close resemblance to a ray, with its flat body and series of horizontal fins. This is another excellent example of convergent evolution. Unlike rays, however, the eyes of Gemuendina were on the top of its head, not the side, and its nostrils were on top as well, not on its ventral (under) surface.

Within Placodermi Gemuendina falls into the clade Rhenanida. This group shares the characters of a ray-like body and the lose series of unfused plates that covered their flat bodies.  While the ray-like body is a shared derived feature that unites the group, the seires of individual plates is likely a retained primitive feature that was also found in the first placoderms, which gave rise to all of the rest, including massive forms such as Dunkleosteus. Gemuendina is one of the earliest well-known members of the clade, but isolated plates from tens of millions of years earlier in the Silurian period may represent the true first rhenanids. Though the fossils are rare and fragmentary, rhenanids swam throughout the Devonian waters all over the world.

Saichania

Mounted specimen on display at Dinosaur Kingdom, in Nakasato, Japan 

Reconstruction by Andrey Atuchin

When: Late Cretaceous (~83 to 70 million years ago)

Where: Mongolia 

What: Saichania was an armored plant eating dinosaur that roamed the deserts of Mongolia in the late Cretaceous. It was about 22 ft (~6 meters) long and heavily built. It was more fearsome looking than most armored dinosaurs as it did not just have flat armor plates on its body, but rather was covered with spikes. These dinosaurs were armored all over, there is even evidence of armored eyelids! This suit of armor would have protected Saichania from predators in the late Mesozoic mongolian desert. Fossils are typically found in deserts and badlands worldwide, but typically these areas were very different environments when the species represented by the fossils were alive. The ancient Gobi Desert was much closer to the harsh modern environment than most. Saichania was well adapted for desert life, with its stocky body and teeth designed for grinding the toughest of the desert plants. 

Saichania falls within Ankylosauridae, a group of armored dinosaurs found almost worldwide. It is one of the last and most derived of the ankylosaurids. One good way to differentiate the deserved ankylosaurids from their armored close relatives is the presence of a tail club. Saichania did not have the most massive club known, but it was still a significant feature. Ankylosaurids were one of the dinosaur groups that made it right up to the end of the Cretaceous period, vanishing with the rest of the non-avian dinosaurs. 

Teleoceras

Mounted specimen on display at the Harvard Museum of Natural History

Reconstruction by Roman Uchytel

When: Miocene and Pliocene (~17.5 - 4.5 million years ago, and maybe a couple million years more!)

Where: North America

What: Teleoceras was an aquatic rhinoceros. It was a very common beast in the North American Miocene. Yes, rhinos in North America! I have been eager to share with you all the amazing diversity of North American rhinos. The discovery of a tremendous amount of rhinos, not just in terms of numbers of species but their diversity, is one of the great surprises of North American paleontological expeditions in the 19th and early 20th centuries. This continent was home to  rhinos the size of modern pigs, rhinos that could run quickly, and even aquatic rhinos! Teleoceras is one of these aquatic rhinos.

Teleoceras had very short legs for a rhino and a nubby horn. This horn is actually pretty large in the scheme of things. As much as the modern rhinos are famous for their horns the vast majority of fossil rhinos show no evidence of having a horn. We can tell this via the presence or lack of a rough surface on the nasal bones. In life Teleoceras would have probably occupied a niche very simular to the modern hippopotamus.

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.

Cotylorhynchus

Fossil specimen on display at the American Museum of Natural History

Reconstruction by Hirokazu Tokugawa

When: Permian (~299 to 265 million years ago)

Where: North America 

What: Cotylorhynchus is a member of one of the most basal groups of synapsids, the  Caseidae.  Cotylorhynchus was a herbivore, and reached lengths of up to 20 feet (~6 meters) long, with a massive barrel chest, putting weight estimates at around 2 tons. This animal is very large for its time… well at least its body is. Cotylorhynchus has one of the most extreme cases of ‘tiny head’ I have ever seen. Even more so than the sail-backed Edaphaosaurus! Which is closer to modern mammals than Cotylorhynchus is. It is one of the most primitive animals known that unambiguously falls on the synapsid lineage. It is so basal that it does not even have any differentiation seen in its dentition, though there are less teeth than found in the non synapsid contemporaries of this wee-headed creature.