Your Daily Fossil

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.

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.

Uintatherium 

Mounted specimen from American Museum of Natural History, and currently part of the traveling Extreme Mammals exhibit.

Reconstruction by Charles Knight

When: Eocene (~49 to 39 million years ago)

Where: North America

What: Uintatherium  is one of the first large mammalian herbivores. It stood about 6 feet (~1.8 meters) high at the shoulder and was roughly 13 feet (~4 meters) long. This isn’t that large for an animal today, but in the Eocene it was a giant! It lived in the lush sub-tropical forests of mid-Eocene North America, most likely eating a combination of terrestrial bushes and shrubs along with aquatic plants from lakes and marshes. Uintatherium has a nasty pair of upper canines, not what you would expect from a herbivore! It is thought that these teeth were involved in sexual display, as they appear to be much larger in males than females. Uintatherium vanishes from the fossil record in the late Eocene, at about the time the temperature of North America was falling and the vegetation was thinning out. 

Uintatherium was also one of the fossils involved in the great ‘Bone Wars’ between Cope and Marsh. It was by far the largest of the fossils to come out of the Fort Bridger fossil localities in Wyoming (this fort gives its name to a land mammal age - The Bridgerian!), and thus highly prized. Cope and Marsh both applied multiple names to specimens from this region which would later prove to all belong to the same species. The name Uintatherium wasn’t even one applied by Cope OR Marsh. Joseph Leidy named this creature in 1872, just barely edging out Marsh’s names of Dinoceras and Tinoceras. So that particular battle in the bone wars was won by someone who didn’t even have much of an interesting in fighting! 

Uintatherium is not thought to have any living descendants, it is possible that the Eocene Uintatherium was the last of its kin. However, the position of Uintatherium and its brethren (grouped as the Dinocerata) within the mammal family tree is highly uncertain. They are well accepted as placental mammals, but beyond that? It is highly debated, and in my opinion, nobody has really done a rigorous enough study to support any one position over another.  

Obdurodon

Skull on display at the American Museum of Natural History, NYC

Reconstruction by Anne Musser

When: Late Oligocene to Miocene (~25 to 12 Million years ago)

Where: Australia

What: Obdurodon is a fossil platypus, as is fairly obvious from a look at its skull. Though upon closer inspection there are some very important differences; Obdurodon had a larger bill than the living platypus and retained teeth as an adult. Modern adult platypus are toothless, shedding all their teeth as juveniles. These teeth are important as they help us place monotremes (platypus and the echidna are the modern representatives) into the mammal family tree. It is now the consensus that marsupials and placentals are more closely related to one another than either is to the monotremes, but there are a great deal of extinct groups of mammals that may fall between therians and the monotremes - such as the multituberculates. Fossils such as Obdurodon which are most assuredly related to modern monotremes, but preserve more primitive features, are critically important for this phylogenetic issue. So then why is it still an issue? All we have of Obdurodon is a skull, despite the full body reconstruction above, and while there are fossils of even older monotremes they are even more scrappy - just isolated teeth or jaw fragments (that still enjoy full body reconstructions…).  

How did Obdurodon live compared to the modern platypus? Well, the living form uses its bill in the water to help it sense prey, and as Obdurodon had an even larger bill, it seem likely it also was aquatic, though without a postcranial skeleton it is unknown if it had the same swimming and digging adaptions seen in its extant relatives. 

Palaeolagus

When: Late Eocene to Mid Oligocene (~38 to 27 million years ago)

Where: North America

What: Palaeolagus is a fossil lagomorph. Lagomorpha is an order of mammals, that contains rabbits, hares, and pikas. Within the bunny-order rabbits and hares are more closely related to either other than either is to the pikas. If you are not familiar with pikas go check out some pictures! They are really cute little guys that resemble guinea pigs more than they do rabbits, but they are most assuredly lagomorphs. Palaeolagus falls outside all living lagomorphs in their evolutionary lineage. It can be thought of as representative of the common ancestor of all living lagomorphs.  

Palaeolagus lived in North America in the late Eocene, after the dense forests had left and the grasslands of the plains started to expand. This 10 inch (~25 cm) long herbivore spread throughout the continent during the Oligocene as the grasslands grew. Palaeolagus could not hop, its hind legs show none of the features that make a hopping locomotion style possible in living rabbits.This ancient bunny is known from a large amount of fossil specimens, some of which are almost complete skeletons, but most are fragmentary pieces of bone or teeth. Most of these Palaeolagus specimens likely met their end as the lunch of one of the many predators roaming the grass lands of prehistoric North America. 

Procoptodon - The giant short faced kangaroo 

Mounted skeleton on display at Victoria Fossil Cave, Naracoorte Caves National Park, South Australia

Reconstruction by Peter Trusler. 

When: Pleistocene (~ 2 million to 15,000 years ago)

Where: Throughout Australia

What: Procoptodon is a giant fossil kangaroo. Exactly how ‘giant’ it is has been a bit exaggerated, heights of up to 10 feet (~3 meters) have been reported, but this would have been its maximum height when it reared up fully on its hind legs, with its arms reaching up for high branches. Procoptodon was capable of this posture, but (like living kangaroos) it did not stand fully upright most of the time. In its normal feeding (and most everything else) poster it would have stood about 6.5 feet (~ 2 meters) tall; about the same height as the largest of the modern red kangaroos. Procoptodon was not the same size as these animals though, it was much more massive and would have been over twice the weight of a red kangaroo of equivalent height. 

Procoptodon was very well adapted for the semiarid conditions that characterized much of Australia during the Pleistocene, but fossil remains have also been found in the more hospitable regions of prehistorical Australia.  The marsupials of Australia are well known for their convergence evolution upon forms from other continents (such as the tasmanian tiger and the marsupial mole), but the kangaroo does not look like any placental mammal known. However, in terms of its lifestyle, the ecological niche that it inhabits, the group is convergent upon hoofed animals, such as deers!  Procoptodon overlapped with human habitation of Australia, and it is thought some Aboriginal folktales are about this massive kangaroo. 

Procoptodon is a member of the group Sthenurinae - the shortfaced kangaroos. As you probably guessed these kangaroos had much shorter snouts than the modern species of kangaroos. This group is completely extinct. It is one of the subgroups of the Macropodidae, the clade of marsupials that contains all kangaroos and wallabies, as well as a few other  groups. It has been proposed that within the Macropodidae the closest living relative of Procoptodon is the Banded hare-wallaby, though this is not universally accepted. 

In the prehistoric outback Procoptodon would have co-exsited with the largest marsupial of all time Diprodoton and was a hunted by the marsupial lion Thylacoleo. And the second link you can see this marsupial predator hunting a close relative of Procoptodon!  

Ambulocetus

Reconstructions by Carl Buell 

When: Eocene (~50 to 48 million years ago)

Where: Pakistan 

What: Ambulocetus is fossil whale relative. This beast was about 10 feet (~3 meters) long, and not very agile in either the land or the water. It was capable of movement on land, but it would have been rather slow and lumbering, as its forelimbs were shortened compared to its fully terrestrial ancestors. In the water it would have been capable of swimming with some speed, but it would not have been able to make quick turns as it chased its prey. Therefore, it has been reconstructed as an ambush-style predator, in the same niche as the modern crocodile. It would have laid in wait in the water, with its relatively dorsal eyes and nose peeking above the sufrace, able to see and smell approaching prey. Once a prey animal got close enough, Ambulocetus would launch itself from the water and try to catch the animal in its powerful jaws, such as is shown above. I think it is some form of basal horse that is trying to avoid the snapping jaws of Ambulocetus. This ambush style strategy could have also worked with aquatic prey, such as schools of fish. Ambush predation is seen in some species of whales today, Orcas (the killer whales) have been recorded ambushing seals on ice flows. 

Ambulocetus lived on the edge of the Tethys Sea (a body of water between India and Asia) in what is now Pakistan. At the time this region was one of many islands off the shore of the island continent of India, which had not yet collided with Asia (this would not happen for tens of millions of years). This warm seaway was full of mammals starting to return to the seas, including other lineages of whale relatives. In the cetacean family tree, Ambulocetus falls between Indohyus and modern whales; it was carnivorous - as all modern whales are-, and far more adapted for aquatic locomotion than Indohyus was, with shortened legs and a much more powerful tail. 

Indricotherium - The largest terrestrial mammal

Skull on display at the American Museum of History of Natural History, New York City

Reconstruction was part of the traveling Extreme Mammals exhibit, photo from when it was at the AMNH. 

When: Eocene and Oligocene (~ 34 to 23 million years ago)

Where: Asia and Eastern Europe 

What: Indricotherium is the largest terrestrial mammal known. It is a member of the rhinoceros family. Some material was found earlier in the 20th century, but the first fairly complete skull and skeletal elements were found by Roy Chapman Andrews in 1922 while on an expedition for the American Museum of Natural History in Mongolia. Indricotherium would have stood about 16.5 feet (~5 meters) tall at the shoulder and is estimated to have weighed in excess of 20 tons. There were sauropod dinosaurs that were smaller than Indricotherium! This giant was a herbivore and filled a simular niche to the sauropods and modern giraffes, so much so that it is sometimes referred to as the ‘giraffe rhinoceros’.  It stripped tall trees bare of leaves using its large front teeth and mobile lips. 

In the family tree of mammals Indricotherium is in the order Perrisodactyla (horses, rhinos, and tapirs). Within this group it in the rhinoceros clade. While rhinos today all look pretty much the same their fossil record shows this group used to be extremely diverse, with two completely extinct major sub groupings. Indricotherium is in the group Hyracodontidae (the running rhinos). This lineage divered from that leading to modern rhinos over 55 million years ago. Not all rhinos in this group were giant sized, the very first ones were no larger than wolves! All members of this group lacked horns like Indricotherium. 

There is a bit of controversy and confusion surrounding the topic of what genus name to apply to this animal. Indricotherium has been proposed by some workers to be synonymous with Paraceratherium and Baluchitherium, but this is not universally accepted. I have used the name Indricotherium for this entry as both examples shown above are based upon material that has held the name Indricotherium. 

Castorocauda

Art by Mark Klingler

When: Middle Jurassic (~164 million years ago)

Where: China

What: Castorocauda is an aquatic mesozoic mammal. It is known from a very well preserved slab specimen, which shows a suite of features indicating an adaptation to aquatic life. Its limbs were powerful, and easily capable of strong swimming or digging. Its tail was flattened, shown both by the soft tissues preserved on the slab, but also by its flattened caudal vertebrae, which are very simular to that of living swimming mammals, such as the beaver, otter, or platypus. This tail is what gives this Jurassic animal its name: Castorocauda translates to ‘beaver tail’. Its teeth were also specalized for aquatic life; they have primary cusps which curve backwards, which is seen in fish eating animals today, such as the seals. Castorocauda was about 17 inches (~43 cm) long, making it one of the larget Jurassic mammals. 

Castorocauda would have looked somewhat like a platypus lacking a bill, but its diet was more like that of a seal. In the mammal family tree Castorocauda is far far removed from any living taxa. It is a member of a group called the Docodonta, just a few branches removed from one of the first Mammaliforms: Morganucodon. As Castorocauda clearly had fur in life, this puts fur extremely far down on the mammalian lineage. It has been hypothesized previously that even more basal taxa had fur, but there has been no conclusive evidence. As Castorocauda was completely coated in fur, except for much of its tail, it is extremely likely fur originated much deeper in the mammalian lineage, possibly in the non-mammalian synapsids. 

The discovery of Castorocauda also shows that mesozoic mammals were much more ecologically diverse than has been previously proposed. Our ancient kin were not only small rat like insectivorous creatures that ran in the shadows of the dinosaurs; they swam, preyed upon dinosaurs themselves, and even flew (more on that one later)!

Hoplophoneus

Mounted specimen on display at the Zurich Natural History Museum. 

When: Late-Eocene to Early Oligocene (~38 to 30 million years ago)

Where: North America

What: Hoplophoneus is a saber-toothed carnivore which is well known from the several deposits in the Western states and provinces of the USA and Canada. This animal is not a felid, but a member of the group Nimravidae. One day I will probably be a true saber-toothed cat on here, but today is not that day! Hoplophoneus is a lot closer to true saber-toothed tigers than Thylacosmilus is, today’s fossil is a placental mammal, and has been closely linked to the order Carnivora, which is the order that includes cats. Exactly how closely linked has been a matter of debate for some time, pretty much since the first nimravid fossils were found in the late 1800s. At first nimravids, including Hoplophoneus, were thought to be felids. They were never thought to be sister taxa to the much later occurring saber-toothed forms however, so they have always represented another event of convergent acquisition of extremely enlarged canines. 

Hoplophoneus and kin were kept as felids for several decades, but their placement was then called into question when relationships within Carnivora were re-examined using cladistic methodology. Since the 1970s they have been, at various times, true felids, non felids in feliformia, in caniformia, or outside of Carnivora all together! The most recent studies, the first to look at all parts of the skeleton, have placed Hoplophoneus and the rest of the nimravids outside of Carnivora, as the sister taxon to the rest of the group. They are neither caniforms (dog like carnivorans) or feliforms (cat like carnivorans). 

This placement means that the leopard sized Hoplophoneus is an even more stunning example of convergent evolution than was first though. Not only are its enlarged canines convergent with some felids, but so are many other features of its anatomy. However, there are many differences as well, and these features are what place nimravids outside of Carnivora. Most of the differences are really specific anatomical features, most of which found in the ear region and the postcranial skeleton, but one easy one to see is the size of the brain. If you look at the reconstruction above the body looks very cat-like, but the head is quite different. According to one friend ‘Its not a cat, its a weasel-cat! sabertooth… thing.’