Your Daily Fossil

Toxodon

Mounted specimen on display at Harvard Museum of Natural History

Reconstruction by Roman Uchytel

When: Pleistocene (~2.6 million to 16,000 years ago) 

Where: South America

What: Toxodon is another one of the large herbivorous animals that roamed over South America. Charles Darwin purchased the skull of the first Toxodon known to the Old World during his journey on the Beagle. This skull was sent back to England were Sir Richard Own described it and named the animal Toxodon - ‘bow teeth’ based on the curving nature of its gigantic molars. Soon complete skeletons of this amazing animal were known. The first interpratations reconstructed Toxodon as a semi-aquatic animal, much like the modern hippo, but later studies of the limbs and teeth of speciemens show this was incorrect. Toxodon  was more the analogue of today’s rhinos than a hippo, a fully terrestrial animal with teeth well adapted for grinding tough plants in somewhat arid environments. Some Toxodon specimens have been found associated with arrowheads, showing that the first people to emigrate into South America had contact with these animals, and appear to have hunted them. 

Where does Toxodon fit into the tree of life? Like its contemporary Macrauchenia (which you can see in the background of the reconstruction), its relationship to living mammals is uncertain. It falls into the larger clade of Notoungulata, literally Southern Ungulates, but the placment of this group within placental mammals is highly uncertain. They maybe have a close relationship with animals in the group Afrotheria but research in mammalian systematics is only beginning to be able to evaluate that, and other hypotheses.  So what is Toxodon? We just don’t know. 

Deinogalerix

Mounted specimen from the National Museum of Natural History in Leiden, the Netherlands. 

Reconstruction by Mauricio Anton with a common hedgehog for scale. 

When: Miocene (~11 - 5 million years ago)

Where: One island that now is part of Italy

What:Deinogalerix is a comparatively giant relative of the hedgehog. It lived on what is now the Gargano peninsula in Italy, but during the Miocene this region was a separate island. Much of Italy during this time period was a series of isolate islands, owing to the higher water level. Deinogalerix was about five times the size of a common hedgehog, more the size of a small fox. However, with a skull about 1/3rd the total length of its whole body, it was proportioned very differently. An eight inch (~20 cm) skull on a 24 inch (~60cm) body isn’t too out of proportion for many of the Lipotyphla (the order that includes hedgehogs, shrews, moles, and solenodons), and it appears Deinogalerix saw no reason to shrink down its head just because of its growth spurt.  I have called this animal a hedgehog, and it is in that grouping, but it did not look much at all like the little spiny animal shown above. Within the hedgehog family, its closet relatives are not true hedgehogs, but rather the gymnures or ‘moon-rats’. These animals have not developed spines as protection and are covered with a coat of long course hairs. 

Livyatan melvillei 

When: Miocene (~12 - 13 million years ago)

Where: Peru

What: Livyatan is a gigantic toothed whale. It is fairly closely related to the living sperm whale, and is thought to have been about the same size, at 45 feet (~14 meters) long. This is an estimate as the whole body was not found, but its head was fairly well preserved, and its skull alone is 10 feet (~3 meters long) Unlike the modern sperm whales, it had a full set of teeth in both its upper and lower jaws, and its lower jaw was not reduced compared to its skull. Inside these giant jaws were giant teeth, the largest of which are 1.2 feet (~36 cm) long. What did they eat with these massive jaws and gigantic teeth? Well, living sperm whales eat very large prey, such as giant squids and megamouth sharks with their comparatively small jaws and teeth. It has been suggested that Livyatan was feeding upon other whales at the time! Such as the reconstruction above where a Livyatan  dramatically ruins the day of a Cetotherium (an extinct baleen whale). 

The name ‘Livyatan melvillei’ is meant to bring to mind Melville and his famous white sperm whale Moby Dick. Originally the name published was Leviathan melvillei, but it had to be changed, as the genus name of Leviathan was already taken! It belongs to a poorly known species of mastodon named by a researcher in the mid 1800s. Thus, the spelling of this giant whale’s name had to be altered, as once a name is applied to something it is there forever! Let this be a lesson to carefully check your species names before you publish them, as there are a few cases of something like this happening. Mostly it seems species of theropod dinosaurs are accidentally given names that have already been applied to beetles. Whoops! 

The area of Peru where Livyatan  was found is today a harsh desert, but geologists think that during the Miocene this area was an ocean paradise; a warm shallow lagoon. Dozens of marine species have been found in this desert, not only a variety of toothed and baleen whales, but also sharks and pinnipeds. 

Reconstruction by C. Letenneur, Muséum National d’Histoire Naturelle, Paris, France

Doedicurus 

Skeleton on display at the Museo Histórico Nacional in Buenos Aires, Argentina. 

When: Pleistocene (2 million to 11,000 years ago)

Where: South America

What: Doedicurus is a glyptodont. The Glyptodontidae were a subclade of armadillos that ranged throughout South America (and North after the land bridge reappeared). Doedicurus was one of the largest glyptodons, coming in at about 12 feet (~3.6 meters) long. Its shell was gigantic, a grown person can crawl inside one of these structures, and there has been some theories that ancient peoples could have used these shells for shelter.  The shell of Doedicurus, like all glyptodonts, was different from that of the living armadillos. The carapaces were thicker and in one solid piece, unlike the several segments present in armadillos that allow them to curl into a ball. Doedicurus had a highly domed shell, that connected to its pelvis posteriorly, but was separated from its shoulder girdle. It has been speculated that glyptodons with this type of shell stored fat in this space above the shoulders, such as a modern camel stores fat in its hump. Doedicurus also had an armored skull cap, which you can see in the fossil image but sadly has been omitted from the reconstruction. 

One of the most distinctive features of Doedicurus is its spiked tail club. In most of these entries when I present something cool that you can imagine being used in intraspecific competition I have to say ‘but it was just for display or protection’. NOT THIS TIME. There is a great amount of evidence for the hypothesis that these spiked tail clubs were used in battles between males. Not all specimens of Doedicurus have a well developed pedestal for the spikes, leading researchers to conclude this was only present in males. It is very unlikely this would have been anymore of a deterrent for predators than the large shell in the first place, and just as unlikely that Doedicurus would have been agile enough to defend itself from a swift carnivorous attacker with this club. Most compelling of all, several Doedicurus specimens have been found with healed wounds in their carapaces that match the predicted impact from a rival’s tail club. 

Doedicurus, like all of the remaining glyptodonts, went extinct about 11-10,000 years ago, at the end of the last major glaciation. 

Chalicotherium

Mounted specimen from the The Museum of Paleontology, Russian Academy of Sciences, Moscow.  

When: Miocene to Pliocene (~16 to 8 million years ago)

Where: Europe, Asia, and Africa

What: Chalicotherium is a member of the Chalicotheriidae, a bizarre group of animals, which resemble a cross between a horse and a gorilla. This group is unique among its relatives for having much longer front legs than hind, and it is the only ungulate to walk on its knuckles. Chalicotherium stood roughly 8.5 feet (~2.6 meters) tall at the shoulder, and was able to reach much higher than this into the tree tops via its long arms. Its posture served to protect the large claws on  its hands, which allowed it to easily pull down leaves and branches. Its dentition suggets this was its primary, if not only, food source, it does not appear to have fed at all on the grasses which were starting to spread at this time. Chalicotheres are related to horses, in the order Perissodactyla; within this order they are more closely related to living  rhinos and tapirs, to the exclusion of horses. 

Let me add that this animal has always freaked me out a bit! Sure, I have seen lots of bizarre fossil forms, but for some reason the mix of a gorilla and a horse that stood almost 9 feet tall hits all the wrong buttons. I am a bit glad this one is extinct. ;) 

Arsinoitherium 

Mounted specimen on display at the British Natural History Museum, London. 

When: Late Eocene - Early Oligocene (36-30 million years ago)

Where: Northern Africa

What: Arsinoitherium is the animal with the largest known horns relative to body size. These gigantic horns were composed entirely of greatly expanded nasal bones. It also had a pair of smaller horns behind these enormous protuberances. This stocky beast was about 6 feet (2 meters) tall at the shoulder, and 10 feet (3 meters) long. It lived in Northern Africa, when this region was covered with tropical rainforests and mangrove swamps, eating most manners of vegetation with its large crushing molars. Arsinoitherium was fairly unspecialized in general, with the exception of its gigantic horns - the function of which is not well understood. 

Though Arsinoitheriumsuperficially resembles rhinos, it is not closely related to them at all (and its large horns have a bone core, unlike the horn of the rhino which has no bony component). It is a member of the extinct order Embrithopoda, which is in turn within the Paenungulata (almost ungulates). Living paenugulates are elephants, manatees, and hyraxes. It is not well known how Arsinoitheriumfits into this group, as there is extremely little fossil record of basal embrithopods. Arsinoitherium was named based on the site of the discovery of the first fossils: they were near the palace of Arsinoë, a Ptolemaic Egyptian queen. 

Patriomanis - The American Pangolin

NOTE: Second image is NOT a reconstruction, but a photo of a modern pangolin. To the best of my knowledge no reconstruction of Patriomanis has been done. 

When: Late Eocene (~35 mya )

Where: Wyoming, USA

What: Patriomanis is a pangolin. Pangolins are commonly know as scaly anteaters; their scales are made from keratin, the same material as finger nails. Patriomanis is not the most well known or studied of the fossil pangolins, but it is the only one known from the western hemisphere. As modern pangolins (the order Pholidota) are found exclusively in Asia and Africa, this was an extremely surprising discovery. All other fossil pangolins (both older and younger) are known from the old world, Patriomanis represents an immigration event to the new world which left no descendants. When compared to extant pangolins, Patriomanis has a more generalized post-cranial skeleton, not specially adapted for either digging or climbing trees. Though there are no scales preserved with any of the known material, more basal members of Pholidota recovered from the german fossil locality of Messel have evidence of scales, albeit more limited than in the modern forms. Therefore, it is highly likely the american pangolin was scaly as well.  

This find was so unexpected that the first specimen of Patriomanis was not recognized as a pangolin for several years after its discovery and collection by field crews from the American Museum of Natural History. The material was found in a drawer in the collections of this museum by then graduate student Robert Emry (who went on to later become a curator at the Smithsonian). The skull was labeled a ”immature ? carnivore” and that was the extent of the previous attempts to identify the material. Emry thought the skull was very reminiscent of South American anteaters when he first examined it, but further studies lead him to concluded this was instead an example of an old world clade in North America.  As this was a very bold claim at the time, he was advised to be extremely sure of what he was saying before he published. An in-depth study of the partial skull and postcranial elements lead to a pangolin attribution as the only possible conclusion.  Dozens of studies of pangolins since the initial publication of Patriomanis in 1970 have only reinforced this allocation. The specimen was collected in 1957, and if it was not for Emry’s investigation into fossils from this locality for an unrelated project, it might still be sitting there in the ‘misc.’ bone drawer today. 

Onychonycteris

When: Eocene (all known fossils from a deposit 52.5 million years old)

Where: Wyoming, USA

What:  Onychonycteris is the most basal bat currently known. It differs from living bats in having claws on all five fingers, whereas living bats have lost them. This form also has relatively shorter arms and fingers, as well as longer legs and tail than any other bat, fossil or extant. Onychonycteris was an extremely important find, as allowed us to answer a long standing question about bat evolution: Which came first, flight or echolocation? This taxon was capable of flight, and detailed examination of the cranium revealed that it could not echolocate.  Thus, bats took to the skies before they developed a system for seeing with their ears. 

This amazing fossil is from the Green River fossil lagerstatten in southwestern Wyoming, and is one of two known complete specimens. This example is not the holotype (the specimen which bears the name) as while it looks absolutely gorgeous, the second specimen was arranged on the rock slab in such a way more of the skull could be studied. Additionally, this specimen was actually in the hands of a private collector, and thus not fully available to science.  That is until the specimen was mailed, unannounced, to Dr. Nancy Simmons at the American Museum of Natural History, New York.  She was working on publishing this taxon at the time, and the private collector had been informed of this, so the family sent the specimen to allow her the best examination possible. That was one awesome package to open, believe me! 

Propalaeotheirum - a tiny tiny horse 

When: Middle Eocene (~50 to 40 million years ago)

Where: Europe and Asia, the best fossils are from the Messel Pit in Germany

What: Propalaeotheirum is a fossil horse. It is maybe the tiniest horse there ever was, even smaller than the oldest horses. The largest specimens are estimated to have stood just under 2 feet (~60cm) at the shoulder, and the smallest adult specimens known come in at just about 1 foot (~30cm) tall at the shoulder. The average estimated weight of Propalaeotheirum is roughly 22 pounds (~10 kilos). Horses at this time had not yet developed the single hooved toe seen in modern forms; this tiny animal had three small hoved toes on each forefoot and four each on its hindfeet. From the exceptionally preserved Messel fossils we can tell this ancient horse ate leaves and berries. It is most often reconstructed with a striped coat, as this is the coloring of most tiny ungulates which live in forests today. 

Propalaeotheirum is thought to be an immigrant into Europe, its lineage migrated from North America, where the oldest horse fossila are found. This tiny European horse lineage indures for a few million years after the last record of Propalaeotheirum, but eventually all members of this sub-clade of horses go extinct. There is no direct connection between this small horse and modern species, it is an excellent example of perhaps the earliest ’side branch’ of equid evolution. 

Megacerops - a titanothere 

Note: The mount being assembled above is still on display today, at the American Museum of Natural History, in NYC. 

When: Latest Eocene (~ 37 to 34 million years ago)

Where: North America, most fossils found in the west. 

What: Megacerops is a brontothere. In the late Eocene it was one of the largest mammals in North America, standing over 8 feet (~2.5 meters) tall at the shoulder, with an estimated weight of over 2000 lbs (~1000kg).  These beasts had very distinctive horns, comprised of an outgrowth from the frontal and nasal bones. It is now understood that these structures grew throughout life and were strongly sexual dimorphic; the oldest males had horns that were radically different from those of females. Some earlier paleontologists, not realizing this, basically erected a new species upon every skull that had different looking horns. The example images give an excellent example of the extreme differences present within the genus; the mounted skeleton has very minor horns, while the hanging skull and reconstructions have the very large characteristic Y-shaped ‘slingshot’ fully grown horn of an adult male. 

The clade Brontotheriidae is a member of the order Perissodactyla, which also includes horses, rhinoceroses, and tapirs. Within Perissodactyla brontotheres are most closely related to horses. The last common ancestor of brontotheres and horses was a small hooved animal that browsed from bushes and lower branches. While later horses shifted to a more grass based diet, it is thought that brontotheres remained dependent on this softer vegetation. Thus, as North America started to become drier and cooler at the close of the Eocene, and forests gave way to grasslands, the brontotheres vanished.