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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.
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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.
On Gargano island Deinogalerix would have been one of the top predators, filling a coyote type niche and hunting smaller vertebrates. Deinogalerix appears to have been endemic (only found in this one spot) to this paleo-island. This isolation is what allowed the species to evolve to such great sizes, another example of island gigantism is the giant rabbit, Nuralagus. -
Indohyus
Reconstruction by Carl Buell.
When: Eocene (~48 million years old)
Where: India and Pakistan
What: Indohyus is a fossil artiodactyl that falls on the lineage leading to whales. The discovery of an almost complete specimen Indohyus helped to answer one of the long standing questions in the early evolution of whales. All living whales are carnivorous (with diets ranging from vertebrate prey to tiny invertebrates), however, all other living artiodactyls are predominately herbivorous. As all fossils assuredly related to whales showed both aquatic and carnivorous adaptations, it was a mystery as to which came first in the evolution of the cetaceans. Enter Indohyus. This fossil lacks any carnivorous adaptions in its dentition, but has several adaptations for spending time submerged - most notable are an ear region that looks a lot like that of previously known fossil whale ancestors and bones with increased density. These features would have allowed the animal to hear better underwater and to stay submerged easier, respectively. Isotopic analysis of its dentition and bones suggests that Indohyus spent a good amount of time in waters, but fed on land plants - much like the modern Hippopotomus. It has been suggested Indohyus fled to the water to avoid predators, like the modern African Mousedeer, which has been documented spending almost five minutes underwater to escape predation. Indohyus was about 3 feet (~1 meter) long from end to end, thus it would have had many potential predators in the early Eocene world.
Phylogenetic analysis place Indohyus at the base of what have traditionally been referred to as ‘archaeocetes’; a paraphyletic lineage of fossils more closely related to whales than to hippos. The term Cetaceamorpha is used for the group that includes all living whales and all fossils more closely related to them than to the hippos. Falling very near Indohyus is an animal called Diacodexis. I will highlight this animal more in a future entry, but to be brief it shows none of the aquatic adaptions of Indohyus, but has simular dentition. Thus, the current hypothesis of basal whale evolution is that small deer-like animals first went into the water, possibly for protection from predators, and then later became carnivorous.
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Paramylodon - Harlan’s Ground Sloth
Mounted specimen on display at the Page Museum, Los Angeles, California, USA.
When: late Pliocene to Pleistocene (~5 million to 11,000 years ago)
Where: Central and North America
What: Paramylodon is the most common of the ground sloths found at the La Brea tar pits fossil site in southern California. Megalonyx is found here as well, and though the two sloths resemble one another very strongly, they are on opposite sides of the family tree of sloths. Megalonyx is very closely related to the living two-toed sloth, but Paramylodon and its kin form a group at the base of sloths with no living relatives. The last common ancestor of these sloths lived roughly 30 million years ago. A suite of detailed morphological features distinguish these two sloths, found thoughout the skeleton, but perhaps the most amazing is that Paramylodon was somewhat of an armored animal. Imbedded within its skin were many tiny dermal ossicals, which would have served to protect it from the many predators that roamed southern California at the time.
The most complete specimens of Paramylodon come from the La Brea tar pits (which is a very redundant name as la brea means the tar, but hey!). The tar formed tens of thousands of years ago, by natural seepage of the sticky and dense material from the bedrock. The tar pits looked nothing like they do today, however. There were no large ‘lakes’ of tar then. Instead what would occur is occasionally a large seepage would collect and then be covered by leaves and dirt, hiding it from view. This would create a natural trap that would ensnare whichever animal was unfortunate enough to stumble upon it. The large expanses of tar visible today are due to the excavation of the site. The site was recognized as fossil bearing in the early 1900s, bones had been discovered on Rancho La Brea for some time previous to this, but they had not been properly identified as fossils. The Page Museum was opened on the site in 1977 in order to provide both a place for researchers to easily access and study the specimens, and to display the wondrous finds to the people of Los Angeles.
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Nuralagus rex - The Minorcan Giant Lagomorph
When: Pliocene (~3-5 Million years ago)
Where: Minorca, a small island in the Mediterranean
What: Nuralagus is a giant rabbit. It lived on the island of Minorca and is estimated to have weighed 25 lbs (~11kg) on average, though the largest bones found could be from an animal twice this weight! Nuralagus is an excellent example of the ‘island effect’. This is where species on an island are dramatically increased (or reduced) in size compared to their mainland close relatives. Nuralagus is six times the size of the living common rabbit, but was ten times the size of its contemporary mainland bunny brother.
Nuralagus is not just a common rabbit scaled up greatly, along with this increase in size came many other morphological transformations. It was not much of a hopper, the characteristic anatomy of the spine which makes rabbits ‘springy’ was lost. It also did not have the relatively large eyes and ears that we associate with most rabbits. These features may seem very far removed from one another, but the loss of both large ears and hopping is related to the lack of predators on the island. Nuralagus didn’t need to be constantly observant and able to leap away quickly upon sight of a predator, as there was nothing on the island able to take down a grown individual.
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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. ;)
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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!
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Arsinotheirum
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: Arsinotheirum 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. Arsinotheirum was fairly unspecialized in general, with the exception of its gigantic horns - the function of which is not well understood.
Though Arsinotheirum superficially 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 Arsinotheirum fits into this group, as there is extremely little fossil record of basal embrithopods. Arsinotheirum was based on the site of the discovery of the first fossils: they were near the palace of Arsinoë, a Ptolemaic Egyptian queen.
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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.
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Epicyon haydeni - the largest dog
When: Mid to Late Miocene (~20 to 5 million years ago)
Where: Throughout much of North America, excepting northern Canada.
What: Epicyon haydeni is the largest canid known. It is estimated to have weighed in at roughly 375 lbs (~170 kg). Even though it was the size of a bear, it still retained the relatively long legs and resulting fast speed that characterizes dogs. These dogs were not just ‘scaled up’ wolves, they were much more solidly built in general and had teeth more adapted for bone crunching. While they were top predators, and perhaps hunted in packs, they were no doubt also scavengers - able to crush bone in order to eat what had been left behind by other hunters.
Epicyon is a genus in the clade Borophaginae. This is one of the three major subclades of the dog family. The last common ancestor of the borophagines and the modern canines lived over 30 million years ago. While this subclade is characterized by large bone crushing dogs, it also contained dogs which more more resemble living forms such as the wolf. In the reconstruction image the large dog is Epicyon haydeni and the smaller is another member of the same genus. On the whole, borophagines were more omnivorous than their canine relatives.
