First mounted specimen is at the American Museum of Natural History, NYC.
Reconstruction by Todd S. Marshall.
When: Cretaceous (~80 million years ago)
Where: Widespread in Cretaceous seas
What: Elasmosaurus is a plesiosaur. It has the longest neck of any known plesiosaur, made up of over 70 cervical vertebrae. In total it was 46 feet (~14 meters) long, with roughly half of this length made up of the neck. Elasmosaurus was named by Cope in the mid 1800s, and in this paper he made a rather famous blunder. He reconstructed the head of Elasmosaurus attached to what we now know is its tail. I say ‘now know’ but almost immediately upon publication of the specimen, the scientific community pointed out Cope’s blunder. To be as fair as possible to Cope, he was a self educated man and at the time was much more familiar with lizards, especially the giant mosasaurs, which do have spectacularly long tails. Additionally the first plesiosaurs with exceptionally long necks were just being discovered in Europe at this time. Still though, it is a good example of how you should be very careful not to let any preconceived notions you may have distort what is right in front of you.
Despite a number of artistic reconstructions, Elasmosaurus could not lift its body, or even most of its neck, out of the water. All it could do is breach the surface of the water with its head for air. As the animal could not survive out of the water, let along drag itself around with its highly compressed paddles, Elasmosaurus must have given birth to live young. While we have no direct evidence of vivipary in this particular plesiosaur there are amazing fossils of closely related forms showing live birth. Elasmosaurus also was not capable of coiling its neck in a ‘snake like’ manner. Its long neck was used to allow it to move its head close to schools of fish, while its body would remain far behind. It would swim beneath its prey and then lift its head up, creating far less disturbances in the water than its large body would, and allowing it to quickly snack on unsuspecting fish.
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.
Mounted specimen on display at the American Museum of Natural History, NYC
When: Late Devonian (~365 million years ago)
Where: The ancient swamps of Greenland, near the Devonian equator.
What: Acanthostega is a basal tetrapod - one of the first vertebrates to develop limbs instead of fins, though it was not fully able to maneuver on land. Its pectoral girdle was constructed much more like that of a fish than a later tetrapod and could not bear the weight of the animal on land. However, it is the first taxon known that did have a pelvic girdle capable of supporting weight and propelling it forwards, this was accomplished by the fusion of either sides of the pelvis to one another ventrally, and a firm contact established between either pelvis and at least two vertebrae - precursors of the fused vertebra that would become the sacrum in later tetrapods. What is the use if only one half of the body is able to be supported by limbs? This type of pelvic girdle most likely did not at first develop for support. This structure also marks a shift from a primarily forelimb driven locomotion mode to one propelled by activity in the hind-limbs. Acanthostega could move in extremely shallow waters by ‘walking’ on the sediment with its hind-limbs, with its forelimbs steering instead of providing the primary movement source.
This interpretation is supported by its jaw structure, which lacks features relating to suction feeding. Rather it is hypothesized this primitive tetrapod would feed by directly biting onto insects and other terrestrial invertebrates that it could reach from the water’s edge. Thus, the predatory mode that characterizes the first terrestrial vertebrates was first developed by an aquatic animal. Later tetrapods were able to emerge from the waters, at least for short periods of time, to hunt prey that were beyond the reach of their ancestors. Another interesting note is that Acanthostega had 8 digits on its forelimb - it took a while in the evolution of tetrapods for five digits on the hands and feet to become established.
Both mounted specimens on display at the American Museum of Natural History, NYC
When: Late Cretaceous (~75 Million years ago)
Where: North America, most fossils known from Alberta and Montana.
What: Styracosaurus is a ceratopsian dinosaur. It is easly distinquished from its more famous relative Triceratops as it lacks the two large brow horns, instead having four to six spike-horns extending from its fenestrated frill. It is also a bit smaller than this giant ceratopsian ‘only’ reaching lengths of 18 feet (~5.5 meters). Styracosaurus material was first collected by the great fossil collector C.M. Sternberg in 1913, from what is now Dinosaur Provincial Park in Alberta, Canada. This area proved to be a treasure trove of Styracosaurs material and has been visited by fossil collectors repeatly over the decades. The large amount of material of this one dinosaur has supports the conclusion that Styracosaurs traveled in herds, as has been proposed for other ceratopsians.
Ceratopsians appear to have originated in Asia in the Jurassic period, but it was after the migration of members of the clade to North America that they greatly increased in size and developed the large neck frills and skull ornamentation the group is famous for. There has been much debate as to the purpose of the horns and frills. The modern consensus is that they functioned for defense from predators, combat between individuals, and for species identification for mating.
When: Late Devonian (380-360 million years ago)
What: Dunkleosteus is one of the biggest placoderms to ever swim in the paleozoic oceans. Placoderms were some of the first jawed vertebrates, and rapidly put these jaws to use, becoming the top predators of the devonian seas. Dunkleosteus was the apex predator of its days, with nothing to fear but other Dunkleosteus (some specimens show evidence of cannibalism). It reached lengths of up to 33 feet (~10 meters) and is estimated to have weighed 8,000 lbs (~3,600 kg). Studies have shown that these giant fish could open their mouths extremely fast, creating massive suction that would draw prey into their mouths. Larger prey would then be captured and crushed by the giant ‘teeth’ of Dunkleosteus. These animals did not have true teeth, but instead what served as their teeth were sharped and exposed projections of bone.
Placoderms were an early off shoot of jawed vertebrates, and have no living descendants. Modern fish are more closely related to land animals than they are to Dunkleosteus. This giant placoderm, along with the rest of it’s clade, went extinct at the end of the Devonian. Their disappearance is primarily attribute to large anoxic (a lack of oxygen) events on the ocean floor, which dramatically disrupted the food chain - leading to one of the largest extinction events in Earth’s history.
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.
Nemicolopterus - perhaps the smallest of the pterasaurs
When: Early Cretaceous (~120 million years ago)
What: Nemicolopterus is a pterosaur. It is the smallest one known, its wing span was just 10 inches (25 centimeters) from tip to tip. It was well adapted for roosting in trees with its highly curved toes and sharp claws and is thought to have eaten insects. Nemicolopterus was one of the few pterosaurs to live far inland, most of the group were fish eaters living near or on coasts. The validity of Nemicolopterus is debated; there are strong arguments in favor of it actually being a juvenile Sinopterus. The single specimen of this proposed minute pterosaur has a very large skull for its size and has a simular level of bone fusion as other known hatchling pterosaurs - it is thought the young could fly at a very young age. Sinopterus has a wingspan of 4 feet (~1.2 meters), which is on the small end for pterosaurs. (In the example images for today, the two on the right are of Sinopterus.)
Pterosaurs are archosaurs, members of the group that also includes crocodiles and dinosaurs. Within Archosauria they are more closely related to dinosaurs than to crocodiles. This clade is the first vertebrate lineage to have evolved powered flight, already flying by the late Triassic (~220 million years ago). The pterosaur wing was primarily supported by a hyper-elongated 4th digit, leaving digits I-III free in most taxa. This makes pterosaurs the only flying vertebrate group to have retained free digits, as both birds and bats lost the full use of their fingers in the evolution of their wing mechanisms. Pterosaurs went extinct at the end of the Cretaceous period (~65 million years ago).
Ceratogaulus - the horned gopher
When: Miocene to early Pliocene (~17 to 5 million years ago)
Where: The great plains region of North America, the best fossils coming from Nebraska
What: Ceratogaulus is an extinct rodent. They are most notable as they are not only the sole horned rodent known, but the smallest horned mammal of all time; reaching an average length of 1 foot (~30cm) as adults. While Ceratogaulus was a digging animal, and lived in burrows, the horns were not useful for digging. For this use it’s horns would need to be both placed more forward on the snout and angled anteriorly. This is also why the horns were not well suited for fighting between individuals. The best interpretation of their use in life is for defense from predation. With their upward angle and rearward position the horns of Ceratogaulus would be excellent for defending the back and neck of the rodent.
Ceratogaulus is a very basal rodent. It’s closest living relative is the mountain beaver, which is in turn somewhat of a living fossil. More broadly it is fairly closly related to the squirrel family.
Megalonyx- Jefferson’s ground sloth
When: Late Miocene to end Pleistocene (~10 million years to 10,000 years ago)
Where: Throughout North America
What: Megalonyx is a giant ground sloth, that grew to roughly 8-10 feet (~2.5 to 3.0 meters) long. They are the genus of giant ground sloth most closely related to the living two-toed sloth Choloepus. Sloths originated, and most of them diversified in South America, moving northward during the great American interchange, but Megalonyx is a major exception. Its ancestors reached North America millions of years prior to the massive migrations of other South America taxa; via island hopping. This relatively early arrival allowed it to spread throughout the northern continent. Megalonyx is the only species of sloth to have reached as far north as Alaska and the Yukon. It was common in many of the lower 48 states. Like many ground sloths, Megalonyx went extinct at the end of the last glacial period.
A more recent historical note about Megalonyx; this genus was the first fossil from the Americas to be described, and the person who did so was none other than Thomas Jefferson. He proposed the name Megalonyx for the genus, based on first material recovered - the gigantic claws. Later this genus name was formalized and a species named in his honor: Megalonyx jeffersoni (this species is the state fossil of West Virginia). Jefferson was very hopeful that living Megalonyx would be found in the uncharted west, he told Lewis and Clark to be sure to be on the look out for this beast and report back when it was discovered.
Deinotherium - Hoe tusker
When: Mid-Miocene to Early Pleistocene (~10 million to 3 million years ago)
Where: Asia, Africa, and Europe
What: Deinotherium is a proboscidiean. The only two living species in Proboscidiea are the African and Indian elephants, but there are dozens of fossil species in this order. Unlike some other groups that not only have a much greater number of fossil species than living but a much wider variety of morphologies to go along with that, most fossil elephants well… look like elephants! That being large, graviportal, and trunked.
However, even though there is less extreme differences in morphology within proboscidieans, there are still a lot of variations on the basic elephant body plan. One great source of variation is in the tusks. The tusks of Deinotherium are enlarged incisors of its lower jaw whereas in modern elephants the tusks are enlarged upper incisors. The clade containing Deinotheirum spilt off from the rest of the order roughly 40 million years ago, and the last common ancestor had slightly enlarged upper and lower incisors - thus it appears that some elephant clades further enlarged one set over the other. Oh, one last note about Deinotheirum… it was over 3 times the size of the modern african elephant. It was the 3rd largest land mammal ever to lumber accross the Earth!