Anteosaurus looked remarkably like a dinosaur caught halfway between evolving into a crocodile: this huge therapsid (a member of the family of mammal-like reptiles that preceded the dinosaurs) had a streamlined, crocodilian body with a huge snout, and its puny-looking limbs lead paleontologists to believe that it spent most of its life in water. As with many therapsids, the feature of Anteosaurus that gets experts’ hearts pounding is its teeth, a melange of canines, molars and incisors that could have been used to rip into everything from overgrown ferns to the small, quivering reptiles of the late Permian period.
So, I’ve made an anatomical study of everyone’s favourite giant hornless rhino.
Paraceratherium lived in Eurasia during the Oligocene epoch, and was one of the largest land mammals ever - its skull alone could reach 1.3m in length*. Exact size of Paraceratherium isn’t known due to lack of complete specimens, but it’s been estimated to be up to 7.4m long, 4.8 to 5.25m tall at the shoulder, and weight between 11 and 20 tonnes.
It was a browser, feeding on relatively soft plants.
I used modern rhinos’ and horses’ muscle systems for reference. And I’ve learned that there exist a shrink-wrapped reconstruction of Paraceraherium, with matchstick legs that in no way would be strong enough to carry animal of that size. Honestly, it’s the stuff of nightmares.
* for reference, I’m 1.58m tall. Sure, that’s not much, but it’s still pretty mind-boggling to think about something’s head only 28cm shorter than me.
Pristerognathus is a extinct genus of therocephalian synapsid (relatives of the mammals) from Permian South Africa. These animals were fairly small only growing to around the same size of a cat, and are characterized by their long and narrow skulls armed with large canine teeth. They probably used these teeth to prey on smaller theraspids and millerettids (a group of parareptiles).
Sinoconodon rigneyi is an ancient mammaliamorph or early mammal (depending on systematic approach) that appears in the fossil record of China in the Sinemurian stage of the Early Jurassic period, about 193 million years ago. While in many traits very similar to reptiles, it possessed of a special, secondarily evolved jaw joint between the dentary and the squamosal bones, which had replaced the primitive reptilian one between the articular and quadrate bones, a trait commonly used to define mammals.
Although the animal is closely related to Morganucodon, it is regarded as the most basal of the mammaliaforms. It differed substantially from the more mammalian Morganucodon in its dental and growth habits. Like the reptiles, it was polyphydont, replacing many of its teeth throughout its lifetime, and it seems to have grown slowly but continuously until its death. Sinoconodon is thus less mammalian than early mammaliaforms like docodonts and morganucodonts. Even the smallest known individuals had already began the teething cycle of the front teeth, and combined with a poorly ossified jaw, it very probably did not suckle. The combination of reptilian and mammalian features makes it straddle the divide between the two classes anatomically and likely ecologically. There are simply no animals like it alive today.
Dimetrodon grandis, a large Sphenacodontid from the Early-Middle Permian.
Despite being a reptile, Dimetrodon is actually more closely related to us than to any contemporary reptile group.
It used its large sail for thermoregulation, turning to the sun when it needed to warm up. The sail also may have had a role in sexual reproduction, as well as a threat display.
As one of the earliest cynodonts, Procynosuchus has many primitive features, but it also has features that distinguish it from all other early therapsids. Some of these features have been interpreted as adaptations for a semi-aquatic lifestyle. For example, the wide zygapophyses of the vertebrae allow for a high degree of lateral flexibility, and Procynosuchus may have used anguilliform locomotion, or eel-like undulation, to swim through the water. The tail of Procynosuchus is also unusually long for a cynodont. The long haemal arches would have given the tail a large lateral surface area for greater propulsion through the water. Relatively flat foot bones may also have been an adaptation toward swimming, as the feet may have been used like paddles. Ridges on the femur are an indication of strong flexor muscles that could have stabilized the leg during limb-driven swimming. When the thigh is pulled back in the water, the lower leg tends to bend forward. Strong flexor muscles would have pulled the lower leg back with the femur, providing the powerful backward thrust that is needed to swim.
Dimetrodon grandis is a large extinct tetrapod, but it is not a dinosaur. They lived in the early Permian (around 280 mya) and went extinct millions of years before dinosaurs evolved. Dimetrodon is in the Synapsida, a taxonomic group that includes mammals, meaning we are much more closely related to these nifty creatures that we are to dinosaurs.
I don’t have time for anything lately, so here’s a silly drawing of a Thylacosmilus atrox I did about two weeks ago and didn’t have time to upload it until now. Inspired by the jowls cat/chin cat discussion, and also by my dog :P
I’ve decided to combine big jowls with big chin, because the idea of sabers covered entirely by really long, floppy jowls doesn’t strike me as very comfortable for the animal, and sabers covered only by sort of flesh-sheaths on the mandible also don’t seem comfortable, so I went with somewhat floppy jowls covering the top part of the teeth, and partial sheaths on the lower jaw covering the rest.
And also, by looking at today’s predators, I’d guess that Thylacosmilus spent a lot of its time doing what predators do best: being lazy.
Thylacosmilus lived between the Late Miocene to the Late Pliocene in South America, and I’d be very surprised if they didn’t flop on their backs at least from time to time.
Probainognathus is a genus of meat-eating mammal-like reptile that lived during the lower Upper Triassic of South America. This creature had an incipient squamosal-dentary jaw-cranium joint, which is a clearly mammalian anatomical feature. It was at the very least closely related to the family of Chiniquodontidae, in which some authors have included it. Some broadly similar teeth from Europe were described under the name of Lepagia.
Known from about three dozen specimens, this creature was only about 10 cm long. Two skulls, including the holotype, were stolen from the University of La Rioja, Argentina, in February 1994. A pair of Probelesodon holotypes, accompanied them.
The name Castorocauda lutrasimilis is derived from the Latin castor- meaning “beaver”, -“cauda” meaning “tail”, lutra meaning “otter”, and -similis meaning “similar to”. The tail was broad with scales interspersed with hairs that grew less frequent toward the tip. Overall it was very similar to the tails of modern beavers and was presumably used for locomotion in water in a similar fashion. The caudal vertebrae were flattened dorso-ventrally and similar overall to those in a beaver or otter. Fossilized impressions of some webbing is also present between the toes.
Features of the limbs suggested that it may have been adapted for digging. The forelimbs are robust, with enlarged olecranon and other processes associated with strong muscle attachment. The limbs are similar to the modern platypus, an animal that both digs and swims. Castorocauda, Haldanodon and perhaps other docodonts were fossorial. These early specializations were also present in the crown-group mammal Fruitafossor, also from the late Jurassic.
Docodonts in general have distinctive teeth, and the teeth of Castorocauda have the distinguishing features of the group. The teeth of Castorocauda are different in many ways from all other docodonts, presumably due to a difference in diet. Most docodonts had teeth specialized for an omnivorous diet. The teeth of Castorocauda suggest that the animal was a piscivore, feeding on fish and small invertebrates. The first two molars had cusps in a straight row, eliminating the grinding function suggesting that they were strictly for gripping and not for chewing. This feature of three cusps in a row is similar to the ancestral condition in mammal relatives (as seen in triconodonts), but is almost certainly a derived character in Castorocauda. These first molars were also recurved in a manner designed to hold slippery prey once grasped. These teeth are very similar to the teeth seen in mesonychids, an extinct group of semi-aquatic carnivorous ungulates, and resemble, to a lesser degree, the teeth of seals.
The discovery of Castorocauda lutrasimilis is the first sign that a close relative of mammals adapted to water before dinosaurs lost dominance 65 million years ago, pushing back the estimated date for mammal relatives adapted to a semi-aquatic lifestyle by 110 million years. Based on fossils known at present, the mammal line would not see another semi-aquatic form evolve until the Eocene. Because few fossilized remains had been found, it was previously thought that, until the Cretaceous–Paleogene boundary, all mammals were tiny, ground-dwelling or tree-dwelling, nocturnal animals akin to shrews, hedgehogs, treeshrews, or tenrecs. This notion has now been falsified by the armadillo-like Fruitafossor, the dinosaur-eating Repenomamus, the flying squirrel-like Volaticotherium and now the otter-like Castorocauda.
The American cheetah is an extinct feline, and it actually has another sepcies in the genus, M. inexpectatus. It lived from the Piacenzian age of the Pliocene epoch of the Neogene, to the Tarantian age of the Pleistocene epoch of the Quaternary, aka, from 2.6 to 0.011 million years ago. It lived in North America, and was very similar to the modern cheetah, but actually wasn’t very closely related to it. The similarities are more likely due to convergent evolution with the modern cheetah. It is most closely related to Puma, and evolved from cougar-like ancestors that either were already in America or migrated over from Asia. Convergent evolution is decidedly one of my favorite things, with two different lineage of cats evolving body morphologies that aided in moving rapidly.
It split from the cougar-like ancestor about 3 million years ago. It was morphologically similar to the modern cheetah, and about the same size as a northern cougar. It would have been about 170 cm long with a tail about 92 cm long and about 85 cm high. It would have weighed about 70 kg, but larger ones could reach 95 kg. It had a shortened face and expanded nasal cavities for increased oxygen intake. It had legs proportioned for swift running, and probably would have been a predator of hoofed plains animals such as the pronghorn. In fact, it might have been an interesting bit of an evolutionary arms race between the pronghorn and Miracinonyx, with the pronghorn evolving to outrun the American cheetah and the American cheetah evolving to catch up.
The woolly rhinoceros was a rhinoceros that lived during the Piacenzian age of the Pliocene epoch of the Neogene, to the Tarantian age of the Pleistocene epoch of the Quaternary, about 3.6 to 0.01 million years ago. It lived in Europe and northern Asia, and was a member of the Pleistocene megafauna, a group of large mammals that lived in Ice Age. It had stocky limbs and thick wooly fur to make it well suited to the tundra environment it lived in, and its closest living relative according to DNA studies (do you realize how amazing it is to write about organisms we have DNA for) is the Sumatran rhinoceros, Dicerorhinus sumatrensis. In fact, it lived so recently and has been so well preserved, there are even mummified individuals from Siberia - and cave paintings!
It would have been about 3 to 3.8 meters long, weighing in at about 1,800 to 2,700 kg. It would have been about 2 meters tall, and it was about the same size or a little bit larger than the living white rhinoceros. The horns on the skull were made of keratin, with the longer horn about 61 centimeters long. It had very thick, very long fur, small ears, short legs, and a stocky body, as shown in the cave painting. Its ancestors migrated to the north from Tibet when the Ice Age began, and it had ranges in the Doggerland and Northern Europe, England, and the North Sea, which was then a cold and arid desert. Its range grew and shrunk as the Ice Age waned between cold and warm cycles, and as such the populations migrated as these cycles occurred. It lived alongside woolly mammoths and other Pleistocene megafauna, as well as humans.
Females of the species gave birth to one or two calves, and it appears that it had the teeth and skull of a grazing herbivore. It even had the gut necessary for digesting cellulose-rich food, allowing it to graze upon grasses and sedges, though it would have needed to do so in large amounts. It also would have had forbs and graminoids. It went extinct around the same time as the rest of the Pleistocene megafauna, and there are a lot of reasons that have been postulated for this, one of which being human hunting. Climate change may have also contributed, but this seems rather unlikely. Populations may have survived until about 8,000 BC in Siberia, however this is uncertain.