The Antaeus lizard, Anteosaurus (1921)

Phylum : Chordata
Class : Synapsida
Order : Therapsida
Suborder : Dinocephalia
Family : Anteosauridae
Genus : Anteosaurus
Species : A. magnificus

  • Late Permian (265,8 - 260,4 Ma)
  • 5 m long and 1 000 kg (size)
  • Eastern Cape province, South Africa (map)

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.

I think this guy is finished… I’ll have to check tomorrow, when I’m actually somewhat awake. I have two versions of this, with one minor difference, but I’m just to tired to decide now which one is better (or if I still need to fix something, add some shadows, and so on).

But anyway, 2 pictures done, 10 more to go!

And a little bit about Haptodus: it’s the most basal sphenacodontian, and member of a lineage that eventually led to mammals. It lived during the Late Carboniferous and Early Permian (299 - 296.4 Ma). It was about a medium-size predator, with individual sizes varying between 60cm and 1.5m in length. It fed on arthropods and small vertebrates. I based my reconstruction on H.garnettensis ( or H. baylei, depending on whether baylei is a valid species or not.)

It’s lying on Cordaites leaves.

Next one will be Pantelosaurus or Tetraceratops.

The chinese spiky tooth, Sinoconodon (1961)

Phylum : Chordata
Class : Synapsida
Order : Therapsida
Suborder : Cynodontia
Family : Sinoconodontidae
Genus : Sinoconodon
Species : S. rigneyi

  • Early Jurassic (210 - 200 Ma)
  • 15 cm long (size)
  • China (map)

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.

The Before dog crocodile, Procynosuchus (1938)

Phylum : Chordata
Class : Synapsida
Order : Therapsida
Family : Procynosuchidae
Genus : Procynosuchus
Species : P. delaharpeae, P. rubidgei

  • Late Permian (260,4 - 253,8 Ma)
  • 60 cm long and 3 kg (size)
  • Southern Africa (map)

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.
New fossil species found in Mozambique reveals new data on ancient mammal relatives

In the remote province of Niassa, Mozambique, a new species and genus of fossil vertebrate was found. The species is a distant relative of living mammals and is approximately 256 million years old. This new species belongs to a group of animals called synapsids. Synapsida includes a number of extinct lineages that dominated the communities on land in the Late Permian (260-252 million years ago), as well as living mammals and their direct ancestors.

The first mountain jaws, Probainognathus (1970)

Phylum : Chordata
Class : Synapsida
Order : Therapsida
Suborder : Cynodontia
Family : Probainognathidae
Genus : Probainognathus
Species : P. jenseni

  • Triassic (230 Ma)
  • 10 cm long (size)
  • South America (map)

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 Beaver tail, Castorocauda (2006)

Phylum : Chordata
Class : Synapsida
Order : Therapsida
Suborder : Docodonta
Family : Docodontidae
Genus : Castorocauda
Species : C. lutrasimilis

  • Jurassic (164 Ma)
  • 45 cm long and 500 g (size)
  • Daohugou beds, Mongolia (map)

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.