Although we thought we were studying only one animal, Asaphestera intermedia, one of our major findings was recognizing that what previous paleontologists had thought was a single animal was actually a composite of multiple fossils of at least three very different animals! We could only be certain of two of them: a new reptile we named Steenerpeton silvae and an early synapsid, Asaphestera platyris, with evidence of a single temporal opening in the skull.
(...) Asaphestera platyris provides the oldest evidence of mammal-like reptiles in the fossil record, establishing a firm date for their diversification around 315 million years ago.
Asaphestera: the earliest amniote? …No Mann et al. 2020 mistakenly reassessed their ‘microsaur’, Asaphestera platyris (Fig. 1), as at ‘the earliest synapsid’. The LRT nests this taxon as a microsaur after demonstrating interpretation and reconstruction errors. Unambiguous? No. Just because they say so, does not mean it is true. (...) Mann et al. 2020 mistakenly reassessed their microsaur, Asaphestera platyris, as a synapsid. The LRT nests it as a microsaur close to Kirktonecta, a taxon essentially overlooked by the authors. Nearly coeval Archaeothyris remains the earliest known synapsid, but several synapsids are more primitive, indicating an earlier radiation. So, they’re out there somewhere! Mann et al. did not find them…yet.
Protoclepsydrops is an extinct genus of early synapsids, found in Joggins, Nova Scotia. The name means 'first Clepsydrops', and refers to it being the predecessor of the other early synapsid Clepsydrops. Like Archaeothyris, Protoclepsydrops resembled a modern lizard in superficial appearance. However, Protoclepsydrops had primitive vertebrae with tiny neural processes typical of their amniote ancestors. Protoclepsydrops is known from a few vertebrae and some humeri. Its skeletal remains indicate that it may have been more closely related to synapsids than to sauropsids, making it a possible stem-mammal. If so, it is the oldest synapsid known, though its status is unconfirmed because its remains are too fragmentary. Protoclepsydrops lived slightly earlier than Archaeothyris.
Archaeothyris is an extinct genus of ophiacodontid synapsid that lived during the Late Carboniferous and is known from Nova Scotia. Dated to 306 million years ago, Archaeothyris, along with a more poorly known synapsid called Echinerpeton, are the oldest undisputed synapsids known. The name means ancient window (Greek), and refers to the opening in the skull, the temporal fenestra, which indicates this is an early synapsid.
Archaeothyris was also more advanced than the early sauropsids, having strong jaws that could open wider than those of the early reptiles. While its sharp teeth were all of the same size & shape, it did possess a pair of enlarged canines, suggesting that it was a carnivore.
Archaeothyris' legs were articulated laterally at its pelvis and shoulders, which gave it a sprawling stance. The first toe is smaller than the second.
Species: A. florensis (type).
Type: Carnivore/Insectivore.
Size: 50 centimetres long.
Echinerpeton is an extinct genus of synapsid, including the single species Echinerpeton intermedium from the Late Carboniferous of Nova Scotia, Canada. The name means 'spiny lizard' (Greek). Along with its contemporary Archaeothyris, Echinerpeton is the oldest known synapsid, having lived around 308 million years ago. It is known from six small, fragmentary fossils, which were found in an outcrop of the Morien Group near the town of Florence. The most complete specimen preserves articulated vertebrae with high neural spines, indicating that Echinerpeton was a sail-backed synapsid like the better known Dimetrodon, Sphenacodon, and Edaphosaurus. However, the relationship of Echinerpeton to these other forms is unclear, and its phylogenetic placement among basal synapsids remains uncertain.
(...) The teeth of both the upper and lower jaws are small and cone-shaped, some having slightly serrated edges, and are only differentiated by slight differences in length (some other synapsids have teeth that vary greatly and shape across their jaws). The three forward-most dentary teeth are angled slightly outward as in more derived synapsids such as Dimetrodon and Sphenacodon. Several features, including straight-margined maxillae and simple conical teeth, are also seen in the earliest reptiles.
(...) The most prominent feature of the vertebrae of Echinerpeton are their tall neural spines, which can be up to seven times higher than they are wide. They are similar in proportion to the spines of Sphenacodon, although Echinerpeton is considerably smaller in overall size. The neural spines of the holotype are thinnest at their tips, suggesting that MCZ 4090 may have been an immature individual with poorly ossified bones.
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