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Herpetoskylax is an extinct genus of which existed in South Africa. The type species is Herpetoskylax hopsoni.Sidor, C.A., and Rubidge, B.S. (2006). " Herpetoskylax hopsoni, a new biarmosuchian (Therapsida: Biarmosuchia) from the Beaufort Group of South Africa" In: Amniote Paleobiology, perspectives on the Evolution of mammals, birds and reptiles, edited by Carrano, M.T., Gaudin, T.J., Blob, R.W., and Wible, J.R. Chicago University Press, p. 76-113 It lived in the Late Permian Period.Palaeocritti - a guide to prehistoric animals. Herpetoskylax hopsoni. Downloaded 25/03/2011
The genus name means 'reptile-puppy', from the Ancient Greek (ἑρπετόν]], 'creeping animal') and (σκύλαξ]], 'young dog'). The juxtaposition of reptilian and mammalian names highlights the transitional characters of non-mammalian therapsids. The type specimen is CGP 1/67, a skull. The skull and lower jaw were the only components found.
Four premaxillary teeth are present with few serrations (likely from attrition), but it is suggested there was an additional tooth based on a gap noted in the region. The genus has no precanine maxillary teeth, but it does have significant canines. Serrations are present on the posterior side of said canines, as well as on the postcanine teeth.
The skull differs from other biarmosuchians in the configuration of the septomaxilla, of which both sides were preserved. The septomaxilla, a small bone associated with the nose area, goes in between the maxilla and the external naris (nose). The maxilla is a smooth, sizable bone. The relation between the premaxilla and maxilla is unknown due to insufficient preservation. The postfrontal bone, dorsal to the eyes, is flat, particularly in contrast with this specimen's relatives, which often have display structures in this region. Sidor and Rubidge comment that the morphology of Herpetoskylax's jugal (cheek bone) is easiest to see compared to other biarmosuchians.
Across non-mammal therapsids, of which Herpetoskylax is part of, in terms of the braincase, the inside shape of the skull is generally primitive. They have no enlargement of their cerebral hemisphere or their cerebellum, no divide between cerebral hemispheres, and they may have had small olfactory bulbs. However, biarmosuchians have more derived features as well, such as a strong flexure at the level of the midbrain.
There is compression in the palate so its finer details are unknown, such as whether the vomer is connected to the palatine or pterygoid.
The species name hopsoni honors James Hopson who did extensive and relevant research on biarmosuchians.
Rubidgina has been proposed as a possible juvenile Herpetosklyax hopsoni, but a study in 2021 by Duhamel et al. advised that this is uncertain.
There are various theories relating to snout sensitivity in non-mammal therapsids; members of the group may have had whiskers, given that they share maxillary features with mammals like specific snout foramen. Similar features are present in reptiles, so it is not a certainty, though it is likely given their relation to mammals.
Paleontologist Robert Bakker theorized that therapsids were endothermic (i.e., warm-blooded), citing evidence that the Permian climate was often cold and therapsids would have needed the advantage to be so prolific during this time. In 1986, a paper by Bennett and Ruben asserted that the Permian was sufficiently warm to support ectothermy (cold-bloodedness), additionally noting that other successful fauna of the time were ectothermic. They concluded, however, that it was possible for therapsids to have been endothermic based on features shared with mammalian groups such as and .Bennett, A. F., & Ruben, J. A. (1986). The Metabolic and Thermoregulatory Status of Therapsids. The Ecology and Biology of Mammal-Like Reptiles, 207-218. Herpetoskylax did not possess nasal turbinals, a trait associated with endothermy in extant mammals and birds, as this character has only been confirmed in more derived therapsids.
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