Herpetoskylax

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Herpetoskylax
Temporal range: Late Permian 259–254  Ma
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Herpetoskylax.jpg
Herpetoskylax hopsoni
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Clade: Therapsida
Suborder:† Biarmosuchia
Genus:† Herpetoskylax
Sidor and Rubidge, 2006
Species:
†H. hopsoni
Binomial name
†Herpetoskylax hopsoni
Sidor and Rubidge, 2006

Herpetoskylax is an extinct genus of biarmosuchian therapsids which existed in South Africa. The type species is Herpetoskylax hopsoni. [2] It lived in the Late Permian Period. [3]

The genus name means ‘reptile-puppy’, from the Ancient Greek herpeto- ( ἑρπετόν , ‘creeping animal’) and skylax ( σκύλαξ , ‘young dog’). The juxtaposition of reptilian and mammalian names highlights the transitional characters of non-mammalian therapsids. [4] The type specimen is CGP 1/67, a skull. The skull and lower jaw were the only components found.

Description

Skull

The skull of Herpetoskylax is noted to have been preserved unusually well in regards to other biarmosuchians. It is approximately 13 centimeters long. [2] Skull sutures can be recognized and the skull itself is only compressed slightly. [2] It displays primitive features such as a convex curve to the skull roof when viewed from the side, a “deep snout,” [2] a small temporal opening, and the absence of a freestanding coronoid process on the lower jaw. It has large eyes, a trait shared with other biarmosuchians. It is inferred that the premaxilla was short, similar to its fellow biarmosuchian, Lycaenodon . [2]  

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. [2]

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, [5] 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. [2] The postfrontal bone, dorsal to the eyes, is flat, [2] particularly in contrast with this specimen’s relatives, which often have display structures in this region. [6] Sidor and Rubidge comment that the morphology of Herpetoskylax’s jugal (cheek bone) is easiest to see compared to other biarmosuchians. [2]

Across non-mammal therapsids, of which Herpetoskylax is part of, in terms of the braincase, the inside shape of the skull is generally primitive. [7] 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. [7]

Palate

Herpetoskylax lacks palatal dentition, which is a feature seen in many tetrapods. [8] It has been theorized that the loss of palatal teeth in more derived tetrapods was perhaps due to changes in feeding or the expansion of the secondary palate, but it cannot be confirmed. [8]

There is compression in the palate so its finer details are unknown, such as whether the vomer is connected to the palatine or pterygoid. [2]

Lower Jaw

In the holotype, the left side of the back lower jaw is missing, but the right side was preserved well. The lower jaw is fairly narrow. Anteriorly, the jaw is shallow, but posteriorly it deepens, which is characteristic of biarmosuchians. [2]

Discovery and Name

The region (in yellow) where Herpetoskylax was found Geology of Karoo Supergroup.png
The region (in yellow) where Herpetoskylax was found

The holotype skull was found in the Beaufort Group in the Karoo Basin of South Africa, located in the Beaufort West District, Western Cape Province. [2] It was found on a farm, and it was determined that the skull was from the Cistecephalus Assemblage Zone, which was used as evidence for the conclusion that its age was Late Permian. [2] The species was described and named by Christian A. Sidor and Bruce S. Rubidge in 2006.

The species name hopsoni honors Dr. James A. Hopson who did extensive and relevant research on biarmosuchians. [2]

Classification

The group Biarmosuchia, including Herpetoskylax
Biarmosuchia

Biarmosuchus

Hipposaurus

Herpetoskylax

Lycaenodon

Ictidorhinus

Lobalopex

Lemurosaurus

Based on Sidor and Rubidge, 2006

Herpetoskylax belongs to the basal non-mammal therapsid group Biarmosuchia, with suggested sister taxa Hipposaurus and Lycaenodon based on Sidor and Rubidge’s phylogenetic trees. [2] More broadly, it is a synapsid.

Rubidgina has been proposed as a possible juvenile Herpetosklyax hopsoni, [2] but a study in 2021 by Duhamel et al. advised that this is uncertain. [9]

Paleobiology

Biarmosuchians, including Herpetoskylax, had skulls specialized for a carnivorous diet, with their large canines and enlarged jaw muscles. [10] Herpetoskylax was estimated to have a hearing range of 8248.16 hertz and a mean frequency of 4691.32 hertz based on an analysis of the skull. [11]

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. [12]

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. [13] 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 monotremes and therians. [14] 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. [14]

Paleoenvironment

Herpetoskylax lived in what is now the Beaufort Group in South Africa, a region in the Karoo Basin. [2] This area in the late Permian is thought to have been seasonal and varied from wet to dry climates. [15] Vegetation along streams and lakes were theorized to provide a diet for reptilians and acted as a foundation for carnivorous non-mammal therapsids like Herpetoskylax. [16]

Related Research Articles

<span class="mw-page-title-main">Therapsida</span> Clade of tetrapods including mammals

A therapsid is a member of the clade Therapsida, which is a major group of eupelycosaurian synapsids that includes mammals and their ancestors and close relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more underneath the body, as opposed to the sprawling posture of many reptiles and salamanders.

<span class="mw-page-title-main">Dinocephalia</span> Extinct clade of stem-mammals

Dinocephalians are a clade of large-bodied early therapsids that flourished in the Early and Middle Permian between 279.5 and 260 million years ago (Ma), but became extinct during the Capitanian mass extinction event. Dinocephalians included herbivorous, carnivorous, and omnivorous forms. Many species had thickened skulls with many knobs and bony projections. Dinocephalians were the first non-mammalian therapsids to be scientifically described and their fossils are known from Russia, China, Brazil, South Africa, Zimbabwe, and Tanzania.

<span class="mw-page-title-main">Biarmosuchia</span> Extinct suborder of therapsids

Biarmosuchia is an extinct clade of non-mammalian synapsids from the Permian. Biarmosuchians are the most basal group of the therapsids. They were moderately-sized, lightly built carnivores, intermediate in form between basal sphenacodont "pelycosaurs" and more advanced therapsids. Biarmosuchians were rare components of Permian ecosystems, and the majority of species belong to the clade Burnetiamorpha, which are characterized by elaborate cranial ornamentation.

<i>Anteosaurus</i> Extinct genus of anteosaurid synapsid from the Permian

Anteosaurus is an extinct genus of large carnivorous dinocephalian synapsid. It lived at the end of the Guadalupian during the Capitanian stage, about 265 to 260 million years ago in what is now South Africa. It is mainly known by cranial remains and few postcranial bones. Measuring 5–6 m (16–20 ft) long and weighing about 600 kg (1,300 lb), Anteosaurus was the largest known carnivorous non-mammalian synapsid and the largest terrestrial predator of the Permian period. Occupying the top of the food chain in the Middle Permian, its skull, jaws and teeth show adaptations to capture large prey like the giants titanosuchids and tapinocephalids dinocephalians and large pareiasaurs.

<i>Euchambersia</i> Extinct genus of therapsid from Late Permian South Africa

Euchambersia is an extinct genus of therocephalian therapsids that lived during the Late Permian in what is now South Africa and China. The genus contains two species. The type species E. mirabilis was named by paleontologist Robert Broom in 1931 from a skull missing the lower jaw. A second skull, belonging to a probably immature individual, was later described. In 2022, a second species, E. liuyudongi, was named by Jun Liu and Fernando Abdala from a well-preserved skull. It is a member of the family Akidnognathidae, which historically has also been referred by as the synonymous Euchambersiidae.

<i>Anomocephalus</i> Extinct genus of therapsids

Anomocephalus is an extinct genus of primitive anomodonts and belongs to the clade Anomocephaloidea. The name is said to be derived from the Greek word anomos meaning lawless and cephalos meaning head. The proper word for head in Greek is however κεφαλή (kephalē). It is primitive in that it retains a complete set of teeth in both jaws, in contrast to its descendants, the dicynodonts, whose dentition is reduced to only a single pair of tusks, with their jaws covered by a horny beak similar to that of a modern tortoise. However, they are in no way closely related.

<i>Burnetia</i> Extinct genus of therapsids

Burnetia is an extinct genus of biarmosuchian therapsids in the family Burnetiidae, from the Late Permian of South Africa. Burnetia is known so far from a single holotype skull lacking the lower jaws described by South African paleontologist Robert Broom in 1923. Due to erosion and dorsoventral crushing, features of the skull are hard to interpret. Stutural lines are further distorted by the unusual shape of the skull roof, including many bosses and protuberances.

<i>Paraburnetia</i> Extinct genus of therapsids

Paraburnetia is an extinct genus of biarmosuchian therapsids from the Late Permian of South Africa. It is known for its species P. sneeubergensis and belongs to the family Burnetiidae. Paraburnetia lived just before the Permian–Triassic mass extinction event.

<i>Lobalopex</i> Extinct genus of therapsids

Lobalopex is an extinct genus of biarmosuchian therapsids. It was alive during the Late Permian and has only been found in the Teekloof Formation in South Africa. The only known species of the genus is Lobalopex mordax. Lobalopex is part of the clade of Burnetiamorpha, which have fossil specimens located in multiple areas of Africa and Russia.

<i>Bullacephalus</i> Extinct genus of animal

Bullacephalus is an extinct genus of biarmosuchian therapsids belonging to the family Burnetiidae. The type species B. jacksoni was named in 2003. It is known from a relatively complete skull and lower jaw, discovered in the Late Permian Tapinocephalus Assemblage Zone of the Beaufort Group of South Africa. This genus of therapsida lived during the Late Permian period, approximately 250 million years ago. The name Bullacephalus comes from the Latin words "bullatus," meaning "bossed" or "knobbed," and "cephalus," meaning "head." This name refers to the distinctive bony knob on the top of the therapsid's skull, which contributes to the history of this genus. This stem based taxon includes Ictidorhinus or Hippasaurs. Bullacephalus can even be characterized as having a, “skull moderately to greatly pachyostotic; swollen boss present above the postorbital bar formed by the postfrontal and postorbital; deep linear sculpturing of the snout; exclusion of the jugal from the lateral temporal fenestra”. These Therapsids have spongy bone skull roof, palatal process of premaxilla are long, diverticulum of naris adding them to the Burnetiamorph. Furthermore, the discovery of Bullacephalus has helped to refine the taxonomic classification of therapsids. Prior to its discovery, there was uncertainty regarding the relationship between different groups of therapsids, particularly the Burnetiamorpha and the Biarmosuchia. However, the distinctive features of Bullacephalus suggest that it is a member of the Burnetiamorpha, and provides a bridge between this group and the Biarmosuchia. The discovery of Bullacephalus has also highlighted the importance of continued exploration and excavation in areas that have yielded few therapsid fossils. The Beaufort Group of South Africa, where Bullacephalus was discovered, has been an important site for therapsid fossils, but much of the area remains unexplored. Further discoveries in this region and other areas around the world may provide new insights into the evolution and diversification of therapsids, as well as other groups of extinct animals. These discoveries will also help to refine our understanding of the history of life on Earth and the processes that have shaped the diversity of organisms that exist today.

Cynosaurus is an extinct genus of cynodonts. Remains have been found from the Dicynodon Assemblage Zone in South Africa. Cynosaurus was first described by Richard Owen in 1876 as Cynosuchus suppostus. Cynosaurus has been found in the late Permian period. Cyno- is derived from the Greek word kyon for dog and –sauros in Greek meaning lizard.

<i>Ictidorhinus</i> Extinct genus of therapsids

Ictidorhinus is an extinct genus of biarmosuchian therapsids. Fossils have been found from the Dicynodon Assemblage Zone of the Beaufort Group in the Karoo Basin, South Africa and are of Late Permian age. It had a short snout and proportionally large orbits. These characteristics may be representative of a juvenile animal, possibly of Lycaenodon. However, these two genera are not known to have existed at the same time, making it unlikely for Ictidorhinus material to be from a juvenile form of Lycaenodon.

<i>Hipposaurus</i> Extinct genus of therapsids

Hipposaurus is an extinct genus of basal therapsids known from the Tapinocephalus Assemblage Zone of the Main Karoo Basin, South Africa. Chronologically this is within the Capitanian stage of the Guadalupian Series. The genus was first described by S.H. Haughton as H. boonstrai on the basis of a skull and associated skeleton and was later considered a gorgonopsian in the family 'Ictidorhinidae' by Robert Broom. It is now considered a basal biarmosuchian, but its affinities remain uncertain. Some authors note the similarity of its braincase with that of Herpetoskylax. H. boonstrai is currently known from only two specimens in the Iziko South African Museum, Cape Town.

<i>Pachydectes</i> Extinct genus of therapsids

Pachydectes is an extinct genus of biarmosuchian therapsids from the Middle Permian of South Africa known from a single skull. The etymology of the name Pachydectes is derived from the Greek word pakhus, meaning "thick" or "thickened", and dektes, meaning "biter". In conjunction this name is representative of the unique pachyostotic bone present above the maxillary canine tooth found in the skull of the specimen. There is only one known species within the genus, Pachydectes elsi which is named in honor of the person who discovered the fossil.

<i>Progalesaurus</i> Extinct genus of cynodonts

Progalesaurus is an extinct genus of galesaurid cynodont from the early Triassic. Progalesaurus is known from a single fossil of the species Progalesaurus lootsbergensis, found in the Lystrosaurus Assemblage Zone of the Balfour Formation. Close relatives of Progalesaurus, other galesaurids, include Galesaurus and Cynosaurus. Galesaurids appeared just before the Permian-Triassic extinction event, and disappeared from the fossil record in the Middle-Triassic.

<span class="mw-page-title-main">Anomocephaloidea</span> Extinct clade of therapsids

Anomocephaloidea is a clade of basal anomodont therapsids related to the dicynodonts known from what is now South Africa and Brazil during the Middle Permian. It includes only two species, Anomocephalus africanus from the Karoo Basin of South Africa and Tiarajudens eccentricus from the Paraná Basin of Brazil. Anomocephaloidea was named in 2011 with the discovery of Tiarajudens, although Anomocephalus itself has been known since 1999.

Rubidgina is a genus of Biarmosuchian therapsid from Patrysfontein, Wellwood, South Africa known from RC 55, a skull with lower jaws. This specimen is a putative juvenile. It has been suggested that this specimen actually represents a juvenile of Herpetoskylax hopsoni. However, because the specimen lacks distinctive features, it cannot be determined if it is actually a juvenile of Herpetoskylax or if its current name of Rubidgina should remain.

<i>Abdalodon</i> Extinct genus of cynodonts

Abdalodon is an extinct genus of late Permian cynodonts, known by its only species A. diastematicus.Abdalodon together with the genus Charassognathus, form the clade Charassognathidae. This clade represents the earliest known cynodonts, and is the first known radiation of Permian cynodonts.

<i>Leucocephalus</i> Extinct genus of therapsids

Leucocephalus is a genus of biarmosuchian belonging to the family Burnetiidae dating to the Wuchiapingian. It was found in the Tropidostoma Assemblage Zone of the Main Karoo Basin of South Africa. It is a monotypic taxon which contains one only species, Leucocephalus wewersi. The genus name Leucocephalus is derived from Greek. Leucos, meaning white; kephalos, meaning skull, as the Leucocephalus skull discovered was unusually pale. The species epithet wewersi comes from the farm employee who found the skull, Klaus ‘Klaasie’ Wewers.

<i>Nyaphulia</i> Extinct genus of dicynodonts

Nyaphulia is an extinct genus of dicynodont therapsid from the middle Permian of South Africa, containing only the type species N. oelofseni. The generic name is in honour of John Nyaphuli of the National Museum of Bloemfontein, who contributed extensively to South African palaeontology and discovered the holotype specimen of Nyaphulia in 1982. Nyaphulia was initially named as a second species of the basal dicynodont Eodicynodon by Professor Bruce Rubidge in 1990 as E. oelofseni, named after his mentor in palaeontology and geology Dr. Burger Oelofsen.

References

  1. ↑ "Fossilworks: Herpetoskylax".
  2. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 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
  3. ↑ Palaeocritti - a guide to prehistoric animals. Herpetoskylax hopsoni. Downloaded 25/03/2011
  4. ↑ Carrano, Matthew T. (2006). Amniote Paleobiology. University of Chicago Press. p. 80. ISBN   978-0-226-09478-6.
  5. ↑ "Palaeos Bones: Dermal Bones: Facial Series: Septomaxilla". palaeos.com. Retrieved 2023-03-02.
  6. ↑ Sidor, C. A.; Welman, J. (2003-09-12). "A second specimen of Lemurosaurus pricei (Therapsida: Burnetiamorpha)". Journal of Vertebrate Paleontology. 23 (3): 631–642. doi:10.1671/0272-4634(2003)023[0631:ASSOLP]2.0.CO;2. ISSN   0272-4634.
  7. 1 2 Benoit, Julien; Fernandez, Vincent; Manger, Paul R.; Rubidge, Bruce S. (2017). "Endocranial Casts of Pre-Mammalian Therapsids Reveal an Unexpected Neurological Diversity at the Deep Evolutionary Root of Mammals". Brain, Behavior and Evolution. 90 (4): 311–333. doi:10.1159/000481525. ISSN   0006-8977.
  8. 1 2 Matsumoto, Ryoko; Evans, Susan E. (2017). "The palatal dentition of tetrapods and its functional significance". Journal of Anatomy. 230 (1): 47–65. doi:10.1111/joa.12534. PMC   5192890 . PMID   27542892.
  9. ↑ Duhamel, Aliénor; Benoit, Julien; Day, Michael; Rubidge, Bruce; Fernandez, Vincent (2021-08-26). "Computed Tomography elucidates ontogeny within the basal therapsid clade Biarmosuchia". PeerJ. 9: e11866. doi: 10.7717/peerj.11866 . ISSN   2167-8359. PMC   8403480 . PMID   34527434.
  10. ↑ Kemp, T. S. (2006). "The origin and early radiation of the therapsid mammal-like reptiles: a palaeobiological hypothesis". Journal of Evolutionary Biology. 19 (4): 1231–1247. doi: 10.1111/j.1420-9101.2005.01076.x . ISSN   1010-061X.
  11. ↑ Benoit, Julien; Manger, Paul R.; Fernandez, Vincent; Rubidge, Bruce S. (2017). "The bony labyrinth of late Permian Biarmosuchia: palaeobiology and diversity in non-mammalian Therapsida" (PDF). Paleontologica Africana. 52: 58–77.
  12. ↑ Benoit, J.; Manger, P. R.; Rubidge, B. S. (2016-05-09). "Palaeoneurological clues to the evolution of defining mammalian soft tissue traits". Scientific Reports. 6 (1): 25604. doi:10.1038/srep25604. ISSN   2045-2322. PMC   4860582 . PMID   27157809.
  13. ↑ Bakker, Robert (1980). A Cold Look at the Warm-Blooded Dinosaurs. Westview Press. pp. 351–462.
  14. 1 2 Bennett, A. F., & Ruben, J. A. (1986). The Metabolic and Thermoregulatory Status of Therapsids. The Ecology and Biology of Mammal-Like Reptiles, 207-218.
  15. ↑ Knight, Cassi, "Late Permian Paleoenvironmental Factors Expounded Through Analysis of a Forest-Floor Paleosol Profile, Karoo Basin, South Africa" (2010). Honors Theses. Paper 584.
  16. ↑ Smith, R.M.H.; Eriksson, P.G.; Botha, W.J. (1993). "A review of the stratigraphy and sedimentary environments of the Karoo-aged basins of Southern Africa". Journal of African Earth Sciences (and the Middle East). 16 (1–2): 143–169. doi:10.1016/0899-5362(93)90164-L.


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