Cynosaurus

Last updated

Cynosaurus
Temporal range: Late Permian, 265.1–254.17  Ma
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Clade: Therapsida
Clade: Cynodontia
Clade: Epicynodontia
Genus: Cynosaurus
Schmidt, 1927
Type species
Cynosaurus suppostus
Owen, 1859
Synonyms
  • BaurocynodonBrink, 1951
  • CynosuchoidesBroom, 1931
  • CynosuchusOwen, 1876
  • MygalesuchusBroom, 1942

Cynosaurus is an extinct genus of cynodonts. Remains have been found from the Dicynodon Assemblage Zone in South Africa. [1] 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.

Contents

History and discovery

Cynosaurus was first described by Richard Owen in 1876. Owen wrote and journal titled “Descriptive and illustrated catalog of the fossil reptilia of South Africa in the collection of the British Museum” in 1876. Owen named the fossil Cynosuchus suppostus Owen, 1876 which later gets renamed as Cynosaurus by K. Schmidt in 1927. [2] Owen described Cynosuchus suppostus as similar to Cynochampsa in where the incisors and canines are located. The difference is that Cynosuchus suppostus had smaller and more upward location of nostril. The external nostril of Cynosuchus suppostus along with the forends of the upper and lower jaws were close in location with the nostril nearly horizontal. Owen described the molar teeth as relatively larger in size. Owen also noted the constriction of the upper jaw as it recedes and is combined with large molar teeth that shows Cynosuchus suppostus to have a broader and shorter skull. The nasal bones are broad and thick and overlapped by the maxillaries. [3]

Description

Derived traits for Cynosaurus are: subvertical mentum on anterior lower jaw, robust mandible with relative high horizontal ramus, broad snout up to 32% of skull length and adult Cynosaurus lacking pineal foramen. [4] In early Cynodonts the parietal bone extends ventrally to the sidewall of the braincase. [5] The epipterygoid is also expanded to make new contact with the frontal as well as the parietal crest is elongated to incorporate the pineal foramen. [5]

Cranium

The septomaxilla is the flat bridge that divides the nasal into upper and lower. [4] The nasal is broader posteriorly than anteriorly. [4] On the surface of the maxilla there are many small nutritive foramina forming two horizontal parallel lines. [4] For the premaxilla there is a gap along the midline between the premaxilla and the palatal processes. [4] The vomer is unpaired and tapers and reaches a point sharp. [4] The vomer also doesn't reach the pterygoid posteriorly. [4] Micro-CT scans allows internal structures of fossil skulls to be observed (Benoit et al., 2017). From micro-CT scans, a pair of ossification orbitosphenoid were observed in four specimens of Cynosaurus. [6] In orbitosphenoid consisted of two thin plate-like structures appear to articulate ventromedially and in cross section, it appears to be in an U-shape. [6]

The rapid evolution of the masseter insertion area is able to show early diversification of early Cynodonts. [7] In Procynosuchus and Dvinia the location of masseteric fossa high on the coronoid process is seen as an initial stage of differentiation of masseter. [7] In Cynosaurus and Nanictosaurus the extension of masseteric fossa is to the base of the dentary. [7]

Parietal foramen (labeled pf in image) of Labidosaurus, an early reptile Image from page 33 of "Water reptiles of the past and present" (1914) (14586262480).jpg
Parietal foramen (labeled pf in image) of Labidosaurus , an early reptile

Parietal foramen

On Cynosaurus there is a sharp sagittal crest that is flattened near the location of the parietal foramen. [8] In a CT scan of a Cynosaurus skull, no parietal tube was present but instead the endocranial cavity is pushed upward. [8] In Cynosaurus whaitsi, a specimen, was shown with the absence of parietal foramen. [8] In another Cynosaurus skull specimen, the absence of the parietal foramen was due to an ontogenetic change as in Massetognathus the parietal foramen closes in adults. [8] In the extant lizard Anolis carolinensis the size of the pineal opening decreases but doesn't disappear. [8] Another specimen showed evidence of a parietal tube, but the absence wasn't due to ontogeny but from intraspecific variability. [8]

Many lizards have a parietal eye on top of their head. [9] In extant ectotherms living near the equator are less frequent to have a pineal opening due to the stability of the environment that makes the third eye not useful. [8] There is a definite relationship between latitudinal distribution of lizards and parietal eye occurrence. [9] Parietal-eyeless lizards are to low latitudes which suggests an equatorial trait. [9]

Tooth

Cynosaurus has simple canines with an ovoid shape that lack cingulum. [10] The post canines are posterior accessory cusp and Cynosaurus have a second posterior accessory cusp in the posterior-most teeth . [10] The anterior accessory cusps on Cynosaurus are not visible. [10] Most early Cynodonts show triconodont postcanines in labial view. [10]

Procynosuchus delaharpeae and Dvinia prima are more basal to Cynosaurus and have 5 or more upper and 4 or more lower incisors while most Cynodonts have 4 upper and 3 lower incisors. [10] Progalesaurus is also basal to Cynosaurus and they have a strong longitudinal grooves or striations on their canines. [4] Galesaurus who are more derived than Cynosaurus have an incomplete bony second palatine processes posteriorly. [4]

Paleoenvironment

Formations in South Africa Geology of Karoo Supergroup.png
Formations in South Africa

Fossils of Cynosaurus have been found in the Cistecephalus and Daptocephalus Assemblage Zones, in the Balfour Formation of the Beaufort Group, pertaining to the Karoo Supergroup of South Africa. [4] In the Karoo Basin of South Africa riverbanks would be over flooded creating floodplains that could hold all that water to start soil accumulation. [11] In the lower Balfour Formation, the soil deposits suggest a lacustrine environment with abundant leaf impressions. [11] This suggests that there was coastal marshes and swamps. [11] There was also trace fossils found in the formation from aquatic organisms. [11]

See also

Related Research Articles

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

Therapsida is a clade composing of 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.

<i>Thrinaxodon</i> Extinct genus of cynodonts of Early Triassic South Africa

Thrinaxodon is an extinct genus of cynodonts, including the species T. liorhinus which lived in what are now South Africa and Antarctica during the Early Triassic. Thrinaxodon lived just after the Permian–Triassic mass extinction event, its survival during the extinction may have been due to its burrowing habits.

<i>Galesaurus</i> Extinct genus of cynodonts from the Triassic of South Africa

Galesaurus is an extinct genus of carnivorous cynodont therapsid that lived between the Induan and the Olenekian stages of the Early Triassic in what is now South Africa. It was incorrectly classified as a dinosaur by Sir Richard Owen in 1859.

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

Emydops is an extinct genus of dicynodont therapsids from the Middle Permian to Late Permian of what is now South Africa. The genus is generally small and herbivorous, sharing the dicynodont synapomorphy of bearing two tusks. In the following years, the genus grew to include fourteen species. Many of these species were erected on the basis of differences in the teeth and the positioning of the frontal and parietal bones. A 2008 study narrowed Emydops down to two species, E. arctatus and the newly described E. oweni.

<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>Bauria</i> Genus of therapsids from the Early Triassic of South Africa

Bauria is an extinct genus of the suborder Therocephalia that existed during the Early and Middle Triassic period, around 246-251 million years ago. It belonged to the family Bauriidae. Bauria was probably a herbivore or omnivore. It lived in South Africa, specifically in the Burgersdorp Formation in South Africa.

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

Endothiodon is an extinct genus of medium to large dicynodont from the Late Permian. Like other dicynodonts, Endothiodon was an herbivore, but it typically lacked the two tusks that characterized most other dicynodonts and instead had long rows of teeth inset in the jaws that replaced in waves. The anterior portion of the upper and lower jaw are curved upward, creating a distinct beak that is thought to have allowed them to be specialized grazers.

<i>Moschorhinus</i> Genus of synapsid from late Permian and early Triassic South Africa

Moschorhinus is an extinct genus of therocephalian synapsid in the family Akidnognathidae with only one species: M. kitchingi, which has been found in the Late Permian to Early Triassic of the South African Karoo Supergroup. It was a large carnivorous therapsid, reaching 1.5 m (4.9 ft) in total body length with the largest skull comparable to that of a lion in size, and had a broad, blunt snout which bore long, straight canines.

<i>Theriognathus</i> Extinct genus of therapsids from late Permian South Africa and Tanzania

Theriognathus is an extinct genus of therocephalian therapsid belonging to the family Whaitsiidae, known from fossils from South Africa, Zambia, and Tanzania. Theriognathus has been dated as existing during the Late Permian. Although Theriognathus means mammal jaw, the lower jaw is actually made up of several bones as seen in modern reptiles, in contrast to mammals. Theriognathus displayed many different reptilian and mammalian characteristics. For example, Theriognathus had canine teeth like mammals, and a secondary palate, multiple bones in the mandible, and a typical reptilian jaw joint, all characteristics of reptiles. It is speculated that Theriognathus was either carnivorous or omnivorous based on its teeth, and was suited to hunting small prey in undergrowth. This synapsid adopted a sleek profile of a mammalian predator, with a narrow snout and around 1 meter long. Theriognathus is represented by 56 specimens in the fossil record.

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

Lemurosaurus is a genus of extinct biarmosuchian therapsids from the Late Permian of South Africa. The generic epithet Lemursaurus is a mix of Latin, lemures “ghosts, spirits”, and Greek, sauros, “lizard”. Lemurosaurus is easily identifiable by its prominent eye crests, and large eyes. The name Lemurosaurus pricei was coined by paleontologist Robert Broom in 1949, based on a single small crushed skull, measured at approximately 86 millimeters in length, found on the Dorsfontein farm in Graaff-Reinet. To date, only two skulls of the Lemurosaurus have been discovered, so body size is unknown. The second larger, more intact, skull was found in 1974 by a team from the National Museum, Bloemfontein.

<i>Styracocephalus</i>

Styracocephalus platyrhynchus is an extinct genus of dinocephalian therapsid that existed during the mid-Permian throughout South Africa, but mainly in the Karoo Basin. It is often referred to by its single known species Styracocephalus platyrhynchus. The Dinocephalia clade consisted of the largest land vertebrates and herbivores during the early to mid-Permian. This period is often also referred to as the Guadalupian epoch, approximately 270 to 260 million years ago.

Angonisaurus is an extinct genus of kannemeyeriiform dicynodont from the Middle Triassic of Africa between 247 and 242 million years ago. Only one species, Angonisaurus cruickshanki has been assigned to this genus. This genus is thought to have been widely spread but rare in southern Gondwana. Though few in number, the fossil record of Angonisaurus cruickshanki contains multiple specimens giving it a measurable stratigraphic range. Sexually dimorphic features are found in Angonisaurus which include presence or absence of tusks and difference is size and robustness of the temporal arch and the rostral.

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

Dicynodontoides is a genus of small to medium-bodied, herbivorous, emydopoid dicynodonts from the Late Permian. The name Dicynodontoides references its “dicynodont-like” appearance due to the caniniform tusks featured by most members of this infraorder. Kingoria, a junior synonym, has been used more widely in the literature than the more obscure Dicynodontoides, which is similar-sounding to another distantly related genus of dicynodont, Dicynodon. Two species are recognized: D. recurvidens from South Africa, and D. nowacki from Tanzania.

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

Daptocephalus is an extinct genus of non-mammalian synapsid anomodont dicynodont, it which was found in Late Permian strata, in a biozone known precisely for the presence of fossils of this dicynodont, the Daptocephalus Assemblage Zone, in the Karoo Basin in South Africa. An additional species, D. huenei, is known from the Usili Formation in Tanzania and was formerly assigned to the genus Dicynodon before a study in 2019 recognised that the type specimen belonged to Daptocephalus.

<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.

Platycraniellus is an extinct genus of carnivorous cynodonts from the Early Triassic. It is known from the Lystrosaurus Assemblage Zone of the Normandien Formation in South Africa. P. elegans is the only species in this genus based on the holotype specimen from the Ditsong National Museum of Natural History in Pretoria, South Africa. Due to limited fossil records for study, Platycraniellus has only been briefly described a handful of times.

<i>Scymnosaurus</i> Extinct genus of therapsids from middle Permian South Africa

Scymnosaurus is a dubious genus of therocephalian therapsids based upon various fossils of large early therocephalians. The genus was described by Robert Broom in 1903 with S. ferox, followed by S. watsoni in 1915 and a third, S. major, by Lieuwe Dirk Boonstra in 1954. Each of these species are considered nomen dubia today and based upon specimens belonging to two separate families of therocephalians. S. ferox and S. major represent specimens of Lycosuchidae incertae sedis, while S. watsoni is Scylacosauridae incertae sedis. Broom named a fourth species in 1907 from KwaZulu-Natal, S. warreni, though he later referred it to Moschorhinus as a valid species in 1932 but now is recognised as being synonymous with M. kitchingi.

<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>Thliptosaurus</i> Extinct genus of dicynodonts

Thliptosaurus is an extinct genus of small kingoriid dicynodont from the latest Permian period of the Karoo Basin in KwaZulu-Natal, South Africa. It contains the type and only known species T. imperforatus. Thliptosaurus is from the upper Daptocephalus Assemblage Zone, making it one of the youngest Permian dicynodonts known, living just prior to the Permian mass extinction. It also represents one of the few small bodied dicynodonts to exist at this time, when most other dicynodonts had large body sizes and many small dicynodonts had gone extinct. The unexpected discovery of Thliptosaurus in a region of the Karoo outside of the historically sampled localities suggests that it may have been part of an endemic local fauna not found in these historic sites. Such under-sampled localities may contain 'hidden diversities' of Permian faunas that are unknown from traditional samples. Thliptosaurus is also unusual for dicynodonts as it lacks a pineal foramen, suggesting that it played a much less important role in thermoregulation than it did for other dicynodonts.

Vetusodon is an extinct genus of cynodonts belonging to the clade Epicynodontia. It contains one species, Vetusodon elikhulu, which is known from four specimens found in the Late Permian Daptocephalus Assemblage Zone of South Africa. With a skull length of about 18 centimetres (7.1 in), Vetusodon is the largest known cynodont from the Permian. Through convergent evolution, it possessed several unusual features reminiscent of the contemporary therocephalian Moschorhinus, including broad, robust jaws, large incisors and canines, and small, single-cusped postcanine teeth.

References

  1. T. S. Kemp: The Origin and Evolution of Mammals Oxford University Press, 2005. ISBN   0-19-850760-7
  2. K. Schmidt. 1927. "New reptilian generic names". Copeia163: 58-59
  3. Owen, R. 1876. Descriptive and illustrated catalog of the fossil reptilia of South Africa in the collection of the British Museum.
  4. 1 2 3 4 5 6 7 8 9 10 Van den Brandt, M.J., Adbala, F. 2018. Cranial morphology and phylogenetic analyses of Cynosaurus suppostus (Therapsida, Cynodontia) from the upper Permian of the Karoo Basin, South Africa. Palaeontologia africana. 52:201-221 ISSN   2410-4418
  5. 1 2 Rubidge, B.S., Sidor, C.A. 2001. Evolutionary patterns among Permo-Triassic therapsids. The Annual Review of Ecology, Evolution, and Systematics. 32: 449-480
  6. 1 2 Benoit, J., Jasinoski, S.C., Fernandez, V., Adbala, F. 2017. The mystery of a missing bone: revealing the orbitosphenoid in basal Epicynodontia (Cynodontia, Therapsida) through computed tomography. The Science of Nature. 104:66-75.
  7. 1 2 3 Botha, J., Adbala, F., Smith, R. 2007. The oldest cynodont: new clues on the origin and early diversification of the Cynodontia. Zoological Journal of the Linnean Society. 149: 477-492
  8. 1 2 3 4 5 6 7 Benoit, J., Abdala, F., Van den Brandt, M.J., Manger, P.R., Rubidge, B.S. 2015. Physiological implications of the abnormal absence of the parietal foramen in a late Permian cynodont (Therapsida). The Science of Nature. 102:69-72.
  9. 1 2 3 Ralph, C.L. 1975. The pineal gland and geographical distribution of animals. International Journal of Biometeorology. 19(4):289-303.
  10. 1 2 3 4 5 Botha-Brink, J., Adbala, F. 2007. A new cynodont record from the Tropidostoma Assemblage Zone of the Beaufort Group: implications for the early evolution of cynodonts in South Africa. Palaeontologia africana. 43: 1-6 ISSN   0078-8554
  11. 1 2 3 4 Viglietti, P.A., Smith, R.M.H., Rubidge, B.S. 2018. Changing palaeoenvironments and tetrapod populations in the Daptocephalus Assemblage Zone (Karoo Basin, South Africa) indicate early onset of the Permo-Triassic mass extinction. Journal of African Earth Sciences. 138: 102-111

Further reading