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{{Short description|Extinct genus of cynodonts}}
{{Taxobox
{{Automatic taxobox
| name = ''Cynosaurus''
| taxon = Cynosaurus
| fossil_range =
| fossil_range = [[Late Permian]], {{fossil_range|259|254}}
| image =
| image_width = 250px
| image =
| authority = Schmidt, 1927
| regnum = [[Animal]]ia
⚫
| type_species = '''''Cynosaurus suppostus'''''
| phylum = [[Chordate|Chordata]]
| type_species_authority = Owen, 1859
| unranked_classis = [[Amniota]]
| subdivision_ranks =
| classis = [[Synapsid]]a
| ordo =
| subdivision =
| synonyms = * ''Baurocynodon'' <small>Brink, 1951</small>
| subordo =
* ''Cynosuchoides'' <small>Broom, 1931</small>
| familia =
* ''Cynosuchus'' <small>Owen, 1876</small>
⚫
| genus = '''''Cynosaurus'''''
* ''Mygalesuchus'' <small>Broom, 1942</small>
}}
}}
⚫
'''''Cynosaurus''''' is an extinct [[genus]] of non-[[mammal]]ian [[synapsid]]. Remains have been found from the [[Dicynodon Assemblage Zone]] in South Africa.<ref name="Kemp">T. S. Kemp: ''The Origin and Evolution of Mammals'' Oxford University Press, 2005. ISBN 0-19-850760-7</ref>


⚫
'''''Cynosaurus''''' is an extinct [[genus]] of [[cynodont]]s. Remains have been found from the [[Dicynodon Assemblage Zone|''Dicynodon'' Assemblage Zone]] in South Africa.<ref name="Kemp">T. S. Kemp: ''The Origin and Evolution of Mammals'' Oxford University Press, 2005. {{ISBN|0-19-850760-7}}</ref> ''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.
⚫
==See also==

== 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.<ref>K. Schmidt. 1927. "New reptilian generic names". ''Copeia'' '''163''': 58-59</ref> 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.<ref>Owen, R. 1876. Descriptive and illustrated catalog of the fossil reptilia of South Africa in the collection of the British Museum.</ref>

== 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.<ref name="VandenBrandt">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}}</ref> In early Cynodonts the parietal bone extends ventrally to the sidewall of the braincase.<ref name="Rubridge">Rubidge, B.S., Sidor, C.A. 2001. Evolutionary patterns among Permo-Triassic therapsids. The Annual Review of Ecology, Evolution, and Systematics. 32: 449-480</ref> 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.<ref name="Rubridge"/>

=== Cranium ===
The septomaxilla is the flat bridge that divides the nasal into upper and lower.<ref name="VandenBrandt"/> The nasal is broader posteriorly than anteriorly.<ref name="VandenBrandt"/> On the surface of the [[maxilla]] there are many small nutritive foramina forming two horizontal parallel lines.<ref name="VandenBrandt"/> For the premaxilla there is a gap along the midline between the premaxilla and the palatal processes.<ref name="VandenBrandt"/> The [[vomer]] is unpaired and tapers and reaches a point sharp.<ref name="VandenBrandt"/> The vomer also doesn't reach the pterygoid posteriorly.<ref name="VandenBrandt"/> 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''.<ref name="Benoit2017">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.</ref> 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.<ref name="Benoit2017"/>

The rapid evolution of the masseter insertion area is able to show early diversification of early Cynodonts.<ref name="Botha2007">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</ref> In ''[[Procynosuchus]]'' and ''[[Dvinia]]'' the location of masseteric fossa high on the coronoid process is seen as an initial stage of differentiation of masseter.<ref name="Botha2007"/> In ''Cynosaurus'' and ''Nanictosaurus'' the extension of masseteric fossa is to the base of the dentary.<ref name="Botha2007"/>
[[File:Image from page 33 of "Water reptiles of the past and present" (1914) (14586262480).jpg|thumb|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.<ref name="Benoit2015">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.</ref> In a CT scan of a ''Cynosaurus'' skull, no parietal tube was present but instead the endocranial cavity is pushed upward.<ref name="Benoit2015"/> In ''Cynosaurus whaitsi'', a specimen, was shown with the absence of parietal foramen.<ref name="Benoit2015"/> 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.<ref name="Benoit2015"/> In the extant lizard Anolis carolinensis the size of the pineal opening decreases but doesn't disappear.<ref name="Benoit2015"/> Another specimen showed evidence of a parietal tube, but the absence wasn't due to ontogeny but from intraspecific variability.<ref name="Benoit2015"/>

Many lizards have a parietal eye on top of their head.<ref name="Ralph1975">Ralph, C.L. 1975. The pineal gland and geographical distribution of animals. International Journal of Biometeorology. 19(4):289-303.</ref> 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.<ref name="Benoit2015"/> There is a definite relationship between latitudinal distribution of lizards and parietal eye occurrence.<ref name="Ralph1975"/> Parietal-eyeless lizards are to low latitudes which suggests an equatorial trait.<ref name="Ralph1975"/>

=== Tooth ===
''Cynosaurus'' has simple canines with an ovoid shape that lack cingulum.<ref name="BothaBrink2007">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}}</ref> The post canines are posterior accessory cusp and ''Cynosaurus'' have a second posterior accessory cusp in the posterior-most teeth .<ref name="BothaBrink2007"/> The anterior accessory cusps on ''Cynosaurus'' are not visible.<ref name="BothaBrink2007"/> Most early Cynodonts show triconodont postcanines in labial view.<ref name="BothaBrink2007"/>

''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.<ref name="BothaBrink2007"/> ''[[Progalesaurus]]'' is also basal to ''Cynosaurus'' and they have a strong longitudinal grooves or striations on their canines.<ref name="VandenBrandt"/> ''[[Galesaurus]]'' who are more derived than ''Cynosaurus'' have an incomplete bony second palatine processes posteriorly.<ref name="VandenBrandt"/>

== Paleoenvironment ==
[[File:Geology of Karoo Supergroup.png|thumb|Formations in South Africa]]
Fossils of ''Cynosaurus'' have been found in the [[Cistecephalus Assemblage Zone|''Cistecephalus'']] and [[Daptocephalus Assemblage Zone|''Daptocephalus'' Assemblage Zone]]s, in the [[Balfour Formation]] of the [[Beaufort Group]], pertaining to the [[Karoo Supergroup]] of South Africa.<ref name="VandenBrandt"/> In the Karoo Basin of South Africa riverbanks would be over flooded creating floodplains that could hold all that water to start soil accumulation.<ref name=Viglietti2018>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</ref> In the lower Balfour Formation, the soil deposits suggest a lacustrine environment with abundant leaf impressions.<ref name=Viglietti2018/> This suggests that there was coastal marshes and swamps.<ref name=Viglietti2018/> There was also trace fossils found in the formation from aquatic organisms.<ref name=Viglietti2018/>

⚫
== See also ==
{{Portal|Paleontology}}
{{Portal|Paleontology}}
* [[List of synapsids]]
* [[List of therapsids]]


{{Clear}}
==References==
{{reflist}}


==External links==
== References ==
{{Reflist}}
⚫
* [http://www.helsinki.fi/~mhaaramo/metazoa/deuterostoma/chordata/synapsida/synapsida_index.html The main groups of non-mammalian synapsids at Mikko's Phylogeny Archive]


== Further reading ==
⚫
[[Category:Cynodonts]]
* {{Cite web|url=http://wiredspace.wits.ac.za/bitstream/handle/10539/16031/1972.V14.HOPSON_AND_KITCHING.REVISED%20CLASSIFICATION%20CYNODONTS.pdf?sequence=1&isAllowed=y|title=A Revised Classification of Cynodonts (Repilia: Therapsida)|last1=Hopson|first1=J.|last2=Kitching|first2=J.W.|year=1972|work=Palaeontologia Africana 14: 71-85}}


== External links ==
{{therapsid-stub}}
⚫
* [http://www.helsinki.fi/~mhaaramo/metazoa/deuterostoma/chordata/synapsida/synapsida_index.html The main groups of non-mammalian synapsids at Mikko's Phylogeny Archive]


{{Cynodontia|E.}}
{{Cynodontia|E.}}
{{Taxonbar|from=Q5199995}}

⚫
[[Category:Epicynodontia]]
[[Category:Permian synapsids of Africa]]
[[Category:Permian South Africa]]
[[Category:Fossils of South Africa]]
[[Category:Beaufort Group]]
[[Category:Trace fossils]]
[[Category:Fossil taxa described in 1927]]

Latest revision as of 16:42, 11 December 2024

Cynosaurus
Temporal range: Late Permian, 259–254 Ma
↓
Scientific classification Edit this classification
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
  • Baurocynodon Brink, 1951
  • Cynosuchoides Broom, 1931
  • Cynosuchus Owen, 1876
  • Mygalesuchus Broom, 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.

History and discovery

[edit]

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

[edit]

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

[edit]

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

Parietal foramen

[edit]

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

[edit]

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

[edit]
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

[edit]

References

[edit]
  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". Copeia 163: 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. ^ a b c d e f g h i j 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. ^ a b 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. ^ a b 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. ^ a b c 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. ^ a b c d e f g 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. ^ a b c Ralph, C.L. 1975. The pineal gland and geographical distribution of animals. International Journal of Biometeorology. 19(4):289-303.
  10. ^ a b c d e 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. ^ a b c d 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

[edit]
[edit]
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