Pachygenelus

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Pachygenelus
Drawing by Pachygenelus

Drawing by Pachygenelus

Temporal occurrence
Hettangium to Sinemurium
201.3 to 190.8 million years
Locations
  • Stormberg group South Africa ( Pachygenelus monus )
  • Fundy Group Nova Scotia Canada ( Pachygenelus cf. P. monus )
  • (Dockum Group Texas (USA) ( Pachygenelus milleri ); doubtful)
Systematics
Synapsids (Synapsida)
Therapsids (Therapsida)
Cynodontia
Eucynodontia
Tritheledontidae
Pachygenelus
Scientific name
Pachygenelus
Watson , 1913
species
  • Pachygenelus monus Watson, 1913 ( type species )
  • Pachygenelus cf. P. monus Shubin et al., 1991
  • ( Pachygenelus milleri Chatterjee, 1983 ) (doubtful)

Pachygenelus is an extinct genus of the Tritheledontidae , a family of the Cynodontia and lived in the "lower" Lower Jurassic ( Hettangium - Sinemurium ) about 201.3 to 190.8 million years ago. Corresponding fossils were found in the Karoo supergroup in South Africa and the upper Fundy group in Nova Scotia ( Canada ). The assignment of finds from the Upper Triassic ( Dockum group ) of Texas to Pachygenelus (" Pachygenelus milleri ") by Chatterjee , 1983, however, is controversial and doubtful.

Etymology and history of research

The generic name is made up of the ancient Greek παχύς ( pachys ), "thick", "fat" and the Latinized diminutive of the ancient Greek γένῠς ( genys ), "(lower) jaw". Pachygenelus can be roughly translated as "thick jaw".

The first description of the genus and type species was carried out in 1913 by D. M. S. Watson . During a stay in what was then the Cape Colony, Watson had received some fossil bone remains from the surveyor Maasdorp and in particular recognized the importance of a fragment of the lower jaw. He was shown the site and identified the find layer as "Red Beds" within the Stormberg Group .

In 1929 Broom put Pachygenelus together with " Karoomys " (= Cynognathus ) and Tritheledon in the group of Ictidosauria ("Wieselechsen"). In 1932 Broom expanded the group to include two more finds, which he initially referred to neutrally as "Ictidosaur A" and "Ictidosaur B". Crompton described these two fossils as Diarthrognathus broomi in 1958 and 1963, respectively . Hopson and Kitching contradicted this analysis in 1972 and evaluated Diarthrognathus broomi as a junior synonym for Pachygenelus monus . At the same time, Broom's "subordination" Ictidosauria was integrated into the "family" of the Tritheledontidae previously established by Broom or equated with it. Only in 1980, through a detailed analysis of the dentition of previously undescribed museum material , did Gow prove that Pachygenelus monus and Diarthrognathus broomi were clearly two different taxa .

1983 Chatterjee described a second species (" Pachygenelus milleri ") from the Dockum group of Texas. The assignment of the find to the genus Pachygenelus is considered controversial due to the poorly preserved fossil material. In some cases it is even doubted that these are the remains of a representative of the Eucynodontia .

In 1991, Shubin et al. another representative of the genus Pachygenelus from the McCoy Brook Formation within the Fundy Group in southeastern Canada is described. Since the Canadian evidence did not show any characteristics that would have allowed a clear distinction to Pachygenelus monus , the first descriptors decided not to list a new species and referred to the findings in the sense of an "open" (ie not regulated by the ICZN ) nomenclature the designation Pachygenelus cf. P. monus to. The abbreviation "cf." stands for the Latin " confer " "compare (with)".

In the first half of the 1990s, a whole series of summarizing works on the early evolution of mammals appeared in which Pachygenelus was also given extensive attention.

2001 Gow first described clearly pachygenelus Monus attributable postcranial skeletal elements from the upper Elliot Formation (Storm Mountain Group) of South Africa.

In 2016, computed tomographic scans were performed on the partially preserved skull of a juvenile specimen (BPI / 1/5691 ) of P. monus , which in particular provided information on the course and development of the infraorbital nerve .

Fossil record

The dubious taxon “ Pachygenelus milleri ” is no longer considered here.

Pachygenelus monus

The holotype originally described by Watson (BMNH R4091) comprises the fragment of a right branch of the lower jaw with the roots of two incisors , a canine tooth and 5 molars. In addition, there is further fossil evidence (selection of the evidence most frequently mentioned in the specialist literature):

  • BPI 4381: A partially preserved skull skeleton, probably identical to BP / 1/4381 as defined by Abdala, 2007
  • SAM K1315: parts of the upper and lower jaw
  • SAM K1329: A partially preserved skull skeleton
  • SAM K1350: small, but almost completely preserved skull skeleton
  • SAM K1394: A partially preserved lower jaw
  • BP / 1/5623: Parts of the skull and the postcranial skeleton with parts of 19 more or less articulated vertebrae, several ribs, the complete shoulder girdle and a large part of the front limbs.
  • BPI / 1/5691: Skull of a juvenile specimen.

Pachygenelus cf. P. monus

The Canadian fossil material includes several individual skull fragments, some of which are very well preserved, including 2 premaxillaries , 10 maxillae and 6 dentals with parts of the dentition.

features

Pachygenelus monus was described by Watson on the basis of the holotype as "about the size of a Fox Terrier ". The previously known skeletal elements of the shoulder girdle and the forelimbs show no anatomical adaptation to a burrowing way of life such as is known from representatives of the related Tritylodontidae , but resemble those of the basal representatives of the Mammaliaformes such as Morganucodon . As a typical reptile feature , however, there is still a very robust, T-shaped "intermediate clavicle " ( interclavicle ) between the actual collarbone (clavicle) and the breastbone (sternum) .

Temporomandibular joint

Pachygenelus had a double temporomandibular joint characteristic of the Ictidosauria (Tritheledontidae) with an articulation between both the articulare and the quadratum (primary temporomandibular joint ) as well as the connection between the dental and the squamous part (pars squamosa) of the temporal bone (secondary temporomandibular joint), which is typical for mammals . Only mammals have a secondary TMJ, while all other tetrapods have a primary TMJ. There is initially disagreement about the degree of development of the secondary temporomandibular joint in Pachygenelus . Gow, 1980 questioned the existence of an articular connection between the dentate and the pars squamosa. Allin & Hopson, 1992 and Luo & Crompton, 1994, however, confirmed the contact between the dental and pars squamosa, although Crompton, 1995, conceded that the connection in Pachygenelus may not have developed into a well-defined synovial joint .

denture

Unless otherwise stated, the description for Pachygenelus monus is based on Gow, 1980.

Pachygenelus has only two incisors in each branch of the jaw. The lower incisors are inclined forward, the wear facets are on the tongue side ( lingual ) or at the tips. The upper incisors are aligned ventrally and slightly curved backwards.

The arrangement of the canine teeth is the opposite; the upper canines are angled slightly forward, while the lower ones are pointed straight up. For most representatives of Cynodont found in the hard palate antero -lingual to the upper canines deep pits which receive the lower canines closed teeth. Such pits are absent in Pachygenelus . Instead occlude the lower canines, like in mammals, however in a slightly different position, with the upper canines.

The number of molars seems to vary between 7 and 10 per branch of the jaw within the species. They only have one root each. The upper and lower jaw each have molars of different shapes. The molars of the upper jaw have a conical main tip and two mesially and distally located secondary tips. The molars of the lower jaw are usually larger than those of the upper jaw and laterally flattened. The anterior molars of the lower jaw show a main mesial tip and two distal secondary tips. The rear molars also show a small, mesial secondary tip in front of the main tip and a third distal secondary tip.

The change of teeth took place permanently (as with reptiles) and alternately, ie new teeth broke out between two fully developed teeth. The upper and lower molar rows occlude with each other, however not like in mammals, but laterally, so that simple wear facets and corresponding sharp cutting edges of the tooth enamel are formed lingually in the upper molars and in the lower ( buccal ).

Another characteristic of Pachygenelus , which is also found in mammals, is the plesiomorphic, prismatic tooth enamel.

Fur and whiskers

Computed tomographic scans on the skull of a juvenile specimen (BPI / 1/5691) show that , similar to mammals, Pachygenelus already had a short, completely bone-sheathed lower eye canal ( canalis infraorbitalis ) for the infraorbital nerve in the upper jaw . The outer opening of the under-eye canal ( foramen infraorbitale ), through which the skin of the entire front and upper face is subsequently supplied with sensors, has dimensions similar to those of modern small mammals . In the latter, the size of the opening correlates in particular with the number of vibrissae and the findings allow the conclusion that at least the anatomical prerequisites for whiskers were present in Pachygenelus and that the animal very likely had them.

A Parietalforamen is also analogous to modern mammals at pachygenelus not exist. The formation or absence of this cranial opening is essentially controlled by the homeotic gene Msx2, which is also responsible for the formation of the fur and the mammary glands in mammals. Following the interpretation of Benoit et al., 2016, it can therefore be assumed that Pachygenelus already had the genetic prerequisites for coat coverage and the development of mammary glands.

Systematics

There is no consensus among experts on the systematic position of Pachygenelus . The importance of the relatively well known and researched taxon for understanding the early evolutionary history of the Mammaliamorpha is widely recognized. The following compilation is to be read as a brief overview of the most important phylogenetic hypotheses on Pachygenelus and is in no way complete.

"Ictidosauria" vs. Tritheledontidae vs. Pachygenelidae / Pachygenelinae

There is broad agreement that Pachygenelus represents a genus of the Tritheledontidae. This group, sometimes referred to as "Tritheledonta" or (incorrectly) as "Trithelodonta" or "Trithelodontidae", was identified by Hopson & Kitching in 1972 with the Ictidosauria and placed together with the Tritylodontidae in the group of the Cynodontia .

Bonaparte , in 1980 proposed the "Pachygenelidae" ( pachygenelus and Chaliminia as a separate clade from the Tritheledontidae () Diarthrognathus and Tritheledon separate). "Pachygenelidae" and Tritheledontidae should form a superordinate clade "Ictidosauria" according to the proposal. This suggestion was generally acknowledged, but received only very little approval from other specialist authors.

  "Ictidosauria"  
  Riograndidae  

 Riograndia


  Tritheledontidae  

 Irajatherium


   
  Chalimininae  

 Chaliminia


   

 Elliotherium



   
  Pachygenelinae  


 Pachygenelus


   

 Diarthrognathus


   

 Tritheledon









Template: Klade / Maintenance / Style
Systematic position of Pachygenelus within the "Ictidosauria" according to Martinelli & Rougier, 2007.

Martinelli & Rougier define the Ictidosauria 2007 as "the last common ancestor of Riograndia guaibensis and Pachygenelus monus and all of its descendants". The Tritheledontidae see them as a subgroup of the "Ictidosauria", defined as "the last common ancestor of Irajatherium hernandezi and Pachygenelus monus and all of his descendants". Two subgroups Chalimininae (are again for the Tritheledontidae Chaliminia + Elliotherium ) and the Pachygenelinae ( pachygenelus + Diarthrognathus + Tritheledon ) was introduced and the taxon Irajatherium compared.

The subdivision of the Tritheledontidae by Martinelli & Rougier, 2007 not only deviates significantly from the original proposal by Bonaparte, 1980, the authors also use the term “Pachygenelinae” instead of the name “Pachygenelidae” proposed by Bonaparte for the clade around Pachygenelus . In 2017 Bonaparte & Crompton adopted this changed subdivision, but used the original name "Pachygenelidae" again.

Systematic and temporal position of Pachygenelus within the epicynodontia . From Ruta et al., 2013

Systematic position on mammals (Mammalia)

With regard to the relationship between Mammalia, Tritylodontidae and Tritheledontidae (and thus also Pachygenelus ) there are essentially two different doctrines:

One “school” represents the “classical” doctrine according to which the Tritheledontidae are the closest related sister taxon of the early Mammalia.

The second "school" sees the Tritylodontidae as the closest related sister taxon of the early Mammalia and interprets the Tritheledontidae as a branch that has split off from the common line of development earlier.

Paleecology

A largely carnivorous diet is assumed for Pachygenelus . Although anatomical indications of a burrowing way of life, as in the case of representatives of the Tritylodontidae, are not recognizable, Pachygenelus is at least considered by some authors, with reservations, as a possible cause of fossil grave structures from the Upper Elliot Formation in South Africa.

The fossils of the South African species Pachygenelus monus come mainly from the Upper Elliot Formation within the Stormberg Group. The upper Elliot Formation is built up by sediments of a fluvio-lacustrine deposit environment under semi-arid climatic conditions, with only seasonally water-bearing, meandering rivers, their alluvial cones and flat, Playa-like lakes, interspersed with aeolian dune sediments. The species-poor palaeoflora of the upper Elliot Formation contains representatives of the Bennettitales ( Otozamites ), horsetail , conifers ( Sphenolepidium ) and other woody naked- seed plants such as Podocarpoxylon or Agathoxylon .

Pachygenelus monus is a representative of the so-called “Massospondylus Range Zone” (MRZ), a faunal association that is characteristic of the upper Elliot formation. The name given to the MRZ is Massospondylus from the group of Sauropodomorpha , whose stratigraphic occurrence within the Elliot formation largely coincides with that of Pachygenelus monus . Other members of this fauna association, and thus contemporaries who shared the same habitat with Massospondylus and Pachygenelus monus , are at least three other representatives of the sauropodomorpha ( Aardonyx , Pulanesaura and Arcusaurus ), the theropods Coelophysis rhodesiensis (= Megapnosaurus rhodesiensis ) and Dracovenator , as well several representatives of the Ornithischia such as Heterodontosaurus , Lycorhinus , Lesothosaurus or Stormbergia .

Besides pachygenelus Monus occur Diarthrognathus and the type genus Tritheledon as other representatives of the Tritheledontidae within the upper Elliot Formation in appearance. The Tritylodontidae are also represented by their type genus Tritylodon ; the basal Mammaliaformes, however, with Erythrotherium and Megazostrodon . Fossil remains of stereospondylic amphibians, representatives of the crocodylomorpha such as Sphenosuchus , Litargosuchus , Protosuchus or Orthosuchus and of the turtle Australochelys africanus complete the picture of the contemporary local vertebrate fauna.

Little is known about the invertebrate fauna . From the most hanging parts of the upper Elliot Formation, the shells of conchostracene are documented from the deposits of only temporarily water-bearing lakes and Xing et al. described in 2015 drill marks on a dinosaur bone which they assigned to the Ichnogenus Cubiculum . These traces are probably due to the larvae of scavenging beetles.

Individual evidence

  1. ↑ a b c d e f g D. MS Watson: On a new Cynodont from the Stormberg In: The Geological Magazine - New Series , Dec. V, Vol. X, No. IV, pp. 145–148, 1913. (digitized version)
  2. ↑ a b c d e f g N. H. Shubin, AW Crompton, H.-D. Sues & PE Olsen: New Fossil Evidence on the Sister-Group of Mammals and Early Mesozoic Faunal Distributions. In: Science , Vol. 251, pp. 1063-1065, 1991. (digitized version )
  3. ↑ a b c d S. Chatterjee: An Ictidosaur Fossil from North America. In: Science , Vol. 220, No. 4602, pp. 1151-1153, 1983. (Abstract)
  4. ↑ a b c C. A. Sidor & PJ Hancox: Elliotherium kersteni, a new Tritheledontid from the Lower Elliot Formation (Upper Triassic) of South Africa. In: Journal of Paleontology , Vol. 80, No. 2, pp. 333–342, 2006 (digitized version )
  5. ↑ JW Martz, B. Mueller, SJ Nesbitt, MR Stocker, WG Parker, M. Atanassov, N. Fraser, J. Weinbaum & JR Lehane: A taxonomic and biostratigraphic re-evaluation of the Post Quarry vertebrate assemblage from the Cooper Canyon Formation (Dockum Group, Upper Triassic) of southern Garza County, western Texas. In: Earth and Environmental Science Transactions of the Royal Society of Edinburgh , Vol. 103, pp. 1–26, 2013. (digitized version)
  6. ↑ a b c J. A. Hopson & JW Kitching: A Revised Classification of Cynodonts (Reptilia; Therapsida). In: Palaeontologia Africana , Vol. 14, pp. 71-85, 1972. (digital copy )
  7. ^ R. Broom: On some recent new Light on the Origin of Mammals. In: Proceedings of the Linnean Society of New South Wales , Vol. 54, pp. 688-694, 1929. (digitized version )
  8. ^ R. Broom: The mammal-like reptiles of South Africa and the origin of mammals. 376 S., HF & G. Witherby, London, 1932.
  9. ^ AW Crompton: The cranial morphology of a new genus and species of ictidosauran. In: Proceedings of the Zoological Society of London , Vol. 130, pp. 183-216, 1958.
  10. ^ AW Crompton: On the lower jaw of Diarthrognathus and the origin of the mammalian lower jaw. With appendix: on the statics of jaw musculature by DG Parkyn. In: Proceedings of the Zoological Society of London , Vol. 140, pp. 697-753, 1963. (digitized version )
  11. ^ R. Broom: On a New Type of Cynodont from the Stormberg. In: Annals of the South African Museum , Vol. 7, pp. 334–336, 1912. (digitized version )
  12. ↑ a b c d e f g h C. E. Gow: The dentitions of the Tritheledontidae (Therapsida: Cynodontia). In: Proceedings of the Royal Society of London , Series B, Vol. 208, pp. 461-481, 1980. (digitized version )
  13. ^ SC Matthews: Notes on Open Nomenclature and on Synonymy Lists , In: Palaeontology , Vol. 16, Part 4, pp. 713–719, 1973. (digitized version )
  14. ^ A b c d E. F. Allin & JA Hopson, JA: Evolution of the Auditory System in Synapsida ("Mammal-Like Reptiles" and Primitive Mammals) as Seen in the Fossil Record . In: OB Webster, RA Fay & AN Popper (Eds.): The Evolutionary Biology of Hearing . Pp. 587–614, Springer Verlag, New York, 1992. (digitized version )
  15. ^ A b c Z. Luo & AW Crompton: Transformation of the Squares (Incus) through the Transition from Non-Mammalian Cynodonts to Mammals . In: Journal of Vertebrate Paleontology , Vol. 14, No. 3, pp. 341-374, 1994. (digitized version )
  16. ^ A b c A. W. Crompton: Masticatory function in nonmammalian cynodonts and early mammals. In: J. Thomason (Ed.): Functional Morphology in Vertebrate Paleontology , pp. 55–75, Cambridge University Press, 1995. (digitized version)
  17. ↑ a b c d e C. E. Gow: A Partial Skeleton of the Tritheledontid Pachygenelus (Therapsida: Cynodontia) In: Palaeontologia Africana , Vol. 37, pp. 93-97, 2001. (digitized version )
  18. ↑ a b c d J. Benoit, PR Manger & BS Rubidge: Palaeoneurological clues to the evolution of defining mammalian soft tissue traits. In: Nature - Scientific Reports , Vol. 6, No. 25604, pp. 1–10, 2016 doi: 10.1038 / srep25604
  19. ^ F. Abdala: Redescription of Platycraniellus elegans (Therapsida, Cynodontia) from the Lower Triassic of South Africa, and the Cladistic Relationships of Eutheriodonts. In: Palaeontology , Vol. 50, Part 3, pp. 591–618, 2007. (digitized version )
  20. ↑ CB Wood, ER Dumont & AW Crompton: New studies of enamel microstructure in Mesozoic Mammals: a review of enamel prisms as a mammalian synapomorphy. In: Journal of Mammalian Evolution , Vol. 6, No. 2, pp. 177–213, 1999. (available)
  21. ^ JF Bonaparte: El primer ictidosaurio (Reptilia-Therapsida) de América del Sur, Chaliminia musteloides, del Triásico Superior de La Rioja, Argentina. In: Actas II Congreso Argentino de Paleontología y Bioestratigrafía y I Congreso Latinoamericano de Paleontología , Vol. 1, pp. 123-133, 1980.
  22. ^ A b A. G. Martinelli & GW Rougier: On Chaliminia musteloides (Eucynodontia: Tritheledontidae) from the Late Triassic of Argentina, and a Phylogeny of Ictidosauria In: Journal of Vertebrate Paleontology , Vol. 27, No. 2, pp. 442–460, 2007. (digitized version )
  23. ^ A b J. F. Bonaparte & AW Crompton: Origin and relationships of the Ictidosauria to non-mammalian cynodonts and mammals. In: Historical Biology , Vol. 30, Issue 1–2, pp. 174–182, 2018. Published online on June 23, 2017 doi : 10.1080 / 08912963.2017.1329911 (pdf)
  24. ^ A b M. Ruta, J. Botha-Brink, SA Mitchell & MJ Benton: The radiation of cynodonts and the ground plan of mammalian morphological diversity In: Proceedings of the Royal Society of London B: Biological Sciences , Vol. 280, Issue 1769, 2013. doi : 10.1098 / rspb.2013.1865
  25. ^ JA Hopson & JW Kitching: A Probainognathian Cynodont from South Africa and the Phylogeny of Nonmammalian Cynodonts. In: Bulletin of the Museum of Comparative Zoology at Harvard College , Vol. 156, No. 1, pp. 5–35, 2001. (digitized version )
  26. ^ BS Rubidge & Ch. A. Sidor: Evolutionary Patterns Among Permo-Triassic Therapsids. In: Annual Review of Ecology and Systematics , Vol. 32, pp. 449-480, 2001. (digitized version )
  27. ^ T. Rowe: Definition, Diagnosis, and Origin of Mammalia. In: Journal of Vertebrate Paleontology , Vol. 8, No. 3, pp. 241-264, 1988. (digitized version )
  28. ^ T. Rowe: Phylogenetic Systematics and the Early History of Mammals. In: FS Szalay, MJ Novacek & MC McKenna (Eds.): Mammal Phylogeny - Mesozoic Differentiation, Multituberculates, Monotremes, Early Therians, and Marsupials. Pp. 129–145, Springer Verlag, 1993 (digitized version)
  29. ^ RN Martinez, CL May & CA Forster: A new carnivorous cynodont from the Ischigualasto Formation (Late Triassic, Argentina), with comments on eucynodont phylogeny In: Journal of Vertebrate Paleontology , Vol. 16, No. 2, pp. 271–284, 1996. (digitized version )
  30. ↑ EM Bordy, L. Sciscio, F. Abdallah, BW McPhee & JN Choiniere: First Lower Jurassic vertebrate burrow from southern Africa (upper Elliot formation Karoo Basin, South Africa) In: Palaeogeography, Palaeoclimatology, Palaeoecology , Vol 468, p. . 362–372, 2017. (Abstract)
  31. ↑ L. Sciscio, EM Bordy, M. Abraham, F. Knoll & BW McPhee: The first megatheropod tracks from the Lower Jurassic upper Elliot Formation, Karoo Basin, Lesotho. In: PLoS ONE , Vol. 12, No. 10: e0185941, 2017. doi : 10.1371 / journal.pone.0185941
  32. ↑ L. Sciscio, F. Knoll, EM Bordy, MO de Kock & R. Redelstorff: Digital reconstruction of the mandible of an adult Lesothosaurus diagnosticus with insight into the tooth replacement process and diet In: PeerJ , 5: e3054, 2017. doi : 10.7717 / peerj.3054
  33. ↑ JW Kitching & MA Raath: Fossils from the Elliot and Clarens Formations (Karoo Sequence) of the Northeastern Cape, Orange Free State and Lesotho, and a suggested Biozonation based on Tetrapods In: Palaeontologia Africana , Vol. 25, pp. 111-125 , 1984. (available)
  34. ↑ BW McPhee, EM Bordy, L. Sciscio & JN Choiniere: The sauropodomorpha biostratigraphy of the Elliot Formation of southern Africa: Tracking the evolution of Sauropodomorpha across the Triassic-Jurassic boundary In: Acta Palaeontologica Polonica , Vol 62, No.. 3, pp. 441–465, 2017. (pdf)
  35. ↑ AM Yates: A new theropod dinosaur from the Early Jurassic of South Africa and its implications for the early evolution of theropods. In: Palaeontologia Africana , Vol. 41, pp. 105–122, 2005. (digitized version )
  36. ^ RJ Butler: The `fabrosaurid´ ornithischian dinosaurs of the Upper Elliot Formation (Lower Jurassic) of South Africa and Lesotho. In: Zoological Journal of the Linnean Society , Vol. 145, Issue 2, pp. 175-218, 2005. doi : 10.1111 / j.1096-3642.2005.00182.x
  37. ↑ CE Gow: A new Skull of Megazostrodon (Mammalia, Triconodonta) from the Elliot Formation (Lower Jurassic) of Southern Africa. In: Palaeontologia Africana , Vol. 26, No. 2, pp. 13-23, 1986. (digitized version)
  38. ^ A. Warren & R. Damiani: Stereospondyl Amphibians from the Elliot Formation of South Africa. In: Palaeontologia Africana , Vol. 35, pp. 45–54, 1999. (digitized version)
  39. ↑ RB Irmis, SJ Nesbitt & H.-D. Sues: Early Crocodylomorpha In: SJ Nesbitt, JB Desojo & RB Irmis (Eds.): Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin , Geological Society, London, Special Publications, Vol. 379, pp. 275-302, 2013 (Digitized version)
  40. ^ ES Gaffney & JW Kitching: The Morphology and Relationships of Australochelys, an Early Jurassic Turtle from South Africa. In: American Museum Novitates , No. 3130, 29 p., American Museum of Natural History, New York, 1995. (available)
  41. ↑ EM Bordy, P. Eriksson: Lithostratigraphy of the Elliot Formation (Karoo Supergroup), South Africa. In: South African Journal of Geology , Vol. 118, No. 3, pp. 311–318, 2015. (digitized version )
  42. ↑ L. Xing, AH Parkinson, H. Ran, CA Pirrone, EM Roberts, J. Zhang, ME Burns, T. Wang, J. Choiniere: The earliest fossil evidence of bone boring by terrestrial invertebrates, examples from China and South Africa . In: Historical Biology. 10 p., 2015. doi : 10.1080 / 08912936.2015.1111884 .

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