Eunotosaurus

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Eunotosaurus
Temporal range: Middle Permian, 265.8–259  Ma
Eunotosaurus.jpg
Fossil specimen, on display at
Karoo National Park
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Reptiliomorpha
Clade: Amniota
Clade: Sauropsida
Genus:† Eunotosaurus
Seeley, 1892
Species:
†E. africanus
Binomial name
†Eunotosaurus africanus
Seeley, 1892

Eunotosaurus ( Latin : Stout-backed lizard) is an extinct genus of amniote, possibly a close relative of turtles. Eunotosaurus lived in the late Middle Permian (Capitanian stage) and fossils can be found in the Karoo Supergroup of South Africa. Eunotosaurus resided in the swamps of southern Africa. [1] Its ribs were wide and flat, forming broad plates similar to a primitive turtle shell, and the vertebrae were nearly identical to those of some turtles. Accordingly, it is often considered as a possible transitional fossil between turtles and their prehistoric ancestors. [2] [3] However, it is possible that these turtle-like features evolved independently of the same features in turtles, since other anatomical studies and phylogenetic analyses suggest that Eunotosaurus may instead have been a parareptile, [4] an early-diverging neodiapsid unrelated to turtles, [5] or a synapsid. [6]

Description

Eunotosaurus reached up to 30 cm (12 in) in total body length. [7] It had a broad body formed by nine pairs of widened ribs that overlap each other. The forward-most ribs are angled slightly backward and the backward-most ribs angle slightly forward. The ribs are T-shaped in cross section, each having a broad, flat surface on the top and a narrow ridge running along its length on the bottom. The upper surface is convex, giving the body of Eunotosaurus a rounded shape. Each pair of ribs connects to an elongated dorsal or back vertebra. Most ribs are fused to the vertebrae, but some smaller specimens of Eunotosaurus have rib pairs that connect with the vertebrae but are not fused to them. There are nine dorsal vertebrae, far fewer than what is seen in other parareptiles. The neck of Eunotosaurus is short, consisting of six short cervical vertebrae. [8] [7]

Histological analysis of cross-sections of the ribs indicate that they grew in three different phases as an individual developed. As is the case in most land vertebrates, the first phase involves the growth of a rib primordium that ossifies into a rib bone. The second phase, which deviates from most other land vertebrates, is the development of a shelf of bone above the main shaft of the rib to form the T-shape. The third and final phase is the widening of the lower ridge into a teardrop-like shape, reinforcing the rib. While the third phase is unique to Eunotosaurus, the second phase is also seen in modern turtles. In turtles, the shelf of bone that forms from the rib shaft becomes a plate of the shell or carapace. In each rib of Eunotosaurus, the posterior surface of the lower ridge has Sharpey's fibers embedded in it. Sharpey's fibers help anchor muscles to bone. Most amniotes have Sharpey's fibers on the posterior and anterior edges of the ribs because the ribs are connected to each other by intercostal muscles, which are muscles that assist in breathing. The lack of Sharpey's fibers on the anterior side of the ribs of Eunotosaurus suggests that it lacked functional intercostal muscles. Turtles also lack intercostal muscles and instead have muscles that connect to the undersides of the ribs for the purpose of locomotion. If Eunotosaurus is close to the ancestry of turtles, it may have had similar sets of muscles. [8]

Even though Eunotosaurus has been traditionally considered an anapsid, it is considered to possess a lower temporal fenestra, though without the temporal bar. Moreover, a juvenile specimen also shows upper temporal fenestrae, meaning the skull demonstrates a fully diapsid condition. In the adult, the upper fenestra is covered by the supratemporal bone. [9]

History of study

Eunotosaurus was named in 1892, but it was not until 1914 that it was proposed to be an ancestor of Chelonia, the turtle order. English zoologist D. M. S. Watson claimed that Eunotosaurus was transitional between cotylosaurs (now referred to as captorhinids) and Chelonia. [10] He compared it to "Archichelone", a name he devised for a hypothetical chelonian ancestor, noting that its ribs appeared to be intermediate between those of turtles and other tetrapods. Watson's "Archichelone" had a pelvic girdle that was pushed back on the vertebral column and placed under the shell. However, fossils of Eunotosaurus show that the pelvis is in the normal tetrapod position and is placed over the ribs rather than within them, as in modern turtles. [11] Many fossils have been found showing a semi-rigid, turtle-like rib cage, one which presumably necessitated a tortoise-like fashion of walking. [12]

Eunotosaurus was considered the ancestor of turtles up until the late 1940s. In his 1956 book Osteology of the Reptiles, American paleontologist Alfred Sherwood Romer claimed that Eunotosaurus could not be included within Chelonia based on the available evidence. He placed it within Anapsida in its own order incertae sedis . [11] [13]

Over a century after its naming, Eunotosaurus was known from less than a dozen specimens, with very little material known from the skull. Despite the paucity of material, it was well described. Two additional skeletons were unearthed from the Karoo Supergroup and described in 1999. They are now housed in the Bernard Price Institute for Palaeontological Research in Johannesburg and the National Museum, Bloemfontein. While relatively rare, Eunotosaurus is common enough in the Karoo to be used as a biostratigraphic marker. It is present in the upper Tapinocephalus Assemblage Zone and in all parts of the succeeding Pristerognathus Assemblage Zone. [14]

Classification

The ribs of Eunotosaurus were very wide and flat, touching each other to form broad plates similar to the carapace of a turtle. Moreover, the number of vertebrae, the size of the vertebrae, and their structure are nearly identical to those of some turtles. Despite its many similarities to turtles, Eunotosaurus has a skull that shares many characteristics with the skulls of more primitive reptiles, resulting in many studies placing it in the extinct group Parareptilia. Phylogenetic analyses that use only the physical features of fossils and living species to determine evolutionary relationships have often shown strong support for both Eunotosaurus and turtles being descendants of parareptiles, in which case Eunotosaurus. [8] However, analyses which also include genetic data from living reptiles strongly support the idea that turtles fall within a group called Diapsida, as close relatives of either lizards (in which case they would be lepidosauromorphs) or birds and crocodiles (making them archosauromorphs). According to this view, the expanded ribs and similar vertebral columns of Eunotosaurus and turtles may be a case of evolutionary convergence. [15] However, the discovery of Pappochelys , a prehistoric species whose fossil remains show a mixture of features found in Eunotosaurus and the toothed stem-turtle Odontochelys , helped to resolve the issue. Though an analysis which included data from Pappochelys found weak support for the idea that Eunotosaurus was a parareptile, it found stronger support for the hypothesis that Eunotosaurus was itself a diapsid closely related to turtles, and that its apparently primitive, anapsid skull was probably developed as part of the turtle lineage, independently of parareptiles. [16] [7]

Eunotosaurus was assigned to its own family, Eunotosauridae, in 1954. [17] However, this name has fallen into disuse. In 1969, it was placed in the parareptile suborder Captorhinomorpha, [18] which is now[ when? ] considered to be within the clade Eureptilia. [19] In 2000, Eunotosaurus was placed in the clade Parareptilia, separate from turtles and cotylosaurs. [20] A 2008 phylogenetic analysis of parareptiles found Eunotosaurus to be the sister taxon of Milleretta and thus within the family Millerettidae. [21]

Eunotosaurus was incorporated in a recent 2010 phylogenetic analysis that sought to determine the origin of turtles. [22] [7] Turtles have recently been considered diapsids on the basis of genetic and phylogenetic evidence, and thus more closely related to modern lizards, snakes, crocodiles, and birds than parareptiles. However, with the inclusion of Eunotosaurus and the Late Triassic stem turtle Proganochelys , the resulting phylogenetic tree placed turtles outside Diapsida in a position similar to turtle's original placement as parareptiles. This study claimed that Eunotosaurus shared derived features of its ribs and vertebrae with the earliest turtles, thus making it a transitional form. The study identified several features that united Eunotosaurus with turtles in a true clade. [7] These include broad T-shaped ribs, ten elongated trunk vertebrae, cranial tubercles (small projections on the surface of the skull), and a wide trunk. The clade consisting of Eunotosaurus and turtles was called Pan-Testudines (defined as all animals more closely related to turtles than to any other living group). More derived pan-testudines, such as the earliest turtle Odontochelys, have a plastron. [22]

The following cladogram shows the phylogenetic position of the Eunotosaurus, from Ruta et al., 2011. [23]

Life restoration Eunotosaurus africanus.jpg
Life restoration
Parareptilia  

The cladogram below follows the most likely result found by another analysis of turtle relationships, published by Rainer Schoch and Hans-Dieter Sues in 2015. This study found Eunotosaurus to be an actual early stem-turtle, though other versions of the analysis found weak support for it as a parareptile. [16]

Archelosauria

The following cladogram is adapted from a 2022 study by Simões et al. Here, Eunotosaurus was recovered as neither a parareptile or a stem-turtle, but as a basal neodiapsid located outside the reptilian crown group. [5]

Sauropsida
Traditional Parareptilia

Related Research Articles

<span class="mw-page-title-main">Anapsid</span> Subclass of reptiles

An anapsid is an amniote whose skull lacks one or more skull openings near the temples. Traditionally, the Anapsida are the most primitive subclass of amniotes, the ancestral stock from which Synapsida and Diapsida evolved, making anapsids paraphyletic. It is however doubtful that all anapsids lack temporal fenestra as a primitive trait, and that all the groups traditionally seen as anapsids truly lacked fenestra.

<span class="mw-page-title-main">Sauria</span> Clade of reptiles

Sauria is the clade containing the most recent common ancestor of Archosauria and Lepidosauria, and all its descendants. Since most molecular phylogenies recover turtles as more closely related to archosaurs than to lepidosaurs as part of Archelosauria, Sauria can be considered the crown group of diapsids, or reptiles in general. Depending on the systematics, Sauria includes all modern reptiles or most of them as well as various extinct groups.

<span class="mw-page-title-main">Diapsid</span> Clade of amniote tetrapods with two holes in each side of their skulls

Diapsids are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years ago during the late Carboniferous period. All diapsids other than the most primitive ones in the clade Araeoscelidia are sometimes placed into the clade Neodiapsida. The diapsids are extremely diverse, and include birds and all modern reptile groups, including turtles, which were historically thought to lie outside the group. Although some diapsids have lost either one hole (lizards), or both holes, or have a heavily restructured skull, they are still classified as diapsids based on their ancestry. At least 17,084 species of diapsid animals are extant: 9,159 birds, and 7,925 snakes, lizards, tuatara, turtles, and crocodiles.

<span class="mw-page-title-main">Sauropsida</span> Taxonomic clade

Sauropsida is a clade of amniotes, broadly equivalent to the class Reptilia, though typically used in a broader sense to include both extinct stem-group relatives of modern reptiles, as well as birds. The most popular definition states that Sauropsida is the sibling taxon to Synapsida, the other clade of amniotes which includes mammals as its only modern representatives. Although early synapsids have historically been referred to as "mammal-like reptiles", all synapsids are more closely related to mammals than to any modern reptile. Sauropsids, on the other hand, include all amniotes more closely related to modern reptiles than to mammals. This includes Aves (birds), which are recognized as a subgroup of archosaurian reptiles despite originally being named as a separate class in Linnaean taxonomy.

<span class="mw-page-title-main">Mesosaur</span> Extinct family of reptiles

Mesosaurs were a group of small aquatic reptiles that lived during the early Permian period (Cisuralian), roughly 299 to 270 million years ago. Mesosaurs were the first known aquatic reptiles, having apparently returned to an aquatic lifestyle from more terrestrial ancestors. It is uncertain which and how many terrestrial traits these ancestors displayed; recent research cannot establish with confidence if the first amniotes were fully terrestrial, or only amphibious. Most authors consider mesosaurs to have been aquatic, although adult animals may have been amphibious, rather than completely aquatic, as indicated by their moderate skeletal adaptations to a semiaquatic lifestyle. Similarly, their affinities are uncertain; they may have been among the most basal sauropsids or among the most basal parareptiles.

<span class="mw-page-title-main">Neodiapsida</span> Clade of reptiles

Neodiapsida is a clade, or major branch, of the reptilian family tree, typically defined as including all diapsids apart from some early primitive types known as the araeoscelidians. Modern reptiles and birds belong to the neodiapsid subclade Sauria.

<span class="mw-page-title-main">Pareiasauria</span> Extinct clade of reptiles

Pareiasaurs are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with osteoderms which covered large areas of the body. They first appeared in southern Pangea during the Middle Permian, before becoming globally distributed during the Late Permian. Pareiasaurs were the largest reptiles of the Permian, reaching sizes equivalent to those of contemporary therapsids. Pareiasaurs became extinct in the Permian–Triassic extinction event.

<i>Milleretta</i> Extinct genus of reptiles

Milleretta is an extinct genus of millerettid parareptile from the Late Permian of South Africa. Fossils have been found in the Balfour Formation. Milleretta was a moderately sized, lizard-like animal, about 60 centimetres (24 in) in length. It was probably insectivorous. Its only known species is Milleretta rubidgei, making Milleretta a monospecific genus.

<span class="mw-page-title-main">Captorhinidae</span> Extinct family of tetrapods

Captorhinidae is an extinct family of tetrapods, typically considered primitive reptiles, known from the late Carboniferous to the Late Permian. They had a cosmopolitan distribution across Pangea.

<span class="mw-page-title-main">Parareptilia</span> Extinct subclass of reptiles (306–201Ma ago)

Parareptilia ("near-reptiles") is an extinct subclass or clade of basal sauropsids/reptiles, typically considered the sister taxon to Eureptilia. Parareptiles first arose near the end of the Carboniferous period and achieved their highest diversity during the Permian period. Several ecological innovations were first accomplished by parareptiles among reptiles. These include the first reptiles to return to marine ecosystems (mesosaurs), the first bipedal reptiles, the first reptiles with advanced hearing systems, and the first large herbivorous reptiles. The only parareptiles to survive into the Triassic period were the procolophonoids, a group of small generalists, omnivores, and herbivores. The largest family of procolophonoids, the procolophonids, rediversified in the Triassic, but subsequently declined and became extinct by the end of the period.

<span class="mw-page-title-main">Procolophonia</span> Extinct suborder of reptiles

Procolophonia is an extinct suborder (clade) of herbivorous reptiles that lived from the Middle Permian till the end of the Triassic period. They were originally included as a suborder of the Cotylosauria but are now considered a clade of Parareptilia. They are closely related to other generally lizard-like Permian reptiles such as the Millerettidae, Bolosauridae, Acleistorhinidae, and Lanthanosuchidae, all of which are included under the Anapsida or "Parareptiles".

<span class="mw-page-title-main">Procolophonomorpha</span> Order of reptiles (fossil)

Procolophonomorpha is an order or clade containing most parareptiles. Many papers have applied various definitions to the name, though most of these definitions have since been considered synonymous with modern parareptile clades such as Ankyramorpha and Procolophonia. The current definition of Procolophonomorpha, as defined by Modesto, Scott, & Reisz (2009), is that of as a stem-based group containing Procolophon and all taxa more closely related to it than to Milleretta. It constitutes a diverse assemblage that includes a number of lizard-like forms, as well as more diverse types such as the pareiasaurs. Lee 1995, 1996, 1997 argues that turtles evolved from pareiasaurs, but this view is no longer considered likely. Rieppel and deBraga 1996 and deBraga and Rieppel, 1997 argue that turtles evolved from sauropterygians, and there is both molecular and fossil (Pappochelys) evidence for the origin of turtles among diapsid reptiles.

<span class="mw-page-title-main">Temporal fenestra</span> Opening in the skull behind the orbit in some animals

Temporal fenestrae are openings in the temporal region of the skull of some amniotes, behind the orbit. These openings have historically been used to track the evolution and affinities of reptiles. Temporal fenestrae are commonly seen in the fossilized skulls of dinosaurs and other sauropsids. The major reptile group Diapsida, for example, is defined by the presence of two temporal fenestrae on each side of the skull. The infratemporal fenestra, also called the lateral temporal fenestra or lower temporal fenestra, is the lower of the two and is exposed primarily in lateral (side) view.

<span class="mw-page-title-main">Turtle shell</span> Shield for the ventral and dorsal parts of turtles

The turtle shell is a shield for the ventral and dorsal parts of turtles, completely enclosing all the vital organs of the turtle and in some cases even the head. It is constructed of modified bony elements such as the ribs, parts of the pelvis and other bones found in most reptiles. The bone of the shell consists of both skeletal and dermal bone, showing that the complete enclosure of the shell likely evolved by including dermal armor into the rib cage.

<i>Acerosodontosaurus</i> Extinct genus of reptiles

Acerosodontosaurus is an extinct genus of neodiapsid reptiles that lived during the Late Permian of Madagascar. The only species of Acerosodontosaurus, A. piveteaui, is known from a natural mold of a single partial skeleton including a crushed skull and part of the body and limbs. The fossil was discovered in deposits of the Lower Sakamena Formation. Based on skeletal characteristics, it has been suggested that Acerosodontosaurus individuals were at least partially aquatic.

<i>Acleistorhinus</i> Extinct genus of reptiles

Acleistorhinus (ah-kles-toe-RYE-nuss) is an extinct genus of parareptile known from the Early Permian of Oklahoma. It is notable for being the earliest known anapsid reptile yet discovered. The morphology of the lower temporal fenestra of the skull of Acleistorhinus bears a superficial resemblance to that seen in early synapsids, a result of convergent evolution. Only a single species, A. pteroticus, is known, and it is classified in the Family Acleistorhinidae, along with Colobomycter.

<i>Owenetta</i> Extinct genus of reptiles

Owenetta is an extinct genus of owenettid procolophonian parareptile. Fossils have been found from the Beaufort Group in the Karoo Basin of South Africa. Although most procolophonians lived during the Triassic, Owenetta existed during the Wuchiapingian and Changhsingian stages of the Late Permian as well as the early Induan stage of the Early Triassic. It is the type genus of the family Owenettidae, and can be distinguished from other related taxa in that the posterior portion of the supratemporal bears a lateral notch and that the pineal foramen is surrounded by a depressed parietal surface on the skull table.

<span class="mw-page-title-main">Evolution of reptiles</span> Origin and diversification of reptiles through geologic time

Reptiles arose about 320 million years ago during the Carboniferous period. Reptiles, in the traditional sense of the term, are defined as animals that have scales or scutes, lay land-based hard-shelled eggs, and possess ectothermic metabolisms. So defined, the group is paraphyletic, excluding endothermic animals like birds that are descended from early traditionally-defined reptiles. A definition in accordance with phylogenetic nomenclature, which rejects paraphyletic groups, includes birds while excluding mammals and their synapsid ancestors. So defined, Reptilia is identical to Sauropsida.

<span class="mw-page-title-main">Pantestudines</span> Clade of reptiles

Pantestudines or Pan-Testudines is the group of all reptiles more closely related to turtles than to any other living animal. It includes both modern turtles and all of their extinct relatives. Pantestudines with a complete shell are placed in the clade Testudinata.

<i>Pappochelys</i> Extinct genus of reptiles

Pappochelys is an extinct genus of diapsid reptile possibly related to turtles. The genus contains only one species, Pappochelys rosinae, from the Middle Triassic of Germany, which was named by paleontologists Rainer Schoch and Hans-Dieter Sues in 2015. The discovery of Pappochelys provides strong support for the placement of turtles within Diapsida, a hypothesis that has long been suggested by molecular data, but never previously by the fossil record. It is morphologically intermediate between the definite stem-turtle Odontochelys from the Late Triassic of China and Eunotosaurus, a reptile from the Middle Permian of South Africa.

References

  1. ↑ Day, Mike; Rubidge, Bruce; Almond, John; Jirah, Sifelani (2013). "Biostratigraphic correlation in the Karoo: The case of the Middle Permian parareptile Eunotosaurus". South African Journal of Science. 109 (3/4): 4. doi: 10.1590/sajs.2013/20120030 . ISSN   0038-2353.
  2. ↑ Cox, C.B. (1969). "The problematic Permian reptile Eunotosaurus". Bulletin of the British Museum of Natural History. 18: 167–196.
  3. ↑ Benton, M.J. (2016). "The Chinese Pareiasaurs". Zoological Journal of the Linnean Society. 18 (4): 813–853. doi:10.1111/zoj.12389. hdl: 1983/6d1a4f9b-a768-4b86-acb1-b3ad1f7ee885 .
  4. ↑ "The trouble with turtles: Paleontology at a crossroads". EARTH Magazine. Naomi Lubick. Retrieved 19 March 2014.
  5. 1 2 Simões, T. R.; Kammerer, C. F.; Caldwell, M. W.; Pierce, S. E. (2022). "Successive climate crises in the deep past drove the early evolution and radiation of reptiles". Science Advances. 8 (33): eabq1898. Bibcode:2022SciA....8.1898S. doi:10.1126/sciadv.abq1898. PMC   9390993 . PMID   35984885.
  6. ↑ Lichtig, Asher; Lucas, Spencer (2021). "Chinlechelys from the Upper Triassic of New Mexico, USA, and the origin of turtles". Palaeontologia Electronica. doi: 10.26879/886 . S2CID   233454789.
  7. 1 2 3 4 5 Hans-Dieter Sues (6 August 2019). The Rise of Reptiles. 320 Million Years of Evolution. Johns Hopkins University Press. pp. 49–50. ISBN   9781421428680.
  8. 1 2 3 Lyson, Tyler R.; Bever, Gabe S.; Scheyer, Torsten M.; Hsiang, Allison Y.; Gauthier, Jacques A. (2013). "Evolutionary origin of the turtle shell". Current Biology. 23 (12): 1–7. doi: 10.1016/j.cub.2013.05.003 . PMID   23727095.
  9. ↑ Bever, G. S.; Lyson, Tyler R.; Field, Daniel J.; Bhullar, Bhart-Anjan S. (2015). "Evolutionary origin of the turtle skull". Nature. 525 (7568): 239–242. doi:10.1038/nature14900. ISSN   1476-4687.
  10. ↑ Watson, D.M.S. (1914). "Eunotosaurus africanus Seeley and the ancestors of the Chelonia". Proceedings of the Zoological Society of London. 11: 1011–1020.
  11. 1 2 Burke, A.C. (1991). "The development and evolution of the turtle body plan: Inferring intrinsic aspects of the evolutionary process from experimental embryology". American Zoologist. 31 (4): 616–627. doi: 10.1093/icb/31.4.616 .
  12. ↑ Sumida, Stuart S; Sean Modesto (2001). "A Phylogenetic Perspective on Locomotory Strategies in Early Amniotes". Integrative and Comparative Biology. 41 (3): 586–597. doi: 10.1093/icb/41.3.586 .
  13. ↑ Romer, A.S. (1956). Osteology of the Reptiles. Chicago: University of Chicago Press. p. 772. ISBN   978-0-89464-985-1.
  14. ↑ Rubidge, B.S.; Modesto, S.; Sidor, C.; Welman, J. (1999). "Eunotosaurus africanus from the Ecca–Beaufort contact in Northern Cape Province, South Africa – implications for Karoo Basin development" (PDF). South African Journal of Science. 95: 553–555. Archived from the original (PDF) on 16 July 2011. Retrieved 1 August 2010.
  15. ↑ "Facts About Turtles: Eunotosaurus And Turtle Evolution". All-About-Reptiles.com. Archived from the original on 12 September 2010. Retrieved 1 August 2010.
  16. 1 2 Schoch, Rainer R.; Sues, Hans-Dieter (24 June 2015). "A Middle Triassic stem-turtle and the evolution of the turtle body plan". Nature . 523 (7562): 584–587. Bibcode:2015Natur.523..584S. doi:10.1038/nature14472. PMID   26106865. S2CID   205243837.
  17. ↑ Haughton, S.H.; Brink, A.S. (1954). "A bibliographical list of Reptilia from the Karoo Beds of South Africa". Palaeontologia Africana. 2: 1–187.
  18. ↑ Cox, C.B. (1969). "The problematic Permian reptile Eunotosaurus". Bulletin of the British Museum (Natural History), Geology Series. 18 (5): 167–196.
  19. ↑ Laurin, M.; Reisz, R.R. (1995). "A reevaluation of early amniote phylogeny". Zoological Journal of the Linnean Society. 113 (2): 165–223. doi:10.1111/j.1096-3642.1995.tb00932.x.
  20. ↑ Modesto, S.P. (2000). "Eunotosaurus africanus and the Gondwanan ancestry of anapsid reptiles". Palaeontologia Africana. 36: 15–20.
  21. ↑ Cisneros, J.C.; Rubidge, B.S.; Mason, R.; Dube, C. (2008). "Analysis of millerettid parareptile relationships in the light of new material of Broomia perplexa Watson, 1914, from the Permian of South Africa". Journal of Systematic Palaeontology. 2008 (6): 453–462. doi:10.1017/S147720190800254X. S2CID   73723455.
  22. 1 2 Lyson, T.R.; Bever, G.S.; Bhullar, B.-A.S.; Joyce, W.G.; Gauthier, J.A. (2010). "Transitional fossils and the origin of turtles". Biology Letters. 6 (6): 830–3. doi:10.1098/rsbl.2010.0371. PMC   3001370 . PMID   20534602.
  23. ↑ Marcello Ruta; Juan C. Cisneros; Torsten Liebrecht; Linda A. Tsuji; Johannes Müller (2011). "Amniotes through major biological crises: faunal turnover among Parareptiles and the end-Permian mass extinction". Palaeontology. 54 (5): 1117–1137. doi: 10.1111/j.1475-4983.2011.01051.x . S2CID   83693335.
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