Erpetonyx
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| Gzhelium | ||||||||||||
| 303.7 to 298.9 million years | ||||||||||||
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| Erpetonyx | ||||||||||||
| Modesto et al., 2015 | ||||||||||||
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Erpetonyx is a relatively basal genus of parareptiles . The remains of the only species described so far, Erpetonyx arsenaultorum , come from the Cape Egmont Formation of the youngest Upper Carboniferous ( Gzhelium ) of Prince Edward Island in southeastern Canada . At this age, Erpetonyx is considered to be the oldest currently known parareptile and one of the oldest known sauropsids .
etymology
The generic name Erpetonyx is composed of the ancient Greek words ἑρπετόν (h) erpeton , creeping animal, reptile, reptile 'and ὄνυξ onyx , claw', consequently means something like "reptile claw". The epithet of the type species honors the Arsenault family in Prince County, Prince Edward Island, who discovered and collected the only known specimen to date.
features
The holotype of Erpetonyx arsenaultorum ( ROM 55402) is an approximately 20 to 25 cm long, almost complete and largely anatomically transmitted skeleton. Before being embedded in the sediment, the skull has almost completely disintegrated into its individual parts.
In addition to the rather small body size, the following diagnostic features are mentioned: a number of 29 presacral vertebrae (five neck and 24 dorsal vertebrae), sometimes unusually small carpal bones, an angle of the distal ("lower") end of the femur (epicondylar angle ) of 45 ° to the longitudinal axis of the Bone, a relatively wide distal end of the metacarpal IV and strong, claw-like terminal phalanges with pronounced humps (tubercles) for the flexor muscle .
Erpetonyx has an original, lizard- like habit. The maxillary had at least 15 pointed, slightly curved teeth. The teeth show a puckering of the dentin (called 'plicidentin'), as known from the parareptile Colobomycter . The dentition is basically homodontic , without caniniform teeth, as occurs in some other basal amniotes (see → Hylonomus and → Paleothyris ). The roof of the mouth, including the square process of the pterygoid, is equipped with small denticles. The bone identified as supratemporal has a small appendage ("croissant") at its rear end.
The total number of vertebrae was about 90. In addition to the 29 presacral vertebrae, there are three sacral vertebrae and about 60 caudal vertebrae. The neural arches have a striking hourglass-like shape in a dorsal view. In principle, the extremities are very similar to those of other primitive reptiles. The material obtained suggests a phalangeal formula of the hand of 2-3-4-5-3 [2].
Systematics
Erpetonyx is the oldest but not the most basic parareptile. It is the sister taxon of the Bolosaurids , whose oldest representatives, Belebey augustodunensis from the extended Carbon-Permian border area of the Autun basin (central France) and Bolosaurus striatus and " Bolosaurus traati " from the lowest Permian ( Asselium ) of North Texas (USA) ) and the Komi Republic (Russia), shared the status of the oldest parareptile until the discovery of Erpetonyx . The name Bolosauria was reactivated and redefined for the common clade of Bolosauridae (represented in the corresponding analysis by Belebey and Eudibamus ) and Erpetonyx . These Bolosauria are the most basic taxon of a clade called Procolophonomorpha, in which the "higher", middle and upper Permian as well as Triassic parareptiles such as the Pareiasaurs and the Procolophonids are found.
meaning
The discovery of Erpetonyx now certainly confirms the hypothesis derived from the cladistic analyzes of the basal sauropsids (= reptilia in the sense of Modesto & Anderson, 2004) that parareptiles, as a sister group of the eureptiles , must have already lived in the Upper Carboniferous. The phylogenetic position of Erpetonyx also extends the number of ghost lineages in the highest carboniferous to four: Mesosauridae, Millerosauria (Millerettidae + Eunotosaurus ), Bolosauridae and Australothyris + Ankyramorpha (Procolophonidae, Pareiasauria etc.).
literature
- Sean P. Modesto, Diane M. Scott, Mark J. MacDougall, Hans-Dieter Sues, David C. Evans, Robert R. Reisz: The oldest parareptile and the early diversification of reptiles. Proceedings of the Royal Society B. Vol. 282, No. 1801, 2015, doi : 10.1098 / rspb.2014.1912 .
Web links
- Erpetonyx arsenaultorum: a new and Oldest Known Parareptile From Gzhelian Pennsylvanian Carboniferous Prince Edward Island. Short article by William Baird on the blog The Dragon's Tale from January 14, 2015 with a drawing and photo of the holotype and cladogram.
Individual evidence
- ↑ Jocelyn Falconnet: First evidence of a bolosaurid parareptile in France (latest Carboniferous-earliest Permian of the Autun basin) and the spatiotemporal distribution of the Bolosauridae. Bulletin de la Société Géologique de France. Vol. 183, No. 6, 2012, pp. 495-508, doi : 10.2113 / gssgfbull.183.6.495
- ↑ P. Martin Sander: Early Permian Depositional Environments of Pond Bonebeds in Central Archer County. Palaeogeography, Palaeoclimatology, Palaeoecology. Vol. 69, No. 1–2, 1989, pp. 1–21, doi : 10.1016 / 0031-0182 (89) 90153-3 (alternative full text access : ResearchGate )
- ↑ Sean P. Modesto, Natalia Rybczynski: The amniote faunas of the Russian Permian: implications for Late Permian terrestrial vertebrate biogeography. Pp. 18–34 in: Michael J. Benton, Mikhail A. Shishkin, David M. Unwin, Evgenii N. Kurochkin (eds.): The Age of Dinosaurs in Russia and Mongolia. Cambridge University Press, Cambridge UK 2000, ISBN 0-521-55476-4
- ^ Jacques A. Gauthier, Arnold G. Kluge, Timothy Rowe: The early evolution of the Amniota. Pp. 103–155 in: Michael J. Benton (Ed.): The phylogeny and classification of the tetrapods, Volume 1: amphibians, reptiles, birds. Clarendon Press, Oxford 1988.
- ↑ Michel Laurin, Robert R. Reisz: A reevaluation of early amniote phylogeny. In: Zoological Journal of the Linnean Society. Vol. 113, No. 2, 1995, pp. 165-223, doi : 10.1111 / j.1096-3642.1995.tb00932.x (alternative full text access : IUCN / SSC Tortoise and Freshwater Turtle Specialist Group ).
- ↑ Sean P. Modesto, Jason S. Anderson: The Phylogenetic Definition of Reptilia. Systematic Biology. Vol. 53, No. 5, 2004, pp. 815-821, doi : 10.1080 / 10635150490503026 (alternative full text access : IUCN / SSC Tortoise and Freshwater Turtle Specialist Group PDF 552 kB).