Euparkeria, meaning "Parker's good animal", named in honor of W.K. Parker, was a small African reptile that lived during the Early Triassic Period, between
248-245 million years ago. Euparkeria was an ornithosuchian, and also thought to represent an early archosaur or archosauriforme. The first fossils were found in South Africa in 1913, but better specimens were found in 1924.
Description[]
Euparkeria had a light, lean body, long tail, and a small skull with tiny, needle-like teeth. Euparkeria had small bony plates that ran along the center of its back and tail, and its hindlegs were one-third longer than its forelimbs; longer than any other reptile of similar size during its time. This has led some paleontologists, such as Carroll, (1988)[1] to suggest that Euparkeria may have been "facultatively bipedal", in that it may have been able to run bipedally for short periods of time. It most likely fed on insects and any other small animals that it could find on the forest floor, and would periodically shed its teeth in order to keep them sharp.
Archosaur characteristics[]
Like other archosaurs, Euparkeria had an opening in the skull between its eyes and nasal breach (the antorbital opening) and two additional apertures in the skull behind one eye (the upper and lower temporal openings). Its teeth were set in sockets, rather than being attached to the side of the jawbone or perched atop it. These teeth were long, sharp, and recurved, which attested to the carnivorous habit that seems to have been common among the first archosaurs. Euparkeria also possessed teeth on its palate, which was also common among earlier reptiles and amphibians.[2]
However, Welman (1995)[citation needed] contends that, based on braincase characters, Euparkeria is closer to birds than to crocodyliforms or dinosaurs. This is highly controversial, however, and runs counter to other archosaur phylogenies. However, Dr. David Gower and ornithologist Erich Weber were able to show that Welman's purported cases of homology between Euparkeria and birds was incorrect or mistaken, and in fact the data supported the following conclusions:[3]
- The division of archosaurs into a crocodile branch and a bird branch
- The nesting of birds within ornithodirans
- The exclusion of Euparkeria from the crocodile-bird crown group.
Euparkeria was one of the smaller reptiles of its time, with the adults reaching the size of a large lizard (55 cm or 22 in). It lived in a world with many predators, so it had to be quick on its feet. It walked on four legs for most of the time, but if a quick getaway was needed, it could rise on to its hind legs and run at a very high speed. Euparkeria had relatively long hind legs, and may have been semi-bipedal, able to move using only its hind legs when running quickly (Carroll, 1988). This tendency towards bipedal locomotion makes Euparkeria one of the earliest reptiles to walk on two legs, a feature that would be retained in some dinosaurs and early Crurotarsi. Another means of defence that Euparkeria possessed was a sharp claw on its thumb, which could have been used as a weapon in close combat.
Classification[]
The family Euparkeriidae is named after Euparkeria. The family name was first proposed by German paleontologist Friedrich von Huene in 1920; Huene classified euparkeriids as members of Pseudosuchia, a traditional name for crocodilian relatives from the Triassic (Pseudosuchia means "false crocodiles"). Early phylogenetic analyses created by Jacques Gauthier in the 1980s provided an alternative hypothesis, that Euparkeria was closer to dinosaurs (including birds) rather than crocodilians. Many genera have been assigned to Euparkeriidae in the past, but only two other valid genera are currently believed to be part of the family, apart from Euparkeria itself: Halazhaisuchus and Osmolskina.
More recent analyses starting with Benton & Clark (1988) place Euparkeria as a member of Archosauriformes in a position outside both crocodilian-line and bird-line (Avemetatarsalian). Although the ancestor to archosaurs likely shared several similarities with Euparkeria, archosaurs are probably not directly descendants of the genus. The precise placement of Euparkeria and other euparkeriids within Archosauriformes is controversial.
Most analyses agree that Euparkeria was a closer relative of archosaurs than the proterosuchids or erythrosuchids were. The one exception is the study of Dilkes & Sues(2009), who found Euparkeria to be less crownward than Erythrosuchus.Nevertheless, these results have not been widely accepted. There still remains some ambiguity over whether Euparkeriidae was truly the sister group of the archosaurs. Many phylogenetic analyses place the long-snouted proterochampsians as more closely related to archosaurs than euparkeriids were. Such studies include Sereno (1991),Parrish (1993), Juul (1994), various analyses by Michael J. Benton, and Ezcurra (2016).
On the other hand, several other notable studies consider Euparkeria to be closer to archosaurs than proterochampsians. Sterling Nesbitt's influential 2011 monograph on archosaurian relationships found a similar result, although he also placed phytosaurs as the sister group to Archosauria, rather than Euparkeria. Roland Sookias, a paleontologist responsible for many studies on euparkeriids in the 2010s, also considers them to be closer archosaur relatives than the proterochampsians. Like Nesbitt (2011), he found phytosaurs to be the closest relatives of Archosauria, followed by the Euparkeria-like reptile Dorosuchus, and then by the euparkeriids.
References[]
- ^ Carroll, R.L. 1988. Vertebrate Paleontology and Evolution. W.H. Freeman, NY.
- ^ Euparkeria. (2009). In Encyclopædia Britannica. Retrieved June 25, 2009, from Encyclopædia Britannica Online: http://www.britannica.com/EBchecked/topic/195356/Euparkeria
- ^ Gower, D. J. and Weber, E. 1998. The braincase of Euparkeria, and the evolutionary relationships of birds and crocodiles. Biological Reviews 73: 367-411.
- Haines, Tim, and Paul Chambers. 2006. The Complete Guide to Prehistoric Life. Pg. 62. Canada: Firefly Books Ltd., 2006.