Ophiacodontidae

Ophiacodontidae is an extinct family of early eupelycosaurs from the Carboniferous and Permian. Archaeothyris, and Clepsydrops were among the earliest ophiacodontids, appearing in the Late Carboniferous. Ophiacodontids are among the most basal synapsids, an offshoot of the lineage which includes therapsids and their descendants, the mammals. The group became extinct by the Middle Permian, replaced by anomodonts, theriodonts, and the diapsid reptiles.

Ophiacodontidae Temporal range: Late Carboniferous to Early Permian 306–280 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Mounted skeleton of Ophiacodon retroversus in the American Museum of Natural History
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Family:	†Ophiacodontidae Nopsca, 1923
Subgroups
See text.

Characteristics

Ophiacodon mirus restoration.

The lifestyle of ophiacodonts has long been controversial. Some studies suggested that they were semi-aquatic, and some even suggested a fairly aquatic lifestyle, but a recent study based on a quantitative inference model[1] suggested that both Clepsydrops and Ophiacodon were terrestrial.[2] Vertebral morphometric data also support, though ambiguously, a rather terrestrial lifestyle for Ophiacodon,[3] which could reach a length of 3.6 m (12 ft).[4] Archaeothyris may also have been terrestrial, but no detailed study of its habitat has been performed so far. The earliest ophiacodontids resembled varanids in body proportions, while others were larger with elongated skulls and massive shoulder girdles, probably to provide muscle attachment to support the weight of the large head.

Classification

Traditionally, Archaeothyris, Ophiacodon, Varanosaurus and the briefly described Baldwinonus, Clepsydrops, Echinerpeton, Stereophallodon and Stereorhachis are included in the Ophiacodontidae. Protoclepsydrops was also regarded as ophiacodontid, however there is debate as to whether or not it was a synapsid. Echinerpeton and Sterophallodon were included for the first time in a phylogenetic analysis by Benson (2012).[5] Echinerpeton was found to be a wildcard taxon due to its small amount of known materials. It occupies three possible positions, falling either as the most basal synapsid, as the sister taxon of Caseasauria plus more derived taxa, or as an ophiacodontid more derived than Archaeothyris. Below is a cladogram modified from the analysis of Benson (2012),[5] after the exclusion of Echinerpeton:[5]

Tseajaia campi     Limnoscelis paludis   Amniota     Captorhinus spp.     Protorothyris archeri     Synapsida     Caseasauria       Ianthodon schultzei       Edaphosauridae     Sphenacodontia           Ophiacodontidae   Archaeothyris florensis       Varanosaurus acutirostris       Ophiacodon spp.     Stereophallodon ciscoensis         Varanopidae   Archaeovenator hamiltonensis       Pyozia mesenensis         Mycterosaurus longiceps       ?Elliotsmithia longiceps (BP/1/5678)     Heleosaurus scholtzi     Mesenosaurus romeri             Varanops brevirostris       Watongia meieri     Varanodon agilis           Ruthiromia elcobriensis       Aerosaurus wellesi     Aerosaurus greenleorum

References

1. Quémeneur, S.; de Buffrénil, V.; Laurin, M. (2013). "Microanatomy of the amniote femur and inference of lifestyle in limbed vertebrates". Biological Journal of the Linnean Society. 109 (3): 644–655. doi:10.1111/bij.12066.
2. Laurin, M.; de Buffrénil, V. (2015). "Microstructural features of the femur in early ophiacodontids: A reappraisal of ancestral habitat use and lifestyle of amniotes". Comptes Rendus Palevol. 15 (1–2): 115–127. doi:10.1016/j.crpv.2015.01.001.
3. Felice, R. N.; Angielczyk, K. D. (2014). "Was Ophiacodon (Synapsida, Eupelycosauria) a Swimmer? A Test Using Vertebral Dimensions". Early Evolutionary History of the Synapsida. Vertebrate Paleobiology and Paleoanthropology. p. 25. doi:10.1007/978-94-007-6841-3_3. ISBN 978-94-007-6840-6.
4. The Macmillan Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals
5. Benson, R.J. (2012). "Interrelationships of basal synapsids: cranial and postcranial morphological partitions suggest different topologies". Journal of Systematic Palaeontology. 10 (4): 601–624. doi:10.1080/14772019.2011.631042.

External links

• Ophiacodontidae - at Palaeos