View source for Eosimops

{{Short description|Extinct genus of dicynodonts}}
{{Automatic taxobox
| fossil_range = [[Middle Permian]]
| image = Eosimops newtoni.jpg
| image_caption = A life restoration of an adult ''Eosimops newtoni''
| taxon = Eosimops
| authority = [[Robert Broom|Broom]], 1921
| subdivision_ranks = Species
| subdivision =
* ''E. newtoni'' ([[type species|type]])
}}
'''''Eosimops''''' is an extinct genus of [[Pylaecephalidae|pylaecephalid]] [[dicynodont]]s. They were small [[synapsid]]s superficially resembling [[Mammal|modern mammals]]. ''Eosimops'' is known from several skull specimens, as well as one complete skeleton. ''Eosimops'' lived during the [[Permian|Middle Permian]] of South Africa.<ref name=":0">{{Cite journal|last1=Angielczyk|first1=Kenneth D.|last2=Rubidge|first2=Bruce S.|title=Skeletal morphology, phylogenetic relationships and stratigraphic range ofEosimops newtoniBroom, 1921, a pylaecephalid dicynodont (Therapsida, Anomodontia) from the Middle Permian of South Africa|journal=Journal of Systematic Palaeontology|volume=11|issue=2|pages=191–231|doi=10.1080/14772019.2011.623723|year=2013|s2cid=129393393 }}</ref>
== Etymology ==
''Eosimops'' was named in by South African paleontologist [[Robert Broom]].<ref name=":0" /> Its name is derived from the Ancient Greek ''Ēṓs'' (“dawn”) and ''ópsis'' (“appearance”).
== Discovery ==
''Eosimops'' was discovered in 1921 by Robert Broom, based on a single skull.<ref name=":0" /> It was found in the [[Tapinocephalus Assemblage Zone|''Tapinocephalus'' Assemblage Zone]] strata of South Africa, an area which provides a rich variety of early [[therapsid]]s and covers a period of almost 100 million years ranging from the [[Permian]] to the [[Jurassic]].<ref>{{Cite journal|last=Rubidge|first=Bruce S.|year=2005|title=Re-uniting lost continents- Fossil reptiles from the ancient Karoo and their wanderlust.|journal=South African Journal of Geology|volume=108|pages=135–172|doi=10.2113/108.1.135}}</ref> Later, other skull specimens as well as a complete skeleton were found. ''Eosimops'' is found above the stratigraphic range of the early dicynodont ''[[Eodicynodon|Eodycynodon]]''. Also found in the [[Pristerognathus Assemblage Zone|''Pristerognathus'' Assemblage Zone]], ''Eosimops'' occurs in association with animals like ''[[Eunotosaurus]]'' and [[Scylacosauridae|scylacosaurid]] [[Therocephalia|therocephalans]].<ref name=":0" />
== Description and paleobiology ==
''Eosimops'' was a small, non-mammalian [[synapsid]]. It was around 34&nbsp;cm in length (13.4 in.), roughly the size of a [[prairie dog]].<ref name=":0" /> It had a long cylindrical body, with sprawling, clawed limbs which it probably used for digging. ''Eosimops'' had two long tusks on its upper jaw,<ref>{{Cite journal|last=Kammerer|first=Christian F.|year=2009|title=A proposed higher taxonomy of anomodont therapsids|url=http://www.mapress.com/zootaxa/2009/f/z02018p024f.pdf|journal=Zootaxa|volume=2018|pages=1–24}}</ref> and a cutting keratinized beak<ref name=":1">{{Cite journal|last1=Angielczyk|first1=Kenneth D.|last2=Cox|first2=C. Barry|title=Distinctive emydopoid dicynodont (Therapsida, Anomodontia) mandibles from the Permian Ruhuhu and Usili formations (Songea Group), Ruhuhu Basin, Tanzania|journal=Journal of Vertebrate Paleontology|volume=35|issue=6|pages=e1008699|doi=10.1080/02724634.2015.1008699|year=2015|bibcode=2015JVPal..35E8699A |s2cid=140615500 |url=https://figshare.com/articles/dataset/Distinctive_emydopoid_dicynodont_Therapsida_Anomodontia_mandibles_from_the_Permian_Ruhuhu_and_Usili_formations_Songea_Group_Ruhuhu_Basin_Tanzania/1588798 }}</ref> for processing vegetation. It likely fed on leaves, stems, roots, and fleshy parts of plants. It has been suggested that some dicynodonts had hair, so ''Eosimops'' may have sported small hairs for insulation and tactile sensation. Its short and stocky proportions could have also aided in heat retention.<ref name=":2">{{Cite journal|last=Bajdek|first=Piotr|year=2016|title=Microbiota and food residues including possible evidence of pre-mammalian hair in Upper Permian coprolites fromRussia|journal=Lethaia|volume=49|issue=4|pages=455–477|doi=10.1111/let.12156}}</ref>
=== Skull ===
Like other pylaecephalids, ''Eosimops'' had a roughly square skull that sported caniform tusks. These tusks have been interpreted as representing [[sexual dimorphism]] within the closely related genus ''[[Diictodon]]'',<ref>{{Cite journal|last=Sullivan|first=Corwin|year=2003|title=The Permian Mammal-like Herbivore Diictodon, the Oldest Known Example of Sexually Dimorphic Armament|jstor=3558758|journal=Proceedings: Biological Sciences|volume=270|issue=1511|pages=173–178|doi=10.1098/rspb.2002.2189|pmid=12590756|pmc=1691218}}</ref> so may have been used for sexual selection. At least one postcanine tooth was present on the dentary blade. Its skull shape is described as being similar to that of its fellow pylaecephalid ''[[Robertia]]'', but likely attaining larger sizes.<ref name=":0" />
''Eosimops'' had indistinguishably fused [[premaxilla]]e, with the single element forming the anterior portion of the snout and alveolar margin along with the anterior edge of the external [[nares]]. The premaxilla forms part of the secondary pallet, and bears two sets of paired anterior ridges as well as a single median posterior palatal ridge. A dorsally directed portion of the premaxilla with a rounded edge projects between the nasals, diagnostic of dicynodonts thanks to the narrow groove along its midline.<ref name=":0" /> The left and right dentaries of ''Eosimops’'' mandible were fused, and the anterior surface sported a [[vascular foramina]] which was likely associated with a keratinaceous beak.<ref name=":1" /> Mandibular teeth were present, along with a well-developed [[dentary]] table.<ref name=":1" /> The dorsal margin of the [[symphysis]] is upturned, forming a cutting edge at the front of the lower jaw.<ref name=":0" /> The jaw joint facilitated a fore and aft sliding motion, allowing the animal to process vegetation effectively.<ref>{{Cite journal|last=Surov|first=Mikhail V.|title=Head kinematics and feeding adaptations of the Permian and Triassic dicynodonts|year=2008|url=https://www.researchgate.net/publication/249023494|journal=Journal of Vertebrate Paleontology|volume=28|issue=4|pages=1120–1129|doi=10.1671/0272-4634-28.4.1120|bibcode=2008JVPal..28.1120S |s2cid=85792653 }}</ref>
=== Skeleton ===
''Eosimops'' had a cylindrical body with 47 [[vertebra]]e, much like its other dicynodont relatives. Six of these were [[Cervical vertebrae|cervical]], and 23 were [[Dorsal vertebrae|dorsal]]. In the one full specimen recovered, no atlantal or axial ribs were observed. Whether or not this represents a true absence or incomplete preservation is uncertain. The dorsal ribs of ''Eosimops'' were long and relatively thin, and there was a ventral component to the curvature of the thorax. The sacral ribs were laterally expanded and robust. Its body likely resembled that of its close relatives ''Robertia'' and ''Diictodon.'' Typical of dicynodonts, the humerus of ''Eosimops'' sported expanded proximal and distal ends. It had a typical anomodont [[Phalanx bone|phalangeal formula]] of 2-3-3-3-3 on its forelimbs. While the hind limbs were not preserved well enough to know for certain, it appears that this formula was present on the hind limbs as well.<ref name=":0" />
Both the fore and hind limbs possessed extended phalanges with long, flattened claws, which suggests that ''Eosimops'' was a digger. It had short limbs, and it likely had a sprawling posture similar to its close relative ''Diictodon''. Like ''Diictodon'', ''Eosimops'' likely used its forelimbs for postural support and digging and its hind limbs for impact loading.<ref>{{Cite journal|last1=Ray|first1=Sanghamitra|last2=Chinsamy|first2=Anusuya|date=2003-01-01|title=Functional aspects of the postcranial anatomy of the Permian dicynodont Diictodon and their ecological implications|journal=Palaeontology|language=en|volume=46|issue=1|pages=151–183|doi=10.1111/1475-4983.00292|bibcode=2003Palgy..46..151R |s2cid=84329913 |issn=1475-4983|doi-access=free}}</ref>
=== Diet ===
Like all other known dicynodonts ''Eosimops'' was [[Herbivore|herbivorous]], using its horny beak to process plant matter. As it didn't have a well-developed mastication system in comparison to modern vertebrates and lacked a gastric mill, ''Eosimops'' likely had a well-developed digestive tract and focused on feeding on high-quality forage. This likely included gymnosperm plants, evidence of which has been found in dicynodont coprolites.<ref>{{Cite journal|last=Bajdek|first=Piotr|year=2014|title=Putative dicynodont coprolites from the Upper Triassic of Poland|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|volume=411|pages=1–17|doi=10.1016/j.palaeo.2014.06.013|bibcode=2014PPP...411....1B }}</ref>
=== Endothermy and hair ===
Dicynodonts, including ''Eosimops'', have been suspected for some time to be [[endotherm]]ic.<ref>{{Cite journal|last=Botha-Brink|first=Jennifer|year=2010|title=Do extraordinarily high growth rates in Permo-Triassic dicynodonts (Therapsida, Anomodontia) explain their success before and after the end-Permian extinction?|url=https://oup.silverchair-cdn.com/oup/backfile/Content_public/Journal/zoolinnean/160/2/10.1111_j.1096-3642.2009.00601.x/2/j.1096-3642.2009.00601.x.pdf?Expires=1489100079&Signature=Eg~ozl1UUyi7aCIkFSC9mLGkm3rjPDnqzkIMDfcE9xpXOJ~Yb~-UNbzCBVZ2T-7IMCjFz2iXpWiPfB~Wm3w0o7Pu~In~V1WTuZqbyrVlbgQHFvzCMnkAD2K~dsAIVaBNK4-qYdC7kzUgR8-p30Rj~4obbBTtxVBeVVUIr6V0SWNEUwjWtUdrgTAhH5iQuNbV94TBiPz--vTIUk6wvVAj4yK4DK3inrUATR6dF-frDkuGTvU0LhGpjwHOX5heGk4EWp6R6Wzwz0MbUyECgeLRmXuuSYMfg1fCRHV~hLhbk7z39wfgQzOPcZNptuSp5f1jR~SJDA1gAFjJjP31EC-hgg__&Key-Pair-Id=APKAIUCZBIA4LVPAVW3Q|journal=Zoological Journal of the Linnean Society|volume=160|issue=2|pages=341–365|doi=10.1111/j.1096-3642.2009.00601.x|doi-access=free}}</ref> In a [[Histology|histological]] study of the closely related ''Diictodon,'' another pylaecephalid, rapid bone growth is shown to be part of their early [[ontogeny]]. Continued growth during adult stages was also observed.<ref>{{Cite journal|last=Ray|first=Sanghamitra|year=2004|title=Diictodon feliceps (Therapsida, Dicynodontia): Bone Histology, Growth, and Biomechanics|jstor=4524703|journal=Journal of Vertebrate Paleontology|volume=24|issue=1|pages=180–194|doi=10.1671/1914-14|bibcode=2004JVPal..24..180R |s2cid=86189707 }}</ref> This rapid growth as well as moderately vascularized bones suggests that ''Diictodon'' could have been an endotherm, and that ''Eosimops'' could have been as well. This would be consistent with the hypothesis that more derived dicynodonts were endotherms, as endothermy would likely have been evolved early in the taxon's history.
''Eosimops'' also potentially had hair. The discovery of hair remains in coprolites from carnivorous species that had consumed dicynodonts suggests that the hair was of dicynodont origin,<ref name=":2" /> so hair could well be present in basal forms such as pylaecephalids.<ref>{{Cite journal|last=Angielczyk|first=Kenneth D.|title=A new pylaecephalid dicynodont (Therapsida, Anomodontia) from theTapinocephalus ''Assemblage'' Zone, Karoo Basin, Middle Permian of South Africa|year=2010|jstor=40864356|journal=Journal of Vertebrate Paleontology|volume=30|issue=5|pages=1396–1409|doi=10.1080/02724634.2010.501447|bibcode=2010JVPal..30.1396A |s2cid=129846697 }}</ref> This, along with ''Eosimops’'' stocky body proportions, would allow the animal to conserve generated heat.<ref name=":2" />
== Species ==
The genus ''Eosimops'' represents a single known species, ''Eosimops newtoni''<ref name=":0" />''. ''
==See also==
{{Portal|Paleontology}}
* [[List of therapsids]]
==References==
<references />
{{Anomodontia|D.}}
{{Taxonbar|from=Q5381893}}
[[Category:Dicynodonts]]
[[Category:Fossil taxa described in 1922]]
[[Category:Taxa named by Robert Broom]]
[[Category:Anomodont genera]]
[[Category:Herbivorous vertebrates]]