Mycterosaurus

{{Short description|Extinct genus of tetrapods}} {{Distinguish|Mycterosuchus}} {{Automatic taxobox | taxon = Mycterosaurus | image = Mycterosaurus NT small.jpg | image_caption = Life restoration of ''Mycterosaurus longcipes'' | fossil_range = Early Permian, {{fossil_range|290.1|272.5}} | authority = Williston, 1915 | type_species = {{extinct}}'''''Mycterosaurus longiceps''''' | type_species_authority = Williston, 1915 | subdivision_ranks = | subdivision = }}

'''''Mycterosaurus''''' (Greek as mykter/mykteros meaning nose/snout, sauros meaning "lizard"<ref>{{Cite book|last=Jaeger|first=Edmund C|title=A Source - Book of Biological Names and Terms|year=1960|volume=6}}</ref>) is an extinct genus of amniotes belonging to the family Varanopidae. It is classified in the varanopid subfamily Mycterosaurinae. ''Mycterosaurus'' is the most primitive member of its family, existing from 290.1 to 272.5 MYA,<ref name=":0">{{Cite web|url=https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=122320|title=Fossilworks: Mycterosaurus longiceps|website=fossilworks.org|access-date=17 December 2021}}</ref> known to Texas <ref name=":1">{{Cite journal|last=Williston|first=Samuel Wendell|date=September 1915|title=A New Genus and Species of American Theromorpha: Mycterosaurus longiceps|journal=The Journal of Geology|volume=23|issue=6|pages=554–559|doi=10.1086/622271|bibcode=1915JG.....23..554W|doi-access=free}}</ref> and Oklahoma.<ref name=":2">{{Cite journal|last1=Maddin|first1=Hillary C.|last2=Evans|first2=David C.|last3=Reisz|first3=Robert R.|date=2006-12-11|title=An Early Permian varanodontine varanopid (Synapsida: Eupelycosauria) from the Richards Spur locality, Oklahoma|journal=Journal of Vertebrate Paleontology|volume=26|issue=4|pages=957–966|doi=10.1671/0272-4634(2006)26[957:aepvvs]2.0.co;2|issn=0272-4634}}</ref><ref name=":0" /> It lacks some features that its advanced relatives have.

''Mycterosaurus'' is a relatively small carnivore, estimated to be around 60&nbsp;cm (23 inches) long with synonyms of ''Eumatthevia bolli'', and possibly ''Basicranodon fortsillensis''.<ref name=":0" /> Restored, ''Mycterosaurus'' appears spindly and grotesque in contrast to the majority of "pelycosaurs" in its proportions and especially unlike edaphosaurids, which are commonly stocky in build.<ref name=":3">{{Cite journal|last1=Romer|first1=Alfred Sherwood|last2=Price|first2=Llewellyn Ivor|date=6 December 1940|title=Review of the Pelycosauria|journal=Geological Society of America Special Papers|pages=405–412|via=Google Books}}</ref>

The number of valid ''Mycterosaurus'' species have varied over the years, with a total of two classifications of ''Mycterosaurus longiceps''<ref name=":1" /> and ''Mycterosaurus smithae.'' <ref name=":4">{{Cite journal|last1=Lewis|first1=George Edward|last2=Vaughn|first2=Peter Paul|date=1965|title=Early Permian Vertebrates from the Cutler Formation of the Placerville Area Colorado|journal=Geological Survey Professional Paper|pages=C34 – C39|via=Google Books}}</ref> However, recent analysis has led to a re-description of ''Mycterosaurus smithae.''<ref name=":5">{{Cite journal|last1=Brocklehurst|first1=Neil|last2=Reisz|first2=Robert R|last3=Fernandez|first3=Vincent|last4=Fröbisch|first4=Jörg|date=22 June 2016|title=A Re-Description of 'Mycterosaurus' smithae, an Early Permian Eothyridid, and Its Impact on the Phylogeny of Pelycosaurian-Grade Synapsids|journal= PLOS ONE|volume=11|issue=6|article-number=e0156810|doi=10.1371/journal.pone.0156810|pmid=27333277|pmc=4917111|bibcode=2016PLoSO..1156810B|doi-access=free}}</ref>

== Description ==

=== Skull === Both the holotype and AMNH 7002 ''"Eumatthevia"'' have been studied and restudied, with additions and modifications to the cranial description. The nares and orbit of ''Mycterosaurus'' are unusually large, with the orbit directed outwardly and circular in manner.<ref name=":1" /> The extremely large size of the orbit has been associated with the relatively small size of the animal.<ref name=":3" /> Additionally, the surface of the supraoccipital that articulates with the parietals dorsally above are cartilaginous, a condition found in that of crocodiles, lizards, and dinosaurs.<ref name=":1" /> The exoccipitals surround the foramen magnum and are loosely attached in a similar fashion to ''Dimetrodon.''<ref name=":1" /> The parietal foramen is situated almost at the extreme posterior end of the parietals and is very close to the dermosupraoccipitals.<ref name=":1" /> The parietal itself is slightly separated on each side from the squamoso-postorbital arch while the squamosal covers the quadate broadly.<ref name=":1" />

=== Dentition === ''Mycterosaurus'' possesses 18-20 maxillary teeth<ref name=":1" /> that are characteristically different from those of ''Varanops'', ''Ophiacaodon'', ''Dimetrodon'', or ''Edaphosaurus''.<ref name=":3" /> The teeth are stout at the base, with slightly recurved and sharp points.<ref name=":3" /> The first four to five maxillary teeth (anterior) are the largest at the primitive position of the canines.<ref name=":3" /><ref name=":1" /> These teeth are moderately elongated, flattened, and present an obtuse apex.<ref name=":1" /> The premaxillary and maxillary teeth are typical thecodont teeth.<ref name=":6">{{Cite journal|last=Broom|first=R|date=20 December 1930|title=On a new Primitive Theromorph (Eumatthevia Bolli)|journal=American Museum Novitates}}</ref> The prevomers presented with a longitudinal row of small teeth and were long and slender in character.<ref name=":6" /> The lower teeth appear to be rather small and isodont, but otherwise unknown due to fossil conditions.<ref name=":3" /> In addition to maxillary teeth, ''Mycterosaurus'' presents small, but numerous palatal teeth.<ref name=":3" /> The pterygoids, on both anterior and middle aspects, show a considerable number of small pointed teeth.<ref name=":6" /> The marginal teeth are serrated on the mesial and distal edges.<ref>{{Cite journal|last1=Reisz|first1=Robert R.|last2=Modesto|first2=Sean P.|title=Heleosaurus scholtzifrom the Permian of South Africa: A varanopid synapsid, not a diapsid reptile|date=September 2007|journal=Journal of Vertebrate Paleontology|volume=27|issue=3|pages=734–739|doi=10.1671/0272-4634(2007)27[734:HSFTPO]2.0.CO;2|issn=0272-4634}}</ref>

=== Post-cranial Skeleton === The vertebrae are similar to that of ''Varanops'', with a thin spine that was no more than 2-3 times in height the centrum.<ref name=":1" /> While the cervicals are unknown due to poor fossil records, details from the posterior aspect are somewhat preserved.<ref name=":3" /> The neural spine is low and broad in both anterior and posterior direction.<ref name=":3" /> The centra has rounded ends and no ventral keel, possessing a characteristic edaphosaurioid spool shape.<ref name=":3" /> Additionally, the dorsal centra is moderately elongate (5 units in length). In contrast, the lumbar centras are much shorter.<ref name=":3" />

The scapula is short and not particularly broad, in contrast to the exceptionally broad procoracoid plate, a feature of edaphosaurids.<ref name=":3" /> The glenoid surface is short, and the supraglenoid foramen is absent.<ref name=":3" /> The pelvis has extreme elongation at the anterior end of the iliac blade with the anterior expansion being greater than the posterior.<ref name=":3" /> The humerus and hind leg bones<ref name=":5" /> are slender, with no ectepicondylar foramen.<ref name=":3" />

The astragalus is L-shaped and the centrum is circular when viewed in ventral view. These observations are consistent with most pelycosaurian grade synapsids.<ref name=":7">{{Cite journal|last1=Kissel|first1=Richard|last2=Shinya|first2=Akiko|date=12 September 2003|title=The Astragalus-Calcaneum Complex of Mycterosaurus and Varanops (Synapsida: Varanopidae): Morphology, Locomotion, and Phylogeny|journal=Journal of Vertebrate Paleontology |volume=23 |issue=3 Suppl|pages=96A–97A|jstor=4524374}}</ref> The fourth distal tarsal is enlarged, with its proximal articular surface facing the convex.<ref name=":7" /> The convex is articulated by the astragalus-calcaneum complex.<ref name=":7" /> This morphology indicates a highly mobile mesotarsal joint in both Varanops and ''Mycterosaurus'', contrasting earlier beliefs that little movement was present in early synapsids.<ref name=":7" /> These observations serve as evidence to suggest that Varanops and ''Mycterosaurus'' used a semidigitigrade stance to ambulate.<ref name=":7" />

== Discovery == The first ''Mycterosaurus'' skull ever discovered was that of ''Mycterosaurus longiceps''. The holotype (FMNH-UC 692) was discovered by Mr. Herman Douthitt in 1915 at a deposit of the<ref name=":1" /> Lower Permian (Leonardian) Clyde Formation of north-central Texas.<ref name=":8">{{Cite journal|last1=Berman|first1=David S|last2=Reisz|first2=Robert R|date=3 December 1982|title=Restudy of Mycterosaurus Longiceps (Reptilia, Pelycosauria) From the Lower Permian of Texas|journal=Annals of Carnegie Museum|volume=51|pages=423–453}}</ref> Samuel Wendell Williston analyzed the holotype, describing the skull and other fragmented portions of the skeleton in his publication ''A New Genus and Species of American Theromorpha.''<ref name=":1" />

In 1930, R Broom identified an unstudied fossil collected by Jacob Boll at the American Museum that he believed had been wrongly labeled by collectors as a small labyrinthodont.<ref name=":6" /> The fossil, AMNH 7002, consisted of a fragmentary skull and partially crushed skeleton.<ref name=":6" /><ref name=":3" /> Broom named the fossil Eumatthevia Bolli after the late American paleontologist Professor W.D. Matthew. Broom noted that the skull of the fossil appeared similar to that of other primitive theromorphs such as ''Glaucosaurus'' and ''Mycterosaurus'', but that it appeared more slenderly built and presented a flatter skull compared to ''Mycterosaurus''.<ref name=":6" /> Despite this difference, an independent junior author's restoration differed in no aspects from ''Mycterosaurus'' except that the skull was lower, a difference attributed to crushing.<ref name=":3" /> As such, Romer concluded that ''Eumatthevia bolli'' was surely a synonym of ''Mycterosaurus longiceps''.<ref name=":3" /><ref name=":8" />

In 1940, Romer and Price reviewed both aforementioned fossil records in their review of pelycosaurs.<ref name=":3" /> The authors note both specimens were affected by different types of crushing, making it difficult to accurately assess the true nature of the skull.<ref name=":3" /> However, Romer and Price estimate the true proportions were likely an intermediate between the narrow shape Williston observed<ref name=":1" /> and the broad low type restored by Broom.<ref name=":6" /><ref name=":3" /> The authors failed to observe contacts between the lacrimal and jugal, ventral of the orbit, as described by Williston and Broom.<ref name=":3" /> Additionally, the authors believe defining features of height, pineal size, and teeth differentiated "''Eumatthevia''" and "''Mycterosaurus''" were inaccurate. Instead, these differences were likely due to crushing and inaccuracies of measurement by Williston.<ref name=":3" /> There is, however, agreement on the large size of the quadratojugal and orbits through all reports.

In 1957, Peter Paul Vaughn published a paper describing the features of a pelycosaur named ''Basicranodon fortsillensis'' that he believed carried very similar features to the Caseidae. However, Romer had previously established that ''Mycterosaurus'' should be classified as an edaphosaur. In 1966, the US Geographic Survey published a paper stating that ''Basicranodon fortsillensis'' could well belong to ''Mycterosaurus'' if better preserved specimens were ever discovered.<ref name=":4" />

In 1953, a new fossil (MCZ 2985), was discovered in Colorado and in 1964 named by Lewis and Vaughn as a new species that they called ''Mycterosaurus smithae'', after Mrs Stockton Smith.<ref name=":4" /> Features on MCZ 2985 such as the measurements of the orbit, temporal region, interorbital width, parietal region, and posteroventral corner of the cheek that matched that of ''Mycterosaurus longiceps'' led Lewis and Vaughn to their designation of a new ''Mycterosaurus'' species.<ref name=":4" />

However, a reexamination conducted by Brocklehurst et al (2016) using synchrotron radiation micro-computed tomography revealed observations that prompted the authors to reclassify ''Mycterosaurus smithae'' into genus Vaughnictis.<ref name=":5" /> The additional preparation and synchrotron scanning showed a lack of slender femur, serrated lateral dentition, teeth present on the coronoid, or a lateral boss on the postorbital, these being the most unambiguous varanopid and ''Mycterosaurine'' synapomorphies.<ref name=":5" />

== Classification == At the time of discovery of the holotype ''Mycterosaurus longiceps'' in 1915, it was believed by Mr. Herman Douthitt that the holotype belonged to the genus ''Varanops''<ref name=":1" /> due to the similar shape and general characters between the holotype and genus ''Varanops''.<ref name=":8" /> However, further analysis of the holotype by Samuel Wendell Williston, led Williston to propose classification of the type as a new species and genus of American Theromorpha.<ref name=":1" /> This matched R. Broom's analysis of ''Eumatthevia Bolli'', which revealed a similar conclusion that ''Eumatthevia Bolli'' <ref name=":6" /> should be classified as a primitive Theromorpha. One should note for clarification that Romer and Price concluded that ''Mycterosaurus longiceps'' is synonymous with the ''Eumatthevia Bolli'' in their 1940 analysis.<ref name=":3" />

Romer and Price, via their observations of ''Eumatthevia Bolli'' and the holotype, concluded that ''Mycterosaurus longiceps'' belonged as a primitive form of edaphosaurs.<ref name=":3" /> Romer and Price believed that while ''M. longiceps'' did not present some features characteristic of advanced edaphosaurs, ''M. longiceps'' most certainly exhibited a number of key characteristics that point to its classification as a edaphosaur.<ref name=":3" /> Specifically, Romer and Price created the Edaphosauria suborder family Nitosauridae within which genus ''Mycterosaurus'' and ''Nitosaurus'' reside.<ref name=":3" />

In 1982, Berman and Reisz rejected the family ''Nitosauride'' and suggested M''ycterosaurus longiceps'' as a primitive member of the family Varanopidae.<ref name=":8" /> Berman and Reisz believed the most important edaphosaur features cited by Romer and Price were mistakenly recorded from an isolated specimen piece that had been confused and misidentified.<ref name=":8" /> Rather, Berm and Reisz concluded the misidentified specimen was not a pelycosaur as Romer and Price had believed, but rather a temnospondyl amphibian.<ref name=":8" /> As a result, Berman and Reisz re-examined all known ''M. longiceps'' specimens which led them to the conclusion that ''Mycterosaurus'' is best interpreted as a member of the family Varanopidae.

Phylogenetic analysis of varanopoid interrelationships in 2006 placed Mycterosaurus under Mycterosaurinae with a sister genus of Mesenosaurus.<ref name=":2" /><ref>{{Cite journal|last1=Campione|first1=Nicolás E.|last2=Reisz|first2=Robert R.|date=2010-05-18|title=Varanops brevirostris(Eupelycosauria: Varanopidae) from the Lower Permian of Texas, with discussion of varanopid morphology and interrelationships|journal=Journal of Vertebrate Paleontology|volume=30|issue=3|pages=724–746|doi=10.1080/02724631003762914|s2cid=84949154|issn=0272-4634}}</ref>

Below is a cladogram modified from the analysis of Benson (in press), after the exclusion of ''Basicranodon'':<ref name="BRJ12">{{cite journal|last=Benson|first=R.J.|year=2012|title=Interrelationships of basal synapsids: cranial and postcranial morphological partitions suggest different topologies|journal=Journal of Systematic Palaeontology|volume=10|issue=4|pages=601–624|doi=10.1080/14772019.2011.631042|s2cid=84706899}}</ref>

{{clade|{{clade |1=''Tseajaia campi'' |2=''Limnoscelis paludis'' |label3=Amniota |3={{clade |1={{clade |1=''Captorhinus'' spp. |2=''Protorothyris archeri''}} |label2=Synapsida |2={{clade |1={{clade |1=Caseasauria |2={{clade |1=''Ianthodon schultzei'' |2={{clade |1=Edaphosauridae |2=Sphenacodontia}} }} }} |2={{clade |label1=Ophiacodontidae |1={{clade |1=''Archaeothyris florensis'' |2={{clade |1=''Varanosaurus acutirostris'' |2={{clade |1=''Ophiacodon'' spp. |2=''Stereophallodon ciscoensis''}} }} }} |label2='''Varanopidae''' |2={{clade |1=''Archaeovenator hamiltonensis'' |2={{clade |1=''Pyozia mesenensis'' |2={{clade |label1='''Mycterosaurinae''' |1={{clade |1=''Mycterosaurus longiceps'' |2={{clade |1=?''Elliotsmithia longiceps'' (BP/1/5678) |2=''Heleosaurus scholtzi'' |3=''Mesenosaurus romeri''}} }} |label2='''Varanopinae''' |2={{clade |1={{clade |1=''Varanops brevirostris'' |2={{clade |1=''Watongia meieri'' |2=''Varanodon agilis''}} }} |2={{clade |1=''Ruthiromia elcobriensis'' |2={{clade |1=''Aerosaurus wellesi'' |2=''Aerosaurus greenleorum'' }} }} }} }} }} }} }} }} }} }}|style=font-size:85%;line-height:100%}}

== Paleobiology == thumb|left|Reconstruction of ''M. longiceps''Very little has been postulated or hypothesized about the paleobiology of ''Mycterosaurus'' due to the small amounts of poorly preserved and incomplete fossil evidence. However, ''Mycterosaurus'' is known to be a small, agile faunivore that likely fed off the likes of insects.<ref>{{Cite journal|last=Vaughn|first=Peter Paul|date=1957|title=A Pelycosaur with subsphenoidal teeth from the Lower Permian of Oklahoma|journal=Journal of the Washington Academy of Sciences|volume=48|pages=44–47}}</ref><ref name=":9">{{Cite journal|last1=Maho|first1=Sigi|last2=Gee|first2=Bryan M.|last3=Reisz|first3=Robert R.|date=2019-10-23|title=A new varanopid synapsid from the early Permian of Oklahoma and the evolutionary stasis in this clade|journal=Royal Society Open Science|volume=6|issue=10|article-number=191297|doi=10.1098/rsos.191297|doi-access=free|pmid=31824730|pmc=6837192|issn=2054-5703}}</ref> Possessing a highly mobile mesotarsal joint, ''Mycterosaurus'' ambulated with a semi-digitigrade stance.<ref name=":7" />

== Paleoecology == ''Mycterosaurus'' occupied similar niches throughout their temporal ranges with ''Mesenosaurus'' and other relatively small bodied carnivorous lizards. Generally, it appears that small-bodied varanopids such as ''Mycterosaurus'' may have successfully occupied similar niches within the trophic networks as relatively small faunivores with no competitive eco-equivalents present until the appearance of small diapsids near the end of the Permian.<ref name=":9" />

== Paleogeography == Fossils of ''Mycterosaurus longiceps'' have been found in the deposits of the Lower Permian (Leonardian) Clyde Formation of north-central Texas.<ref name=":1" /><ref name=":8" /> The Clyde formation belongs to the Wichita group that is almost entirely alternating gray limestone and shale with minuscule amounts of sandstone and siltstone.<ref>{{Cite book|last=Stafford, P. T.|title=Stratigraphy of the Wichita group in part of the Brazos River Valley, north Texas|date=1960|publisher=U.S. G.P.O|page=274|oclc=663714194}}</ref> The Clyde Formation is less known and studied in comparison to other Formations within the Clear Fork Group, such as that of the Arroyo formation. However, the Clyde formation where ''Mycterosaurus longiceps'' was discovered appears to present a similar fauna assemblage. This includes ''Captorhinus, Labidosaurus, Pantylus, Seymouria,'' Varanops, Casea, as well as several large species of ''Dimetrodon'' and ''Edaphosaurus.'' <ref>{{Cite journal|last=Romer|first=Alfred Sherwood|date=1936|title=Studies on American Permo-Carboniferous Tetrapods|journal=Problems of Paleontology|pages=85–93}}</ref>

==See also== * List of pelycosaurs * Varanopidae * ''Mesenosaurus'' * Clyde Formation

==References== {{Reflist}}

{{Basal synapsids|S.}} {{Taxonbar|from=Q3278593}}

Category:Varanopidae Category:Prehistoric synapsid genera Category:Cisuralian synapsids of North America Category:Taxa named by Samuel Wendell Williston Category:Cisuralian genus extinctions Category:Permian geology of Texas