{{Short description|Extinct family of tetrapods}} {{Automatic taxobox | fossil_range = Late Carboniferous - Middle Permian, {{fossil_range|309|260}} | image = Varanops brevirostris Exhibit Museum of Natural History cropped.jpg | image_upright = 1.3 | image_caption = Fossil skeleton of ''Varanops brevirostris'' in the University of Michigan Museum of Natural History | taxon = Varanopidae | authority = Romer and Price, 1940 | subdivision_ranks = Genera | subdivision = See below }}
'''Varanopidae''' is an extinct family of amniotes known from the Late Carboniferous to Middle Permian that resembled monitor lizards (with the name of the group deriving from the monitor lizard genus ''Varanus'') and may have filled a similar niche. Typically, they are considered to be relatively basal synapsids (and thus more closely related to mammals than to reptiles), although some studies from the late 2010s recovered them being taxonomically closer to diapsid reptiles;<ref>{{cite journal |last1=Ford |first1=David P. |last2=Benson |first2=Roger B. J. |year=2018 |title=A redescription of Orovenator mayorum (Sauropsida, Diapsida) using high-resolution μCT, and the consequences for early amniote phylogeny |journal=Papers in Palaeontology |volume=5 |issue=2 |pages=197–239 |doi=10.1002/spp2.1236|s2cid=92485505 |url=https://ora.ox.ac.uk/objects/uuid:3f9d9f16-aa8b-4910-a967-9a6a645e4d74 |doi-access=free |bibcode=2019PPal....5..197F |url-access=subscription }}</ref><ref>{{Cite journal|last=Modesto|first=Sean P.|date=December 23, 2019|title=Rooting about reptile relationships|journal=Nature Ecology & Evolution|language=en|volume=4|issue=1|pages=10–11|doi=10.1038/s41559-019-1074-0|pmid=31900449|s2cid=209672518|issn=2397-334X}}</ref><ref>{{Cite journal|last1=MacDougall|first1=Mark J.|last2=Modesto|first2=Sean P.|last3=Brocklehurst|first3=Neil|last4=Verrière|first4=Antoine|last5=Reisz|first5=Robert R.|last6=Fröbisch|first6=Jörg|date=2018|title=Commentary: A Reassessment of the Taxonomic Position of Mesosaurs, and a Surprising Phylogeny of Early Amniotes|journal=Frontiers in Earth Science|language=English|volume=6|page=99 |doi=10.3389/feart.2018.00099|issn=2296-6463|doi-access=free|bibcode=2018FrEaS...6...99M }}</ref> recent studies from the early 2020s support their traditional placement as synapsids on the basis of high degree of bone labyrinth ossification, maxillary canal morphology, and phylogenetic analyses.<ref>{{Cite journal|last1=Bazzana |first1=K. D. |last2=Evans |first2=D. C. |last3=Bevitt |first3=J. J. |last4=Reisz |first4=R. R. |title=Neurosensory anatomy of Varanopidae and its implications for early synapsid evolution |year=2021 |journal=Journal of Anatomy |volume=240 |issue=5 |pages=833–849 |doi=10.1111/joa.13593 |pmid=34775594 |pmc=9005680 |s2cid=244116303 }}</ref><ref>{{Cite journal|last1=Benoit |first1=J. |last2=Ford |first2=D. P. |last3=Miyamae |first3=J. A. |last4=Ruf |first4=I. |title=Can maxillary canal morphology inform varanopid phylogenetic affinities? |year=2021 |journal=Acta Palaeontologica Polonica |volume=66 |issue=2 |pages=389–393 |doi=10.4202/app.00816.2020 |s2cid=237333701 |doi-access=free }}</ref><ref>{{cite journal |last1=Simões |first1=T. |last2=Kammerer |first2=C. |date=August 2022 |title=Successive climate crises in the deep past drove the early evolution and radiation of reptiles |journal=Science Advances |volume=08 |issue=33 |article-number= eabq1898|doi=10.1126/sciadv.abq1898 |pmid=35984885 |pmc=9390993 |bibcode=2022SciA....8.1898S |s2cid=251694019 |doi-access=free }}</ref><ref name="Jenkins2025" /> A varanopid from the late Middle Permian ''Pristerognathus'' Assemblage Zone (Capitanian) is the youngest known varanopid and the last member of the "pelycosaur" group of synapsids.<ref name="Metal11">{{cite journal |last=Modesto |first=S.P. |author2=Smith, R.M.H. |author3=Campione, N.E. |author4= Reisz, R.R. |year=2011 |title=The last "pelycosaur": a varanopid synapsid from the Pristerognathus Assemblage Zone, Middle Permian of South Africa |journal=Naturwissenschaften |volume=98 |issue=12 |pages=1027–1034 |doi=10.1007/s00114-011-0856-2 |pmid=22009069|bibcode=2011NW.....98.1027M |s2cid=27865550 }}</ref> Thus, Varanopidae vanishes from the fossil record at the same time as dinocephalians,<ref name="Day et al. 2015">{{cite journal |last1=Day |first1=Michael O. |last2=Ramezani |first2=Jahandar |last3=Bowring |first3=Samuel A. |last4=Sadler |first4=Peter M. |last5=Erwin |first5=Douglas H. |last6=Abdala |first6=Fernando |last7=Rubidge |first7=Bruce S. |title=When and how did the terrestrial mid-Permian mass extinction occur? Evidence from the tetrapod record of the Karoo Basin, South Africa |journal=Proceedings of the Royal Society B: Biological Sciences |date=22 July 2015 |volume=282 |issue=1811 |article-number=20150834 |doi=10.1098/rspb.2015.0834 |pmid=26156768 |pmc=4528552 |bibcode=2015RSPSB.28250834D }}</ref> plausibly as a result of a major mass extinction event<ref name="Laurin & Didier 2025">{{cite journal |last1=Laurin |first1=Michel |last2=Didier |first2=Gilles |title=The rise and fall of Varanopidae† (Amniota, Synapsida) |journal=Frontiers in Earth Science |date=20 March 2025 |volume=13 |doi=10.3389/feart.2025.1544451 |doi-access=free |language=English |issn=2296-6463}}</ref> that has been called the "Dinocephalian extinction event".<ref name="Lucas 2017">{{cite journal |last1=Lucas |first1=S. G. |title=Permian tetrapod extinction events |journal=Earth-Science Reviews |date=1 July 2017 |volume=170 |pages=31–60 |doi=10.1016/j.earscirev.2017.04.008 |bibcode=2017ESRv..170...31L |issn=0012-8252}}</ref>
==Description== [[File:Aerosaurus wellesi 4.jpg|left|thumb|Fossil of ''Aerosaurus wellesi'']] No known varanopids developed a sail like ''Dimetrodon''. The length of known varanopids, including the tail, varies from {{convert|1|to|2|m|ft|0}}.<ref>{{cite journal |author= Reisz, R.R. & Laurin, M. |year=2004 |title=A reevaluation of the enigmatic Permian synapsid ''Watongia'' and of its stratigraphic significance |journal=Canadian Journal of Earth Sciences |volume=41 |issue=4 |pages=377–396 |doi=10.1139/e04-016|bibcode=2004CaJES..41..377R }}</ref> Varanopids already showed some advanced characteristics of true pelycosaurs such as their deep, narrow, elongated skulls. Their jaws were long and their teeth were sharp. However, they were still primitive by mammalian standards. They had long tails, lizard-like bodies, and thin legs. The varanopids were mostly carnivorous, but as they were reduced in size, their diets changed from a carnivorous to an insectivorous lifestyle. Compared to the other animals in the Early Permian, varanopids were agile creatures.[[File:Varanodon1DB.jpg|thumb|''Varanodon agilis''|left]] [[File:Mesenosaurus and Varanodon.jpg|thumb|Skulls of ''Mesenosaurus'' (top) and ''Varanodon'' (bottom), showing variation in skull shape.]]
A 2025 paper described scaly body impressions left by an Early Permian sphenacodont (likely ''Dimetrodon teutonis''), which would suggest that other early synapsids, including varanopids, likely had scaly skin as well.<ref>{{cite journal |last1=Marchetti |first1=L. |last2=Logghe |first2=A. |last3=Buchwitz |first3=M. |last4=Fröbisch |first4=J. |year=2025 |title=Early Permian synapsid impressions illuminate the origin of epidermal scales and aggregation behavior |journal=Current Biology |doi=10.1016/j.cub.2025.04.077 |doi-access=free }}</ref> (Fossils of ''Ascendonanus'', originally classified as a varanopid, also revealed scales akin to those of squamates.<ref>Frederik Spindler; Ralf Werneburg; Joerg W. Schneider; Ludwig Luthardt; Volker Annacker; Ronny Rößler (2018). "First arboreal 'pelycosaurs' (Synapsida: Varanopidae) from the early Permian Chemnitz Fossil Lagerstätte, SE Germany, with a review of varanopid phylogeny". PalZ. in press. doi:10.1007/s12542-018-0405-9.</ref> However, a study published in 2025 reclassified ''Ascendonanus'' along with ''Cabarzia'' as neoreptilians, not varanopid synapsids.<ref name="Jenkins2025">{{Cite journal |last1=Jenkins |first1=Xavier A |last2=Benson |first2=Roger BJ |last3=Ford |first3=David P |last4=Browning |first4=Claire |last5=Fernandez |first5=Vincent |last6=Dollman |first6=Kathleen |last7=Gomes |first7=Timothy |last8=Griffiths |first8=Elizabeth |last9=Choiniere |first9=Jonah N |last10=Peecook |first10=Brandon R |date=2025-08-28 |title=Evolutionary assembly of crown reptile anatomy clarified by late Paleozoic relatives of Neodiapsida |journal=Peer Community Journal |language=en |volume=5 |at=e89 |doi=10.24072/pcjournal.620 |issn=2804-3871 |doi-access=free}}</ref>) Parental care is known in ''Heleosaurus'', suggesting that it is ancestral to synapsids as a whole.<ref>Botha-Brink, Jennifer. "A Mixed-Age Classed 'Pelycosaur' Aggregation from South Africa: Earliest Evidence of Parental Care in Amniotes?" Proceedings of the Royal Society B: Biological Sciences 274.1627 (2007): 2829-834. JSTOR. Web. 06 Mar. 2017</ref>
Varanopids are small to medium-sized possible synapsids that have been discovered throughout the supercontinent Pangaea. Varanopids are found in areas of North America, Russia, Europe, and South Africa. The authors Romer and Price (1940) discussed the original positioning of Varanopidae within Synapsida and considered them as the suborder Sphenacodontia. Most phylogenetic analyses have placed Varanopidae as a basal member of Synapsida and due to their positioning, a better understanding of the morphology and phylogeny of varanopids is needed for synapsid evolution. The phylogeny of varanopids is based mostly on cranial morphology.<ref>{{cite journal|last1=Maddin|first1=H. C.|last2=Evans|first2=D. C.|last3=Reisz|first3=R. R.|year=2006|title=An Early Permian Varanodontine Varanopid (Synapsida: Eupelycosauria) from the Richards Spurs 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|jstor=4524646|s2cid=130455511 }}</ref><ref>{{cite journal|last1=Campione|first1=N.|last2=Reisz|first2=R.|year=2010|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|bibcode=2010JVPal..30..724C |s2cid=84949154}}</ref> The atlas−axis complex can be described with little effort with variation of this structure within a small clade. Varanopids, members of synapsid predators, have well preserved atlas−axes permitting a description and examination of morphological variation between taxon. The size of the transverse processes on the axis and the shape of the axial neural spine can be variable. For the small mycterosaurine varanopids, they have small transverse processes that point posteroventrally, and the axial spine is dorsoventrally short, with a flattened dorsal margin in lateral view. The larger varanodontine varanopids have large transverse processes with a broad base, and a much taller axial spine with a rounded dorsal margin in lateral view. Using outgroup comparisons, the morphology of the transverse processes is considered a derived trait in varanodontines, while in mycterosaurines the morphology of the axial spine is the derived trait.<ref>{{cite journal|last1=Campione|first1=N. E.|last2=Reisz|first2=R. R.|year=2011|title=Morphology and Evolutionary Significance of the Atlas-axis Complex in Varanopid Synapsids|url=https://www.app.pan.pl/archive/published/app56/app20100071.pdf|journal=Acta Palaeontologica Polonica|volume=56|issue=4|pages=739–748|doi=10.4202/app.2010.0071|doi-access=free}}</ref>
== Ecology == At least some varanopids such as ''Eoscansor'' (and the possible varanopid ''Ascendonanus'') are amongst the oldest known tree climbing (arboreal) animals, with limbs and digits adapted for grasping. Other varanopids lacked these adaptations and were probably terrestrial.<ref name=":0">{{Cite journal |last1=Lucas |first1=Spencer G. |last2=Rinehart |first2=Larry F. |last3=Celeskey |first3=Matthew D. |last4=Berman |first4=David S. |last5=Henrici |first5=Amy C. |date=June 2022 |title=A Scansorial Varanopid Eupelycosaur from the Pennsylvanian of New Mexico |url=https://www.researchgate.net/publication/361410244 |journal=Annals of Carnegie Museum |volume=87 |issue=3 |pages=167–205 |doi=10.2992/007.087.0301 |bibcode=2022AnCM...87..301L |s2cid=250015681 |issn=0097-4463}}</ref>
==Classification== [[File:ArchaeovenatorDB.jpg|thumb|''Archaeovenator hamiltonensis'']] Family '''Varanopidae''' *''Apsisaurus'' *''Archaeovenator'' *''Ascendonanus'' (or a non-synapsid neoreptilian)<ref name=Jenkins2025 /> *''Basicranodon'' (possible junior synonym of ''Mycterosaurus''<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 |doi=10.1080/14772019.2011.631042 |pages=601–624|bibcode=2012JSPal..10..601B |s2cid=84706899 }}</ref>) *''Eoscansor'' *''Dendromaia'' *''Pyozia'' *''Thrausmosaurus?'' (''nomen dubium'') *Clade '''Neovaranopsia'''<ref name="Spindler2018">{{cite journal |last1=Spindler |first1=F. |last2=Werneburg |first2=R. |last3=Schneider |first3=J. W. |last4=Luthardt |first4=L. |last5=Annacker |first5=V. |last6=Rößler |first6=R. |title=First arboreal 'pelycosaurs' (Synapsida: Varanopidae) from the early Permian Chemnitz Fossil Lagerstätte, SE Germany, with a review of varanopid phylogeny |journal=PalZ |date=2018 |volume=92 |issue=2 |pages=315–364 |url=https://www.researchgate.net/publication/323782950 |doi=10.1007/s12542-018-0405-9|bibcode=2018PalZ...92..315S |s2cid=133846070 }}</ref> **Subfamily '''Mesenosaurinae''' ***''Cabarzia'' (or a non-synapsid neoreptilian)<ref name=Jenkins2025 /><ref>{{Cite journal|last1=Spindler|first1=Frederik|last2=Werneburg|first2=Ralf|last3=Schneider|first3=Jörg W.|date=2019-06-01|title=A new mesenosaurine from the lower Permian of Germany and the postcrania of ''Mesenosaurus'': implications for early amniote comparative osteology|url=https://www.researchgate.net/publication/330501339|journal=PalZ|language=en|volume=93|issue=2|pages=303–344|doi=10.1007/s12542-018-0439-z|bibcode=2019PalZ...93..303S |s2cid=91871872|issn=1867-6812}}</ref> ***''Mesenosaurus'' ***Clade '''Afrothyra'''<ref name="Spindler2018" /> ****''Anningia'' ****''Elliotsmithia'' ****''Heleosaurus'' ****''Microvaranops'' **Subfamily '''Varanodontinae''' ***''Aerosaurus'' ***''Mycterosaurus'' ***''Ruthiromia'' ***''Tambacarnifex'' ***''Varanodon'' ***''Varanops'' ***''Watongia''
''Apsisaurus'' was formerly assigned as an "eosuchian" diapsid. In 2010, it was redescribed by Robert R. Reisz, Michel Laurin, and David Marjanović; their phylogenetic analysis found it to be a basal varanopid synapsid. The cladogram below is modified after Reisz, Laurin, and Marjanović, 2010.<ref name=Reisz2010>{{Cite journal|author=Robert R. Reisz, Michel Laurin and David Marjanović |year=2010 |title=''Apsisaurus witteri'' from the Lower Permian of Texas: yet another small varanopid synapsid, not a diapsid |journal=Journal of Vertebrate Paleontology |volume=30 |issue=5 |pages=1628–1631 |doi=10.1080/02724634.2010.501441 |bibcode=2010JVPal..30.1628R |s2cid=129835335 }}</ref>
{{clade |label1='''Varanopidae''' |1={{clade |1=''Archaeovenator'' |2={{clade |1=''Apsisaurus'' |2={{clade |1=''Mesenosaurus'' |2=''Mycterosaurus'' |3=Varanodontinae }} }} }} }}
The poorly known ''Basicranodon'' and ''Ruthiromia'' were tentatively assigned to Varanopidae by Reisz (1986), but have been neglected in more recent studies. They were included for the first time in a phylogenetic analysis by Benson (2012). ''Ruthiromia'' was found to be most closely related to ''Aerosaurus''. ''Basicranodon'' was found to be a wildcard taxon due to its small amount of known materials, as it is based on a partial braincase from the ?Kungurian stage Richards Spur locality in Oklahoma. It occupies two possible positions, falling either as a mycterosaurine, or as the sister taxon of ''Pyozia''. Although Reisz ''et al.'' (1997) considered ''Basicranodon'' as a subjective junior synonym of ''Mycterosaurus'', Benson (2012) found some differences in the distribution of teeth and shape of the dentigerous ventral platform medial to the basipterygoid processes that may indicate taxonomic distinction. Below is a cladogram modified from the analysis of Benson (2012), after the exclusion of ''Basicranodon'':<ref name=BRJ12/>
{{clade |label1='''Varanopidae''' |1={{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='''Varanodontinae''' |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'' }} }} }} }} }} }} }}
==References== {{Reflist}}
==External links== *[https://web.archive.org/web/20101126153410/http://palaeos.com/Vertebrates/Units/390Synapsida/390.200.html Varanopseidae] - at Palaeos
{{Synapsida|S.}} {{Sauropsida|E.}} {{Taxonbar|from=Q136615}}
Category:Varanopidae Category:Pennsylvanian first appearances Category:Guadalupian extinctions Category:Prehistoric synapsid families Category:Taxa named by Llewellyn Ivor Price Category:Taxa named by Alfred Romer