{{Short description|Extinct genus of reptiles}} {{Confused|Redondasuchus}} {{Automatic taxobox | fossil_range = {{Geological range|215|Rhaetian|[[Late Triassic]] (late [[Norian]] – [[Rhaetian]])}} | image = Redondasaurus_bermani_at_CMNH_04.jpg | image_upright = 1.2 | image_caption = Mounted skeleton of ''Redondasaurus bermani'' at the [[Carnegie Museum of Natural History]] | taxon = Redondasaurus | authority = Hunt & Lucas, 1993 | subdivision_ranks = Species | subdivision = * {{extinct}}'''''R. gregorii''''' Hunt & Lucas, 1993 * {{extinct}}'''''R. bermani''''' Hunt & Lucas, 1993 | range_map = | range_map_caption = }}
'''''Redondasaurus''''' is an extinct [[genus]] or [[subgenus]] of [[phytosaur]] from the [[Late Triassic]] (late [[Norian]] or [[Rhaetian]]) of the southwestern United States. It was named by Hunt & Lucas in 1993, and contains two species, ''R. gregorii'' and ''R. bermani''. It is the youngest and most evolutionarily-advanced of the phytosaurs.
==Specimens==
=== Original specimens (1939-1992) === [[Oklahoma Museum of Natural History|OMNH]] 1250, the first ''Redondasaurus'' specimen to be discovered, was a slender skull found in 1939 by D.E. Savage. Savage discovered the skull in the [[Travesser Formation]] of New Mexico, and originally referred it to the genus ''[[Machaeroprosopus]]''.<ref name="Hunt&Lucas1993">{{cite journal |last1=Hunt |first1=Andrian P. |last2=Lucas |first2=Spencer G. |date=1993 |title=A new phytosaur (Reptilia: Archosauria) genus from the Uppermost Triassic of the Western United States and its biochronological significance |url=https://www.researchgate.net/publication/283271847 |journal=New Mexico Museum of Natural History & Science Bulletin |volume=3 |pages=193–196}}</ref> In 1947, another phytosaur skull ([[Yale Peabody Museum|YPM]] 3294) was discovered by [[Edwin H. Colbert|E.H. Colbert]] and J.T. Gregory in the [[Redonda Formation]] of New Mexico. Colbert & Gregory (1947) were the first to recognize that both skulls may represent a new [[taxon]]. In addition, they proposed that the skulls represented the most derived phytosaur species in North America, due to their [[supratemporal fenestrae]] being covered up by surrounding bones in dorsal view.<ref name="Hunt&Lucas1993" />[[File:Redondasaurus bermani skull.jpg|thumb|left|CM 69727, the holotype skull of ''R. bermani'']]A third skull ([[Carnegie Museum of Natural History|CM]] 69727) was discovered by D.S. Berman in the 1980s. It was recovered from the ''Coelophysis'' Quarry of [[Ghost Ranch]] near [[Abiquiú, New Mexico|Abiquiu, New Mexico]].<ref name="Hunt&Lucas1993" /> The deposits of the ''Coelophysis'' Quarry have variably been referred to as the [[Rock Point Formation]] or the "siltstone member" of the [[Chinle Formation]]. Ballew (1989) referred the Ghost Ranch skull to ''Pseudopalatus'' (now ''[[Machaeroprosopus]]'') ''buceros''.<ref name="Hunt&Lucas1993" />
=== ''Redondasaurus'' named (1993) === The genus ''Redondasaurus'' was named by [[Adrian P. Hunt|A.P. Hunt]] and [[Spencer G. Lucas|S.G. Lucas]] in 1993. The name ''Redondasaurus'' is derived from the Redonda Formation and the Greek word "''saurus''," meaning lizard. The Redonda Formation is named after Mesa Redonda near [[Tucumcari|Tucumcari, New Mexico]].<ref name="Hunt&Lucas1993" /><ref name="NMMNHS">{{Cite web|title=Redondasaurus |website=New Mexico Museum of Natural History and Science |access-date=17 October 2022 |url=http://www.nmnaturalhistory.org/redondasaurus1.html |url-status=unfit |archive-url=https://web.archive.org/web/20151220151328/http://www.nmnaturalhistory.org/redondasaurus1.html |archive-date=December 20, 2015 }}</ref> The authors had previously mentioned the unnamed phytosaur species in a 1992 paper on "Triassic Stratigraphy and Paleontology" in New Mexico.<ref name="Lucas, SPENCER G. 1992">Lucas, SPENCER G., and ADRIAN P. Hunt. "Triassic stratigraphy and paleontology, Chama basin and adjacent areas, north-central New Mexico." New Mexico Geological Society Guidebook 43 (1992): 151-167.</ref>
Hunt & Lucas (1993) named two new species for ''Redondasaurus''. ''Redondasaurus gregorii'' consisted of Colbert & Gregory's Redonda Formation skull (which was termed the [[holotype]]) and Savage's Travesser Formation skull. ''Redondasaurus bermani'' was based on Berman's Ghost Ranch skull.<ref name="Hunt&Lucas1993" /> It is unclear whether the two species are distinct, their major differences are that ''R. gregorii'' has a more narrow snout than ''R. bermani''. These differences may be related to [[sexual dimorphism]], though is difficult to test this idea directly.<ref name=":0" /> Alternatively, they may reflect [[Ontogeny|ontogenetic]] (age-based) changes in form.<ref name=":2">{{Cite journal|title=A detailed redescription of a skeletally immature ‘Redondasaurus’ suggests ontogenetic transformations in the taxon mirror phytosaurian morphological evolution|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/ar.70076|journal=The Anatomical Record|issn=1932-8494|volume=n/a|issue=n/a|doi=10.1002/ar.70076|language=en|first=Erika R.|last=Goldsmith|first2=Michelle R.|last2=Stocker|date=28 November 2025|url-access=subscription}}</ref>
=== Other specimens (1993–present) === [[File:Redondasaurus NMMNH P-31094.jpg|thumb|300x300px|''Redondasaurus gregorii'' specimen NMMNH P-31094]] Many additional specimens have been added to ''Redondasaurus'' apart from the three originally placed in the genus in 1993.<ref name="ReferenceA" /> The first report from outside New Mexico, a skull impression (MNA V3498) from the [[Wingate Sandstone]] of Utah, was initially described by Morales & Ash (1993).<ref name=":0">{{Cite journal |last1=Spielmann |first1=Justin A. |last2=Lucas |first2=Spencer G. |date=2012 |title=Tetrapod Fauna of the Upper Triassic Redona Formation East-central New Mexico: The Characteristic Assemblage of the Apachean Land-vertebrate Faunachron |url=https://books.google.com/books?id=r-woCgAAQBAJ |journal=New Mexico Museum of Natural History and Science Bulletin |volume=55}}</ref><ref name=":1" /> Several skulls from the [[Bull Canyon Formation]] of Texas were mentioned in a [[Master's Thesis|Master's thesis]] by Chavez (2010).<ref name="Lucas_et_al_2013" />
A juvenile skull of ''R. gregorii'' ([[NMMNH]] P-44920) was first mentioned by Rinehart et al. (2009), described in more detail by Lucas et al. (2013),<ref name="Lucas_et_al_2013" /> and redescribed fully by Goldsmith & Stocker (2025).<ref name=":2" /> It was collected from the ''Coelophysis'' Quarry, a site which had previously only produced the holotype of ''R. bermani''.<ref name="Lucas_et_al_2013" /> Heckert et al. (2001) identified a massive flattened skull (NMMNH P-31094) from the Redonda Formation.
All specimens referred to ''Redondasaurus'' up until that point were discussed and redescribed by Spielmann & Lucas (2012). Several of the fossils were newly reported. The two most well-preserved skulls are from the Redonda Formation (an adult, NMMNH P-4983, and a juvenile, NMMNH P-31095). The oldest ''Redondasaurus'' specimen is an incomplete skull ([[University of California Museum of Paleontology|UCMP]] V78034/119436) from the [[Petrified Forest Member]] (Chinle Formation) of [[Rio Arriba County, New Mexico]]. The authors also described a plethora of phytosaur postcranial bones from the Redonda Formation. The large sample of approximately 13 ''Redondasaurus gregorii'' skulls have helped to reconstruct growth series and sexual dimorphism trends in the species.<ref name=":0" />
Additional juvenile material was described by Goldsmith & Stocker (2025), including a nearly complete skull ([[American Museum of Natural History|AMNH]] FR 32182) and part of a snout ([[Cleveland Museum of Natural History|CMNH]] 51002).<ref name=":2" /> ''Redondasaurus'' has the best sample of juvenile specimens (and thus the best-known growth series) of all phytosaurs, helping to demonstrate how changes in skull structure are reflected both through [[evolution]] and individual development.<ref name=":2" />
==Description== ''Redondasaurus'', like other phytosaurs, had a very long snout. Known skull lengths range from {{convert|22|cm|ft|abbr=on}} in juveniles to {{convert|120.5|cm|ft|abbr=on}} in very large adults,<ref name="Lucas_et_al_2013">{{cite journal |last1=Lucas |first1=Spencer G. |last2=Spielmann |first2=Justin A. |last3=Rinehart |first3=Larry F. |date=2013 |title=Juvenile skull of the phytosaur Redondasaurus from the Upper Triassic of New Mexico, and phytosaur ontogeny |url=https://www.researchgate.net/publication/280880541 |journal=New Mexico Museum of Natural History and Science, Bulletin |volume=61 |pages=389–399}}</ref> suggesting total lengths up to {{convert|6.4|m|ft|abbr=on}}.<ref name=NMMNHS/> The teeth of ''Redondasaurus'' have a columnar enamel microstructure while lines of arrested growth are rare. These characteristics are shared with other phytosaurs from Western North America, contrasting with those from Eastern North America ("''[[Rutiodon]]''").<ref>{{Cite journal |last1=Miller-Cam |first1=Jess A. |last2=Heckert |first2=Andrew B. |last3=Hoffman |first3=Devin |date=2021 |title=Tooth enamel microstructure in North American Phytosauria (Diapsida:Archosauriformes): Implications for biogeography and ecology of a Late Triassic clade of crocodylian-like predators |url=https://palaeo-electronica.org/content/2021/3440-phytosaur-tooth-enamel |journal=Palaeontologia Electronica |language=English |volume=14 |issue=3 |pages=1–26 |doi=10.26879/1162 |s2cid=240613459 |issn=1094-8074|doi-access=free }}</ref>
=== Differences between species ===
[[File:Redondasaurus.jpg|thumb|Skeletal mount of ''R. gregorii'']] ''R. gregorii'' is distinguished by the lack of a rostral crest. Complete skulls of this species are uncommon, but some fragmentary narrow-snouted phytosaur specimens from the Redonda Formation may be part of the taxon.<ref name="Hunt&Lucas1993" />{{rp|331}}
''R. bermani'' is distinguished by the presence of a partial crest on the rostrum. Only one skull of this species has been found, but Hunt and Lucas postulate that "by analogy with other phytosaurs, it is likely that this crested species was sub-equal in abundance with [''R. gregorii''].".<ref name="Hunt&Lucas1993" />{{rp|331}}
=== Diagnostic features === The diagnostic criteria given in 1993 for the new genus was as follows:<blockquote>''"Phytosaurid that differs from other genera in possessing supratemporal fenestrae that are essentially concealed in dorsal view and whose anterior margin only slightly emarginates the skull roof and has wide squamosal-postorbital bars."''{{rp|331}}</blockquote>
Hunt and Lucas also extended Colbert and Gregory's analysis that ''Redondasaurus'' was the most derived North American phytosaurs, as: <blockquote>''"Phytosaurs show an evolutionary trend to displace ventrally the posterior portion of the midline of the skull roof. ''Redondasaurus'' represents the most advanced development of this character."''{{rp|331}}</blockquote>
Additional diagnostic criteria were introduced in 2012 by J. Spielmann and S.G. Lucas.<ref name="Hungerbuhler,2012">{{Cite journal |last1=Hungerbühler |first1=Axel |last2=Mueller |first2=Bill |last3=Chatterjee |first3=Sankar |last4=Cunningham |first4=Douglas P. |date=September 2012 |title=Cranial anatomy of the Late Triassic phytosaur Machaeroprosopus, with the description of a new species from West Texas |journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh |volume=103 |issue=3–4 |pages=269–312 |doi=10.1017/S1755691013000364 |issn=1755-6929 |s2cid=129442164}}</ref><ref name="gsa.confex.com">{{Cite web |title=REVISION OF ''REDONDASAURUS GREGORII'' (ARCHOSAURIA: PARASUCHIDAE) FROM THE LATE TRIASSIC (NORIAN-RHAETIAN) OF NEW MEXICO |url=https://gsa.confex.com/gsa/2010AM/finalprogram/abstract_178169.htm |access-date=2015-02-27}}</ref> These include: <blockquote> # Reduced antorbital fenestra # A prominent pre-infratemporal shelf # A septomaxilla forming the anterolateral half of the [[external naris]] # Thickened rim of the orbit # Inflated posterior part of nasal # Thickened dorsal [[osteoderms]] </blockquote>
==Classification== Historically, studies of ''Redondasaurus'' have been hampered by small number of specimens available, of which only four skulls were recognized in literature. More recently, several Norian-Rhaetian phytosaur skulls have been referred to ''Redondasaurus''. These new specimens encompass a range of sizes from hatchlings to adults and possibly include the first evidence of sexual dimorphism in the taxon.<ref name="gsa.confex.com"/> Sexual dimorphism within ''Redondasaurus'' was also hypothesized by J. Spielman and S.G. Lucas on May 11, 2012, at the 64th Annual Meeting of the [[Geological Society of America]].<ref name="ReferenceA">{{Cite web| title = REVISION OF THE REDONDA FORMATION (UPPER TRIASSIC CHINLE GROUP) VERTEBRATE FAUNA AND ITS IMPACT ON THE APACHEAN LAND-VERTEBRATE FAUNACHRON| access-date = 2015-02-27| url = https://gsa.confex.com/gsa/2012RM/finalprogram/abstract_203297.htm}}</ref><ref name=":0" />
=== Validity === Disagreement on the validity of ''Redondasaurus'' emerged in 1995, when Long and Murry did not accept it and referred to the specimen as ''[[Pseudopalatus pristinus]]'' instead. The reason for this may have been that the type specimen of ''Redondasaurus'' is missing the entire narial area, left side of its snout, the anterior two thirds of the right premaxilla, and most of its palate.<ref name="Hungerbuhler,2012" /> In addition to this, the term used by Savage to describe the first specimen found in 1939,<ref name="Hunt&Lucas1993" /> ''[[Machaeroprosopus]]'', continues to be used by some scholars in place of ''Redondasaurus'' as the genus name.<ref name="Hungerbuhler,2012" /> Hungerbühler ''et al.'' argued in 2013 that ''Redondasaurus'' should be regarded as a junior synonym of ''Machaeroprosopus'' because: <blockquote> # Upon a comparison of cranial characters, ''Machaeroprosopus lottorum'' is found to bridge the morphological gap between ''Redondasaurus'' and ''Machaeroprosopus'' in such a way that the distinction becomes arbitrary. # According to cladistic analysis, it is unlikely that ''Redondasaurus'' is in a basal position compared to other North American pseudopalatine phytosaurs. # For ''R. gregorii'' and ''R. bermani'' to be sister taxa, three additional steps would be necessary for forming a phylogenetic tree. This is the case even if the rostral crest, used by Lucas and Hunt to differentiate ''R. gregorii'' and ''R. bermani'', is ignored in the analysis.<ref name=Hungerbuhler,2012 /></blockquote>
==Paleoecology== [[File:Placerias and Redondasaurus.jpg|thumb|''[[Placerias]]'' and ''Redondasaurus'' skeletal mounts, [[New Mexico Museum of Natural History and Science]]]] The [[Chinle Formation|Chinle Group]], where a large portion of ''Redondasaurus'' skulls have been found, is composed of fluvial and lacustrine sediments. Accumulations of fossils in the Chinle Formation can be found in floodplains, bogs, ponds, and fluvial channels. Additional paleontological and sedimentary evidence support the hypothesis that the climate of the Chinle was strongly influenced by high levels of precipitation.<ref>{{Cite journal| doi = 10.1016/0031-0182(89)90144-2| issn = 0031-0182| volume = 72| pages = 227–247| last = Michael Parrish| first = J.| title = Vertebrate paleoecology of the Chinle formation (Late Triassic) of the Southwestern United States| journal = Palaeogeography, Palaeoclimatology, Palaeoecology| series = XIIth INQUA Congress| date = 1989| bibcode = 1989PPP....72..227M}}</ref>
Most ''Redondasaurus'' fossils have been collected from north-central and eastern New Mexico, with a few other occurrences in Texas and Utah.<ref name="Lucas, SPENCER G. 1992"/><ref name=":1">{{Cite journal |last1=Martz |first1=Jeffrey |last2=Irmis |first2=Randall |last3=Milner |first3=Andrew |date=2014-09-09 |title=Lithostratigraphy and biostratigraphy of the Chinle Formation (Upper Triassic) in southern Lisbon Valley, southeastern Utah |url=https://www.researchgate.net/publication/265550976 |journal=Utah Geological Association |volume=43 |pages=396–448}}</ref> The Chinle Group is particularly important to paleontologists interested in [[Aetosaur|aetosaurs]], as it has been critical in establishing their biochronology in the Late Triassic.<ref>{{Cite journal| volume = 17| pages = 57–64| last1 = Lucas| first1 = Spencer G.| last2 = Heckert| first2 = Andrew B.| title = Late Triassic aetosaur biochronology| journal = Albertiana| access-date = 2015-03-06| date = 1996| url = http://work.geobiology.cn/ebook/ALBERTIANA%20NO.17/12%20Late%20Triassic%20aetosaur%20biochronology.pdf| url-status = dead| archive-url = https://web.archive.org/web/20131113115918/http://work.geobiology.cn/ebook/ALBERTIANA%20NO.17/12%20Late%20Triassic%20aetosaur%20biochronology.pdf| archive-date = 2013-11-13}}</ref>
''Redondasaurus'' is important because it serves as an [[index species]] for the Apachean [[Land Vertebrate Faunachron]] (LVF). Indeed, it is considered a true index fossil because ''Redondasaurus'' is temporally restricted and easily identified.<ref>{{Cite journal| doi = 10.1016/S0031-0182(98)00117-5| issn = 0031-0182| volume = 143| issue = 4| pages = 347–384| last = Lucas| first = Spencer G| title = Global Triassic tetrapod biostratigraphy and biochronology| journal = Palaeogeography, Palaeoclimatology, Palaeoecology| date = November 1998 | bibcode = 1998PPP...143..347L| citeseerx = 10.1.1.572.872}}</ref> The biostratigraphic importance of the genus was reaffirmed when it was determined that the beginning of the Apachean was lower than previously concluded. Rather than at the base of the Redonda Formation, the Apachean appears high in the Bull Canyon Formation. Correlating the vertebrate stratigraphy of ''Redondasaurus'' has also allowed for the correlation of Redonda locally within the southwestern USA.<ref name="ReferenceA"/> Given the recent acquisition of additional diagnostic characteristics, and the increase in number of ''Redondasaurus'' skulls recognized in literature, it is likely that the use of the genus as an index fossil will expand to other deposits and even globally.<ref name="gsa.confex.com"/>
==References== {{Reflist}}
==Further reading== * ''The Great Rift Valleys of Pangea in Eastern North America'' By Peter M. LeTourneau, Paul Eric Olsen. Published 2003, [[Columbia University Press]]. {{ISBN|0-231-12676-X}} * ''Palaeogeography, Palaeoclimatology, Palaeoecology'' By Elsevier Science (Firm). Published 1998, Elsevier. v. 143. Original from the [[University of California]].
==External links== *[https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=110224 ''Redondasaurus''] at the [[Paleobiology Database]]
{{Portal|Paleontology}} {{Phytosauria}} {{Taxonbar|from=Q596876}}
[[Category:Phytosauria]] [[Category:Prehistoric reptile genera]] [[Category:Late Triassic reptiles of North America]] [[Category:Chinle fauna]] [[Category:Fossil taxa described in 1993]]