Rugops (meaning 'wrinkle face') is amonospecificgenus of basalabelisauridtheropoddinosaur that lived during theLate Cretaceous period (Cenomanian stage, approximately 95 million years ago) in what is now theEchkar Formation inNiger. The type and only species,Rugops primus, is known only from a partialskull. It was named and described in2004 byPaul Sereno,Jeffery Wilson and Jack Conrad.Rugops has an estimated length of 4.4–5.3 metres (14–17 ft) and weight of 410 kilograms (900 lb). The top of its skull bears several pits which correlates with overlaying scale and the front of the snout would have had an armour-like dermis.
Skeletal diagram of the holotype and only known specimen: MNN IGU1
In 2000, an expedition conducted by theUniversity of Chicago led byAmerican paleontologistPaul Sereno and funded by theNational Geographic Society exploredfossiliferoussandstone outcrops in a site near In-Abangharit on the western edge of theTénéré Desert of Niger. These layers belong to the Echkar Formation, which dates to the Cenomanian age of the Late Cretaceous period, around 96 million years ago. During the expedition, a partial skull of atheropod was collected. This skull was then transported to the University of Chicago for study andpreparation before being returned to theMusee National du Niger and deposited under the catalog number MNN IGU1. The specimen consists of a partial skull which lacks portions of thepalate andskull roof.[1] The type specimen may represent a subadult individual based on its small size, the lack of fusion between thenasals and the presence of thefenestra between theprefrontal,frontal,postorbital andlacrimal bones.[2]
In 2004, this skull was described by American researchers Paul Sereno,Jeffrey Wilson, and Jack Conrad as the holotype (name-bearing) specimen of a new genus and species ofabelisaurid, namedRugops primus. Thegeneric name,Rugops, is derived from theLatin word "ruga" (wrinkle) and theGreek word "opsi" (face). Thespecific name is derived from the Latin word "primus" (first). Both the generic and specific name refer toRugops as being one of the earliest abelisaurids with a textured skull.[1]
In 2005, a partial rightmaxilla of an abelisaurid was described from theKem Kem Group ofMorocco. The maxilla shares some similarities withRugops such as with the morphology of the teeth, the shape of the alveolar, the rugose texture on the lateral sides, the straight border with thepremaxilla, and the position of the palatal shelf.[3] However, the maxilla cannot be referred toRugops as the diagnostic features of the genus are located on different parts of the skull.[4]
In 2010, Paul gaveRugops an estimated length of 6 metres (20 ft) and weight of 750 kilograms (1,650 lb).[5] However, Grillo & Delcourt (2016) gave a lower estimate of 4.4 metres (14 ft) long while Molina-Pérez & Larramendi (2016) gave an estimate of 5.3 metres (17 ft) long and 410 kilograms (900 lb) in weight.[6][7]
The skull length ofRugops was about 31.5 centimetres (12.4 in).[1] As in other abelisaurids, the skull ofRugops has an external surface that is textured, a dental arcade that is U-shaped, maxillary-jugal contact that is broad, the presence of a socket on themaxilla andalveoli that are subrectangular in shape. Theorbital brow is present on the skull, although it is not fully formed. Many of the bones that make up the skull have slender proportions. In addition, the skull also has relatively thinnasals and skullfenestrae that are proportionally large. The upper surface of each nasal bone has a row of several depressions with grooves for vascular supply going into them.[1] A similar condition is seen inCarnotaurus, although the upper surface of the nasals is convex unlikeRugops, as it is concave.[2] Serenoet al. (2004) suggested that the depressions on the dorsal surface of each nasal anchored either sensory structures or soft tissues for display.[1] Delcourt (2018), however, interpreted that they correlate with overlyingscales, as seen in extantreptiles such ascrocodiles andlizards. The anterior-most snout has a papillate texture which indicates the presence of an armour-likedermis. The author suggested that, based on the type specimen probably being a subadult individual, the armour-like dermis may have reached a larger surface as it grew to which it developed a more papillate texture. Delcourt (2018) also proposed that the armour-like dermis may correlate with a low-motionheadbutting behaviour, as seen inmarine iguanas.[8]
A maxilla (NPSJB-PV247) fromPatagonia shows similarities withRugops as the pattern of external ornamentation is nearly identical and the internal details are also have a close similarity.[1][9] InRugops, the interdenticular sulci of thedenticles, the presence of which might possible be asynapomorphic characteristic of Abelisauridae, is absent and has a higher dental formulae than in any other abelisaurid.[10] The nasal sculpturing ofRugops is similar to the ornamentation seen inSkorpiovenator as the surface of the nasals show hummocky-like rugosities and has grooves that lead into eachforamen. However, unlikeSkorpiovenator,Rugops lacks extra foramina on the skull roof that could represent homologues. The external morphology of the nasals are similar to that ofSkorpiovenator as they share a similar foramina pattern. The ventral surface of the nasals have a series of foramina, which has been suggested to connect to an internal system.[11]
The describing authors indicated two distinguishing traits. Both of these are autapomorphies, unique derived characters. The skull roof has small fenestra that are present between the prefrontal, frontal, post-orbital and lacrimal. The dorsal surface of each nasal has a row of seven small depressions.[1]
Speculativelife restorationMaxilla ofRugops (B) compared to that of a similar but indeterminateabelisaurid from Morocco (A)Reconstructed skull
Serenoet al. (2004) initially foundRugops to be the basalmost abelisaurid,[1] a position also recovered by various analyses by Egliet al. (2016),[12] Delcourt (2018),[8] Cerroniet al. (2020)[13] and Rolandoet al. (2020).[14] However,Rugops has also been recovered as being more derived thanRahiolisaurus and/orEoabelisaurus but more basal than other abelisaurids by Pol & Rauhut (2012),[15] Rauhut & Carrano (2016),[16] and Ioriet al. (2021).[17] Other alternative positions includeRugops being more derived thanKryptops,Chenanisaurus and/orSpectrovenator as recovered by Sereno & Brusatte (2008),[18] Zaher et al. (2020),[19] Gianechiniet al. (2021)[20] and Agnolínet al. (2022),[21] and within apolytomy with other abelisaurids such asXenotarsosaurus,Tarascosaurus,Ilokelesia andGenusaurus which has been recovered by Tortosaet al. (2014),[22] Baianoet al. (2020)[23] and Salemet al. (2022).[24]
A phylogenetic analysis conducted by Zaheret al. (2020) is reproduced below.[19]
Rugops is known from the Echkar Formation, the uppermost lithostratigraphic unit of the Tegama Group. The Tegama Group includes two other fossils formations; the Elrhaz Formation and the Farak Formation. The Echkar Formation outcrops themselves are located south of Mount Echkar, the namesake of the formation, in Iguidi in the western Sahara Desert. The Echkar Formation consists of sandstone outcrops, some of which are red, exposed between migrating sand dunes.[25] The sediments of these sandstones are largely sandy with some clayey or calcareous intercalations.[26] As for the environment itself, the Echkar Formation is a fluvial and lacustrine deposit which occurred in a humid or semi-arid conditions. The exact age of the Echkar Formation is debated, with some authors arguing that it is lower Cenomanian in age,[1][25][27] which would place it around 95 million years old, or upper Albian in age, which would place it around 100 million years old.[28][29]
^Lamanna, Matthew C.; Martínez, Rubén D. & Smith, Joshua B. (2002). "A definitive abelisaurid theropod dinosaur from the early Late Cretaceous of Patagonia".Journal of Vertebrate Paleontology.22 (1):58–69.doi:10.1671/0272-4634(2002)022[0058:ADATDF]2.0.CO;2.S2CID86153297.
^Smith, Joshua B. (2007). "Dental morphology and variation inMajungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar". In Sampson, Scott D.;Krause, David W. (eds.).Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. Society of Vertebrate Paleontology Memoir8. Vol. 27. pp. 103–126.doi:10.1671/0272-4634(2007)27[103:DMAVIM]2.0.CO;2.S2CID85729335.{{cite book}}:|journal= ignored (help)
^Cerroni, M. A.; Motta, M. J.; Agnolín, F. L.; Aranciaga Rolando, A. M.; Brissón Egli, F.; Novas, F. E. (2020). "A new abelisaurid from the Huincul Formation (Cenomanian-Turonian; Upper Cretaceous) of Río Negro province, Argentina".Journal of South American Earth Sciences.98 102445.Bibcode:2020JSAES..9802445C.doi:10.1016/j.jsames.2019.102445.S2CID213781725.
^Rauhut, Oliver W. M.; Carrano, Matthew T. (2016). "The theropod dinosaur Elaphrosaurus bambergi Janensch, 1920, from the Late Jurassic of Tendaguru, Tanzania".Zoological Journal of the Linnean Society.178 (3):546–610.doi:10.1111/zoj.12425.
^Iori, Fabiano Vidoi; Araújo-Júnior, Hermínio Ismael de; Tavares, Sandra A. Simionato; Marinho, Thiago da Silva; Martinelli, Agustín G. (2021). "New theropod dinosaur from the late Cretaceous of Brazil improves abelisaurid diversity".Journal of South American Earth Sciences.112 103551.Bibcode:2021JSAES.11203551I.doi:10.1016/j.jsames.2021.103551.ISSN0895-9811.S2CID239682640.
^Agnolín, Federico L.; Cerroni, Mauricio A.; Scanferla, Agustín; Goswami, Anjali; Paulina-Carabajal, Ariana; Halliday, Thomas; Cuff, Andrew R. & Reuil, Santiago (February 10, 2022). "First definitive abelisaurid theropod from the Late Cretaceous of Northwestern Argentina".Journal of Vertebrate Paleontology.41 (4) e2002348.doi:10.1080/02724634.2021.2002348.ISSN0272-4634.S2CID246766133.
^Tortosa, Thierry; Buffetaut, Eric; Vialle, Nicolas; Dutour, Yves; Turini, Eric; Cheylan, Gilles (2014). "A new abelisaurid dinosaur from the Late Cretaceous of southern France: Palaeobiogeographical implications".Annales de Paléontologie.100 (1):63–86.Bibcode:2014AnPal.100...63T.doi:10.1016/j.annpal.2013.10.003.
^Baiano, Mattia; Coria, Rodolfo; Cau, Andrea (2020). "A new abelisauroid (Dinosauria: Theropoda) from the Huincul formation (lower upper Cretaceous, Neuquén Basin) of Patagonia, Argentina".Cretaceous Research.110 104408.Bibcode:2020CrRes.11004408B.doi:10.1016/j.cretres.2020.104408.S2CID214118853.
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