| Tangasaurus | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Neodiapsida |
| Family: | †Tangasauridae |
| Genus: | †Tangasaurus Haughton,1924 |
| Type species | |
| †Tangasaurus mennelli Haughton, 1924 | |
Tangasaurus is anextinctgenus ofaquaticbasaltangasauridneodiapsid known from theLate Permianperiod (lateChanghsingian stage) ofTanga, northeasternTanzania. It contains a single species,Tangasaurus mennelli.[1][2]
Tangasaurus was first described and named bySidney H. Haughton in1924 and thetype species isTangasaurus mennelli. Thegeneric name is derived from the name of theTanga Region in which the only known specimens were found, andGreeksauros, meaning "lizard". Thespecific name honors F. P. Mennell, the geologist who reported and collected the specimens ofTangasaurus.[1]
Tangasaurus is known only from threesyntypes which represent two individuals. The small individual, which is well preserved in two specimens (part and counterpart) and is known from a partialskull and a nearly completepostcranialskeleton, was designated as thelectotype of the genus. The part slab (showing the partial skull and postcranial) is hosted at theBulawayo Museum,Zimbabwe, while the counterpart slabSAM 6231 (showing the other side of the postcranial) is hosted at theSouth African Museum,Cape Town. The third syntype, SAM 6232, represents a nearly complete postcranial skeleton from a larger individual, but it is poorly preserved.[3]
All specimens were collected by F. P. Mennell in 1922 at theMizimbazi River nearTanga City, northeasternTanzania.[3] They were collected from the Ruhuhu Valley, in the middle part of theTanga beds, dating to the lateChanghsingian stage of theLopingianseries, about 252.5–251 million years ago.[2] Although Mennell reported a presence of eight nearly complete individuals from that site, subsequent work couldn't find any evidence for the missing 6 individuals. Mennell's report, alongside some reptilian fragments that were discovered in 1913 and reported by Janensch (1927), are the only reptilian fossils currently known from the Tanga beds.[3]
Numerous well preserved specimens from various Late Permian localities ofMadagascar were initially identified asTangasaurus by Piveteau (1926).[4] During that time theMozambique Channel had just started to open. However, a reexamination of these specimens by Carroll (1981) and Currie (1982) has shown that they represent a different genus,Thadeosaurus, known only from Madagascar. Another specimen from Madagascar,MNHN 1908-32-57, was also tentatively referred toTangasaurus. However, Currie (1980) found it to represent a new and distinct genus which he namedAcerosodontosaurus.[3]
Tangasaurus was described and named bySidney H. Haughton in1924 who found it to be a probablediapsid reptile that, because of the long, powerful, flattened tail, had become adapted for an aquatic existence. Contrary to Haughton, Piveteau (1926) consideredTangasaurus to be a primarily terrestrial animal.[4] Following Nopcsa (1924),[5] he considered it to be related to theAraeoscelis,Kadaliosaurus,Broomia and the "eosuchians" (a defunct clade that used to unite all diapsids more advanced thanAraeoscelis)Saurosternon andPleurosaurus. Described by Piveteau (1926),Hovasaurus boulei from Madagascar was considered to be related toMesosaurus. Although not as specialized asMesosaurus for living in the water, Piveteau noted its short neck, short manus, well developed haemal spines and slight pachyostosis of the ribs.[4] Haughton (1930) restudied Piveteau's specimens from Madagascar, concluding thatTangasaurus (then included the Malagasy specimens) andHovasaurus were allied and that both were diapsids.Tangasaurus was considered to be morphologically intermediate betweenYoungina andHovasaurus which was recognized as an aquatic reptile due to its shortforelimb andcoracoid, smallossification and elongated body.[6] Piveteau (1926) includedBroomia,Saurosternon andTangasaurus in the Tangasaurinae.[4] After Haughton's paper (1930),Tangasaurus andHovasaurus were usually included as the only representatives of the familyTangasauridae.[7][8][9][10][11][12] The known specimens ofTangasaurus were redescribed byPhilip J. Currie (1982). He diagnosed the genus on the basis of twoautapomorphies: It possesses high and rectangular neural spines of thedorsal vertebrae and the height ofneural spine of mid-caudal vertebra about 35% greater than length of associated centrum, and about 75% length of associated haemal arch and spine.[3] The largest "tangasaurid" (sensu Currie, 1982) isHovasaurus with an estimated maximum snout-vent length of about 30 cm (12 in). The largest specimen ofTangasaurus is 20% smaller than that, but its incomplete ossification suggests that larger specimens probably existed. Currie (1982) united to subfamilies within the Tangasauridae: Kenyasaurinae (that he named to includeKenyasaurus andThadeosaurus) and Tangasaurinae (to include Tangasauridae sensu Haughton, 1930). He allied Tangasauridae andYoungina together within superfamily Younginoidea which he named. Currie (1980) namedAcerosodontosaurus, and allied it with Younginoidea in the clade Younginiformes.[3] More recent works that usephylogenetic analyses usually suggest that neither Younginoidea nor Younginiformes aremonophyletic. Constanze Bickelmann, Johannes Müller andRobert R. Reisz (2009) redescribedAcerosodontosaurus and suggested an aquatic lifestyle for it. Their analysis is figured below, and it found support for two distinct families within "Younginiformes": the aquatic Tangasauridae, and the terrestrial Younginidae (in partialpolytomy with Tangasauridae).[13]
More resolved results were obtained by Robert R. Reisz, Sean P. Modesto and Diane M. Scott (2011) in their description ofOrovenator. However, those results required the exclusion of the fragmentary taxaGalesphyrus,Kenyasaurus,Palaeagama andSaurosternon from their analysis. Thecladogram below showsTangasaurus phylogenetic position among other neodiapsids following Reiszet al., 2011.[2]
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