| Indosaurus | |
|---|---|
 | |
| HolotypeBraincase | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Abelisauridae |
| Subfamily: | †Majungasaurinae |
| Genus: | †Indosaurus |
| Species: | †I. matleyi |
| Binomial name | |
| †Indosaurus matleyi | |
Indosaurus (lit. 'Indian lizard') is agenus of carnivoroustheropoddinosaur that lived in what is nowIndia, about 69 to 66 million years ago during theMaastrichtian division of the LateCretaceous.[1][2]
The now-lostholotype was discovered between 1917 and 1919 inJabalpur, India (GSI K27/565), byCharles Alfred Matley.Thetype species,Indosaurus matleyi, was named byHuene and Matley in 1933 makingIndosaurus the firstmajungasaurine to be discovered.[3] The generic name refers to India and thespecific name honours Matley. This species now alsoincludesMegalosaurus matleyi. Somepaleontologists have speculated thatIndosuchus,Lametasaurus andIndosaurus should be considered as nomina dubia.[4]
The parietal of thefrontal-parietal region is broad whereas the lower surface of the frontal is wide, thetransverse crest lies above and behind theorbit. The frontals are concave and decline in to the front of thecranium. Thesupratemporal fossa is short and broad as inAntrodemus.[5] The incomplete skull is of unusual thickness, although it lacked a dome on frontal bones as seen inMajungasaurus. It would have also lacked the paired frontal horns seen inCarnotaurus. BothIndosuchus andIndosaurus had a conservative skull roof which was dorsoventrally thickened but did not process prominences above the skull roof, similar to the condition seen inAbelisaurus.[6]
The speciesI. matleyi weighed roughly 700 kg (1,500 lb).[citation needed]
Originally assigned by Huene to theAllosauridae,Indosaurus is today considered a member of theAbelisauridae family.[7] It shows similarities to the other Abelisaurids from India, such asRajasaurus andRahiolisaurus, and is hence usually placed within Abelisauridae, though the fragmentary nature for this taxon makes it difficult to recognize its exact taxonomic validity.[8]
In 2014 Thierry Tortosa erected the subfamily Majungasaurinae. This was to separateArcovenator,Majungasaurus,Indosaurus,Rahiolisaurus, andRajasaurus from South American abelisaurids based on physical characteristics such as elongatedantorbital fenestrae in front of the eye sockets, and a sagittal crest that widens into a triangular surface towards the front of the head.
It was suggested that the abelisaurids migrated between Africa, Europe, India and Madagascar, which would isolate the South American abelisaurids. It is possible that migration occurred between Europe and India across Africa given its proximity to both, and the volcanic Dras-Kohistan island arc may have allowedisland hopping and an indirect path to Asia, though these are still questionable explanations.[9][10]
The following cladogram was recovered by Tortosa (2014):[9]
Indosaurus lived in theLameta Formation during theMaastrichtian age of theCretaceous period. It is known to have lived alongsidesauropods likeIsisaurus,Jainosaurus and the dubiousTitanosaurus, which it may have preyed upon. Otherceratosaurs such as the abelisauridRajasaurus,Rahiolisaurus andIndosuchus are known from the formation, along with thenoasauridLaevisuchus. TheichnogenusDeltapodus is also known from the formation, which may belong to the youngest knowstegosaurid. Themadtsoiid snakeSanajeh was also contemporaneous toIndosaurus.
The rocks of the Lameta formation appear to have been deposited influvial orlacustrine conditions. The environment at the time of deposition has alternatively been consideredsemi-arid, or tropical humid.[11][12]
The dinosaurs in India probably all went extinct due to volcanic activity around 350,000 years before theCretaceous–Paleogene boundary. Dinosaurs probably avoided areas with volcanicfissure vents andlava flows.[13]
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