Isisaurus (I. colberti) localities from Pab Formation, Pakistan.
The type specimen of Isisaurus colberti, ISI R 335/1-65, was originally described and named as Titanosaurus colberti by Sohan Lal Jain and Saswati Bandyopadhyay in 1997. The specific name honours Edwin Harris Colbert.[1][2] In 2003, the fossils were designated as belonging to its own genus by Wilson and Upchurch.[3] The generic name, "Isisaurus," combines a reference to the Indian Statistical Institute (ISI) with the Greek "saurus," meaning "lizard." It had a short, vertically directed neck and long forelimbs,[citation needed] making it considerably different from other sauropods. The humerus is 148 centimetres long.[1]
A braincase referrable to the species is known from the Pab Formation of Pakistan, which is equivalent in age to the Lameta Formation.[4]
Isisaurus is known from better remains than many other titanosaurs that were known at the time of its description. Much of its postcranial skeleton is known. The skeletal material found by Jain and Bandyopadhyay between 1984 and 1986 was "in associated and mostly articulated condition." The holotype includes cervical, dorsal, sacral and caudal vertebrae, ribs, pelvis, scapula, coracoid, left forelimb and other bones. No skull, hindlimb, or foot bones are known.[1] Since the original description of Isisaurus, unrelated titanosaur fossils belonging to more complete individuals have been discovered elsewhere.[5][6]
Description
Size compared to a human
Isisaurus was a medium-sized sauropod, with some estimates of its body length up to 18 metres (59 ft) long and weighing 15 metric tons (17 short tons).[7] The angle between the occipital bone and occipital condyle in Isisaurus and the fellow Indian titanosaur Jainosaurus is different. In the specimen from Dongargaon it is equal to 120°. In that matter, the cranium of Isisaurus resembles the skulls of Diplodocus and Apatosaurus (genera belonging to the Diplodocidae), but the bone modifications are different.[8]
Classification
While Isisaurus has consistently been considered to be a titanosaurian sauropod, its exact placement within this clade and its relationships with other titanosaurs has been controversial and problematic. Most analyses have recovered it with close affinities to taxa such as Rapetosaurus or the Saltasauridae. Various alternative positions suggested in that past are displayed in the following cladograms:
Fungus in coprolites believed to have been voided by Isisaurus indicate that it ate leaves from several species of tree, since these fungi are known to be pathogens which infect tree leaves.[13]
Isisaurus lived in the area belonging nowadays to India during the Maastrichtian age of the Cretaceous period.[14][15] Its remains are the most complete among the Cretaceous dinosaurs known from that region.[16] Khosla et al. (2003) listed the following Indian sauropods:[17]
Wilson et al. (2009) listed only two Indian titanosaurs, Isisaurus and its distant relative, Jainosaurus. Isisaurus and Jainosaurus lived sympatrically in the area of middle and western India. Isisaurus fossils have also been reported from western Pakistan.[8]
^Curry Rogers, Kristina; Wilson, Jeffrey A. (2005). The Sauropods: evolution and paleobiology. Berkeley: University of California Press. ISBN978-0-520-24623-2.
^Rubilar-Rogers, D.; Vargas, A. O.; González Riga, B.; Soto-Acuña, S.; Alarcón-Muñoz, J.; Iriarte-Díaz, J.; Arévalo, C.; Gutstein, C. S. (2021). "Arackar licanantay gen. et sp. nov. a new lithostrotian (Dinosauria, Sauropoda) from the Upper Cretaceous of the Atacama Region, northern Chile". Cretaceous Research. 124: Article 104802. Bibcode:2021CrRes.12404802R. doi:10.1016/j.cretres.2021.104802. S2CID233780252.
^Sharma, N., Kar, R.K., Agarwal, A. and Kar, R. (2005). "Fungi in dinosaurian (Isisaurus) coprolites from the Lameta Formation (Maastrichtian) and its reflection on food habit and environment." Micropaleontology, 51(1): 73-82.
^Wilson, J. A. (2006). "An Overview of Titanosaur Evolution and Phylogeny"(PDF). Actas de las III Jornadas Internacionales Sobre Paleontología de Dinosaurios y Su Entorno, Salas de los Infantes, Burgos. Retrieved 2 September 2018.
^Jeffrey A. Wilson, Paul C. Sereno, Suresh Srivastava, Devendra K. Bhatt (2003-08-15). "A New Abelisaurid (Dinosauria, Theropoda) Grom The Lameta"(PDF). Contributions from the Museum of Paleontology. 31 (1). The University of Michigan: 1–42. Retrieved 2 September 2018.{{cite journal}}: CS1 maint: multiple names: authors list (link)
