Earliest record of an ankylosaurian dinosaur (Ornithischia: Thyreophora): Dermal armor from Lower Kota Formation (Lower Jurassic) of India
Dermal armor was collected from the Pranhita-Godavari Valley of south-central India. It was found in situ by shallow trenching in a red clay bed 2 m below the prominent limestone marker unit of the Lower Kota Formation (Lower Jurassic, Sinemurian-Pliensbachian). The plates of this important material cannot currently be located, so they are re-described based on published and unpublished photos. There are no symmetrical median scutes or small ossicles as occur in basal thyreophorans (Scutellosaurus, Scelidosaurus, Emausaurus; Lower Jurassic). The numerous small Kota lateral body scutes are more similar to the lateral body scutes of "polacanthid" ankylosaurs than to those of basal thyreophorans. The Kota cervical half ring is very similar to the second cervical half ring of Scelidosaurus and the first and second rings of an Argentinian Upper Cretaceous nodosaurid. The remaining types of Kota plates do not occur in basal thyreophorans but are present in ankylosaurs. The large Kota lateral plates match those of Upper Cretaceous nodosaurids from Kansas, viz., those of Hierosaurus for the very large symmetrical plates and Niobrarasaurus for the large asymmetrical plates. The latter are also matched by some plates of the basal ankylosaurid Gastonia (Lower Cretaceous, USA) and, apart from the presence of a prominent spine, by other plates. The Kota large flat plates with a small cone-like spine have bases that are either irregular or hexagonal. The former were probably part of a dorsal or pelvic shield, being separated by small ossicles from other irregular flat plates as in ankylosaurs. The hexagonal plates were definitely part of such a shield, being adjacent to other hexagonal plates that were either smaller or about the same size. It is concluded that the Kota dermal plates represent an ankylosaur. The earliest fossil records for the Ankylosauria, Stegosauria and Eurypoda are all Middle Jurassic whereas the Kota ankylosaur is from the middle Early Jurassic, indicating a probable early Early Jurassic origin for these groups.
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Document Type: Research Article
Publication date: February 1, 2019
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