A new hybodont shark (Chondrichthyes, Elasmobranchii) from the Upper Triassic Tiki Formation of India with remarks on its dental histology and biostratigraphy

Abstract

A new lonchidiid genus,Pristrisodus, from the Upper Triassic Tiki Formation of India is described based on multiple, well-preserved, isolated teeth. Comparative analysis resulted in synonymizingParvodus tikiensisandLissodus duffini,which are known from the same horizon and resulted in a new taxon,Pristrisodus tikiensisn. comb. These teeth are elongated with mesiodistal length greater than or equal to twice the labiolingual width and have a high principal cusp, lateral cusplets, a distinct ridge near the crown-root junction labially and higher up on the crown lingually, weak ornamentation, and linear depression along the crown-root junction. Five morphotypes based on overall shape, robustness and crown height are determined. The teeth show a gradual monognathic heterodonty. The anterolateral teeth (morphotypes I−II) have high, pyramidal principal cusp with two or three small but pointed cusplets, and triangular labial and lingual protuberance. The posterolateral teeth (morphotypes III−IV) have four incipient cusplets, relatively low principal cusp, bilobed/rounded, hanging labial and incipient lingual protuberances. Morphotype V comprises anterior teeth that are broad, triangular and robust, and have rounded/blunt principal cusp, one cusplet, and low, hanging labial peg. Multivariate analyses corroborate the qualitative assessment of the Indian hybodonts. Dental histology ofPristrisodusn. gen., shows that it is distinctly different from other lonchidiid genera. The assemblage of freshwater sharks, along with other vertebrate microfossils of the Tiki Formation, shows similarity with that of the lower Tecovas Formation of the Chinle Group, USA. The euryhaline nature resulted in the adaptation of the hybodonts to freshwater systems in India during the Carnian.

First record of Mesozoic scroll coprolites: classification, characteristics, elemental composition and probable producers

“…; Bhat et al . , b). These freshwater sharks are considered to be the dominant predators in the Late Triassic vertebrate community (Cuny ) and are mostly known to be euryhaline in nature (Cuny ).…”

“…) and Pristrisodus (Bhat et al . ), which are considered to be euryhaline in nature (Bhat et al . ).…”

“…), which are considered to be euryhaline in nature (Bhat et al . ). Although three distinct morphotypes of scroll coprolite are present in the collection, it is not possible to ascertain whether these morphotypes could be related to any specific taxon.…”

“…However, recent studies on the Tiki fauna have shown a rich assemblage of various hybodontid and xenacanthid sharks, dipnoans and actinopterygians (Bhat et al . , b; Bhat & Ray ). Such high abundance of Late Triassic freshwater fishes is similar to that found in the Chinle Group of USA (Heckert ).…”

“…B, generalized Mesozoic Gondwana stratigraphy of peninsular India (after Bandyopadhyay ; Bhat et al . ) showing different coprolite‐yielding horizons (in bold ).…”