First report of desmatosuchin aetosaurs (Diapsida, Archosauria) from the lower part of Dharmaram Formation and a biostratigraphic re-evaluation of the upper Triassic horizons of India

Article Type

Research Article

Publication Title

Historical Biology

Abstract

Two desmatosuchin aetosaurs, taxa I–II, based on isolated but distinctive paramedian osteoderms, are reported from the lower Dharmaram Formation of India. These are morphologically differentiated based on shape proportions, dorsal ornamentation, nature of anterior bar and dorsal eminence, and tongue-in-groove articulation on both medial and lateral edges (taxon I). Comparison with other aetosaurian osteoderms revealed that taxon I is the first record of Desmatosuchus from India. Taxon II closely resembles Desmatosuchus smalli, and is also assigned to Desmatosuchini. Recognition of these taxa represents the first Indian record of Desmatosuchini and augmented the diversity of endemic desmatosuchins in India as well as in Gondwana. Quantitative analyses corroborate the interrelationships of the major clades of Aetosauria and elucidate the significance of the osteoderm characters. A re-evaluation of the lowest and highest occurrences of Late Triassic tetrapod assemblages from India has led to the identification of Assemblage Eubiozones. The work highlights several new biostratigraphic insights including the absence of synchronicity between faunal and lithological boundaries, absence of diagnostic Rhaetian index fossils, considerable overlap of temporal ranges, and the absence of appreciable biochronological separation resulting in the assignment of a single Upper Maleri-Lower Dharmaram Assemblage Eubiozone of mid-to-late Norian age. LSIDurn:lsid:zoobank.org:pub:6BC1AB57-9B2D-487E-B579-AAC1ED0D2827.

DOI

10.1080/08912963.2025.2569748

Publication Date

1-1-2025

Link to Full Text

Share

COinS