New biological insights from osteoderm histology of Venkatasuchus armatum (Pseudosuchia: Aetosauria)

Abstract

In this contribution, we studied the histology of several selected paramedian and lateral osteoderm(s) of the Late Triassic aetosaur Venkatasuchus armatum , known from the lower part of the Dharmaram Formation of Pranhita‐Godavari Basin in India to assess the growth strategy and functional attributes. The sections revealed a typical diploe structure comprising compact outer and basal cortices surrounding a large and cancellous inner core. The osteoderms had an overall slow and punctuated growth strategy based on the predominance of avascular lamellar bone, crossed parallel‐fibered bone, and multiple LAGs. Extensive secondary remodeling, in the form of secondary osteons of several generations, is seen in the ornamented outer cortex, especially in the ridges or peaks that contrasted with its absence and uniform histological features in the unornamented and consistently thick basal cortex. Other features included high abundance of dense bundles of Sharpey's fibers or extrinsic fibers that suggested presence of an external covering, possibly a keratinized sheath on the osteoderms. Comparison with other aetosaurs showed that the Indian taxon underwent pronounced bone remodeling, which may be explained by influence of regional or developmental factors and/or related to reproductive activity in an ovulating female. Although crossed parallel‐fibered bone tissue differentiates aetosaurian osteoderms from other pseudosuchian osteoderms, there are distinct differences in osteodermal histology and growth strategies among various aetosaurian taxa.