A new typothoracine aetosaur (Archosauria, Pseudosuchia) from the Upper Triassic of India with insights on biostratigraphy, diversification, and paleobiogeography

Abstract

A new typothoracine aetosaur is described based on multiple isolated and articulated left paramedian and lateral osteoderms recovered from the Upper Triassic lower Dharmaram Formation of India. The partial carapace of the new taxon is reconstructed as strongly discoidal based on the curvature of the paramedian osteoderms with the widest one positioned dorsal to the mid-dorsal trunk vertebra. Asymmetric lateral osteoderms with acute flexion are considered as precaudals with the angle of flexion decreasing posteriorly. Phylogenetic analysis recovered the new taxon as deeply nested within the clades Typothoracinae and Paratypothoracini, and a sister taxon to Kocurypelta silvestris. The autapomorphic characters involving paramedian osteoderms dorsal to the trunk vertebrae include dorsal surface ornamented by large, irregular pits surrounding the dorsal eminence and radiating ridges in other areas, straight anterior margin of the anteromedial corner of the anterior bar in dorsal view, and raised or ridged and ornamented posteromedial corner. The current study highlights the significance of the new aetosaur, and the age of the lower Dharamaram Formation is modified here as mid-Norian to Rhaetian based on global correlation with other coeval horizons. The recovery of this taxon marks the first record of Paratypothoracini from high paleolatitudes of the Gondwanan region. The study corroborates the earlier findings of a strong Laurasian faunal influx in India during the Late Triassic suggesting possible land bridges and/or conducive environmental conditions for faunal dispersal.

Garzapelta muelleri gen. et sp. nov., a new aetosaur (Archosauria: Pseudosuchia) from the Late Triassic (middle Norian) middle Cooper Canyon Formation, Dockum Group, Texas, USA, and its implications on our understanding of the morphological disparity of the aetosaurian dorsal carapace

“…Garzapelta muelleri gen. et sp. nov. was incorporated and scored into the most recent matrix of the Aetosauria by Haldar et al (2023), which expands on those of Paes‐Neto et al, (2021b), Parker (2016a), and Reyes et al (2020), using Mesquite v.3.81 (Maddison & Maddison, 2023). We a priori omitted Aetobarbakinoides brasiliensis because it was considered a wildcard taxon by previous authors (e.g., Heckert et al, 2015; Parker, 2016a).…”

“…coccinarum (Long & Murry, 1995; Martz, 2002), V . armatum (Haldar et al, 2023), and in the narrow‐bodied aetosaurs A . scagliai (Desojo & Ezcurra, 2011; Heckert & Lucas, 2002) and A .…”

“…sylvestris (Czepiński et al, 2021), and V . armatum (Haldar et al, 2023). The anterior margin of the paramedian osteoderm is not fully preserved, but it is evident that the element exhibited a thin, smooth, unornamented strip of bone (Figure 6a) rather than an anterior bar or depressed lamina, similar to the condition observed in the preceding region.…”

“…Taxa recovered within the Aetosaurinae (Parker, 2016a) are best exemplified by typothoracines such as Typothorax coccinarum (Heckert et al, 2010) and the paratypothoracin Paratypothorax andressorum (Long & Ballew, 1985), as well as nontypothoracines such as Aetosaurus ferratus (Schoch, 2007). Currently, the Aetosauria includes ~31 species (Desojo et al, 2013; Haldar et al, 2023; Parker, 2016a; Reyes et al, 2020, 2023), thus rivaling the Phytosauria as one of the most diverse and abundant archosaur groups of the Late Triassic (Ezcurra, 2016; Stocker & Butler, 2013). However, in recent years, the taxonomic status of several “dwarf” taxa (e.g., Coahomasuchus chathamensis , Heckert et al, 2017; A .…”

“…Additionally, many aetosaur taxa can sometimes be identified based solely on a combination of osteoderm characters including dorsal ornamentation, proportional shape, and the presence or absence of spines or horns (Desojo et al, 2013; Parker, 2016a; Reyes et al, 2023). Several taxa are known solely or primarily from isolated osteoderms including Lucasuchus hunti (Long & Murry, 1995), Rioarribasuchus chamaensis (Parker, 2007; Zeigler et al, 2003), Tecovasuchus chatterjeei (Martz & Small, 2006), Apachesuchus heckerti (Spielman & Lucas, 2012), Adamanasuchus eisenhardtae (Lucas et al, 2007), Sierritasuchus macalpini (Parker et al, 2008), Redondasuchus rineharti (Spielmann et al, 2006), Kocurypelta sylvestris (Czepiński et al, 2021), Venkatasuchus armatum (Haldar et al, 2023), and Kryphioparma caerula (Reyes et al, 2023).…”