Comparative Anatomy and Mechanics of Deformation in Early Triassic Paedomorphic Amphibians: A Case Study

Indobrachyops panchetensis and Sangaia lavinai, two distinct lacrimal-bearing rhytidosteids, were initially reported and described from India and Brazil, respectively. In this contribution we consider that identification, description, and interpretation of Indobrachyops panchetensis, as established by earlier researchers, are significantly biased by taphonomic deformations. The Indian taxon has numerous fractures and strains, that produced brittle and ductile deformation in a heterogeneous fashion. In light of this, we conducted a retrodeformation study to counter the effect of deformation in Indobrachyops panchetensis and compared its morphological traits with the non-deformed Brazilian Sangaia lavinai in an attempt to produce an accurate anatomical model for the Indian taxon. We conclude that both taxa share several features: presence of lacrimals, presence of interpremaxillary foramen, presence of septomaxilla, short faced trapezoidal skull, lateral position of orbits, frontal and nasal of equal length, presence of otic embayment instead of otic notch, reduced tabular horn composed of both tabular and squamosal and widely spaced occipital condyles that justify the assignment of both species to a single genus. Indobrachyops is the more senior synonym and a new combination, Indobrachyops lavinai comb. nov., is established for the Brazilian taxon ’Sangaia’ lavinai. Despite possessing a longer skull and a smaller orbit, Indobrachyops lavinai exhibits a number of mostly juvenile characteristics such as jagged sutures and reticulate ornamentation in- stead of anastomosing, prominent and comparatively larger center of growth among other characters that point to intraspecific diversity as well as different ontogenetic stages.