On the squamation of Australerpeton cosgriffi Barberena, a temnospondyl amphibian from the Upper Permian of Brazil

Abstract

Abdominal scales of a juvenile specimen of Australerpeton cosgriffi Barberena 1998 are made of primary compact bone rich in osteocyte lacunae; vascular canals and primary osteons are rare with no sign of remodelling of the tissue by resorption and redeposition. In contrast, the abdominal scales of an adult of the same species shows extensive reworking of the bone tissue. The scale grows by apposition of lamellar bone peripherally around the whole scale; the presence of Sharpey fibers in the periphery of the scales both basally and externally suggests that they remained deeply embedded in the dermis; the embryonic scale is completely remodelled in the adult by resorption and redeposition which produces a cancellous bone with large erosion bays and secondary osteons. Remodelling by resorption and redeposition is confined to the core of the scales and does not affect its periphery, contrary to what happens in sarcopterygians with cosmoid scales. The possible biological functions of the squamation in this species, such as mechanical protection, dry protection, cutaneous respiration, hydrostatic control and calcium reservoir, are discussed.

The evolution of the scalation pattern in temnospondyl amphibians

“…In extant crocodilians and Sphenodon , the gastralia develop in the dermis and become secondarily embedded in the rectus abdominis muscle later in ontogeny (Voeltzkow & Döderlein, 1901; Howes & Swinnerton, 1901; Claessens, 2004). In contrast, the ventral scales of the temnospondyl Australerpeton were located in the dermis both in juveniles and adults, as Dias & Richter (2002) were able to demonstrate, and this must also be assumed for other basal tetrapods. To avoid confusion between the more rod‐like gastralia of amniotes, and their probable precursors in basal tetrapods, the term ‘gastralia’ is avoided in the present study, and the term ‘gastral scales’ is used here to refer to the ventral ossifications in basal tetrapods.…”

“…The presence of ossified dermal scales covering the body is widespread in temnospondyls and other basal tetrapods of the Palaeozoic, and is likely to be a heritage from their fish ancestors (Dias & Richter, 2002; Castanet et al ., 2003). In contrast to Palaeozoic sarcopterygian fish, the earliest known tetrapods have eliminated the enamel and dental components of their scales, in convergence with most extant fish (Colbert, 1955; Dias & Richter, 2002; Castanet et al ., 2003).…”

“…His description of the scalation in Trimerorhachis was basically confirmed by Chase (1965) and Berman (1973) in their works on the trimerorhachids Neldasaurus and Lafonius , respectively. Studies dealing exclusively with the ventral scalation of stereospondylomorph temnospondyls were published by Findlay (1968) on Uranocentrodon and by Dias & Richter (2002) on Australerpeton . Further descriptions of dermal scales in stereospondylomorphs are included in the works of Van Hoepen (1915), Broili & Schröder (1937), Nilsson (1946), Konzhukova (1955), Watson (1958), Warren & Hutchinson (1987), Janvier (1992), Hellrung (2003), and Pawley & Warren (2004, 2005).…”

A Microanatomical and Histological Study of the Postcranial Dermal Skeleton in the Devonian SarcopterygianEusthenopteron foordi

“…10). More importantly, the Late Permian temno− spondyl Australerpeton cosgriffi retained a spongy bone layer in its ventral scales (Dias and Richter 2002). There is currently a debate about the affinities of temnospondyls.…”

A new specimen of Australerpeton cosgriffi Barberena, 1998 (Stereospondyli: Rhinesuchidae) from the Middle/Upper Permian Rio do Rasto Formation, Paraná Basin, Brazil

“…This specimen was later reassigned to Australerpeton cosgriffi Barberena, 1998, and further studies have added information about the postcranial skeleton of this taxon (Dias & Richter, 2002;Dias & Schultz, 2003;Ramos & Vega, 2011;Eltink & Langer, 2010, 2011. A. cosgriffi has previously been considered a member of Rhinesuchoidea (Barberena, 1998), Stereospondylomorpha Platyoposaurinae (Werneburg & Schneider, 1996;Schoch & Milner, 2000) and Rhinesuchidae (Dias & Schultz, 2003).…”