Variability of the dermal elements of the pectoral girdle in Platyoposaurus (Temnospondyli, Archegosauridae) from the Middle Permian of Eastern Europe

A.V. Uliakhin

Moscow State University, Moscow, 119991 Russia

Borissiak Paleontological Institute, Russian Academy of Sciences, Moscow, 117647 Russia

E-mail: ulyakhin@paleo.ru

Received March 15, 2021

ORIGINAL ARTICLE

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DOI: 10.26907/2542-064X.2021.2.238-250

For citation: Uliakhin A.V. Variability of the dermal elements of the pectoral girdle in Platyoposaurus (Temnospondyli, Archegosauridae) from the Middle Permian of Eastern Europe. Uchenye Zapiski Kazanskogo Universiteta. Seriya Estestvennye Nauki, 2021, vol. 163, no. 2, pp. 238–250. doi: 10.26907/2542-064X.2021.2.238-250. (In Russian)

Abstract

The variability of the dermal elements of the pectoral girdle (clavicle, interclavicle), as the most morphologically informative part of the postcranial skeleton in the archegosaurid amphibian Platyoposaurus from the Middle Permian of Eastern Europe, was studied. Based on the considered morphological characters of the clavicle and interclavicle in P. watsoni, the increasing complexity of ornamentation of the dermal elements (a growth of the cellular area in the ossification center as additional cells appear, more complex branching of the radial grooves) with size was established for the first time using the morphometric parameters. The age-related ornament transformation favored the acquisition of additional strength with an increase in the load on the shoulder girdle during the growth process and in the body weight. It was found that the structural characters of the cellular area and radial ridges and also the morphometric parameters (lateral inclination angle of the dorsal process, the ratio of the width of the interclavicle plate to its length from the posterior end to the ossification center) can serve as additional diagnostic features to distinguish both Platyoposaurus from others archegosauroids and between the species of the genus under consideration. Individual differences were detected mainly in the analysis of the structure of the dorsal process of the same-sized clavicles: the lamina posterior is straightened or arcuate; the lamina anterior is straight or arcuate.

Keywords: variability, Middle Permian, Temnospondyli, Archegosauridae, Platyoposaurus, East European Platform

Acknowledgments. The study was supported by the Russian Foundation for Basic Research (projects nos. 20-04-00545 and 20-54-12013).

Figure Captions

Fig. 1. Structure of the dermal elements of the pectoral girdle (clavicles and interclavicles) in Platyoposaurus and their position relative to the skull.

Fig. 2. Morphometric parameters of the clavicle (a–c) and interclavicle (d) in Platyoposaurus. Abbreviations: Lсa – length of clavicle plate; Lсb – width of clavicle plate; Lia – length of interclavicle plate; Lib – width of interclavicle plate; Yt – rear inclination angle of the dorsal process; Yl – lateral inclination angle of the dorsal process.

Fig. 3. Morphological characters and type of ornamentation of the dermal elements of the pectoral girdle in P. watsoni: I – clavicle (PIN, no. 161/103): a – ventral view; b – dorsal view; c – side view; d –  posterior view; II – interclavicle (PIN, no. 2250/24): a – ventral view; b – dorsal view; III (а–i) – joint type of sculpture for the clavicle and interclavicle (PIN, no. 161/102, 153; 2250/25). Abbreviations: al – clavicular facet; amr – area marginalis; ar – axilla ridge; b – bulkhead; can – crista anterior; fclt – facies cleithralis; fm – fossa muscularis; la – lamina anterior; lp – lamina posterior; ls – lumpy sculpture; nc – nodal cell; np – nodal points; pd – processus dorsalis; ps – polygonal sculpture in the ossification center (polygonal field); s – incomprehensible canal; sr – sculptural ridge; ta – torus anterior; trc – radial grooves on the dorsal side of the interclavicle; vo – vascular opening. Scale: 10 mm (for II and III).

Fig. 4. Variability of the dermal elements of the pectoral girdle in P. watsoni: a – changes in the common shape and ornament of the clavicle (PIN, no. 161/102, 154, 156); b – character of branching of the radial grooves on the clavicle and interclavicle with the designation of the branching orders (I–IV); c – variabi­lity of the lamina anterior of clavicle (cross section); d – changes in the common form and ornament of the interclavicle (PIN 161/149, 150; 2250/24). Scale: 10 mm.

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