Osmolskina czatkowicensis Borsuk-Białynicka and Evans, 2003

Borsuk-Białynicka, Magdalena, 2018, Diversity of diapsid fifth metatarsals from the Lower Triassic karst deposits of Czatkowice, southern Poland - functional and phylogenetic implications, Acta Palaeontologica Polonica 63 (3), pp. 417-434 : 421-422

Osmolskina czatkowicensis Borsuk-Białynicka and Evans, 2003

Figs. 1E , 2F , 3 .

Material.—MttV: two more or less complete specimens, ZPAL RV/1346, left; ZPAL RV/1347, right; ( Fig. 3A, B ), and 12 fragmentary specimens, ZPAL RV/1976–1988, with roughly estimated lengths (approximately 11 mm).

Description.—The fifth metatarsal attributed to Osmolskina ( Figs. 1F 1 , 2F , 3 ) ranges in roughly estimated length from 10–12 mm, but most are 11 mm, there being no definitely juvenile bones. The Osmolskina MttV morphotype is distinguished from other Czatkowice MttV morphotypes by a conspicuous medio-lateral broadening of the proximal half, symmetrical with respect to the long axis of the shaft with no individualization of the articular part (a neckless type) and a moderate inflection (sensu Robinson’s 1975). The hooking angle is roughly 135°. The articular facet faces proximo-medially, and is slightly inclined onto the dorsal side. The facet is oval, much shorter in its plantar–dorsal axis than in the medio-lateral one (the ratio ~1:2). Proximally the bone ends in a point, where the articular facet sloping away medio-distally meets its proximo-lateral face sloping outwords to the outer process ( Fig. 1E 1 ). The lateral margin displays a crest extending from the outer process down to the distal end ( Figs. 1 E 1 , 3 ), and wrapping onto the plantar surface, thus twisting the distal end of the bone with respect to the proximal one. About one third of the length from the distal end, the crest turns into a tuberosity corresponding to the lateral plantar tubercle. Further distally, the shaft of the bone narrows substantially. A barely developed rugosity on the medial side corresponds to the medial plantar tubercle ( Fig. 3A ), placed proximal to the lateral one. The distal end bears an articular facet for the first phalanx of digit V on its medial corner. The facet is damaged in all specimens studied.

Remarks.—An additional right MttV, ZPAL RV/1993, from the same age and locality, exceeding the size range of O. czatkowicensis , considered an undetermined archosauriform by Borsuk-Białynicka and Sennikov (2009), has been illustrated ( Fig. 3C ) for comparison.

Stratigraphic and geographic range.—Early late Olenekian, Poland.

Figures

Fig. 1. Comparison of the fifth metatarsal architecture. Left bones in plantar view demonstrate hooking and articular facet orientation (A1–C1, D, E1, F1) and in proximal view (plantar surface down) (A2–C2, F2). A. Iguana iguana (Linnaeus, 1758), Iguanidae, Recent. B. Sphenodon punctatus (Gray, 1842), Rhynchocephalia, Recent.C. Sophineta cracoviensis Evans and Borsuk-Białynicka, 2009, Lepidosauromorpha, Early Triassic, Poland. D. Gephyrosaurus bridensis Evans, 1980, Rhynchocephalia, Early Jurassic, South Wales, UK (right MttV reversed). E. Osmolskina czatkowicensis Borsuk-Białynicka and Evans, 2003, Archosauriformes, Early Triassic, Poland. F. Morphotype X, Early Triassic, Poland. The dashed lines approximate the outlines of the fifth metatarsals as seen in proximal view (for additional explanation see Material and methods). ha, hooking angle. Not to scale. A, B1, C, after Robinson (1975); D, after Evans (1981).

Fig. 2. Comparison of fifth metatarsal architecture. Right bones in lateral view (A, B, C1, D, E2, F2) and in medial view (C2, E1, F1). A. Iguana iguana (Linnaeus, 1758), Iguanidae, Recent. B. Sphenodon punctatus (Gray, 1842), Rhynchocephalia, Recent. C. Sophineta cracoviensis Evans and Borsuk- Białynicka, 2009, Lepidosauromorpha, Early Triassic, Poland. D. Gephyrosaurus bridensis Evans, 1980, Rhynchocephalia, Early Jurassic, South Wales, UK; straight line approximates not-inflacted shape of the MttV. E. Morphotype X, Early Triassic, Poland (left MttV reversed). F. Osmolskina czatkowicensis Borsuk-Białynicka and Evans, 2003, Archosauriformes, Early Triassic, Poland. inf, inflection angle. Not to scale. A, B after Robinson (1975); D, after Evans (1981).

Fig. 3. Archosauriform Osmolskina czatkowicensis Borsuk-Białynicka and Evans, 2003 (A, B) and Archosauriformes gen. et sp. indet (C) all from the Lower Triassic Czatkowice locality, Poland. A. ZPAL RV/1347, adult, left MttV in plantar view. B. PAL RV/1346, young adult, right MttV in medial (B1), lateral (B2), and dorsal (B3) views. B1, B2, reversed. C. ZPAL RV/1993, right MttV in dorsal view. SEM photographs; A, B, stereo-pairs.