Stagonolepis olenkae, Sulej, 2010

Sulej, Tomasz, 2010, The skull of an early Late Triassic aetosaur and the evolution of the stagonolepidid archosaurian reptiles, Zoological Journal of the Linnean Society 158 (4), pp. 860-881 : 879

STAGONOLEPIS OLENKAE SP. NOV.

SYN. STAGONOLEPIS ROBERTSONI LUCAS ET AL., 2007

Type locality: Krasiejów, Opole Silesia, Poland .

Type horizon: Late Carnian, probably Drawno Beds coeval to the Lehrberg Beds of Germany.

Etymology: Name refers to the nickname of my wonderful wife, Alexandra. In the Polish language the name ‘Oleńka’ is a more affectionate synonym for ‘Alexandra’.

Holotype: ZPAL AbIII/466/17, skull roof ( Figs 1 , 5 ). The holotype specimen is held in the Institute of Paleobiology, Polish Academy of Sciences, Warsaw.

Diagnosis: The anterior part of the maxilla is proportionally deeper and shorter in S. robertsoni than in S. olenkae . In S. robertsoni the antorbital fossa on the dorsal process of maxilla is proportionally deeper and the angle between the ventral and dorsal margins of the antorbital fossa is greater than in S. olenkae . The area between the anterior edge of the antorbital fossa and the suture between the maxilla and the nasal is wide in S. olenkae , whereas only a ridge is present in S. robertsoni . The ventral edge of the dorsal process of the maxilla is proportionally longer in S. robertsoni than in S. olenkae . The flattened area on the ventral surface of the maxilla between the teeth and the contact with the palatine is relatively larger and wider in S. robertsoni than in S. olenkae . The ventral margin of the maxilla is more strongly convex (in lateral view) in S. robertsoni than in S. olenkae . Stagonolepis robertsoni has a relatively wider supraorbital fenestra (based on the difference between palatines) than S. olenkae . Stagonolepis olenkae has a massive ridge on the ventral surface of the palatine at its anterior end. In S. olenkae , large tubercules are present on the parietals and the medial edge of the dorsal row is straight, whereas in S. robertsoni a small ridge is present in an equivalent position to the tubercules and a distinct curvature occurs on the medial edge of the dorsal row. Stagonolepis robertsoni has nine to ten dentary teeth, compared to seven to nine in S. olenkae . The narrow and unflattened shaft of the tibia distinguishes S. wellesi from S. olenkae .

Remarks: In S. robertsoni the ventral margin of the antorbital fenestra and the ventral edge of the maxilla are almost parallel, whereas in S. olenkae they are at an oblique angle to one another (9° in smaller individuals of S. olenkae and 25° in larger individuals). In S. olenkae the squamosal is relatively deeper and the postorbital is relatively more massive than in S. robertsoni . It is likely that all of these differences may be connected to allometry. In S. robertsoni there is a horizontal ridge on the medial side of the dorsal process of the maxilla that does not occur in S. olenkae . The absence of a massive ridge on the ventral surface of the palatine in S. robertsoni is visible on the specimens BMNH R 8581, GSM 37049, and GSM 37051. According to Long & Murry (1995) and Heckert & Lucas (1999), the presacral vertebrae of S. wellesi have higher neural spines than in S. robertsoni , but this difference is so small that it may represent intraspecific variation. Long & Murry (1995) observed that S. wellesi possesses presacral vertebrae with very long transverse processes, but Parker (2007: 5) stated that ‘these assignments are extremely tentative and should be viewed with great caution’. The morphology of the tibia differentiates S. wellesi from both European stagonolepids. The proposed differences between S. wellesi and S. robertsoni in terms of bosses on the plates are doubtful. Stagonolepis olenkae bears a flat area on the dorsal surface of the narrow anterior process of the nasal.

Figures

Figure 1. The skull roof with braincase ZPAL AbIII/466/17 of Stagonolepis olenkae sp. nov. from Krasiejów, in dorsal (A), lateral (D), posterior (E), and ventral (F) views. Endocranial cavity in dorsal (B) and ventral (C) views.

Figure 5. Reconstruction of the braincase and endocranial cavity of Stagonolepis olenkae sp. nov. from Krasiejów, in ventral (A), dorsal (B), medial (C) ventrolateral (D), and lateral (E) views.