Osteology of a forelimb of an aetosaurStagonolepis olenkae(Archosauria: Pseudosuchia: Aetosauria) from the Krasiejów locality in Poland and its probable adaptations for a scratch-digging behavior

Abstract

Aetosaurs are armored basal archosaurs that played a significant role in land ecosystems during the Late Triassic (237–201 Ma). The polish species Stagonolepis olenkae Sulej, 2010 described from the Krasiejów locality (southern Poland) is one of the oldest known representatives of the group. Abundant and well-preserved material, including partially articulated specimens, allows a detailed description of the forelimbs in this species. The forelimbs of S. olenkae are the most similar to that of large aetosaurs like Desmatosuchus smalli, Desmatosuchus spurensis, Longosuchus meadei, Typothorax coccinarum or Stagonolepis robertsoni. Several characters recognized in the forelimbs of S. olenkae suggest its adaptation for scratch-digging. The most salient of these features are: short forearm, carpus, and hands, with the radius shorter than the humerus, carpus and manus shorter than the radius (excluding terminal phalanges); a prominent deltopectoral crest that extends distally on the humerus and a wide prominent entepicondyle, a long olecranon process with well-marked attachment of triceps muscle; hooked, laterally compressed, claw-like terminal phalanges with ornamentation of small pits (indicative of well-developed keratin sheaths). S. olenkae might have used its robust forelimbs to break through the compacted soil with its claws and proceed to dig in search of food in softened substrate with the shovel-like expansion at the tip of its snout. The entire forelimb of S. olenkae is covered by osteoderms, including the dorsal surface of the hand, which is unusual among aetosaurs and have not been noted for any species up to date.

Skull osteology of Aetosauroides scagliai Casamiquela, 1960 (Archosauria: Aetosauria) from the Late Triassic of Brazil: New insights into the paleobiology of aetosaurs

“…Several osteological features of aetosaurs have been considered as diet informative, such as the edentulous anterior premaxilla and dentary and the shovel-shaped premaxillary tip (Parrish, 1994;Small, 2002;Figure 23H) present in A. scagliai. These features have been interpreted as useful for "digging or grubbing amongst soft vegetation" (Walker, 1961, p. 193), congruent with the idea that aetosaurs used their limbs to dig (Walker, 1961;Heckert and Lucas, 2010;Dróżdż, 2018). Desojo and Vizcaíno (2009) observed disparity in biomechanical aspects of the mandible of some aetosaurs, including the placement of the glenoid (Figure 23J-K).…”

Osteology and relationships of Revueltosaurus callenderi (Archosauria: Suchia) from the Upper Triassic (Norian) Chinle Formation of Petrified Forest National Park, Arizona, United States

“…The distal articular surface is convex with a shallow longitudinal groove on the posterior edge as in P. kirkpatricki (e.g., TTU P‐9002) and H. agilis (AMNH FR 6758; Nesbitt, 2011). This distal groove does not appear to be present in aetosaurs, at least not in S. olenkae for which the forelimb is well documented (Dróżdż, 2018).…”

“…The complete right ulna of PEFO 34561 (Figures 9i–l) is 84% of the length of the humerus. The proximal end is mediolaterally expanded as in aetosaurs (e.g., T. coccinarum , AMNH FR 2713; S. olenkae ; Parker, 2013; Dróżdż, 2018), not compressed as in phytosaurs (Long & Murry, 1995), and bears a well‐developed proximally expanded olecranon process (Figures 9i, k). The olecranon has a mediolaterally broad dorsal process separated by a “sigmoid notch” (Brochu, 1992) from the more mediolaterally constricted anterior process.…”

“…A well‐preserved right radius (PEFO 34561; Figures 9m–p), which corresponds with the ulna just described, is much shorter than the humerus (~69% of the proximodistal length of the humerus). It has a mediolaterally expanded proximal head, the proximal surface is concave, typical for suchians (e.g., B. kupferzellensis , SMNS 80275; S. olenkae , Dróżdż, 2018), and is surrounded by a small rim. The shaft is subcircular in cross section.…”

Beetle-bearing coprolites possibly reveal the diet of a Late Triassic dinosauriform

“…modern birds). These characteristics rule out the majority of the animals known from the body fossil record of the locality as producers (the aetosaur S. olenkae was probably an omnivorous/herbivorous scratch digger too large for solely targeting small beetles [35]; the phytosaur and temnospondyls show clear adaptations to piscivory; the large carnivorous rauisuchian P. silesiacus was too large and the majority of the other reptiles, as lepidosauromorphs or small archosauromorphs were too small to produce such large faeces) but fit well with the dinosauriform S. opolensis (estimated body weight 15 kg), which is known from numerous body fossils in the same fossiliferous interval [30,36]. Silesaurus opolensis possesses anatomical characters which are more similar to those of birds rather than other basal dinosaurs.…”