Anthracosuchus balrogus, HASTINGS, BLOCH & JARAMILLO, 2014

Scavezzoni, Isaure, Fischer, Valentin, Johnson, Michela M. & Jouve, Stéphane, 2024, Form and function of the pelvic girdle of Thalattosuchia and Dyrosauridae (Crocodyliformes), Geodiversitas 46 (6), pp. 135-326 : 256

ANTHRACOSUCHUS BALROGUS HASTINGS, BLOCH & JARAMILLO, 2014

For measurements, see Tables 7-9 .

Pubis

The pelvic girdle of Anthracosuchus balrogus ( Fig. 64 ) is only known from two fragmentary pubes (contra Hastings et al. (2014)). Given the subtle difference in size between the two pubes, slight anatomical variations could presumably explain this effect. It is also possible that both bones belonged to two distinct individuals, since three different specimens have been described from the same strata ( Hastings et al. 2014).

The pubis of Anthracosuchus balrogus ( Fig. 64 ) displays a shape closer to that of Cerrejonisuchus improcerus than those of Hyposaurus natator and Dyrosaurus maghribensis . Indeed, the pubic plate of Anthracosuchus balrogus is slightly laterally deflected in the way of Cerrejonisuchus improcerus but to a lesser extent. This lateral flexure of the pubic apron is presumably caused by the length and orientation of the pubic symphysis and distal margin of the bone. In Anthracosuchus balrogus , the pubic symphysis forms an angle of approximately 136° with the medial margin of the pubis (leading to the shaft), and is relatively long (see Table 9 ) pushing the distal margin of the pubic plate further away distally. The latter is convex, but is also involved in the lateral deflection of the pubic apron: the overall obtuse angle it forms with the pubic symphysis expands the size of the pubic apron laterodistally, especially compared to Hyposaurus natator and Dyrosaurus maghribensis where the angle between the distal margin and the pubic symphysis is closer to 90°. In Anthracosuchus balrogus , the junction between the distal and lateral margins forms a blunt corner in the shape of a Lancet arch, in line with both margins (i.e. not significantly protruding). This shape contrasts with the squared and intensely protruding lateral lump of Cerrejonisuchus improcerus , and with the more discreet but still marked lateral protuberance of both Hyposaurus natator and Dyrosaurus maghribensis .

The lateral margin of the pubis of Anthracosuchus balrogus is slightly concave and appears almost straight, not totally unlike those of Hyposaurus natator and Dyrosaurus maghribensis . Conversely, in Cerrejonisuchus improcerus , the concavity of both lateral and medial margins is more accentuated. In parallel, the medial margin of the pubis of Anthracosuchus balrogus is slightly convex in the proximity of the junction with the pubic symphysis, but the concavity is inverted more proximally. This inversion of concavity coincides with a modification in the thickness of the pubic apron, with the central part of the bone being thicker. Hence, the posterior surface of the pubic apron appears to be slightly undulating. Along the distal margin of the pubic apron, starting from the symphysis and encompassing the lateral corner of the pubic plate, is a rugged area marking the presence of a cartilage in vivo.

Figures

FIG. 64. — Right and left pelvic girdle elements of Anthracosuchus balrogus Hastings, Bloch & Jaramillo, 2014,UF/IGM 68: A, right pubis in posterior view; B, left pubis in posterior view;C, right pubis in anterior view;D, left pubis in anterior view.Dotted lines used to recreate the putative shape of the pubis;the actual length of the shaft is unknown.Blue translucent area highlights the distal rugged portion of the pubis.Target indicates anterior.Cross indicates posterior.Scale bar:1 cm.