Cerrejonisuchus improcerus, HASTINGS, BLOCH, CADENA & JARAMILLO, 2010

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

CERREJONISUCHUS IMPROCERUS HASTINGS, BLOCH, CADENA & JARAMILLO, 2010

For measurements, see Tables 7-9 .

Pubis

The pubis of Cerrejonisuchus improcerus ( Fig. 65 ) displays a unique shape among Dyrosauridae : its slender proximal extremity coupled with its oblong distal blade bear resemblance to a hockey stick. This shape is made possible through the size and shape of its pubic symphysis, its relation with the other margins of the bone, as well as the shape of the lateral protuberance. Like other dyrosaurids, the pubis of Cerrejonisuchus improcerus remains relatively narrow mediolaterally (e.g. Hyposaurus natator , Dyrosaurus maghribensis , and Anthracosuchus balrogus ) whereas elongated proximodistally. Still, the pubis of Cerrejonisuchus improcerus contrasts with that of other dyrosaurids in possessing a large pubic apron (induced by a long pubic symphysis, like Anthracosuchus balrogus ) coupled with a squared lateral protuberance at the extremity of its distal blade.

The pubic peduncle of Cerrejonisuchus improcerus is slightly wider than the pubic shaft mediolaterally, as in Dyrosaurus maghribensis but as opposed to Hyposaurus natator . Distally, the pubic peduncle subtly slims down to form the pubic shaft (or neck). The latter ensures the junction between the pubic peduncle and the distal blade, and is identifiable through to the mediolateral widening distally which marks the start of the pubic apron. As in other dyrosaurids (i.e. Hyposaurus natator , Dyrosaurus maghribensis ), the lateral and medial margins of the shaft are weakly concave, so that they appear almost straight. These concave margins do not stop with the shaft, but rather carry on to form portions of the pubic apron’s margins. The medial concave margin of the pubis is shorter than the lateral one, and ends where the pubic symphysis starts. The concave medial margin is also slightly deeper than the lateral concave margin of the pubis. The later, however, presents a large extension and almost forms the entirety of the lateral margin of the pubis similar to Hyposaurus natator and Dyrosaurus maghribensis , but contra Anthracosuchus balrogus . Distally, the lateral concave margin ends with a small lateral protuberance like those of Hyposaurus natator and Dyrosaurus maghribensis . The protuberance displays a weakly convex border laterally, whereas its dorsal and ventral margins appear relatively straight (notably due to their shortness). The lateral protuberance forms the distal corner of the pubic plate, and thus connect the strictly lateral margin of the pubis with the ventral border of the bone. The ventral margin of the pubic apron is quite straight and reaches about half of the length of the pubic symphysis, with which it forms an obtuse angle of approximately 125°. A similar value can be found in Hyposaurus natator , whereas Dyrosaurus maghribensis displays more of a right angle between its pubic symphysis and its ventral margin. The pubic symphysis of Cerrejonisuchus improcerus ( Fig. 65 ; Table 9 ) is proportionally larger than in any other dyrosaurids (i.e. Hyposaurus natator , Dyrosaurus maghribensis , and Anthracosuchus balrogus ), and presumably play a role in the size of the pubic apron. The pubic symphysis of Cerrejonisuchus improcerus appears almost parallel to the shaft (angle of approximately 20° between them), which was the case for Dyrosaurus maghribensis contra Hyposaurus natator which displayed a greater angle (about 30°). The dorsal corner of the pubic symphysis forms a right angle with the concave medial margin of the pubis, as opposed to the obtuse angle displayed by other dyrosaurids (i.e. Hyposaurus natator , Dyrosaurus maghribensis , and Anthracosuchus balrogus ). Considering the potential existence of a respiration involving pubic movements, such an enlarged pubic apron presumably enabled to displace consequent visceral masses ( Scavezzoni & Fischer 2021). In parallel, the overall size of the pubic apron, and subsequent pubic symphysis, presumably impacted the angle of pubic rotation compared to extant crocodylians ( Claessens 2004).

Figures

FIG. 65. — Right and left pubes of Cerrejonisuchus improcerus Hastings, Bloch,Cadena & Jaramillo, 2010, UF/IGM 31: A, right pubis in anterior view; B, left pubis in anterior view; C, right pubis in posterior view; D, left pubis in posterior view; E, reconstruction of the pelvic girdle of Cerrejonisuchus improcerus in anterior view. Translucent areas represent cartilaginous structures in vivo; their reconstruction is based on the works of Tsai & Holliday (2015) and Tsai et al. (2019). Target indicates anterior. Cross indicates posterior. Modified from Scavezzoni & Fischer (2021). Scale bar: 1 cm.