Suchomimus

Suchomimus (meaning 'crocodile mimic') is a genus of spinosaurid theropod dinosaur that lived between 125 to 112 million years ago in what is now Niger, during the Aptian to early Albian stages of the Early Cretaceous Period. The animal was named and described by Paul Sereno and colleagues, based on a partial skeleton from the Erlhaz Formation. Its long and shallow skull, similar to that of a crocodile, earns it its genus name, while the species Suchomimus tenerensis alludes to the locality of its first remains, the Ténéré Desert. Some palaeontologists consider the animal to be an African species of the European spinosaurid Baryonyx, B. tenerensis. Suchomimus might also be a junior synonym of the contemporaneous spinosaurid Cristatusaurus lapparenti, although the latter taxon is based on much more fragmentary remains. Suchomimus was 9.5 to 11 metres (31 to 36 ft) long and weighed between 2.5 to 5.2 tonnes (2.8 to 5.7 short tons), although the holotype specimen may not have been fully grown. Suchomimus's narrow skull was perched on a short neck, and its forelimbs were powerfully built, bearing a giant claw on each thumb. Along the midline of the animal's back ran a low dorsal sail, built from the long neural spines of its vertebrae. Like other spinosaurids, it likely had a diet of fish and small prey animals. The length of the type specimen of Suchomimus, a subadult, was initially estimated at 10.3–11 metres (34–36 ft), with an estimated weight of between 2.7–5.2 tonnes (3.0–5.7 short tons). Gregory S. Paul, however, gave lower estimations of 9.5 metres (31 ft) and 2.5 tonnes (2.8 short tons). Unlike most giant theropod dinosaurs, Suchomimus had a very long, low snout and narrow jaws, formed by a forward expansion of the praemaxillae (frontmost snout bones) and the anterior ramus (branch) of the maxilla (main upper jaw bone). The praemaxillae had an upward branch excluding the maxilla from the external nares (bony nostrils). The jaws had about 122 conical teeth, pointed but not very sharp and curving slightly backwards, with fine serrations. The tip of the snout was enlarged sideways and carried a 'terminal rosette' of longer teeth, seven per side in the skull and about the same number in the corresponding part of the lower jaw. Further back, there were at least 22 teeth per upper jaw side in the maxilla, while the entire lower jaw side carried 32 teeth in the dentary bone. The upper jaw had a prominent kink just behind the rosette, protruding downwards; this convexly curved part of the maxilla had the longest teeth of the entire skull. The skull is reminiscent of that of crocodilians that eat mainly fish. The internal bone shelves of the maxillae met each other over a long distance, forming a closed secondary palate that stiffened the snout. The external nares were long, narrow and horizontally positioned; the same was true of the larger antorbital fenestrae, a pair of bony openings in front of the eyes. The rear of the skull is poorly known but for a short quadrate bone, separated from the quadratojugal bone by a large foramen quadraticum, shows it must have been low. The lower jaws were greatly elongated and narrow, forming a rigid structure as their dentaries touched each other at the midline, reinforcing the mandible against torsional (bending and twisting) forces. The describers established some autapomorphies (unique derived traits) of Suchomimus. The upwards projecting neural spines of the rear dorsal (back), sacral (hip) and front caudal (tail) vertebrae were expanded in side view. The upper corners of the humerus (upper arm bone) were robust. The humerus had a boss (bone overgrowth) above the condyle that contacted its hook-shaped radius (forearm bone). The neck was relatively short but well-muscled as shown by strong epipophyses. There were about sixteen dorsal vertebrae. Suchomimus had unusually extended neural spines, blade-shaped upward extensions on the vertebrae, which are elongated at the rear back. Those of the five sacral vertebrae were the longest. The elongation of these structures continued until the middle tail. The spines may have held up some kind of low crest or sail of skin that was highest over its hips, lower and extending further to the back than that of Spinosaurus. The furcula (wishbone) is V-shaped and indicates a high and narrow trunk. The humerus was very strongly built, only equalled in size among theropoda by that of Megalosaurus and Torvosaurus. Accordingly, the ulna of the lower arm was well-developed with an enormous olecranon (upper process set-off from the shaft), an exceptional trait shared with Baryonyx. The heavy arm musculature powered sizable hand claws, that of the first digit (or 'thumb') being the largest with a length of 19 cm (7.5 in). In the pelvis, the ilium (main hip bone) is high. The pubis (pubic bone) has a front surface that is wider than the side surface. The femur (thighbone) is straight and robust, with a length of 107 cm (42 in) in the holotype. Its lesser trochanter is markedly plate-like.