Simosuchus (meaning "pug-nosed crocodile" in Greek, referring to the animal's blunt snout) is an extinct genus of notosuchian crocodylomorphs from the Late Cretaceous of Madagascar. It is named for its unusually short skull. Fully grown individuals were about 0.75 metres (2.5 ft) in length. The type species is Simosuchus clarki, found from the Maevarano Formation in Mahajanga Province.
The teeth of S. clarki were shaped like cloves (maple leaves), which coupled with its short and deep snout suggest it was not a carnivore like most other crocodylomorphs. In fact, these features have led many paleontologists to consider it an herbivore.
Description[]
Simosuchus was small, about .75 metres (2.5 ft) long based on the skeletons of mature individuals. In contrast to most other crocodyliforms, which have long, low skulls, Simosuchus has a distinctively short snout. The snout resembles that of a pug, giving the genus its name, which means "pug-nosed crocodile" in Greek. The shape of skulls differs considerably between specimens, with variation in ornamentation and bony projections. These differences may be indications of sexual dimorphism. The front portion of the skull, or preorbital area, is angled downwards. Simosuchus likely held its head so that the preorbital area was angled about 45° from horizontal. The teeth line the front of the jaws and are clove-shaped. At the back of the skull, the occipital condyle (which articulates with the neck vertebrae) is downturned. 45 autapomorphies, or features unique to Simosuchus, can be found in the skull alone.
In most respects, the postcranial skeleton of Simosuchus resembles that of other terrestrial crocodyliforms. There are several differences, however, that have been used to distinguish it from related forms. The scapula is broad and tripartite (three-pronged). On its surface, there is a laterally directed prominence. The deltopectoral crest, a crest on the upper end of the humerus, is small. The glenohumeral condyle of the humerus, which connects to the pectoral girdle in the shoulder joint, has a distinctive rounded ellipsoid shape. The limbs are robust. The radius and ulna of the forearm fit tightly together. The front feet are small with large claws, and the back feet are also reduced in size. There is a small crest along the anterior edge of the femur. On the pelvis, the anterior process of the ischium is spur-like.
Most of the spinal column of Simosuchus is known. There are eight cervical vertebrae in the neck, at least fifteen dorsal vertebrae in the back, two sacral vertebrae at the hip, and no more than twenty caudal vertebrae in the tail. The number of vertebrae in the tail is less than that of most crocodyliforms, giving Simosuchus a very short tail.
Like other crocodyliforms, Simosuchus was covered in bony plates called osteoderms. These form shields over the back, underside, and tail. Unusually among crocodyliforms, Simosuchus also has osteoderms covering much of the limbs. Osteoderms covering the back, tail, and limbs are light and porous, while the osteoderms covering the belly are plate-like and have an inner structure resembling spongy diploë. Simosuchus has a tetraserial paravertebral shield over its back, meaning that there are four rows of tightly locking paramedial osteoderms (osteoderms to either side of the midline of the back). To either side of the shield, there are four rows of accessory parasagittal osteoderms. These accessory osteoderms tightly interlock with one another.
History[]
The first specimen of Simosuchus clarki, which served as the basis for its initial description in 2000, included a complete skull and lower jaw, the front of the postcranial skeleton, and parts of the posterior postcranial skeleton. Five more specimens were later described, representing the majority of the skeleton. Many isolated teeth have also been found in the Mahajanga Basin. Most remains of Simosuchus were found as part of the Mahajanga Basin Project, directed by the Université d'Antananarivo and Stony Brook University. Material was usually found in clays that were part of flow deposits in the Anembalemba Member of the Maevarano Formation.
Classification[]
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