{ { Automatic taxobox
| fossil_range = Campanian - Eocene
| image = Arambourgisuchus.jpg
| image_upright = 1.2
| image_caption = Skull of the dyrosaurid Arambourgisuchus khouribgaensis
| taxon = Dyrosauridae
| authority = de Stefano, 1903
| subdivision_ranks = Genera
| subdivision = *Anthracosuchus
Cerrejonisuchus
Chenanisuchus
GuarinisuchusRodeosuchusPhosphatosaurinaePhosphatosaurusSokotosuchusHyposaurinaeAcherontisuchusAigialosuchusArambourgisuchusAtlantosuchusBrachiosuchusCongosaurusDorbignysuchusDyrosaurusHyposaurusLuciasuchusRhabdognathusTilemsisuchus}}
Dyrosauridae is a family of extinct neosuchian crocodyliforms that lived from the Campanian to the Eocene. Dyrosaurid fossils are globally distributed, having been found in Africa, Asia, Europe, North America and South America. Over a dozen species are currently known, varying greatly in overall size and cranial shape. A majority were aquatic, some terrestrial and others fully marine (see locomotion below), with species inhabiting both freshwater and marine environments. Ocean-dwelling dyrosaurids were among the few marine reptiles to survive the Cretaceous–Paleogene extinction event.
The dyrosaurids were a group of mostly marine, long jawed, crocodile-like quadrupeds up to long. The largest dyrosaurid was probably Phosphatosaurus estimated at in length. Based on bone tissue evidence, it has been hypothesized that they were slow-growing near-shore marine animals with interlocking closed jaws, able to swim as well as walk on land. External nostrils at the posterior end of its snout and an internal naris in its pterygoid indicated a habit of hunting while swimming with the top of the head above the water, enabling it to breathe while stalking prey.
Overview
Dyrosaurids are known to have a very characteristic skull shape with a long and thin snout that is approximately 68% of the total skull length. The most anterior part of the skull and snout is the external naris followed posteriorly by two premaxillae bones until they reach two maxillae bones separated by a single nasal bone.
Typical in dyrosaurids is a single nasal element with a characteristic collection of small pits and a constant width until it widens to contact the lacrimal bones, then tapering off for a short distance until it meets the boundary of the frontals and prefrontals.
Dyrosaurs have a premaxilla with shallow pits that extend posterior to the third maxillary alveoli. There are two premaxillae that are narrow as compared to the maxillary bones and extend in the two long maxilla bones which separated by the single nasal bone. The last premaxilla and first maxilla are widely separated by a fourth dentary tooth. Alveoli are widely spaced anteriorly and the space between them decreases posteriorly from the fifteenth alveolus with the diameter remaining constant.
The maxilla is long (approx. two and a half times the length of jugal) and forms most of the lateral margin of the skull. According to Jouve and Barbosa and perhaps depending on the age of the animal, each maxilla bears 13-19 teeth.
An important feature of the dyrosaurid dentition are deep occlusal pits, present particularly in the posterior region of the maxillae that get less pronounced anteriorly. The pits are indicative of an interlocking closed jaw for dyrosaurids because the pits give a way for the upper and lower jaws to alternate. Although they are still present in dyrosaurus phosphaticus, this feature of deep occlusal pits become less developed and broad. Dyrosaurus teeth are homodont, conical, long, and slender, with asymmetrically labial and lingual surfaces. Posterior teeth are shorter and more compressed than anterior tooth indicating that the tooth size decreased anterior to posterior.
Dyrosaurs have a snout to skull length of about 68% and the genus Rhabdognathus and Atlantosuchus, Dyrosaurus and Arambourgisuchus have the largest snout proportions of all dyrosaurids. Snout length was previously used it to establish dyrosaurid relationships, while considering the lengthening of the snout to be a ‘more evolved’ character. This was not congruent with Jouve's conclusion which was that the longest snout is actually the primitive condition so the shorter or longer snout appears independently at least four times in dyrosaurid evolution.
Paleobiogeography
Dyrosaurids were once considered an African group, but discoveries made starting from the 2000s indicate they inhabited the majority of the continents. In fact, basal forms suggest that their cradle may have been North America.