Dyrosauridae

Not to be confused with Dryosauridae

Filozoa

Dyrosaurids Temporal range: 70–35 Ma PreЄ Є O S D C P T J K Pg N Maastrichtian - Eocene
Dyrosaurus
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	Crocodylomorpha
Stem:	Neosuchia
Suborder:	†Tethysuchia
Family:	†Dyrosauridae de Stefano, 1903
Genera
†Acherontisuchus †Arambourgisuchus †Atlantosuchus †Cerrejonisuchus †Chenanisuchus †Congosaurus †Dyrosaurus †Guarinisuchus †Hyposaurus †Phosphatosaurus †Rhabdognathus †Sokotosuchus †Tilemsisuchus

Dyrosauridae is a family of extinct neosuchian crocodyliforms that lived from the Late Cretaceous (Maastrichtian) to the Eocene. Fossils of this group have been found in almost every continent, specifically Africa, Asia, Europe, North America and South America.

Dyrousaurids were one of the few groups of marine reptiles to survive the End Cretaceous mass extinction. Several distinct genera have been documented, varying in overal size and cranial shape. Genera such as Dyrosaurus possessed long, slender jaws with numerous teeth (indicative of a primarily fish diet much like the extant gharial). It was a large animal, growing up to 6 meters (20 feet) in length. Even bigger, possibly up to 9 meters (30 feet), was Phosphatosaurus. More robust in its morphology, its jaws were relatively shorter, wider and much stronger, with large, partly rounded teeth. This jaw morphology would have been unsuitable for grasping slippery prey; instead a diet involving catching and crushing larger marine animals (such as sea turtles) is more likely.

Paleobiogeography

Dyrosaurids were once considered an African group, but more recent discoveries indicate they inhabited the majority of the continents. In fact, basal forms suggest that their cradle may have been North America.

Systematics

This group is poorly known, due to poor preservation of remains despite being relatively abundant. Despite this, Jouve et al. (2005) found Dyrosauridae to be a clade, based on seven synapomorphies:

• Posteromedial wing of the retroarticular process dorsally situated ventrally on the retroarticular process
• Occipital tuberosities small
• Exoccipital participates largely to the occipital condyle
• Supratemporal fenestra anteroposteriorly strongly elongated
• Symphysis about as wide as high
• Quadratojugal participates largely to the cranial condyle for articulation with the jaw
• 4 premaxillary teeth

Cladogram after Jouve et al. (2005) showing phylogenetic relationships of Dyrosauridae and other closely related neosuchians:

Neosuchia	Eutretauranosuchus Elosuchus Sarcosuchus Terminonaris Dyrosauridae Chenanisuchus Sokotosuchus Phosphatosaurus Dyrosaurus Arambougisuchus Congosaurus Hyposaurus rogersii Rhabdognathus rarus Rhabdognathus sp.

Composite cladogram for Dyrosauridae (from Jouve et al. 2008 and Barbosa et al. 2008):

Dyrosauridae	Chenanisuchus  Phosphatosaurinae  Sokotosuchus Phosphatosaurus  Dyrosaurinae  Dyrosaurus Arambourgisuchus Guarinisuchus Hyposaurus Congosaurus Atlantosuchus Rhabdognathus Dyrosauridae incertae sedis: Tilemsisuchus

Cladogram after Hastings et al. (2011) showing geographic occurrences of taxa:

Neosuchia

Sarcosuchus imperator Terminonaris robusta Elosuchus cherifiensis  Dyrosauridae  Chenanisuchus lateroculi Sokotosuchus ianwilsoni Phosphatosaurus gavialoides Cerrejonisuchus improcerus Arambourgisuchus khouribgaensis Dyrosaurus phophaticus Dyrosaurus maghribensis Hyposaurus rogersii Acherontisuchus guarjiraensis Congosaurus bequaerti Atlantosuchus Guarinisuchus Rhabdognathus keiniensis Rhabdognathus aslerensis

Analysis suggest that the closest relatives of dyrosaurids are Sarcosuchus and Terminonaris.

List

Genus	Status	Age	Location	Description	Images
†Acherontisuchus	Valid.	Paleocene.	South America.	A long-snouted South American dyrosaurid.	Reconstruction of Chenanisuchus lateroculi Fossil jaw fragment of Dyrosaurus phosphaticus Reconstruction of Guarinisuchus munizi
†Arambourgisuchus	Valid.	Paleocene.	Africa.	A recently discovered dyrosaurid from Morocco. Its skull was a full meter in length and it appears to have been a marine predator.
†Atlantosuchus	Valid.	Paleocene.	Africa.	A Morrocan dyrosaurid with extremely elongate jaws.
†Cerrejonisuchus	Valid.	Paleocene	South America	A small, short-snouted Colombian dyrosaurid.
†Chenanisuchus	Valid.	Paleocene.	Africa.
†Congosaurus	Valid.
†Dyrosaurus	Valid.	Eocene.	North Africa.
†Guarinisuchus	Valid.	Paleocene.	South America.
†Hyposaurus	Valid.	Late Cretaceous.
†Phosphatosaurus	Valid.
†Rhabdognathus	Valid.
†Sokotosaurus	Junior synonym.			— junior synonym of Hyposaurus
†Sokotosuchus	Valid.
†Tilemsisuchus	Valid.

Palaeobiology

Habitat

Most dyrosaurids were marine crocodiles. Dyrosaurids found from what is now northern and western Africa are thought to have inhabited the Trans-Saharan Sea, an epicontenental seaway that covered low-lying basins that formed during the late Mesozoic breakup of Africa and South America through crustal attenuation and fault reactivation, during a time of great global sea level elevation.

Dyrosaurids have also been found from nonmarine sediments. In northern Sudan, dyrosaurids are known from fluvial deposits, indicating that they lived in a river setting. Bones from indeterminate dyrosaurids have been found in inland deposits in Pakistan as well. Some dyrosaurids, such as those from the Umm Himar Formation in Saudi Arabia, inhabited estuarine environments near the coast. The recently named dyrosaurids Cerrejonisuchus and Acherontisuchus have been recovered from the Cerrejón Formation in northwestern Colombia, which is thought to represent a transitional marine-freshwater environment surrounded by rainforest more inland than the estuarine environment of the Umm Himar Formation. Cerrejonisuchus and Acherontisuchus lived in a neotropical setting during a time when global temperatures were much warmer than they are today.

Reproduction

In 1978, it was proposed that dyrosaurids lived as adults in the ocean but reproduced in inland freshwater environments. Remains belonging to small-bodied dyrosaurids from Pakistan were interpreted as juveniles. Their presence in inland deposits was viewed as evidence that dyrosaurids hatched far from the ocean. Recently however, the large-bodied and fully mature dyrosaurids of the Cerrejón Formation have shown that some dyrosaurids lived their entire lives in inland environments, never returning to the coast.

References

• Barbosa, J.A., Kellner, A.W.A. and Viana, M.S.S. (2008). New dyrosaurid crocodylomorph and evidences for faunal turnover at the K–P transition in Brazil. Proceedings of the Royal Sociey B: Biological Sciences: Firstcite
• Buffetaut, E. (1985). L'evolution des crocodiliens. Les animaux disparus-Pour la science, Paris 109.
• Jouve, S.; Bouya, B.; Amaghzaz, M. (2008). "A long-snouted dyrosaurid (Crocodyliformes, Mesoeucrocodylia) from the Paleocene of Morocco: phylogenetic and palaeogeographic implications". Palaeontology 51 (2): 281–294. doi:10.1111/j.1475-4983.2007.00747.x. 
• Jouve, S.; Iarochène, M.; Bouya, B.; Amaghzaz, M. (2005). "A new dyrosaurid crocodyliform from the Palaeocene of Morocco and a phylogenetic analysis of Dyrosauridae". Acta Palaeontologica Polonica 50 (3): 581–594. 

External links

• Jouve et al. (2005)
• Mikko's Phylogeny Archive Dyrosauridae page
• Paleopedia page on Dyrosauridae