Dyrosauridae

Not to be confused with Dryosauridae

Dyrosauridae Temporal range: 70–35 Ma PreЄ Є O S D C P T J K Pg N Maastrichtian - Eocene
270px
Skull of the dyrosaurid Arambourgisuchus khouribgaensis
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	Crocodylomorpha
Suborder:	†Tethysuchia
Family:	†Dyrosauridae de Stefano, 1903
Genera
See below

Dyrosauridae is a family of extinct neosuchian crocodyliforms that lived from the Late Cretaceous (Maastrichtian) 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. All were presumably aquatic, with species inhabiting both freshwater and marine environments. Ocean-dwelling dyrosaurids were among the few marine reptiles to survive the Cretaceous–Paleogene extinction event.

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.

Genera

Genus	Status	Age	Location	Description	Images
Acherontisuchus	Valid	Paleocene	Colombia	A large-bodied, long-snouted freshwater dyrosaurid from the Cerrejón Formation
Anthracosuchus	In press	Paleocene	Colombia	A short-snouted freshwater dyrosaurid from the Cerrejón Formation
Arambourgisuchus	Valid	Paleocene	Morocco	A long-snouted marine dyrosaurid
Atlantosuchus	Valid	Paleocene	Morocco	A long-snouted marine dyrosaurid with the longest snout length in proportion to body size of any dyrosaurid
Cerrejonisuchus	Valid	Paleocene	Colombia	A small-bodied, short-snouted freshwater dyrosaurid from the Cerrejón Formation
Chenanisuchus	Valid	Maastrichtian-Paleocene	Mali Morocco	The genus spans the K-Pg boundary	200px
Congosaurus	Valid	Paleocene	Angola
Dyrosaurus	Valid	Eocene	Algeria Tunisia	A large-bodied, long-snouted marine dyrosaurid	200px
Guarinisuchus	Valid	Paleocene	Brazil	A marine dyrosaurid	200px
Hyposaurus	Valid	Maastrichtian-Paleocene	Brazil Mali Nigeria USA	Five species have been named, the most of any dyrosaurid genus; the genus spans the K-Pg boundary
Phosphatosaurus	Valid	Eocene	Mali Tunisia	A large-bodied, long-snouted marine dyrosaurid with blunt teeth and a spoon-shaped snout tip
Rhabdognathus	Valid	Maastrichtian-Paleogene	Mali Nigeria	A large-bodied, long-snouted marine dyrosaurid; the genus spans the K-Pg boundary
Sokotosaurus	Junior synonym			Junior synonym of Hyposaurus
Sokotosuchus	Valid	Maastrichtian	Nigeria	A long-snouted marine dyrosaurid
Tilemsisuchus	Valid	Eocene	Mali

Phylogeny

Jouve et al. (2005) diagnose Dyrosauridae as a clade based on the following seven synapomorphies or shared characters:

• 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

Below is a 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 15px Elosuchus cherifiensis  Dyrosauridae  Chenanisuchus lateroculi Sokotosuchus ianwilsoni Phosphatosaurus gavialoides Cerrejonisuchus improcerus15px Arambourgisuchus khouribgaensis Dyrosaurus phophaticus Dyrosaurus maghribensis Hyposaurus rogersii 15px Acherontisuchus guarjiraensis 15px Congosaurus bequaerti Atlantosuchus Guarinisuchus 15px Rhabdognathus keiniensis Rhabdognathus aslerensis

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

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 Society B: Biological Sciences: Firstcite
• Buffetaut, E. (1985). L'evolution des crocodiliens. Les animaux disparus-Pour la science, Paris 109.

External links

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