Rahul Sharma

Dyrosauridae

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Kingdom  Animalia
Suborder  †Tethysuchia
Rank  Family
Class  Reptilia
Phylum  Chordata
Dyrosauridae httpsuploadwikimediaorgwikipediacommonsthu
Similar  Dyrosaurus, Mesoeucrocodylia, Crocodyliformes, Pholidosauridae, Cerrejonisuchus

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.

Contents

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.

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:


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


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


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

    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

    Dyrosauridae Wikipedia


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