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Paramacellodidae is an extinct family of scincomorph lizards that first appeared in the Middle Jurassic around 170 million years ago (Ma) and became extinct in the Early Cretaceous about 100 Ma.[1] It was one of the earliest groups of lizards to have undergone an evolutionary radiation, with members found across the supercontinent Laurasia. The phylogenetic relationships and constituent species of Paramacellodidae are uncertain.[2][3] Many studies regard it to be closely related to Scincoidea, a large group that includes skinks and their closest extinct relatives, and possibly also to Cordyoidea, a group that includes spinytail lizards and relatives. Like modern skinks, paramacelloidids had rectangular bony plates called osteoderms covering most of their bodies, including their backs, undersides, and tails. They also had short and robust limbs.[1]

Paramacellodidae
Temporal range: Middle JurassicEarly Cretaceous, 170–100 Ma
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Infraorder: Scincomorpha
Family: Paramacellodidae
Estes, 1983
Genera

?Atokasaurus
Becklesius
Mimobecklesisaurus
Naimanosaurus
Paramacellodus
?Parasaurillus
?Pseudosaurillus
Sharovisaurus

The family was named in 1983 to include two well-known genera, Paramacellodus and Becklesius, from the Late Jurassic and Early Cretaceous of Europe. A third genus, Sharovisaurus, was named in 1984 from the Late Jurassic of Kazakhstan, and a fourth, Mimobecklesisaurus, in 1985 from the Late Jurassic of China. Remains of Paramacellodus were later described from the Morrison Formation in Utah. Possible paramacellodid remains have also been found in Late Cretaceous deposits in Mongolia, as well as the Late Jurassic Tendaguru Formation in Tanzania, which would indicate that the family was also present in Gondwana. Three other early scincomorphs—Pseudosaurillus, Saurillodon, and Saurillus—have also commonly been referred to Paramacellodidae, although some recent phylogenetic studies find them to be non-paramacellodid scincomorphs. Collectively, paramacellodids and taxa formerly referred to Paramacellodidae may represent a paraphyletic grade of basal scincomorphs closely related to Scincoidea. In 2002, the newly named genus Atokasaurus from the Early Cretaceous Antlers Formation in Oklahoma was described as a "paramacellodid-grade" scincomorph to reflect this phylogenetic ambiguity.[2]

ReferencesEdit

  1. ^ a b Evans, S.E.; Chure, D.J. (1998). "Paramacellodid lizard skulls from the Jurassic Morrison Formation at Dinosaur National Monument, Utah" (PDF). Journal of Vertebrate Paleontology. 18 (1): 99–114. doi:10.1080/02724634.1998.10011037.
  2. ^ a b Nydam, R.; Cifelli, R. (2002). "Lizards from the Lower Cretaceous (Aptian-Albian) Antlers and Cloverly Formations" (PDF). Journal of Vertebrate Paleontology. 22 (2): 286–298. doi:10.1671/0272-4634(2002)022[0286:lftlca]2.0.co;2.
  3. ^ Nydam, R. (2002). "Lizards of the Mussentuchit Local Fauna (Albian–Cenomanian boundary) and comments on the evolution of the Cretaceous lizard fauna of North America" (PDF). Journal of Vertebrate Paleontology. 22 (3): 645–660. doi:10.1671/0272-4634(2002)022[0645:lotmlf]2.0.co;2.