Paramacellodidae is an extinct

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

lizard Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...

s that first appeared in the

Middle Jurassic The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relativel ...

around 170 million years ago (Ma) and became extinct at the end of the Cretaceous around 66 Ma. It was one of the earliest groups of lizards to have undergone an

evolutionary radiation An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity. A significantly large and diverse radiation within ...

, with members found across the supercontinent

Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...

. The

phylogenetic relationship In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organ ...

s and constituent species of Paramacellodidae are uncertain. Many studies regard them to be scincomorphs, a large group that includes

skink Skinks are a type of lizard belonging to the family (biology), family Scincidae, a family in the Taxonomic rank, infraorder Scincomorpha. With more than 1,500 described species across 100 different taxonomic genera, the family Scincidae is one o ...

s 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

osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amph ...

s covering most of their bodies, including their backs, undersides, and tails. They also had short and robust limbs. Paramacellodids are distinguished from other lizards by the combination two traits in their dentition, the teeth are labiolingually expanded at their bases, and the tooth apices are lingually concave. The family was named in 1983 to include two well-known genera, '' Paramacellodus'' and '' Becklesius'', from the

Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...

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 The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltston ...

in Utah. Possible paramacellodid remains have also been found in Late Cretaceous deposits in Mongolia, as well as the Late Jurassic

Tendaguru Formation The Tendaguru Formation, or Tendaguru Beds are a highly List of fossiliferous stratigraphic units in Tanzania, fossiliferous Lithostratigraphy, formation and Lagerstätte located in the Lindi Region of southeastern Tanzania. The formation represe ...

in Tanzania, which would indicate that the family was also present in

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

. In 2020, this was confirmed with the discovery of the first paramacellodid from Brazil, ''Neokotus sanfranciscanus'', from the Early Cretaceous Sanfranciscana Basin. 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 Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

grade Grade most commonly refers to: * Grading in education, a measurement of a student's performance by educational assessment (e.g. A, pass, etc.) * A designation for students, classes and curricula indicating the number of the year a student has reach ...

of basal scincomorphs closely related to Scincoidea. In 2002, the newly named genus '' Atokasaurus'' from the Early Cretaceous

Antlers Formation The Antlers Formation is a stratum which ranges from Arkansas through southern Oklahoma into northeastern Texas. The stratum is thick consisting of silty to sandy mudstone and fine to coarse grained sandstone that is poorly to moderately sorted. ...

in Oklahoma was described as a "paramacellodid-grade" scincomorph to reflect this phylogenetic ambiguity. In the Late Cretaceous, paramacellodids are only known from the European Archipelago.

References

{{Taxonbar, from=Q16587035 Jurassic lizards Cretaceous lizards

† A dagger, obelisk, or obelus is a typographical mark that usually indicates a footnote if an asterisk has already been used. The symbol is also used to indicate death (of people) or extinction (of species or languages). It is one of the mo ...

Middle Jurassic reptiles Late Jurassic reptiles Early Cretaceous reptiles Middle Jurassic first appearances Early Cretaceous extinctions Scincomorpha