''Cearachelys'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

pleurodira The Pleurodira are one of the two living suborders of turtles, the other being the Cryptodira. The division between these two suborders represents a very deep evolutionary divide between two very different types of turtles. The physical differen ...

turtle Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked t ...

which existed some 110 million years ago. The genus is

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...

, with only

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

''Cearachelys placidoi'' known.

Etymology

The genus was named for Ceará, the Brazilian state where the species was discovered. The specific name was named after Placido Nuvens, a director of the Museu Paleontologico de Santana do Cariri.

Description

In 2001, the remains of two mostly complete turtle skeletons from the Early Cretaceous rocks of the

Santana Group The Santana Group is a geologic group, formerly included as the middle part of the Araripe Group, in the Araripe Basin of northeastern Brazil. The group comprises the Crato, Ipubi and Romualdo Formations and is dated to the Aptian to Albian stag ...

were used to describe ''Cearachelys placidoi''. Both specimens were from the

Romualdo Formation The Romualdo Formation is a geologic Konservat-Lagerstätte in northeastern Brazil's Araripe Basin where the states of Pernambuco, Piauí and Ceará come together. The geological formation, previously designated as the Romualdo Member of the Sa ...

of the group in what is now northwestern

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

. The type specimen, tentatively labeled MPSC-uncatalogued (for the Museu Paleontologico de Santana do Cariri where the specimen resides), consisted of an incomplete skull, the turtle's shell, a few neck vertebrae and some limb bone fragments. The second specimen, TUTg 1798 is a more complete fossil consisting of most of the turtle's axial and appendicular skeleton. While this specimen hails from the same locality, it was actually procured by the museum eight years prior, in 1993. A fragmentary third specimen was identified in 2007 as belonging to ''C. placidoi''. The specimen, MN-6760-V, consisted of a rather complete fossilized carapace and plastron measuring some 20 cm long. The species was identified as a

pleurodire The Pleurodira are one of the two living suborders of turtles, the other being the Cryptodira. The division between these two suborders represents a very deep evolutionary divide between two very different types of turtles. The physical differenc ...

based on a number of distinguishing anatomical characteristics – mainly the arrangement of skeletal elements in its skull and the attachment of its pelvic girdle to its carapace. Further analysis of its skull elements led to its classification in the family

Bothremydidae Bothremydidae is an extinct family of side-necked turtles (Pleurodira) known from the Cretaceous and Cenozoic. They are closely related to Podocnemididae, and are amongst the most widely distributed pleurodire groups, with their fossils having b ...

. However, skull elements also differentiate the species from the other members of its family. Its closest relation seems to be from a taxon that evolved much later, the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

turtle '' Galianemys'' from

Morocco Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria t ...

. Both genera possess a rather retracted

jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...

bone, a characteristic not seen in other bothremydids. In a 2006 paper on the

phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spe ...

of extinct pleurodires, Gaffney united the two closely related genera in the

tribe The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide usage of the term in English is in the discipline of anthropology. This definition is contested, in part due to confli ...

Cearachelyini.

References

{{Taxonbar, from1=Q18578876, from2=Q5055746 Bothremydidae Prehistoric turtle genera Albian life Early Cretaceous reptiles of South America Early Cretaceous turtles Cretaceous Brazil Fossils of Brazil Romualdo Formation Fossil taxa described in 2001 Taxa named by Eugene S. Gaffney