''Santanachelys gaffneyi'' is an extinct species of

sea turtle Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerhe ...

. It is the only species in the genus ''Santanachelys'', which itself is a member of the extinct

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Protostegidae Protostegidae is a family of extinct marine turtles that lived during the Cretaceous period. The family includes some of the largest sea turtles that ever existed. The largest, '' Archelon'', had a head long. Like most sea turtles, they had fl ...

. The species was first described from a 20-centimeter long

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

specimen unearthed in 1998 from the

Santana Formation 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 sta ...

of eastern

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 ...

. From the rock layer from which it was excavated, it was determined that the specimen was from the Early Cretaceous period (112 million years old). It is therefore one of the oldest known sea turtles. but a new fossil named '' Desmatochelys'' ''padillai'' in 2015 is estimated to be as old as 120 million years. While the specimen showed many characteristics of modern sea turtles, it differed from the typical sea turtle body plan in several ways. One glaring difference is that ''Santanachelys'' had distinguishable digits at the tip of its forearms. Instead of the fully fused,

hydrodynamic In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids— liquids and gases. It has several subdisciplines, including '' aerodynamics'' (the study of air and other gases in motion) a ...

paddles that modern sea turtles possess, the early sea turtle's digits were distinct and movable similar to that of non- marine turtles. Like later sea turtles though, ''Santanachelys'' had large

salt gland The salt gland is an organ for excreting excess salts. It is found in the cartilaginous fishes subclass elasmobranchii (sharks, rays, and skates), seabirds, and some reptiles. Salt glands can be found in the rectum of sharks. Birds and reptiles ...

s situated near its eyes, which aided with the excretion of excess salt. This was an adaptation to the highly saline marine environment. Evolutionarily, the morphology of ''Santanachelys'' is typical of what is expected of an early sea turtle. The front appendages not being fully evolved into flippers is a sign of this. The presence of large

foramen In anatomy and osteology, a foramen (;Entry "foramen"
in

in the turtle's skull where

s where is an interesting evolutionary point. It is pointed out that this suggests that the evolutionary return to oceanic waters of the sea turtle line evolved before the finalization and streamlining of the line's paddles.

Taxonomically In biology, taxonomy () is the scientific study of naming, defining ( circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are given ...

, ''Santanachelys'' has been placed in the

along with many other extinct sea turtles. It is the earliest member of the family to date, and the earliest known member of the sea turtle superfamily, Chelonioidea.

Cladistically Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

, it is the sister

taxon In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...

to the rest of the later protostegids, including '' Protostega'' and ''

Notochelone ''Notochelone'' is an extinct genus of sea turtle, which existed about 100 million years ago.Dermochelyidae, the leatherback turtle. Its genus, ''Santanachelys'' was named for the

, the locality where the fossil was found and ''chelys'',

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

for "turtle". The species name, ''S. gaffneyi'' was named in honor of

Eugene S. Gaffney Eugene S. Gaffney is an American paleontologist and leading authority on the morphology and evolutionary history of turtles. Biography Gaffney graduated from Rutgers University, Rutgers State University in 1965 and received his PhD in 1969 with a ...

, a

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

who specialized in

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 ...

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 ...

References

{{Testudines Protostegidae Prehistoric turtle genera Monotypic prehistoric reptile genera Early Cretaceous turtles Early Cretaceous reptiles of South America Cretaceous Brazil Fossils of Brazil Fossil taxa described in 1998 Extinct turtles