Santanachelys

Live reconstruction of Santanachelys gaffneyi

Santanachelys gaffneyi is the oldest known fossil sea turtle.

Fossils of this type were found in the deposits of the highest Lower Cretaceous ( Albian ) and are about 110 million years old. They are thus the characterization and study of the early evolution of the Real sea turtles and leatherback turtles of great importance. Santanachelys gaffneyi is provided by the describer Ren Hirayama in the now extinct family of Protostegidae, whose most prominent representative is Archelon from the Upper Cretaceous of North America, the largest known marine turtle in the Earth's history. Santanachelys gaffneyi was found in eastern Brazil in the Santana Formation, in addition to a variety of fish fossils also some interesting turtles were found. Besides Santanachelys gaffneyi this is about the Araripemydidae the taxon associated type Araripemys barretoi ( Meylan, 1996) and is arranged in the taxon Bothremydidae Cearachelys placidoi (2001, see references ). The holotype ( THUg1386 ), so the first description of the copy underlying, is located in the Teikyo Heisei University, Ichihara, Chiba, Japan. There is a nearly complete and well -preserved skeleton, further finds of Santanachelys gaffneyi are not yet known.

Naming

The scientific name derives from the author of the first description of the site Santana in Brazil and the Greek name for chelys from turtle. The epithet gaffneyi is a tribute to Eugene S. Gaffney, who is regarded in the field of research on fossil turtles as an authority.

Characteristics of Santanachelys gaffneyi

The fossil of Santanachelys gaffneyi is about 20 inches long, the tank reached at its central axis a length of 14.5 centimeters. The most important features Santanachelys gaffneyi shares the paddle-like limbs, and the structure of the skull with the present representatives of the sea turtles. However, the paddles are not as pronounced and were probably useful only for a short swimming distances. The skull has some distinct similarities with those of modern representatives, such as the large interorbital skull window ( a bone gap between the eyes ), which suggests that this species also already owned a salt excretory system with salt glands. Presumably these were already present before the switch was finally turtles in the marine habitat. The salt glands could have been useful in the lagoon, which was probably the Santana Formation 110 million years ago.

Of all other known representatives of the sea turtles differs Santanachelys gaffneyi by the special curved shape of the first rib and through the movable connection of the metacarpal bones ( metacarpals ) and the finger bone and a distinctly different form of the humerus. When obviously very closely related genus Rhinochelys, which is known to only a skull, it is primarily the significantly narrower nose bones, which sets them apart from Santanachelys gaffneyi.

Importance of the fossil discovery

The discovery of the fossil in the Santana Formation shifts the fossil record for the sea turtles from the Upper Cretaceous, derived from the already known fossils of the genera Rhinochelys and Notochelone, approximately ten million years in the Lower Cretaceous. The characteristics of Santanachelys gaffneyi they characterize as the most primitive representatives of the hitherto known Protostegidae. Furthermore, can be detected by this find that a separation of the three sea turtles families, still living real sea turtles ( Cheloniidae ) and leatherback turtles ( Dermochelyidae ) and the extinct Protostegidae, must have taken place during the early Cretaceous period or even before. Even the emergence of the sea turtles relatives ( Chelonioidea ) was accordingly probably much earlier instead than previously thought. As a third feature of the fossil can be found that Santanachelys gaffneyi is the first discovery of a Protostegidae in South America. In the animal found can be assumed that there is an adult specimen; as evidence, the high degree of ossification of the skeleton, especially the skull and limbs are considered.

One of the most important questions on the adaptation of marine turtles is after the date on which the limbs have evolved into paddle-like swimming legs. A separate movement of the fingers is not possible after this time. A primitive form of the paddle with limbs still moving individual fingers were found about the representatives of the genera Toxochelys and Tasbacka within the Real sea turtles from the late Paleocene. The discovery of the relatively primitive paddle-like limbs in Santanachelys gaffneyi means that the paddles have probably developed independently in the three groups of sea turtles.

The evolution of the important in the present-day equivalents of meeresbewohnenden turtles salt glands is an important issue for the development history of sea turtles dar. These glands help the turtles, excess salt, which passes through osmosis into the body to excrete because the kidneys alone this task is not are grown. The salt glands themselves are large glands on the inner rim of the eyes ( they are larger than the brain of the animals) and take place in accordance with a turtle skull. For this reason, the sea turtles have great as " inter-orbital foramen " designated skull window. It is bounded by a bone clasp ( " processus inferior parietal "). The leatherback turtles this brooch is completely absent, correspondingly large salt glands possess the animals. The Real sea turtles and Santanachelys gaffneyi and other representatives of the marine turtles relatives ( Toxochelys, Corsochelys ) hold this processus yet, but as narrow clasp. In a still more distant species it is wider. It is believed that the species have already possessed well-educated salt glands in accordance with a narrow bone clasp and must have lived even in a marine habitat; they have therefore used this long before the development of the swimming paddles.

Systematic position

On the basis of a comparison of a total of 104 features of the skeletons of various extinct and still living sea turtles relatives and some species outside of this taxon ( outgroup comparison) a cladistic pedigree analysis was performed to classify Santanachelys gaffneyi within the system of sea turtles ( Hirayama 1998). The analysis was performed using the PAUP as ( phylogenetic analysis using parsimony ) known software and came to the following result ( simplified):

Santanachelys gaffneyi

Archelon Ischyros

Other Protostegidae ( Notochelone, Desmatochelys )

Leatherback turtles ( Dermochelyidae )

Genuine sea turtles ( Cheloniidae, now living and fossil species)