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Turtle evolution

biology; basic.


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Abstract

Turtles and tortoises have a unique evolution in the bones disposition; pelvic and shoulder girdles moved into the thoracic cage and rib cage in many species is transformed formed by the extension of the ribs, which are welded together forming a shell covered rigid shields keratin, in other cases, the body It covered with leather skin or so.

Its braincase no further perforations to eye (Anapsida), and it is unclear if their ancestors had them or not.

Moreover they all have many pulmonary respiration, which indicates that the semi-aquatic and aquatic held a evolved from terrestrial species. Currently numerous species of aquatic turtles need only come ashore to nest.

Article

Turtles evolution

Some prehistory

To understand the anatomy of current turtles, we must remember something of prehistory. The trace fossil turtles is easy to follow until the Late Triassic, since its adaptations have remained little changed, have only made minor adjustments to the size, habitat, and ornamentation.

Before the Triassic, evolution is diffuse due to convergent evolution of species, conditioned by the same ecosystem, at that time, a large number of species tend to evolve into: Strong, thick, slow-moving legs, skin appendages covered protected large hard plates, as a defense against attack from predators. The previous Triassic fossil record is difficult to follow, other species were marked by similar adjustments turtles.

Remember, even today, not all turtles are protected by shields horn-covered rigid shell, there are species with smooth skin, like leather or cartilage

† Pascodonts (They look like, but they were not ancestors of turtles)

placodont cyamodus Placodont hedonus

In the Triassic there were the Plascodonts, near the plesiosaurs and Pliosaurs group of the Mesozoic Era.

This was highlighted by the dramatic fragmentation of the continent Pangea, the fracture created two great be content placed one in each hemisphere.

Most fossil record comes from Alpine and Germanic Triassic basins of Central Europe. The type genus of this group, placodus, containing species adapted to life on land and sea (Henodus, placochelys and Psephoderma) of marine species, some lacked teeth, had a horny beak and hard, hard shells forming plates, this edge, I came very close to current forms of turtles, but as a group became extinct 200 million years ago. Current paleontology has shown that placodonts are not the ancestors of today's turtles. (2000 Darren Naish)

¿Descendants of Anasides or diapsides?

One of the questions unresolved due to the lack of continuity is whether the turtles come from the old anapsides or other group, currently turtles have the skull without cranial openings behind the eyes (Anapside) but there are many signs that indicate they could come diapside that evolutionarily ancient lost drilling. This seems to support the recent discovery in Germany in 2015 Pappochelys

Turtles evolution

† Eunotosaurus Seeley, 1892 (Quizas) . 260 millones de años:

Fósiles hallados  en el Karoo Medio, Sudáfrica. Es un género extinto de reptiles , posiblemente un pariente cercano de las tortugas , de finales del Pérmico

Eunotosaurus fue nombrado en 1892 , pero no fue hasta 1914 que se propuso ser un antepasado de Chelonia , el orden de las tortugas..(Watson, 1914)

eunotosaurus
Lately, most of the evidence points to an ancestral role Eunotosaurus, a reptile of the late Permian, whose ribs wide, elongated and curved over the back (an amazing foreshadowing of the hard shells of turtles later). Eunotosaurus does seem to have been an ancestor, a dark family of ancient reptiles, the most notable of these was the Scutosaurus member (completely shelled)

Remember that the mass extinction between the Permian-Triassic (PT), which disappeared 90% of species, chop up numerous adaptations.

Until recently, fossil evidence relating to Eunotosaurus ly giant, sea turtles that existed in the late Cretaceous period.

 

† Pappochelys Schoch and Sues, 2015. He lived 240 million years ago

Fossils found in Europe, Germany in the layer of rock called Lower Keuper sediments in Lake Lake Vellberg, dating from the Middle Triassic Ladinian Stage, is a predecessor of today's turtles ?. The recent discovery opens a new avenue in the investigation.

The "Pappochelys" as it has been baptized with the romanization of the Greek words "grandfather" and "turtle"

pappochelys_rosinae_

Although he had no shell, he presented a series of bones along the belly, much wider than the current ribs.

Pappochelys, is structurally and chronologically intermediate between Eunotosaurus and Odontochelys and dates from the Middle Triassic period (~ 240 million years ago). The three taxa share anteroposteriorly large trunk ribs are T-shaped in cross section and lead sculpture, lengthen limbs modified dorsal vertebrae and sashes. Pappochelys closely resembles Odontochelys in various characteristics of the limb girdles. Unlike Odontochelys, it has a shell of solid paired gastralia instead of a bib. Pappochelys provides new evidence that the plastron formed partly through the merger of series gastralia 3, 13. His skull has small upper and lower ventral temporal fenestrae open, supporting the hypothesis of affinities diapsidde turtles (Rainer R. Schoch & Hans-Dieter Sues 2015).

† Odontochelys Li et al., 2008. He lived 220 million years ago.

Fossils found in China. The species was described from three specimens dating back 220 million years, found in an excavation of a Triassic reservoir in Guizhou, China. (Li, Chun et all 2008).

His remains were found weeks later than Eileanchelys. Odontochelis was a soft-shell turtle, had a complete set of teeth, which later gradually lost tortoises for tens of millions of years of evolution.
Odontochelys

Odontochelys prowled the shallow waters of East Asia about 220 million years ago, another important prehistoric turtle, Proganochelys appears in the fossil record of Western Europe about 10 million years later. This much larger turtle had fewer teeth than Odontochelys, and prominent peaks in the neck meant he could not fully retract his head under the shell (which also had a bruised Ankylosaurus tail). Most importantly, the shell of Proganochelys was "fully baked" set hard, and more or less impervious to hungry predators

† Eileanchelys Anquetin et al., 2009. He lived 164 million years ago.

Fossils found Western Europe, Great Britain. Eileanchelys is an extinct genus of primitive turtle Middle Jurassic (Bathonian Period). It is considered by researchers as one of the first sea turtles. Two fossil specimens of the species Eileanchelys waldmani donomino Anquetin et al., 2009 are preserved in the National Museum of Scotland, Edinburgh. Etymology. The Eileanchelys genre comes from the union, "eilean" (Scottish Gaelic word for island) and Chelys (from the Greek word for turtle), the epithet Anquetin was named in honor of Dr. Michael Waldman co-discoverer with Prof . RJG Savage (Anquetin et al 2009)

The giant tortoises of the Mesozoic and Cenozoic period.


By the early Jurassic period, around 200 million years ago, prehistoric turtles and tortoises were virtually locked in s modern body plans, but there is still room for innovation. The most remarkable of the Cretaceous period were a couple of turtles marine giants, Archelon and Protostega, both about 10 meters long from head to tail and weighs about two tons. As expected, these giant turtles were equipped with large fins, facing powerful, the better to push through most of the water closest living relative is the smallest (less than one ton) lute.

You have to advance some 60 million years to the Pleistocene epoch, prehistoric turtle to find the size of the duo approached (this does not mean that the giant tortoises were not present in the following years, but they have not found much evidence). The one-tonne r Asia Colossochelys (formerly classified as a species of Testudo) can almost be described as a Galapagos tortoise and generous, while the slightly smaller Meiolania of Australia improved in the basic body plan turtle with a spiked tail and a huge head, strangely armored. (Incidentally, Meiolania received name - Greek for "little tramp" - in reference to the current Megalania, a lizard two tons.)

Turtles mentioned above belong to the "cryptodire" family, which represents the vast majority of marine and terrestrial species. But there is no discussion about prehistoric turtles would be complete without a mention of the aptly named Stupendemys a two-ton "pleurodire" turtle Pleistocene of South America (which distinguishes pleurodire of cryptodire turtles is pulling head shell with one hand instead of a front-to-back movement). Stupendemys was by far the largest freshwater turtle water that ever lived, more modern "side necks" weighs about 20 kilos, maximum!

The following is a list of the most remarkable and placodonts prehistoric turtles, simply click on the links for more information.

Acknowledgments

Darren Naish, Help to us with Placodonts ilustrations

Bibliography

  •  
  • https://en.wikipedia.org/wiki/Eileanchelys

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