Figure: The phylogeny of the parareptiles.
Known from the Late Devonian to the Early Triassic,
the Anthracosauria probably had a very short amphibian stage of their evolution
and gave rise appearently to all groups of reptiles.
In the Middle Carboniferous the reptilian descendants of anthracosaurs left the water,
took over the land and gradually ousted amphibians from the land communities,
so most amphibians have become freshwater inhabitants since the Late Permian.
The success of reptiles was largely due to reproduction by means of dense-shelled eggs.
In fact, every egg is a very complete "individual basin" protected by the shell,
where the developing organism can become a small likeness of the adult without
going through the intermediate stage of a freely living larva.
Reptiles also developed dense scaled skin to protect the body against drying in the air,
and more effective lung functions, usually provided by the mobility of the ribs.
The process of evolution from amphibians into reptiles, like a transformation from
lobe-finned fishes into amphibians, could also occur more than once.
The principal descendent groups of anthracosaurus are parareptiles (which include
modern turtles along with diverse fossil forms), diapsids (which include, on the one hand,
dinosaurs, pterosaurs, crocodiles, and birds, and on the other hand, lizards and snakes),
and synapsids (among them mammal-like reptiles that gave rise to mammals).
Some primitive representatives of the parareptiles retained many amphibian features,
including soft glandular skin. The parareptiles like their ancestors, the anthracosaurs,
possessed the a skull without openings for jaw muscles, that allows to assign them to
anapsids. This group name means it arch-less". Fossil remains of the diverse parareptiles
are especially abundant in the Late Permian of East Europe. In the "Russian Dinosaur
Exposition", they are represented by relatively small lizard-like Nyctiphruretus,
extraordinarily flattened Lanthanosuchus and huge aquatic Scutosaurus.
The turtles, appeared at the end of the Triassic Period and still exist today.
They are a peak of evolution in the parareptiles. All ground turtles are easily
recognizable by their bony shell. The shell is a protection against enemies.
It also provides, like a thermos, rather stable conditions for the organism.
The turtle shells in the exhibit are the Late Cretaceous Mongoleus and Late Eocene
Ergilemys, both come from southern Mongolia. They look like quite modern, although
they are dated to approximately 74 and 35 million years before present, respectively.
In the primitive parareptiles, breathing was accomplished by the movement of wide neck
ribs. A low level of metabolism has allowed turtles to abandon even this mechanism for
filling the lungs. Instead, movement of their neck and legs changes a space inside of the
rigid shell, that creates some vacuum to fill the lungs with air.