Synapsid
Live image of Edaphosaurus pogonias
- Worldwide
- Pelycosaurier
- Therapsid
The synapsids ( Synapsida; " synapsid " - " fused arch ", also Theromorpha ) are a group of amniotes ( according to the classical view, a subclass of reptiles). They are characterized by a primary skull window in the temporal region ( temporal or pace Ralf St ) behind the eye socket. The synapsids include the Pelycosaurier ( Pelycosauria ) and their descendants, the therapsids ( Therapsida ), the ancestors of mammals ( Mammalia). In the classical system, these groups are, however, distinguished from the synapsids, which latter are a paraphyletic group. The synapsids developed in the Pennsylvanian and flourished in the late Palaeozoic (Permian ) and Early Mesozoic ( Triassic).
Features
Other subclasses of reptiles are the Anapsida (without cranial window), which are represented today by the turtles that Euryapsiden with a small skull window side up ( they include no species living today, the best known representatives of this group were ichthyosaurs and plesiosaurs ) and the Diapsiden with two windows skull behind the eye socket (to them belong the other reptiles and birds). The cranial window were probably the attachment of a stronger jaw muscles and decreased in addition the skull weight.
The synapsids originally looked like typical reptiles and probably also lived so; later forms developed a faster metabolism and thus the same warm body temperature, a hard palate, which enabled them simultaneously eating and breathing, a gland- rich, partly hairy skin and differentiated dentition with incisors, canines and molars. In addition, the posture changed: While many living reptiles have side weggespreizte legs that later synapsids were arranged approximately from the Middle Permian (before about 270 million years ago) under the body and carried him away relatively ground. So they could move faster and more persistent.
The lower jaw of a typical Synapsids consists of several coalesced bones, one of which, the dentary bears teeth. The remaining mandibular bone were always smaller in the history until the lower jaw was finally in the real mammals only completely out of the dentary. Located at the rear end of the lower jaw bone residue form a lever system, which transmits the mechanical vibrations of the tympanic membrane to the inner ear.
Evolution
One of the earliest representatives of the synapsids include the Pelycosaurier (eg Dimetrodon, Sphenacodon and Edaphosaurus ), also a paraphyletic group whose larger species were equipped with a back sail them despite their size ( up to 3.50 m in length ) a more rapid change in their body temperature allowed ( the first steps towards the same warm body temperature), further therapsides the Dinocephalier with their stocky bodies, but also smaller groups like the Theriodontier (Greek: " Tierzähner ").
Many of them perished in the mass extinction at the end of the Permian age, but at least two groups survived until the Late Triassic: the heavily built herbivorous Dicynodontia (Greek: "Two - Hundezähner ", ie animals with two canines, specifically tusks ) with a horned beak instead of the incisors (eg Lystrosaurus ) and the smaller, usually carnivorous Cynodontia ( " Hundezähner " ) with body lengths exceeding one meter ( Cynognathus, Thrinaxodon ) that had long hairy and warm-blooded; from their ranks the first true mammals have emerged towards the end of the Triassic. All species with the exception of the true mammals were finally ousted from dinosaurs; only after the catastrophe at the end of the Cretaceous ( Cretaceous-Tertiary boundary), the synapsids became a dominant, very species- rich animal group that has brought about some very tall forms in the shape of mammals again.
Inside systematics
The basal synapsids are traditionally grouped together as Pelycosauria, any other form the monophyletic taxon Therapsida.
- Synapsida Caseasauria Eothyrididae
- Caseidae
- Varanopseidae
- Ophiacodontidae
- Edaphosauridae
- Sphenacodontia Therapsida Biarmosuchia Biarmosuchidae
- Burnettidae
- Brithopia
- Titanosuchia Titanosuchidae
- Tapinocephalidae
- Styracocephalidae
- Venyukovioidea
- Dromasauroidea
- Dicynodontia Eudicynodontidae
- Eudicynodontia
- Gorgonopsia
- Eutheriodontia Therocephalia
- Cynodontia Procynosuchidae
- Dviniidae
- Epicynodontia Galesauridae
- Thrinaxodontidae
- Eucynodontia
- Mammals ( Mammalia)