Labyrinthodontia
The Labyrinthodontia ( " Labyrinthzähner " ) or Stegocephalia ( " Dachschädler ", " roof skull amphibians " AltGr. Stegos "roof", kephale " head") are in classical biological systematics, a group of extinct original land vertebrates ( Tetrapoda ), which from the late Devonian ( before about 400 million years ago) to the Early Cretaceous ( about 120 million years ago ) existed and was spread worldwide. However, in the modern sense of hierarchy, they are not a natural kinship group. Their name from the Labyrinthodontia the cross-sectional labyrinth-like folded layer of enamel of their teeth. In German-speaking countries, they are also known by the trivial name " tank amphibians ".
System
The term, Labyrinthodontia ' referred to the sense of modern systematics is not a valid taxon (hence set below in quotes), but is partly still in use in the literature. The term " Stegocephalia " or " Stegocephali ", however, now called a monophyletic group, all living and extinct tetrapods and some of its still quite fish-like precursor comprises and is the sister group of the fishy Fleischflossers Panderichthys. Also, the term " Labyrinthodontia " the links between the bony fishes and all land-living vertebrates were filed at that time already.
Formerly the " Labyrinthodontia " counted genera are today found in other groups, especially in the Temnospondyli (the Temnospondyli were at that time itself out as a subgroup of labyrinthodonts ). Some former labyrinthodonts groups do not form a natural affinity group within the meaning of modern systematics, but are merely as species and genera, based on the same evolutionary stage (English, grade ' ) are, construed, what is primarily true for the very early tetrapods (see also → Evolution Biological Aspects ). It should be added that the scheme of the former as " Labyrinthodontia " guided groups is still relatively unstable and varies from author to author more or less.
" Labyrinthodontia " be placed due to their geological age and appearance, for example in exhibitions of prehistoric animals often alongside contemporary reptiles, although they systematically do not belong to the reptiles. As a collective term for both prehistoric amphibians and reptiles has become the more commonly held notion naturalized " dinosaur ".
Characteristics, ecology and importance of group
The earliest " Labyrinthodontia " include those vertebrates that at least at times could use as a habitat dry terrain. Some later representatives had, however, strongly adapted to life on land and may have been keen competitors of the early amniotes (eg Cacops ). In addition to the labyrinth-like folded dentin layer of the teeth which is heavily ossified compared to bony fish, with the braincase is firmly connected (but detached from the shoulder girdle ) and also windowless skull roof of one of the typical features that the group their other scientific names, " Stegocephalia " ( " Dachschädler " ), has entered. The German name " Panzerlurch " refers to a well on the compact skull structure, on the other, the bony plates that had incorporated some representatives of the " Labyrinthodontia " in the back skin (called osteoderms ), much as is the case with today's crocodiles. Another typical feature of the skull of the subject is the parabolic shape in plan view. Some labyrinthodonts, such as Platyoposaurus, however, had relatively elongated jaw.
The representatives of the " Labyrinthodontia " reached sizes of a salamander to that of a large crocodile. The lifestyle of many great labyrinthodonts likely to have been similar to the present-day large crocodiles: they lay in wait in the shallow water near the shore for prey animals who came to the waters to drink. Other potentially lurking in deeper water at the base on a temporary floating labyrinthodonts smaller or larger fish. The smaller forms subsisted probably either small fish or insects.
However, the propagation of the " Labyrinthodontia " that today's frogs and salamanders was similar: The shell-less eggs were released directly into the water and the young stages lived gill breathing in the water and formed only at the transition to adulthood lungs from which they independent of habitat made of water and give them a amphibious, partly also fully terrestrial lifestyle enabled.
Evolution Biological Aspects
The " Labyrinthodontia " originate from like all tetrapods, from a fishy flesh -finned fishes ( Sarcopterygii ). This is illustrated particularly in Devonian sedimentary rocks of North America and Scotland discovered fossils very original labyrinthodonts that the term " Ichthyostegalia " ( " fish skull amphibians " ) have been combined. While this still rather fish-like representatives had four legs, but possessed many of the characteristics of fishy flesh -finned fishes (including the training of the tail or the arrangement of the bones of the cranial vault ). This group also gained outside of paleontology and evolutionary biology a certain notoriety because it represents the evolutionary link between the extant fish and amphibians living today as well as all the rest, primarily land-dwelling vertebrates ( amniotes ).
Systematically in the case of the " Ichthyostegalia " is actually stored, similar to the total Labyrinthodontiern. They form according to the modern view, no self-contained group, but rather represent a certain level of development in the evolution of tetrapods, with some representatives are more closely related to the extant tetrapods than with other Ichthyostegaliern.