Microsauria
| Microsauria | ||||||||||||
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Live reconstructions of some genera: (A) Hyloplesion , (B) Pantylus , (C) Pelodosotis and (D) Rhynchonkos |
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| Temporal occurrence | ||||||||||||
| Carboniferous ( Mississippium ) to Unterperm | ||||||||||||
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| Scientific name | ||||||||||||
| Microsauria | ||||||||||||
| Dawson , 1863 |
The microsauria are a group of extinct terrestrial vertebrates whose fossil remains from the Mississippian (“Lower Carboniferous”) to the early Permian in North America and possibly also in Europe can be detected. John William Dawson considered the group in his first description of 1863 as early reptiles (Microsauria = "small lizards"), today they are classified in the group of amphibian-like envelope vertebrae ( Lepospondyli ).
features
The microsauria were 3.5 to 60 centimeters long and were the most variable lepospondyles in terms of morphology and lifestyle. Most species were salamander-like and lived terrestrially , others amphibious . There were also specialized burrowing underground forms that had long bodies and short limbs and whose skull bones were reduced. Aquatic microsauria retained their outer gills into the adult stage ( neoteny ). Terrestrial forms lacked the pits of the sideline organ . Everyone had limbs, even if they were short and thin. The tail was never specialized, as in the Nectridea , another group of Lepospondyli. The number of vertebrae was 19 to 44. As in other lepospondyles, the centra of the vertebral body are cylindrical and fused with the neural arches. The synapomorphies of the microsauria include the absence of the intertemporal and supratemporal in the skull. In primitive microsauria the cheek region is completely covered, in three progressive families it is deeply indented.
Systematics
The microsauria are no longer considered a monophyletic taxon. The eleven families are divided into two main groups, which are differentiated by their skull morphology:
The Microbrachomorpha , named after the aquatic Microbrachis , are more closely related to the Nectridea than to the other microsaurs. Here in the skull the post-frontal has no contact with the tabular .
In the Tuditanomorpha (after the genus Tuditanus ) these two skull bones touch each other. Above all, terrestrial genera belong to it, for example Pantylus .
In addition, rhynchonchos , which had a long trunk and short legs, may represent a group of their own. This group would be more closely related to the Microbrachis group than to the Tuditanus group and is under discussion as a possible origin of the recent sneak amphibian (Gymnophiona).
Some scientists believe that the salamanders (Caudata) are descended from dinosaurs Micro. The majority goes today but believe that the origin of the combined Anura (Anura) within the dissorophoidea is.
literature
- Robert Lynn Carroll : Paleontology and Evolution of the Vertebrates. Thieme, Stuttgart 1993, ISBN 3-13-774401-6 .
- Michael J. Benton : Paleontology of the vertebrates. 3. Edition. Pfeil, Munich 2007, ISBN 978-3-89937-072-0 .
- Robert Reisz: Lepospondyls and Lissamphibians. Lecture notes or similar ( PDF 19 kB)
Individual evidence
- ↑ John W. Dawson: Air-Breathers of the Coal Period: A Descriptive Account of the Remains of Land Animals Found in the Coal Formation of Nova Scotia with Remarks on their Bearing on Theories of the Formation of Coal and of the Origin of Species. Dawson Brothers, Montreal 1863, p. 47, online
Web links
- Palæos Microsauria