Abdominal rib
Abdominal ribs are skeletal structures in the lower abdominal area, which often occurred in theropods and are only found in recent species in crocodiles (Crocodylia) and bridge lizards ( Sphenodon ). Because of their location, the abdominal ribs are also called gastralia (singular gastrale ), ancient Greek γαστήρ gaster , German 'belly' . These are ventral remnants of skin bone armor that are not connected to the rest of the skeleton.
The gastrial apparatus in prosauropods and lizard-pelvis dinosaurs consists of eight to twenty metameric arched rows that consist of four or, depending on the adhesions, fewer bones. A distinction is made between median (lying towards the middle) and lateral (lying on the edge) bones. With median adhesions there are only three bones per row, with additional lateral adhesions only one. The latter is often the case with the cranial and caudal rows. The bones in a row and the rows with one another can be connected in a joint-like manner; there is no connection to the rest of the skeleton.
Dinosaur gastralia were first described by Eudes-Deslongchamps in Poekilopleuron bucklandii in 1838 , but without having recognized them as dermal bones. Therefore, the Osborn description of the gastralia of a Tyrannosaurus rex from 1906 is often cited as the first description. After Osborn's rediscovery, gastralia were soon found in theropod and prosauropod taxa . In 1994 gastralia were also described in sauropods ( Apatosaurus ). Recent birds no longer have gastralia, but their predecessors such as Archeopteryx or Confuciusornis do . Gastralia have also been described in the primeval bird Sinoris santensis . This archaically preserved feature does not seem to have any influence on flight or sitting posture, but is considered an additional indication that the theropods are the closest relatives of birds.
Traditionally, the gastralia have the protective and supportive functions of the visceral area . As the sketch on the right shows, the gastralia could have controlled the shape of the abdominal cavity and thus supported breathing. Today's bird breathing can possibly be traced back to, as stated in the article Airbag (bird) .
Gastralia are only found in a few recent species, the bridge lizards and the crocodiles . Crocodiles have pairs of curved bone braces on the belly side, eight pairs of real crocodiles , seven pairs of alligators . These are not fused median, but connected by connective tissue .
Individual evidence
- ^ Claessens, Leon PAM (March 2004). Dinosaur gastralia: origin, morphology, and function . Journal of Vertebrate Paleontology, Volume 24 (1): Pages 89-106
- ^ Paul C. Sereno , Rao Chenggang: Early Evolution of the Avian Flight and Perching: New Evidence from lower Cretaceous of China , Science , Volume 255 (February 14, 1992), Number 5046, pp. 845-848
- ↑ Wilfried Westheide , Reinhard Rieger: Special Zoology, Part 2, Vertebrates: Vertebrate or Skull Animals , Spectrum Textbook, ISBN 978-3-8274-2062-6