Polacanthidae
The division of living beings into systematics is a continuous subject of research. Different systematic classifications exist side by side and one after the other. The taxon treated here has become obsolete due to new research or is not part of the group systematics presented in the German-language Wikipedia.
The Polacanthidae or Polacanthinae are a controversial taxon within the Ankylosauria dinosaur group .
Traditionally, the Ankylosauria are divided into two groups, the Ankylosauridae and the Nodosauridae . The Ankylosauridae are characterized among other things by the broad skull and a bony club at the end of the tail, while the Nodosauridae have a narrow skull, no tail club and a conspicuous, bump-like projection of the shoulder blade .
Some ankylosaurs, which were grouped together as Polacanthinae, showed features of both groups, to a certain extent an "ankylosaurid" skull sat on a "nodosaurid" skeleton. Accordingly, the classification of the Polacanthinae was controversial, they were listed as a subfamily of either one or the other traditional group. The systematic classification was made more difficult by the fact that only fragmentary fossils have been preserved from many representatives and the skull is often missing.
After phylogenetic studies, Kenneth Carpenter raised the Polacanthidae to the rank of a separate family alongside Ankylo- and Nodosauridae in 2001. In addition to the features mentioned above, this group was characterized by a relatively uniform structure of the armor - present in all ankylosauria - made of bone plates (osteoderms), which were approximately triangular and thin. Often there were also bony spines and the teeth were comparatively primitive. According to Carpenter, the Polacanthidae lived in the Upper Jurassic and the Lower Cretaceous .
The following genera could have belonged to the Polacanthidae:
However, other classifications do not recognize this taxon. The phylogenetic studies by M. Vickaryous et al. lists Gargoyleosaurus and Gastonia as basic representatives of the Ankylosauridae and classifies the other four genera as "Ankylosauria incertae sedis ", which means that too little data are available for an unequivocal classification.
The main problem is probably the mostly sparse fossils of many ankylosauria, so for the time being the question of whether the Polacanthidae are a valid taxon cannot be answered.
literature
- Matthew K. Vickaryous, Teresa Maryańska and David B. Weishampel: Ankylosauria . In: David Weishampel, Peter Dodson and Halszka Osmólska (eds.): The Dinosauria . University of California Press, 2004. ISBN 0-520-24209-2 ; Pp. 363-392.
- Kenneth Carpenter: Phylogenetic analysis of the Ankylosauria. In Kenneth Carpenter (Ed.): The Armored Dinosaurs . Indiana University Press, Bloomington & Indianapolis, 2001. ISBN 0-253-33964-2 , pp. 455-483.