Toxicofera
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Scorpion-Krustenechse ( Heloderma horridum ) |
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| Toxicofera | ||||||||||||
| Vidal & Hedges , 2005 |
The toxicofera ( Greek τοξίνη , toxins = "poison", Latin ferre = "bear") are a taxon (a systematic group) of Squamata (Squamata). It includes the snakes (Serpentes), the creepy (Anguimorpha) and the iguana (Iguania).
The relationship of these three outwardly different groups is based on molecular biological investigations and is only supported by a few morphological features. According to the family tree of the scale reptiles, which is based on molecular biological data, the crawling and iguana-like sister groups , the unnamed clade formed by both taxa , is the sister group of the snakes.
So far, only the poisonous snakes (Elapidae), the vipers (Viperidae) and the false snakes , as well as the creeping lizards ( Heloderma ), were considered poisonous scaled reptiles . Therefore, an independent, at least two-fold origin of this trait was assumed in the Squamate evolution. The Toxicofera concept, on the other hand, assumes that the ability to produce toxins was developed only once in the course of phylogenesis (ancestral history). The common ancestor of all Toxicofera is believed to have lived in the Upper Triassic around 230 to 200 million years ago .
In the meantime , poison-producing glandular tissue has also been found in the upper and lower jaws of an iguana, the Eastern Bearded Dragon ( Pogona barbata ) . In addition, symptoms that occur after the bites of Komodo dragon , spotted monitor lizard and banded tree monitor (which belong to the crawling species) are no longer interpreted as the result of a bacterial infection, but as the result of active poisonous secretion. In the meantime, venomous glands in the mandibles of the Komodo dragon have been detected with the help of 3D scans of a skull in a magnetic resonance tomograph . There are also indications of the presence of poison glands in fossil creepers from the Upper Cretaceous .
Today around 4600 species of the 7900 scale reptile species, that is around 58 percent, belong to the Toxicofera.
Toxicofera cladogram :
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literature
- T. Townsend, A. Larson, E. Louis, JR Macey: Molecular phylogenetics of squamata: the position of snakes, amphisbaenians, and dibamids, and the root of the squamate tree. In: Syst Biol. , 2004 Oct, 53 (5), pp. 735-757, PMID 15545252 .
- Nicolas Vidal, S. Blair Hedges: The phylogeny of squamate reptiles (lizards, snakes, and amphisbaenians) inferred from nine nuclear protein-coding genes . In: CR Biologies , 328, 2005, pp. 1000–1008, ( PDF ; 164 kB)
Individual evidence
- ↑ Bryan G. Fry, Stephen Wroe, Wouter Teeuwisse et al .: A central role for venom in predation by Varanus komodoensis (Komodo Dragon) and the extinct giant Varanus (Megalania) priscus . In: Proceedings of the National Academy of Sciences. Volume 106, Number 22, June 2, 2009, pp. 8969-8974, doi: 10.1073 / pnas.0810883106 .
- ^ BG Fry, N. Vidal, JA Norman, FJ Vonk, H. Scheib, SF Ramjan, S. Kuruppu, K. Fung, SB Hedges, MK Richardson, WC Hodgson, V. Ignjatovic, R. Summerhayes, E. Kochva: Early evolution of the venom system in lizards and snakes. In: Nature. Volume 439, Number 7076, February 2006, pp. 584-588, doi : 10.1038 / nature04328 , PMID 16292255 .