Sunday, September 28, 2014

New genera of homalopsid snakes

Until recently these two snakes were both in the genus Enhydris.
Both are adults, both have smooth scales and their internasals in
contact. Yet they have different ancestors within the family 
homalopsidae as suggested by their dramatically different body 
shapes. JCM
The colubroid snake family Homalopsidae also known as the Australasian rear-fanged water snakes contained 10 genera and 34 species of rear-fanged semi-aquatic and aquatic snakes in 1970 with the publication of Ko Ko Gyi’s monograph. In 2007 Murphy updated Gyi’s work and the family held the same 10 genera with 37 species plus two genera of uncertain status (Anoplohydrus, Brachyorrhos). Molecular studies published in the first decade of the 21st century demonstrated that while the Homalopsidae is monophyletic, the species-rich genus Enhydris is polyphyletic. Molecular analysis also found Brachyorrhos to be the most basal member of the clade, confirming an earlier hypothesis that it was a fangless homalopsid. Subsequently, two other fangless genera (Calamophis and Karnsophis) of homalopsids were discovered.

In a newly published paper Murphy and Voris (2014) revalidate the genera for the polyphyletic genus Enhydris: Homalophis Peters, Hypsiscopus Fitzinger, Miralia Reuss, Phytolopsis Gray, and Raclitia Gray. They also describe five new genera for species lacking available names: Gyiophis, Kualatahan, Mintonophis, Sumatranus, and Subsessor. The new arrangement for homalopsid names resolves the problem of the formerly polyphyletic genus Enhydris. See tree below.

Gyi (as well as Boulenger and Gunther) placed snakes in the genus Enhydris because they shared smooth dorsal scales and internasals that were in contact. These characters do not necessarily suggest ancestry and many other traits seen in these snakes in fact suggested they were not closely related. Consider the small headed, gracile Enhydris enhydris and the largest known homalopsid, Subsessor (formerly Enhydris) bocourti with a massive body and head (see photo). Placing these snakes in the same genus implies they share a close common ancestor, a hypothesis not supported by morphology or DNA.

With this checklist the family now contains 53 species in 28 genera. Molecular studies suggest homalopsids are old, perhaps separating from their most recent common ancestor with the Lamprophiidae 53 million years ago.

Red lines indicate species considered Enhydris by Gyi. Names at the end of the red lines are current genera.
Recent evidence suggests homalopsids show high levels of endemism and cryptic speciation so it is likely that many more species, and likely more genera will be discovered in the future.

CitationMurphy JC and Voris HK. 2014. A Checklist and key to the homalopsid snakes (Reptilia, Squamata, Serpentes), with the description of new genera. Fieldiana Life and Earth Sciences 8:1-43. doi: http://dx.doi.org/10.3158/2158-5520-14.8.1

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