Showing posts with label squamate diversity. Show all posts
Showing posts with label squamate diversity. Show all posts

Monday, May 16, 2011

How Many Species of Snakes Are There?

The number of species of snakes described each year since 1758.  The text in black notes the authors who contributed a significant number of species in various years where the number of species that were described spiked.
Ask this question on Goggle and most of the top dozen websites provide answers that range from "more than 2000" to "2950." The exception is the Reptile Database website that reports 3149 species as of February, 2008, and 3,315 species as of January 2011. Since this list undoubtedly receives the most detailed attention and updating by herpetologists it is likely to be the most authoritative answer for the moment. But really - how many species of snakes are there?

Using the Reptile Database I graphed the number of currently recognized snake species described each year from 1758 to 2010, divide the 3315 species by the number of months and you get about 1.09 snake species have been described each month for the past 253 years. However, there is reason to believe that there are many species that remain to be described.

Passo and Lynch (2010) revised the cryptozoic snakes in the genus Atractus from the middle and upper Magdalena drainage of Colombia. Prior to the publication of this paper five species were known from the region, they added three new ones, an increase of 60%. Of the 135 currently recognized species of Atractus, 42 (31%) species have been described since 2000. The blind snakes of the genus Typhlops also currently number 135 species, of these 14.8% have been described since 2000. Another species rich genus is Oligodon, the Asian Kukri Snakes. Currently 68 species are recognized, six (8.8%) have been described since 2000. Thus, many snake species clearly remain to be described.

The reasons for this situation appear to be the tendencies of Albert Günther and George Boulenger, both world renowned 19th century herpetologists, to lump species together. They decided that many of the species described between 1758 and 1860 were in fact species that had been named more than once. As they tried to organize the reptiles in the collection at the British Museum of Natural History they described some new species, but they also synonymized many species previously described under names they thought represented the earliest description of a particular species. This could have been a highly useful service to science, but unfortunately they did this many times without actually examining type specimens.

However, other factors are also involved. Species concepts have also changed. Concepts based strictly on scale counts and other morphology have been replaced with concepts based on isolation of gene pools and populations that are on their own evolutionary pathway.

As I worked my way through the homalopsid specimens in the 1990’s, it became clear that specimens labeled Enhydris jagorii represented at least three different species. Most of the specimens labeled jagorii had a mid-ventral stripe, a relatively high ventral count, there was another species with an exceptionally low ventral count, and yet a third species with an intermediate ventral count. Each had a distinctive pattern, but similar dorsal scale row counts, and head scale arrangements. Just laying one of each next to each other, it was clear they were distinct. Thus, three species were considered to be one. This situation is not uncommon, thus it would appear that the actually number of snake species could be conservatively estimated to increase by 1.5 to 2 times.

Murphy, J. C. 2007. Homalopsid Snakes, Evolution in the Mud. Krieger Publishing, Malabar, Florida.

Passos P. and J. D. Lynch. 2010. Revision of Atractus (Serpentes: Dipsadidae) from Middle and Upper Magdalena Drainage of Colombia. Herpetological Monographs, 24:149-173.

Sunday, May 15, 2011

Squamate Diversity - Five New Lizards

The blind snake lizard Dibamus dalaiensis 
Thy et al. 2011. Photo credit Neang Thy
The continuing discovery of new species of terrestrial vertebrates is a reminder that the diversity of life is much greater than was thought even 25 years ago. In the last few week five lizards (3 geckos, 1 skink, and 1 blind snake lizard) have been described from Venezuela, Madagascar, Indonesia, and Cambodia.

The blind snake lizard Dibamus dalaiensis ( family Dibamidae) was described from the Phnom Samkos Wildlife Sanctuary in the Cardamom Mountains of Cambodia by  Neang Thy and colleagues. It is significant because it represents a new family, genus and species record for Cambodia and it raise the number of species in the family Diabamus to 23, eight of these species (34%) have been described in the 21st century.

Marcelo Sturaro and Teresa Avila-Pires described two new species of dwarf day geckos of the genus Gonotodes (family Spaheordactylidae); one from eastern Amazonia, in the states of Pará and Amapá in Brazil (Gonatodes nascimentoi), and another from central Colombia, east of the Andes (Gonatodes riveroi), both are species of the Gonatodes concinnatus complex.The describtion of these geckos raise the number of species in the genus Gonatodes to 26, nine (33%) of which have been described in the 21st century.

Skinks make up the largest family of lizards, with more than 1450 known species. Aurelien Miralles and colleagues have described Madascincus arenicola, a new skink from the sand dunes of northern Madagascar. But, also of interest their molecular analysis found two related species (M. polleni and M. intermedius) genetically distinct, but morphologically indistinguishable. Madascincus now contains 11 species, 2 of which were described in the 21st century.

Djoko Iskandar and colleagues have described Cyrtodactylus batik a new species collected from Mount Tompotika, in the Balantak Mountains of Central Sulawesi, Indonesia. This large Cyrtodactylus (up to 115 mm in body length), forms a lineage with C. wallacei and C. jellesmae that appears to be endemic to Sulawesi. This raises the number of Cyrtodactylus geckos to 139, 59 (42%) of which have been described in the 21st century.

The message here - squamates are much more diverse than previously thought.

Iskandar, D. T., A. Rachmansah and Umilaela. 2011. A new bent-toed gecko of the genus Cyrtodactylus Gray, 1827 (Reptilia, Gekkonidae) from Mount Tompotika, eastern peninsula of Sulawesi, Indonesia. Zootaxa 2838:65-78.

Miralles, A.,  Kohler, J., Glaw, F., and M Vences. 2011. A molecular phylogeny of the “Madascincus polleni species complex”, with description of a new species of scincid lizard from the coastal dune area of northern Madagascar. Zootaxa 2876:1-16.

Thy, N., Holden, J, Eastoe, T., Rathea Seng, Saveng Ith, and Grismer, L.L. 2011. A new species of Dibamus (Squamata: Dibamidae) from Phnom Samkos Wildlife Sanctuary, southwestern Cardamom Mountains, Cambodia. Zootaxa 2828:58-68.

Sturaro, M. J. and T. C. S. Avila-Pires. 2011. Taxonomic revision of the geckos of the Gonatodes concinnatus complex (Squamata: Sphaerodactylidae), with description of two new species. Zootaxa 2869:1-36.