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Sunday, April 30, 2017

The 21st century blindsnake revolution


Brongersma's Wormsnake (Amerotyphlops brongersmianus),
a widespread species from South America
Blindsnakes (Scolecophidia) don't get enough attention. They include the world's most widespread snake species, the world's smallest living snake species, and a diversity of jaw-raking feeding mechanisms unrivaled in bizarreness among land vertebrates. I recently noticed, much to my surprise, the the number of described species of blindsnakes has doubled in the last 13 years, from 305 in 2004 to 599 today; that's 16.5% of all snakes! June 2017 EDIT: This was a big mistake on my part. As of 2017 there are 442 species described instead of 599. I made this mistake because I was confused about the search terms being used on my go-to reference for reptile taxonomy, The Reptile Database. I was assuming that Leptotyphlopidae + Anomalepidae + Typhlopoidea = Scolecophidia, a search term that is no longer available in The Reptile Database, because of several phylogenies that show it to be paraphyletic. If you search for "Typhlopoidea" on The Reptile Database, you get a list of all 442 blindsnakes 442, including Leptotyphlopidae and Anomalepididae, and not only the three families of Typhlopoidea according to Vidal et al. 2010 (Typhlopidae, Xenotyphlopidae, Gerrhopilidae). I thought that Typhlopoidea only returned the latter three families and I added the 139 species of Leptotyphlopidae and 18 species of Anomalepididae to get an incorrect total of 599. Thanks to Claudia Koch of the Alexander Koenig Zoological Research Museum in Bonn for pointing this out to me. There are certainly many undiscovered species of blindsnakes, so it's likely that their numbers will continue to grow (as one recent study put it, "...even our most liberal estimates of species numbers will likely prove to be an underestimate of the true diversity...of secretive blind snakes").

Blindsnake evolutionary tree.
Extinction of the dinosaurs (K-T boundary) was
between the green and pink-shaded areas.
From Vidal et al. 2010
One of the biggest phylogenetic rearrangements within the Scolecophidia was the recognition of two new families in 2010. The new families Gerrhopilidae and Xenotyphlopidae were formerly part of Typhlopidae, but were discovered to be distantly related to other typhlopids and were separated, although these three families are grouped together in the superfamily Typhlopoidea to emphasize their closer relationship to one another than to the other two families of scolecophidians (Leptotyphlopidae and Anomalepididae). The original diversification of blindsnakes is thought to have been caused by the breakup of Gondwana, whereas the later diversification of Typhlopoidea is associated with the breakup of East Gondwana into Antarctica, Madagascar, India, and Australia (with subsequent colonization by typhlopids from West Gondwana [Africa/South America]). Subsequent diversification within the Typhlopidae coincides with the early Paleozoic Era, just after the extinction of the dinosaurs, and includes four major groups: a Eurasian-Australasian one, an African one, a Malagasy one, and a South American-West Indian one. Because sea levels were low at this time, dispersal among continents and islands was relatively easy, at least for a small vertebrate with low metabolism and most likely travelling along with their invertebrate prey. The relationships of blindsnakes track plate tectonics better than those of any other vertebrate group, perhaps because of their tendency to stay put.

Gerrhopilus mirus from Sri Lanka
The two "new" families probably originated on the ancient landmass "Indigascar" (modern India and Madagascar, which were physically connected long after their isolation from other continents and India's subsequent unification with Asia). One family, Gerrhopilidae ("Indo-Malayan blindsnakes"), were formerly known as the Typhlops ater species group. They differ from other blindsnakes in having gland-like structures ‘peppered’ over the head scales. Many species also have a divided preocular and/or ocular scale, and the second supralabialal scale overlaps the preocular in all species but one (G. tindalli). The family contains at least 16 species in the genus Gerrhopilus, and possibly others (the most-recently described species are from 1996 and 2005). This is where it starts to get really weird.

The 1811 Freycinet map of Australia, where
Cathetorhinus melanocephalus was not found
There is another candidate member of the family Gerrhopilidae. The genus Cathetorhinus contains a single species, known from only a single specimen (Natural History Museum, Paris RA-0.138, an adult male). It was collected by French zoologists François Péron and Charles-Alexandre Lesueur on a scientific expedition to Australia led by Nicolas Baudin between 1801 and 1803, and scientifically described (along with an unprecedented and unqeualed number of other new snake species) in the 1844 volume of Duméril & Bibron's opus Erpetologie Générale (the series is also the provenance of the mudsnake plate that I use as a logo for this blog). Cathetorhinus melanocephalus was the only blindsnake they collected, despite visiting the Canary Islands, Mauritius, Timor, and South Africa in addition to Australia (of which members of the expedition later produced the first complete map). Unfortunately, for reasons lost to history and despite their general habits as conscientious collectors1, the location where they found Cathetorhinus melanocephalus was not recorded (I'm speculating here, but it may have been because they were distracted by fearing for their lives—of a total of 24 scientists who went on the expedition, 5 died and 10 disembarked at Mauritius due to illness).

Cathetorhinus melanocephalus
From Wallach & Pauwels 2008
This wouldn't be such a problem (lots of type specimens have vague or missing type localities; Linnaeus correctly attributed fewer than half of his snakes to the right continent "Indiis") except that no other specimens have ever been found. It is taxonomically unique based on its morphology, descriptions of which have been rather inconsistent over the decades, partially because blindsnakes are really small and their scales are really hard to count, especially given the crummy optics of the 19th century. Except for the head glands, Cathetorhinus shares more anatomical characteristics with Gerrhopilus than with any other blindsnakes. A 2008 study reviewed the history of the Baudin expedition and concluded that “the provenance of this species remains unknown: it is certainly Old World, and may be from (in order of probability) Timor, Australia, Mauritius or Tenerife”. And so it would have remained, if not for some really excellent bibliographical sleuthing by biologist and scholar Anthony Cheke, an expert on Mascarene fauna. Cheke reviewed the unpublished original notes made by Lesueur on the voyage, and found a reference to "a very small [snake] species 4–5 inches maximum...the only one found during our stay [on Mauritius in 1803]...found amongst stones while clearing some land...about 8 inches be-low the soil surface". This tantalizing description suggests a blindsnake in size, habitat, and behavior, and although Cheke himself had assumed that it referred to the Brahminy Blindsnake (Indotyphlops braminus), he later realized that the first records of introduction of this widespread species were from 1869, 66 years later.2 Although this isn't concrete proof, it's highly suggestive that Lesueur's blindsnake was Cathetorhinus melanocephalus, since it was the only blindsnake collected on the entire journey.3nbsp;Fossils of an endemic Mauritian typhlopid were discovered around 1900 and described as Typhlops cariei, but direct comparison of the bones with those of Cathetorhinus has not been made. Could Cathetorhinus still survive in the wild? Many non-native blindsnake predators were already introduced to Mauritius when Lesueur and Péron visited, including rats, shrews, and tenrecs, and others have since become established, such as mongeese. Only time, and further field work on Mauritius, will tell.

Malayotyphlops luzonensis (L), M. denrorum (C), and M. andyi (R)
From Wynn et al. 2016
As if that wasn't strange enough, there is a third possible candidate member of Gerrhopilidae: the species known as either Typhlops manilae, Malayotyphlops manilae, or Gerrhopilus manilae. The taxonomic status of this species is currently unclear. It was described by American herpetologist and spy Edward H. Taylor in 1919, from a specimen that was "discovered in the Santo Tomas Museum" in Manila, although even then nobody knew when, where, or by whom it was collected. It appears to have been barely mentioned in the scientific literature until 2014, when its morphological distinctiveness from other members of the Typhlops ater species group/Gerrhopilidae was noted as part of a massive review of typhlopid snakes led by Pennsylvania State University blindsnake specialist and evolutionary biologist Blair Hedges. They suggested it belonged instead to another new genus, Malayotyphlops, also mostly from the Philippines, because it has 28 scale rows (vs. 18 in Gerrhopilus) and a short tail, and because a subocular scale is not unique to Gerrhopilus. Later the same year, a different study disagreed and moved the species back to Gerrhopilus based on the statement from the original description that it has a subocular. However, yet a third study took a close look at Taylor's original description, which contains no illustration, and noted several areas of potential confusion, concluding that without examination of the original specimen, which is still in Manila, "it is not possible to determine to which genus, or even family, T. manilae...belongs".

The three reptile species originally described by Mocquard
and re-discovered at Baie de Sakalava in northern Madagascar
after more than 100 years without records.
The blindsnake Xenotyphlops grandidieri (pink), and two
legless skink species: Paracontias minimus (brown with
longitudinal lines of dark spots) and P. rothschildi
(beige with black flanks). From Wegener et al. 2013
Before you get too discouraged, remember that snake biology is replete with tales of rediscovery. Case in point: the other "new" family, Xenotyphlopidae. This bizarre snake has completely lost any traces of visible eyes. It was known solely from the type specimens, described by French zoologist François Mocquard in 1905 and 1906, for more than 100 years. Their precise locality was unknown. However, Hanna Wegener and a term of German, Belgian, and American herpetologists rediscovered Xenotyphlops in 2013 on a coastal dune under a piece of wood in the sand in a littoral forest at Baie de Sakalava in northern Madagascar, along with two endemic legless skinks in the genus Paracontias also described by Mocquard. Because the new specimens of X. grandidieri overlapped the other species in this genus (X. mocquardi) in most morphological characteristics, the two have now been synonymized, making the family Xenotyphlopidae monotypic (for now). These blindsnakes are unique in having a greatly enlarged and nearly circular rostral scale and an enlarged anal shield, and in lacking a tracheal lung.

The number of less-phylogenetically-distinct but poorly-known blindsnakes is not small. These have received renewed attention due to their placement in new families, but the 21st century blindsnake revolution is just getting started.



1 Péron and Lesueur also collected the first and some of the only specimens of Bolyeria multicarinata from Mauritius, which is now thought to be extinct, although they mistakenly labeled it as being from Australia.



2 Today, only I. braminus and another introduced species, I. porrectus, are found on Mauritius; the latter may have also been introduced in the 1800s but was first conclusively documented only in 1993.



3 A few pieces of evidence against: a length of 4–5 French inches corresponds to 109–136 mm, which is just right for I. braminus but a tad small for the Cathetorhinus specimen, which measures 178 mm (6.6 French inches). Cheke thought that "Lesueur appeared to be writing from memory without the specimen actually before him, so, impressed by its small size, he may have exaggerated how tiny his snake actually was.", maybe the last time in history that somebody underestimated the size of a snake. The other point of confusion is over the exact locality: Lesueur and Péron were clearing land with an upland planter, Toussaint de Chazal, at whose estate in the area now known as Mondrain they were staying. Mondrain is on a plateau adjacent to the Tamarin Gorge, which is 9 km from Grand Bassin, where Lesueur stated that they found the snake.

ACKNOWLEDGMENTS

Thanks to Ruchira Somaweera and Sumaithangi Ganesh for the use of their photos.

REFERENCES

Cheke, A. 2010. Is the enigmatic blind snake Cathetorhinus melanocephalus (Serpentes: Typhlopidae) an extinct endemic species from Mauritius? Hamadryad 35:101-104 <full-text>

Duméril, C., G. Bibron, and A. Duméril. 1854. Erpetologie Générale on Histoire Naturelle Compléte des Reptiles. Librairie Encyclopédique de Roret, Paris <link to Cathetorhinus description>

Hedges, S., A. Marion, K. Lipp, J. Marin, and N. Vidal. 2014. A taxonomic framework for typhlopid snakes from the Caribbean and other regions (Reptilia, Squamata). Caribbean Herpetology 49:1-61 <full-text>

Kraus, F. 2005. New species of blindsnake from Rossel Island, Papua New Guinea. Journal of Herpetology 39:591-595 <abstract>

Pyron, R. and V. Wallach. 2014. Systematics of the blindsnakes (Serpentes: Scolecophidia: Typhlopoidea) based on molecular and morphological evidence. Zootaxa 3829:1-81 <full-text>

Taylor, E. H. 1919. New or rare Philippine reptiles. Philippine Journal of Science 14:105-125 <full-text>

Vidal, N., J. Marin, M. Morini, S. Donnellan, W. R. Branch, R. Thomas, M. Vences, A. Wynn, C. Cruaud, and S. B. Hedges. 2010. Blindsnake evolutionary tree reveals long history on Gondwana. Biology Letters 6:558-561 <full-text>

Wallach, V. 1996. Two new Blind snakes of the Typhlops ater species group from Papua new Guinea (Serpentes: Typhlopidae). Russian Journal of Herpetology 3:107-118 <full-text>

Wallach, V. and O. Pauwels. 2008. The systematic status of Cathetorhinus melanocephalus Duméril & Bibron, 1844 (Serpentes: Typhlopidae). Hamadryad 33:39-47 <full-text>

Wegener, J. E., S. Swoboda, O. Hawlitschek, M. Franzen, V. Wallach, M. Vences, Z. T. Nagy, S. B. Hedges, J. Köhler, and F. Glaw. 2013. Morphological variation and taxonomic reassessment of the endemic Malagasy blind snake family Xenotyphlopidae. Spixiana 36:269-282 <full-text>

Wynn, A. H., R. P. Reynolds, D. W. Buden, M. Falanruw, and B. Lynch. 2012. The unexpected discovery of blind snakes (Serpentes: Typhlopidae) in Micronesia: two new species of Ramphotyphlops from the Caroline Islands. Zootaxa 3172:39–54 <full-text>

Wynn, A. H., A. C. Diesmos, and R. M. Brown. 2016. Two new species of Malayotyphlops from the northern Philippines, with redescriptions of Malayotyphlops luzonensis (Taylor) and Malayotyphlops ruber (Boettger). Journal of Herpetology 50:157-168 <full-text>

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Life is Short, but Snakes are Long by Andrew M. Durso is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

4 comments:

Mark Scherz said...

Very interesting Andrew, good insight. I agree, we certainly seem to be at the beginning of a renaissance of Typhlopoid taxonomy, and other aspects of their biology as well. It is an exciting time, especially in light of new possibilities that are emerging in the study of these ridiculously small animals. I don't want to give too much away at this time, as we are only just starting our work on them, but the holes in the literature surrounding their osteology are really astounding. We hope to fix that!

Andrew Durso said...

Thanks Mark. I'm sure there's a great deal of typhlopoid work going on that hasn't seen the light of day, and I won't be surprised if more "new" families are described in the coming years. Keep up the good work!

Dan Rabosky said...

Great summary of a weird group of animals! One of my favorites is Anilios (formerly Ramphotyphlops) longissimus. Here's what Aplin et al (Rec. West Aust. Museum, 1998) said in the original description:

"...the specimen was one of two individuals that were attached to the outer surface of a section of well-casing pulled from some considerable depth below ground during maintenance of an anode well... on Barrow Island. One specimen was grabbed....while the second 'shot' back down the well and was lost. Because the animal looked more like a worm or eel than a snake, it was placed in a jar of water where it swam around for some time before being rescued by an environmental officer who recognised its true nature. The specimen was delivered several days later, still alive, to the Western Australian Museum."

Aplin et al speculate that this species might live in deep sediment filled karstic caverns on Barrow Island and that some of its morphological traits suggest the possibility of a deep subterranean existence. And to my knowledge, this is the only one ever collected - even though there is a ton of basic monitoring work on Barrow Island that should have uncovered more! What else don't we know about these things?

Andrew Durso said...

Yowza, that is bizarre and awesome. I also like the Etymology explanation for Anilios splendidus:
"(Latin):magnificent!"