Journal
ANATOMICAL RECORD-ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY
Volume 304, Issue 10, Pages 2118-2148Publisher
WILEY
DOI: 10.1002/ar.24716
Keywords
insular dwarfism; osteology; snake miniaturization; threadsnakes; viscera
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Funding
- Conselho Nacional de Desenvolvimento Cientifico e Tecnologico [309560/2018-7]
- Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES) [99999.010032/2014-02]
- Fundacao Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro [E-26/202.403/2017, E26/202.737/2018, E-26/211.154/2019]
- Smithsonian Institution
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The genera Mitophis and Tetracheilostoma exhibit unique osteological and visceral features, possibly as a result of extreme miniaturization driven by the island rule. These two genera distinguish themselves from other leptotyphlopids by lacking specific skeletal structures and internal organ characteristics.
The genera Mitophis and Tetracheilostoma comprise two extant lineages of small-sized threadsnakes that exclusively inhabit several islands of the West Indies. Even though leptotyphlopids are known for their extremely reduced size, miniaturization has only been hypothesized to reflect insular dwarfism for the genus Tetracheilostoma. Herein, we aim to describe the comparative osteology and visceral morphology of both genera, investigating and discussing their several internal morphological simplifications and novelties. Our results indicate that these taxa exhibit several autapomorphies mostly concentrated in the dorsoposterior skull elements and maxillae, as well as in their axial skeleton and viscera. These novelties and simplifications are most likely a result of extreme miniaturization driven by the evolutionary constraints or ecological opportunities possibly imposed by the island rule. Both Mitophis and Tetracheilostoma distinguish from all other Epictinae in lacking a dentigerous process in the maxillae, by having the prootic fused to the otooccipital, and by the lack (except in comparison to a few Epictia) of a cervical vertebrae intercentrum I. Additionally, Mitophis can be distinguished from other Epictinae by the participation of the unpaired supraoccipital in the dorsal border of the foramen magnum, by the absence of the pleurapophyses in the caudal vertebrae, by a higher number of liver segments, and by the extreme degeneration of the pelvic rudiments. Tetracheilostoma differs from other Epictinae by lacking a distinct supraoccipital, which is fused to the parietal. Thus, our results reinforce that morphological characters are extremely valuable for leptotyphlopid systematics given their extremely conserved external morphology.
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