Evolution, biogeography, and fossil history of the Amphisbaenia (Reptilia, Squamata).
Final Report Abstract
The Amphisbaenia, or “worm lizards”, is an enigmatic, poorly understood clade of fossorial, bodyelongated squamates, nearly all of which are limbless. Most of their 190+ species are found in Africa and South America, with some disjunct distributions in tropical and subtropical regions of North and Central America, the West Indies, Europe and the Middle East. Since separating from their closest relatives, lacertid lizards, amphisbaenians have undergone extensive morphological modifications of the cranium and postcranium, most likely as an adaptation to headfirst digging. All but three species lack external fore- and hindlimbs; however, they each retain remnants of the pectoral and pelvic girdles to varying degrees, representing almost the entire evolutionary spectrum between the tetrapodal and limbless condition. Since their fossorial lifestyle presumably limits dispersal abilities, it is unclear if modern distributions are the result of continental breakups or transoceanic movement. The aim of the project was to 1) reevaluate the fossil record of Amphisbaenia, 2) perform a total-evidence analysis of the clade, 3) generate a molecular divergence estimate, and 4) investigate character evolution and biogeography. We generated an unprecedented data set of 3D morphological information of both extant and fossil amphisbaenians, as well as the first phylogenomic data set at the generic level, allowing us to generate an extensive total-evidence matrix for analyzing phylogenetic relationships. The resulting timecalibrated phylogeny challenges previous ideas about the timing of diversification of the major clades of crown amphisbaenians, which largely seems to be restricted to the early Paleogene but did not occur prior to the K-T transition. Our results weaken previously expressed ideas about a major influence of dispersal in explaining modern amphisbaenian biogeographic patterns, and highlight more strongly vicariant processes and large-scale extinctions across former distribution ranges. The phylogeny also reveals a much more refined picture of amphisbaenian character evolution, showing that the independent evolutionary acquisition of similar skull/snout shapes occurred much more frequently than previously assumed. Apart from the phylogeny, our project was also able to show that Paleogene amphisbaenian ecologies were probably more diverse than they are today, and that the modern observation of eye reduction across all extant amphisbaenians may not have been typical for the entire clade, i.e. when fossils are also considered. Also, we applied for the first time geometric-morphometric approaches to amphisbaenian ecology and morphological evolution, with results suggesting a potential relationship between skull shape and soil type. Finally, by using the novel visualization technique of diceCT we were able to show that amphisbaenians retain all of their pectoral muscles but show cladespecific morphologies, providing unprecedented evidence of a decoupling of the musculoskeletal system during the evolution of novel body plans.
Publications
- (2014) Beyond fossil calibrations: realities of molecular clock practices in evolutionary biology. – Frontiers in Genetics 5:138
Hipsley CA, Müller J
(See online at https://dx.doi.org/10.3389/fgene.2014.00138) - (2014) Relict Endemism of Extant Rhineuridae (Amphisbaenia): Testing for Phylogenetic Niche Conservatism in the Fossil Record. – Anatomical Record 297: 473-481
Hipsley CA, Müller J
(See online at https://doi.org/10.1002/ar.22853) - (2016) Ontogenetic allometry constrains cranial shape of the head-first burrowing worm lizard Cynisca leucura (Squamata: Amphisbaenidae). – Journal of Morphology
Hipsley CA, Rentinck M-N, Rödel M-O, Müller J
(See online at https://doi.org/10.1002/jmor.20564) - (2016) Skull osteology of the Eocene amphisbaenian Spathorhynchus fossorium (Reptilia, Squamata) suggests convergent evolution and reversals of fossorial adaptations in worm lizards. – Journal of Anatomy
Müller J, Hipsley CA, Maisano JA
(See online at https://doi.org/10.1111/joa.12513) - (2016) The new rare record of the late Oligocene lizards and amphisbaenians from Germany and its impact on our knowledge of the European terminal Palaeogene. – Palaeobiodiversity and Palaeoenvironments
Čerňanský A, Klembara J, Müller J
(See online at https://doi.org/10.1007/s12549-015-0226-8) - (2016). Diffusible iodine-based contrast-enhanced computed tomography (diceCT): an emerging tool for rapid, high-resolution, 3-D imaging of metazoan soft tissues. – Journal of Anatomy, 228: 889–909
Gignac, PM, Kley, NJ, Clarke, JA, Colbert, MW, Morhardt, AC, Cerio, D, Cost, IN, Cox, PG, Daza, JD, Early, CM, Echols, MS, Henkelman, RM, Herdina, AN, Holliday, CM, Li, Z, Mahlow, K, Merchant, S, Müller, J, Orsbon, CP, Paluh, DJ, Thies, ML, Tsai, HP, Witmer, LM
(See online at https://doi.org/10.1111/joa.12449)
