2/12/2024 0 Comments Snake head shapesThe analysis of morphological data using complementary geometric morphometric approaches has the potential to shed light on these issues 28. Similarly, investigations of the evolution of discrete ossification sequences in skull development could not discern between different ancestral ecological scenarios 27. Recently, modern phylogenetic comparative methods have been developed to estimate the ecological state of snake ancestors 23, but with a limited taxon sampling that hampered the phylogenetic signal. In addition, ancestral ecologies have been typically hypothesized based on sister clades of snakes only, without formal ancestral character state estimates 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 26. Central to this debate are the paucity of intact well-preserved snake fossils 16, 17, 18, 19, the difficulty of deciphering squamate phylogenetics 20, 21, 22, 23, 24, sampling variability and incompleteness 8, 9, 10, 11, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, and incompatible morphological character coding when convergence is expected 9, 10, 12, 13, 14, 15, 16, 17, 18, 19, 20, 26. Therefore, in this study, we performed a large-scale and integrative geometric morphometric analysis of skull bones across squamates to help clarify the ecological and evolutionary origins of snakes.Ĭonflicting ecological hypotheses for early snakes, including aquatic 9, 10, 11, terrestrial 12, 13, 14, fossorial 15, 16, 17, 18, or even multiple habitats 19, have been proposed based on cladistic analysis of discrete traits. The interplay between development and natural selection in driving morphological skull disparities associated with the lizard-to-snake transition remains poorly understood. However, studies assessing the early ecological and evolutionary origins of snakes have so far largely focused on discrete morphological differences, and the adaptive role of skull shape development in the origin and diversification of snakes remains to be tested at large scale. In addition, the evolution and development of the limb and axial skeleton have been recently assessed in snakes, suggesting a correlation between limb loss and body elongation 3, 4, 5, 6, 7, 8. Similar content being viewed by othersĪ century of anatomical and phylogenetic studies have established that snakes evolved from lizards 1, 2, these two groups forming together one of the most-specious clades of terrestrial vertebrates-the squamate reptiles. These results highlight the importance of the interplay between natural selection and developmental processes in snake origin and diversification, leading first to invasion of a new habitat and then to subsequent ecological radiations. Our comprehensive heterochrony analyses further indicate that snakes later evolved novel craniofacial specializations through global acceleration of skull development. Our large-scale data reveal that whereas the most recent common ancestor of crown snakes had a small skull with a shape undeniably adapted for fossoriality, all snakes plus their sister group derive from a surface-terrestrial form with non-fossorial behavior, thus redirecting the debate toward an underexplored evolutionary scenario. Here we use a geometric morphometric approach integrating ecological, phylogenetic, paleontological, and developmental data for building models of skull shape and size evolution and developmental rate changes in squamates. The ecological origin of snakes remains amongst the most controversial topics in evolution, with three competing hypotheses: fossorial marine or terrestrial.
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