Browsing by Subject "evolutionary Developmental Biology"

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  • Oliveira da Silva, Filipe (Helsingin yliopisto, 2021)
    Snakes are intriguing organisms, yet their ancestral ecology and evolutionary history remained uncertain for centuries. This debate received renewed attention due to controversies about the interpretations of fossils, ecologies, and evolutionary relationships. Thus, new approaches were needed to investigate the early evolution of snakes. It is well-known that biological shape can be linked with certain functions and that the skull is an important ecological structure. So, it is relevant to investigate the skull shape to understand more details about the evolution and ecology of early snakes. In this dissertation, I investigated hundreds of skulls of lizards, snakes, and tuatara to address the ecological origin and radiation of snakes from lizards. I used cutting-edge geometric morphometrics (investigates the form of biological structures), comparative (uses phylogenetic trees), and multivariate analyses (takes higher biological complexity into consideration). I evaluated four hypotheses. i: skulls of lizards and snakes that dig in the soil and mostly live underground (fossorial) are more similar than expected under a neutral model of evolution; ii: skull shapes and ecologies are correlated, meaning that certain shapes are commonly associated with certain ecologies, which also allows us to predict the ecology of fossils and estimated ancestors based on the skull shape; iii: snakes evolved from either a fossorial, marine, or terrestrial ancestor; and iv: heterochrony - evolutionary changes due to changes in the rate and length of development - underlies the skull shape development and morphological innovation within and among snakes. I found that the skull shape of fossorial lizards and snakes are convergent, indicating that natural selection played an important role. I found a significant correlation between form and function or skull shape and ecology. In an analogy, this is like thinking about the different kinds of pans you have in your kitchen. The frying pan has a different shape in comparison to the boiling pot and you recognize their use based on their shape. I then estimate the shape of the ancestors and with high statistical confidence the ancestral ecology of snakes. Surprisingly, snakes most likely evolved from a terrestrial lizard-like ancestor. The earliest snake ancestor was most likely small and fossorial. Finally, heterochrony through acceleration in the skull shape development was detected in alethinophidian snakes, likely underlying the rise of evolutionary innovation and ecological radiation. All that said, this dissertation opened new avenues and approaches to investigate snake and vertebrate evolution in innovative ways that led to intelligible, plausible, and fruitful outcomes.