Deconstructing the Gestalt: New concepts and tests of homology, as exemplified by a re-conceptualization of "microstomy" in squamates.

Publisher: John Wiley & Sons Country of Publication: United States NLM ID: 101292775 Publication Model: Print-Electronic Cited Medium: Internet ISSN: 1932-8494 (Electronic) Linking ISSN: 19328486 NLM ISO Abbreviation: Anat Rec (Hoboken) Subsets: MEDLINE

Original Publication: Hoboken, NJ : John Wiley & Sons, 2007-

Anatomy, Comparative* ; X-Ray Microtomography*; Concept Formation

Snakes-a subset of lizards-have traditionally been divided into two major groups based on feeding mechanics: "macrostomy," involving the ingestion of proportionally large prey items; and "microstomy," the lack of this ability. "Microstomy"-considered present in scolecophidian and early-diverging alethinophidian snakes-is generally viewed as a symplesiomorphy shared with non-snake lizards. However, this perspective of "microstomy" as plesiomorphic and morphologically homogenous fails to recognize the complexity of this condition and its evolution across "microstomatan" squamates. To challenge this problematic paradigm, we formalize a new framework for conceptualizing and testing the homology of overall character complexes, or "morphotypes," which underlies our re-assessment of "microstomy." Using micro-computed tomography (micro-CT) scans, we analyze the morphology of the jaws and suspensorium across purported "microstomatan" squamates (scolecophidians, early-diverging alethinophidians, and non-snake lizards) and demonstrate that key components of the jaw complex are not homologous at the level of primary character state identity across these taxa. Therefore, rather than treating "microstomy" as a uniform condition, we instead propose that non-snake lizards, early-diverging alethinophidians, anomalepidids, leptotyphlopids, and typhlopoids each exhibit a unique and nonhomologous jaw morphotype: "minimal-kinesis microstomy," "snout-shifting," "axle-brace maxillary raking," "mandibular raking," and "single-axle maxillary raking," respectively. The lack of synapomorphy among scolecophidians is inconsistent with the notion of scolecophidians representing an ancestral snake condition, and instead reflects a hypothesis of the independent evolution of fossoriality, miniaturization, and "microstomy" in each scolecophidian lineage. We ultimately emphasize that a rigorous approach to comparative anatomy is necessary in constructing evolutionary hypotheses that accurately reflect biological reality.
(© 2021 American Association for Anatomy.)

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DBI-1702421 National Science Foundation; DBI-1701932 National Science Foundation; DBI-1701713 National Science Foundation; DBI-1701714 National Science Foundation; EF-0334961 National Science Foundation; IIS-0208675 National Science Foundation; IIS-9874781 National Science Foundation; DEB-0132227 National Science Foundation; 1541959 National Science Foundation; (#23458) Natural Sciences and Engineering Research Council of Canada (NSERC)

Keywords: ancestral state reconstruction; functional morphology; homology; skull anatomy; snake evolution

Date Created: 20210419 Date Completed: 20220309 Latest Revision: 20220309

20221213

10.1002/ar.24630

33871920