Skull Ossification in the Andean Toad Rhinella spinulosa (Bufonidae) and the Genetic Model Organism Xenopus tropicalis (Pipidae) Reveals Heterochrony Phenomena and Frontoparietal Suture Modifications.

Marco Mundaca,Japhet Rojas,Lefney Cumilaf,Federico Jara,David Muñoz,L. Pastenes,Marco A Méndez,L. M. Tovar,Marcela Torrejón,Germán Montoya-Sanhueza,Sylvain Marcellini

Published 2024 in Journal of Experimental Zoology Part B: Molecular and Developmental Evolution

ABSTRACT

Anurans are famous for having evolved a highly simplified skull through bone loss and fusion events. Nevertheless, their skeleton displays a rich morphological diversity associated with adaptations to diverse lifestyles and ecological niches. Here, we report larval skull ossification in the Andean toad Rhinella spinulosa (Bufonidae), and compare it to the phylogenetically distant genetic model organism Xenopus tropicalis (Pipidae). We find that the ossification timing of most skull bones is conserved between both species, except for the prootic and the angulosplenial that ossify at much later stages in R. spinulosa than X. tropicalis. We propose that a delayed lower jaw ossification in R. spinulosa is tightly related to the more extensive metamorphosis process observed in this species where the ventrally oriented mouth opening shifts anteriorly. We also report two conspicuous notches in the R. spinulosa frontoparietal bone mineralization front which are absent in X. tropicalis, and presumably represent evolutionary remnants of the coronal suture that separates the frontal and parietal bones in most vertebrates. As such notches have not been overtly reported in the literature, we examined the X. tropicalis sibling species Xenopus laevis, and were able to identify similar, albeit transient, indentations in the forming frontoparietal bone, suggesting that vestigial coronal sutures might exist in more frog species than anticipated. Taken together, we show that R. spinulosa represents an ideal organism to study heterochronic shifts and the mechanisms underlying cranial suture loss which drove anuran skull simplification.

PUBLICATION RECORD

  • Publication year

    2024

  • Venue

    Journal of Experimental Zoology Part B: Molecular and Developmental Evolution

  • Publication date

    2024-12-04

  • Fields of study

    Biology, Medicine, Environmental Science

  • Identifiers
  • External record

    Open on Semantic Scholar

  • Source metadata

    Semantic Scholar, PubMed

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