Palatal morphology predicts the paleobiology of early salamanders
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Evaluation Summary:
This paper is of interest to vertebrate paleontologists and other evolutionary biologists interested in the early evolution of amphibians. Using geometric morphometric analysis, the authors demonstrate that both the shape of the palate and several non-shape variables (particularly associated with vomerine teeth) are ecologically informative in early stem- and basal crown-group salamanders. The phylomorphospace analysis reveals that metamorphosis is significant in the expansion of ecomorphospace of the palate in early salamanders. In overall, the main claims of the manuscript are well supported by the data.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #1, Reviewer #2 and Reviewer #3 agreed to share their name with the authors.)
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Abstract
Ecological preferences and life history strategies have enormous impacts on the evolution and phenotypic diversity of salamanders, but the yet established reliable ecological indicators from bony skeletons hinder investigations into the paleobiology of early salamanders. Here, we statistically demonstrate by using time-calibrated cladograms and geometric morphometric analysis on 71 specimens in 36 species, that both the shape of the palate and many non-shape covariates particularly associated with vomerine teeth are ecologically informative in early stem- and basal crown-group salamanders. Disparity patterns within the morphospace of the palate in ecological preferences, life history strategies, and taxonomic affiliations were analyzed in detail, and evolutionary rates and ancestral states of the palate were reconstructed. Our results show that the palate is heavily impacted by convergence constrained by feeding mechanisms and also exhibits clear stepwise evolutionary patterns with alternative phenotypic configurations to cope with similar functional demand. Salamanders are diversified ecologically before the Middle Jurassic and achieved all their present ecological preferences in the Early Cretaceous. Our results reveal that the last common ancestor of all salamanders share with other modern amphibians a unified biphasic ecological preference, and metamorphosis is significant in the expansion of ecomorphospace of the palate in early salamanders.
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Evaluation Summary:
This paper is of interest to vertebrate paleontologists and other evolutionary biologists interested in the early evolution of amphibians. Using geometric morphometric analysis, the authors demonstrate that both the shape of the palate and several non-shape variables (particularly associated with vomerine teeth) are ecologically informative in early stem- and basal crown-group salamanders. The phylomorphospace analysis reveals that metamorphosis is significant in the expansion of ecomorphospace of the palate in early salamanders. In overall, the main claims of the manuscript are well supported by the data.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #1, Reviewer #2 and …
Evaluation Summary:
This paper is of interest to vertebrate paleontologists and other evolutionary biologists interested in the early evolution of amphibians. Using geometric morphometric analysis, the authors demonstrate that both the shape of the palate and several non-shape variables (particularly associated with vomerine teeth) are ecologically informative in early stem- and basal crown-group salamanders. The phylomorphospace analysis reveals that metamorphosis is significant in the expansion of ecomorphospace of the palate in early salamanders. In overall, the main claims of the manuscript are well supported by the data.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #1, Reviewer #2 and Reviewer #3 agreed to share their name with the authors.)
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Reviewer #1 (Public Review):
Ecological preferences and life history strategies impact the evolution and phenotypic diversity of salamanders. Using geometric morphometric analysis, the authors demonstrate that both the shape of the palate and several non-shape variables (particularly associated with vomerine teeth) are ecologically informative in early stem- and basal crown-group salamanders. The morphology of the palate is subject to convergence constrained by feeding mechanisms, and metamorphosis is significant in the expansion of ecomorphospace of the palate in early salamanders. The work will add to the knowledge on the early evolutionary pattern of salamanders.
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Reviewer #2 (Public Review):
In this manuscript, Jia and colleagues statistically demonstrate, using geometric morphometric analysis, that the palate is a reliable proxy in ecological reconstructions for early salamanders, and the morphospace of the palate is predominantly shaped by ecological constraints and also displays stepwise evolutionary pattern. The authors also provide evidence that the common ancestor of salamanders was metamorphosed and terrestrial, and shared unified lifestyles with other modern amphibians. The results of the study are of interest to a wide range of zoologists.
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Reviewer #3 (Public Review):
The manuscript investigates, using a large dataset and a broad array of methods that account for phylogenetic nonindependence of the data, whether the shape of the palate correlates with habitat (water, land, or both) in a clade of extant salamanders. After demonstrating that this is the case, it infers the lifestyles of Cretaceous and Jurassic supposed members of that clade as well as a few other early salamanders. If the used phylogenetic tree is indeed accurate, the conclusions are very robust. The methods will be widely imitated to research similar questions all across the tree of life.
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