Hidden morphological diversity among early tetrapods

dc.contributor.authorPardo, Jason D
dc.contributor.authorSzostakiwskyj, Matt
dc.contributor.authorAhlberg, Per E
dc.contributor.authorAnderson, Jason S
dc.date.accessioned2021-05-08T22:30:39Z
dc.date.available2021-05-08T22:30:39Z
dc.date.issued2017-06-21
dc.description.abstractPhylogenetic analysis of early tetrapod evolution has resulted in a consensus across diverse data sets in which the tetrapod stem group is a relatively homogenous collection of medium- to large-sized animals showing a progressive loss of 'fish' characters as they become increasingly terrestrial, whereas the crown group demonstrates marked morphological diversity and disparity. The oldest fossil attributed to the tetrapod crown group is the highly specialized aïstopod Lethiscus stocki, which shows a small size, extreme axial elongation, loss of limbs, spool-shaped vertebral centra, and a skull with reduced centres of ossification, in common with an otherwise disparate group of small animals known as lepospondyls. Here we use micro-computed tomography of the only known specimen of Lethiscus to provide new information that strongly challenges this consensus. Digital dissection reveals extremely primitive cranial morphology, including a spiracular notch, a large remnant of the notochord within the braincase, an open ventral cranial fissure, an anteriorly restricted parasphenoid element, and Meckelian ossifications. The braincase is elongate and lies atop a dorsally projecting septum of the parasphenoid bone, similar to stem tetrapods such as embolomeres. This morphology is consistent in a second aïstopod, Coloraderpeton, although the details differ. Phylogenetic analysis, including critical new braincase data, places aïstopods deep on the tetrapod stem, whereas another major lepospondyl lineage is displaced into the amniotes. These results show that stem group tetrapods were much more diverse in their body plans than previously thought. Our study requires a change in commonly used calibration dates for molecular analyses, and emphasizes the importance of character sampling for early tetrapod evolutionary relationships.en_US
dc.description.grantingagencyNatural Sciences and Engineering Research Council (NSERC)en_US
dc.identifier.citationPardo, J., Szostakiwskyj, M., Ahlberg, P. et al. Hidden morphological diversity among early tetrapods. Nature 546, 642–645 (2017). https://doi.org/10.1038/nature22966en_US
dc.identifier.doihttp://dx.doi.org/10.1038/nature22966en_US
dc.identifier.grantnumber2017-04821en_US
dc.identifier.urihttp://hdl.handle.net/1880/113382
dc.identifier.urihttps://doi.org/10.11575/PRISM/46097
dc.language.isoengen_US
dc.publisherNatureen_US
dc.publisher.facultyVeterinary Medicineen_US
dc.publisher.hasversionacceptedVersionen_US
dc.publisher.institutionUniversity of Calgaryen_US
dc.publisher.policyhttps://www.nature.com/nature-portfolio/editorial-policies/self-archiving-and-license-to-publish#self-archiving-policyen_US
dc.rightsUnless otherwise indicated, this material is protected by copyright and has been made available with authorization from the copyright owner. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.en_US
dc.subjectvertebrate paleontologyen_US
dc.subjectTetrapodaen_US
dc.subjectLepospondylien_US
dc.subjectLethiscusen_US
dc.subjectAistopodaen_US
dc.subjectphylogenetic analysisen_US
dc.titleHidden morphological diversity among early tetrapodsen_US
dc.typejournal articleen_US
ucalgary.item.requestcopytrueen_US
ucalgary.scholar.levelFacultyen_US
ucalgary.scholar.levelGraduateen_US
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