A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes

Coates, Michael I; Gess, Robert W; Finarelli, John A; Surname, Name - one for each creator; Criswell, Katharine E; Tietjen, Kristen

Title: A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes
Creator: Coates, Michael I
Creator: Gess, Robert W
Creator: Finarelli, John A
Creator: Surname, Name - one for each creator
Creator: Criswell, Katharine E
Creator: Tietjen, Kristen
Date Issued: 2017
Date: 2017
Type: text
Type: article
Identifier: http://hdl.handle.net/10962/72246
Identifier: vital:30021
Identifier: https://doi.org/10.1038/nature20806
Description: Chimaeroid fishes (Holocephali) are one of the four principal divisions of modern gnathostomes (jawed vertebrates). Despite only 47 described living species1, chimaeroids are the focus of resurgent interest as potential archives of genomic data2 and for the unique perspective they provide on chondrichthyan and gnathostome ancestral conditions. Chimaeroids are also noteworthy for their highly derived body plan1,3,4. However, like other living groups with distinctive anatomies5, fossils have been of limited use in unravelling their evolutionary origin, as the earliest recognized examples already exhibit many of the specializations present in modern forms6,7. Here we report the results of a computed tomography analysis of Dwykaselachus, an enigmatic chondrichthyan braincase from the ~280 million year old Karoo sediments of South Africa8. Externally, the braincase is that of a symmoriid shark9,10,11,12,13and is by far the most complete uncrushed example yet discovered. Internally, the morphology exhibits otherwise characteristically chimaeroid specializations, including the otic labyrinth arrangement and the brain space configuration relative to exceptionally large orbits. These results have important implications for our view of modern chondrichthyan origins, add robust structure to the phylogeny of early crown group gnathostomes, reveal preconditions that suggest an initial morpho-functional basis for the derived chimaeroid cranium, and shed new light on the chondrichthyan response to the extinction at the end of the Devonian period.
Format: 16 pages
Format: pdf
Language: English
Relation: Nature
Relation: Coates, M.I., Gess, R.W., Finarelli, J.A., Criswell, K.E. and Tietjen, K., 2017. A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes. Nature, 541(7636), p.208.
Relation: Nature volume 541 number 7636 208 223 January 2017 0028-0836
Rights: Nature Research Open Access
Rights: Use of this resource is governed by the terms and conditions of the Nature Research Open Access statement (https://www.nature.com/openresearch/publishing-with-npg/)

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