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A basal ichthyosauriform with a short snout from the Lower Triassic of China

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A Corrigendum to this article was published on 28 October 2015

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Abstract

The incompleteness of the fossil record obscures the origin of many of the more derived clades of vertebrates. One such group is the Ichthyopterygia, a clade of obligatory marine reptiles that appeared in the Early Triassic epoch, without any known intermediates1. Here we describe a basal ichthyosauriform from the upper Lower Triassic (about 248 million years ago) of China, whose primitive skeleton indicates possible amphibious habits. It is smaller than ichthyopterygians and had unusually large flippers that probably allowed limited terrestrial locomotion. It also retained characteristics of terrestrial diapsid reptiles, including a short snout and body trunk2. Unlike more-derived ichthyosauriforms3, it was probably a suction feeder. The new species supports the sister-group relationships between ichthyosauriforms and Hupehsuchia4, the two forming the Ichthyosauromorpha. Basal ichthyosauromorphs are known exclusively from south China, suggesting that the clade originated in the region, which formed a warm5,6 and humid7 tropical archipelago8 in the Early Triassic. The oldest unequivocal record of a sauropterygian is also from the same stratigraphic unit of the region9.

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Figure 1: Locality and horizon of the new species.
Figure 2: The holotype of Cartorhynchus lenticarpus gen. et sp. nov.
Figure 3: Quantitative comparisons of selected characteristics.
Figure 4: Phylogenetic hypotheses of Cartorhynchus.

Change history

  • 10 November 2014

    Jian-Dong Huang was incorrectly listed as an corresponding author instead of Da-Yong Jiang in the HTML (the PDF was correct). This has been corrected in the HTML.

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Acknowledgements

We thank T. Sato for the excellent preparation of the holotype. The study was enabled by grants from the National Geographic Society Committee for Research and Exploration (8669-09) to R.M., Project 40920124002 and 41372016 from the National Natural Science Foundation of China to D.-Y.J., Project 123102 from State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, CAS) to D.-Y.J., Project 20120001110072 from the Research Fund for the Doctoral Program of Higher Education to D.-Y.J., and a Project of Protection for Geological Heritage from Department of Land and Resource of Anhui Province to G.-B.C.

Author information

Authors and Affiliations

Authors

Contributions

R.M. conceived the study, participated in the relevant fossil excavations, ran all analyses, drew all figures except Fig. 1b, and wrote the manuscript. D.-Y.J. conceived the study, supervised the relevant fossil excavations and preparations, drew Fig. 1b, and revised the manuscript; G.-B.C. conceived the study and supervised off-season fossil collections; A.T. conceived the study, participated in the relevant fossil excavations, and revised the manuscript; O.R. conceived the study, participated in the relevant fossil excavations, and revised the manuscript; C.J. provided an unpublished data matrix, participated in the relevant fossil excavations, and revised the manuscript; J.-D.H. helped supervise off-season fossil collections.

Corresponding authors

Correspondence to Ryosuke Motani or Da-Yong Jiang.

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Competing interests

The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 Phylogenetic hypothesis of diapsid relationships when aquatic adaptations are recoded as ambiguous.

Strict consensus of two most parsimonious trees (tree length (TL) = 805, consistency index (CI) = 0.317, retention index (RI) = 0.587) obtained by a heuristic search in PAUP* 4b10 (hold = 10, nreps = 100, addseq = random, swap = tbr). Numbers associated with clades are Bremer support values calculated in TNT 1.1. Original tree of Fig. 4a. Phylogenetic tree is based on the data described in Supplementary Information.

Extended Data Figure 2 Phylogenetic hypothesis of diapsid relationships when aquatic adaptations are recoded normally.

Strict consensus of 20 most parsimonious trees (TL = 839, CI = 0.311, RI = 0.612) obtained by a heuristic search in PAUP* 4b10 (hold = 10, nreps = 100, addseq = random, swap = tbr). Numbers associated with clades are Bremer support values calculated in TNT 1.1. Original tree of Fig. 4b. Phylogenetic tree is based on the data described in Supplementary Information.

Extended Data Figure 3 Phylogenetic hypothesis of Ichthyosauriformes.

Strict consensus of 82 most parsimonious trees (TL = 527, CI = 0.423, RI = 0.796) obtained by a heuristic search in PAUP* 4b10 (hold = 10, nreps = 100, addseq = random, swap = tbr). Numbers associated with clades are Bremer support values calculated in TNT 1.1. Original tree of Fig. 4c. Phylogenetic tree is based on the data described in Supplementary Information.

Supplementary information

Supplementary Data

This file contains data for the relationships of diapsids, with aquatic adaptations codes as ambiguous (Figure 4a). (PDF 489 kb)

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Motani, R., Jiang, DY., Chen, GB. et al. A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature 517, 485–488 (2015). https://doi.org/10.1038/nature13866

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