Morphology of the earliest reconstructable tetrapod Parmastega aelidae

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Abstract

The known diversity of tetrapods of the Devonian period has increased markedly in recent decades, but their fossil record consists mostly of tantalizing fragments1,2,3,4,5,6,7,8,9,10,11,12,13,14,15. The framework for interpreting the morphology and palaeobiology of Devonian tetrapods is dominated by the near complete fossils of Ichthyostega and Acanthostega; the less complete, but partly reconstructable, Ventastega and Tulerpeton have supporting roles2,4,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34. All four of these genera date to the late Famennian age (about 365–359 million years ago)—they are 10 million years younger than the earliest known tetrapod fragments5,10, and nearly 30 million years younger than the oldest known tetrapod footprints35. Here we describe Parmastega aelidae gen. et sp. nov., a tetrapod from Russia dated to the earliest Famennian age (about 372 million years ago), represented by three-dimensional material that enables the reconstruction of the skull and shoulder girdle. The raised orbits, lateral line canals and weakly ossified postcranial skeleton of P. aelidae suggest a largely aquatic, surface-cruising animal. In Bayesian and parsimony-based phylogenetic analyses, the majority of trees place Parmastega as a sister group to all other tetrapods.

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Fig. 1: Skull roof, cheek and palate of P. aelidae.
Fig. 2: Lower jaw and pectoral girdle of P. aelidae.
Fig. 3: Reconstructions of P. aelidae.

Data availability

In total, 132 specimens comprising 183 skeletal elements were collected during the entire period of excavations (2002–2012). One hundred and six specimens (all of them figured in Supplementary Table 1) have been deposited in the collection of the Institute of Geology, Komi Science Centre (Ural Branch of the Russian Academy of Sciences, Syktyvkar, Russia) under collection number IG KSC 705/. One specimen has been deposited in the Ukhta Local Museum under collection number ULM 2599. The IG KSC and ULM specimens are available for examination. Other specimens have been reserved for sharing with other museums. The Life Science Identifier for Parmastega is urn:lsid:zoobank.org:act:76B5BB03-42FE-4F46-A284-F95E973CEE96.

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Acknowledgements

We thank Y. Gatovsky, A. Zhuravlev and D. Ponomarev for their support of the project, and the dig crews of the 2009–2012 excavations for all their hard work. A. Ivanov identified the first tetrapod mandible from Sosnogorsk, in the Chernyshov Collection. P.A.B. acknowledges the support of National Geographic Society grant 9099-12 and UNDP/GEF project no. 00059042. E.L. acknowledges the support of Latvian Council of Science grant Z-6153-110. P.E.A. acknowledges the support of a Wallenberg Scholarship from the Knut and Alice Wallenberg Foundation.

Author information

P.A.B. initiated and directed the excavation programme at Sosnogorsk, which produced the material for the study. E.L. and P.E.A. participated in excavations. P.A.B. carried out all preparation, consolidation and photography of specimens. P.E.A. made the reconstructions of the skull, lower jaw and shoulder girdle. M.R. performed the phylogenetic analyses. P.E.A. made Figs. 13 and Extended Data Figs. 2, 49. P.A.B. made Extended Data Figs. 1, 3, as well as Supplementary Tables 1, 2. P.A.B, J.A.C., E.L., M.R. and P.E.A. participated in the interpretation of the material and the writing of the paper.

Correspondence to Per Erik Ahlberg.

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Peer review information Nature thanks Nadia Fröbisch and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Extended data figures and tables

Extended Data Fig. 1 The distribution of Parmastega at the Sosnogorsk fossil site.

a, b, Maps of increasing resolution, showing the location of Sosnogorsk within northwest Russia. The box around Ukhta and Sosnogorsk in a indicates the region shown in b. In b, the brown belt that extends from north to south indicates the outcrop of Famennian (D3fm) deposits in the region, and the yellow arrow points to the Sosnogorsk fossil site (Sosnovskiy Geological Monument). c, Stratigraphic column through the Sosnogorsk Formation, and part of the overlying marine Izhma Formation. Note the possible position of the Frasnian–Famennian boundary (D3f–D3fm) in the lower part of the Sosnogorsk Formation. The vertebrate-bearing part of the formation is shown in detail on the right; the tetrapod-bearing level is indicated with a red vertical bar. d, General view of outcrop no. 20 (Sosnovskiy Geological Monument) from the opposite bank of the Izhma River. 1, limestone; 2, dolomite; 3, clay; 4, nodular limestone; 5, scree; and 6, landslide. D3sn, Sosnogorsk Formation, D3iž, Izhma Formation. The distance A′–B′ indicates the area of the main excavation that took place in 2010–2012. e, Main excavation. The distance A–B indicates the area in which all of the tetrapod bones were found, during the excavation in 2012. The photograph was taken on 2 August 2012. f, Sketch map of the main excavation (2012), showing the distribution of tetrapod bones within the bed. The cluster numbers are indicated in orange. The background maps in a and b were taken from https://yandex.ru/maps; the geological features of b were taken from the open-access State Geological Map at https://vsegei.ru/.

Extended Data Fig. 2 Frontal bones of Parmastega.

This figure shows all of the complete and near-complete frontals of Parmastega (eight out of nine known frontals) to scale, oriented with anterior at the top and aligned on the centre of radiation (horizontal line). The right frontals have been reversed so that all bones have the appearance of left frontals. From left to right, the specimens are IG KSC 705/3 (reversed), IG KSC 705/40, IG KSC 705/44 (reversed), IG KSC 705/43, IG KSC 705/45, IG KSC 705/18 (reversed), IG KSC 705/42 and IG KSC 705/41. Scale bar, 10 mm.

Extended Data Fig. 3 Bone associations.

a, b, Diagrammatic images showing the associated bones (in orange) of two individual skulls. a, The holotype IG KSC 705/1. b, The largest individual, IG KSC 705/2–705/14 and IG KSC 705/99. In the lateral view of b, the preserved frontal and nasal are shown (even though they are in fact on the other side of the skull). c, Diagrammatic representation of the number of specimens of different bones in the sample.

Extended Data Fig. 4 Size and shape of Devonian tetrapods.

Silhouette reconstructions of the heads of known, reconstructable Devonian tetrapods. Reconstructions are drawn to the same scale. The lower jaw of Elginerpeton—the largest known Devonian tetrapod, and for which the skull cannot be reconstructed—is also included. All reconstructions except for Acanthostega are assembled from more than one specimen; the specimen numbers indicate the specimen used to determine the scale. The right-hand column shows the largest known individuals. The left-hand column shows the smallest individuals of Parmastega (all from Sosnogorsk) and Ichthyostega (based on the entire East Greenland collection, reviewed in ref. 61). Note the similarity in size range despite the very different nature of the samples. Ventastega and Acanthostega show narrow size ranges, which are not illustrated. Reconstructions modified from the following sources: Ichthyostega, ref. 19; Acanthostega, ref. 31; Ventastega, ref. 32; Elginerpeton, ref. 62.

Extended Data Fig. 5 Relative orbit size.

Plot of orbit length versus skull length for a range of tetrapodomorph fishes, elpistostegids, Devonian tetrapods and post-Devonian tetrapods. Data are taken from ref. 47, except Parmastega, which is based on the largest known individual (Extended Data Fig. 3). Post-Devonian tetrapods from ref. 47 not included in our phylogenetic analysis are not shown. Ac, Acanthostega; Ba b, Baphetes bohemicus; Ba k, Baphetes kirkbyi; Ba l, Baphetes lintonensis; Bal, Balanerpeton; Be, Beelarongia; Br, Bruehnopteron; Cab, Cabonnichthys; Can, Canowindra; Cl, Cladarosymblema; Cra, Crassigyrinus; Den, Dendrerpeton; Ed, Edenopteron; Elp, Elpistostege; Eoh, Eoherpeton; Eu, Eusthenopteron; Gog, Gogonasus; Goo, Gooloogongia; Gre, Greererpeton; Gy, Gyroptychius; He, Heddleichthys; Ich, Ichthyostega; Ko, Koharalepis; Man, Mandageria; Mar, Marsdenichthys; Meg, Megalocephalus; Oss, Ossinodus; Ost, Osteolepis; Pal, Palatinichthys; Pan, Panderichthys; Par, Parmastega; Ped, Pederpes; Pro, Proterogyrinus; Scr, Screbinodus; Sil, Silvanerpeton; Tik, Tiktaalik; Tin, Tinirau; Ven, Ventastega; Wha, Whatcheeria.

Extended Data Fig. 6 Otoccipital morphologies of Devonian tetrapods.

a, Comparative diagram of the otoccipial regions of Parmastega, Ichthyostega (new reconstruction, based on data from refs. 18,20), Ventastega (modified from ref. 32) and Acanthostega (modified from ref. 20, semicircular canals modified from ref. 63) in ventral view. The basioccipital–exoccipital complex is preserved only in Ichthyostega and Acanthostega; in these genera the inner ear is shown only on one side. Drawings are scaled to the same length from pineal region to posterior margin of otic capsule. The inner ear is represented by the grooves for the anterior and posterior oblique semicircular canals, except in Ichthyostega in which it is represented by the sacculus (modified from ref. 20). The braincases are arranged by morphological similarity, so that a minimum number of transformations are required along each branch. b, Consensus phylogeny from the analyses presented in this paper. The phylogenetic topology does not match the similarity dendrogram.

Extended Data Fig. 7 Phylogenetic analysis.

a, Unweighted strict-consensus tree. b, Unweighted Adams consensus tree. c, Single tree resulting from reweighting characters by the rescaled consistency index. d, Bayesian tree, with credibility values at nodes. e, Maximum-agreement subtree of unweighted parsimony analysis. f, Strict consensus of K-weighted trees. g, Maximum-agreement subtree of K-weighted parsimony analysis. h, Adams consensus of all trees from all K-weighted analyses.

Extended Data Fig. 8 Parmastega and caiman.

Comparison in left lateral view of spectacled caiman (Caiman crocodilus) on the left and Parmastega on the right, drawn to the same size, showing the inferred similar cruising posture at the surface. Note the difference in the positions of the nostrils. The caiman image is based on a computed tomography scan of a skull in the Digimorph Archive (http://www.digimorph.org/specimens/Caiman_crocodilus/).

Extended Data Fig. 9 Fit of dentary against upper jaw.

a, Dentary of Parmastega (IG KSC 705-67) fitted against palatal reconstruction to show the difference in curvature between the spade-shaped snout and the relatively straight dentary. b, Lateral view of skull reconstruction of Parmastega with closed mouth, showing mismatch in curvature between upper and lower jaws. c, Composite reconstruction of Ventastega, superimposing lower jaw rami (from ref. 30) on skull reconstruction (from ref. 32), showing shape relationship similar to a. Not to scale.

Supplementary information

Supplementary Table

SI Table 1: specimens of Parmastega registered to Institute of Geology, Komi Science Centre. Illustrated with thumbnail photos of specimens.

Reporting Summary

Supplementary Table

SI Table 2: complete list of the known bones of Parmastega.

Supplementary Information

SI character list: character list for phylogenetic matrix.

Supplementary Information

SI character matrix: character matrix for phylogenetic analysis.

Supplementary Information

SI NEXUS: NEXUS version of character matrix.

Supplementary Information

SI prmrbayesoutput: output of Bayesian analysis.

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Beznosov, P.A., Clack, J.A., Lukševičs, E. et al. Morphology of the earliest reconstructable tetrapod Parmastega aelidae. Nature 574, 527–531 (2019) doi:10.1038/s41586-019-1636-y

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