The phylogeny of Silurian and Devonian (443–358 million years (Myr) ago) fishes remains the foremost problem in the study of the origin of modern gnathostomes (jawed vertebrates). A central question concerns the morphology of the last common ancestor of living jawed vertebrates, with competing hypotheses advancing either a chondrichthyan-1,2,3 or osteichthyan-like4,5 model. Here we present Janusiscus schultzei gen. et sp. nov., an Early Devonian (approximately 415 Myr ago) gnathostome from Siberia previously interpreted as a ray-finned fish6, which provides important new information about cranial anatomy near the last common ancestor of chondrichthyans and osteichthyans. The skull roof of Janusiscus resembles that of early osteichthyans, with large plates bearing vermiform ridges and partially enclosed sensory canals. High-resolution computed tomography (CT) reveals a braincase bearing characters typically associated with either chondrichthyans (large hypophyseal opening accommodating the internal carotid arteries) or osteichthyans (facial nerve exiting through jugular canal, endolymphatic ducts exiting posterior to the skull roof) but lacking a ventral cranial fissure, the presence of which is considered a derived feature of crown gnathostomes7,8. A conjunction of well-developed cranial processes in Janusiscus helps unify the comparative anatomy of early jawed vertebrate neurocrania, clarifying primary homologies in ‘placoderms’, osteichthyans and chondrichthyans. Phylogenetic analysis further supports the chondrichthyan affinities of ‘acanthodians’, and places Janusiscus and the enigmatic Ramirosuarezia9 in a polytomy with crown gnathostomes. The close correspondence between the skull roof of Janusiscus and that of osteichthyans suggests that an extensive dermal skeleton was present in the last common ancestor of jawed vertebrates4, but ambiguities arise from uncertainties in the anatomy of Ramirosuarezia. The unexpected contrast between endoskeletal structure in Janusiscus and its superficially osteichthyan-like dermal skeleton highlights the potential importance of other incompletely known Siluro-Devonian ‘bony fishes’ for reconstructing patterns of trait evolution near the origin of modern gnathostomes.
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Miles, R. S. in Interrelationships of Fishes (eds Greenwood, P. H., Miles, R. S. & Patterson, C. ) 63–103 (Academic, 1973)
Brazeau, M. D. The braincase and jaws of a Devonian ‘acanthodian’ and modern gnathostome origins. Nature 457, 305–308 (2009)
Davis, S. P., Finarelli, J. A. & Coates, M. I. Acanthodes and shark-like conditions in the last common ancestor of modern gnathostomes. Nature 486, 247–250 (2012)
Zhu, M. et al. A Silurian placoderm with osteichthyan-like marginal jaw bones. Nature 502, 188–193 (2013)
Dupret, V., Sanchez, S., Goujet, D., Tafforeau, P. & Ahlberg, P. E. A primitive placoderm sheds light on the origin of the jawed vertebrate face. Nature 507, 500–503 (2014)
Schultze, H.-P. in Fossil Fishes as Living Animals (ed. Mark-Kurik, E. ) 233–242 (Academy of Sciences of Estonia, 1992)
Maisey, J. G. in Major Events in Early Vertebrate Evolution (ed. Ahlberg, P. E. ) 263–288 (Taylor & Francis, 2001)
Maisey, J. G. & Anderson, M. E. A primitive chondrichthyan braincase from the Early Devonian of South Africa. J. Vertebr. Paleontol. 21, 702–713 (2001)
Pradel, A., Maisey, J. G., Tafforeau, P. & Janvier, P. An enigmatic gnathostome vertebrate skull from the Middle Devonian of Bolivia. Acta Zoologica 90, 123–133 (2009)
Schultze, H.-P. Ausgangsform und Entwicklung der rhombischen Schuppen der Osteichthyes (Pisces). Paläontol. Z. 51, 152–168 (1977)
Blieck, A. & Janvier in Palaeozoic Vertebrate Biostratigraphy and Biogeography (ed. Long, J. A. ) 87–103 (Belhaven, 1993)
Gradstein, F. M., Ogg, J. G., Schmitz, M. & Ogg, G. The Geologic Time Scale 2012 (Elsevier, 2012)
Schultze, H.-P. & Cumbaa, S. L. in Major Events in Early Vertebrate Evolution (ed. Ahlberg, P. E. ) 315–332 (Taylor & Francis, 2001)
Basden, A. M. & Young, G. C. A primitive actinopterygian neurocranium from the Early Devonian of Southeastern Australia. J. Vertebr. Paleontol. 21, 754–766 (2001)
Jarvik, E. Basic Structure and Evolution of Vertebrates (Academic, 1980)
Gardiner, B. G. The relationships of the palaeoniscid fishes, a review based on new specimens of Mimia and Moythomasia from the Upper Devonian of Western Australia. Bull. Br. Mus. Nat. Hist. 37, 173–428 (1984)
Maisey, J. G., Miller, R. & Turner, S. The braincase of the chondrichthyan Doliodus from the Lower Devonian Campbellton Formation of New Brunswick, Canada. Acta Zoologica 90 (suppl. 1). 109–122 (2009)
Stensiö, E. Anatomical studies on the arthrodiran head, part I. Kungl. Svensk. Vetenskakad. Handl. 9, 1–419 (1963)
Goujet, D. Les Poissons Placodermes du Spitsberg (Centre National de la Recherche Scientifique, 1984)
Schaeffer, B. The xenacanth shark neurocranium, with comments on elasmobranch monophyly. Bull. Am. Mus. Nat. Hist. 169, 1–66 (1981)
Maisey, J. G. Braincase of the Upper Devonian shark Cladodoides wildungensis (Chondrichthyes, Elasmobranchii), with observations on the braincase in early chondrichthyans. Bull. Am. Mus. Nat. Hist. 288, 1–103 (2005)
Friedman, M. & Brazeau, M. D. A reappraisal of the origin and basal radiation of the Osteichthyes. J. Vertebr. Paleontol. 30, 36–56 (2010)
Brazeau, M. D. & Friedman, M. The characters of Palaeozoic jawed vertebrates. Zool. J. Linn. Soc. 170, 779–821 (2014)
Broughton, R. B.-R., Li, C., Arratia, G., Ortí, G. & Richard, E. Multi-locus phylogenetic analysis reveals the pattern and tempo of bony fish evolution. PLoS Curr. http://dx.doi.org/10.1371/currents.tol.2ca8041495ffafd0c92756e75247483e (2013)
Yu, X.-B. A new porolepiform-like fish, Psarolepis romeri, gen. et sp. nov. (Sarcopterygii, Osteichthyes) from the Lower Devonian of Yunnan, China. J. Vertebr. Paleontol. 18, 261–274 (1998)
Anderson, P. S. L., Friedman, M., Brazeau, M. D. & Rayfield, E. J. Initial radiation of jaws demonstrated stability despite faunal and environmental change. Nature 476, 206–209 (2011)
Botella, H., Blom, H., Dorka, M., Ahlberg, P. E. & Janvier, P. Jaws and teeth of the earliest bony fishes. Nature 448, 583–586 (2007)
Cunningham, J. A., Rucklin, M., Blom, H., Botella, H. & Donoghue, P. C. J. Testing models of dental development in the earliest bony vertebrates, Andreolepis and Lophosteus. Biol. Lett. 8, 833–837 (2012)
Young, G. C. New information on the structure and relationships of Buchanosteus (Placodermi: Euarthrodira) from the Early Devonian of New South Wales. Zool. J. Linn. Soc. 66, 309–352 (1979)
Swofford, D. L. PAUP*: Phylogenetic Analysis Using Parsimony (*And Other Methods) v.4.0b 10 (Sinauer Associates, 2003)
Wilkinson, M. Coping with missing entries in phylogenetic inference using parsimony. Syst. Biol. 44, 501–514 (1995)
Wikinson, M. TAXEQ3: Software and Documentation (Department of Zoology, Natural History Museum, 2001)
Wiens, J. J. Missing data, incomplete taxa, and phylogenetic accuracy. Syst. Biol. 52, 528–538 (2003)
Wiens, J. J. Incomplete taxa, incomplete characters, and phylogenetic accuracy: is there a missing data problem? J. Vertebr. Paleontol. 23, 297–310 (2003)
Long, J. A., Barwick, R. E. & Campbell, K. S. W. Osteology and functional morphology of the osteolepiform fish Gogonasus andrewsae Long, 1985, from the Upper Devonian Gogo Formation, Western Australia. Rec. West. Austral. Mus. 53, 1–89 (1997)
We thank U. Toom for access to material, E. Mark-Kurik for discussions on stratigraphy and specimen provenance, W. Renema and R. Garwood for assistance with scanning. This work was supported by a Natural Environment Research Council Cohort NE/J500045/1 grant to S.G., the Philip Leverhulme Prize and John Fell Fund, both to M.F., and the European Research Council (ERC) under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement number 311092 to M.D.B.
The authors declare no competing financial interests.
The Life Science Identifiers (LSIDs) urn:lsid:zoobank.org:pub:CFD16449-8A34-4401-9E01-289EA91C2C77 (article), urn:lsid:zoobank.org:act:652A7405-164B-4D58-B5AF-F21EDF552303 (genus), and urn:lsid:zoobank.org:act:3BD31DC4-11E1-4510-A185-B295CC626C07 (species) have been deposited in ZooBank.
Extended data figures and tables
a, Photograph of the holotype (GIT 496-6 (Pi.1384)). b, Original interpretation modified with permission from ref. 6. Reinterpretation of bones italicized in brackets (where applicable). c, Photograph of the referred skull roof (GIT 496-7 (Pi.1383)). d, Original interpretation modified with permission from ref. 6. e, New interpretive drawing of the holotype (GIT 496-6 (Pi.1384)). f, New interpretive drawing of the referred skull roof (GIT 496-7 (Pi.1383)). g, Dialipina salgueiroensis, modified with permission from ref. 13.
Extended Data Figure 2 Scales attributed to Dialipina and scanning electron micrograph images of Janusiscus schultzei gen. et sp. nov.
Scales from the localities of the Kureika Formation along the Sida River, Kotui Basin, Siberia, previously referred to D. markae, in: a, external view (GIT 496-8 (Pi.1384a)), previously figured by Schultze6 (plate 1, figure 3); b, internal view (GIT 496-10 (Pi.1385b)); c, external view (GIT 496-16 (Pi.1387)), ventral margin at upper right. d, e, Gross-scale morphology of D. salgueiroensis and referred species of Dialipina. d, Holotype of D. salgueiroensis, from the Emsian of Canada. Reproduced from ref. 10 (Fig. 3h) (with kind permission from Springer Science and Business Media). e, Holotype of D. markae, from the Lochkovian of the New Siberian Islands. Reproduced from ref. 10 (Fig. 3a) (with kind permission from Springer Science and Business Media). f, Scale from the Kureika Formation, Siberia, referred to D. markae and figured previously (reproduced with permission from figure 4 in ref. 6). This scale is the same specimen as in a6. g, New interpretive drawing of scale in a. h, Broken edge of the skull roof in the holotype (GIT 496-6 (Pi.1384)). The histological structure is not preserved. i, The anterior part of the referred skull roof (GIT 496-7). The dermal bone is poorly preserved, with the bone in the centre of each ridge missing. The histological structure is not preserved. j, The holotype (GIT 496-6 (Pi.1384)) in dorsal view, showing the endoskeletal supraoccipital crest and openings of the endolymphatic ducts. Images in a, b, and c are modified slightly with permission from those by the Institute of Geology at Talinn University of Technology and licensed by CC 3.0 (http://geokogud.info/git/specimen_image/496/496-8.jpg; http://geokogud.info/git/specimen_image/496/496-10.jpg; http://geokogud.info/git/specimen_image/496/496-16.jpg).
Extended Data Figure 3 Semi-transparent rendering of the skull of Janusiscus schultzei gen. et sp. nov. showing osteichthyan-like traits not visible externally.
Scale bar, 5 mm.
a, The actinopterygian Kentuckia deani MCZ 5226; tomographs showing extensive and well-developed endochondral ossification in both the sphenoid (top) and otic (bottom) regions. Bright white objects are voids within spongy endochodral bone that have been diagenetically infilled with dense (probably iron) minerals. b, Janusiscus schultzei gen. et sp. nov. GIT 496-6 (Pi.1384); tomographs showing lack of obvious endochondral ossification in either the sphenoid (top) or otic (bottom) regions. There is also no visual indication of endochondral bone in a break across the ethmoid region of this same specimen.
a, Reconstructed tomographs showing that the thickenings along the lateral margins of the sphenoid region of Janusiscus do not represent artefacts of post-mortem compression. b, The ‘acanthodian’ Ptomacanthus anglicus NHMUK PV P 24919a; a silicone peel of the specimen preserved in negative, dusted with ammonium chloride. Portions of the skull other than the neurocranium are partially masked for clarity. c, The chondrichthyan Doliodus problematicus NBMG 10127/1a; a reconstruction of the neurocranium based on CT data. d, Janusiscus schultzei gen. et sp. nov. GIT 496-6 (Pi.1384); a reconstruction of the neurocranium based on CT data. Red arrows in each panel indicate subcranial ridges.
a, Scanning electron micrograph image into left orbit showing endoskeletal bone and surrounding matrix. b, Image based on X-ray computed microtomography scan with matrix digitally removed. c, Lateral view into right orbit, with matrix digitally removed. d, Anterolateral view into right orbit, with matrix digitally removed. e, Interpretive drawing of the orbit, based on a composite of the left and right orbits of the holotype (GIT 496-6 (Pi.1384)). Arrow points to anterior.
a, Macropetalichthys (redrawn from ref. 18). b, Dicksonosteus (redrawn from ref. 19). c, Buchanosteus (redrawn from ref. 29). d, Entelognathus (redrawn from ref. 4). e, Jagorina (redrawn from ref. 19). f, Ramirosuarezia (redrawn from ref. 9). g, Acanthodes (redrawn from ref. 3). h, Doliodus (redrawn from ref. 17). i, Cladodoides (redrawn from ref. 21). j, Orthacanthus (redrawn from ref. 20). k, Janusiscus. l, ‘Ligulalepis’ (redrawn from ref. 14). m, Mimipiscis (redrawn from ref. 16). n, Psarolepis (redrawn from ref. 25). o, Gogonasus (redrawn from ref. 35).
a, Strict consensus of the 522,936 shortest trees (639 steps) for 78 taxa and 236 equally weighted characters. Digits above nodes indicate Bremer decay indices above 1. Digits below nodes indicate percentage bootstrap support. b, Adams consensus tree of the 522,936 shortest trees for 78 taxa and 236 equally weighted characters.
a, Strict consensus tree of 216 trees with a score of 452.52565 resulting from analysis of characters reweighted according to retention index. b, Strict consensus of the 128,395 shortest trees for 77 taxa and 236 equally weighted characters, with Janusiscus removed from the data set.
About this article
Cite this article
Giles, S., Friedman, M. & Brazeau, M. Osteichthyan-like cranial conditions in an Early Devonian stem gnathostome. Nature 520, 82–85 (2015). https://doi.org/10.1038/nature14065
PLOS ONE (2020)
Vertebrate remains and conodonts in the upper Silurian Hamra and Sundre formations of Gotland, Sweden
The pharynx of the stem-chondrichthyan Ptomacanthus and the early evolution of the gnathostome gill skeleton
Nature Communications (2019)
Fish and Fisheries (2019)