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Amphibious stem-insect sheds light on colonization of land

Nature (2026) Cite this article

Abstract

Molecular clock analyses1,2,3, trace fossils4, exceptionally preserved amphibious stem-myriapods5 and sea scorpions6 have recently challenged classical assumptions about the timeline of the animal colonization of land7, suggesting that terrestrial ecosystems may date back as far as the Cambrian period. However, the early evolutionary history of the most successful clade of animals, the insects, has remained elusive, as the period of their early diversification constrained by time divergence estimates falls within the notorious ‘hexapod gap’ in the fossil record8. Here we describe Chosha praecursor gen. et sp. nov. from the Carboniferous period (Late Mississippian epoch, approximately 324 million years ago) Tesnus Formation in Texas. Cross-polarized light imaging reveals that C. praecursor possesses insect apomorphies including an ovipositor and a terminal filament but differs from crown-group insects, most notably with respect to the presence of multisegmented abdominal legs with paddle-like modifications. Our phylogenetic reconstruction recovers C. praecursor as a hexapod, strongly favouring its placement as an early-diverging insect. A revision of three other enigmatic hexapod fossils, the Devonian period Leverhulmia and two undescribed Carboniferous fossils from the Mazon Creek Lagerstätte, demonstrates diverse body organization in Palaeozoic wingless insects. Together, these stem-group fossils represent the earliest uncontested insects and partly reconcile the incongruence between molecular clock estimates and the fossil record. The unusual abdominal gill-like appendages of Chosha suggest a semiaquatic mode of life in at least some stem-insects and revise our understanding of the assembly of insect morphological organization.

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Fig. 1: Anatomy of the stem-group insect C. praecursor from the Carboniferous Tesnus Formation, Texas.
Fig. 2: Morphological details of C. praecursor.
Fig. 3: Anatomical details of stem-group insects and extant wingless insects.
Fig. 4: Evolution of hexapods and life reconstruction of C. praecursor.

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Data availability

All data analysed in this paper, including the morphological character matrix and all full analysis files, are available at Zenodo (https://doi.org/10.5281/zenodo.19565988)75. Character descriptions and character matrix are also available in the Supplementary Information. The paper has been registered at ZooBank (LSID, urn:lsid:zoobank.org:pub:F392D634-11C0-423B-AD17-C847C6B9C8C7).

Code availability

The datasets and the commands necessary to reproduce phylogenetic analyses are included as R and NEXUS formatted files available at Zenodo (https://doi.org/10.5281/zenodo.19565988)75.

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Acknowledgements

We are grateful to the pioneering work by Michael J. Emerson (1954–1990), who co-discovered the holotype of C. praecursor. E.T. thanks T. A. Deméré, K. McComas and K. Randall (San Diego Natural History Museum, California, USA) for a warm welcome in San Diego and access to the palaeontological collections. We also thank S. Rufolo (Canadian Museum of Nature) for the loan of museum specimens. E.T. is further indebted to S. R. Fayers for hosting his visit to the Rhynie chert collection at the University of Aberdeen and sharing images of Leverhulmia, and to N. Butterfield for support with obtaining museum loans.

Funding

C.C. was supported by the National Key Research and Development Program of China (2024YFF0807601) and the National Natural Science Foundation of China (42288201). E.T. was supported by the C-CLEAR Doctoral Training Programme and Harding Distinguished Postgraduate Scholars Programme. J.L-F. was supported by grants CNS2022-135805 and PID2022-137753NA-I00 funded by MICIU/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR.

Author information

Authors and Affiliations

  1. Department of Earth Sciences, University of Cambridge, Cambridge, UK

    Erik Tihelka

  2. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China

    Erik Tihelka & Chenyang Cai

  3. Geoscience Department, Utah State University, Logan, UT, USA

    Carlos Vásquez

  4. Division of Invertebrate Zoology, American Museum of Natural History, New York, NY, USA

    Michael S. Engel

  5. Department of Invertebrate Paleontology, Burke Museum of Natural History, University of Washington, Seattle, WA, USA

    Frederick R. Schram

  6. Department de Genètica, Microbiologia i Estadística & Institut de Recerca de la Biodiversitat (IRBio), Universitat de Barcelona, Barcelona, Spain

    Jesus Lozano-Fernandez

  7. Palaeobiology Research Group, School of Earth Sciences, University of Bristol, Bristol, UK

    Chenyang Cai

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  1. Erik Tihelka
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  2. Carlos Vásquez
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  3. Michael S. Engel
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  4. Frederick R. Schram
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Contributions

E.T., C.V. and C.C. conceived and designed the study. E.T. conducted phylogenetic analyses. E.T. drafted the manuscript, with contributions from C.V., M.S.E., A.N., F.R.S., J.L.-F. and C.C. All authors participated in morphological studies and interpretation.

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Correspondence to Erik Tihelka or Chenyang Cai.

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Nature thanks Dany Azar, Ariel Chipman, Joachim Haug, André Nel and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Fig. 1 Morphological details of Chosha praecursor under low-angle reflected light (a, b, d–i) and inverted, cross-polarized light (c).

a, Habitus view. b, Head with antennae. c, Thoracic legs. d–e, Antenna. f, Posterior abdominal legs. g, Abdominal apex. h–i, Detail of paddle-like posterior abdominal legs. Abbreviations: AI–X, abdominal terga I–X; ac, abdominal cerci; an, antenna; c, coxa; f, femur; hd, head; mp, maxillary palp; op, ovipositor; pe, pedicel; pl, paddle-like modifications of abdominal legs; sc, scape; ta, tarsus; tf, terminal filament; ti, tibia; TI–III, thoracic terga I–III; tr, trochanter. Scale bars: 1 mm (a), 200 μm (b, c, f), 100 μm (d, e), 50 μm (f).

Extended Data Fig. 2 Morphological details of Chosha praecursor, colour coded.

a–b, Abdominal apex. c–d, Head with antennae. e–f, Thoracic legs. Abbreviations: ac, accessory filament; c, coxa; f, flagellum; hd, head; mp, maxillary palp; op, ovipositor; pe, pedicel; sc, scape; ta, tarsus; tf, terminal filament; ti, tibia; TI–III, thoracic terga I–III; tr, trochanter. Scale bars: 200 μm (c–f), 100 μm (a, b).

Extended Data Fig. 3 Morphological details of an undescribed hexapod from Carboniferous of Mazon Creek, Illinois (CMNIF 2342).

a, Habitus view, part. b, Habitus view, counterpart. c, Head, part. d, Head, counterpart. e, Thoracic and anterior abdominal legs, part. f, Thoracic and anterior abdominal legs, counterpart. g, Detail of walking abdominal legs. h, Abdominal apex and appendages Abbreviations: AI–X, abdominal terga I–X; al, abdominal leg; c, coxa; cl, paired claw; e, eye; fe, femur; mta, mesotarsus; pf, profemur; ti, tibia; TI–III, thoracic terga I–III; tr, trochanter. Scale bars: 5 mm (a, b), 2 mm (c–h).

Extended Data Fig. 4 Morphological details of an undescribed hexapod from Carboniferous of Mazon Creek, Illinois (CMNIF 790).

a, Habitus view. b, Head. c, Antenna. d, Abdomen with poorly preserved appendages. e, Detail of terminal filament. f, Abdominal apex with terminal filament. Abbreviations: aa, abdominal appendage; e, eye; f, flagellum; mp, maxillary palp; p, pedicel; pf, profemur; sc, scape; tf, terminal filament. Scale bars: 5 mm (a), 2 mm (b, d–f), 1 mm (c).

Extended Data Fig. 5 Relationships among early-diverging hexapods recovered in (a) parsimony and (b) Bayesian settings, full dataset, with constraints.

Based on a matrix of 58 characters for 23 taxa, with character changes mapped. For clarity, only characters uniting clades with more than one member are shown. a, Strict consensus of 45 most parsimonious trees. Consistency index = 0.595, retention index = 0.755, tree length = 174. b, Majority-rule consensus tree recovered under the Mkv + Γ model in MrBayes.

Extended Data Fig. 6 Relationships among early-diverging hexapods recovered in (a) parsimony and (b) Bayesian settings, full dataset, without constraints.

Based on a matrix of 58 characters for 23 taxa, with character changes mapped. For clarity, only characters uniting clades with more than one members are shown. a, Strict consensus of 41 most parsimonious trees. Consistency index = 0.621, retention index = 0.781, tree length = 164. b, Majority-rule consensus tree recovered under the Mkv + Γ model in MrBayes.

Extended Data Fig. 7 Relationships among early-diverging hexapods recovered in (a) parsimony and (b) Bayesian settings, reduced dataset, with constraints.

Based on a matrix of 58 characters for 17 taxa, with character changes mapped. For clarity, only characters uniting clades with more than one members are shown. a, Strict consensus of 31 most parsimonious trees. Consistency index = 0.764, retention index = 0.805, tree length = 115. b, Majority-rule consensus tree recovered under the Mkv + Γ model in MrBayes.

Extended Data Fig. 8 Relationships among early-diverging hexapods recovered in (a) parsimony and (b) Bayesian settings, reduced dataset, without constraints.

Based on a matrix of 58 characters for 17 taxa, with character changes mapped. For clarity, only characters uniting clades with more than one members are shown. a, Strict consensus of 31 most parsimonious trees. Consistency index = 0.770, retention index = 0.812, tree length = 113. b, Majority-rule consensus tree recovered under the Mkv + Γ model in MrBayes.

Extended Data Fig. 9 Three alternative topological hypotheses analysed in the present study: Chosha as sister to crown-Insecta, crown-Hexapoda, or as a non-hexapod close to Remipedia.

Shimodaira-Hasegawa (SH) topology test results and p-values based on full constrained backbone dataset under the Mkv model in a maximum likelihood framework. The SH test is a one-sided test that intrinsically adjusts for multiple comparisons (selection bias) across all tested candidate topologies by evaluating their likelihoods under the least favourable configuration. Chosha as sister to crown-Insecta (p = 0.6367), or crown-Hexapoda (p = 0.1945) could not be rejected, while three test topologies with Chosha as a non-hexapod close to Remipedia (p = 0.0259, 0.0153, 0.0146) could. Highlighted clades represent total-group Hexapoda and total-group Insecta. Silhouettes created by T. M. Keesey and reproduced from Phylopic, under a CC0 1.0 licence.

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Tihelka, E., Vásquez, C., Engel, M.S. et al. Amphibious stem-insect sheds light on colonization of land. Nature (2026). https://doi.org/10.1038/s41586-026-10961-2

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