Acanthostega
Reference illustration

Acanthostega

Porro LB, Rayfield EJ, Clack JA (2015) Descriptive Anatomy and Three-Dimensional Reconstruction of the Skull of the Early Tetrapod Acanthostega gunnari Jarvik, 1952. PLoS ONE 10(3): e0118882. doi:10.1371/journal.pone.0118882 · CC BY 4.0 · Image source

Image associated with the exact linked encyclopedia article; consult credited file description for its interpretation.

Overview

Acanthostega combined limbs bearing digits with several features associated with life in water. Its famous hands show that the earliest well-known tetrapod anatomy did not simply reproduce the five-digit pattern common today. The animal is therefore important for understanding how limbs emerged before effective terrestrial walking became widespread.

Four humeri showed size did not track ossification. Six growth marks imply years only if annual. Undiminished growth supported juvenile status; delayed ossification suggested aquatic juveniles. Adult size remains unknown.

Digit-bearing limbsAquatic adaptationsBone growth histology
01

Origins & earliest records

Famennian Britta Dal Formation, East Greenland; 365 Ma is representative.

02

Evidence & interpretation

Synchrotron histology supports growth inferences, not direct behavioural observation.

Selected bibliography

Documented works and useful reading. This is not a list of every appearance.

  1. 01

    Life history of the stem tetrapod Acanthostega revealed by synchrotron microtomography

    Sophie Sanchez, Paul Tafforeau, Jennifer A. Clack and Per E. Ahlberg · 2016

    Nature 537:408–411; author manuscript.

Family, evolution & connections

Selected early tetrapod relatives in Swartz’s 2012 morphology analysis

Figure 4 subtree beginning at Tinirau, with the sampled Carboniferous groups collapsed into one terminal; basal fish groups are omitted.

  • Selected Tinirau and elpistostegalian subtree
    • Tinirau
    • Remaining sampled branches
      • Platycephalichthys
      • Sampled elpistostegalians
        • Panderichthys
        • Other sampled elpistostegalians
          • Tiktaalik / Elpistostege pair
          • Remaining sampled digited taxa
            • Elginerpeton
            • Ventastega and remaining sampled taxa
              • Ventastega
              • Acanthostega and remaining sampled taxa
                • Acanthostega
                • Ichthyostega and sampled Carboniferous groups
                  • Ichthyostega
                  • Sampled Carboniferous groups (collapsed)

Single most-parsimonious tree from 46 taxa and 204 equally weighted, unordered morphological characters; Bayesian analysis supplies additional node support. This transfers branching only, omitting geological ages, ghost-range calibration and character transformations. The Tiktaalik / Elpistostege pair has Bremer support 1; other short supported branches are also study-specific. Fossil tips are not arranged as direct ancestors of the subsequent tips. The collapsed Carboniferous terminal contains multiple sampled groups, not one organism.

Swartz (2012), Figure 4 and morphological phylogenetic analysis

Taxonomic classification

A hierarchy of classified groups, not a chain of direct ancestors.

  1. kingdomAnimalia
  2. phylumChordata
  3. familyAcanthostegidae
  4. genusAcanthostega
Documented · evolutionary relationship

Ichthyostega

Figure 4 places Acanthostega as sister to the sampled Ichthyostega plus Carboniferous branches. The diagram treats them as distinct tips and does not identify Acanthostega as Ichthyostega’s direct ancestor.

Swartz (2012), Figure 4 and morphological phylogenetic analysis

Located primary passages

Specific passages supporting details in this entry, grouped by their published witness.

Encyclopedia background

An additional attributed reference, separate from the editorial profile above.

Read the open encyclopedia overview

Acanthostega, from Ancient Greek ἄκανθα (ákantha), meaning "spine", and στέγη (stégē), meaning "roof", is an extinct genus of stem-tetrapod, among the first vertebrate animals to have recognizable limbs. It appeared in the late Devonian period (Famennian age) about 365 million years ago, and was anatomically intermediate between lobe-finned fishes and those that were able to come onto land.

Text from Wikipedia contributors, “Acanthostega”. CC BY-SA 4.0. Extracted introduction; formatting changed. Retrieved 5 October 2026. The source article may have changed since retrieval.

References

Sources supporting this profile. Linked pages have their own scope and editorial standards.

  1. ResearchLife history of the stem tetrapod Acanthostega revealed by synchrotron microtomographyResearch access: 2026-10-05

Image credits

Reference illustration

Acanthostega

Porro LB, Rayfield EJ, Clack JA (2015) Descriptive Anatomy and Three-Dimensional Reconstruction of the Skull of the Early Tetrapod Acanthostega gunnari Jarvik, 1952. PLoS ONE 10(3): e0118882. doi:10.1371/journal.pone.0118882 · CC BY 4.0 · Image source

Image associated with the exact linked encyclopedia article; consult credited file description for its interpretation.

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