Navigate named Elpistostege, Tiktaalik, Acanthostega and Ichthyostega evidence while reading tracks, bodies, internal fin skeletons, digits and mobility models as different evidence—not as a ladder of direct ancestors.
Each step names its evidence claims, with references below. Interactive Explorer states are available in the full application; the narrative remains an editorial synthesis.
A synthesis separates digit-bearing limbs, locomotor changes and full terrestriality. Its broad window organizes unlike evidence; it is not one event or an ancestor-to-descendant sequence.
A transitional character combination can illuminate evolution without making its bearer the direct ancestor of another named fossil.
claim:event:tetrapods-on-landEifelian Zachełmie surfaces preserve quadrupedal tracks and digit impressions. A trace constrains a trackmaker and gait, but cannot supply a named body taxon, complete anatomy or direct ancestor.
The displayed interval is the current Eifelian stage window, not an error bar on one footprint.
claim:event:zachelmie-digit-trackwaysTiktaalik combines scales, fin rays and fish-like jaws with a mobile neck, modified ear region and robust ribs. Anatomy and setting make shallow-water hypotheses testable, not observed terrestrial behaviour.
Intermediate morphology is not evidence that the specimen lies on a direct ancestral line.
claim:event:tiktaalik-body-plan-mosaicTiktaalik's pectoral fin has a robust internal scaffold and wrist-like joints that could transmit load, but fin rays remain and no free digits or track are preserved.
Joint geometry supports a functional inference; it does not replay a witnessed gait.
claim:event:tiktaalik-pectoral-finCT imaging of MHNM 06-2067 reveals branched carpals and distal rows interpreted as digits or putative digits. Lepidotrichia still make the appendage a fin.
Digit homology and sister-group placement are analyses, not labels fixed forever by the specimen.
claim:event:elpistostege-digit-bearing-finAcanthostega's described forelimb has eight digits. Together with seven-digit Ichthyostega and six-digit Tulerpeton, it rejects a fixed primitive five-digit template without proving a terrestrial gait.
Digit count, appendage function and habitat are separate claims.
claim:event:acanthostega-eight-digit-limbThree-dimensional joint reconstruction found that Ichthyostega lacked rotations needed for a typical lateral-sequence walk. It may represent restricted early mobility or a specialization unique to this animal.
Feasible joint motion is a model constraint, not direct observation of behaviour and not a template for every Devonian tetrapod.
claim:event:ichthyostega-joint-mobility