Follow five evidence boundaries that keep isolated skeleton, contested affinity, articulated bodies and modelled crown time distinct.
Each step names its evidence claims, with references below. Interactive Explorer states are available in the full application; the narrative remains an editorial synthesis.
Cambrian Stage 3 stereom ossicles directly record echinoderm skeletal microstructure, but isolated elements do not reveal one complete body plan or a phylum origin date.
The source-reported numerical calibration is approximate and older than the atlas's current chart.
claim:taxon:echinodermata:earliest-stereom-ossiclesYanjiahella was recovered as a stem echinoderm in one analysis, but a published reanalysis found no unambiguous echinoderm synapomorphy or stereom, so it does not set the range.
Competing matrices are evidence of disagreement, not permission to select a convenient endpoint.
claim:taxon:echinodermata:yanjiahella-affinityBy about 510 Ma, articulated echinoderms preserve at least four markedly differentiated body plans, supplying a more robust body-fossil datum than isolated stereom.
A robust sampled fauna is still not the first evolutionary instant of Echinodermata.
claim:taxon:echinodermata:articulated-faunas-510maThe unproblematic crinoid record begins in the middle Tremadocian, while the oldest articulated holothurian used here is late Darriwilian; each class keeps its own specimen and stratigraphic boundary.
Different preservation histories prevent one class record from standing in for every echinoderm class.
claim:taxon:crinoidea:tremadocian-record · claim:taxon:holothuroidea:darriwilian-articulated-recordDarriwilian bothriocidaroid plates anchor total-group Echinoidea, whereas phylogenomic analyses place the crown near the Carboniferous–Permian transition under model-dependent clocks.
A fossil occurrence and a modelled divergence answer different questions and remain separate in the atlas.
claim:taxon:echinoidea:ordovician-stem-record · claim:taxon:echinoidea:crown-origin