Athenacrinus n. gen. and other early echinoderm taxa inform crinoid origin and arm evolution

The unproblematic crinoid fossil record begins in the middle Tremadocian; the Middle Cambrian Echmatocrinus is problematic and is not used here as the Crinoidea first appearance.

The cited systematic study treats named early crinoid taxa and explicitly keeps problematic Middle Cambrian Echmatocrinus outside the unproblematic Crinoidea record used by this profile.

The cited early-crinoid systematic material supplies source-bounded fossil locality context, not a global distribution, endemicity or dispersal reconstruction for Crinoidea.

The cited systematic study does not establish class-wide diet, habitat preference, locomotor performance, body-size distribution or guild for Crinoidea; these fields remain explicitly unresolved beyond marine fossil context.

The source documents anatomical characters in named early crinoid taxa, while the profile keeps those observations source-bounded and does not present them as an invariant class-wide character list.