Urokodia sheds light on the origin of chelicerae and book gills of Chelicerata

Micro-CT reconstructions of Chengjiang Urokodia aequalis reveal pincer-like short great appendages, overlapping exite flaps and a seven-segmented head; their interpretation as intermediates toward chelicerae and book gills and the upper stem-chelicerate placement are morphology-matrix results.

Urokodia aequalis was recovered on the upper chelicerate stem in the cited morphology matrix; navigation placement does not assert direct ancestry.

The profile is limited to Chengjiang material from Yunnan and does not establish a global Urokodia distribution.

Appendage form permits bounded feeding and locomotor hypotheses, but diet, performance and habitual behaviour are not preserved.

Micro-CT reveals pincer-like short great appendages, overlapping exite flaps and a seven-segmented head interpretation.

The 519–518 Ma envelope is a Chengjiang sample interval, not a stem-chelicerate origin date or global species duration.

The Chelicerata route is source-linked here only to the Urokodia aequalis micro-CT character sample and its morphology-matrix placement. That disputed upper-stem interpretation is not a crown-chelicerate origin, global FAD, direct ancestor, or complete chelicerate range.

The 519–500.5 Ma stem-chelicerate evidence route links the Chengjiang Urokodia and Wheeler Megachelicerax samples and does not represent one lineage's temporal duration.