The oldest complete jawed vertebrates from the early Silurian of China

Xiushanosteus mirabilis holotype IVPP V300001 and referred specimens IVPP V300002–V300021 from the middle-to-late Telychian Huixingshao Formation at approximately 436 Ma preserve an approximately 30 mm placoderm-grade stem-gnathostome body and a mosaic skull roof; this is articulated specimen evidence, not a direct ancestor, global dominance estimate or global jawed-vertebrate FAD.

The sole near-complete Shenacanthus vermiformis holotype IVPP V300000 from the approximately 436 Ma Huixingshao Formation combines minute scales, absence of facial dermal bones and a chondrichthyan-like posterior branchial region with large thoracic armour plates; it is total-group chondrichthyan evidence, not a crown-shark diagnosis or a global Chondrichthyes FAD.

Shenacanthus vermiformis is known from the sole near-complete holotype IVPP V300000 and was placed within total-group Chondrichthyes, with exact stem position analysis-sensitive.

IVPP V300000 comes from the Telychian Huixingshao Formation at Yongdong, Xiushan, Chongqing, China; no wider distribution is inferred.

The body is aquatic in form, but the sole fossil does not directly establish diet, habitat preference, swimming performance or feeding guild.

IVPP V300000 combines minute scales and a chondrichthyan-like posterior branchial region with unexpectedly large thoracic armour plates.

The displayed approximately 436 Ma point represents the Huixingshao Formation holotype and is not a global total-group or crown-chondrichthyan FAD.

The Placodermi historical-grade display uses the approximately 436 Ma Huixingshao Formation Xiushanosteus sample as its evidence-linked older anchor; the 358.9 Ma younger edge remains a rounded composite, and neither endpoint is asserted as a global first or last appearance or a direct-ancestor interval.

The Stem-chondrichthyan evidence route navigation entity is source-linked only to the named specimen, dataset and analysis dossiers already cited by its range ledger. Its displayed span is a study-bounded route or sample envelope, not a biological taxon, ancestor sequence, global FAD/LAD or exact origin interval.

Xiushanosteus mirabilis is a placoderm-grade jawed stem gnathostome represented by articulated material; its character mosaic does not establish direct ancestry or resolve historical Placodermi as a natural clade.

Xiushanosteus is documented from the Huixingshao Formation in Xiushan County, Chongqing, South China; the evidence records that locality rather than a global distribution.

The articulated body supplies depositional and anatomical context, but diet, life habitat, trophic guild and measured swimming performance remain unresolved.

Holotype IVPP V300001 and referred IVPP V300002–V300021 preserve approximately 30 mm articulated bodies with cranial armour and a mosaic skull-roof character combination.

The displayed 438.6–432.9 Ma interval is the Telychian time-scale envelope for the Huixingshao Formation Xiushanosteus sample and is not a global genus range, FAD, LAD or gnathostome origin.