Shell microstructure of the early bivalve Pojetaia and the independent origin of nacre within the Mollusca

New Pojetaia shell sections preserve a laminar inner microstructure comparable to foliated aragonite; the study does not identify undisputed Cambrian nacre and instead tests independent later origins of nacre across molluscan classes.

Pojetaia shell sections document a laminar inner microstructure in one Cambrian bivalve sample; they do not establish the global Bivalvia first appearance or continuous class range.

Pojetaia runnegari shell sections preserve laminar inner fabric comparable to foliated aragonite, while undisputed nacre and broader evolutionary precursors remain interpretive.

The cited Pojetaia shell material comes from probably Botomian Ajax Limestone and lowermost Botomian Erkeket Formation units, supporting a Cambrian Stage 4 study-sample envelope of 514.5–506.5 Ma for this Bivalvia route, not a global class FAD, LAD or continuous duration.

More than fifty Pojetaia specimens from probably Botomian Ajax Limestone and lowermost Botomian Erkeket Formation units support a Cambrian Stage 4 sample envelope of 514.5–506.5 Ma; this is not an exhaustive global genus FAD or LAD.

Vendrasco et al. treat the studied shell material as Pojetaia runnegari; the profile retains that species-level identification while keeping bivalve-wide evolutionary placement conditional.

The documented Pojetaia runnegari shell sample is bounded to the Ajax Limestone and Erkeket Formation of South Australia; these localities do not establish the complete geographic distribution of the genus.

Pojetaia shell sections document mineralized shell microstructure but do not directly preserve feeding, locomotion, body size or ecological guild; any shallow-marine setting is limited to the sampled formations.