The Conifer Frenelopsis ramosissima (Cheirolepidiaceae) in the Lower Cretaceous of Texas: Systematic, Biogeographical, and Paleoecological Implications

Until now, our knowledge of the Lower Cretaceous conifer Frenelopsis ramosissima was based exclusively on branches from a few sites in the Potomac Group of eastern Virginia and Maryland. Affinities with the important Mesozoic family Cheirolepidiaceae have been assumed despite the historical absence of diagnostic attached or associated Classopollis‐producing pollen cones. This plant has been reconstructed as a small, stem‐succulent shrub that inhabited diverse, mesic plant communities. Here, we present a reconsideration of F. ramosissima based on new fossils from the Jones Ranch sauropod dinosaur quarry site (Twin Mountains Formation) near Glen Rose, Texas, which represents a ca. 2100‐km range extension for this conifer. Compelling support for assignment to the Cheirolepidiaceae is provided by the first account of associated pollen cones with in situ Classopollis‐type pollen. Features of associated remains are consistent with this determination, including ovulate cones with persistent bracts, cone scales with a probable epimatium, and wood with mixed pitting on the tracheid radial walls. Our analysis of the new Texas fossils refutes or seriously challenges many widely accepted hypotheses regarding the biogeography, structure, and paleoecology of F. ramosissima. For example, this plant can no longer be considered a Potomac Group–endemic taxon. Furthermore, the taphonomy and sedimentology of the Jones Ranch locality indicate a monospecific stand of F. ramosissima plants from a semiarid climate rather than a diverse mesic community, as indicated by the Potomac Group occurrences. Finally, associated logs indicate that F. ramosissima was a large tree (at least 22.4 m tall, extrapolated from maximum trunk diameter) with abundant wood in the trunk and lower branch orders.