Cupressaceous woods in Jurassic geothermal deposits of the Deseado Massif, Patagonia, Argentina with evidence of nurse-log growth strategy

Abstract

The fossil wood record of Cupressaceae is extensive across the Mesozoic and Cenozoic, with a wide distribution in both hemispheres. However, the affinities of some fossil woods are uncertain due to incomplete descriptions, preservation issues, and anatomical traits of ambiguous interpretation. This study describes the anatomy and discusses the affinities of well-preserved Jurassic silicified woods. Samples were collected from geothermal deposits at the ‘Claudia’ locality in the Deseado Massif, Santa Cruz Province, Southern Patagonia, Argentina. The material corresponds to pycnoxylic and homoxylic secondary xylem characterized by a distinctive combination of traits, including mixed pitting on tracheids, cupressoid cross-field pits arranged in a cupressoid pattern, and abundant diffuse axial parenchyma. These characteristics are compatible with Protocupressinoxylon and suggest affinities with Cupressaceae. Additionally, chert blocks preserving fragments of these woods contain vegetative organs (e.g., leaves, roots) with affinities with this family, supporting the suggested affiliation. The studied woods are assigned to the open nomenclature Protocupressinoxylon-type wood, following the IAPT Fossil Committee's recommendations concerning the nomenclature problems of this name, while acknowledging the extensive historical and current use of it. Nurse logs are also recorded based on the presence of several stems and rootlets anchored to some of the studied woods, which expands the fossil record of this growth strategy.