Is Santaniella a ranunculid? Reassessment of this enigmatic fossil angiosperm from the Lower Cretaceous (Aptian, Crato Konservat‐Lagerstätte, Brazil) provides a new interpretation

Abstract

Premise: The Lower Cretaceous Crato Konservat-Lagerstätte (CKL) preserves a rich flora that includes early angiosperms from northern Gondwana. From this area, the recently described fossil genus Santaniella was interpreted as a ranunculid (presumably Ranunculaceae). However, based on our examination of an additional specimen and a new phylogenetic analysis, we offer an alternative interpretation. Methods: The new fossil was collected from an active quarry for paving stones in the state of Ceará, northeastern Brazil. We assessed support for alternative phylogenetic hypotheses using a combined analysis of morphological data and DNA sequence data using Bayesian inference. We used a consensus network to visualize the posterior distribution of trees, and we used RoguePlot to illustrate the support for alternative positions on a scaffold tree. Results: The new material includes a flower-like structure not present in the original material and also includes follicles preserved at early stages of development. The flower-like structure is a compact terminal cluster of elliptical sterile laminar organs surrounding internal filamentous structures that occur on flexuous axes. Phylogenetic analyses did not support the fossil placement among eudicots. Instead, Santaniella appears to belong in the magnoliid clade. Conclusions: The presence of seeds in a marginal-linear placentation and enclosed in a follicle supports the fossil as an angiosperm. However, even though most characters are clearly recognizable, its combination of characters does not provide strong support for a close relationship to any extant order of flowering plants. Its position in the magnoliid clade is intriguing and, based on plicate carpels, it is definitely a mesangiosperm.

Embracing uncertainty: The way forward in plant fossil phylogenetics

“…This method works on dated phylogenies as well, but it can only illustrate the distribution of a single taxon per graph. RoguePlots are rather simple to use, being implemented in an R package (https://github.com/seraklop/RoguePlots/; for a short tutorial, see https://mariocoiro.blog/2020/12/02/how-to-represent-uncertainty-in-phylogenies-rogueplots-to-the-rescue/), and have been successfully applied to plant analyses (Coiro et al, 2020, 2023; López‐Martínez et al, 2023; Pessoa et al, 2023).…”

A cornucopia of diversity—Ranunculales as a model lineage

“…However, the recent description of Santaniella lobata based on fruits and stems from the Cretaceous (Barremian/Aptian, ~125 Ma) of Brazil related to Ranunculales ( Gobo et al , 2022 ) along with the leaf with unknown affinity but close to Ranunculales in shape, named Baderadea pinnatissecta described from the same region ( Pessoa et al , 2021 ), could indicate a Lower Cretaceous origin of the Ranunculales in Gondwana rather than Laurasia. Nevertheless, additional data from S. lobata indicate that this fossil belongs to angiosperms without certainty about the order ( Pessoa et al , 2023 ).…”