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

PremiseThe Lower Cretaceous Crato Konservat-Lagerstatte (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. MethodsThe new fossil was collected from an active quarry for paving stones in the state of Ceara, 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. ResultsThe 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. ConclusionsThe 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.

Automated summary

This study provides a new interpretation of a fossil genus, Santaniella, as belonging to the magnoliid clade instead of the presumed Ranunculaceae. The researchers used a new fossil specimen and conducted a phylogenetic analysis using morphological and DNA sequence data. The results indicate that Santaniella is an angiosperm but its combination of characters does not strongly support a close relationship to any extant order of flowering plants.