First evidence of ranunculids in Early Cretaceous tropics

Abstract

Early Cretaceous floras containing angiosperms were described from several geographic areas, nearly from the Arctic to the Antarctic, and are crucial to understand their evolution and radiation. However, most of these records come from northern mid-latitudes whereas those of lower paleolatitude areas, such as the Crato Fossil Lagerstätte in NE Brazil, are less studied. Here, we describe from this region of northern Gondwanan origin, two fossil-species of eudicots belonging to a new extinct genus Santaniella gen. nov. Together with several vegetative axes and leaves, anatomically well-preserved fruits with seeds and persistent perianth-like organs allowed us to reconstruct its potential affinities with ranunculids, and presumably Ranunculaceae. Previous records putatively assigned to Ranunculales are all from mid-latitudes, and their first unequivocal occurrence in a low-latitude area supports further the hypothesis of a widespread radiation of the earliest diverging eudicot lineage by this early age.

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

“…In each pair of leaflets, a single primary midvein terminates at each leaflet apex and a secondary vein terminates at the apex of the lateral lobe. A fabric of minor veins consistent with that figured by Gobo et al (2022; Figures 1C, 2D, and 4B), showing elongate areoles, is visible in Figure 4D.…”

“…In total, we scored 31 out of 145 characters as morphological characters (22%). There were several characters that we scored differently than Gobo et al (2022) did for Santaniella . We scored the (1) habit as “unknown” instead of “rhizomatous or scandent” because there is no evidence of a rhizome preserved, nor is preserved evidence of perennial woody growth characteristic of the alternative state, “tree or shrub.” We scored (21) phyllotaxis as “alternate” not “opposite”; (26) stipules as “absent” not “unknown,” (27) axillary squamules as “absent” not “unknown,” (29) blade shape as “obovate” not “obovate” and “ovate,” (30) major venation as “bifurcate‐pinnate” (a new state) not “pinnate,” (33) apex of the blade “simple” rather than “unknown.”…”

“…Following Gobo et al (2022), we scored the morphology of Santaniella using the character set of Kvaček et al (2016); however, our interpretation of preserved character states differs from that of Gobo et al (2022) in several ways. First, both stipules (character 26) and axillary squamules (character 27) appear to be absent, so we scored both as (0) absent.…”

“…When scoring leaf venation categories in dicot angiosperms, secondary veins are considered those veins that have a smaller gauge than the primary veins but a larger gauge than the mesh or fabric of the vein system (tertiary veins) and constitute part of the major structural framework of the leaf or leaflet (Ellis et al 2009). Therefore, we created a new alternative character state “bifurcate‐pinnate (3)” for character 30 to accommodate the apomorphic morphology of Santaniella ; however, we followed Gobo et al (2022) in scoring Santaniella as “(1) some or all leaves lobed or compound” for character 34, leaf dissection, even though we question whether this state is homologous in leaves with very different modes of leaf dissection across angiosperms. We also scored character 33 (apex of the blade) as “simple (0),” not “bilobed (1)” because the bifurcate primary vein or petiole in Santaniella is different from an emarginate or bilobed apex as illustrated in Ellis et al (2009).…”

“…The reproductive structures of Santaniella were also compared with some Portuguese taxa known only by fossil flowers at or near anthesis: Kajanthus lusitanicus Mendes, Grimm, Pais & Friis (Mendes et al, 2014), Paisia pantoporata Friis, Mendes, & Pedersen (Friis et al, 2017), Kenilanthus marylandensis Friis, Pedersen & Crane (Friis et al, 2016), and Teixeiria lusitanica von Balthazar, Pedersen & Friis (Von Balthazar et al, 2005). However, the structures in the specimens of Gobo et al (2022) are well‐developed fruits, making comparison difficult. The additional features present in the specimens described here, including the flower‐like structure (Figure 5A, B) and the immature follicetum (Figure 5C, D), combined with our alternative interpretation of the leaves, highlight the uncertainty about the phylogenetic position of this genus.…”