New genus of Cupressaceae from the Upper Cretaceous of Patagonia (Argentina) fills a gap in the evolution of the ovuliferous complex in the family

Abstract

The conifer family Cupressaceae encompasses seven subfamilies. Five of them were once considered to constitute the family Taxodiaceae, later eliminated because of its paraphyletic nature but remaining as an informal category for early‐diverging Cupressaceae lineages. Among the taxodiaceous subfamilies, Athrotaxoideae shows a unique morphology in its ovuliferous complexes (OCs) and a phylogenetically unexplored fossil record. We describe the new genus and species Patagotaxodia lefipanensis, based on OC adpressions associated with leafy branches collected at the Maastrichtian section of the Lefipán Formation (Patagonia, Argentina), and we refer it to Athrotaxoideae. We include Patagotaxodia in total evidence phylogenetic analysis to test its affinity, and we recover it within the subfamilies Athrotaxoideae or Cunninghamioideae. However, we argue that the characters supporting the athrotaxoid affinity are more meaningful in a taxodiaceous systematic context. This placement is also supported by taxon inclusion‐exclusion experiments. We discuss the position of other Cretaceous athrotaxoid records. With basis on the morphological insights provided by the OC morphology of extant and extinct Athrotaxoideae, we study the evolution of the OC morphology in the family in a phylogenetic context and discuss the results in the light of the fossil record of the family. We discuss how and when the different morphologies appeared in the family. Based on phylogenetic, temporal, morphological, and ontogenetic evidence, we conclude that the OC morphology shown by the subfamily Athrotaxoideae is intermediate between two of the most common morphologies within extant and extinct Cupressaceae species, one of which would show adaptative advantages over basal morphologies.

A Flower Bud from the Lower Cretaceous of China

“…Furthermore, all reproductive organs in gymnosperms (fossil and extant) are never known to have more than two layers of papery lateral appendages overlapping each other as in Archaebuda ( Figure 3 a,b). These differences distinguish our fossil from Bennettitales, Ginkgoales, Pentoxylales, Corystopsermales, Peltaspermales, and Gnetales [ 48 , 49 , 50 , 51 , 52 , 53 , 54 ]. Therefore, these gymnosperm groups are not further considered.…”

“…The scaly leaves on the stalk of Archaebuda are adnate to the stalk for most of their length, with triangular pointed tips ( Figure 2 d–f). Among known gymnosperms, scaly leaves of similar morphology are frequently seen in conifers, but so far have never been seen in Bennettitales, Ginkgoales, and Gnetales [ 48 , 49 , 50 , 51 , 52 , 53 , 54 ]. Although cataphylls similar to scaly leaves in Archaebuda are seen in the bottom of some cycad cones, these cataphylls have distal pricks that are lacking in the scaly leaves of Archaebuda ( Figure 2 d–f), and numerous peltate shields or tapering segments of “sporophylls” on the surface of cycad cones [ 55 , 56 , 57 , 58 , 59 ] distinguish cycads from Archaebuda ( Figure 2 a–c).…”

“…Two , although both are stalked, the stalk of Archaebuda is much more slender and elongated (as seen in tulip and poppy flowers) ( Figure 2 a) while the stalks are much more stout in most conifer cones [ 65 , 66 ] (except Amentotaxus , which has an elongated stalk but its integral aril is distinct from the overlapping papery foliar appendages in Archaebuda ) [ 63 ]. Three , a conifer cone usually has multiple lateral appendages helically and vertically arranged around a central axis, and its surface is usually covered with apophyses (except Calocedrus and Juniperus ) [ 52 , 53 , 54 , 63 , 64 , 66 ] ( Figure S1b ), while the surface of Archaebuda is relatively smooth, covered with papery foliar appendages lacking any special features except notched tips ( Figure 2 b and Figure 3 a,b). Indeed, there are exceptional cones in Calocedrus and Juniperus that have a single bract covering almost the whole length of the cones [ 64 , 67 ], and thus demonstrate more similarity to Archaebuda than other conifer cones do.…”

“…The latter case is routine and typical in flower buds of living angiosperms, for example, in Magnolia ( Figure S1a ) and many other angiosperms. Four , the foliar appendages of type I and II in Archaebuda are of distinct sizes and morphologies ( Figure 3 a–d) while lateral appendages (bract–scale–seed complexes) in conifer cones are either uniform or of a gradually transitional appearance ( Figure S1b ) [ 52 , 53 , 54 , 63 , 64 ]. All these differences culminate in the conclusion that Archaebuda is not a conifer cone, and that it represents a flower bud in the Early Cretaceous.…”

The ontogeny of disparity in Cupressaceae seed cones

“…When these laminar scales are borne at a low angle relative to the cone axis, they create an imbricated sheath that covers seeds. Laminar scales are the inferred ancestral state for crown Cupressaceae, although the exact number of shifts to peltate scales is ambiguous (Andruchow‐Colombo et al ., 2022) and lineages often appear to shift back and forth between cone closure strategies.…”