The last Patagonian cycad,Austrozamiastockeyigen. et sp. nov., early Eocene of Laguna del Hunco, Chubut, Argentina

Abstract

Abstract:The cycads pose classic problems in evolutionary biogeography, owing to their far-flung extant distributions and the sparse fossil records of living genera. A noteworthy example is Tribe Encephalarteae of Family Zamiaceae, today consisting of Encephalartos (Africa) and the Australian genera Lepidozamia and Macrozamia. Numerous petrified trunks of Encephalarteae described from the Cretaceous of Patagonia, Antarctica, and India indicate far larger past distributions across Gondwana and subsequent extinctions. The only fossils close to the current range are Paleogene leaf fragments from Australia assigned to Lepidozamia and Macrozamia. Here, we report a large frond piece and several isolated leaflets of a compressed cycad, along with an associated spiny petiole, from the late-Gondwanan, 52.2 Ma Laguna del Hunco flora of Patagonia, Argentina. Austrozamia stockeyi gen. et sp. nov., has the novel combination of an Encephalartos-type leaf and Lepidozamia-type cuticle. The Australian Lepidozamia fossils, widely used for molecular clock calibrations, could also represent an extinct genus. Austrozamia stockeyi demonstrates survival of the Encephalarteae in Patagonia and presumably across Gondwana until its terminal phase, adding a striking new component to the growing list of South American plant extinctions associated with Antarctic separation and related climate changes.

A review of the Cenozoic fossil record of the genus Zamia L. (Zamiaceae, Cycadales) with recognition of a new species from the late Eocene of Panama - evolution and biogeographic inferences

“…In the other three genera epidermal cells are not of the linear type as in the fossil and anticlinal cell walls show a more pronounced concave pattern. In Encephalartos and Lepidozamia the long axis of epidermal cells is frequently oblique to the veins (this is also well observable in the extinct genus Austrozamia, assigned to the Encephalartoideae, Wilf et al 2016), cells of triangular shape occur, and epidermal cells are usually non-elongate (l/w less than 5-7) displaying a distinct concave pattern (Greguss 1968, Hill 1980. In Macrozamia anticlinal walls of epidermal cells display a concave pattern, stomata are parallel to the long axis of leaflet, and encircling/subsidiary cells give an angular (pentagonal, hexagonal) outline of the stomatal pore (see Greguss 1968, Carpenter 1991, unlike our fossil.…”

Eobowenia gen. nov. from the Early Cretaceous of Patagonia: indication for an early divergence of Bowenia?

“…Such phylogenetic evidence, which is lacking for many fossil cycads that have been linked with extant groups, such as Restrepophyllum [38] and Austrozamia [25], as well as for the many fossil leaves assigned to extant genera [21–24, 26–28], make Eobowenia a reliably placed cycad fossil foliage.…”

“…Bowenia would indeed represent yet another case of eastern survival [65]. Even if we know that some cycads persisted in southern South America until the Palaeocene [25], the identification of the precise timing of the extinction of Eobowenia in South America is hindered by the potential rarity of this fossil leaf type in the record. However, it is clear that this fossil represents another important clue to the biogeography of Gondwana coming from Patagonia [20].…”

“…Records considered to be reliable here include leaves and cuticle fragments assigned to Cycas from the Eocene of China [21], Macrozamia from the Oligocene of Australia [22], Lepidozamia from the Eocene of Australia ([23, 24], but see [25]), and Ceratozamia from the Oligocene–Miocene of Central Europe [26–28]. …”

The fossil flip‐leaves (Retrophyllum, Podocarpaceae) of southern South America

“…Previous informal references to what is here described as R. spiralifolium include Podocarpaceae leaf morphotypes TY008 and TY176 of Wilf et al (2005) and mentions of an undescribed Retrophyllum species in several subsequent articles (Wilf et al, 2009, 2013, 2014, 2016; Wilf, 2012; Merkhofer et al, 2015; Quiroga et al, 2016). The holotype was cited informally under field number LH6‐112 by Wilf et al (2005: p. A6); paratype MPEF‐Pb 8917 was referenced informally under field number LH13‐1006 by Wilf et al (2005: p. A9).…”