Rxivist logo

Three new Cenomanian conifers from El Chango (Chiapas, Mexico) offer a snapshot of the geographic mosaic of the Mesozoic conifer decline

By Ixchel Gonzalez-Ramirez, Sergio RS Cevallos-Ferriz, Carl Rothfels

Posted 03 Sep 2021
bioRxiv DOI: 10.1101/2021.09.01.458614

Premise of study: El Chango is a recently discovered quarry that contains extremely well preserved fossils. The Cenomanian age of the locality corresponds to a time when the global flora was transitioning from gymnosperm- to angiosperm-dominated, yet conifers predominate in this locality. These fossils thus provide a rare opportunity to understand the replacement of conifers by angiosperms as the dominant group of plants. Methods: We collected material from El Chango in annual expeditions (2010 to 2014). We selected the three most abundant and best preserved conifer morphotypes and conducted a total-evidence (i.e., including molecular and morphological data) phylogenetic analysis of a sample of 72 extant conifer species plus the three fossils. We use these results to inform our taxonomic decisions. Results: We obtained four equally most-parsimonious trees (consistency index = 44.1%, retention index = 78.8%). Despite ambiguous relationships among some extant taxa, the three fossil conifers had the same phylogenetic position in all four most parsimonious trees; we describe these species as new: Sequoiadendron helicalancifolium sp. nov. (Cupressaceae), and Microcachrys rhomboidea sp. nov. and Dacrydium bifoliosus sp. nov (Podocarpaceae). The ecosystem is interpreted as a coastal humid mixed forest. Conclusions: Our findings contribute to the understanding of Cenomanian equatorialregions, and support the hypothesis of a geographically and ecologically structured rise of angiosperms, with conifers remaining dominant in brackish-water and angiosperms becoming dominant in freshwater-ecosystems. These fossils fill in gaps in the evolutionary history of lineages like Microcachrys, which we demonstrate occurred in the Northern hemisphere before becoming restricted to its current range (Tasmania).

Download data

  • Downloaded 188 times
  • Download rankings, all-time:
    • Site-wide: 150,750
    • In paleontology: 187
  • Year to date:
    • Site-wide: 52,409
  • Since beginning of last month:
    • Site-wide: 15,221

Altmetric data

Downloads over time

Distribution of downloads per paper, site-wide