Abstract
Planktonic foraminifera are one of the most abundant and diverse protists in the oceans. Their utility as paleo proxies requires rigorous taxonomy and comparison with living and genetically related counterparts. We merge genetic and fossil evidence of “Globigerinoides”, characterized by supplementary apertures on spiral side, in a new approach to trace their “total evidence phylogeny” since their first appearance in the latest Paleogene. Combined fossil and molecular genetic data indicate that this genus, as traditionally understood, is polyphyletic. Both datasets indicate the existence of two distinct lineages that evolved independently. One group includes “Globigerinoides” trilobus and its descendants, the extant “Globigerinoides” sacculifer, Orbulina universa and Sphaeroidinella dehiscens. The second group includes the Globigerinoides ruber clade with the extant G. conglobatus and G. elongatus and ancestors. In molecular phylogenies, the trilobus group is not the sister taxon of the ruber group. The ruber group clusters consistently together with the modern Globoturborotalita rubescens as a sister taxon. The re-analysis of the fossil record indicates that the first “Globigerinoides” in the late Oligocene are ancestral to the trilobus group, whereas the ruber group first appeared at the base of the Miocene with representatives distinct from the trilobus group. Therefore, polyphyly of the genus "Globigerinoides" as currently defined can only be avoided either by broadening the genus concept to include G. rubescens and a large number of fossil species without supplementary apertures, or if the trilobus group is assigned to a separate genus. Since the former is not feasible due to the lack of a clear diagnosis for such a broad genus, we erect a new genus Trilobatus for the trilobus group (type species Globigerina triloba Reuss) and amend Globoturborotalita and Globigerinoides to clarify morphology and wall textures of these genera. In the new concept, Trilobatus n. gen. is paraphyletic and gave rise to the Praeorbulina / Orbulina and Sphaeroidinellopsis / Sphaeroidinella lineages.
Highlights
Foraminifera are eukaryotic unicellular protists with a biomineralized shell representing one of the most diverse groups in the modern oceans [1]
One group shows the aperture placed on the sutures between the three last chambers (Globigerinoides bollii, G. conglobatus, G. immaturus, G. obliquus, G. sacculifer and G. trilobus) and the second group shows the aperture on the sutures between the penultimate and antepenultimate chambers (G. elongatus, G. cyclostomus and G. ruber)
The detailed re-investigation of the fossil record allowed us to trace the appearance of specimens with supplementary apertures on the spiral side
Summary
Foraminifera are eukaryotic unicellular protists with a biomineralized shell representing one of the most diverse groups in the modern oceans [1]. One group shows the aperture placed on the sutures between the three last chambers (Globigerinoides bollii, G. conglobatus, G. immaturus, G. obliquus, G. sacculifer and G. trilobus) and the second group shows the aperture on the sutures between the penultimate and antepenultimate chambers (G. elongatus, G. cyclostomus and G. ruber) These pioneering studies on this group did not take into account wall textures but were based only on morphological features. Kennett and Srinivasan [7] identified one lineage of “Globigerinoides” originating from Globigerina sensu stricto with bulloides-type spinose wall texture typical of Globigerina, and one lineage evolving from Zeaglobigerina woodi with spinose and cancellate wall texture They stated that their observation of several species of “Globigerinoides” evolving from different ancestors demonstrates that the genus is polyphyletic and “artificial” In a joint effort between the PPFWG and the Scientific Committee on Oceanic Research/International Geosphere-Biosphere Programme (SCOR/IGBP) Working Group 138 “Planktonic foraminifera and ocean changes”, a detailed revision of the genus “Globigerinoides” has been carried out, combining fossil and molecular genetic evidence
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