9:30 AM - 9:45 AM
[BPT03-03] Extinction and Recovery of planktic foraminiferal assemblages through the K/Pg bounday
Keywords:K/Pg boundary, Planktic foraminifers, Extinction, Recoverty
Planktic foraminifers, that arose in the late Jurassic, have experienced two major extinction events at the Cretaceous/Paleogene (K/Pg) boundary and the Eocene/Oligocene boundary. After those two events, their morphological diversity was reestablished, which used to be considered as the archetypal examples of phenotypic recurrent evolution. However recent advances in molecular phylogeny revealed that each family or superfamily of modern planktics evolved from independent benthic taxa, indicating that apparent morphological recurrence in planktic foraminiferal evolutional history has no genetic background. This finding implies that functional and/or ecological selections are crucial for producing the apparent recurrent evolution.
To understand the functional and/or ecological evolution, we examined the diversity of planktic foraminifers through the K/Pg boundary extinction event. The K/Pg boundary sequence was recovered from Site U1407, IODP Exp. 342 at the Newfoundland Ridge. The sequence is mostly composed of calcareous ooze with abundant well-preserved foraminiferal fossils. However, unfortunately, the section from approximately 69 through 65Ma is missing by the hiatus. We have analyzed the planktic foraminiferal diversity in approximately 80 through 60Ma except for the section missing. In the Cretaceous section, a relative abundance of deeper dwelling keeled taxa was decreased from 75Ma and terminated at the K/Pg boundary. In return, the presumably shallower dwelling serial taxa became more abundant in the latest Cretaceous. At the site we analyzed, we so far identified only one serial species that survived the K/Pg extinction event. In the Paleogene section, the total number of species was significantly smaller than that in the Cretaceous and stayed constant from 64 through 60 Ma. Although the globular taxa were very abundant up to 63Ma, they were replaced by the ovate/hemispherical taxa from 63Ma. The keeled and photosymbiotic taxa appeared in 61Ma and became more abundant. These changes in morphological diversity in the Paleogene indicate that the planktic foraminiferal assemblages matured in 5 m.y.s after the K/Pg boundary extinction.
To understand the functional and/or ecological evolution, we examined the diversity of planktic foraminifers through the K/Pg boundary extinction event. The K/Pg boundary sequence was recovered from Site U1407, IODP Exp. 342 at the Newfoundland Ridge. The sequence is mostly composed of calcareous ooze with abundant well-preserved foraminiferal fossils. However, unfortunately, the section from approximately 69 through 65Ma is missing by the hiatus. We have analyzed the planktic foraminiferal diversity in approximately 80 through 60Ma except for the section missing. In the Cretaceous section, a relative abundance of deeper dwelling keeled taxa was decreased from 75Ma and terminated at the K/Pg boundary. In return, the presumably shallower dwelling serial taxa became more abundant in the latest Cretaceous. At the site we analyzed, we so far identified only one serial species that survived the K/Pg extinction event. In the Paleogene section, the total number of species was significantly smaller than that in the Cretaceous and stayed constant from 64 through 60 Ma. Although the globular taxa were very abundant up to 63Ma, they were replaced by the ovate/hemispherical taxa from 63Ma. The keeled and photosymbiotic taxa appeared in 61Ma and became more abundant. These changes in morphological diversity in the Paleogene indicate that the planktic foraminiferal assemblages matured in 5 m.y.s after the K/Pg boundary extinction.