Tetracentron (Trochodendraceae) in the Paleocene and Miocene of western North America.

Abstract

Although Tetracentron (Trochodendraceae) is endemic to eastern Asia today, the fossil record indicates that it was formerly more widespread across the northern hemisphere. Infructescences from the Paleocene of Wyoming, USA, documented herein, represent the oldest known occurrence of the genus. Details of the morphology, including spikes of sessile, tetracarpellate, apically dehiscent capsules with styles emerging from the lower part of the fruit, and a nectary bulge beneath each style, are revealed by micro-CT scanning of specimens preserved as molds and casts in siltstone. The discovery of Tetracentron linchensis sp. nov. indicates that Tetracentron and Trochodendron had already diverged by about 60 million years ago and were sympatric, along with the extinct relative, Eotrochion, in the Paleocene of Wyoming. North American fossil occurrences of Trochodendraceae, including extinct Eocene and Miocene genera, as well as both extant genera, highlight a former diversity and geographic spread that is no longer evident in the surviving Asian Trochodendraceae.