Abstract Detail

Paleobotany

Matsunaga, Kelly [1], Smith, Selena [2].

Fruit fossils reveal a Late Cretaceous palm diversification.

The plant fossil record provides empirical evidence for the timing of evolutionary events and is therefore essential for understanding the diversification of lineages in deep time. The tropical monocot family Arecaceae (palms) has an extensive macrofossil record that begins approximately 84 million years ago in the Late Cretaceous. This fossil record provides reliable data on the prevalence and geographic distributions of palms through time but reveals relatively little about the origin and early diversification of the family. Most of the macrofossil record of palms comprises stems and leaves, which usually lack diagnostic characters enabling assignment below the family or subfamily level. Although fruit characters are often systematically informative, morphological data on extant palm fruits are sparse and parsing the existing data on fruit structure is challenging owing to substantial morphological diversity and convergence among the 181 extant genera. This leaves few reliable fossil occurrences for major lineages, and consequently divergence time analyses consistently place most of the crown diversification of palms in the Cenozoic. Here we integrate data from DNA, fruit morphology, and fossils to test the prevailing hypothesis of a Cenozoic palm radiation. To fill the gap in our knowledge of palm fruit structure across the family, we assembled a genus-level morphological dataset of palm fruits based on µCT scans of over 200 species representing nearly all valid genera. Six fossil species ranging from Maastrichtian–Eocene in age were selected to evaluate the utility of fruit characters for understanding the systematic relationships of fossil palms. The analyses were performed using maximum likelihood with a dataset containing 10 genes and 45 fruit characters. Support for the phylogenetic position of each fossil was further evaluated using non-parametric bootstrapping of the morphological data with a fixed molecular topology. To test the impact of these fossils on divergence time estimates within palms, we performed a Bayesian molecular dating analysis in Beast2 that co-estimates topology and clade age, using the phylogenetic analyses to inform node calibrations. The age of the fossils, their phylogenetic position, and age estimates obtained from the dating analyses together indicate that palms underwent an extensive Late Cretaceous diversification, with some tribes and subtribes emerging tens of millions of years earlier than previously estimated. A Cretaceous palm radiation has important implications for understanding the drivers and environmental context of palm diversification through time, the origins of tropical plant diversity, and the tempo of angiosperm evolution in the Cretaceous more generally.

1 - University of Michigan, Earth and Environmental Sciences, 1100 North University Ave, Room 2534, NUB, Ann Arbor, MI, 48109, USA
2 - Department Of Earth & Environmental Sciences, 1100 North University Avenue, Room 2534, NUB, Ann Arbor, MI, 48109, United States

Keywords:
Arecaceae
palms
fruits
fossil
phylogeny
node dating
morphology.

Presentation Type: Oral Paper
Session: CK2, Cookson Award Session II
Location: Tucson G/Starr Pass
Date: Monday, July 29th, 2019
Time: 11:30 AM
Number: CK2006
Abstract ID:624
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award