Abstract Detail

Themes of land plant evolution, a celebration of the contributions of Leo J. Hickey

Jud, Nathan [1], Wing, Scott [2].

The evolution of angiosperm ecological strategies.

The leaf-height-seed (LHS) plant strategy scheme was developed as a framework for large scale analyses of modern plant ecological data in order to understand vegetation dynamics under global environmental change. Here we show that a similar framework can be used to examine vegetation dynamics under evolutionary change in the fossil record. Specifically, we examine how angiosperm occupancy of plant functional trait space changed through the Cretaceous and early Paleogene. The challenge for reconstructing plant ecological strategies from the fossil record is to identify characters that are preserved, and that reflect the same fundamental trade-offs in plant resource allocation that are captured by canopy height, specific leaf area, and seed mass in modern studies. Luckily, this challenge has already been met. The relationship between leaf area and petiole width has been shown to predict specific leaf area in fossil leaves. Alternatively, leaf vein density (which correlates with maximum photosynthetic capacity rather than net mass-based photosynthetic capacity) has also been measured in fossils. Trunk diameter and mean tangential diameter of vessels predict plant height and can be measured in fossil wood occurrences. Finally, angiosperm seed size correlates with seed mass, and data from fossils has been published by multiple research groups. Temporal patterns in each of these features have been evaluated independently and have led to different conclusions about the timing of angiosperm dominance. Here we consider changes along the three axes of the LHS plant strategy framework together. Patterns of change through time suggest distinct ecological phases of angiosperm evolution: i) an ancestral phase, from Hauterivian to Aptian/early Albian when angiosperms were herbs and shrubs had small seeds and low maximum photosynthetic capacity, ii) a weedy phase from Aptian-Turonian(Maastrichtian) when species diversity increased rapidly, herbs and shrubs were locally abundant, and medium-large trees grew in riparian environments, but seed size remained small, and iii) a canopy dominant phase beginning in the Paleocene when angiosperms diversity included abundant large trees with large seeds and high vein density. Our results suggest potential solutions to at least two important issues in angiosperm paleoecology. First, the “riparian weed” and “dark and disturbed” models of early angiosperm ecology represent distinct phases rather than conflicting models. Second, the K-T impact event had important ecological consequences for the evolution of angiosperms in that widespread convergent evolution in angiosperms facilitated the occupation of the canopy-dominant niche following the removal of gymnosperm (conifer) incumbents.

Broader Impacts:

1 - 7006 Chansory Lane, Hyattsville, MD, 20782, USA
2 - Smithsonian Institution, Dept. of Paleobiology NHB 121, PO Box 37012, WASHINGTON, DC, 20013-7012, USA

Keywords:
angiosperm
paleoecology
Cretaceous.

Presentation Type: Symposium or Colloquium Presentation
Session: C6
Location: Belle-Chasse/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 3:15 PM
Number: C6007
Abstract ID:173
Candidate for Awards:None