THE ECOLOGY OF EARLY CRETACEOUS ANGIOSPERMS

296 Pages·2014·15.29 MB·English

ABSTRACT

Title of Document: THE ECOLOGY OF EARLY CRETACEOUS
ANGIOSPERMS: INSIGHTS FROM THE
FOSSIL RECORD.

Nathan A. Jud, Doctor of Philosophy, 2014

Directed By: Dr. Charles Mitter, Professor
Department of Entomology

Dr. Scott L. Wing, Adjunct Professor
Department of Biology

The Early Cretaceous diversification of flowering plants was not preceded by
a mass extinction event. This suggests that biotic factors intrinsic to flowering plants
played an important role promoting diversification, but the rarity of fossils of early
flowering plants makes identifying the important features difficult. Here, I present the
results of my specimen-based analysis of plant megafossil collections from Lower
Cretaceous deposits of the United States. First, I describe previously unrecognized
eudicot leaf fossils from a historically important Aptian (Lower Cretaceous) plant
fossil site in the Potomac Group, and I provide a set of characters for recognizing the
fossil leaves of these plants. Then, I present a morphotype catalog for the fossil plants
from and Aptian-early Albian (Lower Cretaceous) site in the Potomac Group. This
collection includes one angiosperm morphotype. Next I describe the angiosperm
morphotype identified in the previous chapter. I show that it is widely distributed
among coeval collections of the Potomac Group and some specimens were previously
described as ferns. The preservation of attached stems leaves and root provides direct
evidence of weedy, fast-growing, herbaceous angiosperms in the Aptian-early Albian.
In the following chapter, I use megafossil data from the literature and museum
collections to test the hypothesis that the diversification of flowering plants is
associated with an increase in alpha diversity during the Early Cretaceous. Despite
the evidence for a high diversification rate among early flowering plants, I found no
relationship between collection age and collection richness, but I found strong
evidence that angiosperms were consistently rare during the Aptan-middle Albian,
and that locally abundant angiosperms became common during the late Albian, long
after the initial diversification. Finally, I use new plant megafossil collections that I
made from the Cloverly and Sykes Mountain Formations in Wyoming, USA, for a
more high-resolution study of early angiosperm diversity, distribution, and
abundance. I show that the Cloverly Formation records the appeareance of flowering
plants in North America, and that by the Albian angiosperms were widely distributed
among available habitats. I test the hypothesis that variation in community
composition (beta diversity) increased with the appearance of angiosperms. I did not
find strong support for the hypothesis that angiosperms increased beta diversity;
however, rarefaction analysis shows that the rate of morphotype discovery in both the
pre-angiosperm and the angiosperm interval is high, which means that additional
sampling may reveal a difference in beta diversity between the two intervals.
Together my findings indicate that flowering plants diversified during the Early
Cretaceous not because they had features that allowed them to displace other plant
groups, but because they were uniquely able to maintain high diversification rates in
the face of rarity and dispersed populations.
THE ECOLOGY OF EARLY CRETACEOUS ANGIOSPERMS:
INSIGHTS FROM THE FOSSIL RECORD.

By

Nathan A. Jud.

Dissertation submitted to the Faculty of the Graduate School of the
University of Maryland, College Park, in partial fulfillment
of the requirements for the degree of
Doctor of Philosophy
2014

Advisory Committee:
Professor Charles Mitter, Chair
Adjunct Professor Scott L. Wing, Co-Chair
Professor Charles Delwiche
Associate Professor Maile Neel
Adjunct Professor William A. DiMichele
© Copyright by
Nathan A. Jud
2014
Acknowledgements
I thank my committee, Drs. Scott Wing, Charlie Mitter, Chuck Delwiche, Bill
DiMichele, and Maile Neel for their guidance and support as I carried out this
research. I also thank Dr. Leo Hickey for his inspiration and guidance. The
paleobotany community at the Smithsonian supported me throughout my graduate
career. In particular I thank Abby Telfer, Carol Hotton, Rich Barclay, Arden
Bashforth, Dan Chaney, and Jon Wingerath. Much of the fossil preparation was done
by several volunteers and their skill made the recognition of these morphotypes
possible. Thanks to Hillary Cochard, Jerome McDonald, Elizabeth Seastrum, and
Mary Lou Fisher. I had several field assistants over the course of four field seasons in
the Wyoming; thanks to Spencer Schecht, Amanda Bender, Hallie Street, James
Super, Sarah DeWitt, and Mike Mosier for all their hard work. Many thanks to my
friends and colleagues in graduate school at the University of Maryland for all of the
support and fun times these last six years. Thanks to my wife, Sarah DeWitt
especially for your support these last six years.
I also acknowledge the funding from the following sources:
The University of Maryland Graduate School
The Smithsonian Peter Buck Predoctoral Fellowship Program
The University of Maryland Program in BEES
The Maryland Agricultural Experiment Station
The Wiley Dissertation Completion Fellowship
Sigma Xi Grant in Aid of Research
The Evolving Earth Foundation
The Finneytown Garden Club.
ii
Table of Contents

Acknowledgements ....................................................................................................... ii 

Table of Contents ......................................................................................................... iii 

List of Tables ................................................................................................................ v 

List of Figures .............................................................................................................. vi 

Chapter 1: A new Early Cretaceous angiosperm from the Potomac Group and its
implications for the evolution of eudicot leaf architecture ........................................... 1 
Abstract ..................................................................................................................... 1 
Introduction ............................................................................................................... 2 
Methods .................................................................................................................... 3 
Geologic and Depositional Setting ....................................................................... 3 
Fossil Preparation .................................................................................................. 4 
Phylogenetic Analysis ........................................................................................... 5 
Results ....................................................................................................................... 7 
Systematics ........................................................................................................... 7 
Phylogenetic Analysis ......................................................................................... 10 
Discussion ............................................................................................................... 11 
Comparisons with Extant and Fossil Plants ........................................................ 11 
Ecological Implications ...................................................................................... 15 
Conclusions ............................................................................................................. 18 
Tables and Figures .................................................................................................. 19 

Chapter 2: Morphotype catalog of a Zone I (Aptian-earliest Albian) flora from the
Fairlington, Virginia, USA ......................................................................................... 26 
Abstract ................................................................................................................... 26 
Introduction ............................................................................................................. 27 
Methods .................................................................................................................. 29 
Description of Morphotypes ................................................................................... 31 
Ferns .................................................................................................................... 31 
Gymnosperms ..................................................................................................... 34 
Angiosperms ....................................................................................................... 40 
Discussion ............................................................................................................... 41 
Tables and Figures .................................................................................................. 43 

Chapter 3: Morphology and ecology of an herbaceous angiosperm from the Lower
Cretaceous of eastern North America ......................................................................... 53 
Abstract ................................................................................................................... 53 
Introduction ............................................................................................................. 54 
Methods .................................................................................................................. 56 
Geologic and Depositional Setting ..................................................................... 56 
iii
Fossil Preparation ................................................................................................ 57 
Systematics ............................................................................................................. 58 
Discussion ............................................................................................................... 62 
Autecology .......................................................................................................... 62 
Comparison with extant and fossil plants ........................................................... 67 
Conclusions ............................................................................................................. 71 
Tables and Figures .................................................................................................. 73 

Chapter 4: Large scale patterns in the distribution of angiosperm diversity based on
Lower Cretaceous plant megafossil collections from the United States ..................... 79 
Abstract ................................................................................................................... 79 
Introduction ............................................................................................................. 80 
Methods .................................................................................................................. 82 
Sample Size ......................................................................................................... 82 
Diversity .............................................................................................................. 83 
Environmental variables ..................................................................................... 85 
Results ..................................................................................................................... 86 
Discussion ............................................................................................................... 89 
Species Richness through Time .......................................................................... 89 
Early Angiosperm Habitats ................................................................................. 91 
Conclusions ............................................................................................................. 93 
Tables and Figures .................................................................................................. 95 

Chapter 5: Plant megafossils from the Lower Cretaceous Cloverly and Sykes
Mountain Formations (Wyoming, USA) and their bearing on early angiosperm
evolution ................................................................................................................... 105 
Abstract ................................................................................................................. 105 
Introduction ........................................................................................................... 106 
Methods ................................................................................................................ 108 
Geologic Setting................................................................................................ 108 
Data Collection and Analysis............................................................................ 110 
Results ................................................................................................................... 113 
Discussion ............................................................................................................. 117 
Tables and Figures ................................................................................................ 121 

Appendix I ................................................................................................................ 129 
Appendix II ............................................................................................................... 211 
Appendix III .............................................................................................................. 246 
Appendix IV .............................................................................................................. 252 
Appendix V ............................................................................................................... 255 
Bibliography ............................................................................................................. 267 
iv
List of Tables

Chapter 1
Table 1………………..……………………..……………………………….19
Chapter 2
Table 1………………..………………………..…………………………….44
Chapter 4
Table 1………………..……………………………………………….…….95
Table 2………………..……………………………………………………..96
v
List of Figures
Chapter 1
Figure 1………………..………………….………………………………….20
Figure 2………………..………………….………………………………….21
Figure 3………………..………………….………………………………….22
Figure 4………………..………………….………………………………….22
Figure 5………………..………………….………………………………….22
Figure 6………………..………………….………………………………….22
Figure 7………………..………………….………………………………….23
Figure 8………………..………………….………………………………….24
Figure 9………………..………………….………………………………….24
Figure 10……………..……..………….…………………………………….24
Figure 11……………..………..……….…………………………………….25
Figure 12……………..…………..…….…………………………………….25
Figure 13……………..……………..….…………………………………….25
Figure 14……………..………………...…………………………………….25

Chapter 2
Figure 1………………..……………….…………………………………….45
Figure 2………………..……………….…………………………………….46
Figure 3………………..…………………………………………………..…47
Figure 4………………..……………………………………………….….…47
Figure 5………………..……………………………..………………………47
Figure 6………………..……………………………..………………………48
Figure 7………………..………………………………..……………………48
Figure 8………………..…………………………………..…………………49
Figure 9………………..……………………………………..………………50
Figure 10……………..………………………………………..…………..…51
Figure 11……………..…………………….…………………..…………….51
Figure 12……………..…………………….……………………..………….51
Figure 13……………..…………………….……………………….......……52

Chapter 3
Figure 1……………..………..……………….…………………………..….73
Figure 2……………..…………..…………….……………………………...74
Figure 3……………..……………..…..……….…………………………….75
Figure 4……………..………………..…..…….…………………………….75
Figure 5……………..…………………..…..….…………………………….75
Figure 6……………..……………………..…...…………………………….75
Figure 7……………..………………………..…...………………………….76
Figure 8……………..…………………………...…..……………………….76
Figure 9……………..…………………………...……..…………………….76
Figure 10………..………………………………………..……………….77-78
Figure 11….………..……………………………………..………………77-78
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