Guest lecture: angiosperm origins and diversification

26 Pages·2014·2.95 MB·English

(cid:2) (cid:1)
Darwin s abominable
(cid:2)
mystery :
The evolution of angiosperms
Fossil Plants
What to know from today(cid:2)s lecture:

1.  When did angiosperms show up in the fossil record?
2.  When did angiosperms radiate taxonomically? When did they
become ecologically dominant?
3.  How did these changes affect other plants—and animals?
4.  What are suggested key opportunities for angiosperms?
Angiosperms (flowering plants)
• Angiosperms make up the
majority of land plants
(>250,000 species)
• Dominate most
ecosystems
(Crepet & Niklas 2009)
Angiosperms (flowering plants)
Nepenthes
• Angiosperms make up the
majority of land plants
(>250,000 species)
• Dominate most
ecosystems
Rafflesia
• Wide ecological range:
! ocean to desert
! obligate autotrophs to
carnivores and
parasites
(cid:1) (cid:2)
Abominable mystery ?
(cid:3)the sudden appearance of so many
Dicotyledons in the Upper Chalk
appears to me a most perplexing
phenomenon to all who believe in
any form of evolution, especially to
those who believe in extremely
gradual evolution(cid:4) (Darwin and
Seward, 1903, p. 239).!
(cid:1) (cid:2)
Abominable mystery ?
(cid:3)The rapid development, as far as
we can judge, of all the higher
plants within recent geological
times is an abominable mystery(cid:4).!
What makes an angiosperm?
Synapomorphies:
• Flower = reproductive structures
surrounded by perianth (modified
bracts?)
• Ovules with two integuments and
enclosed in carpels
Magnolia
What makes an angiosperm?
Synapomorphies:
• Flower = reproductive structures
surrounded by perianth (modified
bracts?)
• Ovules with two integuments and
enclosed in carpels
• Very reduced gametophytes
(mega=4-64 cells; micro=3 nuclei)
• Double fertilization " endosperm (3n)
Coconut
What makes an angiosperm?
Synapomorphies:
Phloem
• Flower = reproductive structures
surrounded by perianth (modified
bracts?)
• Ovules with two integuments and
enclosed in carpels
• Very reduced gametophytes
(mega=4-64 cells; micro=3 nuclei)
• Double fertilization " endosperm (3n)
• Phloem with sieve tubes and companion
cells
What makes an angiosperm?
Synapomorphies:
Xylem
• Flower = reproductive structures
vessels
surrounded by perianth (modified
bracts?)
• Ovules with two integuments and
enclosed in carpels
• Very reduced gametophytes
(mega=4-64 cells; micro=3 nuclei)
• Double fertilization " endosperm (3n)
• Phloem with sieve tubes and companion
cells
Features that most angiosperms have:
• Vessel elements
What makes an angiosperm?
Synapomorphies:
• Flower = reproductive structures
surrounded by perianth (modified
bracts?)
• Ovules with two integuments and
enclosed in carpels
• Very reduced gametophytes
(mega=4-64 cells; micro=3 nuclei)
• Double fertilization " endosperm (3n)
• Phloem with sieve tubes and companion
cells
Features that most angiosperms have:
• Vessel elements
• Pollen with tectate-columellate walls
• Superfast life cycle
Fossil record of angiosperms
• Pollen ~130 Ma (Early Cretaceous)
• Charcoalified flowers ~125 Ma
• Fruit and leaves ~125-120 Ma

Nymphaeceae
Fossil leaves from Early Cretaceous Potomac Group, USA
Fossil record of angiosperms
• Pollen ~130 Ma (Early Cretaceous)
• Charcoalified flowers ~125 Ma
• Fruit and leaves ~125-120 Ma

" Early Cretaceous
evolution of
angiosperms?!
Archaefructus sinensis
Sister taxa of angiosperm?
• How do we know that morphological traits are
homologous?
Morphology-based
phylogeny
(after Doyle 2006)
Sister taxa of angiosperm?
Gnetophytes
• ~70 species in 3 very different genera
• Earliest fossil = Late Permian(?) pollen
• Share many similarities with angiosperms

Gnetum
Welwitschia Ephedra
Sister taxa of angiosperm?
• Depends on type of data and analysis!
Morphology-based
Molecular phylogenies
phylogeny
(Mathews 2009) (after Doyle 2006)
Angiosperm diversification
•  Ecological diversification during the Early-Late
Cretaceous
•  Taxonomic diversification during the Early-Middle
Cretaceous

North America
Age (million years before present)! (Lupia et al 1999)
Angiosperm diversification
•  Ecological diversification during
the Early-Late Cretaceous
•  Taxonomic diversification during
the Early-Middle Cretaceous
•  Rise to ecological dominance ~30
myr after taxonomic
diversification
Angiosperm diversification
•  Changes occurred at the expense of free-sporing plants and
certain seed plant groups (cycads, Cheirolepidaceae conifers)
(Wing & Boucher, 1998)