|Case studies in Paleobiology
Vidal, G., & M. Moczydlowska-Vidal. 1997. Biodiversity, speciation and extinction trends of Proterozoic and Cambrian phytoplankton. Paleobiology 23: 230-246.
Time: Meso – Neo Proterozoic
Organisms: Acritarchs (Phytoplankton)
These single celled phytoplankton left a good fossil record from the Middle Proterozoic into the Paleozoic when few other fossils are available.
They show marked changes in diversity and abundance. Some of these changes can be correlated with paleoclimatic and tectonic events.
Clapham, M. E. G. N. Narbonne & J. G. Gehling. 2003. Paleoecology of the oldest known animal communities: Ediacaran assemblages at Mistaken Point, Newfoundland. Paleobiology 29: 527-544
Time~ 565 Ma
Organisms: Ediacaran soft bottom organisms
The extremely well preserved and varied Mistaken Point assemblages allowed Clapham et al. to test several ecological theories about this fauna. They concluded that in the absence of predation and any evidence of competition the different assemblages exposed on different surfaces represent snapshots of various seres in a successional series. Faunal elements in early stages are small and prostrate. Middle successional stages show the highest diversity. Climax stages are dominated by large plumose upright forms. Perhaps stabilization of the silty sediments by microbial mats allowed the development of these more structures communities.
Zhang, P., H. Zhou, Y-Q Chen, Y-F. Liu & L-H, Qu 2005. Mitogenomic perspectives on the origin and phylogeny of living Amphibians. Systemic Biology 54 391-400
Time: mid-late Paleozoic and Mesozoic
Organisms: Lissamphibians (living amphibian groups)
Extant amphibians belong to three distinct groups: anurans (frogs), Caudata (Salamanders) and Gymnophiona (caecilians). While frogs and salamanders are commonly placed as sister groups some molecular evidence dos not fit this phylogeny.
Zhang et al. use mitochondrial sequences to investigate the phylogeny and molecular clocks to try to date the divergence of the three living groups from possible ancestor groups which may have included Lepospondyli, Lysorophia Temnospondyli and Dissorophoidea. They conclude that the Lissamphibia are monophyletic, the Gymnophiona are sister to the two other groups and that the living amphibians may be sister to the Temnospondyli. They suggest that modern anurans may have originated in Africa-India, Salamanders in North China. From there they spread to North America where they exhibit highest diversity. Caecilians are predominantly Gondwanan and may have had a South America-African origin.
Van de Schootbruigge, B., T. R. Bailey, Y. Rosenthal, M. E. Katz, J. D. Wright, K. G. Miller, S. Feist-Burkhardt and P. G. Falkowsky 2005. Early Jurassic climate change and the radiation of organic-walled phytoplankton in the Tethys Ocean. Paleobiology 31:73-97.
Time: Lower Jurassic Sinemurian/Pliensbachian/Toarcian
Location: North West Tethys
Organisms: Phytoplankton cyst-forming dinoflagellates
A combination of oceanic connections, flooding and recession of shallow seas on continents and inferred currents may have brought paleo-Pacific taxa into the NW Tethys replacing the ‘green’ Prasinophyte phytoplankton with ‘red’ taxa. Later, stagnation may have reduced dinoflagellate abundance and allowed Prasinophytes. Later a boreal Sea intrusion may again have facilitated dinoflagellate diversification which ended with the Toracian Oceanic Anoxic Event
Field, T. S., N. C. Arens, J. A. Doyle, T. E. Dawson & M. J. Donoghue 2004. Dark and Disturbed a new image of early angiosperm ecology
Time: Early Cretaceous (or before?)
Organisms Early Angiosperms
To Charles Darwin the suddenness of the angiosperm appearance and their rapid rise to dominance in the fossil record was both a “perplexing phenomenon” to “those who believe in extremely gradual evolution” and an “abominable mystery” (http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=34068)
Recent work has suggested Amborella (http://www.ucalgary.ca/~laidlaw/amborella/amborella_web.html) may be sister to the remaining angiosperms. Field et al. report on morphological and photobiological studies and suggest that the root angiosperm may have inhabited dark humid habitats they suffered frequent disturbance. Wet understory habitats may have been uncommon in the early Mesozoic so that root angiosperms were very uncommon and/or patchy. With more mesic conditions in the Cretaceous, these plants may have been able to spread and diversify.
Smith, S. A. P. R. Stephens & J. J, Weins. 2005. Replicate patterns of species richness, historical biogeography and phylogeny in Holarctic tree frogs. Evolution. 59: 2433-2450
Time: Eocene – Miocene
Organisms: Hylid frogs (tree frogs)
Smith et al. investigate phylogenies and diversity patterns of clades of Holarctic tree frogs. They test the hypothesis that within-group diversity increases toward lower latitudes. While tree frogs have their global diversity maximum in the tropics (mainly due to the very high diversity in the Neotropics) four temperate clades all show mid-latitude diversity maxima. The authors suggest that these temperate lineages may be ecologically restricted to temperate conditions. This would restrict them from dispersing to low latitudes and so may keep them separate from tropical Hylids. On the other hand there is good phylogenetic evidence that they do disperse easily within temperate latitudes.