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Warren D. Allmon
Significant new developments in paleontology may usefully be grouped into three categories:
1. New data that lead to reassessment or confirmation of previous ideas. This category includes the superlatives: biggest, smallest, oldest, weirdest, and so on. They are the discoveries usually reported in the popular media.
2. New theoretical syntheses, primarily by reanalyzing existing data. These are seldom reported in the media and are in fact more difficult to specify, since they may emerge not in a single study but in a series of publications by multiple authors over a long period of time.
3. New techniques that hold promise for future discoveries.
In 2000, invertebrate paleontology presented many examples of the first, several examples of the second, and at least one example of the third.
New Data
When did photosynthesis originate? A new analysis (Science, v. 289, p. 1724) by Jin Xiong and colleagues of the evolutionary relationships of the genes that control photosynthesis in modern bacteria lends support to the conclusion that the process was present in several lineages of bacteria approximately 3 billion years ago but perhaps much earlier.
The oldest Metazoan traces. In 1998, Indian and German paleontologists claimed that Metazoan trace fossils found in India were 1.1 billion years old. The date was criticized by another Indian paleontologist, who had found 540-million-year-old fossils in rocks immediately overlying the traces. The Geological Society of India asked a team to investigate the controversy.
Their report (Journal of the Geological Society of India, v. 55, 2000, p. 675) concludes that they cannot confirm the younger date. The evolutionary significance of these fossils may not be clear, however. An analysis of traces made by living flatworms and anemones by Collins and others (Paleobiology, v. 26, 2000, p. 47) suggests that complex traces can be made by relatively simple organisms, so that whatever the age of Proterozoic traces, they may be relatively uninformative about the timing of animal diversification.
Vase-shaped microfossils. These common but taxonomically enigmatic components of late Proterozoic fossil assemblages turn out to be testate amoebae, according to an analysis by Porter and Knoll (Paleobiology, v. 26, p. 360).
The world’s largest recorded trilobite. A team of Canadian paleontologists discovered a specimen more than 70 centimeters long — 70 percent larger than the previous record holder. It was found in Late Ordovician rocks in Manitoba, Canada, and appeared on the cover of Geology (v. 28, no. 10) last October.
Extinctions, Permian/Triassic. Based on examination of rocks in China, Erwin and colleagues (Science, v. 289, p. 432) conclude that the P-T extinction occurred suddenly, perhaps even in a single day, around 251.4 million years ago. They also note that the event is coincident with a change in carbon isotopes, suggestive of a change in oceanic productivity, and with an increase in microspherules, which might indicate a meteorite impact. More definitive evidence of impact comes from a study by Becker and others (Science, v. 291, 2001, p. 1530), which looked at helium inside “buckeyballs” found at the P-T boundary and concluded that the helium has an isotopic composition similar to extraterrestrial sources.
Extinctions, Triassic/Jurassic. A study of the age of rocks in the Queen Charlotte Islands off British Columbia suggests that extinction on land preceded extinction in the sea at the end of the Triassic. Pálfy and colleagues (Geology, v. 28, p. 39) suggest that this argues against a “single sudden catastrophic cause” such as extraterrestrial impact. In the next pulse of extinction in the early Jurassic, Pálfy and Smith report (Geology, v. 28, p. 747) that extinction rates peaked around 183 million years ago, synchronous with large flood basalts in southern Africa and Antarctica.
Extinctions, Eocene/Oligocene. New data appear to link cooling at the end of the Eocene to extraterrestrial impact. Vonhof and colleagues (Geology, v. 28, p. 687) argue for cooling following at least two late-Eocene impact events; they note that because the cooling seems to have lasted longer (about 100,000 years) than could be explained by impacts alone, a complex feedback mechanism may have been involved. A study by Ivany and colleagues (Nature, v. 407, p. 887) of oxygen isotopes in fossil fish ear bones from the U.S. Gulf Coastal Plain suggests that colder winter temperatures made the difference at the end of the Eocene.
Emerging synthesis: Does ecology matter?
In a posthumous contribution to the journal he did so much to shape, Sepkoski and colleagues (Paleobiology, v. 26, p. 7) argued that competition between cheilostome and cyclostome bryozoans has contributed to displacement of the latter by the former since the early Mesozoic. Studies continue to argue for the role of escalation in evolution within clades (e.g., Dietl and others, Paleobiology, v. 26, p. 215), although Kelley and Hansen (Evolutionary Paleoecology, Allmon and Bottjer, eds., Columbia University Press, 2000) note that analyses of predator-prey coevolution and escalation suggest that “the processes that regulate large-scale escalation may differ from those that produce changes within lineages.”
New tools: a database of all fossil taxa?
A major attempt to build the next generation of paleobiological databases is underway at the National Center for Ecological Analysis and Synthesis (NCEAS) at the University of California, Santa Barbara. More information about the “Paleobiology Database” is available at www.nceas.ucsb.edu/public/pmpd/. An initial report recently appeared in the Proceedings of the National Academy of Sciences (v. 98, 2001, p. 6261).
In closing, let me draw your attention to the 25th anniversary volume of the journal, Paleobiology (Supplement to v. 26, no. 4, 2000), which was published last year. If you can read only one out of the flood of recent paleo books, this is it.
Allmon is Director of the Paleontological Research Institution in Ithaca, N.Y., and teaches geology and biology at Cornell University. E-mail: wda1@cornell.edu
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