Cambrian-Precambrian
As recently as a few years ago, the Ediacara biota was widely recognized as including the oldest known multicellular fossils, but not much else was clear about it. A major component of the remarkable revolution in knowledge that has occurred about the late Proterozoic and early Cambrian over the past few years is a much better understanding of the age of Ediacara. Thanks to the work of Guy Narbonne of Queens University in Ontario and James Gehling of the South Australian Museum, published in the January 2003 Geology and presented at the November Geological Society of America (GSA) meeting, we now know that Ediacara fossils date to at least 580 million year ago and that they extend across the boundary into the earliest Cambrian. Outcrops in Newfoundland provide a high-resolution bio- and chronostratigraphy of the once monolithic Ediacara biota, revealing that there are at least three recognizable faunas within it.
Last October, heads turned around the world, with the public announcement of a possible vertebrate from the Ediacara. Photos of an enigmatic Ediacara fossil were released to the media, leaving paleontologists to explain it without having examined the specimen thoroughly. (See, e.g., Discovery News.) While admitting that the press coverage was premature, at the November GSA meeting, Gehling said that in his view the problematic form was not easily assignable to any other known Ediacaran group.
Another Cambrian-Precambrian fauna that is the target of intense interest is from the Doushantuo formation of the late Proterozoic in China. It is now clear, mainly from the work of Shuhai Xiao of Virginia Tech (presented at the November GSA meeting) that these amazingly preserved fossils include embryos of at least sponge-grade animals. Remaining to be determined is whether the oldest among the Duoshantuo occurrences is before or after the latest Proterozoic glaciation, a major point in exploring the role of glaciation and the "snowball Earth" hypothesis in the Cambrian explosion. A fascinating paper by Derek Martin of the University of Bristol and colleagues in the January 2003 Geology showed experimentally that invertebrate eggs could be fossilized in a manner resembling the Doushantuo embryos.
Mass Extinction
Mass extinction investigations continue, with extraterrestrial impacts still a major theme. Asish Basu and colleagues at the University of Rochester and Harvard reported in the Nov. 21 Science meteorite fragments associated with the Permian-Triassic boundary in the Transantarctic Mountains in Antarctica. Chemical analysis of the fragments point to an extraterrestrial origin and bear close resemblance to similar fragments reported from the Cretaceous-Tertiary. The team also reported shocked quartz.
Evidence of impact surfaced at a smaller extinction event just before the late Devonian. Brooks Ellwood and colleagues at Louisiana State University reported in the June 13, 2003, Science shocked quartz and high concentrations of elements known to be associated with impact events, along with a Carbon isotope shift, from a site in Morocco.
Marine Biodiversity
Paleontologists continue to contribute to analysis and warnings about the crisis confronting the world's oceans. Following from landmark articles in the Proceedings of the National Academy of Sciences and Science in 2001, Jeremy Jackson of Scripps Institution of Oceanography is collaborating with biologist and filmmaker Randy Olsen to raise awareness of the impending "shifting balance" of the marine biosphere back to, as Jackson puts it, a "Proterozoic state" (see www.shiftingbaselines.org). In Evolutionary Ecology Research (v. 6, p.315), Geerat Vermeij of the University of California at Davis contrasts past mass extinctions in the seas, which struck first at primary productivity, to the modern mass extinction, which is hitting hardest large primary consumers.
The persistent issue of bias in diversity measurements was addressed recently by David Jablonski of the University of Chicago and colleagues in the May 16, 2003, Science. They conclude that the apparent rise in marine diversity over the past 50 to 100 million years is a reality, and not an artifactual result of the "pull of the recent." James Crampton of the Institute of Geological and Nuclear Sciences in New Zealand and colleagues report in the July 18, 2003, Science that a technique recently used to examine the issue of completeness of the fossil record — number of formation names — is a poor predictor of rock volume.
Astrobiology
Paleontologists were seated firmly at the "high table" of planetary exploration as the Mars rovers Spirit and Opportunity began to explore the red planet in late 2003. Andrew Knoll of Harvard is part of the rover project science team and is cautiously optimistic about the future prospects for a genuine extraterrestrial paleobiology (see interview in the February 4, 2004, issue of Astrobiology).
Also Notable
The search for ancient DNA also continues, despite the debunking of almost all previous claims of its discovery. Two molecular biology students from the University of Copenhagen report in the April 18 Science findings of plant and animal DNA from frozen permafrost of Siberia and arid New Zealand cave soil. Eske Willerslev and Anders Hansen set out looking for bacterial DNA but found chloroplast DNA from 19 different plant species in Siberia, as well as DNA from eight animals, including mammoths and bison. The New Zealand samples included DNA of moas.
Notable entries from 2003 in the "oldest ever" category include the first known fossil tunicate, reported by Jun-Yuan Chen and colleagues at the Nanjing Institute of Geology and Paleontology, found in Kunming, south China, dated to the lower Cambrian (circa 520 million years ago), published in the July 8 Proceedings of the National Academy of Sciences. A tiny fragment of silk preserved in Early Cretaceous Lebanese amber is the oldest known spider web, according to a report in the August 7 Nature. The find is about 80 million years older than the previously oldest known, from the Baltic. And ostracodologists and the world media were titilated by discovery of the oldest known male copulatory organ in an exceptionally well-preserved Silurian ostracode from England, reported in the Dec. 5, 2003, Science by David Siveter of the University of Leicester and colleagues.
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