Box 3.4 Lazarus taxa, Elvis taxa and dead clade walking
There is now a whole terminology for fossils that are absent, or seemingly in the wrong place at the wrong time. David Jablonski of the University of Chicago began the story in 1983 when he invented the term Lazarus taxa for species or genera that are present, then seemingly disappear, and then reappear. The name is based on Lazarus in the Bible, who had died, but was brought back to life by Jesus. Clearly species cannot reappear after they have become extinct, so Lazarus taxa identify gaps in the record where fossil preservation is poorer than in the beds below and above.
Doug Erwin of the Smithsonian Institution and Mary Droser of the University of California at Riverside then invented the term Elvis taxa in 1993 for species or genera that disappear, to be replaced some time later by unrelated by strikingly similar impersonators (i.e. highly convergent species). Elvis taxa can be mistaken for Lazarus taxa if the paleontologist does not study the anatomy carefully.
Not to be outdone, David Jablonski then coined the term dead clade walking in 2002 to refer to short-lived survivors of mass extinctions. He had found that many of the organisms that are found after a mass extinction flourish for a while and then go - they had survived the extinction event, but lacked the evolutionary staying power to be a serious part of the recovery.
As Claude Hopkins said in his book Scientific Advertising in 1923, "Often the right name is an advertisement in itself".
fossil finds that add to time ranges almost always fill ghost ranges. In other words, new finds, despite the hype in the press ("oldest human fossil rewrites the text books"), almost always fit into expected patterns in time and space.
Perhaps the clade-stratigraphy comparisons (Box 3.3) are the closest to an assessment of the congruence between the fossil record and reality. To put it bluntly, if the fossils fit closely with a phylogenetic tree based on analysis of the DNA of 100 modern species, then perhaps the fossil record (meaning 1) correctly represents reality (meaning 3). This can never be an entirely decisive demonstration, but the more often congruence is found between trees of living organisms and their fossil record, the more confidence perhaps paleontologists might have that the fossils tell the true story of the history of life.
1 Summarize the key hard and soft tissues in the human body. Which would decay first (the most labile tissues) and which last (the most refractory tissues)?
2 Which of these groups of fossils are likely to be more completely known, and why: dinosaurs or frogs, mollusks or annelids, birds or bats, land snails or clams?
3 When a tree dies, what might happen step by step to its various parts - leaves, nuts, branches, trunk and roots? How long might each element survive, and where might they end up?
4 Why are Cambrian fossils likely to be less abundant and less well preserved than Miocene fossils?
5 If you were determined to find a new species of fossil, how would you plan your expedition to ensure success?
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