Back from the dead? 'Resurrections' of long-missing species lead to revelations.

In December 1938, Marjorie Courtney-Latimer, curator of a natural history museum in East London, South Africa, went to the docks to look for interesting specimens among the day's catch. What she found one day she later described as "the most beautiful fish I had ever seen ... a pale mauve blue with iridescent silver markings." The discovery sent scientists into a frenzy.

The 54-kilogram creature was a lobe-finned fish called a coelacanth. Researchers dubbed it a "living fossil" because the remains of creatures like it had been found only in rocks more than 75 million years old. It seemed that all such fish had died out about 10 million years before the dinosaurs did, yet here was a fresh specimen. And before the century was out, scientists had identified a second living species of coelacanth and had caught or observed the fish in waters from South Africa to Indonesia (SN: 5/5/01, p. 282).

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The apparent resurrections of the coelacanth and other long-missing species have led scientists to give such living fossils another name: Lazarus taxa, after the beggar who was raised from the dead in a biblical parable.

In the strictest sense, the modern representative of a Lazarus taxon belongs to the same species that disappeared from the fossil record many years ago. More loosely, researchers apply the term Lazarus taxon to the extremely close kin of ancient apparent extinctions. Coelacanths fall into this category: Although the living species are remarkably similar to some ancient ones, there are no known fossils of today's coelacanths. The same is true of the Laotian rock rat, a squirrel-size member of a group of rodents previously supposed to have disappeared about 11 million years ago (SN: 4/28/07, p. 260).

How do Lazarus taxa disappear in the first place? Several factors may play a role, scientists suggest. A creature may simply be rare or may live only in an uncommon habitat, or it may live in an environment where remains fossilize poorly or infrequently. In the case of coelacanths, both reasons may apply. Only a few hundred have been found since 1938, and they inhabit deep waters adjoining the steep slopes of volcanic islands, a setting where sediment seldom accumulates quickly enough to bury and preserve a carcass.

To recognize a Lazars taxon, moreover, scientists must identify its modern representative, and such discoveries may depend greatly on serendipity. Both the Indonesian species of coelacanth (SN: 9/26/98, p. 196) and the Laotian rock rat (SN: 5/21/05, p. 324) first came to scientists' attention in the village markets of Southeast Asia.

Lazarus taxa "probably are slightly more common than we think, we just haven't had the chain of events to recognize them," says Mike Macphail, a botanist at the Australian National University in Canberra.

These creatures are more than curiosities. By studying modern representatives of Lazarus taxa, scientists can better understand the environmental conditions in which their ancient relatives lived as well as how those creatures pulled their vanishing acts.

And Lazarus taxa may hold lessons for interpreting the fossil record in general. In a broader use of the term, scientists describe Lazars taxa as a large number of species that seemed to disappear during Earth's greatest mass extinction, to reappear a few million years later, but then to have gone extinct. Some scientists cite these ups and downs as evidence that the fossil record isn't always reliable. However, a new analysis, which considers a broader range of species, suggests that the fossil record may be trustworthy after all.

RARE, REMOTE One of the world's rarest trees, the Wollemi pine, inhabits the Australian version of a secure, undisclosed location. This cone-bearing evergreen is not a true pine. Only a few clumps of the tree seem to remain, and they live in an isolated, rugged area inside Wollemi National Park, about 200 kilometers northwest of Sydney. The few scientists and park rangers who know the trees' whereabouts don't reveal their exact locale, says Susan J. Murch, a botanist at the University of British Columbia in Kelowna.

The first members of Araucariaceae, the plant group to which the Wollemi pine belongs, evolved about 200 million years ago, says Murch. The most recent fossil of a close Wollemi pine relative that includes leaves or stems comes from rocks about 93 million years old, she notes. In September 1994, however, David Noble, a botanically knowledgeable park ranger, trekked into a remote, 600-meter-deep gorge and came across trees that he realized were unusual. The trees, dubbed Wollemi pines, were later identified as surviving relatives of a species long presumed extinct--in other words, a Lazarus taxon.

Wollemi pines don't compete well against other tree species and are difficult to grow under modern climatic conditions, says Murch. She describes the few Wollemi pines living in the wild as "a persistent population" that has grown not from seeds but from runners that sprang from older trees and stumps. The largest known specimen could be around 800 years old. Although the mature trees produce seeds, for some reason very few of those seeds sprout.

The pollen of modern-day Wollemi pines provides clues to the trees' ancient distribution, says Macphail. Until about 2 million years ago, similar pollen was common in sediments throughout Australia, New Zealand, and some parts of Antarctica, indicating that the trees' ancient relatives grew widely even though no remains of their leaves or wood had been preserved more recently than 93 million years ago. Then, around the time that Earth's climate began to include periodic ice ages, the species' pollen vanished from the fossil record.

Rather than going extinct, though, Macphail suggests that the trees "simply became so rare that they were easily overlooked." In recent times, the few living Wollemi pines have been protected by their isolation and by the moist conditions in the deep gorge to which they cling. "There's the scant element of chance that [these trees] were found at all," says Macphail. "If, for example, they had been destroyed by wildfires 30 years ago, we'd have never known they were there."

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FRESH FIND Few regions on Earth are as unexplored as the ocean floor, an area that accounts for more than 70 percent of the planet's surface. Every oceanographic survey seems to find new species. And occasionally, an old species or two show up.

In June of this year, Paul Johnson, an oceanographer at the University of Washington in Seattle, and his colleagues tagged along with an expedition exploring the seafloor about 50 kilometers off the Washington coast. Their mission: to search for open-ocean specimens of reef-building glass sponges, a Lazarus taxon that had been discovered in protected waters off the coast of Canada in the 1990s.

"I'd seen these things on an expedition there in 2005, and I figured I knew where some might be off Washington," Johnson says. The researchers sent their video equipment to the seafloor and, sure enough, they spotted the reefs, which measured dozens of meters across and were teeming with plankton, sardines, crabs, and rockfish.

"It was like looking at an overcrowded aquarium in an expensive Japanese restaurant," says Johnson.

Glass sponges are so called because their skeletons are built from glasslike silica minerals, not carbonates. They are typically solitary creatures, says Johnson. Usually tubular or cup-shaped, and growing no more than 50 centimeters tall, isolated sponges are often found in seafloor ecosystems where nutrients are hard to come by. Millions of years ago, however, some glass sponges grew beside and atop one another in jam-packed communities that rivaled the diversity of modern-day coral reefs.

Such reef-building glass sponges disappeared from the fossil record about 120 million years ago, about the same time that diatoms, a type of single-celled marine algae with cell walls built of silica, first appeared in large numbers, says Johnson. Silica doesn't dissolve well in seawater, making it a rare commodity in marine ecosystems. Many scientists argue that the rise of silica-hungry diatoms led to the demise of the reef-building glass sponges.

The reef-building sponges discovered earlier this year, like those previously found in Canada, live at depths below sunlight's reach, says Johnson. Because diatoms don't thrive there, dissolved silica is more available than it is in shallower waters.

Reef-building glass sponges had previously been found only in the protected waters of a near-shore strait, so researchers had presumed that the creatures could thrive only in certain restricted ecological niches. This summer's find in the open ocean hints, however, that these reef-building sponges may be found in deep waters worldwide, says Johnson.

DEATH AND LIFE Researchers know of many ancient creatures that apparently dropped out of the fossil record, returned from the dead to thrive for a while, then later disappeared for good. Lazarus taxa of this sort commonly reappear in the wake of mass extinctions, says Margaret Fraiser, a paleobiologist at the University of Wisconsin--Milwaukee.

The die-offs that occurred at the end of the Permian period, about 250 million years ago, have been termed "life's closest call" because about 70 percent of known land species and 95 percent of ocean species went extinct during a very short interval (SN: 2/1/97, p. 74). Although a large number of new species evolved following this mass extinction, many of the species that had apparently died out reappeared in the fossil record about 5 million years later, says Fraiser. For example, about 57 percent of the genera of gastropods, or marine snails, found in the fossil record after that 5-million-year gap were Lazarus taxa.

Many scientists contend that the simultaneous reappearance of so many Lazarus taxa indicates that the fossil record from that era can't be trusted, says Fraiser. Others suggest that the missing creatures simply became so rare that they weren't captured in the fossil record. Yet others propose that the creatures survived only in small areas and that their fossils haven't yet been discovered.

To test these ideas, Fraiser and her colleagues analyzed the fossil record of many types of marine creatures both before and after the Permian extinctions. Groups of species included sponges, shelled invertebrates such as brachiopods and bivalves, and echinoderms such as starfish and sea urchins.

Previously, some scientists had assumed that the fossil records of all of those groups of species would show a large number of Lazarus taxa, says Fraiser. That's not what her team found, she reported at a meeting of the Geological Society of America last month in Denver. None of the genera of echinoderms or brachiopods found in the fossil record 5 million years after the end-of-the-Permian extinctions represented Lazarus taxa. Only 12 percent or so of the bivalve genera found at that time had been resurrected, she notes. The dearth of resurrections among these groups suggests that the reappearance of the gastropods is genuine, not a sign that the fossil record during that interval is somehow faulty.

Scientists have also suggested that the fossil record immediately after the mass extinctions was poor because the drastic environmental changes that caused the die-offs also affected modes of fossilization. In particular, those scientists have suggested, tissues weren't being replaced by silica, which produces some of the most durable fossils. However, Fraiser and her colleagues found that about 58 percent of the fossils in the database they studied were formed of silica, which suggests that the fossil record from that era can be trusted. Further analyses will be needed to determine what happened to the Lazarus taxa during the gap in the fossil record immediately after the Permian extinctions, says Fraiser.

"These Lazarus taxa must have been somewhere, maybe in [rocks] that paleontologists haven't sampled yet," says Richard J. Twitchett, a paleoecologist at the University of Plymouth in England. "Or maybe their fossils have been misidentified or overlooked."

Modern discoveries of Lazarus taxa point out the risks of over-interpreting the absence of a creature from the fossil record.

"It's almost impossible to use the fossil record to define when an animal goes extinct," Twitchett adds. "Maybe it just became rare or marginalized."