Jurassic Park’s Blood Meal Cometh. (Well, Almost.)
Posted by Richard Conniff on October 14, 2013
Here’s my latest story for the folks at TakePart.
Somewhere in the afterworld, Jurassic Park author Michael Crichton must be twitching and grinning with the glee of the science fiction writer proved right, or at least not so woefully wrong: Researchers have announced the discovery of specimen USNM 559050, a fossilized mosquito from northwestern Montana, containing what is indisputably a blood meal in its swollen belly.
The specimen, described in today’s Proceedings of the National Academy of Sciences, dates back 46 million years—not quite to the age of dinosaurs, but tantalizingly close. Crichton built his novel Jurassic Park, published in 1990, on what then seemed to be a far-fetched premise: Scientists had supposedly figured out both how to extract DNA from the blood in ancient mosquitoes preserved in amber, and also how to use that DNA to bring the dinosaurs on which those mosquitoes had fed back to life
That premise is still far-fetched, but now just a smidgeon less so. USNM 559050 turned up not in amber, but in shale, like most mosquito fossils found to date. (The fossils in amber are typically midges, which apparently liked to hang around in a certain type of primordial forest and thus sometimes got trapped forever in amber exuded by resin-producing trees.)
Preservation of the mosquito specimen “was an extremely improbable event,” according to biochemist Dale E. Greenwalt and his co-authors. “The insect had to take a blood meal, be blown to the water’s surface, and sink to the bottom of a pond … to be quickly embedded in fine anaerobic sediment, all without disruption of its fragile distended blood-filled abdomen.” In a phone interview, Greenwalt likened the blood-swollen abdomen to “a balloon ready to burst.” He put the probability that it would have been preserved at “almost one over infinity.”
The researchers were able to use modern mineral science technology to analyze the contents of the abdomen without destroying the specimen. They found high levels of iron and porphyrins—both important components of hemoglobin, the oxygen-carrying molecule in red blood cells. It is the first time anyone has found actual blood in a fossilized mosquito, from the host animal it had been feeding on immediately prior to death.
Finding blood remnants is, however, not even close to Crichton’s fantasy of finding intact DNA. Jurassic Park was great entertainment, said Greenwalt, and it also caused scientists to undertake useful research to test the idea of recovering ancient DNA. “But DNA is a very large, very fragile molecule,” he said, “and the consensus now is that it’s just not going to survive.” Researchers have looked for DNA even in insects preserved for as little as 50 to 10,000 years in subfossilized resin, called copal, “and found nothing.”
The new find came about largely through the work of amateur paleontologists. Greenwalt, a retired cell biologist in the biotech industry, now works as a volunteer at the Smithsonian Institution. A few years ago, he happened to be reading a huge tome about insect evolution when his attention riveted on a single paragraph about fossil insect specimens from the Coal Creek member of the Kishenehn Formation.
With permission from the U.S. Forest Service, Greenwalt began collecting there, on the Middle Fork of the Flathead River. He eventually learned that the original insect fossils had been gathered in the early 1980s by a couple from Whitefish, Montana. Norm and Leona Constenius used to hike in the area while their son Kurt was doing his research for a doctorate in geology. They eventually retrieved their collection from their basement and donated it to the Smithsonian. There, Greenwalt found USNM 559050.
The new research proves conclusively that one of our least favorite animal behaviors—insect feeding on blood—has been around for tens of millions of years. USNM 559050 is not the oldest fossil mosquito; other specimens date back into the Cretaceous, when dinosaurs lived. Earlier specimens have also had a proboscis like modern mosquitoes, leading scientists to suspect that they were blood feeders. Moreover, some of those fossils have revealed the presence of blood-borne disease organisms, including the malaria plasmodium. But finding actual blood seals the case.
The study could help researchers patching together the early evolution of insect blood feeding—now practiced by about 14,000 living species, including flies, fleas, lice, bed bugs, and a few vampire moths. It could also improve our understanding of important insect-borne diseases like malaria, yellow fever, and dengue fever. “Mother Nature is always changing,” said Greenwalt, “and we’re never sure how. Any information about the past might help us understand what could happen in the future.”
That leaves one big question: What species did USNM 559050 feed on in the moments before death? The specimen did not have enough detail for co-author Ralph E. Harbach, an entomologist at the Natural History Museum in London, to make a positive identification. But the mosquito most closely resembles a modern genus, Culiseta, in which the mosquitoes feed exclusively on birds.
That is, the blood meal certainly didn’t come from dinosaurs. But it may well have come from the birds that we now know to be their closest living descendants.