October 14, 2013
In the 20 years since the movie Jurassic Park fantasized about how dinosaurs could be cloned from blood found in ancient amber-trapped mosquitoes, fossil collectors have been on the hunt for a similar specimen. Over the years, a few different groups of scientists have claimed to find a fossilized mosquito with ancient blood trapped in its abdomen, but each of these teams’ discoveries, in turn, turned out to be the result of error or contamination.
Today, it was announced that we finally have such a specimen, a blood-engorged mosquito that’s been preserved in shale rock for around 46 million years in northwestern Montana. The most astounding thing about the discovery? It was made three decades ago by an amateur fossil hunter—a geology graduate student named Kurt Constenius—then left to sit in a basement, and only recognized recently by a retired biochemist named Dale Greenwalt who’s been working to collect fossils in the Western U.S. for the Smithsonian Museum of Natural History.
The specimen, described in a paper Greenwalt published with museum researchers and entomologist Ralph Harbach today in the Proceedings of the National Academy of Sciences, is trapped in stone, not amber, and (unfortunately for Jurassic Park enthusiasts) it’s not old enough to be filled with dinosaur blood. But it is the first time we’ve found a fossilized mosquito with blood in its belly.
The rock-encased specimen was originally excavated sometime during the early 80s, when Constenius, then pursuing a master’s degree in geology from the University of Arizona, found hundreds of fossilized insects during weekend fossil-hunting trips with his parents at the Kishenehn Formation in northwestern Montana, near Glacier National Park. In the years since, they’d simply left the fossils sitting in boxes in their basement in Whitefish, Montana and largely forgotten about them.
Enter Greenwalt, who began volunteering at the museum in 2006, cataloging specimens for the paleobiology department. In 2008, he embarked on his own project of collecting fossils from the Kishenehn every summer, in part because he’d read in an insect evolution textbook an offhand mention of Constenius’ discoveries, which had never been rigorously described in the scientific literature.
In the years since, Greenwalt has collected thousands of specimens from 14 different orders of insects. The collection site is remote—he has to raft the Flathead River that runs along the border of the park to a place where the river has cut down through layers of rock of the Kishenehn Formation, which includes shale that formed the bottom of a lake during the Eocene epoch, some 46 million years ago.
“It is a fantastic fossil insect site, arguably one of the best in the world,” he says, noting that a rare combination of circumstances—thin layers of fine-grained sediment and a lack of oxygen—led to a “mind-boggling degree of preservation.” Working there, he’s made a number of significant finds, collecting specimens that led to the description of two new insect species (pdf).
After Greenwalt met the Constenius family in Whitefish and described his work, they decided to donate their fossil collection to the museum. When he began cataloging the boxes the fossils and came across this particular specimen, “I immediately noticed it—it was obvious that it was different,” he says. He suspected that the mosquito’s darkly opaque abdomen, trapped in a thin piece of shale, might contain 46-million-year old blood.
Staff from the museum’s mineral sciences lab used a number of techniques to scan the specimen up close, including energy dispersive X-ray spectroscopy. “The first thing we found is that the abdomen is just chock full of iron, which is what you’d expect from blood,” Greenwalt says. Additionally, analysis using a secondary ion mass spectrometer revealed the presence of heme, the compound that give red blood cells their distinctive color and allows them to carry oxygen throughout the body. Other tests that showed an absence of these compounds elsewhere in the fossil.
The findings serve as definitive evidence that blood was preserved inside the insect. But at this point, scientists have no way of knowing what creature’s fossilized blood fills the mosquito’s abdomen. That’s because DNA degrades way too quickly to possibly survive 46 million years of being trapped in stone (or in amber, for that matter). Recent research had found it has a half-life of roughly 521 years, even under ideal conditions.
This means that even if we miraculously had some DNA of the ancient creature, there are currently a ton of technical problems that prevent the cloning similar to that in Jurassic Park from becoming a reality. Assembling a full genome from DNA fragments requires us to have an understanding of what the whole genome looks like (which we don’t have in this case), and turning that into a living, breathing animal would necessitate putting that DNA into an ovum of a living species very closely related to the mystery creature that we don’t know in the first place.
So, alas, no resurrected ancient creatures will roam free thanks to this new find. Still, the find is scientifically significant, helping scientists better understand the evolution of blood-feeding insects. Previously, the closest thing to a blood-engorged mosquito that scientists had found was a mosquito with remnants of the malaria parasite inside its abdomen (pdf). Though that provides indirect evidence that mosquitoes fed on blood 15-20 million years ago, this new discovery represents the oldest direct evidence of blood-sucking behavior. It also shows for the first time that biological molecules such as heme can survive as part of the fossil record.
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