This tick may look like it's ready to bite, but it's actually 90 million years old. Discovered in an amber outcropping in a vacant lot in New Jersey, it is more than twice the age of the oldest tick fossil ever found. The discovery emphasizes how little ticks have changed in their evolutionary history.
Ticks belong to a group of arthropods called the Chelicerata, which also includes spiders, mites, and horseshoe crabs. Ticks, mites, and their close relatives are known as the Acari. Although there are some 30,000 known species of Acari today, only a half-dozen fossil ticks have ever been found. The oldest to date was one found in 42-million-year-old Baltic amber.
The specimen, just 520 micrometers long, was found by a team from New York City's American Museum of Natural History and is described by Hans Klompen of Ohio State University, Columbus, and the museum's David Grimaldi in a recent issue of the Annals of the Entomological Society of America. It's a so-called soft tick in the larval stage. What's remarkable, Klompen says, is that the tick has a surprising number of hairs on its backside, all arranged in a regular pattern. In contrast, the larvae of living soft ticks are almost completely bald. And the larvae of a related group, known as the hard ticks, are covered with a fairly regular arrangement of hairs. This congruence suggests that the new tick, dubbed Carios jerseyi, is close to "the evolutionary starting point of all ticks."
The similarity to modern ticks amazes tick expert Daniel Sonenshine of Old Dominion University in Norfolk, Virginia. "It's astounding to me that there's so little change," he says. And that's despite a massive change in available hosts some 65 million years ago, when the dinosaurs and other vertebrates went extinct. Whatever their secret, Sonenshine says, "the ticks have done something that's very effective."