On a tree in what's now Burma some 99 million years ago, a cousin of today's daddy longlegs had the best and worst day of his life.
After a months-long puberty, the male harvestman Halitherses grimaldii had finally blossomed into full manhood, sporting a penis that grew to nearly half of his body length when erect.
We know about this H. grimaldii's particular package because, as announced last Thursday in The Science of Nature, he died fully aroused, his tree-side tryst interrupted by oozing resin that entombed his body in what's now a lump of amber.
"It must have been in an amorous state to have it out like this," says Ron Clouse of the American Museum of Natural History, who wasn't involved with the study. "This poor animal."
Unlike male spiders and scorpions, which use modified legs to transfer sperm to females in tidy packets, most harvestmen like H. grimaldii have honest-to-goodness penises, which they insert into genital openings next to the females' mouthparts.
The newly described fossil is the first to capture such a penis in amber—and is among the best preserved ever found, scientists say.
These well-endowed arachnids have been around a long time, nibbling on scraps and rummaging through leaf litter for more than 400 million years.
The arachnids' long track record excites scientists, since understanding the harvestman family tree could give insight into how other life-forms spread across ancient Earth's shifting landmasses.
However, evolution has caused many harvestmen to look the same, so it's often hard to tell who's really related to whom. "It's messy," says Clouse.
Study leader Jason Dunlop, of the Berlin Museum for Natural History, has made a career out of tidying up this mess by hunting for and analysing fossil harvestmen—especially their genitals.
"Different families, and even species, [of harvestmen] can have a characteristic penis shape," he says. "In fact, [penises] are often even more important than the shape of the body and legs."
The specimen is also important beyond its nether regions.
For one, careful 3-D scans and photographs of the H. grimaldii fossil show that its penis' distinctive shape—from the heart-shaped head to its twirled tip—are different from other species', placing the harvestman in its very own family.
It's a move biologist Bill Shear of Hampden-Sydney College had suggested in 2010, but the exquisite specimen gives his analysis added heft.
"It’s gratifying to see a fairly obscure group of animals—and fossils!—drawing attention," says Shear.
The large-eyed harvestman's toothless mouth pincers also confirm it belongs to a rarely collected type of harvestman that was recently snipped from one family tree branch and grafted onto another, a major taxonomic shake-up.
Dunlop acknowledges, however, that the fossil still raises questions. For one, there's no female trapped alongside the helpless H. grimaldii, suggesting a tragic separation—or death throes that inadvertently left him aroused for the ages.
"It might be the case that the animal was struggling as it was trapped in the tree resin," says Dunlop, "and that this caused the blood pressure to shoot up and the penis to become squeezed out accidentally." Ouch.
By Michael Greshko