To round off my brief stint at the Guardian, here’s a piece about a mastodon specimen with what looks like a spear-tip stuck in its rib. This specimen, the so-called “Manis mastodon” has been a source of controversy for several decades. Is that fragment man-made or simply one of the animal’s own bone splinters? Does it imply that humans hunted large mammals hundreds of years earlier than expected, or not?

Having re-analysed the rib in an “industrial-grade” CT scanner, Michael Waters thinks it’s definitely a man-made projectile. He even extracted DNA from the rib and the fragment and found that both belonged to mastodons. So these early hunters were killing mastodons and turning them into weapons for killing more mastodons. How poetically gittish.

Anyway, read the piece for more about why this matters. In the meantime, I want to draw your attention to this delicious tete-a-tete at the end between Waters and Gary Haynes, who doesn’t buy the interpretation. Note, in particular, the very last bit from Waters, which made my jaw drop.

But despite Waters’ efforts, the fragment in the Manis mastodon’s rib is still stoking debate. “It’s not definitely proven that it is a projectile point,” says Prof Gary Haynes from the University of Nevada, Reno. “Elephants today push each other all the time and break each other’s rib so it could be a bone splinter that the animal just rolled on.”

Waters does not credit this alternative hypothesis. “Ludicrous what-if stories are being made up to explain something people don’t want to believe,” he says. “We took the specimen to a bone pathologist, showed him the CT scans, and asked if there was any way it could be an internal injury. He said absolutely not.”

Waters adds, “If you break a bone, a splinter isn’t going to magically rotate its way through a muscle and inject itself into your rib bone. Something needed to come at this thing with a lot of force to get it into the rib.”

The spear-thrower must have had a powerful arm, for the fragment would have punctured through hair, skin and up to 30 centimetres of mastodon muscle. “A bone projectile point is a really lethal weapon,” says Waters. “It’s sharpened to a needle point and little greater than the diameter of a pencil. It’s like a bullet. It’s designed to get deep into the elephant and hit a vital organ.” He adds, “I’ve seen these thrown through old cars.”