What Adam Is Reading · Things I Learned
Zombie Worms of the Tuscan Seafloor
Five million years ago, near what is now Pienza, a worm with no mouth bored into the roots of shark teeth. It left the enamel alone. Even then, Tuscany had standards.
Things I Learned · Fossil Record, November 2025 · 4 sources · October 2026

Italian paleontologists have found evidence of zombie worms in Tuscany. Nothing shambles. Nothing moans. Nobody needs a crossbow. The worms are Osedax, and what they were doing, roughly five million years ago, was eating the roots of shark teeth on the floor of a quiet Pliocene bay.

I wanted to know why anyone calls them zombie worms. As far as I can tell, nobody official does. Osedax is Latin for “bone devourer,” which is accurate and a little dull. The zombie label comes from the press and the popular science blogs, and the logic seems to be that they live on the dead. In the deep sea, that is apparently enough to get you a horror franchise.

The sharks, for the record, were requiem sharks. Of all the names in this story, theirs is the most funereal.

4
fossil Carcharhinus teeth, surface collected near Pienza
~5 Ma
Zanclean age, Early Pliocene
0.16–0.47 mm
boring apertures, invisible without micro CT
0
borings in the enameloid crowns
What They Found in Tuscany

Alberto Collareta (University of Pisa) and ten colleagues examined four requiem shark teeth from the Argille Azzurre Formation, the “blue clays” of the Siena-Radicofani Basin. These are the same Pliocene sediments that erode into the gray badlands south of Siena. Back then the area was a semi-enclosed embayment with low oxygen and plenty of organic matter on the bottom. Good conditions for a worm that eats the dead.

The teeth went into a micro CT scanner at the CNR Institute of Applied Physics in Sesto Fiorentino, with resolution down to 18 micrometers. Inside the root dentine were small, tree shaped cavities, each opening to the surface through a single pinhole. The team reconstructed five of them in three dimensions. Every chamber held less than half a cubic millimeter.

Every boring was in the root. The enameloid crowns, which are the hard, shiny, shark tooth part of a shark tooth, were essentially untouched. The worms went for the dentine, which has more collagen, and skipped the part a collector would pay for.

The borings match a trace fossil called Osspecus tusciae, originally named from Pliocene whale bone at Orciano Pisano, also in Tuscany. It is the first fossil evidence of Osedax in shark teeth anywhere. The only previous sighting was modern and staged, when researchers sank thresher shark jaws near a whale fall off Monterey and the worms moved in.

A note on trace fossils. The worm itself almost never fossilizes. It has no bones, which given its diet is a little ironic. So paleontologists name the hole instead of the animal. Osspecus is the name of the burrow. We know Osedax was there the way you know a raccoon was in the garbage.
How Much to Believe
1
Osedax made these holes

The single entry, branching shape matches known Osedax borings, the site sits in the same Tuscan Pliocene that already produced Osedax traces in whale bone, and the live worm has been shown to eat shark dentine. No body fossil, and four teeth is a small sample. But the identification is about as good as trace fossil work gets.

Mostly Solid
2
Worms help explain all those rootless shark teeth

Fossil and deep sea shark teeth often turn up without roots. The authors propose that Osedax did to tooth roots what it is known to do to whale skeletons, a degradation paleontologists call the “Osedax effect.” These borings are small and probably early snapshots, so complete root loss may be common. Plausible, and testable, but not yet tested at scale.

Mostly Solid
3
Shark teeth carried the worms through the dinosaur extinction

The oldest Osspecus traces date to about 100 million years ago. Then the record goes quiet from the latest Cretaceous to the middle Eocene. Shark teeth are everywhere on the seafloor and survived the extinction just fine, so the authors float them as stepping stones between rare whale and reptile carcasses, and possibly a refuge across the extinction. They are careful to call this open. So am I.

Open Question
The Tuscan Part

Pienza is the hill town Pope Pius II rebuilt in the 1460s as a model of the ideal Renaissance city. Today it is a UNESCO World Heritage site, best known for its views of the Val d’Orcia and its pecorino. Five million years earlier the same ground was the bottom of a murky, low oxygen bay, and its residents were dining on shark.

The palate has always been regional. Some things take longer to age than cheese.

So What

Part of the fossil record is missing because something ate it. In a low oxygen Tuscan bay, a worm with no mouth chose the root over the crown, and five million years later a CT scanner caught it in the act.

Small sample (four teeth, five reconstructed borings). The extinction refuge idea is the authors’ hypothesis, not a finding. The “zombie worm” nickname is popular usage, not taxonomy.

Sources

Primary paper: Collareta A, Mezzasalma O, Agresti J, et al. Trace fossil evidence for Osedax exploiting shark tooth dentine on a Pliocene seafloor. Fossil Record 28(2): 359–375, 2025. doi:10.3897/fr.28.167615. fr.pensoft.net/article/167615

News coverage: “Zombie Worms Caught in the Fossil Record Boring into Pliocene Shark Teeth.” ScienMag. scienmag.com

Osedax biology: Wikipedia, “Osedax.” en.wikipedia.org/wiki/Osedax

Zombie framing: Deep Sea News, “10 Reasons Why Bone Eating Worms Are F’n Awesome,” 2013. deepseanews.com