Lizard tail in 99-million-year-old Myanmar amber preserves direct evidence of voluntary shedding

Researchers from Tel Aviv University, the National and Kapodistrian University of Athens and the Volcani Institute have described a detached lizard tail in Cretaceous amber about 99 million years old from northern Myanmar. The results were published in Palaeontologia Electronica doi.orgPalaeontologia Electronicadoi.orgOpen source ↗. The amber piece is 18 millimeters long. According to the authors, the specimen captures the autotomy event itself, the voluntary shedding of the tail doi.orgPalaeontologia Electronicadoi.orgOpen source ↗.

Micro-CT of the break point

The amber is cloudy, and the structures inside were too small for an ordinary microscope. The team used micro-CT at the Volcani Institute, which combines X-ray images taken from many angles into a three-dimensional reconstruction. This made it possible to examine the specimen without cutting it open.

At the severed end of the tail, the scans revealed a characteristic wedge-shaped ring of muscle. The authors report that it is consistent with the morphology of self-detached tails in modern lizards doi.orgPalaeontologia Electronicadoi.orgOpen source ↗. The separation was relatively clean and symmetrical, without the damage patterns expected if the tail had broken off in an accident. The authors conclude that the structure excludes accidental or traumatic breakage doi.orgPalaeontologia Electronicadoi.orgOpen source ↗.

The tail was found by Dolev Fabrikant, a PhD candidate at Tel Aviv University. He was examining what looked like a twig or an insect fragment and noticed that its surface was covered in tiny scales.

Why earlier fossils were less conclusive

Other reptile fossils preserve natural fracture planes in the tail vertebrae, or regenerated tails showing that the animal had lost part of its tail earlier. These features suggest that ancient reptiles could shed their tails. Fracture planes alone, however, do not show that the animals actually used this defense. The authors state that the Myanmar specimen is the first direct fossil evidence of voluntary tail shedding in a fossil vertebrate doi.orgPalaeontologia Electronicadoi.orgOpen source ↗.

The lizard itself remains unidentified. The skull and the rest of the skeleton are missing, so the specimen can be identified only as a lizard. The authors name possible affinities with the groups that include today's wall lizards or, alternatively, slow worms and monitor lizards.

How the tail ended up in the resin is also unknown. The lizard may have become stuck in sticky resin and shed its tail to free itself. Alternatively, a predator may have attacked the animal, which released its tail, and the tail later landed in the resin.