millipede amber
© Leif Moritz
Held still for 99 million years: a millipede preserved in amber.
The earliest known millipede fossil has been discovered preserved in amber in Myanmar.

The arthropod, just 8.2 millimetres long, was found trapped in a piece of amber dated to 99 million years ago, putting it well into the Cretaceous period.

Writing in the journal ZooKeys, researchers led by Pavel Stoev from Bulgaria's National Museum of Natural History suggest that the newly identified species - dubbed Burmanopetalum inexpectatum - will prompt a substantial rethink of the evolutionary history of the millipede order, Callipodida.

The specimen suggests that millipedes first evolved more than 100 million years ago.

By using 3D X-ray microscopy to construct a virtual model of the find - including its internal details - the researchers concluded that it was significantly different to other early millipedes, and placed it in its own sub-order.

"It came as a great surprise to us that this animal cannot be placed in the current millipede classification," explains Stoev.

"Even though their general appearance has remained unchanged in the last 100 million years, as our planet underwent dramatic changes several times in this period, some morphological traits in Callipodida lineage have evolved significantly."