New fossil discovery reveals how volcanic deposits can preserve the microscopic details of animal tissues

An analysis of a 30,000-year-old fossil vulture from Central Italy has revealed for the first time that volcanic rock can preserve microscopic details in feathers - the first ever record of such a preservation.

An international team, led by Dr Valentina Rossi (University College Cork, Ireland), discovered a new mode of preservation of soft tissues that can occur when animals are buried in ash-rich volcanic sediments.

The new research, published in the scientific journal Geology, reveals that the feathers are preserved in a mineral phase called zeolite, a mode of preservation of soft tissues never reported before.

The fossil vulture was found in 1889 near Rome by a local landowner who recognized its remarkable preservation. The entire body was preserved as a three-dimensional impression, with fine details such as the eye lids and wing feathers. The new research shows that preservation of feathers extends to tiny microscopic feather pigment structures.

Dr Rossi said: “Fossil feathers are usually preserved in ancient mudrocks laid down in lakes or lagoons. The fossil vulture is preserved in ash deposits, which is extremely unusual. When analysing the fossil vulture plumage, we found ourselves in uncharted territory. These feathers are nothing like what we usually see in other fossils”.

By analysing tiny samples of the fossil feathers using electron microscopes and chemical tests, the team revealed that the feathers are preserved in the mineral zeolite, a mode of fossil preservation never reported before.

“Zeolites are minerals rich in silicon and aluminium and are common in volcanic and hydrothermal geological settings” Rossi explains “zeolites can form as primary minerals (with pretty crystals) or can form secondarily, during the natural alteration of volcanic glass and ash, giving the rock a “mudrock-like” aspect”. The alteration of the ash due to passage of water induced the precipitation of zeolites nanocrystals that, in turn replicated the feathers to the tiniest cellular detail.

"The fine preservation of the feather structures indicates that the vulture carcass was entombed in a low temperature pyroclastic deposit."

Prof. Dawid A. Iurino (University of Milan), coordinator of the study said: “We are used to think that volcanic deposits are associated with hot, fast-moving pyroclastic currents that will destroy soft tissues. However, these geological settings are complex and can include low temperature deposits that can preserve soft tissues at the cellular level.”

Prof. Maria McNamara (UCC) said “The fossil record is continually surprising us, be it new fossil species, strange new body shapes, or in this case, new styles of fossil preservation. We never expected to find delicate tissues such as feathers preserved in a volcanic rock. Discoveries such as these broaden the range of potential rock types where we can find fossils, even those preserving fragile soft tissues.”

The discovery of a new mode of preservation of soft tissues potentially specific of volcanic rocks indicates that these deposits can contain remarkable fossils and should be the focus of new research.

ENDS