A surprising find of fossil vulture feathers from central Italy has shown that volcanic deposits can preserve fine tissue structures in unprecedented detail, offering new insights into the fossilization process.
In 1889, at the foot of Mount Tuscolo, 25 kilometers southeast of Rome, farm workers discovered something unusual. Digging for a new vineyard, they came across a layer of rock with a strange hollow. In it was the skeleton of a large bird, including obvious imprints of its plumage on the surrounding rocks.
The strange find prompted the landowner to contact the renowned Italian geologist Romolo Meli. However, by the time Meli arrived on site, the workers had already sent most of the fossil blocks to the trash heap, and many were broken.
After salvaging most of the rocks, Meli identified the specimen as a fossilized bird of the vulture genus, the scavenger, White-headed Sip. He also noted that the preservation of the plumage was unusual, given that the rock was volcanic.
In the same year, Meli published a report on the find, but then the fossil white-headed vulture was safely forgotten and most of the rock specimens were lost. Today, only blocks containing the plumage of one wing and imprints of the bird's head and neck remain.
A breakthrough in research
A few years ago, advances in analytical approaches to studying fossils led researchers to take a renewed interest in this specimen, which likely dates to a period about 30,000 years ago. In 2014, paleontology scientist David Jurino led a new study using computed tomography (CT) imaging of the head and neck imprint.
This revealed three-dimensional details of the eyelids, tongue, and the texture of the bird's skin and neck. This excellent preservation of biological features surpasses even that of the victims of Pompeii.
Photo: theconversation.com
In a new study, a team of scientists from University College Cork, led by Professor Maria McNamara, analyzed the feathers and it became clear, in their words, "that we have something unusual in front of us." Through preliminary microscopic analysis, they discovered that the feathers, which are orange in color and contrast with the rock from which they are made, are preserved in three dimensions.
Three-dimensional fossil feathers are most commonly found in
antar, whereas feathers in rocks are usually two-dimensional thin layers of dark-colored organic matter.
Nevertheless, important questions remained about how the feathers were preserved in the volcanic deposits, so scientists conducted additional research.
A new way to fossilize
More detailed microscopic analysis showed that the three-dimensional preservation extended to the thin branches of the feathers. The researchers were even able to see feather structures less than one micron (0.001 mm) wide, in particular tiny cell organelles (parts of the cell) called melanosomes, whose pigments determine feather coloration.
Even stranger was the fact that the fossil feather was imprinted in a mineral called zeolite.
Zeolites are silicon- and aluminum-rich minerals that typically form in hydrothermal and volcanic environments, and they have also played a role as a preservative, creating accurate three-dimensional replicas of feather cells.
These minerals are not associated with any other fossil tissue, opening up a mode of fossilization that has never been recorded before. This is made possible because zeolite is formed by dissolving volcanic ash and glass.
The level of detail in the fossil tissue, as well as the chemical composition of the feathers, indicate some important differences between the pyroclastic flows that buried the white-headed sip and the flows that buried
Pompeii.
The ancient inhabitants of Pompeii were buried alive by hot, fast-moving turbulent streams of gas and ash, known as pyroclastic flows, at temperatures of more than 500 degrees Celsius. At such temperatures, their soft tissues vaporized, leaving only skeletons and charcoal.
Photo: theconversation.com
On the other hand, it remains unknown exactly how the white-headed vulture died. Perhaps it was suffocated by toxic clouds of volcanic gas, or perhaps it was killed directly by the pyroclastic flow. All that is known is that the flow was relatively cold because it was diluted with water or was far from the volcanic source.
The processes by which the volcanic deposits hardened into rock and formed zeolite happened relatively quickly (within days), which may explain why fine structures like feathers are well preserved in three dimensions.
Prospects
This opens up the possibility that many other volcanic rocks with high ash content may contain remarkable fossils, and thus are exciting new subjects for paleontological research.
The discovery may shed light on the evolution of
birds and their distant ancestors, revealing new facets of their adaptations. Feathers are amazing structures that serve not only for flight, but also for thermoregulation, camouflage, and communication. Their microscopic structure, including the arrangement of pigment structures, may hold the key to unraveling ancient mechanisms of survival and evolutionary transitions.