Archaeopteryx feather considered as impressions are in fact remnant body fossil structures
For the first time ever, chemical analysis of Archaeopteryx — a transitional fossil between dinosaurs and bird — has been carried out, and first ever maps of dinobird's chemistry have been created. The maps reveal half a dozen elements (mainly phosphorus, sulphur, zinc, calcium, manganese, iron) that were actually part of the living animal.
The study marks a paradigm shift in the way palaeontology samples are studied in future. Chemical analysis of fossils, both hard and soft tissues, along with the rock in which they are embedded (matrix), would soon become a norm.
The study was published recently in the Proceedings of National Academy of Sciencejournal. The Archaeopteryx sample studied was from the Solnhofen region of Bavaria, Germany.
The sample was studied using a bright X-ray beam (synchrotron rapid scanning X-ray fluorescence). This technique has the potential to know structures that are not apparent in visible light, macronutrient and trace element distribution in bones and soft tissues, and the chemical processes of fossilisation.
For instance, the study has shown that portions of feather so far considered as impressions on the rock are in fact remnant body fossil structures.
Archaeopteryx specimens posses both reptilian features such as jaws with teeth and a long bony tail, and avian feather like feathered wings. The presence of featured wings is critical for considering Archaeopteryx as a transitional fossil.
Till recently, the feather structures were considered nothing but impressions left behind by the soft tissue. But chemical analysis has changed all that. The feather structures can also be called as ‘ chemical fossils.'
In fact, the chemical analysis has revealed previously unkown details about the “chemical preservation of soft tissue, and elemental distribution patterns most likely related to the organism's life processes.”
The most striking feature is that in addition to bone structures, the chemical composition of shafts from the flight feathers has been revealed. The amount of phosphorus seen in the feathers is nearly the same as seen in other extant feathers, while the levels of sulphur are nearly three times lower.
According to them, phosphorus content in the bones is greater than what is seen in the matrix (rock) and hence “strongly supports the inference that part of the feather chemistry is preserved.”
According to the researchers, the distribution of zinc is controlled by fossil bone material; skull contains the highest levels of zinc.
Many earlier studies have shown that zinc is well conserved within bones and their levels are high in the bone material. But when compared to modern bone and other fossils, there has been some loss of zinc.
Based on these facts, the authors conclude that “high zinc levels in Archaeopteryx bone have been inherited from the original organism.”
As expected, the concentration of several elements is greater in the skull, teeth, claws, and postcranial skeletons. But certain elements are removed at higher levels from the skeletons. For instance, loss of phosphorus is extensive; calcium loss is nearly minimal.
The relatively lower loss of calcium has got to do with the matrix of limestone in which the fossil is found. The Archaeopteryx fossil studied is hosted in a high calcium environment; loss has therefore been minimal.
On the other hand, phosphorus loss is extensive as the region in which the fossil was found has quite low phosphorus concentrations.
“Therefore sediment chemistry probably served to enhance phosphorus removal but inhibit Ca [calcium] loss from the Archaeopteryxbone and also kept levels of Mn [manganese] and Fe [iron] relatively low in the fossilised bone. Retention of Ca may also have helped immobilise Zn [zinc],” they write.
The oxidizing or reducing environment has played a role too in the loss of elements from the fossil.
This study shows the importance of studying the matrix as well to know what led to the loss or retention of elements in the fossils. Fossils as such cannot be studied.