How do organisms become fossils?
There are many ways that an animal or plant is fossilized. Most of the time, it is done when an organism dies in a watery environment and is buried in mud and silt. When the soft tissues decompose, it leaves the bones and hard shells on the rock. Then over time, sediments will form on top and harden the rock. These secrets in the stone are only revealed after the process of erosion occurs.
The term fossil refers to any trace of past life that can be an organism's remains such as plant, shells, teeth or bones. It can also be of the activity of an organism like footprints, burrows, and feces. These organisms may be preserved through permineralization, natural casts, a preserved amber, trace fossils, and preserved remains.
The Recent Discovery
Amber is considered an excellent preservative of ancient remains. Small animals can be enclosed in a drop of tree resin that hardens over time. The University of Bonn has now examined a rare find from the Dominican Republic. It is a tiny forefoot of a lizard of the genus Anolis that is enclosed in amber only about two cubic centimeters in size. There are still Anolis lizards that live until this day.
Vertebrate inclusion in amber is very rare
According to Jonas Barthel, a doctoral student in the Institute for Geosciences at the University of Bonn, "vertebrate inclusions in amber are very rare, the majority are insect fossils." That is why scientists are using this opportunity to examine the fossilization of this very well preserved vertebrate fragment.
The present study was conducted within the framework of a joint research project of the University of Bonn with the German Research Foundation in 2018, which contributes to the understanding of fossilization using experimental and analytical approaches.
Barthel and colleagues had thin sections prepared for microscopy at the Institute for Evolutionary Biology at the University of Bonn. The left forelimb of the Anolis lizard is visible in the honey-brown amber mass in a 2-cm piece of a 15-20 million-year-old Dominican amber.
The analyses revealed that the forefoot is broken in two places and one fracture is surrounded by swelling. Scientists proposed that the lizard might have been climbing the tree when it suddenly got into contact with the flow of resin and could not escape and then after some time a predator saw it and ripped off the lizard. The second fracture happened after the fossil was embedded and become deposited within the surrounding soil exactly at the place where a small crack runs through the amber.
Amber did not protect from environmental influences
The Raman spectroscopy, which is a method used to examine the chemical composition of a material, revealed that the mineral known as hydroxyapatite in the bone had been transformed into fluorapatite by the penetration of fluorine.
Surprisingly, amber is not the reason for the preservation of the fossil. The small crack may have encouraged the chemical transformation by allowing entry of the mineral-rich solutions. Furthermore, the spectroscopy has also shown that the collagen had largely degraded even with the seemingly very good state of preservation, there was very little left of the original tissue structure.
Although amber is considered ideal preservation. The acids in the tree resin might have accelerated the degradation process of the lizard's bone. It has probably attacked the apatite in the bone similar to what happens with tooth decay.
