Based on a DNA analysis of a fossilised eggshell fragment of ostrich, Indian researchers have for the first time found molecular evidence to confirm the presence of these birds in India more than 25,000 years ago. Scientists found 92% genetic similarity between the fossil eggshell samples and Struthio camelus, an ostrich species found in Africa. The results were published in the journal PLOS ONE.
Eggshell fragments of ostrich discovered from India before have been studied using morphological features, which is insufficient to confirm the existence of ostrich in India. This is the first time that molecular evidence indicating their presence in India has been obtained.
Proves the continental drift
The ostrich sample analysed has close proximity to the African ostrich species and underlines the movement of these birds between Africa and India before the Indian landmass drifted away from Africa.
Eleven fossilised eggshell samples from eight archaeological sites in Rajasthan, Gujarat and Madhya Pradesh were studied. The DNA was isolated from five samples and a tiny portion (43 base pairs) of a highly-conserved mitochondrial region was amplified and then sequenced from one of the samples. The other four samples had less than 30 base pairs and hence were not included in the study.
“We could amplify only a small portion of the DNA as the sample was highly degraded. It is scientifically challenging to isolate DNA from ancient samples. And in this case, the samples were exposed to hostile environment,” says Dr. Kumarasamy Thangaraj from the Centre for Cellular and Molecular Biology (CCMB), Hyderabad and one of the authors of the paper.
This is a hard shell to crack
“It is very difficult to study ancient DNA as it is often broken into small fragments. In this case, the DNA was highly fragmented. So we could amplify only a smaller overlapping DNA fragment,” Dr. Thangaraj says. “We are happy that we could get this much information considering that the sample was very old and not well-preserved.”
It is the first time that long-term DNA preservation in fossil eggshell collected from tropical environments, as seen in India, has been studied.
“Eggshells are a better substrate than bones for preserving ancient DNA. The intracrystalline structure of the shell minimises microbial contamination,” says Sonal Jain from the Department of Biotechnology, Indian Institute of Technology (IIT) Roorkee and the first author of the paper.
“X-ray diffraction and electron backscattering diffraction studies helped in finding which eggshells were good and which were bad. The shells are made of calcium carbonate. If calcium changes to magnesium and if there is more magnesium then the sample is more degraded,” says Jain.