Biological Black Boxes Carry Tales of Past

Black Box of a plane is perhaps the most significant hardware! It is the only witness to the tragedy, in case of a plane crash. And interesting thing about the black box is that it records too! Therefore, whether land or ocean wherever the plane crashes the black box is much sought object.

Natural disasters for example in the abyss of the oceans are often witnessed only by mute organisms. Matters become complex when we talk of disasters that struck millions of years ago. For example we talk of drifting of continents, continental collision, global chilling and global sea level changes in the past. Such disasters have been truthfully recorded by and particular species of fossils like the sequence of events recorded in a Black Box. Geologists are able to locate, identify and interpret such black boxes and use the information to unfold the mysteries of nature.

It was a windfall for Sabyasachi Shome of Geological Survey Of India, Kolkata who discovered in the Kutch region of Gujarat few such ammonite fossils that are now being considered as marine black boxes. Shome along with a team of experts from the Department of Earth Sciences, Jadavpur University and Indian Statistical Institute, Kolkata published the findings in Current Science (January, 2004) and described the significance of the fossils discovered.

It is indeed intriguing that some of the organisms of the bygone eras appeared on the Planet only for a short while, yet their bio-geographical spread was wide. It was as if these organisms were trying to spend a 'little hour of grace on our Earth. Such fossils are described as 'fleeting fossils' say Shome and his co-workers. 

Ammonites are an extinct group of marine animals belonging to the class Cephalopoda and Phyllum Mollusca. They are excellent index fossils says the Wikipedia. In other words some species of ammonites are such that one can establish the time period when a particular layer of rock was deposited in the sea.

Many of the ammonites are fleeting fossils. Such fossils are sort of biological stopwatches, with the help of which the paleontologists are able to decipher the minute details of the earth's history. Ammonites are environment sensors too. They are exclusively marine organisms and many species are restricted to particular latitudes. With the help of such fossils it is therefore possible to reconstruct the past geography too.

Rifts and polarizations in the contemporary society are order of the day. Reasons for such incidents could be many. It is an irony that drifting and polarization of continents has been going on since times immemorial. In the geological past when human evolution had not taken place the forces of nature made the continents drift apart or collide. The process of the last fragmentation of the earth's continent began in the Jurassic period of the earth's history some 203 to 141 million years ago (Ma). India was then part of a super-continent, the Gondwanaland and started drifting away nearly 120 Ma to make its solitary journey of approximately 8000 km before hitting the Asian Plate. The wandering Indian continent carried all the living and the dead (fossils) including the ammonites too like a giant Noah's Arc.

At the beginning of the 'split', around 170 to 140 Ma, West Gondwana that comprised of Africa and South America separated from East Gondwana consisting of India, Antarctica and Australia. Palaeontological evidences indicate that eastern part of Africa and Madagascar and western coast of India support a fauna typically endemic to Indo-Madagascar faunal province. 

It is believed that India and the southern part of Africa were land-locked till about 140 Ma. During this time sea level fluctuations were galore on major continental shelves (land sloping in to the sea). The region now called Kutch in Gujarat was facing a regression of the sea. Thus while in India during end of Jurassic period (about 141 Ma) and beginning of Cretaceous period there was a steep fall in the sea level, Madagascar coast had open sea, meaning regression was not there. Naturally this type of sea had a typical ammonite fauna. At the end of Jurassic period there was a global 'flooding'. The sea level rose. 

This facilitated many of the ammonite families to have a circum-global distribution. Shome and his friends have been lucky in locating ammonites belonging to the subfamily Himalayantinae. The genera belonging to this subfamily had a greater bio-geographical spread. Ammonites being highly sensitive to sea level changes vanished from an area as soon as the sea level went down. This character was common with the ammonites of the upper most Jurassic that is 141 Ma. Prior to discovery made by Shome and his colleagues the genera of the subfamily Himalayantinae were known only from the Tethys (Himalayas), East Africa, Mediterranean and Pacific provinces. The discovery of ammonites of this subfamily from Kutch has created a history of sorts as because of them it is possible to mark the palaeo-latitudinal position of Kutch. One of the fossil genera Tethopeltoceras was earlier only known from the Mediterranean.

Ammonite palaeobiogeographical distribution is controlled by palaeoclimate and temperature says Shome and his co-workers. These two factors are influenced by paleolatitudes. The fossil Tethopeltoceras is latitudinally sensitive and its presence in Kutch indicates that this part of the coast was near 300 latitude. The find also suggests the presence of a sea connection between India and Africa during the end phase of Jurassic period. 

Not only fossils, even living organisms have interesting 'black boxes' with in them. For example, Statoliths are calcareous structures located in the equilibrium organs of cephalopods, which serve to detect body accelerations during movement in water. They are perfect 'black boxes' because they record a lot of information about the lives of squid and cuttlefish. For instance, it is possible to reveal the hatchling size and temperature of embryonic development, estimate age and growth rates of the animal with daily precision, date life transitions, analyze possible migratory routes and population structure of squid using trace element analysis, and even reveal how many spawning events a given animal has had by analyzing statolith microstructure. Statoliths are usually one of the few remains of squid in fossil records, and their features can be used to infer ideas about the life styles of extinct species. 

Man's inquisitiveness about the past and the future is boundless. How the life came in to being on this Planet, what was the configuration of past continents and oceans, what was the food for the fauna and flora of those days etc are some of the questions that haunt the paleo-biologists and paleo-geographers alike. Knowledge about the past opens the windows to the future. 

May be we find someday a 'black box' that might tell us the secrets of longevity and happiness!    


More by :  V. K. Joshi (Bijji)

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