Sunday, January 26, 2014

Late Cretaceous Dinosaurs In India- Diversity, Habitat And Extinction

I attended a talk on Friday by Dr. Dhananjay Mohabey former Deputy Director General of the Geological Survey of India at the Agarkar Research Institute in Pune. The subject was Late Cretaceous dinosaurs along with a history of dinosaur research in India and some anecdotes that come with a long interesting career in the field.

Here is the summary of the talk which was handed to us and which I am reproducing below:

Late Cretaceous Dinosaurs In India- Diversity, Habitat And Extinction - Dr. Dhananjay Mohabey

The first dinosaur from the Indian subcontinent was discovered in the year 1828 by Captain W. H. Sleeman of the Bengal Army from the Lameta Formation near Jabalpur. The bones collected were passed on to a series of learned amateur palaeontologists that included Spilsbury to James Princep (1832) to Thomas Oldham (1862) to Hugh Falconer who identified them as reptilian bones (1868). Richard Lydekker studied these bones along with the bones collected by H.B Medlicot (1877) from the overlying horizons at Jabalpur and established a type species Titanosarus indicus - the first dinosaur to be describe from India. During the period, a few more finds of dinosaurs were recorded that included collections of bones by W.T. Blanford from Lameta of Pisdura, later described as T. blanfordi and Laplatosaurus madagascariensis by Lydekker (1877). The majority of initial discoveries in India came from the Late Cretaceous sediments of the Central Province during the periods 1828-1879.  Between 1917 and 1933, Charles Matley carried out systematic excavations in two expeditions (1918-1919 and 1932-1933) in the Lameta sediments at Bara Simla and Chota Simla at Jabalpur and also the Lameta bed at Pisdura. He published his monumental work on systematics of Indian Late Cretaceous dinosaurs in 1933. Following years, 1960 onwards, witnessed excavations of thousands of dinosaur bones from the Late Cretaceous sediments, mostly Lameta of Jabalpur in Madhya Pradesh. Pisdura-Dongargaon in Maharshtra and Kheda in Gujarat. Discovery of dinosaur eggs in the Lameta sediments revived interest in research on India dinosaurs particularly with repect to their nesting behavior, habitat and environments. The discovery of plant bearing coprolites in the years 2000 provided a rare insight in to the dietary habit of the Indian sauropods. 

Of the vast collection of dinosaur bones since 1828, very few associated bones could be collected. Based mostly on the study by Charles Matley, at least twenty species of sauropod and theropod dinosaurs were described in India. However, current understanding based on the revised taxonomy recognises only two sauropod genera of Titanosauriforme dinosaurs viz Isisaurus colbeti and Jainosaurus septemtrionalis and four large-bodied abelisauridai theropods - Rajasaurus narmadensis, Rahiolisaurus gujaratensis, Indosuchus matleyi and Indosaurus raptorius and a small bodied theropod Laevishuchus indicus. 

Our study suggests that Late Cretaceous dinosaurs in India first appeared during the Maastrichtian in magnetochron C30n, ca. 500K years before the Cretaceous-Palaeogene boundary. Both titanosauriforme sauropods and abelisaurid theropods diversified and well established during C30n-C29r (Maastrichtian) with acme of their breeding and nesting. A change in biodiversity and abundance in dinosaur fauna from C30n to C29r is observed. The diversity and abundance of dinsoaurs of C30n -C29r declined rapidly with initiation of Deccan volcanism. Only a single or two titanosauriforme species with few individuals could survive the initial volcanic onslaught. The last stratigraphic level of the surviving dinosaurs in recorded in the C29r of Maastrichtian and 350k before the Cretaceous-Palaeogene boundary and they were all extinct before the K-Pg boundary. Continued work by the Geological Survey of India on the existing collection and new discoveries of dinosaur material from India, Pakistan and elsewhere in Gondwana have begun to resolve the composition and affinities of Indian dinosaurs.

Taking the Mesozoic as a whole the dinosaur record of India is quite poor. That does look like a preservation artifact. Jurassic rift basins of Western most India are mostly marine. Further in the Central and East parts, Early -Mid Mesozoic fluvial sedimentation in India took place in continental rift basins known as Gondwana basins since India at that time was a part of Gondwanaland.  These basins closed by around mid Jurassic except the Satpura and Godavari basins. There are some fluvial deposits of mid Jurassic and younger age from the Godavari basin especially (Kota Formation) that have yielded a few dinosaur fossils but the sample is too small to be able to say much about their diversity. Later in the Cretaceous E-W trending basin formed in West and Central India along the Narmada rift zone. Significant terrestrial sediments i..e sediments deposited in rivers and lakes accumulated in these basins.  These contain dinosaur remains preserved in the Maastrichtian Lameta Formation. So, much of the Jurassic to mid Cretaceous record is missing from Central and Eastern basins either due to erosion or non-deposition. There is only a tiny time slice of about 150 thousand years of the Maaschrictian with a record good enough to address in details questions about dinosaur diversity and evolution.

Overall it was an interesting talk. Some 400 crates of fossils of dinosaurs and other fossils were shipped out of India in the 1930' s by the British. The GSI is actively trying to trace if any of that collection still remains in British archives. There are archives in India too that have remain unstudied and so the picture of dinosaur diversity will certainly change as more archives are opened up and the fossils analyzed.

On the disheartening side we heard stories of dinosaur fossils being stolen from both the field site as well as museums. Field sites rich in dinosaur and other biota are being destroyed often to creeping urbanization around cities like Jabalpur and other towns in Gujarat. There were some really beautiful pictures of dinosaur nests with impressions of the clutch of eggs clearly seen. And one remarkable nest had preserved the remains of a snake, coiled and with jaws opened up in readiness to swallow an egg. And then there was a memorable picture of a large oblong dinosaur egg being used as a Shiva Lingam in a local temple near Dhar in Madhya Pradesh.

If the stratigraphic calibration that Dr. Mohabey presented is robust then it does seem clear that the Deccan volcanism wiped out dinosaurs in Central India at least. As Gerta Keller and colleagues have demonstrated, the volcanism had an impact on marine life in this part of the world as well and appears to have contributed to the mass extinction that took place 65 million years ago. This does not mean that the asteroid impact scenario is wrong. Just that 65 million years ago the earth experienced multiple cataclysmic events that reshaped ecology and life.

5 comments:

  1. 1. Are you aware of this --> https://www.quora.com/Rahul-Ajmera-1/Posts/Indias-ignored-Dinosaur-Treasures-at-Kutch-Gujarat

    2. Is there a scope of more places in the country where there could be dinosaur fossils but we are not looking

    3. If no, why is India so poor in Dino fossils compared to say US, despite that the subcontinent has sort of intact craton for large part of the Dino age

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  2. Khalil- reg 2 and 3.. the Indian subcontinent did develop sedimentary basins during the Jurassic and Cretaceous in the western most regions like Cambay, Kutch, Rajasthan and also in south Indian in Tamil Nadu.. they were mostly marine environments. in central ( within the Narmada rift) and eastern India (Godavari rift) the rock record of the Jurassic is poorer due to episodic sedimentation and erosion. only in the latest Cretaceous in central India and south India are there fluvial and lacustrine environments of deposition conducive to preservation of dinosaur bones. so we have pretty much looked at the available sedimentary record.. we just don't have sediment deposited in the right environments for long periods of the Mesozoic..hence the poor record.

    thanks for the link...

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  3. Nice to see that Thug-chasing Sleeman had the time to look around too! The lack of appreciation for the environment is plain depressing. Somewhere near Ariyalur in Tamil Nadu is a vast field of fossils and apparently they are good for use in cement - so they are taken out by the truckload thanks to our mining leases. Ashok Sahni talks about the exceptional insect fossils in Indian amber from Surat which even has good DNA. Again all of it is taken out by the truckload for burning with the lignite. The burning of books by the illiterate? But perhaps we need literacy.

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  4. Between the UK archives and the Indian ones, I am quite sure things are safer outside. I fail to understand why the GSI can't make all their publications, collection catalogues online. After all, most of the expertise now is in the universities (if not among citizens around the world) and not in these organizations.

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  5. Shyamal- India.. Govt... data ...available... easily online... long way to go for that! :)

    regarding your earlier observation.. I have been to Ariyalur in my college days.. that is the prime area for mid-late Cretaceous fossils and you are right.. many great localities are being torn apart along with other locales you mention..we certainly do need stronger protection of some sites which GSI along with expert organization deem to be of exceptional geological importance.

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