Sunday, January 26, 2014
Late Cretaceous Dinosaurs In India- Diversity, Habitat And Extinction
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.