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.

Monday, January 20, 2014

When California Was An Island And Other Stories

Economist Tim Harford is hosting a fun podcast series on BBC Pop-Up Ideas. There are 3 episodes on maps which make great listening:

1) Tim Harford- The Power of Maps

2) Jerry Brotton - Mapping History  He is the author of the book A History Of The World In 12 Maps which is definitely of my reading list.

3) Simon Garfield- Maps And Mistakes.. which tells us the story of how in the late 1600's California became an island on the maps of the day..

Very fun to listen to..

Tuesday, January 14, 2014

Quote: Werner Breuckner On Cyclic Carbonates

JSR Paper Clips highlights a paper from 1953 on cyclic carbonates with a memorable quote from Werner Breuckner:

“When a detailed study of limestones is made, their interpretation becomes more difficult.”

The 1950's was the time when such sentiments were apt as far as carbonate sediments were concerned. Giant oil deposits in carbonate rocks were being discovered in Texas, Gulf of Mexico and the Middle East. Research on carbonate rocks took on a new focus and urgency.

One can get a view of the importance of this new field in sedimentary geology using Google Ngram Viewer which tracks frequency of word usage in published books. I have used the terms "carbonate platforms" and "sedimentary petrology" to illustrate how the field of carbonate sedimentology gained significance from the late 1950's onwards. 

Werner Breuckner's paper abstract also says something interesting about the state of the science:

Cyclic variation in the CaCO 2 content of Cretaceous calcareous sediments in the Helvetic zone of the Swiss Alps is attributed to temperature changes in the waters of the depositional basin caused by climatic variations, rather than to alternating uplift and subsidence of the basin floor. The significance of cyclic calcareous sedimentation for stratigraphic correlation, as well as paleogeographic and paleoclimatic investigations, is noted. 

He suggests that cyclicity is due to periodic changes in temperature and associated chemical conditions in sea water rather than the alternative of uplift and subsidence of the basin floor. Periodic tectonic movements can lead to depositional cycles but the time scales involved are generally in the hundreds of thousands of years at least. Many carbonate sequences show cyclicity of a much higher frequency measured in tens of thousands of years. 

Today, different causal mechanisms are invoked to explain deposition of these higher frequency cycles. Among them, especially relevant to shallow water intertidal and shelf areas is the autocyclic model of carbonate deposition (Ginsburg 1971) wherein feedbacks between sediment production and accumulation, current and sediment dispersal results in a kind of a playback loop wherein environments of deposition at certain time intervals keep shifting their positions resulting in one burying the other. The result is a repeated  stacking of the same facies sequence or a depositional cycle. The other mechanism is sea level fall and rise due to glacial and interglacial conditions. It was not until the early mid 1970's that geologists began started taking seriously the link between ice ages and carbonate cyclicity, prodded to some extent by J. D. Hays, John Imbrie and N. J. Shackleton's classic paper Variations in the Earth's Orbit: Pacemaker of the Ice Ages. This now has been used to explain the origin of many cyclic carbonate sequences.

Walter Breuckner in the 1950's though was working on a frontier area when a detailed look at carbonates opened up more questions than answers.

Sunday, January 12, 2014

Sunday Reading: Science Of The Himalayas- Open Access

Current Science has a special section on the science of the Himalayas with papers on a wide range of topics including papers on the seismic importance of major fault systems, interplay of faulting, climate change and sedimentary processes and a surprise!... a study of volcanic arc associated Cretaceous carbonate reefs.. built not by corals but by those enigmatic weird bivalves.. Rudists... enjoyed reading that!

Friday, January 3, 2014

Confused Article In The Hindu On Evolution, Disease And Paleolithic Lifestyles

What's up with The Hindu?.. another terrible article on science and evolution and biology by a medical professional soon after the recent ignorant hateful essay on homosexuality. Following reader outrage and detailed corrections that article on homosexuality has been retracted by The Hindu.

This one is by a cardiologist Dr Hegde. He begins thus:

Darwinian evolution has become outdated and its place is taken by the Lamarckian hypothesis of evolution by environmental compulsions. Darwin himself agreed with Lamarck but the neo-Darwinians, who have a big business interest in keeping the status quo, are at it even now. Even Erasmus was for environmental evolution long before Darwin came into the picture. Most of our pathophysiology of diseases is based on the Darwinian model unfortunately and it has to change for good. Earlier the better.

Darwinian evolution dead but kept alive by a conspiracy of big business... What utter rubbish! Later Dr. Hegde complains that "medical doctors do not go into evolutionary biology, even if a few of them go into biology". I hope he has counted himself in that list of medical doctors not getting into evolutionary biology for the above para is as uninformed as it gets.

Lets gets some terminology out of the way.