Dinosaur Engineers, Laterite Plateau, Social Insects

The latest batch of readings and a video for you readers.

1) How the death of the dinosaurs reengineered Earth. Here is an interesting linkage between dinosaurs, sedimentary rock type distribution and river geometry. Fluvial sedimentary environments are different before (Cretaceous) and just after (Paleocene) dinosaur extinction.

In the latest Cretaceous, large bodied dinosaurs destroyed riverside vegetation, destabilizing banks and preventing stable meanders. Natural levees were breached causing sand to spill onto the floodplains, resulting in an open riverine environment. Post dinosaur extinction, vegetation growth stabilized banks, forming stable channels and meander belts, promoting a sharper division between the constrained channel sands and surrounding floodplain fine mud and organic rich swamps.

Ecosystem engineering by dinosaurs!

2) The Rocky Life: Plateaus of the Monsoon. South of the town of Satara in Maharashtra, the crest of the Western Ghats is mantled by a thick hard iron rich soil known as laterite. This red crust is a deep weathering profile that developed by chemical breakdown of the Deccan basalts (in Maharashtra) and of Precambrian metamorphic rocks (Goa and southern Western Ghats) around 50 million years ago in the Eocene during a warm and wet climate phase. For long, these high regions were treated as "wastelands", devoid of vegetation and wildlife. 

But as biologist Varad Giri explains in this excellent video, there is a hidden world that a careful observer will notice. 

And conservation biologist Neha Sinha writes about (under paywall) the plant life on these rocky plateaus- Why India's "wastelands"are biodiversity hotspots in disguise.  As she evocatively wrote about the Kaas Plateau near Satara on her X timeline- "Lakhs of flowers - carnivorous, parasitic, wild, mesmerising, ephemeral, resilient".

3) One mother for two species via obligate cross-species cloning in ants.  Social insects must rank as some of the most amazing creatures.

In one species of ants, the mother gives birth to offspring of two different species! This happens because the mother uses sperm from another species male to produce the worker caste.

Yes, they have caste too!

I’ll reproduce the abstract here and leave you to roll your eyes in wonder-

“Living organisms are assumed to produce same-species offspring. Here, we report a shift from this norm in Messor ibericus, an ant that lays individuals from two distinct species. In this life cycle, females must clone males of another species because they require their sperm to produce the worker caste. As a result, males from the same mother exhibit distinct genomes and morphologies, as they belong to species that diverged over 5 million years ago. The evolutionary history of this system appears as sexual parasitism that evolved into a natural case of cross-species cloning, resulting in the maintenance of a male-only lineage cloned through distinct species’ ova. We term females exhibiting this reproductive mode as xenoparous, meaning they give birth to other species as part of their life cycle”.

I love the first line-  Living organisms are assumed to produce same-species offspring. After all, we never tried too hard to prove it!

Articles: Dehradun, Early Dogs, Warm Blooded Dinos, Louisiana Delta

Sharing some links from the past few days:

1) Dehradun.

A story of the transformation of a beautiful hill town to an ugly unplanned urban center. We shrug resignedly at many such tales from across the country. This one is of Dehradun. Himalaya towns can only be described as disasters in the making. Unscientifically built infrastructure on steep slopes, no garbage management resulting in enormous stray dog and pig populations roaming the streets, and a dwindling water supply. Yet these towns continue to grow, pointing to worsening opportunities for making a livelihood in the Himalayan rural landscapes. The 'smart city' reference is the ultimate insult of all.

Vanishing landscape of ‘smart city’ Dehradun.

2) Early Dogs.

The early stages of dog domestication may have seen a marked behavioral shift appearing before any distinct morphological change. This change in behavior, arising from docile wolves or 'protodogs' living near human camps would have entailed a change in diets.  Scientists have compared wolf and dog like remains from a 28,500 year old site in the Czech Republic. They looked at the dental microwear pattern of these two groups of canids and noticed that the dog like canids show a pattern consistent with eating more hard brittle foods. The wolves show patterns consistent with eating more flesh. 'Throw this dog a bone" wasn't an insult then.

Dental microwear as a behavioral proxy for distinguishing between canids at the Upper Paleolithic (Gravettian) site of Předmostí, Czech Republic

write up: Dog domestication during ice age.

3) Warm Blooded Dinos?

Were Dinosaurs warm blooded like mammals? This debate has raged on for decades. Bone growth patterns have not given any unambiguous evidence of body temperature regulation. A new method known as clumped isotopes may provided a more reliable indicator of estimating body temperatures. Fossilized dinosaur egg shells contain the original calcium carbonate from which these shells were built. A variety of carbon isotopes (C12, C13) may bond with a variety of oxygen isotopes (O16, O17, O18) in the carbonate molecules (CO3). The degree of bonding or clumping of the heavier isotopes i.e. C13 to O18 varies with the temperature during mineral growth. Clumping is more at lower temperatures.

Scientists compared this C13-O18 clumpiness in dinosaur egg shells with C13-O18 clumpiness in the calcium carbonate of mollusc shells from the same fossil bed. Mollusc geochemistry is taken to be a proxy for the ambient conditions. They found out that the egg shells grew at temperatures between 25- 43 deg C, while the molluscs record growth at 25 -30 deg C. This suggests that dinosaurs were capable of maintaining a higher body temperatures than their surroundings.  As a carbonate sedimentologist, I found the details of methods in this paper  of great interest. The researchers used a variety of techniques to make sure that the egg shells had not been altered or subjected to higher temperatures later in their history, which would have made them an unreliable archive of the original temperature during growth. The analyzed egg shells came from Sauropods, Theropods and Ornithischians, a sample across the three main groups of dinosaurs. Very interesting study.

Eggshell geochemistry reveals ancestral metabolic thermoregulation in Dinosauria

write up - Fossil Eggshells Suggest All Dinosaurs May Have Been Warm-Blooded

4)  Eroding Louisiana Coastline.

Over the past several decades, barrages and levees have drastically reduced the amount of sediment that the Mississippi river is carrying to the sea. As a result, the famed Mississippi delta and coastline is eroding away. Efforts are on in a Boston warehouse to figure out a way to reverse this change. An ambitious engineering project which aims at opening up a portion of the levee to funnel sediment into the Barataria Basin south of  New Orleans is being planned. The hope is that the new channel will transport and deposit enough sediment to rebuild part of the endangered delta. A scale model built in a warehouse near Boston is testing the efficacy of this idea.

Fascinating to read the various problems geologists and engineers have to deal with when grappling with modifying nature at this scale.

To Save Louisiana’s Vanishing Coast, Build a Mini Mississippi Near Boston.

Maniraptoran Dinosaurs Show No Decline In Disparity Before Mass Extinction

Its hard to unravel and unpack complex phenomenon like patterns of faunal turnover during mass  extinctions. The methods chosen, the materials (fossils) available for study and the granularity of the study influences the results.

My last post was about a modeling study that concluded that for 40 million years before the mass extinction,  extinction rates exceeded the evolution of new species in many dinosaur lineages. Dinosaur diversity was declining towards the end of  the Cretaceous. Only a few herbivorous dinosaurs showed an increase in diversity.

Now a different study by Derek W. Larson, Caleb M. Brown , David C. Evans published in Current Biology focuses on just one sub group  of dinosaurs and comes to a different conclusion. This is an analysis of over 3000 teeth  of bird-like maniraptoran dinosaurs from 18 stratigraphic units in Western N. America which shows that there was no decline in disparity in different maniraptoran lineages for the last 18 million years before the mass extinction. The maniraptors were largely omnivorous but may have included specialized carnivorous and as well as herbivorous species.

Disparity is a measure of the range of variation of morphology, in this case teeth shape. This in turn is something of a proxy for the range of ecologic niches being exploited.

The authors remark-

Overall, these inferred ecomorphological patterns indicate that toothed maniraptorans, including toothed birds, were ecologically diverse and stable leading up to the end-Cretaceous mass extinction, at least in North America.

An interesting angle explored  in the paper is why toothed bird-like maniraptors and some lineages of toothed birds died out, while their physiologically and morphologically close relatives, the ancestors of modern birds, the Neornithes,  survived the mass extinction.

In the fallout of the bolide impact that marks the end of the Cretaceous, terrestrial food webs that relied on photosynthesis would have collapsed. However, seed banks derived from plants, including relatively abundant angiosperms, could have been a common, nutrient-rich resource that would have persisted among the detritus, which itself has been suggested as a key food source related to species survival across the boundary. With clearing of vegetation, either during a global firestorm or widespread burning of dead ground cover, exposed seeds in these areas worldwide could have been exploited by granivores. This pattern is observed in modern fire succession communities, where granivorous birds are the first avians to re-occupy disturbed habitats due to food resource accessibility. A persistent seed bank, which can remain viable for more than 50 years in modern temperate forests, most likely outlasted the catastrophic ecosystem collapse caused by a bolide impact and associated infrared thermal pulse, acid rain, darkness, and impact winter. Toothed maniraptorans, with their feeding systems adapted to faunivorous or potentially folivorous diets, would have been restricted to food chains dependent on living plant matter and unable to access these seed banks. Therefore, dietary specialization toward granivory in some lineages of crown group birds may have been one of the key factors in their survival through the end-Cretaceous mass extinction.

Although very similar to maniraptors, the Neornithes had evolved a unique dietary specialization. The presence of a beak, which served as a crushing apparatus, may have helped these ancestors of modern birds exploit seeds as a food source.

Decline In Dinosaur Diversity 40 Million Years Before Asteroid Impact

This is based on modeling of speciation and extinction rates.

Manabu Sakamotoa, Michael J. Benton,and Chris Vendittia

Whether dinosaurs were in a long-term decline or whether they were reigning strong right up to their final disappearance at the Cretaceous–Paleogene (K-Pg) mass extinction event 66 Mya has been debated for decades with no clear resolution. The dispute has continued unresolved because of a lack of statistical rigor and appropriate evolutionary framework. Here, for the first time to our knowledge, we apply a Bayesian phylogenetic approach to model the evolutionary dynamics of speciation and extinction through time in Mesozoic dinosaurs, properly taking account of previously ignored statistical violations. We find overwhelming support for a long-term decline across all dinosaurs and within all three dinosaurian subclades (Ornithischia, Sauropodomorpha, and Theropoda), where speciation rate slowed down through time and was ultimately exceeded by extinction rate tens of millions of years before the K-Pg boundary. The only exceptions to this general pattern are the morphologically specialized herbivores, the Hadrosauriformes and Ceratopsidae, which show rapid species proliferations throughout the Late Cretaceous instead. Our results highlight that, despite some heterogeneity in speciation dynamics, dinosaurs showed a marked reduction in their ability to replace extinct species with new ones, making them vulnerable to extinction and unable to respond quickly to and recover from the final catastrophic event.

The paper is under a paywall so I won't comment on the details of the analysis. Ed Yong has written a good summary of the paper in The Atlantic.

I heard this research being covered on BBC News and out came the inevitable statement.. " dinosaurs may have been on their way out"... meaning even if there had been no asteroid impact the dinosaurs would have gone extinct soon. I am not  sure the researchers actually think this way. The dinosaurs were a very long lived group, originating in the Triassic about 230 million  years ago, with all the non-avian groups going  extinct 66 million years ago. In that time frame there were boom and  bust  phases. There were earlier episodes of rapid diversification , then decline and then recovery. The overall pattern seems to be a late Triassic to mid Jurassic phase of diversification, followed by a slowing down or small declines and small expansions of different groups thereafter.

Who knows, maybe the late Cretaceous decline would have given way to another period of recovery and diversification. Or, the branches of the dinosaur tree may have gotten pruned with many groups going extinct, but with some groups continuing to prosper. Dinosaurs were not one entity. They were a varied group.  The extinction of all non-avian dinosaurs 66 million years ago may create an illusion that their evolutionary fates were always co-dependent, but that need not be so. This analysis shows that even when many dinosaurs groups were declining in the late Cretaceous, a few herbivorous groups were diversifying.  All this came to an abrupt end because of the asteroid impact. Only the avian lineage of dinosaurs survived.

The one conclusion that can be definitely drawn from the dinosaur story is that random events and chance have played a huge role in shaping the history of life.

Fossils And The Origin And Diversification Of Birds

Stephen Brusatte and colleagues have a fine review article in Current Biology that brings together findings from the fossil record and molecular phylogeny work that throw light of the long history of bird evolution from Jurassic-Cretaceous to modern species.

Did you know .. that the remarkable Jehol Biota from northeastern China from 130  to 120 million years ago preserves thousands of bird fossils and accounts for nearly half of the global Mesozoic bird diversity? The Jehol Biota represents fossilization in wetland and lake sediments. The fine grained sediment size would have aided the superb preservation of these creatures. This fauna included small arborealists, semi-aquatic birds and large generalists but certain modern ecotypes like large aerial forages and aquatic specialists are not present. The End Cretaceous mass extinction produced empty ecologic niches for a greater diversity of bird forms to evolve.

..or that birds retain a single functional ovary and oviduct and a single oocycte is ovulated, shelled and laid per 24 hour cycle. Microstructural egg shell characteristics and small clutch size evolved incrementally in bird-like dinosaur ancestors who did retain two ovaries though. Earliest birds like Jeholornis and enantiornithines ( a basal group of birds) apparently had one ovary indicating that birds may have lost one ovary perhaps due to body lightening in response to the evolution of flight.

There is plenty of information in this essay on the long evolutionary history of bird like characters in dinosaur ancestors and the subsequent diversification of early (and now extinct) and post Cretaceous modern birds. It is not true that the end Cretaceous mass extinction affected only non-avian dinosaurs. Early birds had diversified into distinct groups by late Cretaceous and the mass extinction wiped out many of these lineages as well. Some lineages of the early birds (neornithines)did make it through the mass extinction. Molecular phylogeny indicates that all modern lineages formed within the first 15 million years after the extinction and then diversified quite rapidly and are today represented by 10,000 odd species.

But why write so much? The old adage " a picture is worth a thousand words" can be so true!

Just take a look at this lovely inforgraphic.

 Source: The Origin and Diversification of Birds

It summarizes the evolutionary relationship (phylogeny) of dinosaurs and birds and superimposes the evolution of traits that we recognize as typical of birds on a timeline from Triassic to the earliest birds (where Avialae/Aves branch out) . What we see is that these features evolved piecemeal over a 100 million year period in dinosaurs and some in the earliest birds, but not as a crazy spurt of morphological innovation that would have marked the geologically sudden appearance of a radically different creature.  Traits like bipedal posture, hollowed bones, wishbone, three fingered hands, wings and feathers, all appeared at successive stages in dinosaurs. Other traits like keeled breastbone to support flight muscles, endothermic metabolism and rapid growth, highly reduced tail, true muscle powered flight, and the loss of that one ovary, appeared in early bird lineages. The long story is that a lineage of therapod dinosaurs very gradually evolved bird-like characters so much so that experts find it difficult to separate bird-like dinosaurs from dinosaur-like birds.

Creationists smirk that experts can't even decide what is a bird and what is a dinosaur. Or that bird-like dinosaur fossils are younger than the earliest birds and so dinosaurs can't be the ancestors of birds. They are missing the point that the later appearance in the fossil record of bird-like dinosaurs is simply an artifact of preservation potential. This means that older bird-like dinosaurs haven't been found yet and that after birds branched out from dinosaurs the ancestral dinosaur lineage survived alongside birds. So, the sampled bird-like dinosaurs are not the direct ancestor species of birds but co-existing cousins. More importantly, the difficulty in taxonomic identification means that morphological transformations are being captured in the fossil record. This is strong evidence for evolution.

Meanwhile, just a thought from another paper I read recently on styles of diversification in the fossil record by Douglas Erwin. In the article he points out that the evolution of morphological novelty and spurts of diversification are often de-coupled  i.e.  novelty may arise in a species but that may not immediately result in an adaptive response in terms of exploitation of new resources and ecological space. Many novel traits that we recognize as typical of birds evolved much earlier in dinosaurs and it is not clear whether their evolution lead to an adaptive radiation in that dinosaur lineage. What did happen though is that at some point a threshold was crossed during maniraptoran (the closest relatives of birds) dinosaur evolution. We can think of  this as the dinosaur-bird transition. A collection of traits which had evolved piecemeal and under different evolutionary circumstances worked really well together and were co-opted and modified to serve different functions. The bird body plan then very successfully diversified into many different and new ecological roles.

Brusatte, S., O’Connor, J., & Jarvis, E. (2015). The Origin and Diversification of Birds Current Biology, 25 (19) DOI: 10.1016/j.cub.2015.08.003

Erwin, D. (2015). Novelty and Innovation in the History of Life Current Biology, 25 (19) DOI: 10.1016/j.cub.2015.08.019

Sherlock Holmes And Long Term Evolutionary Patterns In Dinosaur Body Size

This week's (in Pune, India) Sherlock Holmes Elementary featured a murder mystery involving a smuggled dinosaur fossil. The fossil is believed by some palaeontologists to be entombed in rocks of the earliest Paleocene, making that dinosaur a survivor of the end Cretaceous mass extinction. Other palaeontologists strongly disagree with this survivor fauna scenario, which the drama turns into a motive for murder. There was a fair amount of geology and palaeontology in the episode and a reference to a term "dead clade walking".  This term is real life was coined by David Jablonski a palaeontologist from University of Chicago.  The term means that a clade or a lineage has survived a mass extinction but its fate has been sealed. Over a period of time say a few million years after the mass extinction that group does eventually go extinct.

Some dinosaur species may have survived the mass extinction but by early Palaeocene they were certainly all gone... except one lineage.. the Availea or birds. They prospered in the Cenozoic, radiating into a hundreds of species. Their success may have had deep roots and one important factor may have been the small size of their ancestors.

A paper in PLOS Biology explores the long term evolutionary patterns of dinosaurs and finds a positive relationship between high rates of evolution and small size-

Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage:

Author Summary

Animals display huge morphological and ecological diversity. One possible explanation of how this diversity evolved is the "niche filling" model of adaptive radiation—under which evolutionary rates are highest early in the evolution of a group, as lineages diversify to fill disparate ecological niches. We studied patterns of body size evolution in dinosaurs and birds to test this model, and to explore the links between modern day diversity and major extinct radiations. We found rapid evolutionary rates in early dinosaur evolution, beginning more than 200 million years ago, as dinosaur body sizes diversified rapidly to fill new ecological niches, including herbivory. High rates were maintained only on the evolutionary line leading to birds, which continued to produce new ecological diversity not seen in other dinosaurs. Small body size might have been key to maintaining evolutionary potential (evolvability) in birds, which broke the lower body size limit of about 1 kg seen in other dinosaurs. Our results suggest that the maintenance of evolvability in only some lineages explains the unbalanced distribution of morphological and ecological diversity seen among groups of animals, both extinct and extant. Important living groups such as birds might therefore result from sustained, rapid evolutionary rates over timescales of hundreds of millions of years.

In general the rapid-evolvers would be the smallest-bodied species -- the ones that reach reproductive age quickly and while they are still small. Rates of evolution depend on generational time. Which predicts that large-bodied/long-generation-time species would have more difficulty adapting to rapidly-changing extinction conditions.

The authors also mention that body size evolution in many non-avian dinosaur lineages seem to follow Cope's Rule, an increase in body size of descendant species over time. The earliest species in that lineage would be small and over time there would be a trend towards evolution of larger bodied species.

What could cause such a trend? Is larger body size advantageous and hence being favored by natural selection? Again the relationship to mass extinctions is intriguing. The authors mention that during the late Triassic mass extinction many branches of dinosaurs became extinct. If larger bodied dinosaur species were disproportionately killed off the survivor species of dinosaurs in early Jurassic would have been small bodied. This could explain Cope's Rule in a rather novel way (as explained by my adviser Anthony Arnold - who has worked on size evolution in foraminfera - in an email to me) - "since it means that rather than evolution favoring size increase, mass extinction selectively removes larger-bodied species, leaving behind the smaller guys as survivors. Since they don't have much room to get smaller the survivors could even speciate at random and the only direction in which the variance has room to expand is toward larger size.

Maybe!.. arm waving.."

So ecological crises may lead to species sorting based on size with smaller size being favored and then evolution of a trend towards larger size that reflects simply an inability to become any smaller!..
 

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.

Recommended Attire When Searching For Dinosaur Eggs

How about an elegant light grey suit? ..Will help you keep away the scorching Indian sun.

That's an unnamed senior Indian government official at a photo-op (source) leaning over a row of dinosaur eggs found recently from the Upper Cretaceous (about 80 million years ago according to the report) of the Narmada river valley central India.

The Narmada river flows westwards within an ancient rift zone which originated during early Proterozoic and has been reactivated to become a sedimentary basin several times thereafter. Mid-late Cretaceous was one such time of reactivation, several linear east west oriented basins forming in response to the crustal stresses generated as India wrenched itself away from Africa, then Madagascar and then Seychelles.

Mid late Cretaceous was a time of globally high sea levels. Marine incursions into these basins took place from the west, but there are fluvial (river) and lacustrine (lake) sediments also in the Cretaceous basins of central India. The recently found dinosaur eggs along with other reptilian fossils are from lacustrine and fluvial deposits preserved in the Dhar district of Madhya Pradesh.

The terrestrial Cretaceous sediments of central India have been yielding a rich trove of dinosaur and reptilian fossils. These are thin patchy deposits. Large portions of these deposits are likely buried under the Deccan basalts, entombed by lavas that began erupting around 65 mya. The deposits that do outcrop are being threatened by increased farming activities and urbanization. So, its really good to hear that the Madhya Pradesh government is planning on creating a dinosaur park which will hopefully protect at least some of these fossil sites.

Meanwhile.. I found this geological map of Madhya Pradesh from the Geological Survey of India Geology and Mineral Map series which is worth sharing.. below is a portion of the map showing western Madhya Pradesh. The red arrow indicates the general location of the Upper Cretaceous outcrops (blue) of Dhar district.

 Click here for the full pdf version.

An Inane Sentence About Dinosaur Extinction

This from the Daily Mail about the discovery of a sudden shift in Early Cretaceous climate and its potential impact on dinosaurs:

The temperature drop during the Cretaceous period would almost certainly have wiped out an 'abundance' of the world's dinosaurs.

The scientists behind the ground-breaking study claim this would have been the first major step dinosaurs took on their eventual road to extinction.

Hmmm...I had heard stories about lemmings committing mass suicide but didn't know that the dinosaurs too came to an agreement in the early Cretaceous to take decisive major steps towards eventual extinction.

I know..I know.. the writer didn't mean it that way...but the sentence does come out reading that odd.

More seriously Dr Gregory Price of Plymouth University, one of the scientists involved in the study suggests that climatic shifts possibly caused by a dysfunction to the nascent Gulf Stream which brings warm waters to the north Atlantic resulted in a temperature drop about several degrees beginning around 137 mya and similar events recurring throughout the Cretaceous may have caused a gradual dying out of the dinosaurs.

If that is true it should be reflected in the patterns of dinosaur diversity through the Cretaceous period. Dinosaur diversity should show a systematic decline beginning around 137 mya.

What does the paleontological record show?

I dug around for references and came across several studies that have measured and estimated dinosaur diversity through time. They show that:

1) There is no trend of a systematic gradual decline in dinosaur diversity beginning around 137 mya (Ref).

2) There seems to be an expansion of dinosaur diversity early in the history of the group in the late Triassic - mid Jurassic. After that there were periods of minor expansion and diversification - as recognized by origin of new dinosaur groups - in the later Jurassic and in the mid - late Cretaceous (Ref).

3) The raw data i.e. the observed diversity from the collected fossil record shows a major expansion of diversity in the mid -late Cretaceous. That however may be an artifact of sampling. This can occur in a number of ways. Perhaps the mid-late Cretaceous has been sampled more intensively due to an interest in the late Cretaceous mass extinction. Or more Cretaceous strata is exposed and is available for study than earlier times (Ref) .

Corrected for these biases the increase in diversity in mid-late Cretaceous is more muted.

Figure below shows the patterns of dinosaur diversity through the Mesozoic.

Source: Dinosaurs and the Cretaceous Terrestrial Revolution

Fig a is an estimate of the frequency of new lineages originating through time and the pattern suggests that the majority of new groups seem to have evolved in the earlier 1/3rd history of dinosaurs,

Fig b, solid line shows observed diversity with peaks in the early history of the group with a Jurassic maxima and a later increase in the mid-late Cretaceous. Dashed line shows diversity corrected for ghost ranges, which are estimates of the total geological range of the fossil. Many times the first appearance of a  group in the fossil record may not coincide with the origin of that group. Therefore the earlier existence of that group is estimated based on evolutionary relationships with related groups. So for example the appearance of several new groups in the mid-late Cretaceous may not mean those groups originated then. If one applies estimates of when that group actually originated i.e. includes their basal ghost range, then the diversification peaks for mid-late Cretaceous are moderated.

Dotted lines show diversity corrected for sampling bias. The result suggests that diversification rates are heavily influenced by sampling. In other words the data corrected for sampling bias indicates neither an increase nor a decrease in dinosaur diversity throughout the Cretaceous.

Fig c shows the likelihood of shifts in diversity through time. The trend line suggests an overall decrease in diversity shifts (lineage branching events) after an early (late Triassic - early Jurassic) peak. The likelihood of lineage branching events (increases in diversity) fluctuated moderately throughout the Cretaceous (Ref).

4) Some studies show that dinosaurs did decline in diversity a few million years (10 million or so) before the K-Pg mass extinction event. Others suggest that no such pattern in discernible once you take into account not just observed diversity but estimated diversity as well. Estimated diversity is a measure of how much of the actual diversity remains to be discovered.

In summary.. the data does not seem to support Dr. Price's contention that there was a gradual decline in dinosaurs initiated by climatic changes around 137 mya over a time period of some 70 million years before the K-Pg mass extinction and certainly does not even come close to supporting the crackpot headline in the Daily Mail that Dinosaurs 'killed off by a sudden drop in temperature and NOT by a comet'

Dinosaurs were a group with a world wide distribution. There would have been throughout their history local extinction events brought about by environmental perturbations. A possible cooling of the earth about 137 mya may have harmed dinosaurs in the very northern latitudes but did not set the stage (in a non-teleological sense of the phrase) for a long term globally widespread decline of the dinosaurs through the rest of the Cretaceous. In fact, there may have been a moderate expansion of dinosaur diversity in the mid-late Cretaceous. Globally the dinosaurs seemed to be doing quite well until their rapid demise 65 mya.