Monday, March 08, 2010
Greater India Before the Himalayas; Dinosaur Eating Snakes
by Jeff Wilson
I. GONDWANALAND, MIGRATION, AND DINOSAURS
Greater India has long inspired geographers with its singularly wondrous shape: an inverted triangle bounded on two sides by waters of the Indian Ocean and on its third side by the Himalayan Mountain Range. Nourished by the Indus and Ganges Rivers, Greater India covers nearly 4.5 million km². Those more familiar with its geography will know that within Greater India is a smaller triangle known as the Deccan Plateau. Bounded by Western Ghats, Eastern Ghats, and the Satpura and Vindhya Ranges, the Deccan is a catchment area (14,21,000 km2) for several large rivers and sanctuary to many of India’s endemic species. This geography becomes more interesting when we take into account its deeper history and evolution.
Throughout most of the 545 million years during which there has been visible life on Earth (the Phanerozoic Eon), Greater India was not part of Asia, and it was not a peninsula. The majestic Himalayas, the mighty Indus and Ganges Rivers, and the expansive Deccan Plateau did not yet exist. These geographical features, which are integral to modern characterizations of Greater India, did not emerge until well after the extinction of dinosaurs at the end of the Mesozoic Era, 65 million years ago. The Greater India that was known to early dinosaurs and their antecedents was interlocked with Antarctica, Africa, Madagascar, Australia, and South America. These conjoined southern landmasses were called “Gondwana” or “Gondwanaland”, owing to their shared flora and fauna (du Toit 1937; Sorkhabi 1996). The break-up of Gondwana later in the Mesozoic Era remains a fascinating event in Earth history because it led to the creation of islands, each initially seeded with a common flora and fauna, that became progressively isolated from one another. Greater India in particular is interesting because it rifted from Gondwana and drifted across the equator some 6,000 km to Asia. The evolutionary changes and extinction events manifest during that journey remain the subject of investigation by many paleontologists.
Dinosaurs are one of the best groups for studying the potential effects of paleogeographic changes on evolution because dinosaurs were large animals that were capable of traversing continent scale-distances. For example, early in the Mesozoic Era, when the Earth's continental landmasses were connected, dinosaur faunas worldwide are generally similar. Carnivorous dinosaurs from North America, for example, bear striking resemblance to those from southern Africa, and herbivorous dinosaurs from China resemble those from South America. Later in the Mesozoic Era, however, this is not the case. Dinosaur faunas worldwide became more distinctive from one another due to evolutionary changes and extinction associated with increased isolation.
The first reported dinosaur from Greater India was discovered in 1828 by Captain W. H. Sleeman, famous for eradicating the ‘thaggi’ from central India, who encountered bones in Cretaceous sediments on Bara Simla hill near Jabalpur (Sleeman 1844). At that time, the name "Dinosauria" had not yet been coined, and Sleeman's discovery was not formally described and interpreted for some years. After passing through several hands, those first bones finally reached the Geological Survey of India. In 1877, Richard Lydekker named India's first dinosaur Titanosaurus indicus, or "India's titan lizard". Although the remains were fragmentary (tail bones and a thigh bone), they indicated a large, herbivorous dinosaur that resembled the sauropod Cetiosaurus ("whale lizard"), known from Jurassic rocks of England. Lydekker named other species of Titanosaurus in a second paper in 1879, but few dinosaur discoveries followed.
Intensive excavations at Bara Simla and nearby localities by Charles Matley (of the Geological Survey of India) in the late 1910s to early 1920s and again in the early 1930s led to the discovery of some of the most important dinosaur remains from Greater India. Matley and dinosaur specialist Friedrich von Huene described these bones in a seminal monograph published in 1933 that named many new species, including the carnivorous dinosaurs Indosaurus, Indosuchus, and Laevisuchus and the herbivorous dinosaur Antarctosaurus (now known as Jainosaurus). However, many of the bones Matley discovered were isolated, and dinosaur specialists are still sorting out their validity and affinities. Following Matley's final collecting season in India in 1933, few dinosaur discoveries were reported until the 1960s, when teams from the Indian Statistical Institute (ISI)began discovering early dinosaurs from the Lower Jurassic rocks of the Pranhita-Godavari Valley of southern India. Among other discoveries, the ISI team brought to light what was then the earliest-known bona fide sauropod dinosaur, which they named Barapasaurus tagorei (Jain et al. 1975) after its “big leg” (bara pā) and its discovery on the centenary of Rabindranath Tagore’s birth. Later, in the 1970s, ISI teams also discovered a very important Cretaceous dinosaur skeleton from near the village of Dongargaon in central India. This specimen, which they named Titanosaurus colberti, represented the first well preserved Cretaceous dinosaur skeleton known from Indo-Pakistan (Jain & Bandyopadhyay 1997. The genus has since been renamed Isisaurus in honor of the Indian Statistical Institute.
In the 1980s, geologists from the Geological Survey of India discovered dinosaur eggs from Cretaceous rocks in Gujarat, western India (Mohabey 1982). Today, hundreds of eggs have been recovered, representing both carnivorous and herbivorous dinosaurs. In addition to eggs, GSI paleontologists discovered a rich bone bed near a temple at Rahioli that preserved the first carnivorous dinosaur skeleton, which would eventually be named Rajasaurus narmadensis (Wilson et al. 2003).
Finally in 2000 the first dinosaurs were discovered in contemporaneous sediments in Balochistan, Pakistan by the Geological Survey of Pakistan (Malkani 2006). Many isolated bones have been recovered, and early signs indicate that much of the fauna known from India is also present in Pakistan, as we would expect—fossil reptiles did not recognize current geopolitical boundaries. But there are fossil reptiles present in Pakistan that have not yet been recovered from India. One such example is the crocodylomorph Pabwehshi pakistanensis—a blade-toothed form whose closest evolutionary relative is found in Brazil (Wilson et al. 2001).
Paleontologists from India, Pakistan, and abroad continue to search for, excavate, and describe Cretaceous dinosaurs from Indo-Pakistan. Although much remains to be learned about the fauna, a few preliminary statements can be made about Greater India’s geographical migration. There is as yet no sign that the geographic isolation inferred for Greater India led to an endemic fauna during the Mesozoic. On the contrary, Greater India’s dinosaurs, smaller reptiles, and mammals all share close affinities with contemporaries from other Gondwanan landmasses—Australia, Africa, Madagascar, South America. This pattern needs to be tested with continued exploration in India and Pakistan. But some tantalizing discoveries have already come to light . . .
II. DINOSAUR-EATING SNAKES
The Mesozoic Era is known informally as the “Age of Reptiles”, but the literal translation is “middle life”, owing to the position of the Mesozoic after the “ancient life” of the Paleozoic and before the “modern life” of the Cenozoic. The Mesozoic truly was a transitional time, both geographically and evolutionarily speaking. Most of the major groups of limbed, backboned animals alive today got their start in the Mesozoic. Although the Mesozoic is sometimes envisioned in strictly dinosaurian terms, smaller animals were also present, if less conspicuous. Frogs, salamanders, caecilians (limbless amphibians), sphenodontids, lizards, snakes, crocodiles, birds, and mammals lived alongside dinosaurs in Mesozoic ecosystems and doubtless interacted with them. But the nature of those interactions, as well as much of the anatomy of early members of these groups, remains poorly understood.
Snakes are iconic animals in much of South East Asia today. Despite the lack of limbs they move extremely well—above ground, underground, in aquatic environment, and even in the air.
They developed a sophisticated skull that allows them to take in large prey, and they are able to stuff it down their throats without the benefit of front limbs. The evolution of these snake adaptations (limblessness, large gape, mobile skull) from their lizard ancestor is of great interest to paleontologists, but snake origins and early evolution remain a subject of intense debate. Snakes first appear in the fossil record 100 million years ago, but most Mesozoic snake fossils consist of isolated vertebrae—complete skeletons are extraordinarily rare and limited to a handful of specimens collected from Patagonia, the Levant, and southern Europe. Differing interpretations of these early snake skeletons, some of which bear relictual hind limbs, have polarized views on snake origins, ecology, and ancestral habitat.
Last week, my colleagues and I published a paper in PLoS Biology describing a new snake from 67 million year old sediments in Gujarat, western India that was preserved in an extraordinary setting—within a sauropod dinosaur nest, coiled around an egg and adjacent the remains of a ca. 0.5-m-long hatchling (Wilson et al. 2010). We named this new snake Sanajeh indicus, which is an amalgam of the Sanskrit words sanaj (“ancient”), jeh (“gape”), and sindhu (referring to the Indus River) that together mean “ancient gaped one from Greater India”. This paper is the culmination of an odyssey for me and colleague Dhananjay Mohabey, who first discovered the specimen in 1984.
Working with the sediment-covered and inscrutable specimen, Dhananjay recognized dinosaur eggshell and limb bones on the blocks, but he was unable to fully interpret the specimen (Mohabey 1987). I saw the specimen in 2001, after completing field work in western India, and was stunned to see the vertebrae of a snake peeping out from the stony matrix. I was as certain as I could be about the presence of a snake in that block, but paleoecological meaning behind the snake’s association with eggs and a hatchling was then only a tantalizing possibility—one which I didn’t dare make too much of at such an early stage. I was frank with my suspicion about the identity of the snake bones, and Dhananjay was refreshingly receptive to the idea. We embarked on a joint collaboration, which we formalized in 2004. The bones were transported to University of Michigan, where stony matrix was removed with needles, occasionally loosened by formic acid. It took a year to bring the specimen to its final state, but our wait was rewarded by a fantastically-detailed specimen replete with skull and partial skeleton arranged in a coil.
An exciting story emerged. The snake bones were arranged into a coil surrounding a crushed dinosaur egg, with the skull resting atop the coil. Adjacent to the snake were two intact, uncrushed eggs and the bones of a small sauropod hatchling that was probably about 0.5 meters long. We suspected, based on the anatomical arrangement of elements and the life-like pose of the bones that we were looking at an example of animals “caught in the act”; that is, in which they were captured behaving. To better understand the geological circumstances that led to this event, as well as to prospect for additional bones, Dhananjay and I, together with colleagues Jason Head and Shanan Peters, conducted reconnaissance field work at the original locality of Dholi Dungri (Gujarat). We learned that the snake-dinosaur fossil was probably covered rapidly and deeply by a thick plug of wet sand loosened by a storm, and we discovered several other instances of snakes and eggs together. Both were key discoveries that allowed us to hypothesize that the snake-dinosaur fossil was providing critical insight into snake ecology.
Sanajeh preserves critical information that helps resolve the early diversification of snakes and the evolution of their gape. Modern large-mouthed snakes are able to eat large prey because they have mobile skulls and wide gapes. Sanajeh bears only some of the traits of modern large-mouthed snakes and provides insight into how they evolved. Sanajeh was capable of ingesting the half meter-long sauropod hatchling because it was quite large itself. Somewhat ironically, the sauropod hatchlings that Sanajeh preyed upon include the largest animals capable of walking on land. But the combination of untended nests and small hatchling size made them ready prey items for Sanajeh, which probably lived off the spoils from dinosaur nesting grounds during parts of the year. Sanajeh and its ilk would have provided an evolutionary pressure on sauropods that might be responsible for their fast growth rates, which got them out of danger from Sanajeh-sized predators by the end of their first year of life.
University of Chicago paleoartist prepared a life-sized reconstruction of Sanajeh and the sauropod at the moment just before entombment in the fossil record. The sculpture is dynamic and brings to life this 67 million year old scene. We will donate the first cast of this sculpture to the Geological Survey of India at a press conference in Mumbai this Friday, March 12. Persons interested in learning more about the press conference should contact Jeff Wilson (firstname.lastname@example.org).
Jeff Wilson's website can be found here.
du Toit, A.L. 1937. Our Wandering Continents; An Hypothesis of Continental Drifting, Oliver & Boyd, London, 366 pp.
Huene, F. V., and C. A. Matley. 1933. Cretaceous Saurischia and Ornithischia of the Central Provinces of India. Palaeontologia Indica 21:1–74.
Jain, S. L., and S. Bandyopadhyay. 1997. New titanosaurid (Dinosauria: Sauropoda) from the Late Cretaceous of Central India. Journal of Vertebrate Paleontology 17:114–136.
Jain, S. L., T. S. Kutty, and T. K. Roy-Chowdhury. 1975. The sauropod dinosaur from the Lower Jurassic Kota Formation of India. Proceedings of the Royal Society of London A 188:221–228.
Lydekker, R. 1877. Vertebrata from tertiaries and secondaries of India. Records of the Geological Survey of India 10:38–41.
Lydekker, R. 1879. Titanosaurus from the Lameta Group of Jabalpur and Pisdura. Palaeontologica Indica (series 4) 1:20–33.
Malkani, M. S. 2006. Biodiversity of saurischian dinosaurs from the Latest Cretaceous Park of Pakistan. Journal of Applied and Emerging Sciences, 1:108–140.
Mohabey D. M. 1982. On the occurrence of dinosaurian fossil eggs from infratrappean limestone, Kheda District, Gujarat. Current Science 52:1194–1195.
Mohabey, D. M. 1987. Juvenile sauropod dinosaur from Upper Cretaceous Lameta Formation of Panchmahals District, Gujarat, India. Journal Geological Society of India 30:210–216.
Sleeman, W. H. 1844. Rambles and Recollections of an Indian Official. Volume I. J. Hatchard & Son, London, xxi + 478 pp.
Sorkhabi, R. B. 1996. What's in a name—'Gondwana' or 'Gondwanaland'? Episodes 19:82–84.
Wilson, J. A., M. S. Malkani, and P. D. Gingerich. 2001. New crocodyliform (Reptilia: Mesoeucrocodylia) from the Upper Cretaceous Pab Formation of Vitakri, Balochistan (Pakistan). Contributions from the Museum of Paleontology, The University of Michigan 30:321–336.
Wilson, J. A., D. M. Mohabey, S. E. Peters, and J. J. Head (2010). Predation on hatchling dinosaurs by a new snake from the Late Cretaceous of India. PLoS Biology 8:1–5. (doi:10.1371/journal.pbio.1000322.g005)
Wilson, J. A., P. C. Sereno, S. Srivastava, D. K. Bhatt, A. Khosla, and A. Sahni. 2003. A new abelisaurid (Dinosauria, Theropoda) from the Lameta Formation (Cretaceous, Maastrichtian) of India. Contributions from the Museum of Paleontology, The University of Michigan 31:1–42.
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