Showing posts with label India. Show all posts
Showing posts with label India. Show all posts
Taphonomy of an Upper Triassic Rhynchosaur Bonebed From India
Mukherje, D. and & S. Ray. 2012. Taphonomy of an Upper Triassic vertebrate bonebed: A new rhynchosaur (Reptilia; Archosauromorpha) accumulation from India. Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication) http://dx.doi.org/10.1016/j.palaeo.2012.03.010
Abstract - The Upper Triassic Tiki Formation of India is a rich storehouse of varied vertebrate fossil assemblages. So far, there is no information on taphonomic signatures of the Tiki vertebrate assemblages in comparison to that of other fossiliferous horizons of India. We report a new, low diversity, mono-dominant, multitaxic vertebrate accumulation where rhynchosaurs constitute the dominant component. The formation of the rhynchosaur bonebed is attributed to biological aggregation with a hydraulic overprint resulting in a mixed-origin concentration. Other taxa include rauisuchid, phytosaur, small indeterminate archosaur and cynodonts. Taphonomic study based on 617 skeletal specimens of rhynchosaurs collected from nine sites within an area of about 250x217 sq m shows that most of the specimens are disarticulated and disassociated but in close spatial proximity to one another; some are associated specimens and few are articulated. About 13 to 20 individuals of rhynchosaur at different ontogenetic stages are estimated from the specimens collected, suggesting gregarious behaviour, possibly herding. These specimens show varying degree of weathering, breakage, encrustation, abrasion and deformation. The bonebed is preserved within the Tiki red mudstone unit and is found in association with paleosol profiles, suggesting prolonged subaerial exposure. Spatial distribution and relative bone frequencies show differential susceptibility of the skeletal specimens to fluvial transport. 55.4% of the collected skeletal specimens belonged to Voorhies Group I, whereas 12.4% and 24% constituted Voorhies Group II and III respectively, and 8.2% of the collected specimens belonged to the intermediate group I and II. It appears that the animals concentrated in the vicinity of the water sources during prolonged period of aridity and died possibly during high seasonal rainfall that resulted in a major flood event. Subsequently, the soft tissues decomposed, and the skeletons suffered prolonged subaerial exposure when the water receded leading to disarticulation and fragmentation followed by minor dispersion by low velocity water currents. This resulted in segregation of skeletal specimens, which were gradually covered by mud deposited during later flooding events. Based on the known flora and fauna, the Tiki Upper Triassic ecosystem is reconstructed for the first time. In the aquatic ecosystem, the metoposaurid labyrinthodonts occupied the top of the food pyramid together with the semi-aquatic parasuchids, which occupied an ecological niche similar to that of the present day crocodilians. The abundance of herbivorous rhynchosaurs at the base with few large and carnivorous rauisuchids and parasuchids at the top suggest a trophic structure similar to that of a modern day terrestrial ecosystem.
Panchetocynodon damodarensis, a New Cynodont from the Lower Triassic of India
Das, D. P., and A. Gupta. 2012. New cynodont record from the lower Triassic Panchet Formation, Damodar valley. Earth and Environmental Science Journal of the Geological Society of India Volume 79, Number 2, 175-180 DOI: 10.1007/s12594-012-0022-2
Abstract - This paper reports the find of a new non-mammalian cynodont from the Lower Triassic Panchet Formation of the Damodar valley, West Bengal, India. The fossil, recovered from a clay pellet rich calcareous sandstone bed, is a part of left lower jaw having five post canines that are damaged to various extents. A combination of mammal-like advanced characters such as much enlarged dentary, reduced post dentary bones, high coronoid process, large masseteric fossa, each post canine with a large central cusp flanked by a distal and a mesial accessory cusps with two additional lingually positioned cingular cusps, incipient root division and clearly demarcated crown-root juncture prompted to erect a new taxon Panchetocynodon damodarensis gen. et sp. nov.
Stratigraphic Correlations of Gondwanan Basins in India and the "Laurasian" Fauna of Northern Gondwana in the Late Triassic
Here is a fairly obscure, but interesting new paper providing updated correlations of strata (including that of Triassic age) in the Gondwanan Basins of India. The final paper could have benefited from some more editing, but overall it provides a decent synthesis and outlines some of the problems of correlations in this are of Gondwana. Most significant is that there are no absolute time constraints available for these strata because of the lack of datable volcanic materials. The overall climate for the entire Triassic for this area is given as arid with a key sea level regression in the Norian. Note, however, that the authors explicitly use the 2004 ISC timescale, and that under currently proposed revisions to this timescale the Carnian is more restricted.
The Triassic vertebrate fauna of India has always struck me as bizarre, mainly because the Early Triassic fauna is extremely similar to that of the Lystrosaurus assemblage zone of South Africa, and does contain several species of Lystrosaurus. Yet the Middle and Late Triassic fauna has much more of a Laurasian feel to it, especially the Late Triassic fauna, which includes basal phytosaurs such as Parasuchus, and more advanced phytosaurs such as a Leptosuchus-like form. Aetosaurs are represented by a paratypothoracisine form, which are only known from North America and Europe. Finally, metoposaurid temnospondyls are also common as in North America and Europe.
This seems very odd to me given that in paleogeographic reconstructions throughout the Triassic, India is firmly nestled on the western edge of modern day Africa, contacting Australia, and Antarctica, and separated from North America by all of northern Africa and from Europe by the Tethys. Unfortunately the Triassic fauna of North Africa is extremely sparse, although the Moroccan fauna is very similar to that of India and Laurasia. Perhaps Northern Africa served as a corridor for the Laurasian-type fauna, whereas there was some restriction from South America and South Africa in the Latest Triassic. Thus it seems that at this time there are not distinct Laurasian and Gondwanan distributions of tetrapods, but rather separate southern Gondwana and northern Gondwana/Laurasia distributions.
Mukhopadhyay, G., Mukhopadhyay, S. K., Roychowdhury, M., and P. K. Parui. 2010. Stratigraphic Correlation between Different Gondwana Basins of India.
Journal of the Geological Society of India 76:251-266. DOI: 10.1007/s12594-010-0097-6
Abstract - Gondwana Basins of India occur within the suture zones of Precambrian cratonic blocks of Peninsular India along some linear belts. More than 99% of the total coal resource of the country is present within these basins. The basins are demarcated by boundary faults having graben or half-graben geometry. These basins preserve a thick sedimentary pile deposited over nearly 200 million years from latest Carboniferous to Lower Cretaceous. However, due to lack of well-constrained data, age of most of the formations is assigned tentatively. This has resulted in diversified views on both intra- and inter-basinal stratigraphic correlation particularly in case of Upper Gondwana formations. It is well recognised that there are distinct spatial and temporal similarities in lithological, faunal and floral distribution in different Gondwana Basins of southern continents, including India, that were once part of supercontinent Gondwanaland. To address the problems of Indian Gondwana stratigraphy, during the present study, some unique events, also recognised in other parts of Gondwanaland, like marine flooding surfaces, large scale tectonic events or major change in depositional environment have been used as a tool for temporal correlation within the Gondwana Basins of India. Many of these events have been dated from different basins elsewhere. Considering these major events as time planes the total time span of deposition in Gondwana Basins has been classified into seven time slots. Recognition of these time planes helps in interbasinal correlation of different formations in Indian Gondwana basins and assigning the age, wherever available. This approach also helps in better understanding of basinal history. Unless otherwise mentioned, the time scale proposed by International Commission on Stratigraphy (2004) has been followed in this paper.
The Triassic vertebrate fauna of India has always struck me as bizarre, mainly because the Early Triassic fauna is extremely similar to that of the Lystrosaurus assemblage zone of South Africa, and does contain several species of Lystrosaurus. Yet the Middle and Late Triassic fauna has much more of a Laurasian feel to it, especially the Late Triassic fauna, which includes basal phytosaurs such as Parasuchus, and more advanced phytosaurs such as a Leptosuchus-like form. Aetosaurs are represented by a paratypothoracisine form, which are only known from North America and Europe. Finally, metoposaurid temnospondyls are also common as in North America and Europe.
This seems very odd to me given that in paleogeographic reconstructions throughout the Triassic, India is firmly nestled on the western edge of modern day Africa, contacting Australia, and Antarctica, and separated from North America by all of northern Africa and from Europe by the Tethys. Unfortunately the Triassic fauna of North Africa is extremely sparse, although the Moroccan fauna is very similar to that of India and Laurasia. Perhaps Northern Africa served as a corridor for the Laurasian-type fauna, whereas there was some restriction from South America and South Africa in the Latest Triassic. Thus it seems that at this time there are not distinct Laurasian and Gondwanan distributions of tetrapods, but rather separate southern Gondwana and northern Gondwana/Laurasia distributions.
Mukhopadhyay, G., Mukhopadhyay, S. K., Roychowdhury, M., and P. K. Parui. 2010. Stratigraphic Correlation between Different Gondwana Basins of India.
Journal of the Geological Society of India 76:251-266. DOI: 10.1007/s12594-010-0097-6
Abstract - Gondwana Basins of India occur within the suture zones of Precambrian cratonic blocks of Peninsular India along some linear belts. More than 99% of the total coal resource of the country is present within these basins. The basins are demarcated by boundary faults having graben or half-graben geometry. These basins preserve a thick sedimentary pile deposited over nearly 200 million years from latest Carboniferous to Lower Cretaceous. However, due to lack of well-constrained data, age of most of the formations is assigned tentatively. This has resulted in diversified views on both intra- and inter-basinal stratigraphic correlation particularly in case of Upper Gondwana formations. It is well recognised that there are distinct spatial and temporal similarities in lithological, faunal and floral distribution in different Gondwana Basins of southern continents, including India, that were once part of supercontinent Gondwanaland. To address the problems of Indian Gondwana stratigraphy, during the present study, some unique events, also recognised in other parts of Gondwanaland, like marine flooding surfaces, large scale tectonic events or major change in depositional environment have been used as a tool for temporal correlation within the Gondwana Basins of India. Many of these events have been dated from different basins elsewhere. Considering these major events as time planes the total time span of deposition in Gondwana Basins has been classified into seven time slots. Recognition of these time planes helps in interbasinal correlation of different formations in Indian Gondwana basins and assigning the age, wherever available. This approach also helps in better understanding of basinal history. Unless otherwise mentioned, the time scale proposed by International Commission on Stratigraphy (2004) has been followed in this paper.
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