Join Date: Mar 2008
Location: London, UK.
Fraud and fossils in India - controversial Cambrian fossils are a billion years older
This is an interesting story.
A decade-old dispute over the authenticity of Indian fossils that are some of the earliest examples of multicellular life seems to have been resolved. As a result, an Indian researcher has been cleared of simmering suspicions of specimen tampering.
The controversy began when palaeontologist Rafat Azmi of the Wadia Institute of Himalayan Geology in Dehra Dun reported in 1998 that he had found shell-like fossils in rocks from the Vindhyan mountain chain in central India that dated to 1.6 to 1.7 billion years ago1.
Uproar followed, because the finding suggested that animal forms had evolved much earlier than previously believed. Shelled creatures are thought to have first evolved at the beginning of the Cambrian 'explosion of life' around 550 million years ago.
In 2000, the Geological Society of India, based in Bangalore, sent a team to the site, but could not verify Azmi's initial report. When the society's journal subsequently wrote that Azmi's study was "far from convincing", media reports accused him of faking the fossils — damaging his career, Azmi says.
But research published this week in the Proceedings of the National Academy of Sciences2 reinterprets the fossils in question as traces of algae and bacteria. The purported shell-like fossils are, the authors claim, the marks of gas bubbles trapped in bacterial mats.
The samples also contain fossilized remains of filamentous algae, confirmed to be about 1.6 billion years old and possibly the earliest example of a multicellular eukaryote yet found. Similar algae had already been found in rocks dating from 400 to 600 million years later than the Vindhayan samples, but despite claims of older examples their existence before that time had remained an open question.
The samples "represent an exquisitely preserved biota of cyanobacteria and multicellular eukaryotes, previously unknown from such old rocks", says Stefan Bengtson, a palaeozoologist at the Swedish Museum of Natural History in Stockholm, who led the study. "It's a remarkable window onto ancient life, opened thanks to Dr Azmi."
"I see no evidence of fraud," he adds. "Science often progresses by the need to test 'crazy' ideas. If Azmi had not insisted on his 'Cambrian' fossils, we would not have known about this remarkable biota. He definitely didn't deserve being branded as a fraud in the Indian media."
Martin Brasier, a palaeobiologist at the University of Oxford, UK, wasn't involved in the research but has followed the debate since Azmi's original paper was published. He says the new study clears the way through the accusations to concentrate on interpretations of the fossils and their preservation. "This is what the original debate was all about," says Brasier. "The evidence is starting to show there were no animals in 'deep time'. The Cambrian explosion of animals after 550 million years ago was a real evolutionary event — like an avalanche in evolution."
Azmi says that the Geological Society of India now "has a moral duty to retract what they wrote about my work", noting that their accusations had "delayed the whole process of confirmation for nearly a decade".
The society's vice president, geologist S. V. Srikantiah, says that a retraction cannot be based on the results of foreign researchers. "It is for Azmi to prove he was right," he told Nature.
Bengtson, S. et al. (2009) The controversial “Cambrian” fossils of the Vindhyan are real but more than a billion years older. PNAS, advance online.
The age of the Vindhyan sedimentary basin in central India is controversial, because geochronology indicating early Proterozoic ages clashes with reports of Cambrian fossils. We present here an integrated paleontologic–geochronologic investigation to resolve this conundrum. New sampling of Lower Vindhyan phosphoritic stromatolitic dolomites from the northern flank of the Vindhyans confirms the presence of fossils most closely resembling those found elsewhere in Cambrian deposits: annulated tubes, embryo-like globules with polygonal surface pattern, and filamentous and coccoidal microbial fabrics similar to Girvanella and Renalcis. None of the fossils, however, can be ascribed to uniquely Cambrian or Ediacaran taxa. Indeed, the embryo-like globules are not interpreted as fossils at all but as former gas bubbles trapped in mucus-rich cyanobacterial mats. Direct dating of the same fossiliferous phosphorite yielded a Pb–Pb isochron of 1,650 ± 89 (2σ) million years ago, confirming the Paleoproterozoic age of the fossils. New U–Pb geochronology of zircons from tuffaceous mudrocks in the Lower Vindhyan Porcellanite Formation on the southern flank of the Vindhyans give comparable ages. The Vindhyan phosphorites provide a window of 3-dimensionally preserved Paleoproterozoic fossils resembling filamentous and coccoidal cyanobacteria and filamentous eukaryotic algae, as well as problematic forms. Like Neoproterozoic phosphorites a billion years later, the Vindhyan deposits offer important new insights into the nature and diversity of life, and in particular, the early evolution of multicellular eukaryotes.
The Vindhyan basin in Central India contains a thick unmetamorphosed sequence of sandstones, shales, and carbonate rocks together with volcaniclastic rocks (Fig. 1). Estimates of the age span of this Vindhyan Supergroup have varied considerably, but geochronologic evidence supports a Paleo- to Mesoproterozoic age [1.7 to 1.6 billion years ago (Ga)] of the Lower Vindhyan (ref. 1 and references therein). Although a Neoproterozoic age has often been inferred for the Upper Vindhyan (1), firm geochronologic evidence for this has been missing, and recent paleomagnetic–geochronologic work even suggests a late Mesoproterozoic age (1.0–1.07 Ga) of the uppermost Vindhyan units (2).
These age assignments have been persistently challenged by reports of Ediacaran and Cambrian fossils from the Vindhyan rocks (3–8). In response to a claim for Mesoproterozoic animal trace fossils from the Lower Vindhyan Chorhat Sandstone at Chorhat (9), Rafat J. Azmi argued that the presence of Cambrian skeletal fossils in beds conformably overlying the Chorhat removed any need to postulate a Mesoproterozoic age (10). In the debate that followed (11–19), errors in Azmi’s reports were taken to suggest that they were fundamentally flawed and that the skeletal fossils did not exist (20).
Although most of Azmi’s fossils were convincingly reinterpreted as diagenetic artifacts (12), a few others remained as potential anomalies. Furthermore, recent publications by Azmi and coworkers (4, 5, 8) reported a number of apparently well-preserved Lower Vindhyan fossils closely resembling forms previously known to be characteristic of the Cambrian: annulated tubes, embryo-like globules, and calcified cyanobacteria. If these and earlier reports are correct, they have profound implications: either the radiometric dating consistently reflects inherited dates not related to sedimentation, as suggested by Azmi and coworkers (4, 8), or Cambrian-like fossils occur in rocks that are a billion years older than the Cambrian. It is thus necessary to resolve the controversy.
Our results show that the fossil biota reported from the Lower Vindhyan of the Chitrakoot region by Azmi et al. (4) is indigenous to the rock rather than being due to sample contamination. We also demonstrate, however, that the published assignments of the fossils to Cambrian taxa of skeletal fossils are in error, and our new geochronologic work confirms a Paleoproterozoic age of the rocks.
The Lower Vindhyan thus presents a spectacular preservational window into a Paleoproterozoic biota. The main factors responsible for this preservation seem to be the low level of metamorphism, and—in the case of the Tirohan Dolomite—the presence of sedimentary phosphate, both unusual for rocks of this age. Phosphatization is often responsible for exquisite preservation of soft parts in the Neoproterozoic and Cambrian (29, 30, 50), whereas such preservation is comparatively uncommon in older and younger parts of the geologic column. A long-standing problem in Precambrian paleobiology has been why calcifying cyanobacteria are so rare, compared with their massive occurrence in the Cambrian (51). This has been ascribed to high concentrations of dissolved inorganic carbon combined with low levels of Ca2 in Proterozoic oceans (52), to high Proterozoic ambient CO2 levels (23), or simply to preservational bias (53). The presence of Girvanella-like cyanobacteria in the Lower Vindhyan may help to elucidate levels of inorganic carbon in mat environments of the late Paleoproterozoic.
In terms of the evolution of major taxa, the most significant information to come out of the Vindhyan phosphorites is the detailed 3-dimensional morphologic evidence for late Paleoproterozoic multicellular eukaryotes (filamentous algae). Previously accepted multicellular eukaryotes were only known from the late Mesoproterozoic or early Neoproterozoic (54) (i.e., some 400– 600 million years later), although some older discoveries had at least suggested the possibility that they had a longer prehistory (e.g., refs. 40, 55, and 56).
The potential of the Vindhyan phosphorites to yield fresh information on the Paleoproterozoic biotas is thus considerable, and the ‘‘shelly’’ biota discovered by Azmi et al. gives new insight into the nature of the Paleoproterozoic biosphere. The discredited reports of ‘‘Cambrian’’ fossils turned out to be an important discovery.
This is related to a paper published by occasional TR poster Joe Meert last year (ref 2 above is Joe's paper). He mentioned it in this thread:
I'll ask Joe if he minds popping in and commenting.
Last edited by SteveF; 04-28-2009 at 11:56 AM.