Rupture along the Himalayan Front

In their article for Lithosphere on 12 March, authors Kristin Morell and colleagues write, “The ∼700-km-long ‘central seismic gap’ is the most prominent segment of the Himalayan front not to have ruptured in a major earthquake during the last 200-500 years. This prolonged seismic quiescence has led to the proposition that this region, with a population of more 10 million, is overdue for a great earthquake. Despite the region’s recognized seismic risk, the geometry of faults likely to host large earthquakes remains poorly understood.”

A little more than a month on, the area experience a magnitude 7.8 earthquake, centered in Nepal (25 Apr. 2015).

Date and rupture patches for large historical Himalayan earthquakes (Rajendran and Rajendran, 2005; Kumar et al., 2006) with reference to the Uttarakhand region of the central seismic gap, and the physiographic transition 2 of Uttarakhand (UPT2 ) and Nepal (NPT2 ) (Wobus et al., 2006a). (B) Simplified geologic map for area shown in A (Célérier et al., 2009a; Webb et al., 2011). Focal mechanisms of all earthquakes within the recording period (Mw 5-7) are shown with location as white circle. Earthquake locations are based on Ni and Baranzangi (1984) and the National Earthquake Information Center (NEIC) catalog (earthquake.usgs.gov). Focal mechanisms are based on Ni and Baranzangi (1984) or the Global Centroid-Moment-Tensor (CMT) catalog (globalcmt.org). STD--South Tibetan Detachment; THS--Tethyan Himalayan Sequence; MCT--Main Central Thrust; GHS--Greater Himalayan Sequence; LHS--Lesser Himalayan Sequence; MBT--Main Boundary Thrust; MFT--Main Frontal Thrust. Credit: Morell et al. and Lithosphere

Date and rupture patches for large historical Himalayan earthquakes (Rajendran and Rajendran, 2005; Kumar et al., 2006) with reference to the Uttarakhand region of the central seismic gap, and the physiographic transition 2 of Uttarakhand (UPT2 ) and Nepal (NPT2 ) (Wobus et al., 2006a). (B) Simplified geologic map for area shown in A (Célérier et al., 2009a; Webb et al., 2011). Focal mechanisms of all earthquakes within the recording period (Mw 5-7) are shown with location as white circle. Earthquake locations are based on Ni and Baranzangi (1984) and the National Earthquake Information Center (NEIC) catalog (earthquake.usgs.gov). Focal mechanisms are based on Ni and Baranzangi (1984) or the Global Centroid-Moment-Tensor (CMT) catalog (globalcmt.org). STD–South Tibetan Detachment; THS–Tethyan Himalayan Sequence; MCT–Main Central Thrust; GHS–Greater Himalayan Sequence; LHS–Lesser Himalayan Sequence; MBT–Main Boundary Thrust; MFT–Main Frontal Thrust.
Credit: Morell et al. and Lithosphere

In their study, Morell and colleagues use a series of complementary geomorphic and erosion rate data to define the ramp-flat geometry of the active detachment fault that is likely to host a large earthquake within the hinterland of the northwest Himalaya. Their analysis indicates that this detachment is sufficiently large to host another great earthquake in the western half of the central Himalayan seismic gap.

Specifically, their data sets point to a distinctive physiographic transition at the base of the high Himalaya in the state of Uttarakhand, India, characterized by abrupt strike-normal increases in channel steepness and a tenfold increase in erosion rates.

When combined with previously published geophysical imaging and seismicity data sets, Morell and colleagues interpret the observed spatial distribution of erosion rates and channel steepness to reflect the landscape response to spatially variable rock uplift due to a structurally coherent ramp-flat system of the Main Himalayan Thrust. They write, “Although it remains unresolved whether the kinematics of the Main Himalayan Thrust ramp involve an emergent fault or duplex, the landscape and erosion rate patterns suggest that the décollement beneath the state of Uttarakhand provides a sufficiently large and coherent fault segment capable of hosting a great earthquake.”

In conclusion, they note, “While this hypothesis remains speculative, it is supported by independent records of historical seismicity.”

Citation:Geological Society of America. “Rupture along the Himalayan Front.” ScienceDaily. ScienceDaily, 30 April 2015. <www.sciencedaily.com/releases/2015/04/150430134933.htm>.

Journal Ref: K. D. Morell, M. Sandiford, C. P. Rajendran, K. Rajendran, A. Alimanovic, D. Fink, J. Sanwal. Geomorphology reveals active decollement geometry in the central Himalayan seismic gap. Lithosphere, 2015; DOI: 10.1130/L407.1

WFS: Ariyalur Fossils ( Arctostrea )

WFS: Ariyalur Fossils ( Arctostrea ):   This upper Cretaceous oyster is characterized by long and curved valves. Stout ribs cross the upper valve. The sample is obtained from Ariyalur/Dalmiapuram area. samples collected by Riffin T Sajeev and Russel T Sajeev from World Fossil society.

The Rastellum genus of oysters lived between 161 to 65 million years ago during the Jurassic and Cretaceous periods. Occurring in many locations across the globe, the Rastellum oyster species inhabited shallow marine environments such as lagoons, bioherms and biostromes, and peritidal areas exposed to air and more harsh extreme variations of temperature, salinity, and storm activity, and also lived in shallow subtidal areas, above, on, and below reefs, coastal areas, and offshore shelves along continents. Rastellum oysters would remain stationary, attached to the surfaces of rocks, pilings, and to the sea floor itself, where they would filter feed on small foods suspended in the water column. This specimen is Rastellum carinatum, a species which seems to have occurred from 144 to 65 million years ago, evidently becoming extinct during the same event that ended the reign of the dinosaurs.

Arctostrea (Rastellum Species). Specimen Collected by Riffin T Sajeev & Russel T Sajeev Of World Fossil Society .Photo Copyright@ World Fossil Society.

Arctostrea (Rastellum Species). Specimen Collected by Riffin T Sajeev & Russel T Sajeev Of World Fossil Society .Photo Copyright@ World Fossil Society.

Phylum :
Mollusca
Class :
Bivalvia
Family :
Ostreidae
Genus :
Rastellum (Arctostrea)
Species :
carinatum (Lamarck)
Stage :
Cenomanian

 

Brachiopod shell shows sign of evolution

Researchers of Ludwig-Maximilians-Universitaet (LMU) in Munich have carried out the first detailed study of the molecular mechanisms responsible for formation of the brachiopod shell. Comparison with shell synthesis in other groups reveals the deep evolutionary roots of the process.

Brachiopods (lamp shells) are marine invertebrates, which were a highly successful and widespread group in the Palaeozoic era. Indeed, the group is best known for its rich fossil record. Some 30,000 fossil species have been described so far, and the oldest specimens date from Cambrian times, and are thus around 500 million years old. Brachiopods are now represented by comparatively few species, which are found in various regions of the world’s oceans. One of their most characteristic features is their bipartite shell. “The molecular basis of how this shell is actually built has been virtually unknown up to now,” says Professor Gert Wörheide of the Department of Earth and Environmental Sciences and the Geobio-Center at LMU. “To find out more, we have carried out the first comprehensive survey of the genes and proteins involved in shell formation in brachiopods.” The results of the study appear in the journal Genome Biology and Evolution.

Although brachiopods look very much like mollusks at first sight, they are not related to the latter. In contrast to the typical mollusk shell, their bipartite shell is not left/right symmetrical. Instead it comprises an upper (dorsal) part and a lower (ventral) ‘valve’, with the ventral valve usually being the larger. The valves are made of either calcium carbonate (calcite) or calcium phosphate in association with a diverse array of proteins and polysaccharides, which are secreted by the cells of the underlying mantle during shell formation and are incorporated into the biomineral formed. “This is why the proteins occluded within the shell can provide insights into its mode of formation,” Wörheide explains.

brachiopod shell

brachiopod shell

To gain such insights, the researchers identified the complete set of proteins (the proteome) found in the shell of the South American brachiopod Magellania venosa. This enabled them to then characterize the genes that encode the blueprints for synthesis of the proteins from the mantle tissue secreting the shell (the mantle transcriptome). “This is the first time that such a screening approach has been applied to any species of brachiopod, and it was the combination of the two methods that allowed us to identify the molecular components involved in formation of the shell,” Wörheide points out.

The results of these two types of molecular screen are of particular interest when compared with data from other groups of shell-forming organisms, such as corals, sea urchins and mollusks. The seven most abundant proteins found in the Magellania shell turn out to be unique to brachiopods, but they exhibit biochemical features similar to those of proteins that are known to serve similar functions in other animal phyla. Other proteins show significant structural resemblances to shell proteins that are known from other animals. Based on these analyses, the researchers conclude that the genetic program and the molecular mechanisms utilized in biomineralization — the biochemical processes by which living organisms synthesize mineral-based structures in a controlled manner — have, in part, been evolutionarily conserved among invertebrates. “Our results provide entirely new insights into the evolution of shell formation in the brachiopods,” Wörheide says, “and these data will also be very useful in future studies.”

WFS: Dinosaur Diary: AVIMIMUS

Name Means: “Bird mimic” Length: 5 feet (1.5 m)
Pronounced: AYV-ee-MIME-us Weight: 45 pounds (20 kilos)
When it lived: Late Cretaceous – 95 MYA
Where found: Mongolia, China
    Avimimus was discovered by Russian paleontologist Sergei Mikhailovich Kurzanov during the exploration of the Joint Soviet-Mongolian paleontological expedition in the summer of 1973, at the Udan-Sayr (southern Gobi) location in Mongolia. It was a  fairly complete skeleton of a bird-like theropod. With the exception of a crushed skull fragment, the bones were very well preserved.   Udan-Sayr is in the foothills of the Gurvan-Sayhan mountain range.  The red colored sand he deposits are 15 meters thick and can be very accurately dated. This is proven by the presence of teeth from  Tarbosaurus, a carnosaur, known from the deposits of that age from various locations in the Southern Gobi. Three other partial skeletons were later recovered.  It was named by Kurzanov in 1981.
     Avimimus looked so much like a bird that its name literally means that it imitates a bird.  It looks like a large reptilian roadrunner. Avimimus had a long, lean neck topped by a short skull that was equipped with a toothless beak and a relatively large braincase. It had long, slender back legs built for fast running. But its front limbs had not yet evolved into wings.  They were lightly built and equipped with sharp, curved claws. The bones in it’s wrists were actually fused together, much like that of the modern day cockatoo. In fact, Avimimus had the ability to fold its whole arm against its body, much like the wings of a bird. Unlike a bird however, Avimimus had a long bony tail. What’s more, its pelvis resembled that of other theropods.
It was the first dinosaur to so clearly express bird features, in such large numbers.  It is also the first theropods with such unusual structure of the pelvis. Such a combination of unique features places Avimimus in a category all its own.

Roadrunner – Geococcyx californianus

   It is possible that Avimimus had feathers, however, deposits around its body are too coarse for such features to be preserved. However it was unearthed near other dinosaurs similar to itself, particularly Sinosauropteryx and Caudipteryx and their feathers were preserved. Even though none have so far been found, there is evidence that Avimimus could have had feathers.  There are small ridges on its forearm that could be anchor points for feather shafts.  Modern birds have bone “dimples” at the point of feather attachment, however the ridges present in Avimimus could be a pre-adaptation to feather attachment. Even if Avimimus did have feathers, it would seem very unlikely that it would be able to achieve flight, particularly due to its large body.
     One of the great enigmas to have surfaced in the last quarter century of dinosaur paleo, Avimimus has features that could be ascribed to sauropods, hadrosaurids, basal theropods, oviraptorids, birds, and ornithomimids.  Sometimes considered a chimera, recent remains indicate it was an Oviraptor.

Avimimus belonged to the:

  • Kingdom Animalia (animals)
  • Phylum Chordata (having a hollow nerve chord ending in a brain)
  • Class Archosauria (diapsids with socket-set teeth, etc.)
  • Order Saurischia – lizard-hipped dinosaurs
  • Suborder Theropoda – bipedal carnivores
  • Infraorder Coelurosauria – lightly-built fast-running predators with hollow bones and large brains
  • Superfamily Maniraptoriformes – advanced coelurosaurs with a fused wrist bone
  • Family Avimimidae
  • Genus Avimimus
  • Species portentosus (the type species, Kurzanov, 1981)
  • Avimimus illustration

    Avimimus illustration

 

‘platypus’ dinosaur: Vegetarian relative of T. rex

Although closely related to the notorious carnivore Tyrannosaurus rex, a new lineage of dinosaur discovered in Chile is proving to be an evolutionary jigsaw puzzle, as it preferred to graze upon plants.

Palaeontologists are referring to Chilesaurus diegosuarezi as a ‘platypus’ dinosaur because of its bizarre combination of characters that resemble different dinosaur groups. For example, Chilesaurus boasted a proportionally small skull, hands with two fingers like Tyrannosaurus rex and feet more akin to primitive long-neck dinosaurs.

Chilesaurus diegosuarezi is nested within the theropod group of dinosaurs, the dinosaurian group that gathers the famous meat eaters Velociraptor, Carnotaurus and Tyrannosaurus, and from which birds today evolved. The presence of herbivorous theropods was up until now only known in close relatives of birds, but Chilesaurus shows that a meat-free diet was acquired much earlier than thought.

Artist's interpretation of Chilesaurus diegosuareziis. Credit: Gabriel Lío

Artist’s interpretation of Chilesaurus diegosuareziis.
Credit: Gabriel Lío

Chilesaurus diegosuarezi is named after the country where it was collected, as well as honouring Diego Suárez, the seven year old boy who discovered the bones. He discovered the fossil remains of this creature at the Toqui Formation in Aysén, south of Chilean Patagonia, in rocks deposited at the end of the Jurassic Period, approximately 145 million years ago.

Diego was in the region with his parents, Chilean geologists Manuel Suarez and Rita de la Cruz, who were studying rocks in the Chilean Patagonia, with the aim to better understand the formation of the Andes mountain range. Diego stumbled across the fossils while him and his sister, Macarena, were looking for decorative stones.

Due to Chilesaurus‘ unusual combination of characters, it was initially thought that Diego had uncovered several species. However, since Diego’s find, more than a dozen Chilesaurus specimens have been excavated, including four complete skeletons — a first for the Jurassic Period in Chile — and they demonstrate that this dinosaur certainly combined a variety of unique anatomical traits.

Most of the specimens are the size of a turkey, but some isolated bones reveal that the maximum size of Chilesaurus was around three metres long. Chilean and Argentinian palaeontologists from institutions including the University of Birmingham, along with Diego’s parents, have been studying these skeletons, with the findings published in full in Nature on April 27th.

Other features present in very different groups of dinosaurs Chilesaurus adopted were robust forelimbs similar to Jurassic theropods such as Allosaurus, although its hands were provided with two blunt fingers, unlike the sharp claws of fellow theropod Velociraptor. Chilesaurus‘ pelvic girdle resembles that of the ornithischian dinosaurs, whereas it is actually classified in the other basic dinosaur division — Saurischia.

The different parts of the body of Chilesaurus were adapted to a particular diet and way of life, which was similar to other groups of dinosaurs. As a result of these similar habits, different regions of the body of Chilesaurus evolved resembling those present in other, unrelated groups of dinosaurs, which is a phenomenon called evolutionary convergence.

Chilesaurus represents one of the most extreme cases of mosaic convergent evolution recorded in the history of life. For example, the teeth of Chilesaurus are very similar to those of primitive long-neck dinosaurs because they were selected over millions of years as a result of a similar diet between these two lineages of dinosaurs.

Martín Ezcurra, Researcher, School of Geography, Earth and Environmental Sciences, University of Birmingham said: ‘Chilesaurus can be considered a ‘platypus’ dinosaur because different parts of its body resemble those of other dinosaur groups due to mosaic convergent evolution. In this process, a region or regions of an organism resemble others of unrelated species because of a similar mode of life and evolutionary pressures. Chilesaurus provides a good example of how evolution works in deep time and it is one of the most interesting cases of convergent evolution documented in the history of life.

Chilesaurus shows how much data is still completely unknown about the early diversification of major dinosaur groups. This study will force palaeontologists to take more care in the future in the identification of fragmentary or isolated dinosaur bones. It comes as false relationship evidence may arise because of cases of convergent evolution, such as that present in Chilesaurus.’

Dr. Fernando Novas, Bernardino Rivadavia Natural Sciences Museum, Buenos Aires, Argentina, led the research on Chilesaurus and said: ‘Chilesaurus is the first complete dinosaur from the Jurassic Period found in Chile and represents one of the most complete and anatomically correct documented theropod dinosaurs from the southern hemisphere. Although plant-eating theropods have been recorded in North America and Asia, this is the first time a theropod with this characteristic has been found in a southern landmass.

Chilesaurus was an odd plant-eating dinosaur only to be found in Chile. However, the recurrent discovery in beds of the Toqui Formation of its bones and skeletons clearly demonstrates that Chilesaurus was, by far, the most abundant dinosaur in southwest Patagonia 145 million years ago.’

courtesy & Citation: University of Birmingham. “Bizarre ‘platypus’ dinosaur: Vegetarian relative of T. rex.” ScienceDaily. ScienceDaily, 27 April 2015. <www.sciencedaily.com/releases/2015/04/150427124631.htm>

mammoths back to life !

An international team of researchers has sequenced the nearly complete genome of two Siberian woolly mammoths — revealing the most complete picture to date — including new information about the species’ evolutionary history and the conditions that led to its mass extinction at the end of the Ice Age.

“This discovery means that recreating extinct species is a much more real possibility, one we could in theory realize within decades,” says evolutionary geneticist Hendrik Poinar, director of the Ancient DNA Centre at McMaster University and a researcher at the Institute for Infectious Disease Research, the senior Canadian scientist on the project.

“With a complete genome and this kind of data, we can now begin to understand what made a mammoth a mammoth — when compared to an elephant — and some of the underlying causes of their extinction which is an exceptionally difficult and complex puzzle to solve,” he says.

While scientists have long argued that climate change and human hunting were major factors behind the mammoth’s extinction, the new data suggests multiple factors were at play over their long evolutionary history.

Researchers from McMaster, Harvard Medical School, the Swedish Museum of Natural History, Stockholm University and others produced high-quality genomes from specimens taken from the remains of two male woolly mammoths, which lived about 40,000 years apart.

One had lived in northeastern Siberia and is estimated to be nearly 45,000 years old. The other -believed to be from one of the last surviving mammoth populations — lived approximately 4,300 years ago on Russia’s Wrangel Island, located in the Arctic Ocean.

“We found that the genome from one of the world’s last mammoths displayed low genetic variation and a signature consistent with inbreeding, likely due to the small number of mammoths that managed to survive on Wrangel Island during the last 5,000 years of the species’ existence,” says Love Dalén, an associate professor of Bioinformatics and Genetics at the Swedish Museum of Natural History.

Tip of the trunk of a baby mammoth. Credit: Love Dalen

Tip of the trunk of a baby mammoth.
Credit: Love Dalen

Scientists used sophisticated technology to tease bits and pieces of highly fragmented DNA from the ancient specimens, which they then used to sequence the genomes. Through careful analysis, they determined the animal populations had suffered and recovered from a significant setback roughly 250,000 to 300,000 years ago. However, say researchers, another severe decline occurred in the final days of the Ice Age, marking the end.

“The dates on these current samples suggest that when Egyptians were building pyramids, there were still mammoths living on these islands,” says Poinar. “Having this quality of data can help with our understanding of the evolutionary dynamics of elephants in general and possible efforts at de-extinction.”

The latest research is the continuation of the pioneering work Poinar and his team began in 2006, when they first mapped a partial mammoth genome, using DNA extracted from carcasses found in permafrost in the Yukon and Siberia.

The study is published online in the Cell Press journal Current Biology.

Sexual Dimorphism in the Plated Dinosaur Stegosaurus

Abstract

Conclusive evidence for sexual dimorphism in non-avian dinosaurs has been elusive. Here it is shown that dimorphism in the shape of the dermal plates of Stegosaurus mjosi (Upper Jurassic, western USA) does not result from non-sex-related individual, interspecific, or ontogenetic variation and is most likely a sexually dimorphic feature. One morph possessed wide, oval plates 45% larger in surface area than the tall, narrow plates of the other morph. Intermediate morphologies are lacking as principal component analysis supports marked size- and shape-based dimorphism. In contrast, many non-sex-related individual variations are expected to show intermediate morphologies. Taphonomy of a new quarry in Montana (JRDI 5ES Quarry) shows that at least five individuals were buried in a single horizon and were not brought together by water or scavenger transportation. This new site demonstrates co-existence, and possibly suggests sociality, between two morphs that only show dimorphism in their plates. Without evidence for niche partitioning, it is unlikely that the two morphs represent different species. Histology of the new specimens in combination with studies on previous specimens indicates that both morphs occur in fully-grown individuals. Therefore, the dimorphism is not a result of ontogenetic change. Furthermore, the two morphs of plates do not simply come from different positions on the back of a single individual. Plates from all positions on the body can be classified as one of the two morphs, and previously discovered, isolated specimens possess only one morph of plates. Based on the seemingly display-oriented morphology of plates, female mate choice was likely the driving evolutionary mechanism rather than male-male competition. Dinosaur ornamentation possibly served similar functions to the ornamentation of modern species. Comparisons to ornamentation involved in sexual selection of extant species, such as the horns of bovids, may be appropriate in predicting the function of some dinosaur ornamentation.

Oldest fossils controversy resolved

New analysis of world-famous 3.46 billion-year-old rocks by researchers from the University of Bristol, the University of Oxford and UWA (the University of Western Australia) is set to finally resolve a long running evolutionary controversy.

The new research, published this week in Proceedings of the National Academy of Sciences, shows that structures once thought to be Earth’s oldest microfossils do not compare with younger fossil candidates but have, instead, the character of peculiarly shaped minerals.In 1993, US scientist Bill Schopf described tiny carbon-rich filaments within the 3.46 billion-year-old Apex chert (fine-grained sedimentary rock) from the Pilbara region of Western Australia, which he likened to certain forms of bacteria, including cyanobacteria.

These ‘Apex chert microfossils’ — between 0.5 and 20 micrometres wide — soon became enshrined in textbooks, museum displays, popular science books and online reference guides as the earliest evidence for life on Earth. In 1996, these structures were even used to test and help refute the case against ‘microfossils’ in the Martian meteorite ALH 84001.

Even so, their curious colour and complexity gave rise to some early questions. Gravest doubts emerged in 2002, when a team led by Oxford’s Professor Martin Brasier (co-author of this current study) revealed that the host rock was not part of a simple sedimentary unit but rather came from a complex, high-temperature hydrothermal vein, with evidence for multiple episodes of subsurface fluid flow over a long time. His team advanced an alternative hypothesis, stating that these curious structures were not true microfossils but pseudofossils formed by the redistribution of carbon around mineral grains during these hydrothermal events.

Although other research teams have since supported the hydrothermal context of Professor Brasier, the ‘Apex microfossil’ debate has remained hard to resolve because scientific instrumentation has only recently reached the level of resolution needed to map both chemical composition and morphology of these ‘microfossils’ at the sub-micrometre scale.

Now Dr David Wacey, a Marie Curie Fellow in Bristol’s School of Earth Sciences, in collaboration with the late Professor Brasier, has come up with new high-spatial resolution data that clearly demonstrate that the ‘Apex chert microfossils’ comprise stacks of plate-like clay minerals arranged into branched and tapered worm-like chains. Carbon was then absorbed onto the edges of these minerals during the circulation of hydrothermal fluids, giving a false impression of carbon-rich cell-like walls.

 

Dr Wacey and team used transmission electron microscopy to examine ultrathin slices of ‘microfossil’ candidates, to build up nanoscale maps of their size, shape, mineral chemistry and distribution of carbon.

Dr Wacey said: “It soon became clear that the distribution of carbon was unlike anything seen in authentic microfossils. A false appearance of cellular compartments is given by multiple plates of clay minerals having a chemistry entirely compatible with a high temperature hydrothermal setting.

“We studied a range of authentic microfossils using the same transmission electron microscopy technique and in all cases these reveal coherent, rounded envelopes of carbon having dimensions consistent with their origin from cell walls and sheaths. At high spatial resolution, the Apex ‘microfossils’ lack all evidence for coherent, rounded walls. Instead, they have a complex, incoherent spiky morphology, evidently formed by filaments of clay crystals coated with iron and carbon.”

Before his death Professor Brasier commented: “This research should, at long last, provide a closing chapter for the ‘Apex microfossil’ debate. Such discussions have encouraged us to refine both the questions and techniques needed to search for life remote in time and space, including signals from Mars or beyond. It is hoped that textbooks and websites will now focus upon recent and more robust discoveries of microfossils of a similar age from Western Australia, also examined by us in the same article.”

University of Bristol. “Oldest fossils controversy resolved.” ScienceDaily. ScienceDaily, 20 April 2015. <www.sciencedaily.com/releases/2015/04/150420154823.htm>.

WFS : Ariyalur Fossils : Rastellum Carinatum

Rastellum (Arctostrea) carinatum (Lamarck)

This upper Cretaceous oyster is characterized by long and curved valves. Stout ribs cross the upper valve. The sample is obtained from Ariyalur/Dalmiapuram area. samples collected by Riffin T Sajeev and Russel T Sajeev from World Fossil society.

The Rastellum genus of oysters lived between 161 to 65 million years ago during the Jurassic and Cretaceous periods. Occurring in many locations across the globe, the Rastellum oyster species inhabited shallow marine environments such as lagoons, bioherms and biostromes, and peritidal areas exposed to air and more harsh extreme variations of temperature, salinity, and storm activity, and also lived in shallow subtidal areas, above, on, and below reefs, coastal areas, and offshore shelves along continents. Rastellum oysters would remain stationary, attached to the surfaces of rocks, pilings, and to the sea floor itself, where they would filter feed on small foods suspended in the water column. This specimen is Rastellum carinatum, a species which seems to have occurred from 144 to 65 million years ago, evidently becoming extinct during the same event that ended the reign of the dinosaurs.

Phylum :
Mollusca
Class :
Bivalvia
Family :
Ostreidae
Genus :
Rastellum (Arctostrea)
Species :
carinatum (Lamarck)
Stage :
Cenomanian
Rastellum Carrinata from Ariyalur/Dalmiapuram : Photo copyright@ WFS,Riffin T Sajeev&Russel T Sajeev

Rastellum Carrinata from Ariyalur/Dalmiapuram : Photo copyright@ WFS,Riffin T Sajeev&Russel T Sajeev

A new birth story for mosasaurs discovered.

They weren’t in the delivery room, but researchers at Yale University and the University of Toronto have discovered a new birth story for a gigantic marine lizard that once roamed the oceans.

Thanks to recently identified specimens at the Yale Peabody Museum of Natural History, paleontologists now believe that mighty mosasaurs — which could grow to 50 feet long — gave birth to their young in the open ocean, not on or near shore.The findings answer long-held questions about the initial environment of an iconic predator that lived during the time of the dinosaurs. Mosasaurs populated most waters of the Earth before their extinction 65 million years ago.

“Mosasaurs are among the best-studied groups of Mesozoic vertebrate animals, but evidence regarding how they were born and what baby mosasaur ecology was like has historically been elusive,” said Daniel Field, lead author of a study published online April 10 in the journal Palaeontology. Field is a doctoral candidate in the lab of Jacques Gauthier in Yale’s Department of Geology and Geophysics.

Giant sea lizards in the age of dinosaurs: A new beginning for baby mosasaurs

Giant sea lizards in the age of dinosaurs: A new beginning for baby mosasaurs

Credit: Illustration by Julius T. Csotonyi

In their study, Field and his colleagues describe the youngest mosasaur specimens ever found. Field had come across the fossils in the Yale Peabody Museum’s extensive collections. “These specimens were collected over 100 years ago,” Field said. “They had previously been thought to belong to ancient marine birds.”

Field and Aaron LeBlanc, a doctoral candidate at the University of Toronto at Mississauga, concluded that the specimens showed a variety of jaw and teeth features that are only found in mosasaurs. Also, the fossils were found in deposits in the open ocean.

“Really, the only bird-like feature of the specimens is their small size,” LeBlanc said. “Contrary to classic theories, these findings suggest that mosasaurs did not lay eggs on beaches and that newborn mosasaurs likely did not live in sheltered nearshore nurseries.”