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According to a study, published in the journal Monthly Notices of the Royal Astronomical Society, mass extinctions occurring over the past 260 million years were likely caused by comet/asteroid showers.

For more than three decades, researchers have argued about a controversial hypothesis relating to periodic mass extinctions and asteroid/comet impact craters on Earth.

Dr Ken Caldeira of Carnegie Institution and Dr Michael Rampino of New York University offer new support linking the age of these craters with recurring mass extinctions of life, including the demise of the dinosaurs.

Specifically, they show a cyclical pattern over the studied period, with both impacts and extinction events taking place every 26 million years.

This cycle has been linked to periodic motion of the Sun and planets through the dense mid-plane of our Milky Way Galaxy.

Scientists have theorized that gravitational perturbations of the distant Oort comet cloud that surrounds the Sun lead to periodic comet showers in the inner Solar System, where some comets strike our planet.

To test their hypothesis, the team performed time-series analyses of impacts and extinctions using available data offering more accurate age estimates.

“The correlation between the formation of these impacts and extinction events over the past 260 million years is striking and suggests a cause-and-effect relationship,” said Dr Rampino, who is the lead author on the study.

The scientists found that six mass extinctions of life during the studied period correlate with times of enhanced impact cratering on Earth.

“One of the craters considered in the study is the Chicxulub impact structure in the Yucatan, which dates to about 65 million years ago – the time of a great mass extinction that included the dinosaurs.”

“Moreover, five out of the six largest impact craters of the last 260 million years on Earth correlate with mass extinction events,” they said.

“This cosmic cycle of death and destruction has without a doubt affected the history of life on our planet,” Dr Rampino concluded.

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Michael Rampino & Ken Caldeira. Periodic impact cratering and extinction events over the last 260 million years. MNRAS, published online October 20, 2015

Source: www.sci-news.com, 2015

Sinraptor is a genus of theropod dinosaur from the Late Jurassic.

Sinraptor is a dinosaur which lived approximately 150 million years ago. It was first discovered by a joint Chinese and Canadian expedition in the Shishugou Formation of China in 1987. In 1994, it was named by Philip J. Currie and Xian Zhao, who gave it the name Sinraptor because it means “Chinese raptor”. The specific name dongi honours Dong Zhiming. Despite its name, Sinraptor is not related to dromaeosaurids (often nicknamed “raptors”) like Velociraptor.

This dinosaur was around 25 feet long, 10 feet tall and weighed approximately 2000 pounds or 1 ton. It was probably a fierce—albeit small—carnivore that probably hunted very well. Since many of the herbivores in this part of the world were giant, they probably hunted the juvenile members of them. Perhaps separating these young sauropods from their parents to hunt them. However, it probably also had to contend with other larger predators who may have given it some grief during the
course of its life.

An interesting fact about Sinraptor is that it isn’t a true raptor. Sure, it was bipedal like a raptor but that is where the similarities end. It would be millions of years after the death of this dinosaur before raptors would come on the scene.

Paleontologists actually think that the Sinraptor was an Allosaur.

The skeleton of Sinraptor hepingensis (formerly referred to Yangchuanosaurus) is on display at the Zigong Dinosaur Museum, Zigong, China.

Source: www.Wikipedia.org

New work from an international team of researchers including Carnegie’s Lara Wagner improves our understanding of the geological activity that is thought to have formed the Rocky Mountains. It was published by Nature in August 2015.

Subduction is a geological process that occurs at the boundary between two of the many plates that make up the Earth’s crust. An oceanic crustal plate sinks and slides under another plate—either oceanic or continental—and is plunged deep into Earth’s mantle.

Usually the lower plate slides down into the mantle at a fairly steep angle, sinking rapidly into the warmer, less-dense mantle material. However, in a process called “flat-slab” subduction, the lower plate moves nearly horizontally underneath the upper plate, sometimes for great distances.

When the largest modern-day plant-eaters — elephants — are confined to too small an area, they devastate the vegetation. So 15,000 years ago, when the herbivores like the Columbian mammoth, mastodons and giant ground sloths were even larger, more numerous and more widely distributed, how did the landscape survive?

A pack of saber-tooth cats (Smilodon) fight with adult Colombian mammoths over a juvenile mammoth they’ve felled. A new analysis by a team of biologists concludes that ‘hypercarnivores’ such as these working in concert could have taken down juveniles of the largest herbivores.

The answer was probably enormous predators, creatures called “hypercarnivores” by a team of evolutionary biologists appearing online the week of Oct. 26 in the Proceedings of the National Academy of Sciences.

These ancient carnivores would have been about twice as large as the wolves, lions and hyenas we know today.

Based on a series of mathematical models for the sizes of predators and prey in the late Pleistocene age (about 1 million to 11,000 years ago), the team concludes that the largest cave hyena might have been able to take down a 5-year-old juvenile mastodon weighing more than a ton. Hunting in packs, those hyenas could possibly bring down a 9-year-old mastodon weighing two tons, the authors conclude.

“From the present day, it seems that big animals like elephants are immune to predation,” said Duke University biologist V. Louise Roth. “In fact, Pleistocene ecosystems were a lot more complex and predators could have had a larger impact.”

It’s also true that humans have picked off most of the larger predators, changing our estimates pretty dramatically, said lead author and UCLA paleoecologist Blaire Van Valkenburgh. “So much of our science is based on the last 50 or 100 years,” she said, but populations of big cats and wolves would have been much larger before humans arrived on the scene.

The work grows out of a 2014 symposium on the consequences of megafauna extinctions in the Pleistocene. Most of the discussion at the conference in Oxford was on herbivores, Van Valkenburgh said.

Saber-tooth cats (Smilodon) working together may have been capable of taking down juveniles of the largest Pleistocene herbivores, such as this young hippo, according to a new analysis appearing in the Proceedings of the National Academy of Sciences.

Source: www.phys.org

Rajasaurus (‘Raja’ meaning “king” (derived from Sanskrit) here,”king of lizards”) is a genus of carnivorous abelisaurian theropod dinosaur with an unusual head crest. Between 1982 and 1984, its fossilized bones were discovered by Suresh Srivastava of the Geological Survey of India (GSI). Excavated from the Narmada River valley in Rahioli in the Mahisagar district of Gujarat, India, the find was announced as a new genus of dinosaur by American and Indian scientists on August 13, 2003.

Paleontologists Paul Sereno of the University of Chicago, Jeff Wilson of the University of Michigan, and Srivastava worked together as an Indo–American group to study the Narmada River fossils. The fossils represented the partial skeleton of the new species Rajasaurus narmadensis, which means “princely lizard from the Narmada Valley.” The fossilized bones of Rajasaurus have also been found in the upriver region of the Narmada, at Jabalpur, in the state of Madhya Pradesh.

Rajasaurus was an abelisaurid, a member of a group of theropod predators known to have lived only on landmasses that were part of the supercontinent Gondwana, such as Africa, India, Madagascar, and South America. Rajasaurus closely resembles Majungasaurus, a contemporary abelisaur from Madagascar, an island that had separated from the Indian landmass about 20 million years earlier. It was found to be an abelisaurid through a phylogenetic analysis of anatomical characteristics, and was described as a carnotaurine abelisaurid (the subfamily including Carnotaurus) because of the configuration of its nasal bones and its possession of a growth (“excrescence”) on its frontal bone. Rajasaurus is distinguished from other genera by its single nasal-frontal horn, the elongated proportions of its supratemporal fenestrae (holes in the upper rear of the skull), and the form of the ilia (principle bones of the hip) which feature a transverse ridge separating the brevis shelf from the hip joint.

Rajasaurus was identified from a partial skeleton including a part of the skull (braincase), backbone, hip bones, parts of the hind legs and tail. This specimen, GSI 21141/1–33, serves as the type specimen of the genus and species. In 2010, Gregory S. Paul estimated its body length at eleven metres, its weight at four tonnes. In 2016, its length was estimated to be 6.6 metres (21.7 ft) in a comprehensive analysis of abelisaur size. What is preserved of the skull shows it bore a distinctive low rounded horn, made up of outgrowths from the nasal and frontal bones.

The discovery of Rajasaurus could lead to additional information on the evolutionary relationships of abelisaurs, since previously described specimens from India were mainly isolated bones. At a press conference held in 2003 on the discovery of Rajasaurus, Sereno stated:

The discovery, which will be put for examination before global experts, was important since it would help in adding to the current knowledge of dinosaur belonging to the family of Abelisaur predators and adding a new angle to dinosaurs in the Indian subcontinent.

Rajasaurus has been found in the Lameta Formation. This rock unit represents a forested setting of rivers and lakes that formed between episodes of volcanism. The volcanic rocks are now known as the Deccan Traps. Rajasaur and sauropod fossils are known from river and lake deposits that were quickly buried by Deccan volcanic flows. Other dinosaurs from the Lameta Formation include the noasaurid Laevisuchus, abelisaurids Indosaurus and Indosuchus, and the titanosaurian sauropods Jainosaurus, Titanosaurus, and Isisaurus.

Coprolites have been recorded in the Lameta Formation, and the presence of fungi in coprolites indicates that leaves were eaten by the dinosaurs which lived in a tropical or subtropical climate. Another scientific study of similarities in egg taxa suggested close phyletic relationships that supports the existence of a terrestrial connection between dinosaurian fauna in India and Europe during the Cretaceous, and between two Gondwanan areas, Patagonia and India.

Source: www.Wikipedia.org

Skorpiovenator is a genus of abelisaurid theropod dinosaur from the late Cretaceous period of Argentina.

The type species, Skorpiovenator bustingorryi, is known from a single, nearly complete skeleton (MMCH-PV 48K) missing only sections of the tail and the majority of the forelimbs. The specimen was recovered from the lower part of the Huincul Formation in Patagonia, dating to the late Cenomanian stage, about 95 million years ago. It would have lived alongside other carnivorous dinosaurs such as the carcharodontosaurid Mapusaurus and another abelisaurid, Ilokelesia.

In 2008, Canale et al. published a phylogenetic analysis focusing on the South American carnotaurines. In their results, they found that all South American forms (including Skorpiovenator) grouped together as a sub-clade of Carnotaurinae, which they named Brachyrostra, meaning “short snouts”. They defined the clade Brachyrostra as “all the abelisaurids more closely related to Carnotaurus sastrei than to Majungasaurus crenatissimus.”

Ekrixinatosaurus (‘explosion-born reptile’) is a genus of theropod dinosaur which lived during the Late Cretaceous. Its fossils have been found in Argentina. The type species, Ekrixinatosaurus novasi, was first described in 2004 by Argentinian paleontologist Jorge Calvo, and Chilean paleontologists David Rubilar-Rogers and Karen Moreno. It was discovered in the Candeleros Formation, a geologic formation that outcrops in Río Negro, Neuquén, and Mendoza provinces of Argentina. The formation dates from 100-97 mya.

Ekrixinatosaurus novasi is a large ceratosaur with a relatively large head and robust limbs, the only known specimen being between 7–8 m (23–26 ft) in length, some suggested that this specimen actually represented the largest ceratosaur yet described at 10–11 m (33–36 ft) in length, surpassing the type of Carnotaurus. However, it was later noted by other researchers that this estimate was based only on the absolute size of the skull, ignoring that limb bone comparisons clearly show Carnotaurus was larger, thus Carnotaurus was larger than Ekrixinatosaurus but with a proportionally smaller head. Most recently, a 2016 study again found it to be smaller (7.4 m) than Carnotaurus (7.8 m).

Ekrixinatosaurus shared its environment with the titanosaurian sauropod Andesaurus and the rebbachisaurid sauropods Limaysaurus and Nopcsaspondylus. Iguanodont ornithischian remains have reportedly also been found. The carcharodontosaurid Giganotosaurus was possibly the apex predator. Smaller predators also inhabited the area. These included the dromaeosaurid Buitreraptor, the alvarezsaurid Alnashetri, and the basal coelurosaurian Bicentenaria. The primitive snake Najash lived here as well, along with turtles, fish, frogs, and cladotherian mammals. Pterosaurs also lived in the area.

Afrovenator (“African hunter”) is a genus of megalosaurid theropod dinosaur from the middle Jurassic Period of northern Africa. It was a bipedal predator, with three claws on each hand.

There is one named species, Afrovenator abakensis. The generic name refers to its predatory nature, and its provenance from Africa. The specific name refers to Abaka, the Tuareg name for the region of Niger where the fossil was found. The original short description of both genus and species is found in a 1994 paper which appeared in the prestigious journal Science. The primary author was well-known American paleontologist Paul Sereno, with Jeffrey Wilson, Hans Larsson, Didier Dutheil, and Hans-Dieter Sues as coauthors.

The remains of Afrovenator were discovered in 1993 in the Tiourarén Formation of the department of Agadez in Niger. The Tiourarén was originally thought to represent the Hauterivian to Barremian stages of the early Cretaceous Period, or approximately 132 to 125 million years ago (Sereno et al. 1994). However, re-interpretation of the sediments showed that they are probably mid-Jurassic in age, dating Afrovenator to the Bathonian to Oxfordian stages, between 167 and 161 mya. The sauropod Jobaria, whose remains were first mentioned in the same paper which named Afrovenator, is also known from this formation.

Afrovenator is known from a single relatively complete skeleton, holotype UC OBA 1, featuring most of the skull minus its top (likewise the mandible, or lower jaws, are lacking apart from the prearticular bone), parts of the spinal column, partial forelimbs, a partial pelvis, and parts of the hind limbs. This skeleton is housed at the University of Chicago.

Most analyses place Afrovenator within the Megalosauridae, which was formerly a “wastebasket family” which contained many large and hard-to-classify theropods, but has since been redefined in a meaningful way, as a sister taxon to the family Spinosauridae within the Megalosauroidea.

Source: www.Wikipedia.org, www.NatGeo.com

A dinosaur that walked the Earth 100 million years ago but wasn’t discovered until 2012 was actually the largest to ever exist, according to a new study. The plant-eating behemoth averaged 122 feet long and weighed 76 tons.

In short, the dinosaur was as heavy as a space shuttle or a Boeing 737.

Those numbers make the Tyrannosaurus rex and other meat-eaters “look like dwarfs when you put them against one of these giant titanosaurs,” Pol said.

But despite their intimidating size, Pol believes the vegetarian P. mayorum was a gentle giant.

“I don’t think they were scary at all,” he said. “They were probably massive big slow-moving animals.”

“Getting up. Walking around. Trying to run. It’s really challenging for large animals,” he added.

Researchers aren’t quite clear on how the species became so big, but study co-author José Luis Carballido, from the Museum of Palaeontology Egidio Feruglio in Argentina, believes part of it had to do with available food.

“We do not know yet why we have such drastic change in body mass at this time here in Patagonia. There are some major events that are occurring at this time relating to weather and plant availability. Titanosaurs were herbivores, so certainly they had the food they needed, and plants are directly constrained by the weather. Probably the weather helped [cultivate] a particular group of plants living in Patagonia,” Carballido told Newsweek, adding that giant titanosaurs are thought to have only lived in Patagonia.

He went on to state that the P. mayorum, like other herbivores, likely grew to be very large so it could better avoid being attacked by predators.

“The bigger it was, the less predators will try to attack it,” he said.

A cast of the dinosaur’s skeleton is on display at the American Museum of National History in New York. However, it’s so big that its head sticks out into a hallway.

Despite its impressive size, Carballido believes an even larger dinosaur could have walked the Earth, but it probably wasn’t much bigger than the P. mayorum.

“There could be [bigger], but probably we are pretty close to the size limit,” he said.

Prior to the discovery of the P. mayorum, scientists believed the title of world’s biggest dinosaur belonged to the Argentinosaurus, another titanosaur.

The study conducted by Pol and Carballido was published in the journal Proceedings of the Royal Society B: Biological Sciences on Tuesday.

- 2017

The Thyreophora are a group of small to quite large armored plant-eating dinosaurs. The most familiar are Stegosaurus and Ankylosaurus, though there were many others. Ornithopods are one of three major groups of Ornithischia, or “bird-hipped” dinosaurs.

The earliest Thyreophoran was Scutellosaurus, a slender-tailed beast known from the earliest Jurassic of western North America, and is among the earliest known Ornithischians. It is among the smallest of the armored dinosaurs, and grew to only one and one-half meters long. Like its kin, it had armor plates set into the skin of its back, though these were not as large as in later Thyreophorans.

The next known Thyreophoran is Scelidosaurus, which lived in western Europe a little over 180 million years ago. This dinosaur grew to about four meters long and a little over a meter tall, walking on all four legs. Like later armored dinos, it had spikes along its back, and hoof-like claws. Though this is a very important dinosaur for understanding the evolution of this group, it was not discovered until 1980!

The remaining Thyreophorans consist of two major groups: the Stegosauria and the Ankylosauria. The stegosaurids had two rows of spikes or plates runnning along their backs and tails. They were most diverse in the late Jurassic, though the genus Dravidosaurus lived in southern India in the late Cretaceous, when the group went extinct. Stegosaurids are known from most of the globe.

The other group, the Ankylosauria, had more extensive armoring, and often whole patches of external bone were fused into plates. Early in the Cretaceous, most of these belonged to the Nodosaurid subgroup (though one genus, Sarcolestes, is known from the Jurassic). In the later Cretaceous, most are Ankylosaurids, distinguished by their broad heads, spikes extending from the backs of their skulls, and heavy club-like tails. It is generally believed that the club could be used as a defensive weapon against predators.

Source: www.NatGeo.com