Stories tagged cretaceous

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"Reporting in the Proceedings of the National Academy of Sciences, researchers describe a new predatory dinosaur from the late Cretaceous period in Europe. Balaur bondoc (Romanian for "stocky dragon") is huskier than its closest relative the Velociraptor and has unusual feet."
Apr
30
2009

Killer asteroid?: Artist conception of impact event
Killer asteroid?: Artist conception of impact eventCourtesy NASA
The old “What really killed the dinosaurs” controversy is back in the news. And once again, it’s Princeton geophysicist Gerta Keller stirring up the pot.

Death from above?: Perhaps not.
Death from above?: Perhaps not.Courtesy Mark Ryan
Keller and her colleague Thierry Adatte of the University of Lausanne in Switzerland have published yet another paper challenging the prevailing theory that an asteroid was the major cause of the extinction of the dinosaurs at the end of the Cretaceous Period 65 million years ago. The extinction affected over 60 percent of animal species including all of the non-avian dinosaurs.

Actually a number of events were occurring around the end of the Cretaceous including long-term volcanic activity, rapid marine regression, and the infamous asteroid impact. There’s also evidence that some of the dinosaur population was already in decline 10 million years prior to the events. But the scenario is usually played out with the meteor coming late in the sequence and delivering the deathblow to an already weakened eco-system, and paving the way for mammals to take over the ecological gap.

K-T boundary layer: The Cretaceous-Tertiary boundary layer located near Trinidad, Colorado. The pale-gray 1-inch iridium layer (arrow) is sandwiched between coal layers and contains shocked quartz and other evidence of a large asteroid impact. The scale bar is 6 inches in length.
K-T boundary layer: The Cretaceous-Tertiary boundary layer located near Trinidad, Colorado. The pale-gray 1-inch iridium layer (arrow) is sandwiched between coal layers and contains shocked quartz and other evidence of a large asteroid impact. The scale bar is 6 inches in length.Courtesy Mark Ryan
The asteroid impact hypothesis was first proposed in 1980 by Luis Alvarez of the University of California after he and his son Walter discovered a claystone layer rich in the rare-earth element iridium and peppered with shocked quartz in many locations around the world. Iridium is a rare element not commonly found on the Earth’s surface but abundant in meteorites. Shocked quartz was first noticed in sand grains in craters created by nuclear test bombs and later in meteor impact sites. Alvarez hypothesized that the only other possible source for this naturally deposited strata would be from a large extraterrestrial object hitting the Earth. From studying the amount of iridium found in Cretaceous-Tertiary (K-T) boundary formations, he calculated that a bolide about 6 miles across would have been necessary to create that much iridium around the world. But at the time evidence of such an was unknown. It wasn’t until after Luis Alvarez’s death in 1988 that a crater on the Yucatan Peninsula near Chicxulub Mexico became the chief suspect. The Chicxulub impact crater was the right size and the right age fitting all the criteria of a Cretaceous extinction event.

But Keller claims the asteroid came too early to put the coup de grace on dinosaurs or any species for that matter. Her study of spherules in strata at localities in Mexico has convinced her that the asteroid collided with Earth 300,000 years before any mass extinction.

At El Penon, a location very near the impact crater site, Keller and Adatte studied a 30-ft layer of sandstone above the iridium layer that they calculated had been laid down at a rate of about 1-inch per thousand years. This means it took 300,000 years to pile up the entire section of sediment.

Fossils were analyzed on either side of the iridium layer and the researchers found that of 52 species counted below the iridium layer (meaning before the impact), the same 52 species were found above it, meaning the asteroid hadn’t caused any extinction. But at the top of the 30 feet of sandstone overlaying the iridium claystone things were different.

"The mass extinction level can be seen above this interval," Keller says. "Not a single species went extinct as a result of the Chicxulub impact."

The more likely culprit, according to Keller, is India’s Deccan Traps flood basalts which for several million years poured out tremendous amounts of lava and noxious fumes into the atmosphere that would have had put long and tremendous stress on the existing ecosystem. Keller seems to roll out a paper on the subject every year or so in the last decade. We covered some of her Deccan Traps research 2007 which you can read here.

Whatever the case we do know is that non-avian dinosaurs left the planet after the Cretaceous, as none of their fossils have been found above the K-T Boundary. Well, even that doesn’t appear to be the case anymore. Recent dinosaur fossils found in the San Juan Basin in northwestern New Mexico are suspected to come from a stratum that post-dates the Cretaceous extinction. More research needs to be done on the find, but even this wouldn’t be unexpected. Even after the host declares the party’s over, there are always some stragglers who just don’t want to leave.

Keller's paper was published this week in the Journal of the Geological Society.

MORE LINKS
ScienceDaily story
What Killed the Dinosaurs?
Gerta Keller's Chicxulub Debate
Dinosaur Killer May Have Been Volcanism

Jun
18
2006

Isisfordia duncani crocodile: photo by Art Oglesby   Isisfordia duncani crocodile found in Australia provides link between modern and ancient crocodiles.
Isisfordia duncani crocodile: photo by Art Oglesby Isisfordia duncani crocodile found in Australia provides link between modern and ancient crocodiles.

Fossils of the world's most primitive modern crocodilian have been discovered near the outback town of Isisford, in central-western Queensland, Australia. Discovered by former Deputy Mayor of Isisford, Ian Duncan, after whom the new species has been named, the first fossils of Isisfordia were found in the mid-1990s in a dried-up creek bed on the outskirts of town.
Living 98-95 million years ago, Isisfordia predates the first recorded appearance of alligators and gharials by almost 20 million years, and the first true crocodiles by over 30 million.

An international team of palaeontologists, headed by Dr Steve Salisbury from The University of Queensland's (UQ) School of Integrative Biology Published a paper in the Proceedings of the Royal Society B (pdf).

Abstract from paper

While the crocodyliform lineage extends back over 200 million years (Myr) to the Late Triassic, modern forms—members of Eusuchia—do not appear until the Cretaceous. Eusuchia includes the crown group Crocodylia, which comprises Crocodyloidea, Alligatoroidea and Gavialoidea. Fossils of non-crocodylian eusuchians are currently rare and, in most instances, fragmentary. Consequently, the transition from Neosuchia to Crocodylia has been one of the most poorly understood areas of crocodyliform evolution. Here we describe a new crocodyliform from the mid-Cretaceous (98–95Myr ago; Albian–Cenomanian) Winton Formation of Queensland, Australia, as the most primitive member of Eusuchia. The anatomical changes associated with the emergence of this taxon indicate a pivotal shift in the feeding and locomotor behaviour of crocodyliforms—a shift that may be linked to the subsequent rapid diversification of Eusuchia 20Myr later during the Late Cretaceous and Early Tertiary. While Laurasia (in particular North America) is the most likely ancestral area for Crocodylia, the biogeographic events associated with the origin of Eusuchia are more complex. Although the fossil evidence is limited, it now seems likely that at least part of the early history of Eusuchia transpired in Gondwana.

Link to a pdf of the entire paper; Proceedings of the Royal Society B (pdf)
University of Queensland press release
View proof images of Isisfordia and stills from the field and lab work.