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Domingo 8/24/2014

(251 notas)

romkids:

A Silurian “Shark” Tale: Nerepisacanthus denisoni 

What comes to mind when you hear or read the word “jaws”? For many, it will be the eponymous 1975 Hollywood blockbuster, starring a memorable mechanical menace in the form of a ravenous Great White Shark – along with a few notable human actors, of course. Or perhaps it invokes images of beasts of a slightly later cinematic – but much earlier geological – vintage, and you conjure up one of the slavering carnivorous dinosaurs depicted in the Jurassic Park series. Whatever your imagination runs to, aquatic or terrestrial – living or extinct, it will likely involve some sort of nasty animal with a backbone and lots of pointy teeth in those snapping jaws.    

But it hasn’t always been that way. Vertebrate predators with definitive jaws and teeth did not make their evolutionary debut on this planet until sometime around 440 million years ago, at the beginning of the Silurian Period, and long after the likely origin of jawless vertebrate animals in the so-called Cambrian Explosion. These most ancient gnathostomes (from the Greek words for ‘jaw’ and ‘mouth’) belong to an extinct group of odd-ball fishes called the Acanthodii, whose earliest fossil remains consist almost entirely of tiny mineralized body scales, larger fin spines, and rare jaw bones, isolated or dispersed over rock surfaces. The rest of the internal skeleton of acanthodians was not bony - it consisted instead of cartilage, like sharks and their relatives. This feature, along with a generally streamlined body shape and the rigid fin-supporting spines, has given rise to their colloquial group name of “spiny sharks.” Although there is general agreement among palaeontologists that they predate the evolution of true sharks, the precise affinities of acanthodians have been hotly debated.

The recent discovery by an amateur fossil collector of exciting new evidence in upper Silurian rocks (about 420 million years old) in southern Ontario is now shedding much needed light on the shadowy early history of jaw-bearing vertebrates. Until now, most of what we knew about acanthodians was based on relatively rare, but far more complete, fossils from geologically younger freshwater deposits of Devonian and Carboniferous age, after the group had evolved a variety of traits that tend to obscure their deeper origins. The unique new specimen, generously donated to the Royal Ontario Museum by its discoverer, represents the only near-complete acanthodian from pre-Devonian rocks anywhere in the world, and provides the first clear ‘road map’ of how all the dispersed elements of these very early gnathostomes fit together into a compact swimming predator. It forms the basis of a new paper co-authored by Dr. Carole Burrow (Queensland Museum, Brisbane – a world authority on early fossil fishes) and me in the journal PLOS ONE [published August 5th]. The fossil is assigned to Nerepisacanthus denisoni, a species previously named from only partially articulated incomplete remains found in Silurian rocks in New Brunswick.

The new fossil, consisting of part and counterpart on opposing faces of a rock split, measures just 112 millimetres in length, from the tip of the jaws almost to the end of the tail fin - it likely represents an immature fish. Although difficult to see without close examination, the specimen retains a wealth of minute detail.

Working with the authors of the paper, talented palaeo artist Danielle Dufault has painstakingly created a beautiful 2D reconstruction of the toothy little fish against the backdrop of its tropical Silurian lagoon home.  

More information

Guest Post By Dave Rudkin. Last Updated: August 10th, 2014.

(vía scientificillustration)

mises.org Razonamiento Económico

mises.org/etexts/EconReasoning.pdf.

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Viernes 5/23/2014

cosmosontv:

Behind-the-Scenes: New best friends, Bruno Braga and Emma Oreck-Pope snooze in the COSMOS New Mexico production offices.-Sarah Mozal, Assistant to Ann Druyan and Mitchell Cannold
Martes 5/20/2014

(89 notas)

cosmosontv:

Behind-the-Scenes: New best friends, Bruno Braga and Emma Oreck-Pope snooze in the COSMOS New Mexico production offices.

-Sarah Mozal, Assistant to Ann Druyan and Mitchell Cannold

cosmosontv:

Take the Cosmos Quest!

Students and teachers - Make COSMOS part of your learning experience. Download the study guide to Episode 11.

(66 notas)

cosmosontv:

Take the Cosmos Quest!

Students and teachers - Make COSMOS part of your learning experience. Download the study guide to Episode 11.

foreignaffairsmagazine:

How the battle between the European Parliament and Angela Merkel could shape the EU political system for years to come: http://fam.ag/1jvIFea

(24 notas)

foreignaffairsmagazine:

How the battle between the European Parliament and Angela Merkel could shape the EU political system for years to come: http://fam.ag/1jvIFea

rhamphotheca:

Jurassic Predators Had Surprisingly Sensitive Snouts
by Jeff Hecht
Pliosaurs had massive jaws, crushing teeth – and sensitive snouts. That is the conclusion of a study on an exceptionally preserved 2-metre-long fossil skull.
Pliosaurs were the top marine predators of the Jurassic, growing up to 12 metres long, but their biology is poorly understood because nothing quite like them is alive today.
Davide Foffa at the University of Bristol, UK, may now have added an important piece to the puzzle of how they detected prey. He has found channels in a pliosaur skull that probably contained nerves and blood vessels, suggesting that it had a well-developed sensory system extending to the tip of the snout.
Palaeontologists have long recognised that pliosaur skulls, like those of many other vertebrates, have small holes called foramina leading into the interior. In living species these connect to nerves. However, this is the first time anyone has been able to trace the networks inside a fossil…
(read more: New Scientist)
illustration by Dmitry Bogdanov

(322 notas)

rhamphotheca:

Jurassic Predators Had Surprisingly Sensitive Snouts

by Jeff Hecht

Pliosaurs had massive jaws, crushing teeth – and sensitive snouts. That is the conclusion of a study on an exceptionally preserved 2-metre-long fossil skull.

Pliosaurs were the top marine predators of the Jurassic, growing up to 12 metres long, but their biology is poorly understood because nothing quite like them is alive today.

Davide Foffa at the University of Bristol, UK, may now have added an important piece to the puzzle of how they detected prey. He has found channels in a pliosaur skull that probably contained nerves and blood vessels, suggesting that it had a well-developed sensory system extending to the tip of the snout.

Palaeontologists have long recognised that pliosaur skulls, like those of many other vertebrates, have small holes called foramina leading into the interior. In living species these connect to nerves. However, this is the first time anyone has been able to trace the networks inside a fossil…

(read more: New Scientist)

illustration by Dmitry Bogdanov

(vía scientificillustration)

(322 notas)

oupacademic:

image

This year marks the centenary of the beginning of the First World War. Oxford University Press is sharing numerous resources for scholars and students looking for new understanding of the war and its legacy: the physical trauma of the war and the rapid changes in the medical field in the…

(vía scientificillustration)

atelierentomologica:

Beetles, Edward Donovan, before 1837
From John Ruskin’s collection at the Ashmolean, Oxford

(168 notas)

atelierentomologica:

Beetles, Edward Donovan, before 1837

From John Ruskin’s collection at the Ashmolean, Oxford

(Fuente: ruskin.ashmolean.org, vía scientificillustration)

amnhnyc:

Happy birthday to Carl Akeley, born 150 years ago today. 
Explorer and Museum taxidermist, Akeley is remembered for his pioneering method of taxidermy, combining field observations with sculptural techniques, and for his contributions to the iconic Museum hall that bears his name: The Akeley Hall of African Mammals.
Akeley is also remembered for his contributions to conservation. In the course of researching and collecting specimens to create the now-famous mountain gorilla diorama, he was among the first to accurately document mountain gorillas as intelligent and social animals that, even then, were under grave threat from overhunting. His research inspired him to dedicate the last few years of his life to the conservation and protection of the mountain gorilla.
Watch a video about Carl Akeley’s legacy. 

(91 notas)

amnhnyc:

Happy birthday to Carl Akeley, born 150 years ago today.

Explorer and Museum taxidermist, Akeley is remembered for his pioneering method of taxidermy, combining field observations with sculptural techniques, and for his contributions to the iconic Museum hall that bears his name: The Akeley Hall of African Mammals.

Akeley is also remembered for his contributions to conservation. In the course of researching and collecting specimens to create the now-famous mountain gorilla diorama, he was among the first to accurately document mountain gorillas as intelligent and social animals that, even then, were under grave threat from overhunting. His research inspired him to dedicate the last few years of his life to the conservation and protection of the mountain gorilla.

Watch a video about Carl Akeley’s legacy. 

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We humans have been around for about 2.5 million years, but the beating of our hearts is controlled by something much older than Homo sapiens—an ancient molecular pathway that, according to Huck Institutes faculty researcher Tim Jegla, may be on the order of 700 million to a billion years old. The Jegla Lab studies the evolution of the nervous and muscular systems, using model organisms such as the cnidarian Nematostella vectensis—also known as the starlet sea anemone—to investigate conserved traits and the molecular pathways and genes that underpin them. According to Jegla, the starlet sea anemone is in essence an animal that’s as evolutionarily far away from humans as possible while still sharing the same neuromuscular signaling systems. Comparisons of humans and cnidarians reveal that only the fundamentally important mechanisms are conserved—such as those required to make a neuron or, in this case, a neuromuscular signal. “Basically,” he says, “when we compare a human and a sea anemone, we’re looking at somewhere between 700 million and a billion years’ evolutionary separation. Anything that’s not fundamentally critical to life as a mobile, multicellular animal is different. And the things we have in common were there in the nervous system of the animal we both evolved from; they were there in the ancestor of virtually all modern animal life other than sponges and comb jellies. Only the fundamental mechanisms are conserved. And this gives us a window into what things we have in common that are extremely important. It tells us a lot about the history of how animals evolved.” “We make the case in this paper,” Jegla continues, “that the properties of the human Erg channel and the ancient Nematostella channel are tuned extremely well to repolarize the long action potentials that you need to get a strong muscular contraction, or a prolonged wave contraction like you have in a heartbeat.

In a study recently published in Proceedings of the National Academy of Sciences, the Jegla Lab identified in the Nematostella sea anemone the same gene family (Erg) that is responsible for the slow-wave contractions of the human heart. After cloning the genes for further investigation, the researchers found that the ion channel it encodes has retained its function relatively unchanged since the time of humans’ and cnidarians’ divergence from their common ancestor almost a billion years ago.

"This discovery," says Jegla, "shows that at least some of the molecular mechanisms through which we control electrical activity in things like the heart evolved in some of the earliest animals, long before the existence of hearts or even cardiac tissue."

"This fits a broad pattern we’re finding," Jegla continues, "that almost all the major signaling systems used in our brains and muscles evolved hundreds of millions of years ago in an ancestor of bilaterians which seems to have had a very versatile and molecularly complete set of tools for neuronal function that has been conserved throughout subsequent animal evolution and tuned to the specific needs of the major animal phyla. It appears that a lot of the signaling that we do in our complex neuromuscular systems is based on pre-existing programs that are just adapted to our specific physiological needs."

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(117 notas)