ancient mammals

AMBULOCETUS


Ambulocetus quite literally means “walking whale”, and rightfully so as the ancient mammal is the suggested ancestor to the whales. Living around 50 million years ago, Ambulocetus was one of the biggest animals of its time, and one of the biggest successes. Ambulocetus had an immense advantage being able to walk on land and being an excellent swimmer.
The hunting techniques of this primitive whale were not unlike modern crocodiles, submerging itself under the water of river banks and shorelines waiting for an unsuspecting animal to approach for a drink, then pouncing with a bone crushing bite. Once prey was locked in its jaws, Ambulocetus would pull it into the water and drown it. 

Despite its appearance, Ambulocetus was already well on the way to evolving for permanent underwater living. The shape of the skull and teeth are like that of modern whales, but more intriguingly, Ambulocetus did not have ears to pick up vibrations, but instead detected them through its jaw. This form of hearing is typical of marine animals, the direction from which vibrations come from can be pinpointed with great accuracy, a quality that only adds to the success of an ocean-bound predator. 


Fossils of Ambulocetus have most commonly been found in Pakistan, it is estimated to have been able to reach up to 3 metres long. Due to Ambulocetus’s ancestry to the whales, it is described as a transitional fossil. Ambulocetus lived in a period of great significance in the whales evolutionary history, living in the middle Eocene, whale evolution accelerated and by the end of the Eocene, whales had fully immersed themselves into underwater life, they had left the land for good.
As far as evidence goes, Ambulocetus was an important but very short lived animal in life’s evolutionary history. By 49 million years ago, traces of Ambulocetus disappeared and there are few clues as to why.

This Fossil Friday, learn about a fossil hunt at the bottom of the world.

Home to penguins, particularly hardy mosses, and the occasional seal paying a visit to dry land, Antarctica is a unique and uniquely harsh environment. Snow and ice cover 98 percent of the landmass, and with wind chill, temperatures in the center of the continent can plunge to 100 degrees below zero.

But it wasn’t always this way. Tens of millions of years ago, Antarctica was the heart of the supercontinent known as Gondwana, pressed between would-be South American and Australian continents at first and then likely joined to each by land bridges for millions of years after they started to drift apart. Though it was still at Earth’s southern pole, Antarctica was then much warmer. And, as fossils recovered there show, the continent was home to a diverse group of vertebrates, including non-avian dinosaurs and, later, during the Eocene period about 45 million years ago, mammals.

Paleontologists think the continent still has more fossils to yield—remnants which could show the dinosaurs that roamed there 65 million years ago shared the continent with even more ancient mammals. In February, Abagael West, a graduate student who studies South American mammals at Columbia University in a collaborative program with the Museum’s Richard Gilder Graduate School (RGGS), joined Museum Curators Ross MacPhee and Jin Meng as they headed south on a seven-week expedition in search of the evidence.

Read the full story on the Museum blog. 

like, it occurs to me now that i understand things better that monotremes actually make complete sense with our understanding of evolutionary history (since mammals came from egg-laying reptile-like ancestors) but it’s just so weird that they still exist today. these little dudes don’t care that they’re seen as a stepping stone between ancient synapsids and mammals; they want to keep doing their monotreme thing, because evolution is a tree, not a flight of stairs

Scientific Expedition to Antarctica Will Search for Dinosaurs, Ancient Mammals

Museum Curator Ross MacPhee is part of an international team of researchers traveling to Antarctica this month to search for evidence that the now-frozen continent may have been the starting point for some important species that roam the Earth today.

Millions of years ago, Antarctica was a warm, lush environment ruled by dinosaurs and inhabited by a great diversity of life. But today, the fossils that could reveal what prehistoric life was like are mostly buried under the ice of the harsh landscape, making the role Antarctica played in the evolution of vertebrates a mystery.

Aided by helicopters, scientists on this month-long expedition will conduct research in the James Ross Island group off the tip of the Antarctic Peninsula, one of the few spots on Antarctica where fossil-bearing rocks are accessible.

The team is specifically searching for fossils from the Cretaceous through Paleogene, a period about 100 million to 40 million years ago that includes the end of the Age of Dinosaurs and the beginning of the Age of Mammals. MacPhee, who has worked on the continent before, is looking to learn more about some of those early mammals during this journey.

“What I hope to achieve this time is to discover the first evidence of mammals in the Cretaceous of Antarctica, species that lived at the end of the Age of Dinosaurs,” MacPhee said. “If we can find them, they will have a lot to tell us about whether any evolutionary diversifications took place in Antarctica, and whether this was followed by species spreading from there to other portions of the ancient southern supercontinent Gondwana.”

The team is led by paleontologists from the Carnegie Museum of Natural History, The University of Texas at Austin, Ohio University, and the American Museum of Natural History and supported by the National Science Foundation as part of the Antarctic Peninsula Paleontology Project, or AP3. You can follow their exploits on Twitter at @antarcticdinos.

Our ancient mammal response to stress is skittering into the bole of a tree and trying to calm our miniature hearts down to only a thousand beats per minute. We’re bigger, and we’ve made all the forests smaller, but our electric jungle has far more hiding places. Twitter and Facebook take hiding in plain sight to global extremes. You can be sitting at a desk covered with work and not see one speck of it for years. Facebook alone can keep whole herds of offices peacefully grazing on each others’ emissions while their worries crouch by the “sign out” button, waiting to spring the second they disconnect.

Ancient Human Occupation of Britain

  • from BBC
“The ancient inhabitants of Britain; when did they get here? Who were they? And how do we know? Alice Roberts meets some of the AHOB team, who have been literally digging for answers. The Natural History Museum’s Chris Stringer, is the Director of AHOB, the Ancient Human Occupation of Britain, a project which, over the past 12 years, has brought together a large team of palaeontologists, archaeologists, geologists and geographers, to pool their expertise in order to unpick British History.

Nick Ashton from the British Museum has been in charge of the north Norfolk site of Happisburgh, where the crumbling coast line has revealed the oldest examples of human life in Britain, 400,000 years earlier than previous findings of human habitation, in Boxgrove in Sussex.

The ancient landscape had its share of exotic animals. Hippos have been dug up from Trafalgar Square, mammoths have been excavated from Fleet Street. Professor Danielle Schreve is an expert in ancient mammal fossils, and tells us what these bones reveal about the ancient climate. Less glamorous than the big fossils, the humble vole is so useful and accurate as a dating tool that it has been nicknamed "the Vole Clock.”

Carbon dating has improved vastly in the past few years. Rob Dinnis, from Edinburgh University, explains why the AHOB team has been returning to old collections and redating them.“

***Haven’t listened

(Source BBC)

sabrielhasablog-blog  asked:

Emily, what IS a dinosaur? We grow up playing with dinosaur toys and watching Juraissic Park and a lot of us think we know all about dinosaurs, but nobody ever talks about why they're dinosaurs and not just big reptiles... What are the traits that makes a paleontologist go, "Yep, that's a dinosaur!"

Great question!

“Dinosauria” is a clade, a grouping that includes a common ancestor and all the descendants (living and extinct) of that ancestor. So, any animal that has been determined to fall within this clade is a dinosaur. In order to be classified as such, however, that animal has to meet certain criteria with genetic characteristics which have been inherited somewhere along that evolutionary line.

For instance, birds are classified as avian dinosaurs (a T. rex would be a non-avian dinosaur) because they evolve from a commonly shared ancestor as other dinosaurs. Because of these genetic relationships, members of a clade have many physiological common traits - like, all dinosaurs have an opening in the socket of their pelvises and carry their legs directly beneath their bodies (alligators’ and those of lizards sprawl out to the side). There can be a lot of variation, too - but morphologies alone cannot determine species relatedness, like the presence of wings and flight ability ‘cuz convergent evolution is a thing.

Dimetrodon is not a dinosaur because it’s in a different clade - Synapsida - which began evolving around 308 million years ago, 77 million years before Dinosauria existed. These two groups broke apart very early on and evolved completely independent of one another. As a result, humans and all mammals are Synapsids, distant relatives of those early, sail-back creatures, and birds evolved within Dinosauria. 

Evolution.

Angielczyk, K. (2009) Dimetrodon is not a dinosaur: Using Tree Thinking to Understand the Ancient Relatives of Mammals and their Evolution

Nesbitt, S. (2011) The Early Evolution of Archosaurs: Relationships and the Origin of Major Clades

Ancient nightlife: Forebearers of mammals were nocturnal partiers

A nocturnal existence is a way of life for numerous mammals, from bats that swoop through dark skies to skunks that emit their noxious spray under moonlight and majestic lions, tigers and leopards that prowl the night.

But this love of nightlife appears to have begun much earlier than previously believed in the lineage that led to mammals - perhaps 300 million years ago - way before the first true mammals skittered under the feet of the dinosaurs about 100 million years later.

Scientists on Wednesday said a study of fossils of small ring-shaped bones embedded in the eyes of an important group of ancient mammal relatives called synapsids indicated that many of them thrived at night or in the twilight.

The findings appear in the journal Proceedings of the Royal Society B.

The mammal relatives arose around 320 million years ago and became the dominant land creatures during the Permian Period that preceded the rise of the dinosaurs in the Triassic Period that followed. They prospered worldwide, with plant and meat-eating beasts.

“The study does give us new insights into the daily lives of some of our most ancient relatives,” said Kenneth Angielczyk, a paleontologist with the Field Museum of Natural History in Chicago.

The findings indicate nocturnal activity has a deep history in the lineage leading to mammals. This contradicts the conventional wisdom that the nocturnal lifestyle emerged with the appearance of the first bona fide mammals about 200 million years ago because they needed to slink around in the dark to avoid becoming dinosaur chow.

The researchers focused on bones called scleral ossicles that reveal the eye’s dimensions and enable predictions about light sensitivity, indicating whether an animal was nocturnal or active during daytime or active in twilight conditions. Modern mammals lack these bones.

The researchers scoured museum collections around the world and found 38 specimens comprising 24 species, mostly from the United States and South Africa but also from Russia and Brazil.

“Specimens with well-preserved scleral rings are rare, so it took a lot of searching,” Angielczyk said.

Researchers found that the eyes of ancient synapsids likely spanned a range of light sensitivities, some suited to nighttime and others favoring daylight. The oldest synapsids possessed eye dimensions consistent with night activity. Predators were more likely than herbivores to be nocturnal.

One of the best known and oldest of the ancient synapsids is Dimetrodon, a sharp-toothed, 11-foot-long (3.5 meters), four-legged predator whose back was topped by a remarkable semicircular sail-like structure. The study found Dimetrodon probably was nocturnal, hunting at night like many big cats today.

“Nocturnality comes with advantages and disadvantages,” said another of the researchers, Lars Schmitz, a biology professor at Claremont McKenna, Pitzer and Scripps Colleges in California.

“It’s cooler at night, which may be beneficial for some species. As a hunter, it may be easier to approach prey. On the other hand, the dim light levels make it difficult for animals. Keen senses are beneficial,” Schmitz added.

(Reporting by Will Dunham; Editing by Leslie Adler)

New fossil find reveals tiny hedgehog the size of your thumb

Researchers in British Columbia have unearthed a 52 million year old fossil of the smallest hedgehog known to science.

The animal was fully grown when it died, and just two inches long – about the length of your thumb. The research team named it Silvacola acares, which means “tiny forest dweller.”

This little guy was so eensy-weensy that that his back molars were just 1 millimeter in length. His bones were so delicate that the researchers were worried his fossil would break apart if they tried to get it out of the rock.

Instead, they decided to leave the fossilized parts of the animal’s skull embedded in the rock and do a micro-CT scan on it to figure out exactly what mammal they were looking at.

“I compared the scan of his molars to hundreds of little, tiny teeth,” said Jaelyn Eberle, who studies ancient mammals at the University of Colorado at Boulder. “But before too long I realized there isn’t anything that looks exactly like this guy’s teeth.”

Finally she realized she had not just a new species, but a new genus on her hands. Eberle is the lead author of a paper describing the hedgehog, as well as a tapir-like animal that was also the found at the site, that was published Tuesday in the Journal of Vertebrate Paleontology.

Unfortunately, we can only get to know this mini-hedgehog through fossils. Silvacola acares lived during the early Eocene era, when the Earth was the warmest it has been since the time of the dinosaurs.

At that time, this part of British Columbia was covered by an unusual rain forest where palm trees and spruce trees stood side by side. The average temperature was probably somewhere in the mid-50s Fahrenheit. The palm trees suggest that it never got below freezing.

Eberle said the tiny hedgehog was an omnivore that probably ate insects and plants it found on the forest floor.

The Silvacola fossil was discovered in the Driftwood Creek Beds near Smithers, B.C., about 420 miles north of Vancouver. It was once the site of an ancient lake, and it is a popular place to find fossils of early Eocene era plants and insects, but the hedgehog and the tapir relative were the first mammal fossils discovered at the site.

Eberle thinks there are almost certainly more fossilized remains of mammals hidden in the rocks.

“It just wasn’t on anyone’s radar for fossil mammals, so when they found them, they were rather shocked,” she said. “I think there are more to be found; we just have to go look.”