Dinosaur-killing impact set the world on fire

NASA

The mass extinction events that we understand well all seem to have relatively local causes: volcanic activity in Asia or Pangea, an impactor striking the Yucatan. But the events are so large that the environmental disruption goes global, killing off species across the planet and even in ecosystems, like the oceans, that might not be directly affected.

Massive volcanic eruptions can clearly create global destruction by dimming sunlight, causing sudden climate swings and acidifying the ocean. But it might be a bit harder to see how the impact of a large rock from space can reach into habitats halfway around the globe. Yet that's exactly what we think happened during the extinction that killed off all the non-avian dinosaurs (along with a host of other species). A paper in the Journal of Geophysical Research reviews the evidence for what its authors consider the most plausible model for global mayhem caused by the impact: its debris lit all the world's forests on fire at once.

The basic outlines of the scenario are pretty straightforward. The energy released by the impact sent lots of material high into and above the atmosphere, a lot of it near the escape velocity, which allowed it to spread around the planet. That is, after all, how we got the global layer of iridium that pointed to an impact being involved in the first place. But it's this material's return through the Earth's atmosphere that caused problems for vegetation. The heat of re-entry for all this material set off what's termed a "global infrared pulse."

Read 8 remaining paragraphs | Comments

Re-re-re-thinking the rise of mammals and death of the dinosaurs

Grandma? An artist's conception of the appearance of the first placental mammal.

Carl Buell

The end of the era of dinosaurs and rise of the mammals has held a fascination for me since I was young (and I suspect I'm not alone). But it's a tale that has been retold many times now.

In the earliest versions, I recall ideas about clever, fast-moving mammals outcompeting the slow, lumbering dinosaurs. With time, however, that story changed. The dinosaurs became quicker and actually survived, albeit as birds (papers now refer to the loss of "non-avian dinosaurs"). The mammals became less clever and more lucky, in that it took a freak hit from an asteroid to trigger the mass extinction. As DNA data came in, the amount of luck involved seemed more and more significant. Data indicated some of the lineages of modern placental mammals had been around for millions of years before the dinosaurs died, but didn't really do much until after the extinction event.

A new analysis, published in Science now pushes back against the molecular data. A large team of authors tracked thousands of individual traits in more than 125 species (40 of them known only from fossils) to build the biggest reconstruction of the history of mammals ever attempted. In doing so, they find the first placental mammal probably didn't exist until after the non-avian dinosaurs were gone, the study even provides some hints of what it might have looked like.

Read 9 remaining paragraphs | Comments

Too hot to handle: Triassic temps may have killed tropical species

These mountains in China preserve the ocean floor of the Permian-Triassic period.

ASU.edu

When ecologists talk about climate change, they tend to recognize there will be winners and losers. While it could drive some species to extinction, others will migrate readily to follow their shifting habitats or adapt to the changing conditions. For the most part though, nobody's expecting we'll end up with ecosystems that are largely barren.

But a new study of the aftermath of a mass extinction event suggests temperatures once got so hot that they left our planet's equatorial regions a place of "lethally hot temperatures," where the few survivors were mostly stunted invertebrates.

As a whole, life on Earth didn't have a lot going well for it at the start of the Triassic. The previous geological period, the Permian, ended with the massive eruptions that generated the Siberian Traps and triggered the biggest mass extinction event on record: the Great Dying. The volcanic activity and subsequent ecosystem changes pumped massive amounts of carbon dioxide into the atmosphere, leaving the few survivors to face intense greenhouse warming and oceans where it was difficult to obtain oxygen.

Read 7 remaining paragraphs | Comments

New fossils complicate human family tree

A recently discovered lower jaw helps clarify evolutionary relationships.

Mike Hettwer, courtesy of National Geographic

About two million years ago, the lineage that eventually produced humans underwent a significant transition, with species from the genus Homo appearing and eventually displacing their ancestors, the Australopithecines. But the exact nature of this transition has, until very recently, been poorly understood. We weren't sure which species of Australopithecus was likely to have given rise to Homo species, or which species was the first on the Homo lineage.

In 2010, however, researchers announced the discovery of Australopithecus sediba, which shared many features with Homo species, helping clarify the older side of this transition. But things remained obscure on the Homo side of the transition, where the earliest fossils included a face that lacked a lower jaw, and jaws that didn't seem to match the face, leading to arguments over whether they belonged to a single species or if two (H. rudolfensis and H. habilis) were present.

Now, additional fossils from this era are being reported, and their discoverers are using them to argue that there were clearly two species present in Africa at this time. The key find is a face that includes a lower jaw and comes from a smaller, late juvenile. The smaller size is key, since some had suggested that the differences between fossils were because they came from members of the same species that were simply different sizes (perhaps large males and smaller females).

Read 5 remaining paragraphs | Comments

Recalibrated DNA clock suggests we can stop looking for early primate fossils

The earliest primate fossils unearthed thus far are only 56 million years old, but molecular estimates of the rate of primate evolution predict that there should be some dating back to the Late Cretaceous, closer to 82 million years ago. This is embarrassing for scientists, akin to the time in 1929 when Edwin Hubble measured the age of the Universe as less than half the age of the Earth.

One possible explanation is that earlier fossils are out there, but that no one has found them yet. But Michael Steiper and Erik Seiffert have proposed an alternate reconciliation in a new study of the molecular rate of evolution. Their work was published in the Proceedings of the National Academy of Sciences.

Read the comments on this post

Feathers may have helped T. rex’s relatives ride out a cold climate

Feathers are the defining feature of birds, but that wasn't always the case. For millions of years, various species of dinosaurs sported feathers, some of which have left behind fossilized impressions. But for the most part, the feathers we've found have been attached to smaller dinosaurs, many of them along the lineage that gave rise to birds.

That situation was changed dramatically by a species that is described in today's issue of Nature. Three nearly complete skeletons have revealed a feathered dinosaur that its finders term "gigantic." At nearly 1,500kg and over forty times the weight of any previous feathered dinosaur, Yutyrannus huali was a beast—almost certainly an apex predator, and related to the ancestors of Tyrannosaurus Rex.

Read the comments on this post

The rock record got a bad rap. Fossil diversity accurately reflects history

Say an EKG machine is monitoring your heart, when it suddenly flatlines. You'd be keenly interested to know whether your heart had stopped or the machine had simply gone on the fritz. Paleontologists have faced a similar (if slightly less urgent) puzzle when it comes to the geologic record of life: does the fossil record we see reflect the state of ancient ecosystems, or is it just the readout from a defective instrument? A recent paper in Science gives reassuring support to the fidelity of the rock record.

It’s fascinating to study how species diversity has changed through time, since we can see the effects of major events in Earth’s past and watch evolution play out. It's literally reading the history of life on Earth. That’s a story we naturally want to know and tell. But fossils are difficult to come by—after all, less than one percent of extinct species are represented in the fossil record. As an imperfect recorder, we have to worry how much the evidence in the rocks is telling us about the organisms, and how much we're just seeing changes in the rocks themselves.

Read the comments on this post

It’s got 16,000 eyes on you—the vision of a Cambrian-era predator

Those of you who get a bit weirded out by spiders and other arthropods would probably have a coronary if an Anomalocaris were to swim in your direction. The animals were about a meter long, and shaped as a flattened oval, a bit like a modern flounder. That's about the only similarity with a fish, though. Instead of fins, the Anomalocarids propelled themselves through the water using a series of elongated paddle-like structures running down both edges of the body. In front, a pair of appendages could shovel prey into a circular mouth located on its underside.

And then there were the large, bulging eyes, springing from each side of the animal's head. Until now, we could only guess at what the eyes looked like, but some spectacular, 515 million-year-old fossils from Australia have now shown that they had a huge number of small lenses, arranged much like those in modern insects and other arthropods. The finding suggests that the compound eyes evolved right at the origin of this branch of the evolutionary tree, long before the sorts of hard exoskeletons we now consider typical of arthropods.

Read the comments on this post

Four-winged dinosaur fossilized after swallowing a bird

Feathered dinosaurs existed for millions of years before the origin of birds and, for a time, there was a period where feathered dinosaurs and early birds coexisted with animals that don't fit neatly into either category. One of the latter was microraptor, a feathered dinosaur that doesn't appear to have been of the avian lineage but still seems to have had wing-like feathers on all four of its limbs. Researchers have now found that microraptor did have a close relationship with birds: it ate them.

Microraptor, as its name implies, was a small dinosaur, maybe a meter long counting its tail. Based on the number of fossils we've recovered, it was about as unremarkable as a pigeon in its day, which was about 120 million years ago. But most reconstructions suggest it looked rather unusual by modern standards. That's because microraptor featured wing-like forelimbs that retained claws, and hindlimbs that had an array of feathers similar to that on its forelimbs. A number of researchers suggest it could fly or glide, possibly using all four limbs for lift.

Read the comments on this post