"Opposite Birds:" Why Being Grounded May Have Been the Counterintuitive Key to Survival

     The asteroid impact that caused a mass extinction 66 million years probably also triggered the collapse of forests worldwide, a new investigation of the plant fossil record concludes. 

     Needing trees and extensive plant cover for nesting or food could have been a fatal drawback for winged dinosaurs, including some ancient birds.

        Here is the caption for the diagram above: 

         "Ancestral Ecological Reconstructions Reveal Bias toward Non-arboreal Birds across the K-Pg:

      Bayesian ancestral ecological reconstructions (AERs) indicate that the most deeply diverging crown bird clades, including Neornithes (all crown birds), Neognathae (Galloanserae + Neoaves), and Neoaves, were ancestrally non-arboreal (pp > 0.99 for each node), with numerous independent transitions toward arboreality arising in the early Cenozoic, presumably after global forests had recovered from the Chicxulub impact. Concentric background rings demarcate geologic periods: the inner gray circle at the center indicates the Late Cretaceous, with the K-Pg boundary (66.02 Ma) indicated by the red dashed line; the white ring indicates the Paleogene (66.02–23.03 Ma), separated from the Neogene (23.03–2.58 Ma) by the dashed blue line. Tips extend to the present. Pie charts at the nodes indicate SIMMAP posterior probabilities for ancestral ecology, under our model. Branch colors represent a single randomly sampled stochastic character map from a posterior sample of 1,000 maps. The underlying phylogeny and taxonomy follow; qualitatively identical patterns are inferred using an alternative phylogenetic hypothesis."

       Reconstructing the ecology of ancient birds suggests that modern birds descended from species that survived because they could live on the ground, a research team proposes in the June 4, 2018, Current Biology.

      “You probably would have died anyway regardless of habitat,” says study coauthor Dr. Daniel Field, an evolutionary paleobiologist at the University of Bath in England. “But if you could get along on the ground, you at least had a shot at surviving across this devastated landscape.”

     The shock wave from the strike probably flattened trees within a radius of 1,500 kilometers, Dr. Field says. Wildfires ignited around the planet and then came the acid rain. Clouds of ash and dust may have darkened the sky for several years, and researchers suspect that photosynthesis waned. Yet some lucky birds, but no other dinosaurs, survived the hellscape.

     For clues to what made a survivor, researchers turned to fossilized pollen from before and after the fiery impact. Abundant kinds of flower-bearing and cone-bearing plants left pollen just before the asteroid hit and again starting about a thousand years afterward. In between those times of diversity, however, ferns dominated, the team notes. A kind of “disaster flora,” ferns (making spores instead of flowers and seeds) do well at recolonizing land. Seed plants, however, weren’t thriving.

     Analyzing evolutionary histories of modern birds supports the idea of tree dependence as a vulnerability for the earliest fowl, the researchers say. Specialists in bird evolution now generally agree on the lowest, oldest branches of the bird family tree, Field says. The bottommost one, for instance, includes such modern species as ground-dwelling ostriches and smaller, flight-capable birds called tinamous, which might be more like the ancient birds that dodged extinction.

     Working backward along these low branches, researchers used fossils and known bird traits to reconstruct the most likely lifestyles of the earliest survivors. These probably weren’t tree-dependent birds, the researchers conclude.

     The glory days of dinosaurs had had plenty of flying tree-dwellers. So far, paleontologists have identified at least 80 kinds of what are called “opposite birds,” the Enantiornithes. “If you saw one flying around today, you’d say, ‘Well, that’s a bird,’ ” Field explains. Their feet looked like those of birds that perch on tree limbs, so he’s not surprised that a fossil of an opposite bird from this probably arboreal group has never been found in rock formed after the dinosaur doomsday.

     What did happen, however, was that when trees and forests came back after the disaster, birds quickly evolved arboreal lifestyles, the team says.

     Many people don’t realize that birds almost died off during the mass extinction, too, says paleontologist Stephen Brusatte of the University of Edinburgh who has studied bird evolution but was not involved in the new study. What let the few survivors squeak through, he says, has been a mystery for a long time. The whole scenario of a ground-dweller’s advantage and then a return to the trees “makes a lot of intuitive sense.”

     Essentially, surviving on the ground, without much flying, for awhile may be what ultimately made the later arboreal environments so rich with modern-day birds.

No, er, YES, GROUSE about it!

Steph

Extensive Mid-Oceanic Magma Eruption at the Cretaceous-Paleogene Time Boundary

     The asteroid that hit earth 66 million years ago appears to have caused large amounts of magma to spew out of the bottom of the ocean, a new study of seafloor data finds.

      The discovery, described today in the journal Science Advances, adds to the picture of an extinction event that was as complex as it was deadly.

      For decades, researchers have pointed to a cataclysmic asteroid crashing into the planet as the reason the dinosaurs, and many other species of life on Earth, were wiped out during the Cretaceous-Paleogene (K-Pg) extinction event. That impact, which scientists think left the roughly 110-mile-wide Chicxulub crater in the Gulf of Mexico, would have vaporized living things nearby and sent choking clouds of debris into the air, obscuring the sun.

      But scientists have also pointed to another culprit: the Deccan Traps in present-day India, one of the largest volcanic provinces in the world, which just happened to be very active at the time of the extinction event. The ash and noxious gases from the Deccan Traps are really what killed the dinosaurs, some scientists say, downplaying the asteroid's role.

     "People still argue about which one was actually the primary driver of environmental changes that resulted in the death of dinosaurs," said senior author Dr. Leif Karlstrom, an earth scientist at the U. of Oregon.

     Researchers have also suggested that perhaps the two were connected — perhaps the asteroid triggered Deccan Trap volcanism, producing a brutal one-two punch that ultimately knocked out roughly three-quarters of the earth's plant and animal species. But recent work has shown that the traps started spewing roughly a quarter-million years before the asteroid hit, Dr. Karlstrom said.

     Yet, scientists have wondered if there might indeed be some kind of connection between the two. And lead author Dr. Joseph Byrnes, a geophysicist at the U. of Minnesota, realized something: If the asteroid impact had had a major impact on volcanism at the time, that effect should have shown up in the activity along the Earth's mid-ocean ridges. So he and Dr. Karlstrom went looking for it.

     As we've discussed here at Partial Ellipsis of the Sun before, the mid-ocean ridges are long cracks in the Earth's crust at the bottom of the ocean floor where tectonic plates meet. As the plates pull apart, hot magma rises up between them, flowing out on either side of the crack before cooling, creating new seafloor in the process. With more than 40,000 miles of ridges, this network of cracks forms the longest mountain chain on earth.

   
     Scientists used magnetic data compiled by other researchers and combined it with another data set showing the gravitational field of the surface beneath the ocean. The stronger the gravitational field in a given spot, the more mass there is. 

    "We have a topographic map of the Earth's surface and we have topographic maps of Mars and Venus, but we don't have that for the ocean floor," Dr. Byrnes said. "We have it for places where people have taken ships, but it would take something like 900 years to survey the whole ocean floor. It's just too resource-intensive — so we have to use the gravitational anomalies as a proxy."

     The graph below shows a spike in the creation of new seafloor about 66 million years ago. That's when the Chicxulub asteroid struck the Earth, wiping out the dinosaurs. The impact also instigated the release of massive amounts of magma.

     Sure enough, the scientists found that at the time the asteroid hit the Earth, there was a sudden surge in the magma pouring out of these mid-ocean ridges, which put out on the order of a hundred thousand to a million cubic kilometers of volcanic material. That's not too far behind the estimated several million cubic kilometers or so of magma produced by the Deccan Traps.

     It's possible that the powerful seismic waves produced by the impact triggered the release of reservoirs of magma beneath the surface, Dr. Karlstrom said. And if it affected the mid-ocean ridges this way, it could have played a similar role in the Deccan Traps, triggering even more volcanism than before.

     The mid-ocean ridges, then, could be a bellwether for a similar phenomenon occurring in the already-active Deccan Traps.

       But did that marine magma release do any damage of its own? While it's unclear whether this extra load of ocean floor magma worsened the extinction event, it could potentially have played a role by further acidifying the oceans. Previous work indicates that marine species that were more sensitive to ocean acidification were worse hit by the extinction event. But probing that possibility will take more research, the scientists added.

      "That's what we need to work on next, I would say: trying to tease out what the effects on the environment were of the volcanic activity," Dr. Byrnes said.

Thoughts on this new data? Have you been to the Deccan Traps?
Steph

Speaking of stitches, here's the full quilt my friend made:

     

Mammals Evolved Three Times Faster after Dinosaur Extinction

     Our ancestors evolved three times faster in the 10 million years after the extinction of the dinosaurs than in the previous 80 million years, according to University College of London researchers.

     The research team found the speed of evolution of placental mammals (a group that today includes about 5000 species including humans) was constant before the extinction event but exploded after, resulting in the varied groups of mammals we see today.

     Lead (not lead ;-)) researcher, Dr. Thomas Halliday said: "Our ancestors, the early placental mammals, benefitted from the extinction of non-avian dinosaurs and dwindling numbers of competing groups of mammals. Once the pressure was off, placental mammals suddenly evolved rapidly into new forms."

     "In particular, we found a group called Laurasiatheria quickly increased their body size and ecological diversity, setting them on a path that would result in a modern group containing mammals as diverse as bats, cats, rhinos, whales, cows, pangolins, shrews and hedgehogs."

        Laurasiatheria is a superorder of placental mammals believed to have originated on the northern supercontinent of Laurasia. Thus it was the northern landmasses that produced much of the mammal explosion.

     The team found that the last common ancestor for all placental mammals lived in the late Cretaceous period, about three million years before the non-avian dinosaurs became extinct 66 million years ago. This date is about 20 million years younger than suggestions from previous studies which used molecular data from living mammals and assumed a near-constant rate of evolution.

     In this study the researchers analysed fossils from the Cretaceous to the present day, and used the dates of their occurrence in the fossil record to estimate the timing of divergences based on an updated tree of life. The new tree was released in 2015 and has the largest representation of Paleocene mammals to date.

     The scientists measured all the small changes in the bones and teeth of 904 placental fossils and mapped the anatomical differences between species on the tree of life. From measuring the number of character changes over time for each branch, they found the average rate of evolution for early placental mammals both before and after the dinosaur extinction event. They compared the average rate of evolution over the geological stages before the extinction and the geological stages after to see what impact it had.

     Senior author, Professor Anjali Goswami said, "Our findings refute those of other studies which overlooked the fossils of placental mammals present around the last mass extinction. Using rigorous methods, we've successfully tracked the evolution of early placental mammals and reconstructed how it changed over time. While the rate differed between species, we see a clear and massive spike in the rates of evolution right after the dinosaurs become extinct, suggesting our ancestors greatly benefitted from the demise of the dinosaurs. The huge impact of the dinosaur extinction on the evolution of our ancestors really shows how important this event was in shaping the modern world."

      Professor Paul Upchurch, co-author of the study, added: "Our large and refined data set allows us to build a clearer picture of evolutionary history. We plan on using it to study other large-scale evolutionary patterns such as how early placental mammals dispersed across the continents via land bridges that no longer exist today."

       I'd like to take that land bridge from South America to Africa in the southern land masses of Gondwanaland. 

      How about you? Does "Reunite Gondwanaland!" ring true to you?

Steph