Amphibians and dinosaurs were the new large predators after the mass extinction
Some 252 million years ago the largest extinction event occurred at the end of the Permian age. It wiped out almost 90 percent of all life in water. So far researchers had assumed that the ecosystems gradually recovered from this catastrophe over a long stretch of eight to nine million years and that large predators at the uppermost end of the food chain were the last to reappear. A Swiss-American team of palaeontologists headed by Torsten Scheyer and Carlo Romano from the University of Zurich demonstrate in their new study that the food nets during the Early Triassic did not recover in stages. Large predators like, for instance, crocodile-like amphibians and later the precursors of the known plesiosaurs and ichthyosaurs went in search of prey in the oceans soon after the end of the mass extinction.
Large predators in on the action from the very start
Apex predators -- large predators at the uppermost end of the food chain -- are extremely important for the health and stability of an ecosystem. They eradicate sick and weak animals and exercise constantselection pressure on the species they prey on. Hence, Scheyer and his colleagues wanted to establish whether the apex predators really were missing from the oceans after the mass extinction and how the ecosystems functioned.
The researchers looked at the global distribution of predatory marine vertebrates and their body size in the Early and Middle Triassic and came to surprising conclusions. "The apex marine predators recovered after the large extinction over a very, comparatively short period of time," says Torsten Scheyer. The researchers were also able to refute a second theory. Earlier it had been assumed that marine predators grew continuously larger from the Early to the Middle Triassic culminating in the apex predators. "We now demonstrate that already in the Early Triassic large predators hunted in the seas," adds Carlo Romano."The length of the food chains was not shortened by the end-Permian mass extinction. Nor are there any signs of a gradual re-emergence of the classical trophic pyramids from the base to the top," explains Hugo Bucher. To gain greater understanding of food webs, attention had to be paid not only to the shape of the food webs but also to the dynamics, i.e. the evolutionary rates of the participating species.
New actors in old roles
The large end-Permian mass extinction led to a completely new composition of apex predators. Large predatory fish were dominant in the Permian age but they had to share this role with predatory crocodile-like amphibians after the mass extinction. Another extinction event around two million years later, the End Smithian crisis, triggered changes in the group of apex predators. From this point in time fish and for the first time reptiles like, for instance, Askeptosaurus were at the uppermost end of the food chains.
"The role of the large predators always remained the same in the ecosystems; only the actors changed over the course of time," comments Torsten Scheyer when summing up the new results. The researchers are convinced that insight into events in the past will contribute to better understanding of the impact of today's climate changes on ecosystems.
Story Source:
The above story is based on materials provided by University of Zurich. Note: Materials may be edited for content and length.
Journal Reference:
- Torsten M. Scheyer, Carlo Romano, Jim Jenks, Hugo Bucher. Early Triassic Marine Biotic Recovery: The Predators' Perspective. PLoS ONE, 2014; 9 (3): e88987 DOI: 10.1371/journal.pone.0088987
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Nearly complete 'chicken from hell,' from mysterious dinosaur group
A team of researchers has announced the discovery of a bizarre, bird-like dinosaur, named Anzu wyliei, that provides paleontologists with their first good look at a dinosaur group that has been shrouded in mystery for almost a century. Anzu was described from three specimens that collectively preserve almost the entire skeleton, giving scientists a remarkable opportunity to study the anatomy and evolutionary relationships of Caenagnathidae (pronounced SEE-nuh-NAY-thih-DAY) -- the long-mysterious group of theropod dinosaurs to which Anzu belongs.
The three described fossil skeletons of Anzu were unearthed in North and South Dakota, from roughly 66 million-year-old rocks of the Hell Creek Formation, a rock unit celebrated for its abundant fossils of famous dinosaurs such as Tyrannosaurus rex and Triceratops. The scientific paper describing the discovery appears today in the freely-accessible journal PLOS ONE.
The team of scientists who studied Anzu was led by Dr. Matthew Lamanna of Carnegie Museum of Natural History in Pittsburgh. Dr. Lamanna's collaborators include Dr. Hans-Dieter Sues and Dr. Tyler Lyson of the Smithsonian Institution's National Museum of Natural History in Washington, DC, and Dr. Emma Schachner of the University of Utah in Salt Lake City. According to Dr. Lamanna, "Anzu is far and away the most complete caenagnathid that has ever been discovered. After nearly a century of searching, we paleontologists finally have the fossils to show what these creatures looked like from virtually head to toe. And in almost every way, they're even weirder than we imagined."
Hell's Chicken
At roughly 11 feet long and five feet tall at the hip, Anzu would have resembled a gigantic flightless bird, more than a 'typical' theropod dinosaur such as T. rex. Its jaws were tipped with a toothless beak, and its head sported a tall, rounded crest similar to that of a cassowary (a large ground bird native to Australia and New Guinea). The neck and hind legs were long and slender, also comparable to a cassowary or ostrich. Although the Anzu specimens preserve only bones, close relatives of this dinosaur have been found with fossilized feathers, strongly suggesting that the new creature was feathered too. The resemblance to birds ends there, however: the forelimbs of Anzu were tipped with large, sharp claws, and the tail was long and robust. Says Dr. Lamanna, "We jokingly call this thing the 'Chicken from Hell,' and I think that's pretty appropriate. So we named it after Anzu, a bird-like demon in ancient mythology."
The species is named for a Carnegie Museums of Pittsburgh Trustee's grandson, Wylie.
Not only do the fossils of Anzu wyliei paint a picture of this particular species, they shed light on an entire group of dinosaurs, the first evidence of which was discovered almost 100 years ago. In 1924, paleontologist Charles Whitney Gilmore described the species Chirostenotes pergracilis from a pair of fossil hands found a decade earlier in ~74 million-year-old rocks in Alberta, Canada. Later, in 1940, Caenagnathus collinsi was named, based on a peculiar lower jaw from the same beds. More recently, after studies of these and other fragmentary fossils, Hans Sues and other paleontologists determined that Chirostenotes and Caenagnathus belonged to the same dinosaur group, Caenagnathidae, and that these animals were close cousins of Asian oviraptorid theropods such as Oviraptor.
Asian relations
Oviraptor ('egg thief') is widely known because the first fossil skeleton of this animal, described in 1924, was found atop a nest of dinosaur eggs, suggesting that the creature had died in the act of raiding the nest. This thinking prevailed until the 1990s, when the same type of egg was found with a baby oviraptorid inside, demonstrating that, rather than a nest plunderer, Oviraptor was a caring parent that perished while protecting its eggs. More than a dozen oviraptorid species have been discovered, all in Mongolia and China, and many are known from beautifully-preserved, complete or nearly complete skeletons. Additionally, beginning in the 1990s, several small, primitive relatives of oviraptorids were unearthed in much older, ~125 million-year-old rocks in northeastern China. Many of these are also represented by complete skulls or skeletons, some of which preserve fossilized feathers. Researchers have established that caenagnathids, oviraptorids, and these more archaic Chinese species are closely related to one another, and have united them as the theropod group Oviraptorosauria. The occurrence of oviraptorosaurs in both Asia and North America was not a surprise to paleontologists, because these continents were frequently connected during the Mesozoic Era (the 'Age of Dinosaurs'), allowing dinosaurs and other land animals to roam between them. However, because their fossils were so incomplete, caenagnathids remained the most poorly known members of Oviraptorosauria, and indeed, one of the least understood of all major dinosaur groups. "For many years, caenagnathids were known only from a few bits of the skeleton, and their appearance remained a big mystery," says Dr. Sues.
More fossils, more knowledge
The nearly completely represented skeleton of Anzu opens a window into the anatomy of this and other caenagnathid species. Armed with this wealth of new information, Dr. Lamanna and his team were able to reconstruct the evolution of these extraordinary animals in more detail than ever before. Analysis of the relationships of Anzu reaffirmed that caenagnathids form a natural grouping within Oviraptorosauria: Anzu, Caenagnathus, Chirostenotes, and other North American oviraptorosaurs are more closely related to each other than they are to most of their Asian cousins -- a finding that had been disputed in recent years. Furthermore, the team's analysis confirmed the recent hypothesis that the enormous (and aptly-named) Gigantoraptor -- at a weight of at least 1.5 tons, the largest oviraptorosaur known to science -- is an unusual member of Caenagnathidae as well, instead of an oviraptorid as had initially been proposed. "We're finding that caenagnathids were an amazingly diverse bunch of dinosaurs," says Dr. Lamanna. "Whereas some were turkey-sized, others -- like Anzu and Gigantoraptor -- were the kind of thing you definitely wouldn't want to meet in a dark alley. Apparently these oviraptorosaurs occupied a much wider range of body sizes and ecologies than we previously thought."
The anatomy and ancient environment of Anzu provide insight into the diet and habitat preferences of caenagnathids as well. Although the preferred food of these oviraptorosaurs remains something of a puzzle, Dr. Lamanna and collaborators think that caenagnathids were probably omnivores -- like humans, animals that could eat either meat or plants. Moreover, studies of the rocks in which several of the most complete caenagnathid skeletons have been found show that these strata were laid down in humid floodplain environments, suggesting that these dinosaurs favored such habitats. In this way, caenagnathids appear to have differed greatly from their oviraptorid cousins, all of which have been found in rocks that were deposited under arid to semi-arid conditions . "Over the years, we've noticed that Anzu and some other Hell Creek Formation dinosaurs, such as Triceratops, are often found in mudstone rock that was deposited on ancient floodplains. Other dinosaurs, like duckbills, are found in sandstone deposited in or next to rivers," says Dr. Lyson, who found his first Hell Creek fossil on his family's ranch in North Dakota when he was only six years old.
Anzu led a life that was fraught with danger. In addition to sharing its Cretaceous world with the most notorious carnivore of all time -- T. rex -- this oviraptorosaur seems to have gotten hurt a lot as well. Two of the three specimens show clear evidence of injuries: one has a broken and healed rib, while the other has an arthritic toe bone that may have been caused by an avulsion fracture (where a tendon ripped a piece off the bone to which it was attached). Says Dr. Schachner, "These animals were clearly able to survive quite a bit of trauma, as two of the specimens show signs of semi-healed damage. Whether these injuries were the result of combat between two individuals or an attack by a larger predator remains a mystery."
As much insight as the Anzu skeletons provide, paleontologists still have much to learn about North American oviraptorosaurs. Ongoing studies of these and other important fossils promise to remove more of the mystery surrounding these remarkable bird-like creatures. "For nearly a hundred years, we paleontologists knew almost nothing about these dinosaurs," concludes Dr. Lamanna. "Now, thanks to Anzu, we're finally starting to figure them out."
A fully-articulated cast of Anzu wyliei is on public view in Carnegie Museum of Natural History's Dinosaurs in Their Time exhibition.
Story Source:
The above story is based on materials provided by Carnegie Museum of Natural History. Note: Materials may be edited for content and length.
Journal Reference:
- Lamanna MC, Sues H-D, Schachner ER, Lyson TR. A New Large-Bodied Oviraptorosaurian Theropod Dinosaur from the Latest Cretaceous of Western North America. PLoS ONE, 2014 DOI: 10.1371/journal.pone.0092022
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Fossils of earliest stick insect to mimic plants discovered: Ancient stick insect species mimicked plant leaves
An ancient stick insect species may have mimicked plant leaves for defense, according to a paper published in the open-access journal PLOS ONE on March 19, 2014 by Maomin Wang, from Capital Normal University, China and colleagues.
Many insects have developed defense mechanisms, including the ability to mimic the surrounding environment. Stick and leaf insects mimic plants from their environment, but scientists know little about the original of this interaction due to little or no previous stick insect fossil records showing this adaptation. The scientists discovered three specimens, one female and two males, belonging to a new fossil stick insect referred to as Cretophasmomima melanogramma, in Inner Mongolia at the Jehol locality, a site from the Cretaceous period (approximately 126 million years ago). The species possessed adaptive features that make it resembling a plant recovered from the same locality.
The insects' wings have parallel dark lines and when in the resting position, likely produced a tongue-like shape concealing the abdomen. Fossils from a relative of the ginkgo plant have been documented in the area with similar tongue-shaped leaves along with multiple longitudinal lines. The authors suggest the insect used this plant as a model for concealment.
The new fossils indicate that leaf mimicry was a defensive strategy performed by some insects as early as in the Early Cretaceous, but that additional refinements characteristic of recent forms, such as a curved part of the fore legs for hiding the head, were still lacking.
The new fossil suggests that leaf mimicry predated the appearance of twig and bark mimicry in these types of insects. The diversification of small-sized, insect-eating birds and mammals may have triggered the acquisition of such primary defenses.
Story Source:
The above story is based on materials provided by PLOS. Note: Materials may be edited for content and length.
Journal Reference:
- Wang M, Béthoux O, Bradler S, Jacques FMB, Cui Y, et al. Under Cover at Pre-Angiosperm Times: A Cloaked Phasmatodean Insect from the Early Cretaceous Jehol Biota. PLoS ONE, 2014 DOI: 10.1371/journal.pone.0091290
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Oldest fossil evidence of modern African venomous snakes found in Tanzania
Ohio University scientists have found the oldest definitive fossil evidence of modern, venomous snakes in Africa, according to a new study published March 19 in the journal PLOS ONE.
The newly discovered fossils demonstrate that elapid snakes -- such as cobras, kraits and sea snakes -- were present in Africa as early as 25 million years ago, said lead author Jacob McCartney, a postdoctoral researcher in the Ohio University Heritage College of Osteopathic Medicine. He's part of a team that has been examining the Rukwa Rift Basin of Tanzania over the last decade to understand environmental change through time in the East African Rift System.
Elapids belong to a larger group of snakes known as colubroids, active foragers that use a variety of methods, including venom, to capture and kill prey.
Colubroid fossils are documented as early as 50 million years ago. But they weren't expected to constitute such a large part of the African snake fauna 25 million years ago, as they became dominant in Europe and North America much later.
"In the Oligocene epoch, from about 34 to 23 million years ago, we would have expected to see a fauna dominated by booid snakes, such as boas and pythons. These are generally 'sit and wait' constricting predators that hide and ambush passing prey," McCartney said.
In fact, the recent study includes a description of the oldest evidence of African booid snakes, he said. The researchers have named this new species Rukwanyoka holmani; the genus name combines the Rukwa region name with the Swahili word for snake, and the species name is in honor of J. Alan Holman, a paleontologist and mentor.
However, the team was surprised to discover that the fauna actually revealed more colubroids than booids. That higher-than-expected concentration of colubroid snakes suggests that the local environment became more open and seasonally dry -- and, in turn, more hospitable to these active foraging types of snakes that don't require cover to hide and ambush prey -- at an earlier time in Africa than in most other parts of the world, as documented in previous studies.
"This finding gives further strength to the idea that tectonic activity in the East African Rift has helped to shape animal habitats in fascinating ways," said Nancy Stevens, an associate professor of biomedical sciences at Ohio University and co-author of the study. "The fossils suggest a fundamental shift toward more active and potentially venomous snakes that could exert very different pressures on the local fauna."
More fossils from additional locations should indicate whether colubroid snakes dominated all of Africa during the Oligocene or just the local region around the Rukwa Rift, McCartney said.
The study published in PLOS ONE describes eight different types of fossil snakes from the Rukwa Rift (five colubroid and three booid), with vertebrae ranging in length from 2.6 mm to just over 5 mm.
Story Source:
The above story is based on materials provided by Ohio University. Note: Materials may be edited for content and length.
Journal Reference:
- Jacob A. McCartney, Nancy J. Stevens, Patrick M. O’Connor. The Earliest Colubroid-Dominated Snake Fauna from Africa: Perspectives from the Late Oligocene Nsungwe Formation of Southwestern Tanzania. PLoS ONE, 2014; 9 (3): e90415 DOI: 10.1371/journal.pone.0090415
Ohio University. "Oldest fossil evidence of modern African venomous snakes found in Tanzania." ScienceDaily. ScienceDaily, 20 March 2014. <www.sciencedaily.com/releases/2014/03/140320101515.htm>.
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