First amphibious ichthyosaur discovered, filling evolutionary gap
The first fossil of an amphibious ichthyosaur has been discovered in China by a team led by researchers at the University of California, Davis. The discovery is the first to link the dolphin-like ichthyosaur to its terrestrial ancestors, filling a gap in the fossil record. The fossil is described in a paper published in advance online Nov. 5 in the journal Nature.
The fossil represents a missing stage in the evolution of ichthyosaurs, marine reptiles from the Age of Dinosaurs about 250 million years ago. Until now, there were no fossils marking their transition from land to sea.
"But now we have this fossil showing the transition," said lead author Ryosuke Motani, a professor in the UC Davis Department of Earth and Planetary Sciences. "There's nothing that prevents it from coming onto land."
Motani and his colleagues discovered the fossil in China's Anhui Province. About 248 million years old, it is from the Triassic period and measures roughly 1.5 feet long.
Unlike ichthyosaurs fully adapted to life at sea, this one had unusually large, flexible flippers that likely allowed for seal-like movement on land. It had flexible wrists, which are essential for crawling on the ground. Most ichthyosaurs have long, beak-like snouts, but the amphibious fossil shows a nose as short as that of land reptiles.
Its body also contains thicker bones than previously-described ichthyosaurs. This is in keeping with the idea that most marine reptiles who transitioned from land first became heavier, for example with thicker bones, in order to swim through rough coastal waves before entering the deep sea.
The study's implications go beyond evolutionary theory, Motani said. This animal lived about 4 million years after the worst mass extinction in Earth's history, 252 million years ago. Scientists have wondered how long it took for animals and plants to recover after such destruction, particularly since the extinction was associated with global warming.
"This was analogous to what might happen if the world gets warmer and warmer," Motani said. "How long did it take before the globe was good enough for predators like this to reappear? In that world, many things became extinct, but it started something new. These reptiles came out during this recovery."
Story Source:
The above story is based on materials provided by University of California - Davis. Note: Materials may be edited for content and length.
Journal Reference:
- Ryosuke Motani, Da-Yong Jiang, Guan-Bao Chen, Andrea Tintori, Olivier Rieppel, Cheng Ji, Jian-Dong Huang. A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature, 2014; DOI: 10.1038/nature13866
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Giant groundhog-like creature: Newly discovered fossil is a clue to early mammalian evolution
A newly discovered 66-70 million-year-old groundhog-like creature, massive in size compared to other mammals of its era, provides new and important insights into early mammalian evolution. Stony Brook University paleontologist David Krause, PhD, led the research team that unexpectedly discovered a nearly complete cranium of the mammal, which lived alongside Late Cretaceous dinosaurs in Madagascar. The findings, which shake up current views on the mammalian evolutionary tree, will be published in the journal Nature on November 5.
"We know next to nothing about early mammalian evolution on the southern continents," said Dr. Krause, a SUNY Distinguished Service Professor in the Department of Anatomical Sciences at Stony Brook. "This discovery, from a time and an area of the world that are very poorly sampled, underscores how very little we know. No paleontologist could have come close to predicting the odd mix of anatomical features that this cranium exhibits."
The new fossil mammal is named Vintana sertichi. Vintana belongs to a group of early mammals known as gondwanatherians, which previously were known only from isolated teeth and a few scrappy jaw fragments. The well-preserved skull allows the first clear insight into the life habits and relationships of gondwanatherians.
"The discovery of Vintana will likely stir up the pot," added Krause. "Including it in our analyses reshapes some major branches of the 'family tree' of early mammals, grouping gondwanatherians with other taxa that have been very difficult to place in the past." The skull is huge, measuring almost five inches long, twice the size of the previously largest known mammalian skull from the entire Age of Dinosaurs of the southern supercontinent of Gondwana. At a time when the vast majority of mammals were shrew- or mouse-sized, living in the shadows of dinosaurs, Vintana was a super heavyweight, estimated to have had a body mass of about 20 pounds, twice or even three times the size of an adult groundhog. Adding to the intrigue is the fact that the cranium of Vintana has a peculiar shape, being very deep, with huge eye-sockets, and long, scimitar-shaped flanges for the attachment of massive chewing muscles.
The initial discovery was made in 2010 and, like many in science, came about by chance.
Vintana means luck and refers to the circumstances that its discoverer, Joseph Sertich, a former graduate student of Dr. Krause's at Stony Brook University, had in finding the fossil in 2010. Sertich, now a curator at the Denver Museum of Nature & Science, collected a 150 block of sandstone filled with fish fossils. When the block was CT scanned in Stony Brook's Department of Radiology the images revealed that something exceedingly rare lay inside -- a nearly complete cranium of a previously unknown ancient mammal. The specimen represents only the third occurrence of mammalian skulls from the Cretaceous of the entire Southern Hemisphere, the other two being from Argentina.
"When we realized what was staring back at us on the computer screen, we were stunned," said Joe Groenke, Krause's technician and the first to view the CT images. Groenke spent the next six months extracting the skull from the surrounding rock matrix, one sand grain at a time.
Dr. Krause and his team conducted a comprehensive analysis of the skull, much of it using micro-computed tomography and scanning electron microscopy to reveal minute aspects of its anatomy, including areas like the braincase, nasal cavity, and inner ear that are poorly known in almost all early mammals. They compared the skull to those of hundreds of other fossil and extant mammals.
Various features of its teeth, eye sockets, nasal cavity, braincase, and inner ears revealed that Vintana was likely a large-eyed herbivore that was agile, with keen senses of hearing and smell. These and other features were also used to analyze its relationships to other early mammals. This phylogenetic analysis demonstrated that Vintana and other gondwanatherians were close relatives of multituberculates, the most successful mammalian contemporaries of dinosaurs on the northern continents. Gondwanatherians and multituberculates also grouped with another enigmatic taxon, the Haramiyida. The analysis by Krause's team is the first to find strong evidence for clustering these three groups together, primarily because the cranial anatomy of gondwanatherians was previously completely unknown.
Dr. Krause emphasizes that a major question remains for scientists: How did such a peculiar creature evolve?
With its long-term isolation from the rest of the world, Madagascar had been an island for over 20 million years prior to the time in which the strata containing Vintana were deposited. Dr. Krause and his team theorize that the very primitive features of the cranium are holdovers from when the ancient lineage that ultimately produced Vintana was marooned on the island. It was this isolation, first from Africa, then Antarctica/Australia, and finally the Indian subcontinent, that allowed for the evolution of unique and bizarre features amidst Vintana's primitive foundation of characteristics.
The research by Dr. Krause and colleagues on Vintana sertichi is supported by the National Science Foundation and the National Geographic Society.
Dr. Zhe-Xi Luo, a leading expert on early mammalian evolution from the University of Chicago, reviewed the manuscript for Nature. He hailed the Vintana as "the discovery of the decade for understanding the deep history of mammals; it offers the best case of how plate tectonics and biogeography have impacted animal evolution -- a lineage of mammals isolated on a part of the ancient Gondwana had evolved some extraordinary features beyond our previous imagination. This new study of Vintana is a giant leap forward toward resolving the long-standing mystery of gondwanatherian mammals, which has puzzled paleontologists for decades." Luo went on to say, "Vintana is also a galvanizing discovery for the future decades. With features so remarkably different from those of other mammals previously known to science, this fossil tells us how little we knew about the early evolution of mammals -- it will stimulate paleontologists to conduct more field exploration in order to advance the frontier of deep time history and evolution."
Dr. Guillermo Rougier from the University of Louisville, another expert who also reviewed the Nature paper, concurred, calling the study "a remarkable achievement" and predicted that the paper "will shake the field upon publication; the specimen is exceptional."
"This is the first discovery of a cranial fossil from a very enigmatic extinct group of mammals called Gondwanatheria in the Southern Hemisphere," says Dr. Yusheng (Chris) Liu, Program Director in the National Science Foundation (NSF)'s Division of Earth Sciences, which funded the research. "This important find will help us better understand the early evolution of gondwanatherians and their relatives."
Story Source:
The above story is based on materials provided by Stony Brook University. Note: Materials may be edited for content and length.
Journal Reference:
- David W. Krause, Simone Hoffmann, John R. Wible, E. Christopher Kirk, Julia A. Schultz, Wighart von Koenigswald, Joseph R. Groenke, James B. Rossie, Patrick M. O'Connor, Erik R. Seiffert, Elizabeth R. Dumont, Waymon L. Holloway, Raymond R. Rogers, Lydia J. Rahantarisoa, Addison D. Kemp, Haingoson Andriamialison. First cranial remains of a gondwanatherian mammal reveal remarkable mosaicism. Nature, 2014; DOI: 10.1038/nature13922
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Exquisite ancient horse fossil preserves uterus with unborn foal
A specimen of the ancient horse Eurohippus messelensis has been discovered in Germany that preserves a fetus as well as parts of the uterus and associated tissues. It demonstrates that reproduction in early horses was very similar to that of modern horses, despite great differences in size and structure. Eurohippus messelensis had four toes on each forefoot and three toes on each the hind foot, and it was about the size of a modern fox terrier. The new find was unveiled at the 2014 Annual Meeting of the Society of Vertebrate Paleontology in Berlin.
"Almost all of the bones of the fetus are still articulated in their original position. Only the skull is crushed," said Dr. Jens Lorenz Franzen of the Senckenberg Research Institute, lead author of the study. The study's co-authors are Dr. Jörg Habersetzer, also of the Senckenberg Research Institute, and Dr. Christine Aurich of the University of Veterinary Medicine at Vienna and head of the Graf Lehndorff Institute of Equine Sciences.
The specimen was discovered by a team from the Senckenberg Research Institute nearly 15 years ago, but its extent was not fully appreciated until it was studied using micro x-ray. The micro x-ray analysis revealed a structure known as the broad ligament that connects the uterus to the backbone and helps support the developing foal. Remnants of the wrinkled outer uterine wall became visible after the specimen was prepared, a feature shared between Eurohippus and modern horses. The placenta in this specimen is only the second one that has been described for a fossil placental mammal.
The oil shales at Grube Messel have long been known for their marvelous fossils. These oil shales formed at the bottom of ancient Lake Messel and preserve the remains of mammals, birds, and other animals that were living near what is now Darmstadt, Germany about 47 million years ago (the Eocene epoch). No oxygen was present at the bottom of the lake when the dead animals sank down and finally became embedded in the muddy sediments. There, anaerobic bacteria immediately began to decompose skin, muscles, and other soft tissues. As a result, the bacteria produced carbondioxid, which in turn precipitated iron ions present in the lake water. In this way, the bacteria petrified themselves, developing only a very thin bacterial lawn depicting the soft tissue as black shadow. Consequently, Messel fossils preserve these remains not directly, but as images.
The size of the fetus and the presence of fully developed milk teeth indicate that it was close to term when it and its mother died. Nevertheless, its position in the uterus indicates that the two did not die during the birthing process. The fetus was upside down rather than right side up, and its front legs were not yet extended as they should be just before birth.
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The above story is based on materials provided by Society of Vertebrate Paleontology. Note: Materials may be edited for content and length.
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Tricky take-off kept pterodactyls grounded
A new study, which teamed cutting-edge engineering techniques with paleontology, has found that take-off capacity may have determined body size limits in extinct flying reptiles. The research simulated pterodactyl flight using computer modeling, and will be presented at the upcoming Society of Vertebrate Paleontology meeting in Berlin. Findings suggest that a pterodactyl with a wingspan of 12m or more would simply not be able to get off the ground.
Pterosaurs (commonly known as pterodactyls) were truly giants of the sky. With wingspans of up to 10m, the largest species may have weighed as much as a quarter of a ton. They would have dwarfed the largest known bird at just one third this size. How could such behemoths stay aloft? What prevented them from becoming even bigger?
These questions sparked a novel partnership between Colin Palmer: entrepreneur, mechanical engineer and now doctoral student at Bristol University (UK); and Mike Habib: anatomist and paleontologist at University of Southern California.
"It has been fascinating to apply an engineering approach to understanding biological systems" says Palmer, who has worked on yachts, hovercraft, sailing vessels and windmills before turning to pterosaurs. "Working with Colin has been particularly rewarding" says paleontologist Habib "as we have complementary skill sets and come at the problem from different backgrounds."
The pair used 3D imaging of fossils to create a computer model of a pterosaur with a 6m wingspan. This model was then scaled up to create enlarged models with 9m and 12m wingspans. They were used to estimate the wing strength, flexibility, flying speed and power required for flight in massive pterosaurs.
Results showed that even the largest pterosaur model could sustain flight by using intermittent powered flight to find air currents for gliding. It could also slow down sufficiently to make a safe landing because the pterosaurs wing is formed from a flexible membrane.
Take-off, on the other hand, proved an entirely greater challenge. Unlike modern birds, pterosaur anatomy suggests that they used both their arms and legs to push themselves off the ground during take-off, a maneuver known as the 'quadrupedal launch'. However, once wingspans approached 12m, the push-off force required to get the model off the ground was too great.
The challenge of propelling a 400kg animal using a quadrupedal launch kept the 12m-wingspan model strictly on terra firma. Palmer concludes "Getting into the air ultimately limited pterosaur size. Even with their unique four legged launch technique, the iron laws of physics eventually caught up with these all time giants of the cretaceous skies."
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The above story is based on materials provided by Society of Vertebrate Paleontology. Note: Materials may be edited for content and length.
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