Redescription of the oldest-known dolphin skull sheds light on their origins and evolution

Dolphins are the most diverse family of living marine mammals and include species such as the bottlenose dolphin and the killer whale. However, their early evolution and fossil record has been steeped in mystery due to lack of good specimens. A new paper published in latest issue of the Journal of Vertebrate Paleontology re-describes the oldest species of dolphin with a new name: Eodelphis kabatensis. Although the partial skull was previously described in the 1970s the scientific community largely overlooked it. The new re-description has important implications for the evolutionary history of dolphins

The skull of Eodelphis kabatensis was originally collected from a small tributary of the Oshirarika River in Hakkaido, Japan from an outcrop of the Mashike Formation. Researchers working on the specimen have narrowed its age to the late Miocene (13.0-8.5 million years ago), making it the earliest true dolphin species described. "The early evolution of true dolphins is still covered in mystery. Eodelphis kabatensis informs us about the morphology of early dolphins," said lead author Mizuki Murakami.

Eodelphis is an important link in the evolutionary history of dolphins. Prior to this study, there was inconsistency between the fossil record of the dolphins and molecular-based studies. The oldest true dolphin fossils found were less than 6 million years old, while molecular studies suggested they originated and started to diversity between 9-12 million years ago. "Eodelphis kabatensis, being discovered from sediments that were deposited 8-13 million years ago, has largely resolved this discrepancy and provides the best glimpse yet of what the skull of the first dolphins may have looked like," said Jonathan Geisler, a marine mammal paleontologist at the New York Institute of Technology College of Osteopathic Medicine.

In addition to its importance as the earliest true dolphin, this new study also incorporates the most comprehensive analysis of the relationships within the Delphinoidea, the group that encompasses toothed whales. By including Eodelphis in the analysis, the authors were able to get a much clearer picture of the evolution of the toothed whales. Furthermore, the presence of Eodelphis in the Pacific Ocean during the late Miocene has implications for the geographic history of dolphins. While more specimens need to be discovered, this study suggests that dolphins might have had their origins in the Pacific.

Shrinking helped dinosaurs and birds to keep evolving

Although most dinosaurs went extinct 65 million years ago, one dinosaur lineage survived and lives on today as a major evolutionary success story -- the birds.

An Oxford University-led team studied how dinosaurs evolved into a huge range of shapes and sizes over 170 million years. Shrinking their bodies may have helped the group that became birds to continue exploiting new ecological niches throughout their evolution.

A study that has 'weighed' hundreds of dinosaurs suggests that shrinking their bodies may have helped the group that became birds to continue exploiting new ecological niches throughout their evolution, and become hugely successful today.

An international team, led by scientists at Oxford University and the Royal Ontario Museum, estimated the body mass of 426 dinosaur species based on the thickness of their leg bones. The team found that dinosaurs showed rapid rates of body size evolution shortly after their origins, around 220 million years ago. However, these soon slowed: only the evolutionary line leading to birds continued to change size at this rate, and continued to do so for 170 million years, producing new ecological diversity not seen in other dinosaurs.

A report of the research is published in PLOS Biology.

'Dinosaurs aren't extinct; there are about 10,000 species alive today in the form of birds. We wanted to understand the evolutionary links between this exceptional living group, and their Mesozoic relatives, including well-known extinct species like T. rex, Triceratops, and Stegosaurus,' said Dr Roger Benson of Oxford University's Department of Earth Sciences, who led the study. 'We found exceptional body mass variation in the dinosaur line leading to birds, especially in the feathered dinosaurs called maniraptorans. These include Jurassic Park's Velociraptor, birds, and a huge range of other forms, weighing anything from 15 grams to 3 tonnes, and eating meat, plants, and more omnivorous diets.'

The team believes that small body size might have been key to maintaining evolutionary potential in birds, which broke the lower body size limit of around 1 kilogram seen in other dinosaurs.

'How do you weigh a dinosaur? You can do it by measuring the thickness of its leg bones, like the femur. This is quite reliable,' said Dr Nicolás Campione, of the Uppsala University, a member of the team. 'This shows that the biggest dinosaurArgentinosaurus, at 90 tonnes, was 6 million times the weight of the smallest Mesozoic dinosaur, a sparrow-sized bird called Qiliania, weighing 15 grams. Clearly, the dinosaur body plan was extremely versatile.'

The team examined rates of body size evolution on the entire family tree of dinosaurs, sampled throughout their first 160 million years on Earth. If close relatives are fairly similar in size, then evolution was probably quite slow. But if they are very different in size, then evolution must have been fast.

'What we found was striking. Dinosaur body size evolved very rapidly in early forms, likely associated with the invasion of new ecological niches. In general, rates slowed down as these lineages continued to diversify,' said Dr David Evans at the Royal Ontario Museum, who co-devised the project. 'But it's the sustained high rates of evolution in the feathered maniraptoran dinosaur lineage that led to birds -- the second great evolutionary radiation of dinosaurs.'

The evolutionary line leading to birds kept experimenting with different, often radically smaller, body sizes -- enabling new body 'designs' and adaptations to arise more rapidly than among larger dinosaurs. Other dinosaur groups failed to do this, got locked in to narrow ecological niches, and ultimately went extinct. This suggest that important living groups such as birds might result from sustained, rapid evolutionary rates over timescales of hundreds of millions of years, which could not be observed without fossils.

'The fact that dinosaurs evolved to huge sizes is iconic,' said team member Dr Matthew Carrano of the Smithsonian Institution's National Museum of Natural History. 'And yet we've understood very little about how size was related to their overall evolutionary history. This makes it clear that evolving different sizes was important to the success of dinosaurs.'

Habitat of early apes: Evidence of the environment inhabited by Proconsul

University of Rhode Island anthropologist, along with colleagues from an international team of scientists, has discovered definitive evidence of the environment inhabited by the early ape Proconsul on Rusinga Island, Kenya. The findings provide new insights into understanding and interpreting the connection between habitat preferences and the early diversification of the ape-human lineage

The early ape Proconsul (center) and the primate Dendropithecus (upper right) inhabited a warm and relatively wet, closed canopy tropical seasonal forest 18 million years ago in equatorial eastern Africa (Rusinga Island, Kenya).

Their research, which was published today in the journal Nature Communications, demonstrates thatProconsul and its primate relative Dendropithecusinhabited "a widespread, dense, multistoried, closed canopy" forest.

Holly Dunsworth, URI assistant professor of anthropology, said that the research team found fossils of a single individual of Proconsul, which lived 18 to 20 million years ago, among geological deposits that also contained tree stump casts, calcified roots and fossil leaves. The discovery underscores the importance of forested environments in the evolution of early apes.

"To have the vegetation of a habitat preserved right along with the fossil primates themselves isn't a regular occurrence in primate paleontology," she said. "It's especially rare to have so many exquisite plant fossils preserved at ancient ape sites."

Rusinga has been known since the 1980s for preserving a fossil ape and other creatures in a hollowed out, fossilized tree trunk. But it wasn't until the research team's discovery of additional tree trunks and fossil primates preserved in the same ancient soil that there was a strong link between the ape and its habitat at the site.

"It's probably the best evidence linking ape to habitat that we could ask for," Dunsworth said. "Combined with analyses of the roots, trunks and even beautifully preserved fossil leaves, it's possible to say that the forest was a closed canopy one, meaning the arboreal animals, like Proconsul, could easily move from tree-to-tree without coming to the ground. This environmental evidence jibes with our behavioral interpretations of Proconsul anatomy--as being adapted for a life of climbing in the trees--and with present-day monkey and ape ecology."

Additional evidence from the excavation site has shown that the landscape was stable for many years while the forest grew.

According to co-author Daniel Peppe of Baylor University, evidence from the forest soil suggests "the precipitation was seasonal with a distinct wet and dry period. During the dry season, there was probably relatively little rainfall," he said. "Additionally, by studying fossil leaves at the site, we were able to estimate that there was about 55 to 100 inches of rainfall a year and the average annual temperature was between 73 and 94 degrees Fahrenheit."

Research on Rusinga Island has been ongoing for more than 80 years and has resulted in the collection of thousands of mammal fossils, including many well-preserved specimens of Proconsul and other primates. Evidence from these fossils indicate that Proconsul probably had a body position somewhat similar to modern monkeys, but that details of its anatomy suggest some more ape-like climbing and clambering abilities. Since 2011, the research team's work at the fossil forest site has resulted in the collection of several additional new primate fossils.

Dunsworth said that her work at the site is continuing.

"We don't know exactly what we're going to find, but without a doubt, if we keep searching, we're going to find knowledge about early ape evolution, which was, of course, a significant chapter in our own history," she said.