No teeth? No problem: Dinosaur species had teeth as babies, lost them as they grew

Researchers have discovered that a species of dinosaur, Limusaurus inextricabilis, lost its teeth in adolescence and did not grow another set as adults. The finding, published today in Current Biology, is a radical change in anatomy during a lifespan and may help to explain why birds have beaks but no teeth.

The research team studied 19 Limusaurus skeletons, discovered in “death traps,” where they became mired in mud, got stuck and died, in the Xinjiang Province of China. The dinosaurs ranged in age from baby to adult, showing the pattern of tooth loss over time. The baby skeleton had small, sharp teeth, and the adult skeletons were consistently toothless.

“This discovery is important for two reasons,” said James Clark, a co-author on the paper and the Ronald Weintraub Professor of Biology at the George Washington University’s Columbian College of Arts and Sciences. “First, it’s very rare to find a growth series from baby to adult dinosaurs. Second, this unusually dramatic change in anatomy suggests there was a big shift in Limusaurus’ diet from adolescence to adulthood.”

Limusaurus is part of the theropod group of dinosaurs, the evolutionary ancestors of birds. Dr. Clark’s team’s earlier research of Limusaurus described the species’ hand development and notes that the dinosaur’s reduced first finger may have been transitional and that later theropods lost the first and fifth fingers. Similarly, bird hands consist of the equivalent of a human’s second, third and fourth fingers.

These fossils indicate that baby Limusaurus could have been carnivores or omnivores while the adults were herbivores, as they would have needed teeth to chew meat but not plants. Chemical makeup in the fossils’ bones supports the theory of a change in diet between babies and adults. The fossils also could help to show how theropods such as birds lost their teeth, initially through changes during their development from babies to adults.

“For most dinosaur species we have few specimens and a very incomplete understanding of their developmental biology,” said Josef Stiegler, a graduate student at George Washington University and co-author. “The large sample size of Limusaurus allowed us to use several lines of evidence including the morphology, microstructure and stable isotopic composition of the fossil bones to understand developmental and dietary changes in this animal.”

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New prehistoric bird species discovered

A team of geologists at the University of Rochester has discovered a new species of bird in the Canadian Arctic. At approximately 90 million years old, the bird fossils are among the oldest avian records found in the northernmost latitude, and offer further evidence of an intense warming event during the late Cretaceous period.

“The bird would have been a cross between a large seagull and a diving bird like a cormorant, but likely had teeth,” says John Tarduno, professor and chair of the Department of Earth and Environmental Sciences at the University and leader of the expedition.

Tarduno and his team, which included both undergraduate and graduate students, named the bird Tingmiatornis arctica; “Tingmiat” means “those that fly” in the Inuktitut language spoken in the central and eastern Canadian Arctic (Nunavut territory).

Their findings, published in Scientific Reports, add to previous fossil records Tarduno uncovered from the same geological time period and location in previous expeditions. Taken together, these fossils paint a clearer picture of an ecosystem that would have existed in the Canadian Arctic during the Cretaceous period’s Turonian age, which lasted from approximately 93.9 to 89.8 million years ago.

“These fossils allow us to flesh out the community and add to our understanding of the community’s composition and how it differed from other places in the world,” says Donald Brinkman, vertebrate paleontologist and director of preservation and research at the Royal Tyrrell Museum in Alberta, Canada.

Building historic climate records further helps scientists determine the effects of climate on various communities, ecosystems, and the distribution of species and could help predict the effects of future climatic events.

“Before our fossil, people were suggesting that it was warm, but you still would have had seasonal ice,” Tarduno says. “We’re suggesting that’s not even the case, and that it’s one of these hyper-warm intervals because the bird’s food sources and the whole part of the ecosystem could not have survived in ice.”

From the fossil and sediment records, Tarduno and his team were able to conjecture that the bird’s environment in the Canadian Arctic during the Turonian age would have been characterized by volcanic activity, a calm freshwater bay, temperatures comparable to those in northern Florida today, and creatures such as turtles, large freshwater fish, and champsosaurs — now-extinct, crocodile-like reptiles.

“The fossils tell us what that world could look like, a world without ice at the arctic,” says Richard Bono, a PhD candidate in earth and environmental sciences at the University and a member of Tarduno’s expedition. “It would have looked very different than today where you have tundra and fewer animals.”

The Tingmiatornis arctica fossils were found above basalt lava fields, created from a series of volcanic eruptions. Scientists believe volcanoes pumped carbon dioxide into Earth’s atmosphere, causing a greenhouse effect and a period of extraordinary polar heat. This created an ecosystem allowing large birds, including Tingmiatornis arctica, to thrive.

Tarduno’s team unearthed three bird bones: part of the ulna and portions of the humerus, which, in birds, are located in the wings. From the bone features, as well as its thickness and proportions, the team’s paleontologist, Julia Clarke of the University of Texas, was able to determine the evolutionary relationships of the new birds as well as characteristics that indicate whether it likely was able to fly or dive.

“These birds are comparatively close cousins of all living birds and they comprise some of the oldest records of fossil birds from North America,” Clarke says. “Details of the upper arm bones tell us about how features of the flightstroke seen in living species came to be.”

Previous fossil discoveries indicate the presence of carnivorous fish such as the 0.3-0.6 meter-long bowfin. Birds feeding on these fish would need to be larger-sized and have teeth, offering additional clues to Tingmiatornis arctica’s characteristics.

Physiological factors, such as a rapid growth and maturation rate, might explain how this line of bird was able to survive the Cretaceous-Paleogene mass extinction event that occurred approximately 66 million years ago and eliminated approximately three-quarters of the plant and animal species on Earth.

These physiological characteristics are still conjecture, Tarduno emphasizes, but he says the bird’s environment gives clear indications as to why the bird fossils were found in this location.

“It’s there because everything is right,” Tarduno says. “The food supply was there, there was a freshwater environment, and the climate became so warm that all of the background ecological factors were established to make it a great place.”

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Journal Reference:

Richard K. Bono, Julia Clarke, John A. Tarduno, Donald Brinkman. A Large Ornithurine Bird (Tingmiatornis arctica) from the Turonian High Arctic: Climatic and Evolutionary Implications. Scientific Reports, 2016; 6: 38876 DOI: 10.1038/srep38876

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University of Rochester. “New prehistoric bird species discovered.” ScienceDaily. ScienceDaily, 19 December 2016. .

Fossilized water fleas: Evolution of the micro-crustacean group Cladocera

Scientists of the Senckenberg Institute have studied the evolutionary history of the so-called “water fleas.” These tiny crustaceans from the order Cladocera form the basis of the trophic pyramid and therefore play an important role in modern ecosystems. Due to the fact that they are rarely preserved as fossils, little is known about the water fleas’ evolution. In their study, which was recently published in the scientific journal “Earth-Science Reviews,” the team of scientists presents the first comprehensive inventory of all Cladocera fossils in an ecological context. The scientists show that the animals’ morphology has undergone very little change over the course of geological history. Nevertheless, the water fleas demonstrate a high adaptability to changes in environmental conditions.

A search for organisms in any lake or puddle will very likely turn up a representative of the Cladocera. With more than 700 species, these tiny animals — commonly referred to as “water fleas” due to their bouncing locomotion — inhabit almost all types of freshwater environments. “Despite this wealth of species and habitats, little is known about the evolutionary history of the Cladocera,” explains Dr. Kay Van Damme of the Senckenberg Research Institute in Frankfurt, and he continues, “Since the animals do not possess a calcareous shell or carapace, they are only rarely preserved as fossils.”

For the first time, Van Damme and his colleague, Prof. Alexey A. Kotov of the A.N. Severtsov Institute of Ecology and Evolution in Moscow, have now compiled a complete inventory of all known Cladocera species. “The Cladocera constitute a crucial group in our effort to understand the development of freshwater ecosystems throughout geological history,” says Van Damme in explanation of the team’s motivation. Even today, water fleas still form the basis of many food chains, which makes them an important component of aquatic ecosystems.

Moreover, the tiny crustaceans are very sensitive to environmental changes and can thus be used to monitor water quality — for years, the genus Daphnia has served as a model organism in this regard. “In addition, Daphnia is the first representative of the crustaceans whose genome has been published — therefore, water fleas play a similar role in aquatic environmental genomics as does the fruit fly Drosophila in terrestrial environments,” adds Van Damme.

According to the team of researchers, the first representatives of the water fleas appeared in the early Jurassic, about 180 million years ago. “Since then, the basic design of the Cladocera has hardly changed,” says the biologist from Frankfurt, and he continues, “Nevertheless, this ‘living fossil’ was able to adapt very well to a variety of different environmental conditions.” For example, the water fleas developed various defense mechanisms to escape predators. “Daphnia and company were even able to survive the massive extinction event at the Cretaceous/Tertiary boundary, which, among others, claimed all of the terrestrial dinosaurs,” says Van Damme in closing.

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Mammals in age of dinosaurs packed powerful bite

Move over, hyenas and saber-toothed cats; there’s a mammal with an even stronger bite. A new study by Burke Museum and University of Washington paleontologists describes an early marsupial relative called Didelphodon vorax that lived alongside ferocious dinosaurs and had, pound-for-pound, the strongest bite force of any mammal ever recorded.

Published in the journal Nature Communications, the team’s findings suggest mammals were more varied during the Age of Dinosaurs than previously believed. Didelphodon was able to eat a variety of foods, and was likely a scavenger-predator who could eat prey ranging from snails to small dinosaurs.

In addition, the team re-traced the origins of marsupials. Previous theories attribute South America as the origin of marsupials, but anatomical features of the Didelphodon point to marsupials originating in North America 10-20 million years earlier than originally thought, and later dispersing and diversifying in South America.

“What I love about Didelphodon vorax is that it crushes the classic mold of Mesozoic mammals,” Dr. Gregory P. Wilson, Burke Museum Adjunct Curator of Vertebrate Paleontology and University of Washington Associate Professor of Biology, said. “Instead of a shrew-like mammal meekly scurrying into the shadows of dinosaurs, this badger-sized mammal would’ve been a fearsome predator on the Late Cretaceous landscape — even for some dinosaurs.”

All of these findings are made possible by four fossil specimens recently discovered in the 69-66 million-year-old deposits of the Hell Creek Formation in Montana and North Dakota. Prior to these discoveries, the 60 known species of metatherians (marsupials and their closest relatives) from the Cretaceous of North America — including Didelphodon — were almost all identified through fragments of jaw bones or teeth, providing a limited glimpse into marsupials’ closest relatives. These four fossils include a nearly-complete skull from the North Dakota Geological Survey State Fossil collection, a partial snout and an upper jaw bone from the Burke Museum’s collections, and another upper jaw from the Sierra College Natural History Museum.

By analyzing never-before-seen parts of Didelphodon’s anatomy, Dr. Wilson and his colleagues were able to determine these marsupial relatives were about the size of today’s Virginia opossum and were the largest metatherian from the Cretaceous. With a nearly complete skull to measure, they were able to estimate the overall size of Didelphodon, which ranged from 5.3-11.5 pounds. To test the bite force of Didelphodon, Abby Vander Linden, a UW Biology research technician in Burke Museum Curator of Mammalogy Dr. Sharlene Santana’s lab and now a graduate student at University of Massachusetts Amherst, CT-scanned the fossils and compared the gaps in reconstructed skulls where jaw muscles would go to present-day mammals with known bite forces. Bite force measurements indicate that pound-for-pound, Didelphodon had the strongest bite force of any mammal that has ever lived. In addition to the bite force, Didelphodon’s canines were similar to living felines and hyenas — suggesting they could handle biting into bone, biting deep and killing prey. Its shearing molars and big rounded premolars, combined with powerful jaws and jaw muscles indicate it had a specific niche in the food web as a predator or scavenger capable of crushing hard bone or shells, and was capable of eating prey as big as it was — even possibly small dinosaurs.

“I expected Didelphodon to have a fairly powerful bite based on the robust skull and teeth, but even I was surprised when we performed the calculations and found that, when adjusted for body size, it was capable of a stronger pound-for-pound bite than a hyena,” Vander Linden said. “That’s a seriously tough mammal.”

Co-author Dr. Jonathan Calede, former UW Biology graduate student and now a visiting assistant professor at Bucknell University, also examined “microwear” patterns, or tiny pits and scratches on the specimens’ teeth, to indicate what the animals were eating as their “last suppers” (most likely one-to-two days before the animals died). By comparing the microwear patterns from Didelphodon to the teeth of other fossilized species and current-day mammals with known diets from the Burke’s mammal collection, Calede found Didelphodon was an omnivore that likely consumed a range of vertebrates, plants and hard-shelled invertebrates like molluscs and crayfish, but few insects, spiders and annelids (earthworms and leeches).

“The interesting thing about these fossils is that they allowed us to study the ecology of Didelphodon from many angles,” Calede said. “The strength of the conclusions come from the convergence of microwear with bite force analysis, studies of the shape and breakage of the teeth, as well as the shape of the skull as a whole.”

In addition to learning much more about the biology of Didelphodon, the newly-described skull features on these fossils provide clues that help clarify the origin of all marsupials. The team found five major lineages of marsupial ancestors and marsupials themselves diverged in North America 100-85 million years ago. Marsupial relatives also got larger and ate a wider variety of foods, coinciding with an increase in diversity of other early mammals and flowering plants. Most of this North American diversity was then lost gradually from the late Campanian to Maastrichtian (79-66 million-years-ago) and then abruptly during the Cretaceous-Palaeogene (66 million-years-ago) mass extinction that also killed all dinosaurs except birds. Around this time, marsupials’ diversity and evolution shifted to South America.

“Our study highlights how, despite decades of paleontology research, new fossil discoveries and new ways of analyzing those fossils can still fundamentally impact how we view something as central to us as the evolution of our own clade, mammals,” Dr. Wilson said.

Amber specimen offers rare glimpse of feathered dinosaur tail

Researchers from China, Canada, and the University of Bristol have discovered a dinosaur tail complete with its feathers trapped in a piece of amber.

The finding reported today in Current Biology helps to fill in details of the dinosaurs’ feather structure and evolution, which can’t be surmised from fossil evidence.

While the feathers aren’t the first to be found in amber, earlier specimens have been difficult to definitively link to their source animal, the researchers say.

Ryan McKellar, from the Royal Saskatchewan Museum in Canada, said: “The new material preserves a tail consisting of eight vertebrae from a juvenile; these are surrounded by feathers that are preserved in 3D and with microscopic detail.

“We can be sure of the source because the vertebrae are not fused into a rod or pygostyle as in modern birds and their closest relatives. Instead, the tail is long and flexible, with keels of feathers running down each side. In other words, the feathers definitely are those of a dinosaur not a prehistoric bird.”

The study’s first author Lida Xing from the China University of Geosciences in Beijing discovered the remarkable specimen at an amber market in Myitkyina, Myanmar in 2015.

The amber piece was originally seen as some kind of plant inclusion and destined to become a curiosity or piece of jewellery, but Xing recognized its potential scientific importance and suggested the Dexu Institute of Palaeontology buy the specimen.

The researchers say the specimen represents the feathered tail of a theropod preserved in mid-Cretaceous amber about 99 million years ago. While it was initially difficult to make out details of the amber inclusion, Xing and his colleagues relied on CT scanning and microscopic observations to get a closer look.

The feathers suggest the tail had a chestnut-brown upper surface and a pale or white underside. The specimen also offers insight into feather evolution. The feathers lack a well-developed central shaft or rachis. Their structure suggests that the two finest tiers of branching in modern feathers, known as barbs and barbules, arose before a rachis formed.

Professor Mike Benton from the School of Earth Sciences at the University of Bristol, added: “It’s amazing to see all the details of a dinosaur tail — the bones, flesh, skin, and feathers — and to imagine how this little fellow got his tail caught in the resin, and then presumably died because he could not wrestle free.

“There’s no thought that dinosaurs could shed their tails, as some lizards do today.”

The researchers also examined the chemistry of the tail inclusion where it was exposed at the surface of the amber. The analysis shows that the soft tissue layer around the bones retained traces of ferrous iron, a relic left over from haemoglobin that was also trapped in the sample.

The findings show the value of amber as a supplement to the fossil record. Ryan McKellar added: “Amber pieces preserve tiny snapshots of ancient ecosystems, but they record microscopic details, three-dimensional arrangements, and labile tissues that are difficult to study in other settings.

“This is a new source of information that is worth researching with intensity, and protecting as a fossil resource.”

The researchers say they are now “eager to see how additional finds from this region will reshape our understanding of plumage and soft tissues in dinosaurs and other vertebrates.”