Utah fossil reveals global exodus of mammals' near relatives to major continents

A nearly 130-million-year-old fossilized skull found in Utah is an Earth-shattering discovery in one respect.

The new species Cifelliodon wahkarmoosuch is estimated to have weighed 2.5 pounds and probably grew
to be about the size of a small hare [Credit: Keck School of Medicine of USC/Jorge A. Gonzalez]

The small fossil is evidence that the super-continental split likely occurred more recently than scientists previously thought and that a group of reptile-like mammals that bridge the reptile and mammal transition experienced an unsuspected burst of evolution across several continents.

"Based on the unlikely discovery of this near-complete fossil cranium, we now recognize a new, cosmopolitan group of early mammal relatives," said Adam Huttenlocker, lead author of the study and assistant professor of clinical integrative anatomical sciences at the Keck School of Medicine of USC.

The study, published in the journal Nature, updates the understanding of how mammals evolved and dispersed across major continents during the age of dinosaurs. It suggests that the divide of the ancient landmass Pangea continued for about 15 million years later than previously thought and that mammal migration and that of their close relatives continued during the Early Cretaceous (145 to 101 million years ago).

"For a long time, we thought early mammals from the Cretaceous (145 to 66 million years ago) were anatomically similar and not ecologically diverse," Huttenlocker said. "This finding by our team and others reinforce that, even before the rise of modern mammals, ancient relatives of mammals were exploring specialty niches: insectivores, herbivores, carnivores, swimmers, gliders. Basically, they were occupying a variety of niches that we see them occupy today."

The study reveals that the early mammal precursors migrated from Asia to Europe, into North America and further onto major Southern continents, said Zhe-Xi Luo, senior author of the study and a paleontologist at the University of Chicago.

Fossil find: a new species

Huttenlocker and his collaborators at the Utah Geological Survey and The University of Chicago named the new species Cifelliodon wahkarmoosuch.

The new species Cifelliodon wahkarmoosuch is estimated to have weighed 2.5 pounds and probably grew
to be about the size of a small hare [Credit: Keck School of Medicine of USC/Jorge A. Gonzalez]

Found in the Cretaceous beds in eastern Utah, the fossil is named in honor of famed paleontologist Richard Cifelli. The species name, "wahkarmoosuch" means "yellow cat" in the Ute tribe's language in respect of the area where it was found.

Scientists used high-resolution computed tomography (CT) scanners to analyze the skull.

"The skull of Cifelliodon is an extremely rare find in a vast fossil-bearing region of the Western Interior, where the more than 150 species of mammals and reptile-like mammal precursors are represented mostly by isolated teeth and jaws," said James Kirkland, study co-author in charge of the excavation and a Utah State paleontologist.

With an estimated body weight of up to 2.5 pounds, Cifelliodon would seem small compared to many living mammals, but it was a giant among its Cretaceous contemporaries. A full-grown Cifelliodon was probably about the size of a small hare or pika (small mammal with rounded ears, short limbs and a very small tail).

It had teeth similar to fruit-eating bats and could nip, shear and crush. It might have incorporated plants into its diet.

The newly named species had a relatively small brain and giant "olfactory bulbs" to process sense of smell. The skull had tiny eye sockets, so the animal probably did not have good eyesight or color vision. It possibly was nocturnal and depended on sense of smell to root out food, Huttenlocker said.

Supercontinent existed longer than previously thought

Huttenlocker and his colleagues placed Cifelliodon within a group called Haramiyida, an extinct branch of mammal ancestors related to true mammals. The fossil was the first of its particular subgroup - Hahnodontidae - found in North America.

The fossil discovery emphasizes that haramiyidans and some other vertebrate groups existed globally during the Jurassic-Cretaceous transition, meaning the corridors for migration via Pangean landmasses remained intact into the Early Cretaceous.

Most of the Jurassic and Cretaceous fossils of haramiyidans are from the Triassic and Jurassic of Europe, Greenland and Asia. Hahnodontidae was previously known only from the Cretaceous of Northern Africa. It is to this group that Huttenlocker argues Cifelliodon belongs, providing evidence of migration routes between the continents that are now separated in northern and southern hemispheres.

"But it's not just this group of haramiyidans," Huttenlocker said. "The connection we discovered mirrors others recognized as recently as this year based on similar Cretaceous dinosaur fossils found in Africa and Europe."

Source: University of Southern California [May 23, 2018]

Why birds don't have teeth

Why did birds lose their teeth? Was it so they would be lighter in the air? Or are pointy beaks better for worm-eating than the jagged jaws of dinosaur ancestors?

New research suggests that birds gave up teeth to speed up egg hatching
[Credit: Yuri Kadobinov/AFP]

Actually, birds gave up teeth to speed up egg hatching, a research paper published in Biology Letters suggests, challenging long-held scientific views on the evolution of the toothless beak.

Compared to an incubation period of several months for dinosaur eggs, modern birds hatch after just a few days or weeks.

This is because there is no need to wait for the embryo to develop teeth -- a process that can consume 60 percent of egg incubation time, said researchers Tzu-Ruei Yang and Martin Sander from the University of Bonn.

While in the egg, the embryo is vulnerable to predators and natural disasters, and faster hatching boosts survival odds.

This would be a concern for dinos and birds -- all egg layers. In mammals, embryos are protected inside the mother.

"We suggest that (evolutionary) selection for tooth loss (in birds) was a side effect of selection for fast embryo growth and thus shorter incubation," Yang and Sander wrote in the journal Biology Letters.

Previous studies had concluded that birds -- living descendants of avian dinosaurs -- lost their teeth to improve flight.

Oviraptosaurs were omnivores but had a toothless beak [Credit: University of Nagoya,
Japan/Masato Hattori/AFP] 

But this did not explain why some non-avian dinosaurs in the Mesozoic era had independently evolved similar toothless beaks, said the duo.

Other studies had concluded that beaks were better for eating bird food.

But some dinosaurs with a very different, meat-eating diet had also discarded teeth in favour of pointed beaks.

Yang and Sander said their breakthrough came from a study published last year, which found that the eggs of non-flying dinosaurs took longer to hatch than previously thought -- about three to six months.

This was because of slow dental formation, which researchers analysed by examining growth lines -- almost like tree rings -- in the fossilised teeth of two dinosaur embryos.

Faster incubation would have been aided by early birds and some dinos taking to brooding their eggs in open nests rather than burying them as of old, said the research team.

They conceded their hypothesis was not consistent with toothlessness in turtles, which still have a long incubation period.

Source: AFP [May 23, 2018]

Study casts doubt on traditional view of pterosaur flight

Most renderings and reconstructions of pterodactyls and other extinct flying reptiles show a flight pose much like that of bats, which fly with their hind limbs splayed wide apart. But a new method for inferring how ancient animals might have moved their joints suggests that pterosaurs probably couldn't strike that pose.

This is an image of a reliable reconstruction. Soft tissues like ligaments play a big role in determining a joint's range
of motion. But soft tissues rarely fossilize, causing problems for paleontologists trying to reconstruct who extinct
creatures may have lived. Now researchers have shown a new method for inferring the extent to which ligaments
inhibit joint movement, which could be helpful in reconstructing ancient species
[Credit: Armita Manafzadeh]

"Most of the work that's being done right now to understand pterosaur flight relies on the assumption that their hips could get into a bat-like pose," said Armita Manafzadeh, a Ph.D. student at Brown University who led the research with Kevin Padian of the University of California, Berkeley. "We think future studies should take into account that this pose was likely impossible, which might change our perspective when we consider the evolution of flight in pterosaurs and dinosaurs."

The research, published in Proceedings of the Royal Society B, is an effort to help paleontologists infer the range of motion of joints in a way that takes into account the soft tissues -- particularly ligaments -- that play key roles in how joints work. Generally, soft tissues don't fossilize, leaving paleontologists to infer joint motion from bones alone. And there aren't many constraints on how that's done, Manafzadeh says. So she wanted to find a way to use present-day animals to test the extent to which ligaments limit joint motion.

It's an idea that started with grocery store chickens, Manafzadeh says.

"If you pick up a raw chicken at the grocery store and move its joints, you'll reach a point where you'll hear a pop," she said. "That's the ligaments snapping. But if I handed you a chicken skeleton without the ligaments, you might think that its joints could do all kinds of crazy things. So the question is, if you were to dig up a fossil chicken, how would you think its joints could move, and how wrong would you be?"

For this latest study, she used not a grocery store chicken, but dead quail. Birds are the closest living relative of extinct pterosaurs and four-winged dinosaurs. After carefully cutting away the muscles surrounding the birds' hip joints, she manipulated the joints while taking x-ray videos. That way, she could determine the exact 3-D positions of the bones in poses where the ligaments prevented further movement.

This technique enabled Manafzadeh to map out the range of motion of the quail hip with ligaments attached, which she could then compare to the range of motion that might have been inferred from bones alone. For the bones-only poses, Manafzadeh used traditional criteria that paleontologists often use -- stopping where the two bones hit each other and when the movement pulled the thigh bone out of its socket.

She found that over 95 percent of the joint positions that seemed plausible with bones alone were actually impossible when ligaments were attached.

The next step was to work out how the range of motion of present-day quail hips might compare to the range of motion for extinct pterosaurs and four-winged dinosaurs.

The assumption has long been that these creatures flew a lot like bats do. That's partly because the wings of pterosaurs were made of skin and supported by an elongated fourth finger, which is somewhat similar to the wings of bats. Bat wings are also connected to their hind limbs, which they splay out widely during flight. Many paleontologists, Manafzadeh says, assume pterosaurs and four-winged dinosaurs did the same. But her study suggests that wasn't possible.

In quail, a bat-like hip pose seemed possible based on bones alone, but outward motion of the thigh bone was inhibited by one particular ligament -- a ligament that's present in a wide variety of birds and other reptiles related to pterosaurs. No evidence, Manafzadeh says, suggests that extinct dinosaurs and pterosaurs wouldn't have had this ligament, too.

And with that ligament attached, this new study suggests that the bat-like pose would be impossible. According to Manafzadeh's work, this pose would require the ligament to stretch 63 percent more than the quail ligament can. That's quite a stretch, she says.

"That's a huge difference that would need to be accounted for before it can be argued that a pterosaur or 'four-winged' dinosaur's hip would be able to get into this bat-like pose," Manafzadeh said. And that, she says, may require a rethinking of the evolution of flight in these animals.

In addition to calling into question traditional ideas about flight in pterosaurs and early birds, the research also provides new ways of assessing joint mobility for any joint of any extinct species by looking at its living relatives.

"What we've done is to provide a reliable way to quantify in 3-D everything a joint can do," Manafzadeh said.

She hopes other researchers will use the method to study other joint systems and to better understand how other species may have moved their joints, walked and flown.

Source: Brown University [May 22, 2018]

Genome structure of dinosaurs discovered by bird-turtle comparisons

A discovery by scientists at the University of Kent has provided significant insight into the overall genome structure of dinosaurs.

This is an Apalone spinifera spiny softshell turtle hatchling [Credit: Nicole Valenzuela]

By comparing the genomes of different species, chiefly birds and turtles, the Kent team were able to determine how the overall genome structure (i.e. the chromosomes) of many people's favourite dinosaur species - like Velociraptor or Tyrannosaurus - might have looked through a microscope.

The research was carried out in the laboratory of Professor Darren Griffin, of the University's School of Biosciences, and is now published in the journal Nature Communications. It involved extrapolating the likely genome structure of a shared common ancestor of birds and turtles that lived around 260 million years ago - 20 million years before the dinosaurs first emerged.

Dr Becky O'Connor, senior postdoctoral researcher and co-author of the paper, then traced how chromosomes changed over evolutionary time from a reptile ancestor to the present day.

The team found that, although the individual chromosomes rearranged their genes internally, this did not occur much at all between the chromosomes - what the scientists describe as 'a significant discovery'.

Birds (which are themselves living dinosaurs) have a lot of chromosomes compared to most other species and that is possibly one of the reasons why they are so diverse. This research suggests that the pattern of chromosomes (karyotype) seen in early emerging dinosaurs and later theropods is similar to that of most birds and, again, may help explain their great diversity.

The new discovery suggests that, had scientists had the opportunity to make a chromosome preparation from a theropod dinosaur, it might have looked very similar to that of a modern-day ostrich, duck or chicken.

One of the key pieces of biotechnology that made it possible was the development of a set of fluorescent probes derived from birds that worked well on the chromosomes of turtles.

Source: University of Kent [May 21, 2018]

What we inherited from our bug-eating ancestors

People who advocate adding insects to the human diet may be channeling their distant ancestors. Based on an analysis of the genomes of 107 different species of mammals, University of California, Berkeley, scientists conclude that our distant ancestors – the small, furry creatures that scurried around the feet of the dinosaurs 66 million years ago – were mostly insect eaters.

A spectral tarsier (Tarsius tarsier) feeding on a grasshopper in Tangkoko National Park, Northern Sulawesi, Indonesia
. Tarsiers have five chitinase genes to digest the high amount of chitin in their insectivorous diet, which likely
represents the ancestral condition of all placental animals, including humans
[Credit: Quentin Martinez]

The scientists inferred this because the genes for the enzymes that allowed these early ancestors of all mammals to digest insects are still hanging around in nearly all mammal genomes today. Even animals like tigers and seals that would never touch an insect have non-functional pieces of these genes sitting in their chromosomes, betraying their ancient ancestors’ diet.

“One of the coolest things is, if you look at humans, at Fido your dog, Whiskers your cat, your horse, your cow; pick any animal, generally speaking, they have remnants in their genomes of a time when mammals were small, probably insectivorous and running around when dinosaurs were still roaming Earth,” said postdoctoral fellow Christopher Emerling. “It is a signature in your genome that says, once upon a time you were not the dominant group of organisms on Earth. By looking at our genomes, we are looking at this ancestral past and a lifestyle that we don’t even live with anymore.”

The genetic evidence independently corroborates the conclusions paleontologists reached years ago based on the shapes of fossils and teeth from early mammals.

“In essence, we are looking at genomes and they are telling the same story as the fossils: that we think these animals were insectivorous and then dinosaurs went extinct. After the demise of these large carnivorous and herbivorous reptiles, mammals started changing their diets,” he said.

The finding could shed light on other roles played by these enzymes, called chitinases, which are found not only in the gut but the salivary glands, the pancreas and the lungs, where they may be involved in asthma.

Emerling and colleagues Michael Nachman, a professor of integrative biology and director of the UC Berkeley Museum of Vertebrate Zoology, and Frédéric Delsuc of the French National Center for Scientific Research (CNRS) and Université de Montpellier in France, report their findings in the journal Science Advances. Emerling currently is a PRESTIGE & Marie Curie postdoctoral fellow in Montpellier working on the ConvergeAnt project.

Breaking down insects’ exoskeletons

Many bacteria have genes that produce an enzyme that breaks down insects’ hard, outer shells, which are composed of a tough carbohydrate called chitin. It’s not surprising that humans and mice have a chitinase gene, since many humans today include insects in their diets, as do mice.

But humans actually have remnants of three other chitinase genes in their genome, though none of them are functional. Emerling showed that these gene remnants in humans aren’t unique to humans or primates, but instead can be traced to the ancestral placental mammals.

In all, he and his colleagues found five different chitinase enzyme genes by looking through the genomes of the largest group of mammals, those that have placentas that allow longer development in the womb, which excludes marsupials like opossums and egg-laying monotremes like the platypus. These placental mammals ranged from shrews and mice to elephants and whales.

Detailed artistic reconstruction of an ancestral placental mammal living during the Age of Dinosaurs 66 million
years ago, showing teeth adapted to capturing and eating insects [Credit: Carl Buell]

They found that the greater the percentage of insects in an animal’s diet, the more genes for chitinase it has.

“The only species that have five chitinases today are highly insectivorous, that is, 80 to 100 percent of their diet consists of insects. Since the earliest placental mammals likely had five chitinases, we think that this makes for a strong argument that they were highly insectivorous,” Emerling said.

As you would expect, ant and termite specialists such as aardvarks and certain armadillos have five functioning chitinase genes. But so do the insect-loving primates called tarsiers. They appear to be the only primates that have so many functional chitinase genes, Emerling said.

Dominated by dinosaurs

The story told by these chitinase genes is one of early mammals hunkering down eating insects while the big guys, the huge herbivorous dinosaurs like the brontosaurus and the big meat-eaters like T. rex gobbled up the most abundant food resources. Only 66 million years ago at the end of the Cretaceous Period, when all non-bird dinosaurs died out, were mammals able to expand into other niches, which they quickly did. The first carnivorous and herbivorous mammals, as indicated by their teeth, arose within 10 million years of the dinosaurs’ demise.

Emerling, who compares genomes to see how mammals and humans evolved, was interested in what mammal genomes could tell us about that transition from insectivory to herbivory and carnivory since the last mass extinction.

He focuses primarily on weird animals that eat insects, including anteaters and armadillos, the unrelated aardvark and the distantly related pangolin. In exploring how these animals are able to digest insects, he decided to look at chitinases, whose roles in mammals are still poorly understood. It’s not known, for example, whether the enzymes allow animals to break down chitin into its component sugars and use them for energy, or if chitinases’ sole function is to break up the exoskeleton to allow access to the soft interiors of insects.

Using databases of animal genomes, plus newly sequenced genomes of armadillos and a lesser anteater (tamandua) obtained by colleagues at the Broad Institute at MIT and Harvard, he searched for genes similar to the known chitinase gene and dredged up four new varieties.

Based on what is known about chitinase genes in bacteria and other animals, he was able to deduce which genes are functional and which are not, and draw conclusions about the tissues in which the genes are expressed and the enzyme active.

Among the surprises was that the insect-eating-specialist pangolin has only one functional chitinase gene, in contrast to the five in the aardvark and four in the lesser anteater. All eat ants and termites exclusively, but pangolins may have possibly evolved from carnivores that lost their chitinase genes shortly after taking over the ecological niche opened up when meat-eating dinosaurs died out.

Bison, gibbons and the dromedary camel have only one functional chitinase. Tigers, rhinos and polar bears have none.

Emerling has many other questions he thinks chitinases can answer about mammal evolution and physiology.

“This is suggesting that there are a lot of these enzymes that might be helping organisms digest their food. This goes from being a simple curiosity – humans have a chitinase, how cool! – to being something that can help us understand how different animals are adapted to their specialized diets.”

Source: University of California - Berkeley [May 16, 2018]

How does a one-tonne dino hatch its eggs? Carefully

Most dinosaurs buried their eggs and hoped for the best, but some species - including a few hefty ones - built nests and pampered unhatched offspring much as birds do today, researchers reported Wednesday.

Feathered carnivores called oviraptorosaurs did not sit directly on their eggs,
so as not to crush them, a new study found [Credit: AFP]

Which raises an intriguing question: How did creatures nearly as heavy as a hippo brood eggs without squashing them?

"Large species may have not sat directly on their eggs," explained Kohei Tanaka, a researcher at Nagoya University Museum and lead author of a study in Biology Letters that details the incubation strategy of feathered carnivores called oviraptorosaurs.

"Eggs are arranged in a circular pattern with a large central opening," he told AFP, describing clutches of potato-shaped eggs found in China up to half-a-metre (20 inches) long and weighing up to seven kilos (15 pounds) each.

"The dinosaurs likely sat in the middle of the nest so that they didn't crush the eggs."

That didn't keep the unborn dinos warm, but it may have protected them from predators and the elements, Tanaka speculated.

Modern birds descend from a large group of mostly carnivorous dinosaurs called theropods, all of which -- including the fearsome T-rex -- are thought to have laid eggs.

But very few theropods built nests, which is why the brooding displayed by oviraptorosaurs -- a clade of several dozen species ranging from the turkey-sized Caudipteryx to the 1.4-tonne Gigantoraptor -- is so important.

Sitting on eggshells

"The incubation behaviour of birds -- such as adults sitting in the nest and possibly brooding -- likely evolved from theropod dinosaurs," said Tanaka. "Our research provides additional evidence."

Oviraptorosaurs lived during the Cretaceous period, the 80 million years leading up to the asteroid or comet strike blamed for wiping out non-avian, terrestrial dinosaurs.

They had short snouts and beak-like jaws with few or no teeth, and some sported bony crests on their heads. Evidence of generous plumage -- especially on the tail -- has been found on several species.

Besides the spoke-like arrangement of the fossilised eggs, the eggshell itself provided further evidence that large oviraptorosaurs sat near their unborn progeny, not on top of them.

The eggs of big dinos, the researchers discovered, were more fragile than the eggs of smaller ones, which were clearly designed to carry more weight.

How big is too big to park a dino butt on top of unhatched eggs?

"That's hard to say," said Tanaka. "There is a gap in the data, but the threshold should be between 200 and 500 kilos (440 and 1,110 pounds)."

Oviraptorosaurs were falsely accused by early paleontologists of stealing the eggs so often found along side their fossil remains, giving rise to their name: "egg-thief lizards."

Author: Marlowe Hood | Source: AFP [May 16, 2018]