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]

Establishing a timescale for more than 10 million years ago

The timescale is the base to reconstruct the history of the Earth and the biological evolution. A research on a chronostratigraphic sequence of the Chinese Neogene with accurate geological datings was published online in Science China: Earth Sciences.

This is an image of the exposure of the Neogene strata in the Linxia Basin of Gansu Province
[Credit: Science China Press]

The Chinese Neogene terrestrial deposits are widely exposed. In the Linxia Basin of Gansu Province, for example, there are continuous deposits from Oligocene to Pleistocene, covering complete Neogene period and bearing rich mammalian fossils. The rapidly evolved mammalian fossils contribute efficiently to the division and correlation of Neogene strata.

A uniform Neogene biostratigraphic framework for China has already been established, with seven mammalian ages named. With a developed stratigraphic basis for the geochronologic ages, seven chronostratigraphic stage have been established for the Chinese Neogene terrestrial strata, namely the Miocene Xiejian, Shanwangian, Tunggurian, Bahean, and Baodean stages, and the Pliocene Gaozhuangian and Mazegouan stages.

This is an image of an upper jaw fossil and a reconstruction of Hipparion forstenae
[Credit: Chen Yu/Science China Press]

Based on a series of research achievements, refined biostratigraphic, paleomagnetic and isotopic methods were combined and applied to continuous sections, and a Chinese Neogene chronostratigraphic sequence with accurate geological ages was established and improved by the research team of Prof. Deng Tao at the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences in recent years.

In Eurasia, Chinese Neogene deposits are more suitable for the establishment of an accurate Neogene biostratigraphic sequence than those of Europe, since the terrestrial deposits in Europe often limited, and many important faunas are unearthed from fissure-fillings. Chinese Neogene deposits are widespread and well suited for magnetostratigraphic analysis, despite the few radiometric dates available.

This is an image of the comprehensive column section at Xiejia of the Xining Basin, Qinghai Province
[Credit: Science China Press]

The lower boundaries of most of the stages could be correlated with those of the marine stages in the International Chronostratigraphic Chart, except the Tunggurian Stage, which is correlated with the European land mammal age. The biostratigraphic markers of the Chinese Neogene stages are usually first appearance of a single taxon, some representing regional species replacement, others indicating intercontinental migration of certain taxa.

For instance, the lower boundaries of the two Upper Miocene stages, Bahean and Baodean have the first appearances of Hipparion dongxiangense and H. forstenae as biostratigraphic markers, respectively, and the geological ages of their lower boundaries are corresponding to those of the marine Tortonian (11.63 Ma) and Messinian (7.25 Ma).

The Chinese Neogene mammalian biostratigraphic divisions have become the core to establish the Asian framework. Candidate stratotype sections have been proposed for all the Chinese Neogene stages according to the principle and rule of modern stratigraphy, and other Chinese Neogene strata in different regions are comprehensively correlated.

Source: Science China Press [May 21, 2018]

Feeding habits of ancient elephants uncovered from grass fragments stuck in their teeth

A new study, published in Scientific Reports, examines the feeding habits of ancient elephant relatives that inhabited Central Asia some 17 million years ago.

Replica of a reconstructed Gomphotherium steinheimense skeleton on display at the Naturhistorisches Museum Basel
[Credit: Zhang Hanwen, University of Bristol]

Professor Wang Shiqi from IVPP, the study's senior author, said: "We found ancient elephant teeth in the Junggar Basin, in China's far North West and they belong to two species, Gomphotherium connexum, and the larger G. steinheimense."

Zhang Hanwen, from Bristol's School of Earth Sciences, added: "Gomphotherium was most obvi-ously different from modern elephants by its very long lower jaw that still had lower tusks.

"It also had a shorter, more elongate, barrel-like body shape compared to modern elephants. In essence, a small elephant with short legs."

Professor Wang explained: "Our study of their evolution shows that Gomphotherium connexum became extinct, but G. steinheimense was part of the line that eventually gave rise to the modern elephants."

To understand if feeding preference was playing a role in survival and extinction of these ele-phants, Dr Wu Yan of IVPP, the study's lead author, analysed tiny remnants of plant matter found stuck to the fossil teeth, called phytoliths.

About 30 percent of the phytoliths extracted from the teeth of G. connexum are from soft foliage, whereas another 50 percent or so comes from grasses.

Phytoliths of grass and foliage found adhered to a molar of Gomphotherium connexum (bottom-right)
from the Miocene deposits of Junggar Basin, Xinjiang, China. The bar chart from the bottom-left indicate
relative abundance of different phytolith types from Gomphotherium teeth examined in this study
 [Credit: Wu Yan, Institute of Vertebrate Paleontology and Paleoanthropology,
Chinese Academy of Sciences, Beijing]

Dr Wu said: "Given that foliage naturally produces far less phytoliths than grasses, this indicates that G. connexum was mainly feeding on foliage, maybe a generalist feeder of all kinds of plant matter.

"When I examined the phytoliths extracted from the cheek teeth of G. steinheimense, I saw a very different pattern -- grass phytoliths comprise roughly 85 percent of the total, suggesting this spe-cies was perhaps primarily a grazer 17 million years ago."

To confirm these results, the team also examined tiny wear patterns on the fossil tooth surfaces called microwear.

Zhang Hanwen added: "Now things start to get interesting. When our team analysed fossil pollen samples associated with the sediments where the Gomphotherium teeth were found, we realised that woodlands were rapidly transforming into semi-arid savannahs when the two species lived together.

"By adopting a much more grass-based diet, G. steinheimense was apparently responding better to this habitat change than G. connexum.

"Gomphotherium had primitive dentition consisting of low molar crowns, and numerous conical cusps arranged in few transverse enamel ridges on the chewing surface of the teeth.

"This was adapted for feeding on leaves, the primitive diet. But later on, the lineage leading to modern elephants and the extinct mammoths evolved an increased number of enamel ridges, and these eventually became densely packed tooth plates for shearing tough vegetation.

"Our new evidence shows that the diet switch from leaves to grass happened long before the anatomical switch in tooth shape."

Source: University of Bristol [May 17, 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]

Researchers uncover genomic info linking extinct giant ground sloth to modern species

Researchers have uncovered important genomic data from the remains of an ancient giant ground sloth, or Mylodon darwinii, the emblematic creature named after Charles Darwin, whose discovery of fossilized remains in South America is considered to be one of his significant scientific achievements.

The Mylodon cave in which the bone analyzed by researchers was collected
[Credit: Walter Ferry Dissmann]

Using a bone fragment which dates back nearly 13,000 years, scientists teased out and reconstructed DNA fragments to obtain a high-quality mitochondrial genome and nuclear genomic information. The analysis, they say, proves for the first time that the giant ground sloth--which went extinct approximately 10,000 years ago--is a close relative of the modern two-fingered sloth, believed to be one of the world's slowest mammals.

The research, published online in the Proceedings of the Royal Society B, suggests the two species diverged from one another approximately 22 million years ago. The much smaller, modern sloth evolved over time to inhabit trees, where it spends virtually its entire life suspended upside down.

"Our study confirms the convergent evolution of the two, tree dwelling modern sloths from two distinct lineages of extinct giant ground sloths," says Hendrik Poinar, a lead author of the study and director of the McMaster Ancient DNA Centre and principal investigator at the Michael G. DeGroote Institute for Infectious Disease Research. "This means tree-living evolved independently, twice, which is remarkable."

Scientists say the sample was exceptionally well-preserved. It was taken from the famous Mylodon Cave in Chile, which derives its name from the numerous remains of ground sloths found inside. The constant cold and dry conditions of the cave have preserved a scientific treasure trove including bones, claws, feces and even large pieces of mummified skin still covered with blond fur.

"The incredible conservation of the bone sample we used in this study offers promising prospects for sequencing the full genome of this extinct species because of the high percentage of DNA that it contains," says Frédéric Delsuc, co-author of the paper and Director of Research at the Centre National de Recherche, France.

"This will certainly generate more insights and information into their unique features and ultimate extinction," he says.

These remains found within the exceptional site of Mylodon Cave, in Patagonia, Chile, were the first non-human samples used by scientists in early genetic tests which yielded genuine ancient DNA.

Advances in sequencing technology have led to a deeper understanding of ancient and extinct species, including the Columbian and woolly mammoths, giant lemurs and steppe bison.

Source: McMaster University [May 15, 2018]

Ancient skull shows early 'baleen whale' had teeth

Today's baleen whales (Mysticetes) support their massive bodies by filtering huge volumes of small prey from seawater using comb-like baleen in their mouths much like a sieve. But new evidence reported in the journal Current Biology based on careful analysis of a 34-million-year-old whale skull from Antarctica--the second-oldest "baleen" whale ever found--suggests that early whales actually didn't have baleen at all. Their mouths were equipped instead with well-developed gums and teeth, which they apparently used to bite large prey.

Life-like reconstruction of Llanocetus denticrenatus, an ancient 'baleen' whale
[Credit: Carl Buell]

"Llanocetus denticrenatus is an ancient relative of our modern gentle giants, like humpback and blue whales," says Felix Marx of the Royal Belgian Institute of Natural Sciences. "Unlike them, however, it had teeth, and probably was a formidable predator."

"Until recently, it was thought that filter feeding first emerged when whales still had teeth," adds R. Ewan Fordyce at the University of Otago in New Zealand. "Llanocetus shows that this was not the case."

Like modern whales, Llanocetus had distinctive grooves on the roof of its mouth, the researchers explain, which usually contain blood vessels that supply the baleen. In Llanocetus, however, those grooves cluster around tooth sockets, where baleen would have been useless and at risk of being crushed.

"Instead of a filter, it seems that Llanocetus simply had large gums and, judging from the way its teeth are worn, mainly fed by biting large prey," Marx says. "Even so, it was huge: at a total body length of around 8 meters, it rivals some living whales in size."

The findings suggest that large gums in whales like Llanocetus gradually became more complex over evolutionary time and, ultimately, gave rise to baleen. That transition probably happened only after the teeth had already been lost and whales had switched from biting to sucking in small prey--as many whales and dolphins now do. Marx and Fordyce suggest that baleen most likely arose as a way to keep such small prey inside the mouth more effectively.

Soft tissues, including baleen, normally rot away, making it difficult to study their evolution. As a result, researchers must rely on indicators preserved on the bones, such as tell-tale grooves or lumps indicating the position of a muscle, or holes for the passage of particular blood vessels and nerves.

"Llanocetus presents a lucky combination, where the shape of the bones, small features suggesting the course of soft tissues, and tooth wear all combine to tell a clear story," Fordyce says. "Crucially, Llanocetus is also extremely old and lived at the very time when Mysticetes first appeared. As such, it provides a rare window into the earliest phase of their evolution."

In the new study, Fordyce and Marx found that the broad rostrum of Llanocetus had sharp, widely spaced teeth with marked tooth wear suggesting that they were used to bite and shear prey. As in living Mysticetes, the palate bears many grooves, which have commonly been interpreted as evidence for baleen. However, the researchers showed that those grooves instead converged on the bony tooth sockets, suggesting a peri-dental blood supply to well-developed gums, rather than racks of baleen.

The findings show that the evolution of filter feeding wasn't as straightforward as previously thought, the researchers say. They'd now like to sort out when filter feeding and baleen first evolved.

"The giants of our modern ocean may be gentle, but their ancestors were anything but," Marx says. "Llanocetus was both large and a ferocious predator and probably had little in common with how modern whales behave."

Source: Cell Press [May 10, 2018]