Millions of years ago, the deep ocean was largely devoid of oxygen and thus inhospitable to many lifeforms. Now, the same dark zones host an array of marine mammals and fish. Researchers once speculated that this habitat expansion followed a great oxygenation event more than 500 million years ago, but they didn’t have enough data to support the link.

New research shows that deep-ocean oxygenation did support animal evolution, but it didn’t occur until 390 million years ago, when plants began to take root above ground. The accumulation of woody biomass altered atmospheric conditions enough to influence aquatic oxygen levels. The research draws a clear connection between oxygenation of the ocean and the evolution of most modern vertebrates.

in Proceedings of the National Academy of Sciences on Aug. 25.

“When oxygen levels rose, animals grew larger and moved to places that were previously uninhabitable,” said lead author , a 91̽�� doctoral student in Earth and space science. “This meant more room, and more competition. Animals evolved different strategies to survive, which led to new species.”

The first animals appeared in the fossil record during an era called the Neoproterozoic, leading researchers to postulate that this was also when ocean oxygenation occurred. Recent studies indicated that permanent ocean oxygenation instead occurred later, but still left “a 60-million-year window of uncertainty,” Bubphamanee said. “The Neoproterozoic Oxygenation Event temporarily oxygenated the deep ocean, but not long enough to allow for permanent colonization.”

According to research, ocean oxygenation was a gradual process. Shallow areas near the shore were oxygenated first, and inhabited by breathing species. As oxygen permeated deeper and deeper, ocean-dwellers followed, leading to a rapid expansion of jawed vertebrates, or gnathostomes.

“This study gives a strong indication that oxygen dictated the timing of early animal evolution, at least for the appearance of jawed vertebrates in deep-ocean habitats,” said co-lead author , an assistant professor of Earth and climate sciences at Duke University, who began this research as a doctoral scholar at UW.

In this study, the researchers started putting together a global timeline for ocean oxygenation, using 97 sedimentary rock samples from five continents collected between 252 and 541 million years ago.

They pulverized the rocks and extracted selenium, an element that indicates whether there was enough oxygen underwater to support breathing animals. Selenium is an element with several isotopes of distinct mass. Different isotope ratios develop depending on the oxygen level present when the sediment was deposited.

The ratio of selenium isotopes in the samples indicated whether there was enough oxygen present in the deep sea to sustain animal life. In the older samples, collected before 390 million years ago, there wasn’t, but in those collected later, there was.

“Selenium is great for tracking deep-ocean oxygen levels, but extracting it from rocks is tricky, so few researchers have done it,” Bubphamanee said. Compiling the existing dataset took the team more than five years.

The rock samples were collected from areas near the edges of continental shelves, where shallow seas give way to deep, open ocean. Their data supported the hypothesis that permanent deep-ocean oxygenation didn’t occur until 382 to 393 million years ago, during the Middle Devonian period.

At the same time, woody plants were spreading above ground and trapping carbon-rich biomass, such as animal remains, in the sediment. This released oxygen back into the atmosphere and fed phosphorus — a sort of organic fertilizer — into the ocean. The water, now oxygen and nutrient rich, could support more energy-intensive life than before.

“Oxygen enables more metabolically active lifestyles,” Kipp said. “Predation consumes calories, and animals burn calories using oxygen. Until the deep ocean had ample dissolved oxygen, it would not have been viable to live there as a large predator.”

The findings also reveal just how critical oxygen levels are to marine life. Although there is abundant oxygen in the atmosphere now, certain human activities can impact how much oxygen is present in the ocean.

“Runoff from agricultural and industrial activity contains chemicals that fuel plankton blooms that suck up oxygen when they decay, causing levels to plummet,” Kipp said. “This work shows very clearly the link between oxygen and animal life in the ocean. This was a balance struck about 400 million years ago, and it would be a shame to disrupt it today in a matter of decades.”

Co-authors include , a 91̽��professor in Earth and space science and astrobiology; a 91̽��graduate student in Earth and space science; , a reader in Earth and environmental sciences at the University of St. Andrews; , a professor in Earth and environmental science at Syracuse University; , an associate professor of geology at SUNY New Paltz; , a professor of geology at the University of Cincinnati; , a professor in the Research School of Earth Sciences at Australian National University; , an associate professor of geobiology at the University of Copenhagen; , a postdoctoral candidate at Australian National University; and , a professor of geochemistry at CalTech.

This research was funded by the National Science Foundation, the Agouron Institute and the NASA Astrobiology Institute Virtual Planetary Laboratory.

For more information, contact Bubphamanee at kubu7847@uw.edu or Kipp at michael.kipp@duke.edu.

Adapted from .

They don’t know it, but changed the world. These closely related species — native to the Galapagos Islands — each sport a uniquely shaped beak that matches their preferred diet. Studying these birds helped Charles Darwin develop the theory of evolution by natural selection.

A group of bats has a similar — and more expansive — evolutionary story to tell. There are more than 200 species of noctilionoid bats, mostly in the American tropics. And despite being close relatives, their jaws evolved in wildly divergent shapes and sizes to exploit different food sources. A published Aug. 22 in Nature Communications shows those adaptations include dramatic, but also consistent, modifications to tooth number, size, shape and position. For example, bats with short snouts lack certain teeth, presumably due to a lack of space. Species with longer jaws have room for more teeth — and, like humans, their total tooth complement is closer to what the ancestor of placental mammals had.

According to the research team behind this study, comparing noctilionoid species can reveal a lot about how mammalian faces evolved and developed, particularly jaws and teeth. And as a bonus, they can also answer some outstanding questions about how our own pearly whites form and grow.

“Bats have all four types of teeth — incisors, canines, premolars and molars — just like we do,” said co-author , a 91̽�� professor of biology and curator of mammals at the . “And noctilionoid bats evolved a huge diversity of diets in as little as 25 million years, which is a very short amount of time for these adaptations to occur.”

“There are noctilionoid species that have short faces like bulldogs with powerful jaws that can bite the tough exterior of the fruits that they eat. Other species have long snouts to help them drink nectar from flowers. How did this diversity evolve so quickly? What had to change in their jaws and teeth to make this possible?” said lead author , an incoming faculty member at the Institute of Evolutionary Science of Montpellier in France, who began this project as a postdoctoral researcher at the University California, Los Angeles.

Scientists don’t know what triggered this frenzy of dietary adaptation in noctilionoid bats. But today different noctilionoid species feast on insects, fruit, nectar, fish and even blood — since this group also includes the infamous vampire bats.

The team used CT scans and other methods to analyze the shapes and sizes of jaws, premolars and molars in more than 100 noctilionoid species. The bats included both museum specimens and a limited number of wild bats captured for study purposes. The researchers compared the relative sizes of teeth and other cranial features among species with different types of diets, and used mathematical modeling to determine how those differences are generated during development.

The team found that, in noctilionoid bats, certain “developmental rules” caused them to generate the right assortment of teeth to fit in their diet-formed grins. For example, bats with long jaws — like nectar-feeders — or intermediate jaws, like many insect-eaters, tended to have the usual complement of three premolars and three molars on each side of the jaw. But bats with short jaws, including most fruit-eating bats, tended to ditch the middle premolar or the back molar, if not both.

“When you have more space, you can have more teeth,” said Sadier. “But for bats with a shorter space, even though they have a more powerful bite, you simply run out of room for all these teeth.”

Having a shorter jaw may also explain why many short-faced bats also tended to have wider front molars.

“The first teeth to appear tend to grow bigger since there is not enough space for the next ones to emerge,” said Sadier.

“This project is giving us the opportunity to actually test some of the assumptions that have been made about how tooth growth, shape and size are regulated in mammals,” said Santana. “We know surprisingly little about how these very important structures develop!”

Many studies about mammalian tooth development were done in mice, which have only molars and heavily modified incisors. Scientists are not entirely sure if the genes and developmental patterns that control tooth development in mice also operate in mammals with more “ancestral” sets of chompers — like bats and humans.

Sadier, Santana and their colleagues believe their project, which is ongoing, can start to answer these questions in bats — along with many other outstanding questions about how evolution shapes mammalian features. They’re expanding this study to include noctilionoid incisors and canines, and hope to uncover more of the genetic and developmental mechanisms that control tooth development in this diverse group of bats.

“We see such strong selective pressures in these bats: Shapes have to closely match their function,” said Santana. “I think there are many more evolutionary secrets hidden in these species.”

Co-authors are Neal Anthwal, a research associate at King’s College London; Andrew Krause, an assistant professor at the Durham University in the U.K.; Renaud Dessalles, a mathematician with Green Shield Technology; Robert Haase, a researcher at the Dresden University of Technology in Germany; UCLA research scientists Michael Lake, Laurent Bentolila and Natalie Nieves; and Karen Sears, a professor at UCLA. The research is funded by the National Science Foundation.

For more information, contact Santana at ssantana@uw.edu and Sadier at alexa.sadier@gmail.com.

published April 14 in the journal Science paint a new picture about apes, ancient Africa and the origins of humans. Many scientists had once hypothesized that the first apes to evolve in Africa more than 20 million years ago ate primarily fruit and lived within the thick, closed canopy of a nearly continent-wide forest ecosystem. Instead, the new research indicates that early apes ate a leafy diet in a more arid ecosystem of varyingly open woodlands with abundant grasses.

The findings by an international team of paleontologists, primate experts and plant scientists — including paleobotanists at the 91̽�� — push the origin of tropical ecosystems dominated by C₄ grasses back by more than 10 million years. In doing so, they link the emergence of C₄ grasses — named for the type of photosynthesis they employ to make food from the sun’s energy — to the emergence of the forerunners to all apes living today. That includes the most abundant ape in history: humans.

Previously, many researchers argued that during the early Miocene, between about 15 and 20 million years ago, equatorial Africa was covered by a semi-continuous forest. Under that hypothesis, more open habitats with C₄ grasses didn’t proliferate until about 8 to 10 million years ago. Yet one study showed some evidence of C₄ grasses in East Africa around 15 million years ago. The research team wanted to understand if that study was an anomaly or a clue to the true diversity of ecosystems at that time.

“The history of grassland ecosystems in Africa prior to 10 million years had remained a mystery, in part because there were so few plant fossils,” said co-author , the Estella B. Leopold Professor of Biology at the UW.

The international collaboration — funded largely by the National Science Foundation — drew together multiple different lines of evidence to try to reconstruct the species that dominated East Africa in the early Miocene. Researchers incorporated analyses of fossil soils, animal fossils, stable isotopes and phytoliths, which are plant silica microfossils.

Strömberg, who is an expert in phytoliths, worked with co-authors Alice Novello, a former 91̽��postdoctoral scientist who is currently working at Aix-Marseille University in France, and of the National Museums of Kenya and the Max Planck Institute of Geoanthropology in Germany to reconstruct what types of plants were present at several sites in East Africa during the early Miocene.

“Phytoliths are particularly informative for revealing the history of grassland ecosystems. They can tell us not just that there were grasses, but which grasses were there and how abundant they were on the landscape,” said Strömberg, who is also curator of paleobotany at the UW’s .

Their data, combined with other lines of evidence, essentially disproved the theory that equatorial Africa in the early Miocene was heavily forested. The findings have important implications for understanding the features and adaptations of early apes.

“Multiple lines of evidence show that C₄ grasses and open habitats were important parts of the early Miocene landscape and that early apes lived in a wide variety of habitats, ranging from closed canopy forests to open habitats like scrublands and wooded grasslands with C₄ grasses,” said co-author , an associate professor of geosciences at Baylor University. “It really changes our understanding of what ecosystems looked like when the modern African plant and animal community was evolving.”

“What we found was thrilling, and very different from what was the accepted story,” said Strömberg. “We used to think tropical, C₄ dominated grasslands only appeared in the last 8 million years or so, depending on the continent. Instead, both phytolith data and isotopic data showed that C₄ dominated grassy environments appeared over 10 million years earlier, in the early Miocene in eastern Africa.”

In addition to its findings about C₄ grassy habitats, the team is also reporting discoveries about a 21-million-year-old fossil ape, Morotopithecus. Anthropologists long thought that our ape ancestors evolved an upright torso in order to pick fruit in forests. With an upright posture, an ape can more easily grab onto different branches with its hands and feet. Morotopithecus definitely had an upright stature. Paleontologists on the team performed careful analyses of the shape of its molars, as well as the chemical composition of its dental enamel, to determine its diet.

“The expectation was: We have this ape with an upright back. It must be living in forests and it must be eating fruit,” said co-author , a professor of anthropology at the University of Michigan. “But as more and more bits of information became available, the first surprising thing we found was that the ape was eating leaves. The second surprise was that it was living in woodlands.”

Together, the evidence showed that Morotopithecus lived in a seasonal woodland with a broken canopy composed of trees and shrubs and open, grassy areas. In addition, the team’s plant and climate reconstruction efforts determined that, for at least part of the year, Morotopithecus had to rely on leaves and other plant material — instead of fruit — for food.

The fact that abundant C₄ grass and woodland ecosystems arose much earlier than once thought also upends another view of human origins: That our bipedalism evolved as a response to the emergence of grassland environments in Africa between 10 and 7 million years ago.

“Now that we’ve shown that such environments were present at least 10 million years before bipedalism evolved, we need to really rethink human origins, too,” said MacLatchy.

In addition to MacLatchy, Strömberg, Kinyanjui and Peppe, other lead researchers on the collaboration behind these discoveries include co-authors , associate professor of anthropology and archaeology at the University of Calgary; , a professor of anthropology at the University of Minnesota; , professor of Earth and environmental sciences at the University of Minnesota; and , an associate professor of anthropology at the University of Michigan. Many members of the team participated through the Research on East African Catarrhine and Hominoid Evolution — or — Project. Strömberg and Novello initially participated through separate funding from the European Union to study the evolution of grasslands in East Africa.

For more information, contact Strömberg at caestrom@uw.edu.

Adapted from press releases by the and .

White-necked jacobin hummingbirds sport a colorful blue-and-white plumage as juveniles. When they grow into adulthood, males retain this dazzling pattern, while females develop a more “muted” palette of green and white — at least, most females. Curiously, about 20% of females defy the norm and retain male-like plumage into adulthood.

“Why do some female jacobins look like males? It’s a mystery made up of multiple pieces,” said , a postdoctoral researcher at the 91̽��. “Is there a benefit? Is there a cost? Is it just appearance, or do these females also act like males?”

Now those pieces are falling into place. In research Sept. 7 in the Proceedings of the Royal Society B, Falk and co-authors at the UW, Cornell University and Columbia University report that adult female white-necked jacobins with male-like plumage are mimicking male appearance — but not male behavior. In addition, their strength and body size are similar not to males, but to fellow females with muted plumage.

The study shows that the 1 in 5 adult females with male-like plumage are engaging in “deceptive mimicry”: They are essentially trying to pass themselves off as males, without acting like them. In the process they receive quite a benefit. As Falk and his colleagues in a published last year in Current Biology, females with male-like plumage suffer less aggression from males compared to females with the more typical muted plumage, and can hang out longer at feeders.

Falk began this research as a graduate student at Cornell University and continued it as a postdoctoral fellow with co-author , a 91̽��assistant professor of biology and curator of ornithology at the UW’s .

White-necked jacobins are common in tropical lowlands of the Americas. Males of this species, put simply, are bullies. They defend territories, chase rivals away from food sources, court females and fight. That aggressive behavior relies on an underlying difference in body size and physiology: Male jacobins are larger and are better at combative flight compared to dull-colored females.

An unanswered question from Falk’s previous study was whether females with male-plumage also displayed male-like flight power or behavior. At a field site in Panama, he briefly captured male jacobins and females with both types of plumage. He discovered that females — regardless of plumage — had essentially identical body and wing sizes, whereas males were slightly larger. Before releasing the birds, Falk also tested their “burst power” — or muscle capacity during flight — by seeing how high they could fly while lifting a chain of small, weighted beads. Females of both types of plumage had identical burst power, while males could lift more on average.

Using data from radio-tagged birds in the wild, the team also discovered that more males fed in a “territorial” pattern — spending longer amounts of time at a smaller number of feeding sites. All females, regardless of plumage, showed the opposite pattern: feeding for shorter periods of time at sites across a larger territory.

“Females with male-like plumage don’t seem to be behaving any differently than other females,” said Falk. “All evidence instead indicates that females that look like males are engaging in deceptive mimicry.”

Many examples of deceptive mimicry occur between species: a harmless species will mimic the coloration of a noxious species as an anti-predator defense. In the Americas, for example, some non-venomous kingsnake species have evolved colorful banding patterns that resemble venomous species in the same area, such as coral snakes. showed that this deceptive mimicry decreased predation of the kingsnakes, which are not venomous. What Falk and his colleagues found in white-necked jacobins appears to be an example of deceptive mimicry within a species.

Scientists have reported females with male-like plumage in other hummingbird species. If so, male mimicry within hummingbird species may be more common than currently known. Next year, Falk will move to the University of Colorado Boulder to study the genetic differences between females with muted and male-like plumage — and potentially identify how this deception evolved.

But differences between the sexes are not the whole story.

“Even when I found average differences in female and male morphology, burst power or behavior, I also found quite a bit of overlap between the sexes,” said Falk. “That indicates that sex isn’t the only important factor, and that variation among and between individuals plays an important role.”

Falk and Rico-Guevara are currently studying the role of individual variation in these traits, regardless of sex.

Additional co-authors on the study are Michael Webster of Cornell University and Dustin Rubinstein of Columbia University. The research was funded by Smithsonian Tropical Research Institute, National Science Foundation, Cornell University, the Walt Halperin Endowed Professorship at the UW, the Washington Research Foundation, the Society for the Study of Evolution and the American Society of Naturalists.

###

For more information, contact Falk at jjfalk@uw.edu.

This diversity can be deceiving, at least when it comes to how mammals create the next generation. Based on how they reproduce, nearly all mammals alive today fall into one of two categories: and . Placentals, including humans, whales and rodents, have long gestation periods. They give birth to well-developed young — with all major organs and structures in place — and have relatively short weaning periods, or lactation periods, during which young are nursed on milk from their mothers. Marsupials, like kangaroos and opossums, are the opposite: They have short gestation periods — giving birth to young that are little more than fetuses — and long lactation periods during which offspring spend weeks or months nursing and growing within the mother’s pouch, or marsupium.

For decades, biologists saw the marsupial way of reproduction as the more “primitive” state, and assumed that placentals had evolved their more “advanced” method after these two groups diverged from one another. But new research is testing that view. In a published July 18 in The American Naturalist, a team led by researchers at the 91̽�� and its present evidence that another group of mammals — the extinct — likely reproduced in a placental-like manner. Since multituberculates split off from the rest of the mammalian lineage before placentals and marsupials evolved, these findings question the view that marsupials were “less advanced” than their placental cousins.

“This study challenges the prevalent idea that the placental reproductive strategy is ‘advanced’ relative to a more ‘primitive’ marsupial strategy,” said lead author , a postdoctoral researcher at the University of Michigan who conducted this study as a 91̽��doctoral student. “Our findings suggest that placental-like reproduction either is the ancestral reproductive route for all mammals that give birth to live young, or that placental-like reproduction evolved independently in both multituberculates and placentals.”

Multituberculates arose about 170 million years ago in the Jurassic. Most were small-bodied creatures, resembling rodents. For much of their history, multituberculates were the most abundant and diverse group of mammals. But scientists know very little about their life history, including how they reproduced, because of their generally poor fossil record. The last multituberculates died out about 35 million years ago.

Weaver reasoned that the microscopic structure of fossilized bone tissues can house useful life-history information about multituberculates, such as their growth rate. Working under co-author , a 91̽��professor of biology and curator of vertebrate paleontology at the Burke Museum, Weaver and his colleagues obtained cross sections of 18 fossilized femurs — the thigh bone — from multituberculates that lived approximately 66 million years ago in Montana.

All 18 samples showed the same structural organization: a layer of disorganized bone “sandwiched” between an inner and outer layer of organized bone. Disorganized bone, or woven bone, indicates rapid growth and is so named because, under a microscope, the layers of bone tissue are laid out in a crisscrossed fashion. In organized bone, which reflects slower growth, layers are parallel to one another.

The researchers then examined femoral cross sections taken from 35 small-bodied mammalian species that are living today — 28 placentals and seven marsupials, all from Burke Museum collections. Nearly all of the placental femurs showed the same “sandwich” organization as the multituberculates. But all of the marsupial femurs consisted almost entirely of organized bone, with only a sliver of disorganized bone.

The team believes that is stark difference likely reflects their divergent life histories.

“The amount of organized bone in the outermost layer, or cortex, of the femur strongly correlates with the length of the lactation period,” said Weaver. “Marsupials have long lactation periods and a lot of organized bone in the outermost cortex. The opposite is true for placentals: a short lactation period and much less organized bone in the outermost cortex.”

The outermost layer of organized bone was laid down after birth as the femur’s diameter increased. For tiny marsupial newborns, bones must grow much more to reach adult size, so they deposit a greater amount of outer organized bone compared to placentals, according to Weaver.

“This is compelling evidence that multituberculates had a long gestation and a short lactation period similar to placental mammals, but very different from marsupials,” said Weaver.

Based on this correlation, the researchers estimate that multituberculates had a lactation period of approximately 30 days — similar to today’s rodents.

These findings cast further doubt on an old view that marsupials have a “more primitive” and placentals a “more advanced” reproductive strategy. The common ancestor of multituberculates, placentals and marsupials may have had a placental-like mode of reproduction that was retained by placentals and multituberculates. Alternatively, multituberculates and placentals could have evolved their long-gestation and short-lactation reproductive methods independently.

Future studies of multituberculate life history may clarify which explanation is true, as well as other outstanding questions of this, and other, ancient branches of our mammalian family tree.

“The real revelation here is that we can cut open fossil bones and examine their microscopic structures to reconstruct the intimate life history details of long-extinct mammals,” said Wilson Mantilla. “That’s really incredible to me.”

Additional co-authors are former 91̽��undergraduate researcher Henry Fulghum, now a graduate student at Indiana University; 91̽��postdoctoral researcher David Grossnickle; 91̽��graduate students William Brightly and Zoe Kulik; and Megan Whitney, a 91̽��doctoral alum and current postdoctoral researcher at Harvard University. The research was funded by the National Science Foundation, the UW, the Burke Museum, the Society of Vertebrate Paleontology, the Paleontological Society and the American Society of Mammalogists.

For more information, contact Weaver at lukeweav@umich.edu and Wilson Mantilla at gpwilson@uw.edu.

Many animals have tusks, from elephants to walruses to hyraxes. But one thing today’s tusked animals have in common is that they’re all mammals — no known fish, reptiles or birds have them. But that was not always the case. In a published Oct. 27 in the Proceedings of the Royal Society B, a team of paleontologists at Harvard University, the Field Museum, the 91̽�� and Idaho State University traced the first tusks back to ancient mammal relatives that lived before the dinosaurs.

“Tusks are this very famous anatomy, but until I started working on this study, I never really thought about how tusks are restricted to mammals,” said lead author , a postdoctoral researcher at Harvard University and a 91̽��doctoral alum.

“We were able to show that the first tusks belonged to animals that came before modern mammals, called dicynodonts,” said co-author , a curator at the Field Museum in Chicago. “Despite being extremely weird animals, there are some things about dicynodonts — like the evolution of tusks — that inform us about the mammals around us today.”

Dicynodonts lived from about 270 to 201 million years ago, largely before the so-called “time of the dinosaurs.” They ranged from rat- to elephant-sized. Modern mammals are their closest living relatives, but they looked more reptilian, with turtle-like beaks. One of their defining features is a pair of protruding tusks in their upper jaws. The word dicynodont means “two canine teeth.”

Not all protruding teeth are tusks. Their composition and growth patterns reveal whether they count.

“For this paper, we had to define a tusk, because it’s a surprisingly ambiguous term,” said Whitney.

For a tooth to be a tusk, the researchers argued it must extend out past the mouth, keep growing throughout the animal’s life and, unlike most mammals’ teeth — including ours — tusks’ surfaces are made of dentine rather than hard enamel.

Under these parameters, elephants, walruses, warthogs and hyraxes have tusks. Other big teeth in the animal kingdom don’t make the cut, though. For instance, rodent teeth, even though they sometimes stick out and are ever-growing, have an enamel band on the front of the tooth, so they don’t count.

Some of the dicynodont tusks that the team observed in Zambia didn’t fit the definition of a tusk either: They were coated in enamel instead of dentine.

The different makeup of teeth versus tusks gives scientists insights into an animal’s life.

“Enamel-coated teeth are a different evolutionary strategy than dentine-coated tusks,” said Whitney. “It’s a trade-off.”

Enamel teeth are tougher than dentine. But because of the geometry of how teeth grow in the jaw, if you want teeth that keep growing throughout your life, you can’t have a complete enamel covering.

Animals like humans made an evolutionary investment in durable but hard-to-fix teeth — once our adult teeth grow in, we’re out of luck if they get broken. Tusks are less durable, but they grow continuously, even if they get damaged. It’s like the compromise of getting a car that’s very reliable but very difficult to get repaired, versus driving a beater that needs frequent repairs but is cheap and easy to fix.

The different kinds of teeth animals have evolved tell scientists about the pressures those animals faced that could have produced those teeth. Animals with tusks might use them for fighting or for rooting in the ground, exposing them to little injuries that would be risky for enamel teeth that don’t grow continuously.

To study whether dicynodonts tusks really were tusks, the researchers cut paper-thin slices out of the fossilized teeth of 19 dicynodont specimens, representing ten different species, and examined their structure under a microscope. They also used micro-CT scans to examine how the teeth were attached to the skull, and whether their roots showed evidence of continuous growth.

The scientists found that some dicynodont teeth are indeed tusks, while others, particularly those of some of the earlier species, were just large teeth. It wasn’t a strict progression from non-tusks to tusks, though — different members of the dicynodont family evolved tusks independently.

They also discovered some adaptations that dicynodonts needed to evolve true tusks, including flexible ligament attachments between tooth and jaw and reduced rates of tooth replacement, according to Angielczyk.

The study, which shows the earliest known instance of true tusks, could help scientists better understand evolutionary processes.

“Tusks have evolved a number of times, which makes you wonder how — and why? We now have good data on the anatomical changes that needed to happen for dicynodonts to evolve tusks,” said co-author , a 91̽��professor of biology and a curator at the UW’s Burke Museum of Natural History & Culture. “For other groups, like warthogs or walruses, the jury is still out.”

Most of the dicynodont fossils analyzed in the study were collected during fieldwork in Tanzania and Zambia. These specimens, which are currently stored at the Burke Museum and other U.S. museums, will be repatriated at the end of the project and become part of the permanent collections at the National Museum of Tanzania and the Livingstone Museum in Zambia. This partnership allows for researchers across the globe to study the fossils, and ultimately bring the specimens back to their home nations for further research.

Future studies could examine other dicynodont species and how their tusks — or non-tusks — developed. Sidor’s lab at 91̽��is one of a handful across the country where the fossilized bones and teeth are routinely analyzed at the microscopic scale.

“Thin-sectioning can also provide a lot of useful information, because bones and teeth can capture a record of an animal’s life in their tissues,” said Sidor. “On a tusk that’s ever-growing, the dentine records a daily measure of how fast the animal was growing. Did it grow faster or slower over certain seasons? Stop growing for a certain period of time? Creating thin sections of bones and teeth opens up a lot of other interesting things about the animal almost like analyzing tree rings. These are the types of questions we can continue to research.”

Co-author is 91̽��doctoral alum , an assistant professor at Idaho State University and assistant curator of vertebrate paleontology at the Idaho Museum of Natural History. The research was funded by the National Science Foundation and National Geographic.

Adapted from a release by the Field Museum and Harvard University.

A team of paleontologists from the 91̽�� and its excavated four dinosaurs in northeastern Montana this summer. All fossils will be brought back to the Burke Museum where the public can watch paleontologists remove the surrounding rock in the .

The four dinosaur fossils are: the ilium — or hip bones — of an ostrich-sized theropod, the group of meat-eating, two-legged dinosaurs that includes Tyrannosaurus rex and raptors; the hips and legs of a duck-billed dinosaur; a pelvis, toe claw and limbs from another theropod that could be a rare ostrich-mimic Anzu, or possibly a new species; and a Triceratops specimen consisting of its skull and other fossilized bones. Three of the four dinosaurs were all found in close proximity on Bureau of Land Management land that is currently leased to a rancher.

In July 2021, a team of volunteers, paleontology staff, K-12 educators who were part of the and students from 91̽��and other universities worked together to excavate these dinosaurs. The fossils were found in the , a geologic formation that dates from the latest portion of Cretaceous Period, 66 to 68 million years ago. Typical paleontological digs involve excavating one known fossil. However, the Hell Creek Project is an ongoing research collaboration of paleontologists from around the world studying life right before, during and after the that killed off all dinosaurs except birds. The Hell Creek Project is unique in that it is sampling all plant and animal life found throughout the rock formation in an unbiased manner.

“Each fossil that we collect helps us sharpen our views of the last dinosaur-dominated ecosystems and the first mammal-dominated ecosystems,” said , a 91̽��professor of biology and curator of vertebrate paleontology at the Burke Museum. “With these, we can better understand the processes involved in the loss and origination of biodiversity and the fragility, collapse and assembly of ecosystems.”

All of the dinosaurs except the Triceratops will be prepared in the Burke Museum’s fossil preparation laboratory this fall and winter. The Triceratops fossil remains on the site because the dig team continued to find more and more bones while excavating and needs an additional field season to excavate any further bones that may be connected to the surrounding rock. The team plans to finish excavation in the summer of 2022.

Called the “Flyby Trike” in honor of the rancher who first identified the dinosaur while he was flying his airplane over his ranch, the team has uncovered this dinosaur’s frill, horn bones, individual rib bones, lower jaw, teeth and the occipital condyle bone — nicknamed the “trailer hitch,” which is the ball on the back of the skull that connects to the neck vertebrae. The team estimates approximately 30% of this individual’s skull bones have been found to date, with more potential bones to be excavated next year.

The Flyby Trike was found in hardened mud, with the bones scattered on top of each other in ways that are different from the way the bones would be laid out in a living animal. These clues indicate the dinosaur likely died on a flood plain and then got mixed together after its death by being moved around by a flood or river system, or possibly moved around by a scavenger like a T. rex, before fossilizing. In addition, the Flyby Trike is one of the last Triceratops living before the K-Pg mass extinction. Burke paleontologists estimate it lived less than 300,000 years before the event.

“Previous to this year’s excavations, a portion of the Flyby Trike frill and a brow horn were collected and subsequently prepared by volunteer preparators in the fossil preparation lab. The frill was collected in many pieces and puzzled together fantastically by volunteers. Upon puzzling the frill portion together, it was discovered that the specimen is likely an older ‘grandparent’ Triceratops,” said Kelsie Abrams, the Burke Museum’s paleontology preparation laboratory manager who also participated in this summer’s field work. “The triangular bones along the frill, called ‘epi occipitals,’ are completely fused and almost unrecognizable on the specimen, as compared to the sharp, noticeable triangular shape seen in younger individuals. In addition, the brow horn curves downwards as opposed to upwards, and this feature has been reported to be seen in older animals as well.”

Amber and seed pods were also found with the Flyby Trike. These finds allow paleobotanists to determine what plants were living alongside Triceratops, what the dinosaurs may have eaten, and what the overall ecosystem was like in Hell Creek leading up to the mass extinction event.

“Plant fossil remains from this time period are crucial for our understanding of the wider ecosystem. Not only can plant material tell us what these dinosaurs were perhaps eating, but plants can more broadly tell us what their environment looked like,” said Paige Wilson, a 91̽��graduate student in Earth and space sciences. “Plants are the base of the food chain and a crucial part of the fossil record. It’s exciting to see this new material found so close to vertebrate fossils!”

Museum visitors can now see paleontologists remove rock from the first of the four dinosaurs — the theropod hips — in the Burke’s paleontology preparation laboratory. Additional fossils will be prepared in the upcoming weeks. All four dinosaurs will be held in trust for the public on behalf of the Bureau of Land Management and become a part of the Burke Museum’s collections.

For high resolution images, videos and interviews, contact burkepr@uw.edu.

A published Aug. 11 in the Proceedings of the Royal Society B by researchers at the 91̽�� and Stony Brook University reports on how bats and pepper plants in Central America have coevolved to help each other survive.

The team — led by , a 91̽��professor of biology and curator of mammals at the Burke Museum of Natural History and Culture — focused on the complex mixture of volatile organic compounds, or VOCs, produced by fruits on pepper plants in the genus Piper at prime ripeness. The study showed how these VOCs may have evolved to attract scent-oriented, short-tailed fruit bats from the genus Carollia, who then eat the fruits and excrete the seeds into the landscape.

Plant–animal interactions have captured the attention of biologists for centuries, and are key to maintaining the biodiversity of tropical ecosystems. The dispersal syndrome hypothesis — an explanation of how mutually beneficial relationships between plants and fruit-eating animals may lead to coevolution — proposes that, when animals are effective seed dispersers, they may select for fruit traits, including size, color and odor, that match their sensory abilities, such as vision and olfaction. But few studies have tested this hypothesis for complex traits like fruit scents. This research provides one of the first tests of bat-driven, fruit scent evolution.

The study is based on data collected during fieldwork at La Selva Biological Station in Costa Rica. There, Piper is highly diverse, with more than 50 recognized species. It is also a location where three Carollia species — C. castanea, C. sowellii and C. perspicillata — are some of the most abundant bats year-round and coexist with approximately 62 other bat species.

The team spent hundreds of hours searching and collecting ripe fruits from Piper to extract and quantify the VOCs that make up their fragrant scent. They also collected fecal samples from live bats and then released them back into the wild to determine which Piper species the bats were eating and how much. In addition, the researchers conducted behavioral experiments with wild bats where they offered options of unripe fruits enhanced with the most common VOCs found in local Piper plants. Video cameras and microphones recorded the bats’ feeding behaviors and echolocation calls.

The team found Piper fruit scent bouquets were complex and diverse. The authors identified and quantified 249 VOCs in ripe fruit scents across 22 Piper species. Some compounds were found in the fruit scent of most species — like alpha-caryophyllene, which has a spicy scent like cinnamon or cloves. Others, like 2-heptanol, were only found in a few Piper species. The diet experiments showed that, while the three Carollia fruit bat species varied in their reliance on Piper as a food source, all consumed a lot of a few Piper species, and a little of many others. Surprisingly, this was not related to how abundant the Piper species are at La Selva, so the bats must choose Piper fruits based on other characteristics and not just how well represented they are across the landscape. The team’s behavioral experiments provided some clues to what might be happening: Bats preferred samples spiked with 2-heptanol, a VOC found in the fruit scents of the Piper species they eat the most.

“These findings suggest bats use specific chemicals in the fruit scent bouquet not only to select ripe fruits, but to find the specific Piper species that make up the bulk of their diet,” said Santana, who is co-lead author on the study. “By helping them communicate with the bats, these chemical signals are likely a component of a dispersal syndrome in these plants.”

Through statistical and evolutionary analyses of the data on fruit scent chemistry and bat diet, the team further demonstrated that the evolutionary patterns of chemical diversity and the presence of specific compounds in Piper fruit scents is associated with greater bat consumption and scent preferences. This highlights the potential effect of bat fruit consumption on the evolution of fruit chemistry, a relationship that contributes to the extreme diversity of tropical fruiting plants worldwide.

“Flying in the dark means bats cannot find ripe fruit by sight, but rely on olfaction instead,” said co-author , a professor at Stony Brook University. “Olfaction is the bridge between the plant signal and bat fruit consumption, and finding the specific VOCs bats respond to opens the door to matching olfactory receptor genes to important VOCs, which has been impossible until now.”

Understanding the relationship between bats and pepper plants not only contributes to knowledge about coevolution of these species, but also has benefits for rainforest habitat conservation. Piper are some of the first plants to grow in forest gaps and edges, and Carollia ― as key dispersers of Piper seeds ― can help restore plant life in logged areas.

“Our current and future work is identifying the odorant receptors that allow the bats to detect the fruit scents. This will allow us to link the ecology and evolution of these relationships with the physiological mechanisms,” said co-author , a 91̽��professor of biology.

Co-lead author on the paper is former 91̽��postdoctoral researcher Zofia Kaliszewska. Other co-authors are 91̽��doctoral alum Leith Leiser-Miller, M. Elise Lauterbur at the University of Arizona and Jessica Arbour at Middle Tennessee State University. The research was funded by the National Science Foundation.

For high-resolution images, video and interviews, contact burkepr@uw.edu.

Modern cetaceans — which include dolphins, whales and porpoises — are well adapted for aquatic life. They have blubber to insulate and fins to propel and steer. Today’s cetaceans also sport a unique type of nasal passage: It rises at an angle relative to the roof of the mouth — or palate — and exits at the top of the head as a blowhole.

This is an apt adaptation for an air-breathing animal at home in the water. Yet as embryos, the cetacean nasal passage starts out in a position more typical of mammals: parallel to the palate and exiting at the tip of the snout, or rostrum. Cetacean experts have long puzzled over how the nasal passage switches during embryonic and fetal development from a palate-parallel pathway to an angled orientation terminating in a blowhole.

“The shift in orientation and position of the nasal passage in cetaceans is a developmental process that’s unlike any other mammal,” said , a postdoctoral researcher at the 91̽�� School of Dentistry. “It’s an interesting question to see what parts remain connected, what parts shift orientation and how might they work together through a developmental process to bring about this change.”

New research by Roston and , a professor of biology at Duke University, is shedding light on this process. By measuring anatomical details of embryos and fetuses of pantropical spotted dolphins, they determined the key anatomical changes that flip the orientation of the nasal passage up. Their findings, July 19 in the Journal of Anatomy, are an integrative model for this developmental transition for cetaceans.

“We discovered that there are three phases of growth, primarily in the head, that can explain how the nasal passage shifts in orientation and position,” said lead author Roston, who began this study as a doctoral student at Duke.

The three phases of growth are:

1. Initially parallel, the roof of the mouth and the nasal passage become separated as the area between them grows into a triangular shape. This phase begins during embryonic development after the face starts forming, which, for the pantropical spotted dolphin, is in the first two months after fertilization.
2. The snout grows longer at an angle to the nasal passage, further separating the nostrils from the tip of the snout. This phase begins later in fetal development and may continue even after birth.
3. The skull folds backward, and the head and body become more aligned. This rotates the nasal passage up so that it becomes nearly vertical relative to the body axis. This phase begins in late embryonic development and continues through fetal development.

“While the nose moves to the top of the head, many of the important angular changes are actually in the bottom, or base, of the skull. That’s not necessarily something you’d expect to find!” said Roston.

The three phases of growth do not unfold in a step-by-step process, but instead overlap with each other temporally, Roston said. They represent distinct developmental transformations that, put together, shift the nasal passage to the top of the head.

Roston and Roth developed this model using anatomical data obtained by photographs and CT scans of 21 embryonic and fetal pantropical spotted dolphin specimens held by the Smithsonian Institution’s National Museum of Natural History and the Natural History Museum of Los Angeles County. The specimens represented a wide range of embryonic and fetal development.

For comparison, they obtained data from eight fin whale fetuses, also at the National Museum of Natural History, and found significant differences between them and the pantropical spotted dolphin. In fin whales, the skull folded in a region in the back of the skull, near where the skull joins with the vertebral column. In the pantropical spotted dolphin, the folding is centered near the middle of the skull.

The model Roston and Roth developed could inform how scientists view cetacean evolution. These creatures began to evolve from a four-legged, land-dwelling mammalian ancestor, which had a nasal passage parallel to the palate, more than 50 million years ago. As cetaceans evolved, the blowhole gradually migrated from the tip of the snout to the back of the snout, and then gradually up to the top of the skull.

In addition, the two species represent different branches of the cetacean family tree that diverged more than 30 million years ago. Dolphins — along with porpoises, orcas, sperm whales and beaked whales — are odontocetes, commonly known as toothed whales. Fin whales are from a group called the baleen whales, named for their distinct feeding apparatus.

“I’m struck by two interesting discoveries that emerged from this work,” said Roth. “Although they both develop blowholes, there are key differences between a baleen and a toothed whale in how they reorient their nasal passages during development. Moreover, surprisingly, accompanying the processes of developing upwardly oriented nostrils there are profound changes within the braincase.”

In the future, examining more species from both lineages could indicate whether all baleen and toothed whales differ in this manner, Roston said.

“This model gives us a hypothesis for the developmental steps that had to occur to make that anatomical transformation happen, and will serve as a point of comparison for additional studies of growth and development in whales, dolphins and porpoises,” said Roston.

The research was funded by Duke University. Roston has also been supported by the National Institutes of Health.

For more information, contact Roston at rroston@uw.edu and Roth at vlroth@duke.edu.

A new published Feb. 24 in the journal Royal Society Open Science documents the earliest-known fossil evidence of primates.

A team of 10 researchers from across the U.S. analyzed several fossils of Purgatorius, the oldest genus in a group of the earliest-known primates called plesiadapiforms. These ancient mammals were small-bodied and ate specialized diets of insects and fruits that varied by species. These newly described specimens are central to understanding primate ancestry and paint a picture of how life on land recovered after the Cretaceous-Paleogene extinction event 66 million years ago that wiped out all dinosaurs — except for birds — and led to the rise of mammals.

, a 91̽�� professor of biology and curator of vertebrate paleontology at the UW’s , co-led the study with of Brooklyn College and the City University of New York. The team analyzed fossilized teeth found in the Hell Creek area of northeastern Montana. The fossils, which are now part of the collections at the University of California Museum of Paleontology, are estimated to be 65.9 million years old, about 105,000 to 139,000 years after the mass extinction event. Based on the age of the fossils, the team estimates that the ancestor of all primates —including plesiadapiforms and today’s primates such as lemurs, monkeys and apes — likely emerged by the Late Cretaceous and lived alongside large dinosaurs.

“It’s mind blowing to think of our earliest archaic primate ancestors,” said Wilson Mantilla. “They were some of the first mammals to diversify in this new post-mass extinction world, taking advantage of the fruits and insects up in the forest canopy.”

The fossils include two species of Purgatorius: Purgatorius janisae and a new species described by the team named Purgatorius mckeeveri. Three of the teeth found have distinct features compared to any previously known Purgatorius species and led to the description of the new species.

Purgatorius mckeeveri is named after Frank McKeever, who was among the first residents of the area where the fossils were discovered, and also the family of John and Cathy McKeever, who have since supported the field work where the oldest specimen of this new species was discovered.

“This was a really cool study to be a part of, particularly because it provides further evidence that the earliest primates originated before the extinction of non-avian dinosaurs,” said co-author Brody Hovatter, a 91̽��graduate student in Earth and space sciences. “They became highly abundant within a million years after that extinction.”

“This discovery is exciting because it represents the oldest dated occurrence of archaic primates in the fossil record,” said Chester. “It adds to our understanding of how the earliest primates separated themselves from their competitors following the demise of the dinosaurs.”

Co-author on the study was the late who was a professor emeritus at the University of California, Berkeley and former director of the UC Museum of Paleontology. Additional co-authors are Jason Moore and Wade Mans of the University of New Mexico; Courtney Sprain of the University of Florida; William Mitchell of Minnesota IT Services; Roland Mundil of the Berkeley Geochronology Center; and Paul Renne of UC Berkeley and the Berkeley Geochronology Center. The research was funded by the National Science Foundation, the UC Museum of Paleontology, the Myhrvold and Havranek Charitable Family Fund, the UW, the CUNY and the Leakey Foundation.

For high resolution images and interviews, contact burkepr@uw.edu.