Marine fish won an evolutionary lottery 66 million years ago
Why do our oceans contain such a staggering diversity of fish of so many different sizes, shapes and colors? A UCLA-led team of biologists reports that the answer dates back 66 million years, when a six-mile-wide asteroid crashed to Earth, wiping out the dinosaurs and approximately 75 percent of the world’s animal and plant species.
Slightly more than half of today’s fish are “marine fish,” meaning they live in oceans. And most marine fish, including tuna, halibut, grouper, sea horses and mahi-mahi, belong to an extraordinarily diverse group called acanthomorphs. (The study did not analyze the large numbers of other fish that live in lakes, rivers, streams, ponds and tropical rainforests.)
The aftermath of the asteroid crash created an enormous evolutionary void, providing an opportunity for the marine fish that survived it to greatly diversify.
“Today’s rich biodiversity among marine fish shows the fingerprints of the mass extinction at the end of the Cretaceous period,” said Michael Alfaro, a professor of ecology and evolutionary biology in the UCLA College and lead author of the study.
To analyze those fingerprints, the “evolutionary detectives” employed a new genomics research technique developed by one of the authors. Their work is published in the journal Nature Ecology and Evolution.
When they studied the timing of the acanthomorphs’ diversification, Alfaro and his colleagues discovered an intriguing pattern: Although there were many other surviving lineages of acanthomorphs, the six most species-rich groups of acanthomorphs today all showed evidence of substantial evolutionary change and proliferation around the time of the mass extinction. Those six groups have gone on to produce almost all of the marine fish diversity that we see today, Alfaro said.
He added that it’s unclear why the other acanthomorph lineages failed to diversify as much after the mass extinction.
“The mass extinction, we argue, provided an evolutionary opportunity for a select few of the surviving acanthomorphs to greatly diversify, and it left a large imprint on the biodiversity of marine fishes today,” Alfaro said. “It’s like there was a lottery 66 million years ago, and these six major acanthomorph groups were the winners.”
The findings also closely match fossil evidence of acanthomorphs’ evolution, which also shows a sharp rise in their anatomical diversity after the extinction.
The genomic technique used in the study, called sequence capture of DNA ultra-conserved elements, was developed at UCLA by Brant Faircloth, who is now an assistant professor of biological sciences at Louisiana State University. Where previous methods used just 10 to 20 genes to create an evolutionary history, Faircloth’s approach creates a more complete and accurate picture by using more than 1,000 genetic markers. (The markers include genes and other DNA components, such as parts of the DNA that turn proteins on or off, and cellular components that play a role in regulating genes.)
The researchers also extracted DNA from 118 species of marine fish and conducted a computational analysis to determine the relationships among them. Among their findings: It’s not possible to tell which species are genetically related simply by looking at them. Seahorses, for example, look nothing like goatfish, but the two species are evolutionary cousins — a finding that surprised the scientists.
“We demonstrate this approach works, and that it sheds new light on evolutionary history for the most species-rich group of marine vertebrates,” Alfaro said.
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First an alga, then a squid, enigmatic fossil is actually a fish
A fossil slab discovered in Kansas 70 years ago and twice misidentified — first as a green alga and then as a cephalopod — has been reinterpreted as the preserved remains of a large cartilaginous fish, the group that includes sharks and rays. In a study published in the Journal of Paleontology, American Museum of Natural History researchers describe the fishy characteristics of the animal, which lived between 70-85 million years ago.
“There are many examples of temporarily misplaced taxa in paleontological history, including ferns that were once thought to be sponges and lungfish teeth thought to be fungi,” said the lead author, Allison Bronson, a comparative biology Ph.D.-degree student in the Museum’s Richard Gilder Graduate School. “In this case, the misidentification didn’t happen because of a lack of technology at the time — scientists familiar with cartilage structure could easily see this was a chondrichthyan fish. The researchers used reasonable arguments for their interpretations, but didn’t look outside of their own fields.”
The enigmatic specimen, Platylithophycus cretaceum, is roughly 1.5-feet long by 10-inches wide and from the Niobrara Formation in Kansas. The Niobrara Formation is one of the most diverse fish-fossil sites in North America, preserving late Cretaceous animals that lived in and around the Western Interior Seaway, a broad expanse of water that split North America into two land masses.
In 1948, two paleobotanists from the Colorado School of Mines and Princeton University compared the texture of the fossil slab with that of green algae. They described two parts of a plant: surfaces covered with hexagonal plates, which they called “fronds,” and supposedly calcium carbonate-covered thread-like filaments. In 1968, two researchers from Fort Hays Kansas State College studying cephalopods from the Niobrara Formation compared the specimen with a cuttlefish, based primarily on its textural similarities to a cuttlebone — the unique internal shell of cuttlefish. The reclassification made Platylithophycus the oldest sepiid squid then on record.
In both of these earlier studies, the hard tissue was assumed to be composed of calcium carbonate, but no tests were performed. For the new study, Bronson and co-author John Maisey, a curator in the Museum’s Division of Paleontology, applied a small amount of dilute organic acid to the specimen — a method that has been widely used in paleontology since the time of the initial description of Platylithophycus. If there is a reaction, the fossilized material is likely made from calcium carbonate. But if there is no reaction, which was the case when Bronson and Maisey performed the test, it is likely made from calcium phosphate, as are the fossilized skeletons of cartilaginous fish like sharks and rays.
The most obvious clue that Platylithophycus was a cartilaginous fish are the hexagonal plates on the surface of the specimen. After taking a closer look with a scanning electron microscope, Bronson and Maisey reinterpreted that feature as tessellated calcified cartilage, found on both extinct and living sharks and rays. The new study suggests that the “filaments” earlier described are actually part of the gill arches, made up of tessellated cartilage. Gill arches are cartilaginous curved bars along the pharynx, or throat, that support the gills of fish. The “fronds” are reinterpreted as gill rakers, finger-like projections that extend from the gill arches and help with feeding.
“We think this was a rather large cartilaginous fish, possibly related to living filter-feeding rays such as Manta and Mobula,” Maisey said. “This potentially expands the range of diversity in the Niobrara fauna.”
But because this fossil only preserves the animal’s gills and no additional identifying features like teeth, it cannot be given a new name or reunited with an existing species. So until then, this fish will still carry the name of a plant.
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The dinosaur menu, as revealed by calcium
By studying calcium in fossil remains in deposits in Morocco and Niger, researchers have been able to reconstruct the food chains of the past, thus explaining how so many predators could coexist in the dinosaurs’ time. This study, conducted by the Laboratoire de géologie de Lyon: Terre, planètes et environnement (CNRS/ENS de Lyon/Claude Bernard Lyon 1 University), in partnership with the Centre for Research on Palaeobiodiversity and Palaeoenvironments (CNRS/French National Museum of Natural History/Sorbonne University), is published on April 11, 2018 in the Proceedings of the Royal Society of London B.
A hundred million years ago, in North Africa, terrestrial ecosystems were dominated by large predators — giant theropod dinosaurs, large crocodiles — with comparatively few herbivores. How were so many carnivores able to coexist?
To understand this, French researchers have studied fossils in the Gadoufaoua deposits in Niger (dating from 120 million years ago) and the Kem Kem Beds in Morocco (dating from 100 million years ago). These two sites are characterized by an overabundance of predators compared to the herbivorous dinosaurs found in the locality. More specifically, the researchers measured the proportions of different calcium isotopes(1) in the fossilized remains (tooth enamel and fish scales).
Among vertebrates, calcium is almost exclusively derived from food. By comparing the isotopic composition of potential prey (fish, herbivores) with that of the carnivores’ teeth, it is thus possible to retrace the diet of those carnivores.
The data obtained show similar food preferences at the two deposits: some large carnivorous dinosaurs (abelisaurids and carcharodontosaurids) preferred to hunt terrestrial prey such as herbivorous dinosaurs, while others (the spinosaurids) were piscivorous (fish-eating).(2) The giant crocodile-like Sarcosuchus had a diet somewhere in between, made up of both terrestrial and aquatic prey. Thus, the different predators avoided competition by subtly sharing food resources.
Some exceptional fossils, presenting traces of feeding marks and stomach content, had already provided clues about the diet of dinosaurs. Yet such evidence remains rare. The advantage of the calcium isotope method is that it produces a global panorama of feeding habits at the ecosystem scale. It thus opens avenues for further study of the food chains of the past.
Rare Scottish dinosaur prints give key insight into era lost in time
Dozens of giant footprints discovered on a Scottish island are helping shed light on an important period in dinosaur evolution.
The tracks were made some 170 million years ago, in a muddy, shallow lagoon in what is now the north-east coast of the Isle of Skye.
Most of the prints were made by long-necked sauropods — which stood up to two metres tall — and by similarly sized theropods, which were the older cousins of Tyrannosaurus rex.
The find is globally important as it is rare evidence of the Middle Jurassic period, from which few fossil sites have been found around the world.
Researchers measured, photographed and analysed about 50 footprints in a tidal area at Brothers’ Point — Rubha nam Brathairean — a dramatic headland on Skye’s Trotternish peninsula.
The footprints were difficult to study owing to tidal conditions, the impact of weathering and changes to the landscape. In spite of this, scientists identified two trackways in addition to many isolated foot prints.
Researchers used drone photographs to make a map of the site. Additional images were collected using a paired set of cameras and tailored software to help model the prints.
Analysis of the clearest prints — including the overall shape of the track outline, the shape and orientation of the toes, and the presence of claws — enabled scientists to ascribe them to sauropods and theropods.
The study, carried out by the University of Edinburgh, Staffin Museum and Chinese Academy of Sciences, was published in the Scottish Journal of Geology. It was supported by a grant from the National Geographic Society, and subsidiary funding from the Association of Women Geologists, Derek and Maureen Moss, Edinburgh Zoo and Edinburgh Geological Society.
Paige dePolo, who led the study, conducted the research while an inaugural student in the University’s Research Master’s degree programme in palaeontology and geobiology.
Ms dePolo said: “This tracksite is the second discovery of sauropod footprints on Skye. It was found in rocks that were slightly older than those previously found at Duntulm on the island and demonstrates the presence of sauropods in this part of the world through a longer timescale than previously known. This site is a useful building block for us to continue fleshing out a picture of what dinosaurs were like on Skye in the Middle Jurassic.”
Dr Steve Brusatte of the University of Edinburgh’s School of GeoSciences, who led the field team, said: “The more we look on the Isle of Skye, the more dinosaur footprints we find. This new site records two different types of dinosaurs — long-necked cousins of Brontosaurus and sharp-toothed cousins of T. rex — hanging around a shallow lagoon, back when Scotland was much warmer and dinosaurs were beginning their march to global dominance.”
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127-million-year-old baby bird fossil sheds light on avian evolution
The tiny fossil of a prehistoric baby bird is helping scientists understand how early avians came into the world in the Age of Dinosaurs.
The fossil, which dates back to the Mesozoic Era (250-65 million years ago), is a chick from a group of prehistoric birds called, Enantiornithes. Made up of a nearly complete skeleton, the specimen is amongst the smallest known Mesozoic avian fossils ever discovered.
It measures less than five centimetres — smaller than the little finger on an average human hand — and would have weighed just three ounces when it was alive. What makes this fossil so important and unique is the fact it died not long after its birth. This is a critical stage in a bird’s skeletal formation. That means this bird’s extremely short life has given researchers a rare chance to analyse the species’ bone structure and development.
Studying and analysing ossification — the process of bone development — can explain a lot about a young bird’s life the researchers say. It can help them understand everything from whether it could fly or if it needed to stay with its parents after hatching or could survive on its own.
The lead author of the study, Fabien Knoll, from The University of Manchester’s Interdisciplinary Centre for Ancient Life (ICAL), School of Earth and Environmental Sciences, and the ARAID — Dinopolis in Spain explains: ‘The evolutionary diversification of birds has resulted in a wide range of hatchling developmental strategies and important differences in their growth rates. By analysing bone development we can look at a whole host of evolutionary traits.’
With the fossil being so small the team used synchrotron radiation to picture the tiny specimen at a ‘submicron’ level, observing the bones’ microstructures in extreme detail.
Knoll said: ‘New technologies are offering palaeontologists unprecedented capacities to investigate provocative fossils. Here we made the most of state-of-the-art facilities worldwide including three different synchrotrons in France, the UK and the United States.’
The researchers found the baby bird’s sternum (breastplate bone) was still largely made of cartilage and had not yet developed into hard, solid bone when it died, meaning it wouldn’t have been able to fly.
The patterns of ossification observed in this and the other few very young enantiornithine birds known to date also suggest that the developmental strategies of this particular group of ancient avians may have been more diverse than previously thought.
However, the team say that its lack of bone development doesn’t necessarily mean the hatchling was over reliant on its parents for care and feeding, a trait known as being ‘altricial’. Modern day species like love birds are highly dependent on their parents when born. Others, like chickens, are highly independent, which is known as ‘precocial’. Although, this is not a black-and-white issue, but rather a spectrum, hence the difficulty in clarifying the developmental strategies of long gone bird species.
Luis Chiappe, from the LA Museum of Natural History and study’s co-author added: ‘This new discovery, together with others from around the world, allows us to peek into the world of ancient birds that lived during the age of dinosaurs. It is amazing to realise how many of the features we see among living birds had already been developed more than 100 million years ago.’
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Origins of photosynthesis in plants dated to 1.25 billion years ago
The world’s oldest algae fossils are a billion years old, according to a new analysis by earth scientists at McGill University. Based on this finding, the researchers also estimate that the basis for photosynthesis in today’s plants was set in place 1.25 billion years ago.
The study, published in the journal Geology, could resolve a long-standing mystery over the age of the fossilized algae, Bangiomorpha pubescens, which were first discovered in rocks in Arctic Canada in 1990. The microscopic organism is believed to be the oldest known direct ancestor of modern plants and animals, but its age was only poorly dated, with estimates placing it somewhere between 720 million and 1.2 billion years.
The new findings also add to recent evidence that an interval of Earth’s history often referred to as the Boring Billion may not have been so boring, after all. From 1.8 to 0.8 billion years ago, archaea, bacteria and a handful of complex organisms that have since gone extinct milled about the planet’s oceans, with little biological or environmental change to show for it. Or so it seemed. In fact, that era may have set the stage for the proliferation of more complex life forms that culminated 541 million years ago with the so-called Cambrian Explosion.
“Evidence is beginning to build to suggest that Earth’s biosphere and its environment in the latter portion of the ‘Boring Billion’ may actually have been more dynamic than previously thought,” says McGill PhD student Timothy Gibson, lead author of the new study.
Pinpointing the fossils’ age
To pinpoint the fossils’ age, the researchers pitched camp in a rugged area of remote Baffin Island, where Bangiomorpha pubescens fossils have been found There,despite the occasional August blizzard and tent-collapsing winds, they collected samples of black shale from rock layers that sandwiched the rock unit containing fossils of the alga. Using the Rhenium-Osmium (or Re-Os) dating technique, applied increasingly to sedimentary rocks in recent years, they determined that the rocks are 1.047 billion years old.
“That’s 150 million years younger than commonly held estimates, and confirms that this fossil is spectacular,” says Galen Halverson, senior author of the study and an associate professor in McGill’s Department of Earth and Planetary Sciences. “This will enable scientists to make more precise assessments of the early evolution of eukaryotes,” the celled organisms that include plants and animals.
Because Bangiomorpha pubescens is nearly identical to modern red algae, scientists have previously determined that the ancient alga, like green plants, used sunlight to synthesize nutrients from carbon dioxide and water. Scientists have also established that the chloroplast, the structure in plant cells that is the site of photosynthesis, was created when a eukaryote long ago engulfed a simple bacterium that was photosynthetic. The eukaryote then managed to pass that DNA along to its descendants, including the plants and trees that produce most of the world’s biomass today.
Origins of the chloroplast
Once the researchers had gauged the fossils’ age at 1.047 billion years, they plugged that figure into a “molecular clock,” a computer model used to calculate evolutionary events based on rates of genetic mutations. Their conclusion: the chloroplast must have been incorporated into eukaryotes roughly 1.25 billion years ago.
“We expect and hope that other scientists will plug this age for Bangiomorpha pubescens into their own molecular clocks to calculate the timing of important evolutionary events and test our results,” Gibson says. “If other scientists envision a better way to calculate when the chloroplast emerged, the scientific community will eventually decide which estimate seems more reasonable and find new ways to test it.”
Early avian evolution: The Archaeopteryx that wasn‘t
Paleontologists at Ludwig-Maximilians-Universitaet (LMU) in Munich correct a case of misinterpretation: The first fossil “Archaeopteryx” to be discovered is actually a predatory dinosaur belonging to the anchiornithid family, which was previously known only from finds made in China.
Even 150 million years after its first appearance on our planet, Archaeopteryx is still good for surprises. The so-called Urvogel has attained an iconic status well beyond the world of paleontology, and it is one of the most famous fossils ever recovered. In all, a dozen fossil specimens have been assigned to the genus. Archaeopteryx remains the oldest known bird fossil, not only documenting the evolutionary transition from reptiles to birds, but also confirming that modern birds are the direct descendants of carnivorous dinosaurs. LMU paleontologist Oliver Rauhut and Christian Foth from the Staatliches Museum für Naturkunde in Stuttgart have re-examined the so-called Haarlem specimen of Archaeopteryx, which is kept in Teylers Museum in that Dutch city and has gone down in history as the first member of this genus to be discovered.
In the journal BMC Evolutionary Biology, Foth and Rauhut now report that this fossil differs in several important respects from the other known representatives of the genus Archaeopteryx. In fact, their taxonomic analysis displaces it from its alleged perch on the phylogenetic tree: “The Haarlem specimen is not a member of the Archaeopteryx clade,” says Rauhut, a paleontologist in the Department of Earth and Environmental Sciences at LMU who is also affiliated with the Bavarian State Collections for Paleontology and Geology in Munich.
Instead, the two scientists assign the fossil to a group of bird-like maniraptoran dinosaurs known as anchiornithids, which were first identified only a few years ago based on material found in China. These rather small dinosaurs possessed feathers on all four limbs, and they predate the appearance of Archaeopteryx. “The Haarlem fossil is the first member of this group found outside China. And together with Archaeopteryx, it is only the second species of bird-like dinosaur from the Jurassic discovered outside eastern Asia. This makes it even more of a rarity than the true specimens of Archaeopteryx,” Rauhut says.
Made in China
The Haarlem specimen was found about 10 km to the northeast of the closest Archaeopteryx locality known (Schamhaupten) a full four years before the discovery of the skeleton that would introduce the Urvogel to the scientific world in 1861. Schamhaupten was once part of the so-called Solnhofen archipelago in the Altmühl Valley in southern Bavaria, the area from which all known specimens of the genus Archaeopteryx originated. Its taxonomic reassignment therefore provides new insights into the evolution of the bird-like dinosaurs in the Middle to Late Jurassic. “Our biogeographical analysis demonstrates that the group of dinosaurs that gave rise to birds originated in East Asia — all of the oldest finds have been made in China. As they expanded westward, they also reached the Solnhofen archipelago,” says Christian Foth. Thus, the fossil hitherto incorrectly assigned to the genus Archaeopteryx must have been one of the first members of the group to arrive in Europe.
Around 150 million years ago, the area known today as the Altmühl Valley was dotted with the coral and sponge reefs and lagoons of the Solnhofen archipelago, and the open sea lay to the West and South. The Haarlem fossil was originally recovered from what was then the eastern end of the archipelago, quite close to the mainland. Unlike Archaeopteryx, anchiornithids were unable to fly, and might not have been able to reach areas further offshore. On the other hand, all true fossils of Archaeopteryx found so far were recovered from the lithographic limestone strata further to the west, closer to the open sea. Based on the new findings, Rauhut argues that other known Archaeopteryx fossils may need reassessment: “Not every bird-like fossil that turns up in the fine-grained limestones around Solnhofen need necessarily be a specimen of Archaeopteryx,” he points out.
The authors of the new study have proposed that the Haarlem specimen be assigned to a new genus, for which they suggest the name Ostromia — in honor of the American paleontologist John Ostrom, who first identified the fossil as a theropod dinosaur.
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Feathered dinosaurs were even fluffier than we thought
A University of Bristol-led study has revealed new details about dinosaur feathers and enabled scientists to further refine what is potentially the most accurate depiction of any dinosaur species to date.
Birds are the direct descendants of a group of feathered, carnivorous dinosaurs that, along with true birds, are referred to as paravians — examples of which include the infamous Velociraptor.
Researchers examined, at high resolution, an exceptionally-preserved fossil of the crow-sized paravian dinosaur Anchiornis — comparing its fossilised feathers to those of other dinosaurs and extinct birds.
The feathers around the body of Anchiornis, known as contour feathers, revealed a newly-described, extinct, primitive feather form consisting of a short quill with long, independent, flexible barbs erupting from the quill at low angles to form two vanes and a forked feather shape.
The observations were made possible by decay processes that separated some of these feathers from the body prior to burial and fossilisation, making their structure easier to interpret.
Such feathers would have given Anchiornis a fluffy appearance relative to the streamlined bodies of modern flying birds, whose feathers have tightly-zipped vanes forming continuous surfaces. Anchiornis’s unzipped feathers might have affected the animal’s ability to control its temperature and repel water, possibly being less effective than the vanes of most modern feathers. This shaggy plumage would also have increased drag when Anchiornis glided.
Additionally, the feathers on the wing of Anchiornis lack the aerodynamic, asymmetrical vanes of modern flight feathers, and the new research shows that these vanes were also not tightly-zipped compared to modern flight feathers. This would have hindered the feather’s ability to form a lift surface. To compensate, paravians like Anchiornis packed multiple rows of long feathers into the wing, unlike modern birds, where most of the wing surface is formed by just one row of feathers.
Furthermore, Anchiornis and other paravians had four wings, with long feathers on the legs in addition to the arms, as well as elongated feathers forming a fringe around the tail. This increase in surface-area likely allowed for gliding before the evolution of powered flight.
To assist in reconstructing the updated look of Anchiornis, scientific illustrator Rebecca Gelernter worked with Evan Saitta and Dr Jakob Vinther, from the University of Bristol’s School of Earth Sciences and School of Biological Sciences, to draw the animal as it was in life.
The new piece represents a radical shift in dinosaur depictions and incorporates previous research.
The color patterns for Anchiornis are known from fossilised pigment studies, the outline of the flesh of the animal has been constructed by examining fossils under laser fluorescence, and previous work has described the multi-tiered layering of the wing feathers.
Evan Saitta said: “The novel aspects of the wing and contour feathers, as well as fully-feathered hands and feet, are added to the depiction.
“Most provocatively, Anchiornis is presented in this artwork climbing in the manner of hoatzin chicks, the only living bird whose juveniles retain a relic of their dinosaurian past, a functional claw.
“This contrasts much previous art that places paravians perched on top of branches like modern birds.
“However, such perching is unlikely given the lack of a reversed toe as in modern perching birds and climbing is consistent with the well-developed arms and claws in paravians.
“Overall, our study provides some new insight into the appearance of dinosaurs, their behavior and physiology, and the evolution of feathers, birds, and powered flight.”
Rebecca Gelernter added: “Paleoart is a weird blend of strict anatomical drawing, wildlife art, and speculative biology. The goal is to depict extinct animals and plants as accurately as possible given the available data and knowledge of the subject’s closest living relatives.
“As a result of this study and other recent work, this is now possible to an unprecedented degree for Anchiornis. It’s easy to see it as a living animal with complex behaviours, not just a flattened fossil.
“It’s really exciting to be able to work with the scientists at the forefront of these discoveries, and to show others what we believe these fluffy, toothy almost-birds looked like as they went about their Jurassic business.”
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Bryozoans: Fossil fills missing evolutionary link
Lurking in oceans, rivers and lakes around the world are tiny, ancient animals known to few people. Bryozoans, tiny marine creatures that live in colonies, are “living fossils” — their lineage goes back to the time when multi-celled life was a newfangled concept. But until now, scientists were missing evidence of one important breakthrough that helped the bryozoans survive 500 million years as the world changed around them.
Today, the diverse group of bryozoans that dominate modern seas build a great range of structures, from fans to sheets to weird, brain-like blobs. But for the first 50 or 60 million years of their existence, they could only grow like blankets over whatever surface they happened upon.
Scientists recently announced the discovery of that missing evolutionary link — the first known member of the modern bryozoans to grow up into a structure. Called Jablonskipora kidwellae, it is named after UChicago geophysical scientists David Jablonski and Susan Kidwell.
Both are prominent scholars in their fields: Jablonski in origins, extinctions and other forces shaping biodiversity across time and space in marine invertebrates; Kidwell in the study of how fossils are preserved and the reliability of paleobiologic data, especially for detecting recent, human-driven changes to ecosystems. They also happen to be married.
“We were absolutely thrilled. What a treat and an honor, to have this little guy named after us,” said Jablonski, the William R. Kenan Jr. Distinguished Service Professor of Geophysical Sciences.
“I never expected to have a fossil named after me,” said Kidwell, the William Rainey Harper Professor in Geophysical Sciences, “and here it’s one that is an evolutionary breakthrough. We’re still smiling about it.”
Jablonskipora kidwellae lived about 105 million years ago, latching on to rocks and other hard surfaces in shallow seas — a bit like corals, though they’re not related. The fossils came from southwest England, along cliffs near Devon, originally collected in 1903 and analyzed by co-discoverers Paul Taylor and Silviu Martha from London’s Natural History Museum.
Bryozoans never figured out a symbiotic partnership with photosynthetic bacteria, as coral did, so their evolution took a different turn. Each one in a colony is genetically identical, but they have specialized roles, like ants or bees. Their shelly apartment complexes house thousands of the creatures, which have soft bodies with tiny tentacles to catch nutrients.
Growing upright was an evolutionary hack for Jablonskipora kidwellae, the two professors said: building bigger colonies extending upward from just a tiny attachment site was a good evolutionary move, allowing it to tap the water flowing above the sea floor — both for food and to scatter its offspring further. “This is a huge competitive advantage for them,” Jablonski said, “but it required some evolutionary organization to create a vertical structure.” Kidwell added: “This is the next level of cooperation among these individuals within the colony.”
They expressed a fondness for the creature, which they said was, like other bryozoans, “small and slow, but fierce.” Bryozoan fossils are sometimes found having bulldozed right over neighboring colonies in an intense battle for growing space. In a manner of speaking: this all would have taken place in extremely slow motion.
“They’re pretty fabulous little animals,” Kidwell said.
Jablonski and Kidwell have been friends with Taylor, one of the discoverers, since they spent summers on various research at the London Natural History Museum in the 1980s, but they said his news took them both completely by surprise. Jablonski had previously co-authored one paper with Taylor; Kidwell is currently collaborating with him on a study of bryozoan skeletal debris in modern sediments from the Channel Islands off Los Angeles.
It is the second honor of the year for both Kidwell and Jablonski: In April she received the Moore Medal from the Society for Sedimentary Geology, and in October he received the Paleontological Society Medal, that society’s highest honor.
Jablonski had one previous species named after him — a tiny clam — but Jablonskiporawill now be a genus in addition to a species.
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Colorado River’s connection with the ocean was a punctuated affair
The Colorado River’s initial trip to the ocean didn’t come easy, but its story has emerged from layers of sediment preserved within tectonically active stretches of the waterway’s lower reaches.
A scientific team, led by geologist Rebecca Dorsey of the University of Oregon, theorizes that the river’s route off the Colorado Plateau was influenced by a combination of tectonic deformation and changing sea levels that produced a series of stops and starts between roughly 6.3 and 4.8 million years ago.
Dorsey’s team lays out its case in an invited-research paper in the journal Sedimentary Geology. The team’s interpretation challenges long-held conventional thinking that once a river connects to the ocean it’s a done deal.
“The birth of the Colorado River was more punctuated and filled with more uneven behavior than we expected,” Dorsey said. “We’ve been trying to figure this out for years. This study is a major synthesis of regional stratigraphy, sedimentology and micropaleontology. By integrating these different datasets we are able to identify the different processes that controlled the birth and early evolution of this iconic river system.”
The region covered in the research stretches from the southern Bouse Formation, near present-day Blythe, California, to the western Salton Trough north of where the river now trickles into the Gulf of California. The Bouse Formation and deposits in the Salton Trough have similar ages and span both sides of the San Andreas Fault, providing important clues to the river’s origins.
Last year, in the journal Geology, a project led by graduate student Brennan O’Connell, a co-author on the new study, concluded that laminated sediments found in exposed rock along the river near Blythe were deposited by tidal currents 5.5 million years ago. The Gulf of California, it was argued, extended into the region, but the age of the deposits and tectonic and sea level changes at work during that time were not well understood.
Analyses by Kristin McDougall, a micropaleontologist with the U.S. Geological Survey and co-author on the new paper, helped the team better pinpoint the timing of the limestone deposits to about 6 million years ago, when tiny marine organisms lived in the water and were deposited at the same time.
About 5.4 million years ago, conditions changed. Global sea level was falling but instead of bay water levels declining, as would be expected, the water depth increased due to tectonic subsidence of the crust, the researchers discovered.
The basal carbonate material left by marine organisms was then inundated by fresh water as the river swept down into lower elevations, bringing with it clay and sand from mountain terrain, they found.
“The bay filled up with river sediment as the sediment migrated toward the ocean,” Dorsey said. “As more sediment came in, transport processes caused the delta front to move down the valley, transforming the marine bay into a delta and then the earliest through-flowing Colorado River.”
The river had arrived in the gulf, but only temporarily. A tug-of-war lasting for 200,000 to 300,000 years began some 5.1 million years ago, when the river stopped delivering sediments from upstream. The delta retreated and seawater returned to the lower Colorado River valley for a short time. The evidence is in the stratigraphy and fossils. Researchers found that clay and sand from the river became mixed with and then covered by marine sediment.
Something, Dorsey said, apparently was happening upstream, trapping river sediment. A good bet, the researchers think, is tectonic activity, perhaps earthquakes along a fault zone in the river’s northern basin that created subsidence in the riverbed or deep lakes along the river’s path.
At roughly 4.8 million years ago, the river resumed depositing massive amounts of sediment back into the Salton Trough and began rebuilding the delta. Today’s view of the delta, however, reflects human-made modern disturbances to the river’s sediment discharge and flow of water reaching the gulf.
To meet agricultural demands for irrigation and drinking water for human consumption, Hoover Dam was constructed on the river to form Lake Mead during the 1930s. In 1956-1966, Glen Canyon Dam was built, forming Lake Powell.
“If we could go back to 1900 before the dams that trap the sediment and water, we would see that the delta area was full of channels, islands, sand bars and moving sediment. It was a very diverse, dynamic and rich delta system. But humanmade dams are trapping sediment today, eerily similar to what happened roughly 5 million years ago,” Dorsey said.
The bottom line of the research, she said, is that no single process controlled the Colorado River’s initial route to the sea. “Different processes interacted in a surprisingly complicated sequence of events that led to the final integration of that river out to the ocean,” she said.
The research, Dorsey said, provides insights that help scientists understand how such systems change through time. The Colorado River is an excellent natural laboratory, she said, because sedimentary deposits that formed prior to and during river initiation are well exposed throughout the lower river valley.
“This research,” Dorsey said, “is very relevant to today because we have global sea level rising, climate is warming, coastlines are being inundated and submerged, and the supply of river sediment exerts a critical control on the fate of deltas where they meet the ocean. Documenting the complex interaction of these processes in the past helps us understand what is happening today.”
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