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Pterosaur Feathers Deepen Debate Over Their Evolution

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pterosaur feathers

Artist rendering of a short-tailed pterosaur feathers and all. (Credit: Yuan Zhang/Nature Ecology & Evolution)

The discovery of novel filaments on two species of pterosaur suggests that the extinct flying reptiles had complex coats of “feathers” and fuzz, say the authors of a new study. The presence of these apparent pterosaur feathers may indicate that the ancestor of both pterosaurs and their cousins, dinosaurs, sported similar coverings — but that’s not the only hypothesis.

Like dinosaurs, pterosaurs are archosaurs. This group of reptiles, which also includes crocodilians, likely emerged in the Late Permian Period (more than 250 million years ago) and dominated the Mesozoic Era that followed. Archosaurs abounded, all the way up until about 66 million years ago and the end-Cretaceous mass extinction, which spared only one dinosaur lineage (birds) and some crocodilians.

True feathers, with complex, branched structures, have been found on several theropods — one of the main branches of the dinosaur family tree and the lineage that includes birds. Less complex filaments, akin to fuzz or down, have been found on a few non-theropod dinosaurs.

For decades, paleontologists have also found filaments on well-preserved pterosaur fossils. These filaments, known as pycnofibers, have been simple structures — think a hollow, unbranched tube — that illustrators typically render as a fur-like covering when recreating the animals.

A More Complex Story Takes Shape

Today, however, researchers announce that they have found four different types of pycnofibers on two specimens of short-tailed pterosaurs from the Middle-Late Jurassic of China, more than 160 million years ago.

Type 1, as described in the new study, is the simple, hollow pycnofiber seen on other pterosaur fossils. This type covers most of the body of each specimen, reminiscent of mammalian underfur, say the authors, suggesting it may have played a role in thermoregulation.

The other three types, however, appear to be branched structures and are present only in specific areas. Type 4, for example, which superficially resembles a tree branch (see (n) in image below), occurs only on the wing membranes.

Fossilized filamentous structures. Credit: Baoyu Jiang, Michael Benton et al./Nature Ecology & Evolution

Fossilized pterosaur pycnofibers found on the individuals include Type 1, a simple hollow tube (e) and three more complex types that the authors say have branching structures similar to true feathers (h, k, n). (Credit: Baoyu Jiang, Michael Benton et al./Nature Ecology & Evolution)

Types 2 and 3 (h and k, above) appear to have different branching structures and were found only on small areas of the head, neck and limbs of one specimen.

Further analysis of all four types of pycnofibers revealed they have a chemical signature similar to that of human hair and the feathers of living birds.

Preserved within the pycnofibers, say the authors, are melanosomes: cellular structures that provide clues to the animal’s pigmentation in life. Fossilized melanosomes recently have been used to reconstruct iridescent dinosaur feathers, but the pterosaurs were apparently not quite so flamboyant. Based on their melanosomes, the flying reptiles would have been mostly brown.

Convergent Controversy

The presence of apparently branched pycnofibers on the fossils reinvigorates a general debate over feathers in Archosauria. Researchers and armchair paleontologists alike have long argued over when true feathers evolved and in which lineages.

(Most scientists believe the first feathers probably emerged for insulation and display, such as to signal an individual’s fitness to a potential mate. Only much later along the evolutionary road were they co-opted, by some species, for use in flight.)

One school of thought holds that true, branched feathers evolved among theropod dinosaurs, though not every theropod sported them. There is no evidence, for example, that T. rex and other iconic megapredators had feathers. This hypothesis suggests that any unbranched feathers or other filamentous structures found on pterosaurs and non-theropod dinosaurs were examples of convergent evolution, when unrelated species occupying the same ecological niche evolve similar traits.

According to this hypothesis, pterosaurs’ pycnofibers arose independently from dinosaur feathers.

The new analysis of the two Chinese pterosaurs’ pycnofibers, however, could be seen as evidence for another hypothesis: that the currently unknown archosaur ancestor of both dinosaurs and pterosaurs had feathers of some type, and passed the trait down to both groups.

Phylogenetic comparative analysis of integumentary filament and feather evolution in pterosaurs and archosaurs. Credit: Baoyu Jiang, Michael Benton et al./Nature Ecology & Evolution

The authors of today’s research included a comparative analysis of filament and feather evolution in pterosaurs and other archosaurs, notably dinosaurs. (Credit: Baoyu Jiang, Michael Benton et al./Nature Ecology & Evolution)

Today’s paper is not the first time researchers have declared they’ve essentially found pterosaur feathers. Pycnofibers on another Chinese pterosaur, Pterorhynchus wellnhoferi, were described as branching and homologous to feathers, though subsequent analysis by other paleontologists questioned those conclusions. That earlier paper, like today’s study, is no slam-dunk in part because analysis of the pycnofibers is as much art as science, and open to interpretation.

The new research appears in Nature Ecology & Evolution.

 

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Ecology

Today’s letters: ‘Visionary’ plans don’t always work in Ottawa

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The opinion piece written by Tobi Nussbaum, CEO of the NCC, declares that a “bold, visionary transit plan” would showcase the capital.

As a long-term resident of Ottawa, I’ve had it with visionary plans. In the 1950s, the streetcars serving Ottawa so well were sent to the scrapyards. In the early ’60s, Queensway construction bulldozed established neighbourhoods and ripped the city apart. Later in the decade, the downtown railway station, which could have formed the hub of a commuter network, was relocated to the suburbs. These actions, in the name of “progress,” were undertaken with the “vision” to make Ottawa a car-reliant city.

Now we have an LRT, built just in time for most people to realize that they do not have to go downtown as they can work from home.

Current thinking is pushing a new “link” between Ottawa and Gatineau, with yet more expensive and disruptive infrastructure projects being touted, including a tramway or another tunnel under the downtown core.

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Ecology

That was then: Biggest earthquake since 1653 rocked Ottawa in 1925

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A regular weekly look-back at some offbeat or interesting stories that have appeared in the Ottawa Citizen over its 175-year history. Today: The big one hits.

The Ottawa Senators were playing a Saturday night game against the Montreal Canadiens at the Auditorium, the score tied 0-0 halfway through the second period. Sens’ rookie Ed Gorman and the Habs’ Billy Boucher had just served penalties for a dustup when the building began to make “ominous creaking sounds.” A window crashed to the ground.

Nearby, at Lisgar Collegiate, all eyes were on teenager Roxie Carrier, in the role of Donna Cyrilla in the musical comedy El Bandido. She had the stage to herself and was singing “Sometime” when the building rocked, the spotlight went out, and someone in the audience yelled “Fire!”

At a home on Carey Avenue, one woman’s normally relaxed cat suddenly arched its back, rushed around the room two or three times, spitting angrily, and climbed up the front-window curtains.

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Ecology

Ottawa delays small nuclear reactor plan as critics decry push for new reactors

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TORONTO — Canadians will have to wait a little while longer to see the federal government’s plan for the development of small nuclear reactors, seen by proponents as critical to the country’s fight against global warming.

Speaking at the opening of a two-day virtual international conference on Wednesday, the parliamentary secretary to the minister of natural resources said the plan will lay out key actions regarding the reactors. Its launch, Paul Lefebvre said, would come in the next few weeks.

“We’re still putting the finishing touches on it,” Lefebvre said. “The action plan is too important to be rushed.”

Small modular reactors — SMRs — are smaller in size and energy output than traditional nuclear power units, and more flexible in their deployment. While conventional reactors produce around 800 megawatts of power, SMRs can deliver up to 300 megawatts.

Proponents consider them ideal as both part of the regular electricity grid as well as for use in remote locations, including industrial sites and isolated northern communities. They could also play a role in the production of hydrogen and local heating.

“SMRs will allow us to take a bold step of meeting our goal of net-zero (emissions) by 2050 while creating good, middle class jobs and strengthening our competitive advantage,” said Lefebvre.

Natural Resources Minister Seamus O’Regan had been scheduled to speak at the conference but did not due to a family emergency.

Industry critics were quick to pounce on the government’s expected SMR announcement. They called on Ottawa to halt its plans to fund the experimental technology.

While nuclear power generation produces no greenhouse gas emissions, a major problem facing the industry is its growing mound of radioactive waste. This week, the government embarked on a round of consultations about what do with the dangerous material.

Dozens of groups, including the NDP, Bloc Quebecois, Green Party and some Indigenous organizations, oppose the plan for developing small modular reactors. They want the government to fight climate change by investing more in renewable energy and energy efficiency.

“We have options that are cheaper and safer and will be available quicker,” Richard Cannings, the NDP natural resources critic, said in a statement.

Lefebvre, however, said the global market for SMRs is expected to be worth between $150 billion and $300 billion a year by 2040. As one of the world’s largest producers of uranium, Canada has to be part of the wave both for economic and environmental reasons, he said.

“There’s a growing demand for smaller, simpler and affordable nuclear technology energy,” Lefebvre said.

Joe McBrearty, head of Canadian Nuclear Laboratories, told the conference the company had signed a host agreement this week with Ottawa-based Global First Power for a demonstration SMR at its Chalk River campus in eastern Ontario. A demonstration reactor will allow for the assessment of the technology’s overall viability, he said.

“When talking about deploying a new technology like an SMR, building a demonstration unit is vital to the success of that process,” McBrearty said. “Most importantly, it allows the public to see the reactor, to kick the tires so to speak, and to have confidence in the safety of its operation.”

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