It has been determined when mammals became warm b;ooded

[shunyadragon]

Source: https://www.livescience.com/warm-blooded-mammals-evolution

Scientists pinpoint the exact moment in evolutionary time when mammals became warm-blooded

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Source: https://www.livescience.com/warm-blooded-mammals-evolution

By Ben Turner published 6 days ago

And it happened much more quickly than scientists expected.

Scientists have pinpointed the moment in time our earliest ancestors evolved to be warm-blooded, and it happened much later and far more quickly than the researchers expected.

The discovery, made by studying the minuscule tubes of the inner ear, places the evolution of mammalian warm-bloodedness at around 233 million years ago — 19 million years later than scientists previously thought.

These semicircular canals are filled with a viscous fluid, called endolymph, that tickles tiny hairs lining the canals as the fluid sloshes around. These hairs transmit messages to the brain, giving it instructions for how to keep the body balanced. Like some fluids, the honey-like endolymph gets runnier the hotter it is, requiring the semicircular canals to change their shape so the fluid can still do its job. In ectothermic, or cold-blooded, animals, this ear fluid is colder and thus behaves more like molasses and needs wider spaces in which to flow. But for endothermic, or warm-blooded, animals, the fluid is more watery and small spaces suffice

This temperature-based property makes tiny, semicircular canals a perfect place to spot the moment when ancient mammals' cold blood turned hot, researchers wrote in a paper published July 20 in the journal Nature(opens in new tab).

"Until now, semicircular canals were generally used to predict locomotion of fossil organisms," study co-lead author Romain David, an evolutionary anthropologist at the Natural History Museum in London, said in a statement(opens in new tab). "However, by carefully looking at their biomechanics, we figured that we could also use them to infer body temperatures.

"This is because, like honey, the fluid contained inside semicircular canals gets less viscous [syrupy] when temperature increases, impacting function," David explained. "Hence, during the transition to endothermy, morphological adaptations were required to keep optimal performances, and we could track them in mammal ancestors."

To discover the time of this evolutionary change, researchers measured three inner ear canal samples from 341 animals — 243 living species and 64 extinct species — spanning the animal kingdom. The analysis revealed that the 54 extinct mammals included in the study developed the narrow inner ear canal structures suitable for warm-blooded animals 233 million years ago.

Before this study, scientists thought mammals inherited warm-bloodedness from the cynodonts — a group of scaly, rat-like lizards that gave rise to all living mammals — that were thought to have evolved warm-bloodedness around the time of their first appearance 252 million years ago. However, the new findings suggest that mammals diverged from their early ancestors more markedly than expected.

And this drastic change happened surprisingly fast. Heat-friendly ear canals didn't just appear later in the fossil record than the scientists expected. It happened far more rapidly, too — popping up around the same time the earliest mammals began evolving whiskers, fur and specialized backbones.

"Contrary to current scientific thinking, our paper surprisingly demonstrates that the acquisition of endothermy seem[s] to have occurred very quickly in geological terms, in less than a million years," study co-lead author Ricardo Araújo, a geologist at the University of Lisbon in Portugal, said in the statement. "It was not a gradual, slow process over tens of millions of years as previously thought, but maybe was attained quickly when triggered by novel mammal-like metabolic pathways and origin of fur."

Follow-up studies will need to confirm the findings via other means, but the researchers said they are excited that their work will help to answer one of the longest-standing questions about the evolution of mammals.

"The origin of mammalian endothermy is one of the great unsolved mysteries of paleontology," study senior author Kenneth Angielczyk, the Field Museum's MacArthur curator of paleomammalogy, said in the statement. "Many different approaches have been used to try to predict when it first evolved, but they have often given vague or conflicting results. We think our method shows real promise because it has been validated using a very large number of modern species, and it suggests that endothermy evolved at a time when many other features of the mammalian body plan were also falling into place."

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[rogue06]

[shunyadragon]

There is more to this than the fact that mammals became warm-blooded 233 million years ago. Yes, this is the time that mammals became truly mammals. What happened 233 million years ago?

This is a subject that has interested me for a long time, I visited several fossil sites in California some years back. It is the Carnian Pluvial Event where a wide spread of volcanism caused a radical extinction event and rapid evolution of many of new species of plants and animals.

Source: https://www.universetoday.com/147929/a-new-mass-extinction-has-been-discovered-wiping-out-life-233-million-years-ago-and-leading-to-the-rise-of-the-dinosaurs/

The Triassic Period began about 252 mya with the Induan Age. The Cretaceous Period ended about 72 mya, at the end of the Maastrichtian Age. The Wrangell Province formed in the middle-late Triassic and joined North America in the late Jurassic or early Cretaceous Period. Image Credit: Wikipedia
One of the first indications of climate change and extinction during the Carnian was evidence of a prolonged period of increased rainfall. Geologists first discovered this rainfall in the 1980s, and they thought the period lasted about one million years. As the climate changed during that time, it caused a major loss of biodiversity, on land and in the oceans.

As a result of that extinction, coniferous forests expanded, and other, newer types of plant life appeared. The Earth’s ecosystems began to look more like modern-day Earth. But the shift meant a food crisis for existing herbivores.

“The new floras probably provided slim pickings for the surviving herbivorous reptiles,” said Professor Mike Benton. “I had noted a floral switch and ecological catastrophe among the herbivores back in 1983 when I completed my PhD. We now know that dinosaurs originated some 20 million years before this event, but they remained quite rare and unimportant until the Carnian Pluvial Episode hit. It was the sudden arid conditions after the humid episode that gave dinosaurs their chance.”

This is a photograph of the Nikolai Formation along Glacier Creek in the Wrangell Mountains, Alaska. It’s part of the Wrangellis Igneous Province, and shows a deposit of basaltic lava about 1000 meters tall. The yellow line shows the top of the basalt, with a limestone formation above it. The volcanic activity that created this basalt also caused the climate to change rapidly, creating an extended period of rainfall, the Carnian Pluvial Event. That event triggered a mass extinction. Image Credit: Greene et al, 2008.
A bunch of new species appeared at the same time. The Carnian Pluvial Episode didn’t just create space for dinosaurs. The first turtles, crocodiles, lizards, and mammals also appeared. In the oceans, the first coral reefs appeared, as well as many modern plankton groups. The changes in the oceans’ plankton suggest “profound changes in the ocean chemistry and carbonate cycle,” according to the authors.

In their paper they write that “In the sea, the rise of the first scleractinian reefs and rock-forming calcareous nannofossils points to substantial changes in ocean chemistry. On land, there were major diversifications and originations of conifers, insects, dinosaurs, crocodiles, lizards, turtles, and mammals.”

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My interest is that this geologic extinction event demonstrated that evolution is environmentally driven, and a radical change in the environment resulted in probably the , most radical evolutionary change in life forms that lead to the biodiversity of of life today.