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Mammals get smaller when the climate heats up?

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larger earlier vs smaller later specimen/U New Hampshire

Researchers suggest so based on studies of early fossil rabbit and horse types. From ScienceDaily:

More than 50 million years ago, when the Earth experienced a series of extreme global warming events, early mammals responded by shrinking in size. While this mammalian dwarfism has previously been linked to the largest of these events, new research has found that this evolutionary process can happen in smaller, so-called hyperthermals, indicating an important pattern that could help shape an understanding of underlying effects of current human-caused climate change.

Researchers propose that the body change could have been an evolutionary response to create a more efficient way to reduce body heat. A smaller body size would allow the animals to cool down faster. Nutrient availability and quality in plants may have also played a role. Previous research shows that both the PETM and the ETM2 hyperthermals coincided with increased levels of carbon dioxide in the atmosphere and that could have limited nutrient quality in plants, which may have contributed to the smaller mammal body size. Hydrological records during the PETM also suggest less precipitation and drought which could have led to drier soils and even fire which may have affected vegetation growth and eventually possibly offspring size. After both hyperthermal events, body sizes on all mammals rebounded. Paper. (public access) – Abigail R. D’Ambrosia, William C. Clyde, Henry C. Fricke, Philip D. Gingerich, Hemmo A. Abels. Repetitive mammalian dwarfing during ancient greenhouse warming events. Science Advances, 2017; 3 (3): e1601430 DOI: 10.1126/sciadv.1601430More.

It’s logical from a physics perspective, of course (increasing surface to volume area). And size variations can be due to a variety of other factors. Islands, for example, can produce great changes in size, probably due to specialized food sources and predation. These change may be more flexible than we think. It will be interesting to find out if some of them are enabled by that vast library of “junk” in the genome.

From USA Today:

Three different species shrank noticeably about 54 million years ago when the planet suddenly heated up. One of them — an early, compact horse — got 14 percent smaller, going from about 17 pounds (7.7 kilograms) to 14.6 pounds (6.6 kilograms), according to an analysis of fossil teeth in Wednesday’s journal Science Advances.

In hotter climates, mammals and other warm-blooded animals need to shed heat so they shrink. Smaller animals have more skin — or fur — per pound than bigger animals so more heat can escape, making them better adapted for warmer climate. Larger animals do better in the cold because they have less skin per pound and keep their heat.

See also: Researchers: Island rule of size evolution does apply to rodents

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By contrast, Ice Age mammals could get pretty big

asauber, True! But fiction, (religion, faith etc) just has less evidence to make these guesses. 'It is estimated' that there are one hundred billion stars in our galaxy. It is 'guessed' that the universe contains at least, one hundred billion galaxies. If each star in this one hundred billion times one hundred billion star galaxy universe, has planets (and current science suggests they do), then the chances of life are very high. You and yours say, 'impossible'! Far from it, highly highly, probable, but very poorly designed.. rvb8
language based on intuition, good guesses, the possible, what realistically may of happened, the best scenerio, within the realm of nature and not the SUPERNATURAL, also uses the language you ridicule
So does fiction. Andrew asauber
asauber, language based on intuition, good guesses, the possible, what realistically may of happened, the best scenerio, within the realm of nature and not the SUPERNATURAL, also uses the language you ridicule. rvb8
rvb8, You lost me. What's your point? Andrew asauber
News @ 3 - Good news. We have more data. Bergmann's rule isn't just about appendages, it's now used for body size generally. Bob O'H
asauber, Detectives said: "The killers 'could have been' between 1.8-1.95m tall judging from the break in point at the window. The murders 'may have contributed' to a speight of copycat incidents, and, 'coincided' with the terrible weather as cover. All of this 'could have led' to the large number of tourists who left the city. We don't want to 'suggest' a direct correlation 'which may have' serious repercussions on the local economy, it's just very well supported by past events in other tourist towns. 'Possibly', uninquisitive people will ignore this evidence, but I rather doubt a balanced observer would." rvb8
Elephants and giraffes don't have small appendages. Armand Jacks
Would the giant mammals of Africa get bigger if their habitat cooled down? ppolish
I was just informing you what it is called. And if my memory is correct (no guarantee) it was more about reduced size of appendages relative to body at higher latitudes than it was about body size. Which makes sense thermodynamically. Armand Jacks
Armand Jacks at 1, it is far from clear that there is a rule. One needs way more data for that. The authors are right to be cautious in the way that asauber notes at 2. News
"could have been" "may have contributed" "coincided" "could have led" "suggest" "which may have" "possibly" If that doesn't convince you of somethin', nothin' will! Andrew asauber
Back in my school days this was called Bergman's rule. Something observed in 1847. Armand Jacks

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