Very interesting read Quarry. I am glad I am a very large mammal !
I choose to interpret this news as indicative of Basenoters being among the most highly evolved of our species. ~ Q
* * *From a public-domain press release:
Large Brains in Mammals First Evolved for Better Sense of Smell
Ability to sense touch through fur also a factorImages available: click herePittsburgh, Pennsylvania… Paleontologists have often wondered why mammals—including humans—evolved to have larger brains than other animals. A team of paleontologists now believe that large brains may have developed in mammals to facilitate an acute sense of smell, according to a new paper published today in the prestigious journal Science. The team also noticed enlargement in the areas of the brain that correspond to the ability to sense touch through fur; this sense is acutely developed in mammals.
Scientists used high-resolution CT scans to study rare 190-million-year-old fossil skulls of Morganucodon and Hadrocodium, two of the earliest known mammal species. The research team of Timothy Rowe (University of Texas at Austin), Thomas Macrini (St. Mary’s University of Texas), and Zhe-Xi Luo (Carnegie Museum of Natural History) discovered that these tiny mammals from the Jurassic fossil beds of China had much larger brains than expected for specimens of their period. Carnegie paleontologist Luo and his colleagues were the first to discover Hadrocodium, a tiny early Jurassic age mammal that weighed just two grams. Luo noticed that this animal had a very large cranium compared to its tiny body mass, and named it accordingly (“Hadro” being Latin for “fullness”; codium for “head”).
“Our new study shows clearly that the olfactory part of the brain and the part of the brain linked to tactile sensation through fur were enlarged in these early mammals,” says Luo. “A sophisticated sense of smell and touch would have been crucial for mammals to survive and even thrive in the earliest part of our evolutionary history.”
Using computed tomography, also known as CT scanning, the team took a series of X-rays, inching along the specimens and then reassembling the images into a single, detailed image of the interior anatomy of the fossils.
“I have spent years studying these fossils, but until they were CT scanned it was impossible to see the internal details unless you were willing to destroy the skulls to look inside,” says Luo. “I was absolutely thrilled to see the shape of the brain of our 190-million-year-old mammal relatives.”
“This is a great example of technology allowing us to examine classic scientific questions in a new way,” says University of Texas at Austin paleontologist Rowe. “We had studied the outside features of these fossils for years but knew that the inside held the answers. Until now, getting to those answers required destructive methods. With high-resolution CT scanning, we can take a good look into the braincase without damaging the precious fossils—we can have our cake and eat it too.”
Thomas Macrini of St. Mary’s University (Texas), an expert in analyzing interior structures of fossils through CT scanning, was able to construct a virtual cast of the brains of these mammals. These were compared to the team’s CT-scan data from more than a dozen other fossils and some 200 mammal species living today. The results were surprising: Even 190 million years ago, the brains of the earliest mammals were notably large (as relative to body mass), with brain-to-body sizes approaching the proportions seen in modern mammals.
From previously discovered fossil evidence, scientists knew that the nasal structure in some early mammals was quite advanced. From the CT scans of Morganucodon and Hadrocodium researchers were able to determine that area of the brain that had grown the largest in these early mammals was the region responsible for the sense of smell. The CT scans of Morganucodon and Hadrocodium also revealed that the area of the brain mapped to tactile sensations from fur was enlarged. Mammals have a uniquely well developed ability to sense touch through their fur. Jurassic mammals such as Hadrocodium are considered by scientists to have had full coats of dense hair.
“Our mammal ancestors didn’t develop that larger brain for contemplation, but for the sense of smell and touch. But thanks to these evolutionary advancements, which gave mammals a head start toward developing a large brain, humans some 190 million years later can ponder these very questions of natural history and evolution,” said Luo.
Carnegie Museum of Natural History, one of the four Carnegie Museums of Pittsburgh, is ranked among the top five natural history museums in the country. It maintains, preserves, and interprets an extraordinary collection of 20 million objects and scientific specimens used to broaden understanding of evolution, conservation, and biodiversity. More information is available by calling 412.622.3131 or by visiting the Web site, www.carnegiemnh.org.
Very interesting read Quarry. I am glad I am a very large mammal !
Petty small minded people have no place in my life.
Thank you, Quarry. You don't suppose other mammals with large brains also have a nose for scents? Dogs?
I imagine the role it plays in smelling danger (water, fire) or choosing suitable mates?
"...her fragrance all in my keeping; softly she comes in the night." Lyrics, Gordon Lightfoot, "Softly."
Very cool! Thanks for the very interesting info!
Sorry, but this is uncritical reading... correlation does not imply causation correlation does not imply causation correlation does not imply causation.
Now that that's out of my system, many mammals today (e.g. rodents) have, compared to their overall brain volume, very large olfactory bulbs. (Just google image rat brain, the prominent anterior portion of their brain is the olfactory bulb). How do we interpret this? It seems promising to interpret it as suggesting that a robust olfactory system is highly adaptive, and that rats that had larger olfactory bulbs were more likely to survive over evolutionary history. But this is a logical fallacy. We are fitting our explanation to the data. The fact is we don't really know what caused those rats with larger olfactory bulbs to survive.
Similar situation here, we don't really know what happened--there's a tendency to speak of evolution as if it has direction, it does not it does not it does not. Evolution works on variation. The mammalian brain did not "evolve" for a better sense of smell. All the data says is that the individuals with smaller olfactory bulbs were not as reproductively successful as those with larger olfactory bulbs.
Further, the existence of prehistoric mammals with large olfactory bulbs does not have very many implications for the evolutionary ontogeny of primates. A case in point is the rat, they have large olfactory bulbs too, but we certainly don't call them "large brained": the fact that we have an evolutionary ancestor that has a large olfactory bulb is not very meaningful for us except insofar as it helped them survive (e.g. if they became extinct, perhaps we wouldn't be here today). I should add some numbers: mice have 910 intact olfactory receptor genes, humans only have 363. Dogs have ~1 billion olfactory receptor neurons, rabbits have ~100 million, humans only have ~40 million. The human olfactory bulb is smaller than that of the rabbit and the dog. What differentiates primates and humans in particular is enlarged cortex, i.e. outer layer of the human brain. Humans rely less on olfaction than dogs and rats. The olfactory bulb size of a 190 million year old common ancestor may not really mean that much for large brains after all.
Such a panoply of variations contributed to mammals’ spectrum of evolutionary qualities that no factor would be attributed singular or linear credit. A more capable sense of smell hypothetically allowed some early mammals to avoid some dangers and/or locate some food and/or recognize their mate and/or rear their young in ways that tipped the balance in allowing a combination of adaptations to advance through generations. It could even be that the proclivity for more-capable olfactory biology happened to repress other traits which would put individuals at a disadvantage.
If you knew me, inscents, you'd know I was just being funny about Basenoters’ evolutionary superiority. It's been my observation that BNers have a superior sense of smell, sense of humor and above-average critical thinking skills.
By the by, it's "data are" (plural), compound modifiers should be hyphenated ("190-million-year-old common ancestor"), and you could bone up on your use of commas. See how fun gets bullied out of a thread when someone sweeps in and assumes superiority?
Do I have to be an evolutionarily-superior large mammal to smell trouble?
For what precious little it is worth, I enjoyed and appreciated reading all of the posts in this thread, if not necessarily the tone underlying them.
Thanks for the thread, Quarry.
I grant that I used the word 'data' as if it were singular once. I also grant that I did not hyphenate that compound modifier. I think the comma question is beside the point, which was emphasis.
I question your implication that I'm in any way assuming superiority. I'm trying to start a more critical discussion, which may or may not be working. If you felt offended by my accusation that this was an uncritical reading, please direct your attention to the fact that I began my post with an apology. And you're very right to say that I don't know you: please try to look at this mishap from my perspective--a naive observer reading words posted on the internet. I'm sorry if you felt offended.
As to the actual on-topic part of your post, I concede that, " A more capable sense of smell hypothetically allowed some early mammals to avoid some dangers and/or locate some food and/or recognize their mate and/or rear their young in ways that tipped the balance in allowing a combination of adaptations to advance through generations." Hypothetically. I can also concede the latter hypothesis. Thank you for supplying the word this time. Nevertheless, since these are explanations fit to the data, we should practice caution when trying to extrapolate.
I maintain that the only warranted claim here is that our 190-million-year-old evolutionary ancestors with larger olfactory bulbs were probably more reproductively successful than those with smaller olfactory bulbs, without positing a potentially unverifiable mechanism. This must be a probability statement even though we have no a priori reason to think that small and large olfactory bulb size produce differential patterns (because what if they do?) of fossilization except as a function of reproductive success.