Early mammal could help answer one of biology’s biggest question
August 14, 2024 12:29 PM Subscribe
Early mammal could help answer one of biology’s biggest question, say experts. Krusatodon kirtlingtonensis, which lived 166 million years ago, "a piece of the puzzle" explaining mammals’ success.
Mmmm... I'd say it addresses the how of mammals' success. I think the "why" is, these were the kinds of land tetrapods that could survive the K/T event, so that after the K/T boundary they are the only game in town. Of course they radiate into all kinds of niches.
Childhood is important in the way that changes to morphology are changes in childhood development. Plausibly having this rapid childhood phase gave one lineage a lever that it could use to get into a lot of niches, fast.
posted by Aardvark Cheeselog at 2:34 PM on August 14
Childhood is important in the way that changes to morphology are changes in childhood development. Plausibly having this rapid childhood phase gave one lineage a lever that it could use to get into a lot of niches, fast.
posted by Aardvark Cheeselog at 2:34 PM on August 14
A shorter lifespan means you need less cancer defenses. I'd expect cancer defenses must be expensive since in mammals they corrolate so closely with size.
A childhood might seperate when you allocate energy for development from when you allocate energy for reproduction. It's maybe that short lifespans that permit faster evolution, includng expansion into more niches, with childhood merely being a strategy to further shortten lifespans.
Annuals vs bi-annuals vs perennials vs bushes/trees maybe similar, with reptiles being like perennials or bushes/trees, and mammals being more like annuals or bi-annuals. It's easy for plants to evolve back n forth among these strategies though, but not so easy for animals.
In this, it's possible short lifespans plus childhood fit endotherms better, meaning if you waste energy heating yourself then you should die young, so selection pressures acts fast, but if you depend upon the ambient warmth then your life adjusts more anyways, so slow continuous growth remains advantageous.
Importantly, mammals and birds both developed endothermy, shorter lifespans, and childhood independently, since their split goes much further back, so likely the same selection pressures acted independently upon both, and maybe concurrently.
We think human civilization emerged becasue the climate remained exceptionally stable for the past 12,000 years, but we've a similar story for reptiles and mammals if we look much further back.
Amniotes evolved 350 mya, but reptiles evolved 315 mya when the climate wiggles became way less nasty. Around 95 mya ago birds emerge at the beginning of a long overall downward trend for temperatures, so maybe all these traits, in both mammals and birds, comes from adapting to ever colder & colder climates?
Amusingly, childhood sounds important for intelegence, so maybe one could subivide the intelegence term in the Drake equation. In fact, you might first rule out intelegence from emerging around starts that've started becomming brighter with age, and then require that animals with childhoods be pushed back into long lifespans, say by occupying niches after a long cooling, meteor strike, etc. Alright, that's going too far, but amusing.
posted by jeffburdges at 4:46 PM on August 14
A childhood might seperate when you allocate energy for development from when you allocate energy for reproduction. It's maybe that short lifespans that permit faster evolution, includng expansion into more niches, with childhood merely being a strategy to further shortten lifespans.
Annuals vs bi-annuals vs perennials vs bushes/trees maybe similar, with reptiles being like perennials or bushes/trees, and mammals being more like annuals or bi-annuals. It's easy for plants to evolve back n forth among these strategies though, but not so easy for animals.
In this, it's possible short lifespans plus childhood fit endotherms better, meaning if you waste energy heating yourself then you should die young, so selection pressures acts fast, but if you depend upon the ambient warmth then your life adjusts more anyways, so slow continuous growth remains advantageous.
Importantly, mammals and birds both developed endothermy, shorter lifespans, and childhood independently, since their split goes much further back, so likely the same selection pressures acted independently upon both, and maybe concurrently.
We think human civilization emerged becasue the climate remained exceptionally stable for the past 12,000 years, but we've a similar story for reptiles and mammals if we look much further back.
Amniotes evolved 350 mya, but reptiles evolved 315 mya when the climate wiggles became way less nasty. Around 95 mya ago birds emerge at the beginning of a long overall downward trend for temperatures, so maybe all these traits, in both mammals and birds, comes from adapting to ever colder & colder climates?
Amusingly, childhood sounds important for intelegence, so maybe one could subivide the intelegence term in the Drake equation. In fact, you might first rule out intelegence from emerging around starts that've started becomming brighter with age, and then require that animals with childhoods be pushed back into long lifespans, say by occupying niches after a long cooling, meteor strike, etc. Alright, that's going too far, but amusing.
posted by jeffburdges at 4:46 PM on August 14
Of course they radiate into all kinds of niches.
There is definitely an "everyone who makes a wheel makes it round" element to this. Things evolve and fill niches and specialize. Then an extinction event happens and the critters that stayed generalists are the ones that can hold on. Things get stable and with all the niches clear, whatever is still around evolves to fill those niches.
But it's still true that a long snout with rows of small sharp is the best way to catch quick little fish. Dense forests tend to favor large ambush predators which then pushes prey to get larger (or smaller), plains and grasslands favor small lighter faster critters. The same body plans evolve over again all the time.
posted by VTX at 7:54 PM on August 14 [1 favorite]
There is definitely an "everyone who makes a wheel makes it round" element to this. Things evolve and fill niches and specialize. Then an extinction event happens and the critters that stayed generalists are the ones that can hold on. Things get stable and with all the niches clear, whatever is still around evolves to fill those niches.
But it's still true that a long snout with rows of small sharp is the best way to catch quick little fish. Dense forests tend to favor large ambush predators which then pushes prey to get larger (or smaller), plains and grasslands favor small lighter faster critters. The same body plans evolve over again all the time.
posted by VTX at 7:54 PM on August 14 [1 favorite]
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The article is telling us that the mammalian advantage was childhood. Rapid development to a big-enough adult size, rather than just slowly getting bigger and bigger like a lobster.
These protomammals didn't have childhood.
“Specifically, these little shrew-like animals, despite appearances, probably lived and died more like reptiles, with a long growth trajectory through childhood to maturity, and then a much longer lifespan than the live fast, die young approach of today’s small mammals”
posted by justsomebodythatyouusedtoknow at 1:25 PM on August 14 [2 favorites]