Science

Researchers rebuild the genome of the great-grandparent of all mammals

View 2 Images
The last common ancestor of all modern mammals likely looked like this recreation of a fossil animal, Morganucodon, which lived about 200 million years ago
The last common ancestor of all modern mammals likely looked like this recreation of a fossil animal, Morganucodon, which lived about 200 million years ago
Genus-level tree of modern mammals, all of which descended from a common ancestor, with some of Australia's odd marsupials like the platypus, kangaroo and koala among the earliest to diverge
OrthoMaM team at the Institute of Evolutionary Sciences of Montpellier (ISEM) and at the University of Montpellier. Licensed under Creative Commons Attribution-Share Alike 4.0 International

Some 180 million years ago, there lived an early mammal – built a lot like the guilty looking fella above – that became the earliest-known ancestor to all mammals on Earth, from the blue whale, to the camel, the rhino, the koala, and your good self.

Frankly, I'd be looking a little guilty myself if I was that guy, he's single-handedly responsible for the multiple unskippable ads in front of YouTube videos, among other grim tragedies. Mammals diverged from the rest of the vertebrate kingdom in the Carboniferous period, some 300-odd million years ago, distinguishing themselves from fish, reptiles, birds and amphibians with mammary glands for feeding their offspring with milk, as well as fur or hair, three middle-ear bones and a neocortex region in the brain.

It was, and remains, a potent recipe. The mammalian class branched out in countless different directions from that point, and eventually more or less took over much of the planet, some burrowing underground, some making their home on the plains, some climbing up into the trees like our primate ancestors, and others returning to the oceans to evolve into some of the biggest creatures that have ever lived on Earth.

Genus-level tree of modern mammals, all of which descended from a common ancestor, with some of Australia's odd marsupials like the platypus, kangaroo and koala among the earliest to diverge
OrthoMaM team at the Institute of Evolutionary Sciences of Montpellier (ISEM) and at the University of Montpellier. Licensed under Creative Commons Attribution-Share Alike 4.0 International

All modern mammals, however, have a single common ancestor, according to genetics researchers, and while little is known about this animal, an international team of researchers has now computationally reconstructed the organization of its genome.

Led by evolution and ecology specialists at UC Davis, the team analyzed high-quality genome sequences from 32 living mammal species, including humans, manatees, bats, pangolins, rabbits and wombats, using the genomes of chickens and Chinese alligators as comparison groups from outside the mammalian class.

The team found 1,215 blocks of genes that consistently appear, in order and on the same chromosome, across all 32 genomes. The researchers deduced that our common ancestor had 21 chromosomes, including 19 autosomal chromosomes and two sex chromosomes. They found nine whole chromosomes, or fragments thereof, where the order of genes matched up perfectly with the chromosomes of modern birds, demonstrating the extraordinary stability of some genetic sequences, even across more than 300 million years of evolution.

The sections between these well-preserved chunks had more repetitive sequences, and proved more susceptible to the breakages, duplications and rearrangements that drive genetic evolution.

Tracing the chromosomes forward in time, the researchers were able to track the rate of chromosome rearrangement across different lineages, noting for example an acceleration in genetic rearrangement around 66 million years ago, right about when an asteroid strike ended the rule of the dinosaurs and cleared the path for mammals to take over as the dominant group on the planet.

The research is open access at PNAS.

Source: UC Davis

  • Facebook
  • Twitter
  • Flipboard
  • LinkedIn
8 comments
anthony88
They Might Be Giants need to rewrite "Mammals".
Thomas VE
Probable not, complex systems do not develop by them selves by way of mutations. Entropy prohibits the increase in complexity through chance, it describes the exact opposite.
Loc
Impressive nonsense. Even Darwin said there is missing information to validate his theory. Just a theory and not a very good one either.
TechGazer
To Thomas VE: a quick Google search showed this: "The total complexity of the universe is increasing, due to the inevitable march of entropy (or information), which is exactly the measure of complexity." Life is just a conversion of the universe's higher energy state to a lower one. The basic chemicals of the lifeless Earth formed amino acids because that was a lower energy state than CH4, NH3, or H+ (hydrogen gradient in hot seawater). Amino acids joined to lower their energy state. One such combination was self-replicable. Humans are just exploiting potential energy more effectively than that first replicating organic molecule.

I'm curious as to where in the tree of life hair/fur occurred. Were there hairy reptilians that led to mammals?
Aladdin Connolly
LOL at Thomas VE You don't even know what entropy is. It is not as you state the inability for increased complexity through random interactions. It is the tendency for a closed system as a whole to become more uniform over time. Our "closed system" is the universe. Pockets of which are become more and less complex. The average among all areas is becoming less complex that's because the majority of the universe is essentially empty which is about as non complex as you can get, and that "empty" space is constantly expanding. It has zero to do with evolution, and only willfully ignorant science deniers, and those who lap up their lies spout that nonsense.
TechGazer
I found the answer to my question: hair evolved before mammals (about 300 million years ago). Logically, hair was a crucial step in evolving mammals. Hair would have allowed smaller reptiles to survive in cool weather. Evidence shows that some dinosaurs did give live birth, but perhaps our pre-mammalian ancestors re-developed live birth, and that's probably easier for smaller animals. The sweat glands that came with hair led to the development of milk (mammary glands are highly evolved sweat glands) That evolutionary experiment was obviously successful.
ReservoirPup
Many thanks to Loz for a playful presentation of the excellent research that invites even more appreciation. Science rocks!
bwana4swahili
Evolution is VERY opportunistic. If there's a hole, evolution will fill it!