Tiny fossils reveal how shrinking was essential for successful evolution

Tiny fossils reveal how shrinking was essential for successful evolution
Life reconstruction of the mammaliaform Morganucodon found in Jurassic sediments of Wales and China. Morganucodon was one of the smallest fossil mammal ancestors with a size of 4-6cm. Credit: Bob Nicholls, Paleocreations.com

A new study published today in Nature shows that getting smaller was a key factor contributing to the exceptional evolution of mammals over the last 200 million years.

The origin of modern mammals can be traced back more than 200 million years to the age of dinosaurs. But while dinosaurs evolved to become some of the largest land animals, for the following 150 million years, the ancestors of all modern mammals pursued an entirely different strategy: getting very small.

An international team of scientists from the United Kingdom and the US have used modern computer analysis to take a look at what happened to the skeleton of our tiny ancestors.

Modern mammals are unique in having a lower jaw consisting of just a single that bears teeth. In contrast, all other vertebrates possess complex lower jaws formed by at least five or more bones joined together. In the course of , fossils show that the lower jaw of mammalian ancestors became simplified and a new jaw joint was formed, while some of the other bones moved into the middle ear to aid in hearing.

The team's research focussed on the long-standing question of how it was possible to simplify and restructure the lower jaw, while still being able feed and hear. Using X-ray computed tomography (CT) scanning of several fossil skulls and lower , the researchers generated digital models which were subjected to different computer simulations.

Their results showed that the small size of the fossil mammals significantly reduced the stresses in the jaw bones when feeding, while still being powerful enough to capture and bite through prey, such as insects.

Dr. Stephan Lautenschlager, lead author and lecturer at the University of Birmingham, said: "Our results provide a new explanation of how the mammalian jaw evolved over 200 million years ago. Getting very small appears to have been crucial for our mammalian ancestors. This allowed them to reduce the stresses in the jaw during feeding and made the restructuring of the possible."

Professor Emily Rayfield from the University of Bristol who lead the study added: "The evolution of the mammalian jaw joint has perplexed palaeontologists for over 50 years. Using computational methods we can offer explanations to how our mammalian ancestors were able to maintain a working jaw while co-opting bones into a complex sound detection system. Our research is about testing ideas of what makes mammals unique among the animal kingdom, and how this may have come about."

'The role of miniaturisation in the evolution of the mammalian jaw and middle ear' by Stephan Lautenschlager, Pamela Gill, Zhe-Xi Luo, Michael J. Fagan and Emily Rayfield is published in Nature.


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More information: The role of miniaturization in the evolution of the mammalian jaw and middle ear, Nature (2018). DOI: 10.1038/s41586-018-0521-4 , https://www.nature.com/articles/s41586-018-0521-4
Journal information: Nature

Citation: Tiny fossils reveal how shrinking was essential for successful evolution (2018, September 17) retrieved 25 May 2019 from https://phys.org/news/2018-09-tiny-fossils-reveal-essential-successful.html
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Sep 21, 2018
Wait....wait....now let me see: First to survive you had to be the biggest, meanest thing on the block. Then suddenly you had to be the smallest thing going....right!
How did those large animals get so big in the first place?
Didn't it all supposedly start off from a single-cellular organism ( via abiogenesis of some sort )?
That thing must have been extremely small already, so why would it "evolve" into something as big as a dinosaur in the first place?
Oh, and by the way where did all the information come from for firstly multi-cellular organization, then complex structures like eyes, noses, mouths, lips, tongues, blood, necks, shoulders, bones, spines, inter-spinal cartilage, usage of vitamin C, absorption of vitamin B-12, the immune system, the sexual organs, the most fundamental of all - repair system - right from the gene level to the systematic level of liver repair or lung repair or survival of leaves in harsh UV light?
Where did all that knowledge come from? Where?

Sep 21, 2018
First to survive you had to be the biggest, meanest thing on the block. Then suddenly you had to be the smallest thing going..

In a dynamic environment sometimes big is good sometimes small is good. If you look at the fossil records for example predators and prey went through several cycles of:
- tougher hides (for prey)
- bigger teeth/claws (for predators)
- scales (for prey)
- tougher jaws (for predators).
- less tough hides/scales in favor of speed (for prey...because with all the huge jaws/teeth predators have become slow)
- and then it starts all over again.

so why would it "evolve" into something as big as a dinosaur

E.g. with more oxygen in the atmosphere a higher metabolism rate can be sustained - which means larger animals are possible (there were some truly enormous insects bag then).

Environments change- things adapt (or die). Don't assume environments always remain the same. Environment can also mean 'other animals' - not just climate.

Sep 21, 2018
Where did all that knowledge come from? Where?

Why is it up to us to try to correct your closed mind of its misconceptions about chemistry, physics, biology, and information theory?

Sep 21, 2018
Where did all that knowledge come from? Where?

That's not how it works. Some mutated and were a better fit and the others died (more easily). The 'knowledge' is passively created by weeding out the less fit.

I think it's best summed up by this quote from bash.org:

Some people...have the idea that evolution is a f*ing system of..."oh i need flippers, i'd better grow some" type bs
It's more like "Oh sh*t look at that freak over there with the flippers hahaha OH SH*T I AM DROWNING OH GOD SAVE ME FLIPPER BOY".



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