Researchers suggest rate of evolution change can explain discrepancy between molecular clocks and fossil evidence

August 27, 2014 by Bob Yirka, report

A four-day-old mouse. Credit: Wikipedia/CC BY-SA 3.0
( —A pair of researchers affiliated with several institutions in Australia, believe they may have found a way to solve the discrepancy problem that exists between molecular biologists and paleontologists who disagree on the likely first appearance of placental mammals. They describe their new dating approach, which they call a "morphological clock" in their paper published in Proceedings of the Royal Society B: Biological Sciences.

To date the first appearance of a something in the biological record, modern scientists have two main tools—dating fossils and using what's known as a , where DNA techniques are used to follow the evolution of species divergence. Problems come in when the two methods offer different results. That's been the case with researchers attempting to date the first arrival of . The earliest fossils suggest they showed up on the scene approximately 66 million years ago. The molecular clock approach, however, suggests it happened long before that, approximately 90 to 100 million years ago. In this new effort, the research pair suggest a way to resolve the difference (without claiming that the difference is because older fossils have just not been found.) They call their approach a morphological clock, which is based on the progression of anatomical differences that arise in a species, rather than DNA tracing.

Using it, they suggest it's possible that placental mammals first arrived as early as 160 million years ago. But they have a caveat, they suggest, that the speed at which evolutionary changes took place could have changed, which if taken into account, would bring the time frame closer to 66 million years ago. As for why a change in speed of evolution might have taken place, the team notes that it might have occurred soon after the dinosaurs went extinct—which would have opened up a whole new niche that could have been filled very quickly by the advent of placental mammals.

If this new approach is to be taken seriously, it would cast doubts on the accuracy of molecular clocks in general—they're based on the assumption that evolution occurs at a fixed rate. It could also help explain the "sudden" appearance of a wide variety of species 540 million years ago—the Cambrian explosion—which many believe led to the appearance of all modern animal groups.

Explore further: Research team claims fossil-only study of placental mammalian evolution time frame is wrong

More information: Ancient dates or accelerated rates? Morphological clocks and the antiquity of placental mammals, Proc. R. Soc. B 22 October 2014 vol. 281 no. 1793 20141278. rspb.royalsocietypublishing.or … nt/281/1793/20141278

Analyses of a comprehensive morphological character matrix of mammals using 'relaxed' clock models (which simultaneously estimate topology, divergence dates and evolutionary rates), either alone or in combination with an 8.5 kb nuclear sequence dataset, retrieve implausibly ancient, Late Jurassic–Early Cretaceous estimates for the initial diversification of Placentalia (crown-group Eutheria). These dates are much older than all recent molecular and palaeontological estimates. They are recovered using two very different clock models, and regardless of whether the tree topology is freely estimated or constrained using scaffolds to match the current consensus placental phylogeny. This raises the possibility that divergence dates have been overestimated in previous analyses that have applied such clock models to morphological and total evidence datasets. Enforcing additional age constraints on selected internal divergences results in only a slight reduction of the age of Placentalia. Constraining Placentalia to less than 93.8 Ma, congruent with recent molecular estimates, does not require major changes in morphological or molecular evolutionary rates. Even constraining Placentalia to less than 66 Ma to match the 'explosive' palaeontological model results in only a 10- to 20-fold increase in maximum evolutionary rate for morphology, and fivefold for molecules. The large discrepancies between clock- and fossil-based estimates for divergence dates might therefore be attributable to relatively small changes in evolutionary rates through time, although other explanations (such as overly simplistic models of morphological evolution) need to be investigated. Conversely, dates inferred using relaxed clock models (especially with discrete morphological data and MRBAYES) should be treated cautiously, as relatively minor deviations in rate patterns can generate large effects on estimated divergence dates.

Related Stories

Animals first flex their muscles

August 26, 2014

An unusual new fossil discovery of one of the earliest animals on earth may also provide the oldest evidence of muscle tissue – the bundles of cells that make movement in animals possible.

Fossil primate shakes up history of strepsirrhines

December 11, 2013

Fossils discovered in Tunisia challenge several hypotheses concerning the origin of toothcombed primates (Malagasy lemurs, Afro-Asian lorises and African galagos). The fossils are of a small primate called Djebelemur, which ...

Recommended for you

Study suggests trees are crucial to the future of our cities

March 25, 2019

The shade of a single tree can provide welcome relief from the hot summer sun. But when that single tree is part of a small forest, it creates a profound cooling effect. According to a study published today in the Proceedings ...

Matter waves and quantum splinters

March 25, 2019

Physicists in the United States, Austria and Brazil have shown that shaking ultracold Bose-Einstein condensates (BECs) can cause them to either divide into uniform segments or shatter into unpredictable splinters, depending ...

Apple pivot led by star-packed video service

March 25, 2019

With Hollywood stars galore, Apple unveiled its streaming video plans Monday along with news and game subscription offerings as part of an effort to shift its focus to digital content and services to break free of its reliance ...


Adjust slider to filter visible comments by rank

Display comments: newest first

5 / 5 (11) Aug 27, 2014
If evolution were true, there would millions and billions of transitional fossils, which would easily show the progression. Without these, it's anyones guesswork at what happened. I understand evolution to be a farce. So many bogus claims with very little science to support it.

This discredited theory should be thrown out.

Why don't you just admit your rejection of evolution is based on your religious beliefs and not on science? Your anti-evolution posts show a lack of honesty and integrity.
Captain Stumpy
5 / 5 (9) Aug 27, 2014
there would millions and billions of transitional fossils
of course, this also assumes that EVERY animal that died left a fossil, or at least more than 50% did, which is not logical... You can't get those numbers out of a graveyard, let alone a couple Billion years of history here

but even skipping past that... the methodology for learning in science is based upon the scientific method, empirical evidence, repeatable experiments and verified second party... something that your faith does NOT have
which then means that, like Vietvet states, you are demonstrating a lack of honesty and integrity, therefore violating some of the core laws of your own faith.

and you want everyone to assume that your posts are valid based upon NO proof or supporting evidence (that is FAITH, not SCIENCE)

sorry V... you are failing miserably with your argument


Budding Geologist
5 / 5 (1) Aug 27, 2014
Punctuated equilibrium vs gradualism... It's reassuring to see somebody is trying the help bridge the gap between biology and paleontology... sometimes it borders on the absurd.
5 / 5 (4) Aug 28, 2014
When science makes progress, the anti-scientists cry "foul". What else can they do? They have no working alternative at all, never mind the better one required.

Don't mind the troll. He is taking a piece from the Gish gallop from 2 decades ago, and googling would have showed him the futility of erroneous claims:

"Given all the species that exist and have existed, there should be billions of transitional fossils in the fossil record; we should have found tens of thousands at least." [Gish, 1994]


1. Some important factors prevent the formation of fossils from being common: ..."

CC200.1 [ http://www.talkor...0_1.html ]
Whydening Gyre
5 / 5 (4) Aug 28, 2014
If evolution were true, there would millions and billions of transitional fossils, which would easily show the progression. Without these, it's anyones guesswork at what happened. I understand evolution to be a farce. So many bogus claims with very little science to support it.

This discredited theory should be thrown out.

That's what science is trying to do - find the transitional fossils. We've been fairly successful at finding the ones we have, so far. But, it's actually a pretty big planet out here, with lot's of little hiding places. so it's gonna take a little time.
(and some more archaeologists...)

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.