Sloths are no slouches when it comes to evolution

giant sloth
The giant sloth succumbed to the advance of humans. Credit: Wikimedia Commons

Today's sloths might be known as slow, small animals, but their ancestors developed large body sizes at an amazing rate, according to an evolutionary reconstruction published today in the open access journal BMC Evolutionary Biology. The fast rate of change suggests that factors such as environmental conditions, or competition with other species must have strongly favored the bigger sloths, before they died out.

Scientists from UCL (University College London) and University College Dublin looked at existing models for reconstructing how diversified, with some as large as elephants, and some shrinking down to their current small sizes from a large ancestor. The study showed that some sloth lineages increased in size by over 100 kilos every million years – some of the fastest rates of body size evolution known for mammals.

Dr Anjali Goswami (UCL Earth Sciences), an author on the paper, said: "Today's sloths are really the black sheep of the sloth family. If we ignore the fossil record and limit our studies to living sloths, as previous studies have done, there's a good chance that we'll miss out on the real story and maybe underestimate the extraordinarily complex evolution that produced the species that inhabit our world."

The two existing groups of sloth species bear very little resemblance to some of their extinct relatives. The species Megatherium americanum was an elephant-sized ground sloth which could reach up to four tonnes. Fossilised track marks suggest they could walk upright on their hind legs. Eremotherium eomigrans could weigh five tons and their claws grow to a foot long. All but two sloth groups died out around 11,000 years ago, with the sloths living today reaching a maximum of 13 lbs.

The team took information about all known sloth species, both living and in the fossil record, and tested how existing evolutionary models explained the range in body sizes. They showed that models based only on living species were inadequate to explain the changes in size. Models which incorporated fossil species showed that they evolved at an extremely fast rate, and that the environmental conditions at the time must have really favored larger body sizes, such as the climate, or competition between species.

The authors say the method could be used to pry into the evolutionary past of other species.

Dr John Finarelli (University College Dublin Earth Institute), who co-authored the study, says: "There are many other groups, such as hyaenas, elephants and rhinos, that, like sloths, have only a few living species. But if we look into the distant past, these groups were much more diverse, and in many cases very different to their current forms."


Explore further

Identifying sloth species at a genetic level

More information: BMC Evolutionary Biology, www.biomedcentral.com/1471-2148/14/184
Journal information: BMC Evolutionary Biology

Provided by BioMed Central
Citation: Sloths are no slouches when it comes to evolution (2014, September 10) retrieved 16 October 2019 from https://phys.org/news/2014-09-sloths-slouches-evolution.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
0 shares

Feedback to editors

User comments

Sep 10, 2014
Pure speculation that "evolution" caused any of this.

..as opposed to? C'mon...you must have something that you don't call 'speculation' up your sleeve, right? Maybe we can find out this way where your tumor is.

No wonder so many consider the theory of evolution as debunked.

No wonder that no scientists are among them (you know...smart people).

And others wouldn't know what 'debunked' actually constitutes as they couldn't tell "scientific" from "not scientific" if their pastor spelled it out to them in sky-high flaming letters..

Sep 10, 2014
Don't feed the trolls.

Sep 10, 2014
Pure speculation that "evolution" caused any of this. Zero hard facts and science.
No wonder so many consider the theory of evolution as debunked.

Please study the ancient animals. But please free your minds of the chains of nonsense evolution.



Did you go and search for those fossils yet?

Sep 10, 2014
verkle: Did you read the actual article? Here, I'll help you find it: http://www.biomed...8/14/184

And if you're too lazy to click the link, here's a relevant statement: "Here, we used a dataset of 57 species of living and fossil sloths to examine changes in body mass mean and variance through their evolution, employing a general time-variable model that allows for analysis of evolutionary trends in continuous characters within clades lacking fully-resolved phylogenies, such as sloths."

If you'd like to debate the relevance of their data set or their model choice, go ahead--that's what scientists do! But don't claim it's all merely speculation, when this is based on a lot of data.

Sep 10, 2014
verkle cannot see the obvious irony/hypocrisy of his blurt here
Pure speculation that "evolution" caused any of this. Zero hard facts and science.
Where are the 'hard facts' that your god is SO loving when he punished ALL of creation because a young woman was set up ?

verkle made odd claim
No wonder so many consider the theory of evolution as debunked.
So many ? being the uneducated such as so many which cannot or will not handle probability, permutations, microbiology etc

verkle might have an idea but will he take his own advice with ?
Please study the ancient animals. But please free your minds of the chains of nonsense evolution.
Yes please, all the ancient life forms, start with bacteria - the common amino acid complexes which can arise in ammonia atmospheres.

You do know don't you verkle ALL life on earth is made from amino acids - ie Amines, the NH2 complex - which is easy to produce in an Ammonia atmosphere - guess what early earth had - Ammonia atmosphere !

Sep 11, 2014
@Verkle I see you're posting more drivel.

You challenge people to "debate you", people can't debate crap like"

"No wonder so many consider the theory of evolution as debunked."

"So many unfounded "assumptions" in evolutionist thinking. Another nail in the coffin of evolutionists."

"Just first tell how how you can believe in the magic of evolution"

"Evolution is a made up story and people are now trying to "prove" it is right. Science the wrong way.

"But please free your minds of the chains of nonsense evolution."

What we can and will do is point out you're posting drivel then point and laugh at you.

NOM
Sep 11, 2014
All he has done is take someone's post arguing against creationism and replaced the words with evolution. He, as usual, has completely issed the point.
Creationism needs a magical being to work, evolution doesn't.
Evolution is based on physical evidence and proven science, creationism is based on the misinterpreted accounts of some ancient bored sheep farmers.

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