Nav: Home

New research shakes up the sloth family tree

June 06, 2019

New research on the evolutionary relationships between tree sloths and their extinct giant relatives is challenging decades of widely accepted scientific research.

A team of international researchers including scientists from the McMaster ancient DNA centre and the University of Montpellier, have reached almost precisely the same novel results, working independently, in two separate studies published today in the journals Current Biology and Nature Ecology and Evolution.

While the sloth's evolutionary tree was previously based almost exclusively on the study of anatomical features, or morphology, new molecular (DNA and protein) evidence appears to overturn a longstanding consensus on how the major group of sloths are related to one another.

The scientific community has long believed that modern tree-dwelling sloths evolved independently from their large ground-dwelling ancestors . But by using different tools - relying mitochondrial genomic evidence and on bone collagen teased from ancient and modern specimens--researchers discovered the ancient sloths may have been at home on both land and in the trees.

"Mining the fossil record for these organic residues helps us write new histories about sloth evolution and biogeography," says evolutionary geneticist Hendrik Poinar, director of the Ancient DNA Centre at McMaster and also a corresponding author on the paper published in Current Biology.

Poinar and his team used state of the art analysis of ancient DNA to sequence 10 extinct sloth mitogenomes, which included the iconic continental ground sloths Megatherium, Megalonyx, Mylodon and Acratocnus, the recently extinct Caribbean sloths Parocnus and Acratocnus, and all living tree sloths, the two-toed (Choloepus) and the three-toed (Bradypus).

The results have forced researchers to rethink the entire evolutionary relationships.

For example, the three-toed sloth, has long been regarded as being so anatomically different from other sloths that it was classified on its own, as a completely separate, evolutionary lineage.

But both the mitochondrial and protein evidence suggest that this is incorrect, and that amazingly, the three-toed sloth fits within Megatherioidea, a group that also includes the largest of all sloths, the elephant-sized ground sloth Megatherium.

Similarly, the two-toed sloth, was found to belong to another major group of sloths called the mylodontoids, whereas it had previously been placed within a very different group called the Megalonychidae, a family which also includes the extinct North American ground sloth Megalonyx as well as a number of island species that lived in the West Indies until a few thousand years ago.

"Our work demonstrates the power of ancient DNA to decipher evolutionary radiations whose species have been decimated by the latest megafaunal extinctions," says Frederic Delsulc, director of research at the Institute of Evolutionary Sciences, University of Montpellier. "This study reveals how little we know about morphological evolution and the new molecular phylogenetic framework provides an opportunity to better understand the underlying processes."

The combined molecular evidence suggests that the West Indian sloths diverged from the ancestor of both megatherioids and mylodontoids more than 30 million years ago and this means that the first sloths to reach the Greater Antilles or what we know today as the Caribbean islands may have entered them over a temporary land connection between these islands and South America.

In taxonomic terms, that makes these recently extinct species the closest relative or sister group of all other sloths (giant and small), whereas they had previously been regarded as a late-evolving group.

"Although the molecular results conflict with current paleontological views based on anatomical features, there can be only one history of life," says Ross MacPhee, a corresponding author and curator in the division of vertebrate zoology at the American Museum of Natural History.

"The job now is to reconcile these differing methods of inference, which means a lot more work on everyone's part. We are going to learn a lot, and that's exciting," he says.
-end-


McMaster University

Related Dna Articles:

Scientists now know what DNA's chaperone looks like
Researchers have discovered the structure of the FACT protein -- a mysterious protein central to the functioning of DNA.
In one direction or the other: That is how DNA is unwound
DNA is like a book, it needs to be opened to be read.
DNA is like everything else: it's not what you have, but how you use it
A new paradigm for reading out genetic information in DNA is described by Dr.
A new spin on DNA
For decades, researchers have chased ways to study biological machines.
From face to DNA: New method aims to improve match between DNA sample and face database
Predicting what someone's face looks like based on a DNA sample remains a hard nut to crack for science.
Self-healing DNA nanostructures
DNA assembled into nanostructures such as tubes and origami-inspired shapes could someday find applications ranging from DNA computers to nanomedicine.
DNA design that anyone can do
Researchers at MIT and Arizona State University have designed a computer program that allows users to translate any free-form drawing into a two-dimensional, nanoscale structure made of DNA.
DNA find
A Queensland University of Technology-led collaboration with University of Adelaide reveals that Australia's pint-sized banded hare-wallaby is the closest living relative of the giant short-faced kangaroos which roamed the continent for millions of years, but died out about 40,000 years ago.
DNA structure impacts rate and accuracy of DNA synthesis
DNA sequences with the potential to form unusual conformations, which are frequently associated with cancer and neurological diseases, can in fact slow down or speed up the DNA synthesis process and cause more or fewer sequencing errors.
Changes in mitochondrial DNA control how nuclear DNA mutations are expressed in cardiomyopathy
Differences in the DNA within the mitochondria, the energy-producing structures within cells, can determine the severity and progression of heart disease caused by a nuclear DNA mutation.
More Dna News and Dna Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

In & Out Of Love
We think of love as a mysterious, unknowable force. Something that happens to us. But what if we could control it? This hour, TED speakers on whether we can decide to fall in — and out of — love. Guests include writer Mandy Len Catron, biological anthropologist Helen Fisher, musician Dessa, One Love CEO Katie Hood, and psychologist Guy Winch.
Now Playing: Science for the People

#543 Give a Nerd a Gift
Yup, you guessed it... it's Science for the People's annual holiday episode that helps you figure out what sciency books and gifts to get that special nerd on your list. Or maybe you're looking to build up your reading list for the holiday break and a geeky Christmas sweater to wear to an upcoming party. Returning are pop-science power-readers John Dupuis and Joanne Manaster to dish on the best science books they read this past year. And Rachelle Saunders and Bethany Brookshire squee in delight over some truly delightful science-themed non-book objects for those whose bookshelves are already full. Since...
Now Playing: Radiolab

An Announcement from Radiolab