Scientists report evidence for a new -- but now extinct -- species of
ancient ground-dwelling sloth
Study advances evolutionary history of the slow-moving mammals that now
live only in trees

Date:
October 12, 2021
Source:
Johns Hopkins Medicine
Summary:
Scientists report new evidence that some 5,000 years ago, a sloth
smaller than a black bear roamed the forest floor of what is now
the Dominican Republic in the Caribbean Sea, living a lowland life
different from its cousins on the other side of the island.



FULL STORY ========================================================================== Scientists at Johns Hopkins Medicine and the Philadelphia College of Osteopathic Medicine report new evidence that some 5,000 years ago,
a sloth smaller than a black bear roamed the forest floor of what is
now the Dominican Republic in the Caribbean Sea, living a lowland life different from its cousins on the other side of the island. The newly identified mammalian species -- now extinct -- was smaller and had
anatomical differences in its forelimb that gave it greater range of
motion, possibly to help the animal occupy more lowland areas than its tree-dwelling kin.


==========================================================================
The evidence was uncovered initially in January 2009, when divers found
the sloth's bones in a flooded cave on the island of Hispaniola, now
home to the Dominican Republic and Haiti. After extensive study of the
partial skeleton and bones from several other specimens, the scientists
have concluded it is a previously unknown species of ground sloth,
which they dubbed Parocnus dominicanus.

The scientists say the discovery is important because, "It allows us to
explain variation in the fossil record," says Sioba'hn Cooke, Ph.D.,
assistant professor of functional anatomy and evolution at the Johns
Hopkins University School of Medicine. "If we're trying to reconstruct
an animal's life, we need to understand their relationships, anatomy
and habitat." No sloths live on the island today, although fossil
evidence shows they were the largest mammal there at the very end of
the 2.5-million-year Stone Age.

The researchers' findings were published Aug. 31 in Vertebrate Anatomy Morphology Palaeontology.

Cooke notes that the two- and three-toed, tree-dwelling sloths found in
today's forests of Central and South America are smaller than the diverse
group of sloths that existed 5,000 years ago. The ancient precursors
to modern sloths migrated as far north as parts of present-day North
America, some species as large as elephants, faster and semiaquatic,
like otters living part of the time in the sea and on land.

"I'm biased, but I think sloths are wonderful animals," says Robert
McAfee, Ph.D., associate professor of anatomy at the Philadelphia College
of Osteopathic Medicine. "They are an underappreciated species, with
unique adaptations to live in a variety of habitats," he adds. "Some 80
types of sloths have existed across 50 million years, and we're left
with just two species today." On Hispaniola, scientists previously
found six or seven species of ancient sloths.



========================================================================== Evidence of the new addition, says Cooke, was found in a now flooded
but once dry cave, called Padre Nuestro, on the eastern tip of the
Dominican Republic.

To explore the cave, the scientists collaborated with diving experts
who specialize in navigating water-filled cave environments.

The scientists don't know if the sloths fell into the cave or crawled
in and could not escape.

Compared with the first-identified species of sloth on the island, P.

dominicanus was about 10% to 15% smaller in all measurements of the
discovered bones. The scientists also found that the location where
deltoid muscles attached to the forelimb was different from previously identified species P.

browni and P. serus.

The difference in the muscle attachments placed the muscles in a different position, potentially providing a greater range of motion, strength and
ability to manipulate its forearms, a potential advantage for walking on
its forearms in more lowland habitats rather than climbing and hanging
upside down in trees, hallmarks of modern sloths.

To solidify their belief that P. dominicanuswas a new species, they
studied fossil records of ancient and extinct sloths found across
Caribbean islands.

The new bone specimens, they say, were consistently smaller. "We accounted
for some level of size variation due to male/female size differences,
but overall, P. dominicanus was much smaller," says Cooke.

Sloths disappeared from the Caribbean about 4,000 years ago, and humans
arrived about 5,000-6,000 years ago. So, people and sloths coexisted in
the region for about 1,000 years, say the researchers. It's not clear,
they say, whether sloths were widely hunted on the islands or if they disappeared due to human- spurred change in the habitat.

Funding for the expedition and research was provided by 2015 Ernst Mayr
Travel Grants in Animal Systematics from Harvard's Museum of Comparative Zoology.

In addition to Cooke and McAfee, other contributors to the research
included Sophia M. Beery from Ohio University, Renato Ri'moli from the
Museo del Hombre Dominicano, Dominican Republic, Juan Almonte from the
Museo Nacional de Historia Natural, Dominican Republic, and Phillip
Lehman from the Dominican Republic Speleological Society.

========================================================================== Story Source: Materials provided by Johns_Hopkins_Medicine. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Robert McAfee, Sophia Beery, Renato Rimoli, Juan Almonte, Phillip
Lehman,
Siobhan Cooke. New species of the ground sloth Parocnus from the
late Pleistocene-early Holocene of Hispaniola. Vertebrate Anatomy
Morphology Palaeontology, 2021; 9 (1) DOI: 10.18435/vamp29369 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211012154739.htm

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