Paleontologists are always straining against the pull of the recent. In short, this means that the closer in geologic time you get to the present, the better the fossil record is - we have a better picture of life 50 million years ago than 100 million years ago, and we understand life 100,000 years ago better than 50 million years ago. Yet, despite over two centuries of dedicated searching and study, there's still a great deal left to uncover in even the relatively recent fossil record. A 4.9 million year old giant sloth is one such example.

Zacatzontli tecolotlanensis, named by paleontologists Gregory McDonald and  Oscar Carranza-Castañeda, is a sloth that seems out of place. Known only from a lower jaw and two broken teeth, this beast from Jalisco, Mexico is a messenger from another place. That's what makes it so special.

The new sloth lived right in the middle of a critical window for animals of Americas. Between 9 and 1.6 million years ago, as North and South America edged ever closer and eventually joined through prehistoric Panama, various animals moved across the gap. That's why there are jaguars in Brazil and armadillos in Texas. Giant sloths were part of this Great Biotic Interchange, too, and Zacatzontli suggests that the trundling beasts came in waves.

In terms of family relationships, McDonald and Carranza-Castañeda point out, Zacatzontli more closely resembles giant sloths of South American origin than those that eventually evolved in the north. This is despite the fact that giant sloths had already been moving north for millions of years prior. What this means, the researchers note, is that there was an earlier wave of sloths moving from south to north and a later one now represented by Zacatzontli and another giant sloth called Meizonyx in El Salvador. These sloths didn't have an easy time of it. At 4.9 million years ago there was still a significant stretch of water between the continents. But somehow Zacatzontli made it, and now bears the name of the Aztec god of travelers.

Three views of the Zacatzontli jaw. Credit: McDonald and Carranza-Castañeda 2017

Name: Zacatzontli tecolotlanensis

Meaning: Zacatzontli is named for the Aztec god of travelers, and tecolotlanensis is named after the town Tecolotlán where the sloth was found.

Age: Miocene, about 4.9 million years ago.

Where in the world?: Jalisco, Mexico. 

What sort of organism?: A giant ground sloth.

How much of the organism’s is known?: A partial lower jaw and two broken teeth.


Royo-Torres, R., Upchurch, P., Kirkland, J., DeBlieux, D., Foster, J., Cobos, A., Alcala, L. 2017. Descendants of the Jurassic turiasaurs from Iberia found refuge in the Early Cretaceous of western USAScientific Reports. doi: 10.1038/s41598-017-14677-2

Previous Paleo Profiles:

The Light-Footed Lizard
The Maoming Cat
Knight’s Egyptian Bat
The La Luna Snake
The Rio do Rasto Tooth
Bob Weir's Otter
Egypt's Canine Beast
The Vastan Mine Tapir
Pangu's Wing
The Dawn Megamouth
The Genga Lizard
The Micro Lion
The Mystery Titanosaur
The Echo Hunter
The Lo Hueco Titan
The Three-Branched Cicada
The Monster of Minden
The Pig-Footed Bandicoot
Hayden's Rattlesnake Demon
The Evasive Ostrich Seer
The Paradoxical Mega Shark
The Tiny Beardogs
The Armored Fish King
North America's Pangolin
The Invisible-Tusked Elephant
The Mud Dragon
The Spike-Toothed Salmon
The Dream Coast Crocodile
Buriol's Robber
Ozimek's Flyer
The Northern Naustoceratopsian
The High Arctic Flyer
The Tomatillo From the End of the World
The Short-Faced Hyena
The Mighty Traveler from Egg Mountain
Keilhau's Ichthyosaur
Mexico's Ancient Horned Face
Mauricio Fernández's Plesiosaur
New Zealand's Giant Dawn Penguin
The Orange Sea Lion
Mongolia's Ginkgo Cousin
The Geni River Frog
Isabel Berry's Dinosaur
The Whale Caiman
The Moab Lizard
Yang Zhongjian's Lizard
The Little Anubis
The Shuangbai Lizard
The Wyvern Dinosaur
The "Need Helmet" Dinosaur
The Jianianhua Dragon
The Liaoning Hunter
The Dalian Lizard
Crompton's Aleodon
Jenkins' Amphibian Serpent From the Chinle
The Large Ancestor Lizard
The Crown Tooth
Currie's Alberta Hunter
The Elephant Bird Mimic
The Crested Thief
The Hiding Hunter
The Horned Lizard
The Silk Bird
The Sieve-Toothed Plesiosaur
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Burian's Lizard
The Small Whaitsiid
The Beautiful Bird
The Fierce Cat
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The King of the Miocene Iberian Giraffes
Miera's Lizard