Glyptodont
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Glyptodonts are an extinct
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
of large, heavily armoured
armadillo Armadillos () are New World placental mammals in the order (biology), order Cingulata. They form part of the superorder Xenarthra, along with the anteaters and sloths. 21 extant species of armadillo have been described, some of which are dis ...
s, reaching up to in height, and maximum body masses of around 2 tonnes. They had short, deep skulls, a fused vertebral column, and a large bony carapace made up of hundreds of individual scutes. Some glyptodonts had clubbed tails, similar to ankylosaurid dinosaurs. The earliest widely recognised fossils of glyptodonts in South America are known from the late
Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
, around 38 million years ago, and they spread to southern North America after the continents became connected around 2.7 million years ago. The best-known genus within the group is '' Glyptodon.'' Glyptodonts were historically considered to constitute the distinct family Glyptodontidae, with their relationships to modern armadillos being contested. In 2016, an analysis of the mitochondrial genome of '' Doedicurus'' found that it was, in fact, nested within the modern armadillos as the
sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...
of a
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
consisting of Chlamyphorinae (fairy armadillos) and Tolypeutinae (giant, three-banded and naked-tailed armadillos). For this reason, glyptodonts and all armadillos but '' Dasypus'' (long-nosed or naked-tailed armadillos) were relocated to a new family, Chlamyphoridae, and glyptodonts were demoted to the subfamily Glyptodontinae. Other authors have continued to use Glyptodontidae. Based on the morphology of the inner ear, a close relationship with pampatheres has also been proposed. Glyptodonts abruptly became extinct approximately 12,000 years ago at the end of the
Late Pleistocene The Late Pleistocene is an unofficial Age (geology), age in the international geologic timescale in chronostratigraphy, also known as the Upper Pleistocene from a Stratigraphy, stratigraphic perspective. It is intended to be the fourth division ...
, as part of the end-Pleistocene extinction event, along with most other large animals in the Americas. Evidence has been found suggesting that they were hunted by recently arrived Paleoindians, which may have played a role in their extinction.


Evolution

Glyptodonts first evolved during the
Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
in
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
, which remained their center of species diversity. For example, an Early Miocene glyptodont with many primitive features (comparatively to other species), '' Parapropalaehoplophorus septentrionalis,'' was discovered at a now-elevated site in
Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...
and described in 2007. After the
Isthmus of Panama The Isthmus of Panama, historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North America, North and South America. The country of Panama is located on the i ...
formed about three million years ago, the genus '' Glyptotherium'' spread north as part of the
Great American Interchange The Great American Biotic Interchange (commonly abbreviated as GABI), also known as the Great American Interchange and the Great American Faunal Interchange, was an important late Cenozoic paleozoogeographic biotic interchange event in which land ...
, as did pampatheres,
armadillo Armadillos () are New World placental mammals in the order (biology), order Cingulata. They form part of the superorder Xenarthra, along with the anteaters and sloths. 21 extant species of armadillo have been described, some of which are dis ...
s and a number of other types of xenarthrans (e.g.,
ground sloth Ground sloths are a diverse group of extinct sloths in the mammalian superorder Xenarthra. They varied widely in size with the largest, belonging to genera '' Lestodon'', ''Eremotherium'' and ''Megatherium'', being around the size of elephants. ...
s). Analysis of inner ear morphology corroborates this position, while also finding that pampatheres are the closest relatives of glyptodonts: Glyptodonts are divided into two major groups, which split during or prior to the Early
Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
. The first is the traditional Glyptodontinae, which is includes the well known genera of '' Glyptodon'' and '' Glyptotherium'', which probably originated in Northern South America, while the second is the unnamed "Austral clade", containing the majority of glyptodont diversity, which as the name suggests probably originated in Southern South America. Cladogram after Barasoain et al. 2022:


Description

The largest glyptodonts like ''Doedicurus'' reached a height of and in length, with a body mass of over two tonnes. The body of glyptodonts was covered in a large immobile carapace made up of hundreds of bony scutes/
osteoderms Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of Extant taxon, extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, Temnospondyli, ...
, with the underside of the body and the top of the head also being protected with osteoderms. This protection reached a thickness of . The vertebrae of the back were extensively fused to each other. The limbs were short and robustly built, with the pectoral girdle being wide. The head was short and blunt, with deep jaws. The teeth were grooved, and were evergrowing. The tail was covered in rings composed of osteoderms, which allowed the tail to flex. In many glyptodonts (members of the "Austral clade" other than ''Propalaehoplophorus'' and ''Eucinepeltus''), the end of the tail was covered in a completely fused "caudal tube". The end of caudal tubes of at least some glyptodonts are covered in depressions which in life are suggested to have been anchoring points for horny, likely keratinous spikes, allowing for the tail to function as an effective weapon when swung. These "tail clubs" are similar in construction to those of ankylosaurid dinosaurs.


Ecology

Glyptodonts are thought to have been herbivores that fed on low lying vegetation, with mixed feeding or grazing based diets. Some glyptodonts were likely selective feeders, while others were likely bulk feeders. Damage to some glyptodont carapaces suggested to be caused by tail club impacts suggests that tail clubs may have been used in combat between rival males.


Extinction

At the end of the
Late Pleistocene The Late Pleistocene is an unofficial Age (geology), age in the international geologic timescale in chronostratigraphy, also known as the Upper Pleistocene from a Stratigraphy, stratigraphic perspective. It is intended to be the fourth division ...
, all then-living glyptodont species, which belonged to the genera '' Glyptodon, Hoplophorus, Glyptotherium, Panochthus, Neuryurus, Doedicurus and Neosclerocalyptus'', abruptly became extinct around 12,000 years ago as part of the end-Pleistocene extinction event, simultaneously with the vast majority of other large mammals in the Americas. These extinctions followed the first arrival of humans in the Americas, and the importance of human vs climatic factors in these extinctions has been the subject of contention. Several sites across South America are suggested to document hunting of glyptodonts by the recently arrived Paleoindians, which may have played a role in their extinction. At the Muaco and Taima-Taima sites in
Falcón Falcón State (, ) is one of the 23 States of Venezuela, states of Venezuela. The state capital is Coro, Venezuela, Coro. The state was named after Juan Crisóstomo Falcón. History Early history Present day Falcón State was first explored ...
State in northwestern Venezuela, several skulls of ''Glyptotherium'' display distinctive fracture marks on the skull roof that occurred around the time of death, suggested to have been caused by a deliberate percussive blow to a relatively thin part of the skull by a club or stone tool.


References


External links


Glyptodont article at ScienceBlogs
with photos * {{Taxonbar, from1=Q23015579, from2=Q132641 Cingulata Prehistoric cingulates Lutetian first appearances Holocene extinctions Taxa named by Hermann Burmeister