Glyptodonts are an extinctclade of large, heavily armouredarmadillos, reaching up to 1.5 metres (4.9 ft) 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 hadclubbed tails, similar toankylosaurid dinosaurs.[1]
The earliest widely recognised fossils of glyptodonts in South America are known from the lateEocene, around 38 million years ago, and they spread to southern North America after the continents became connected around 2.7 million years ago.[2] The best-known genus within the group isGlyptodon.
Glyptodonts were historically considered to constitute the distinct familyGlyptodontidae, with their relationships to modern armadillos being contested. In 2016, an analysis of themitochondrial genome ofDoedicurus found that it was, in fact, nested within the modern armadillos as thesister group of aclade consisting ofChlamyphorinae (fairy armadillos) andTolypeutinae (giant, three-banded and naked-tailed armadillos). For this reason, glyptodonts and all armadillos butDasypus (long-nosed or naked-tailed armadillos) were relocated to a new family,Chlamyphoridae, and glyptodonts were demoted to the subfamilyGlyptodontinae.[2][1] Other authors have continued to use Glyptodontidae.[3] Based on the morphology of the inner ear, a close relationship withpampatheres has also been proposed.[4]
Glyptodonts abruptly became extinct approximately 12,000 years ago at the end of theLate Pleistocene, as part of theend-Pleistocene extinction event, along with most other large animals in the Americas. Evidence has been found suggesting that they were hunted by recently arrivedPaleoindians, which may have played a role in their extinction.[3]
Glyptodonts first evolved during theEocene inSouth America, which remained their center ofspecies diversity. For example, an Early Miocene glyptodont with many primitive features (comparatively to other species),Parapropalaehoplophorus septentrionalis, was discovered at a now-elevated site inChile and described in 2007.[5] After theIsthmus of Panama formed about three million years ago, the genusGlyptotherium spread north as part of theGreat American Interchange, as didpampatheres,armadillos and a number of other types of xenarthrans (e.g.,ground sloths).
| Cladogram of Cingulata[2][6][7] |
Analysis of inner ear morphology corroborates this position, while also finding thatpampatheres are the closest relatives of glyptodonts:[4]
Glyptodonts are divided into two major groups, which split during or prior to the EarlyMiocene. The first is the traditional Glyptodontinae, which is includes the well known genera ofGlyptodon andGlyptotherium, 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.[8]
Cladogram after Barasoain et al. 2022:[8]
| Glyptodonts |
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The largest glyptodonts likeDoedicurus reached a height of 1.5 metres (4.9 ft) and 4 metres (13 ft) 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, with the underside of the body and the top of the head also being protected with osteoderms. This protection reached a thickness of 2.5 centimetres (0.98 in). The vertebrae of the back were extensively fused to each other. The limbs were short and robustly built, with thepectoral girdle being wide. The head was short and blunt, with deep jaws. The teeth were grooved, and were evergrowing.[1] The tail was covered in rings composed of osteoderms, which allowed the tail to flex. In many glyptodonts (members of the "Austral clade" other thanPropalaehoplophorus andEucinepeltus), the end of the tail was covered in a completely fused "caudal tube".[8] 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, likelykeratinous spikes, allowing for the tail to function as an effective weapon when swung. These "tail clubs" are similar in construction to those ofankylosaurid dinosaurs.[9]
Glyptodonts are thought to have been herbivores that fed on low lying vegetation, with mixed feeding or grazing based diets.[10] Some glyptodonts were likely selective feeders, while others were likely bulk feeders.[10][11] 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.[12]
At the end of theLate Pleistocene, all then-living glyptodont species, which belonged to the generaGlyptodon,Hoplophorus,Glyptotherium,Panochthus,Doedicurus andNeosclerocalyptus, abruptly became extinct around 12,000 years ago as part of theend-Pleistocene extinction event, simultaneously with the vast majority of other large mammals in the Americas. These extinctions followedthe 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 arrivedPaleoindians, which may have played a role in their extinction.[13][3] At the Muaco and Taima-Taima sites inFalcón State in northwestern Venezuela, several skulls ofGlyptotherium 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.[3]
