Glyptotherium

An extinct genus of mammals belonging to the armadillo order of xenarthrans

Automatic taxobox
| fossil range = Early Pliocene Late Pleistocene (Blancan Rancholabrean) (Ensenadan Lujanian)~
| image = Glyptotherium. jpg
| image caption = G. texanum, National Museum of Natural History
| taxon = Glyptotherium
| authority = Osborn, 1903
| type species = Glyptotherium texanum
| type species authority = Osborn, 1903
| subdivision ranks = Other Species
| subdivision = * G. cylindricum (Brown, 1912)
| range map = Glyptodon and Glyptotherium Distribution Map2. jpg
| range map caption = Distribution of Glyptotherium (orange) compared to Glyptodons (green). | synonyms = * Boreostracon Simpson, 1929
Brachyostracon Brown, 1912
Xenoglyptodon Meade, 1953

Glyptotherium (from Greek for 'grooved or carved beast') is a genus of glyptodont (an extinct group of large, herbivorous armadillos) in the family Chlamyphoridae (a family of South American armadillos) that lived from the Early Pliocene, about 3.6 million years ago, to the Late Pleistocene, around 15,000 years ago. It had a wide distribution, living in the United States, Mexico, Guatemala, Costa Rica, Honduras, El Salvador, Panama, Venezuela, and Brazil. The genus was first described in 1903 by American paleontologist Henry Fairfield Osborn with the type species being, G. texanum, based on fossils that had been found in the Pliocene Blancan Beds in Llano Estacado, Texas, USA. Glyptotherium fossils have since been unearthed from many more fossil sites, from Florida to Colombia. Another species, G. cylindricum''', was named in 1912 by fossil hunter Barnum Brown on the basis of a partial skeleton that had been unearthed from the Pleistocene deposits in Jalisco, Mexico. The two species differ in several aspects, including age, with G. texanum being from the older Early Pliocene to Early Pleistocene strata, whereas G. cylindricum is exclusive to the Late Pleistocene. Glyptotherium was a large, quadrupedal (four legged), herbivorous armadillo with an armored carapace (top shell) that was made of hundreds of interconnected osteoderms (structures in dermis composed of bone). Other pieces of armor covered the tail and cranium roof, the skull being tall with hypsodont (high crowned) teeth. As for the postcranial anatomy, pelves fused to the carapace, an amalgamate vertebral column, short limbs, and small digits are characteristic of Glyptotherium and its relatives. Glyptotherium reached up to 2 meters (6.56 feet) long and 400 kilograms (880 pounds) in weight, making it one of the largest glyptodonts but not as large as its close relative Glyptodon or Doedicurus, the largest known glyptodont. Glyptotherium is morphologically and phylogenetically most similar to Glyptodon, however they differ in several ways. Glyptotherium is smaller on average, with a shorter carapace, a relatively longer tail, and a slender zygoma, or cheek bone. Glyptodonts evolved first during the Eocene, but greatly diversified in the Miocene and Pliocene, largely in the Santacrucian sites of Argentina. However, their diversity diminished into the Pleistocene, though they peaked in size during this period. Glyptotherium is considered an example of North American megafauna, of which most have become extinct, and may have been wiped out by changing climate or human interference. Glyptotherium was primarily a grazer, but also had a mixed diet of fruits and other plants, that lived on open grasslands. The armor could protect the animal from predators, of which many coexisted with Glyptotherium during its existence, including the "saber tooth cat" Smilodon, the "bone crushing dog" Borophagus, and the "short faced bears" (Tremarctinae). History and phylogeny
Fossils attributable to Glyptotherium have been found as early as the 1870s, when civil engineers J. N. Cuatáparo and Santiago Ramírez collected a skull, nearly complete carapace, and associated postcranial skeleton of a glyptodont from a drainage canal near Tequixquiac, Mexico, the fossils coming from the Rancholabrean age of the Pleistocene. This was the first discovery of a glyptodont in North America. Both of these species have since been synonymized with G. cylindricum. but Cope did not give the species a proper description that followed ICZN rules, making it a nomen nudum and it has since been synonymized with G. cylindricum. that were collected from Pleistocene deposits in DeSoto County, Florida. This species is now seen as a nomen vanum and considered a junior synonym of Glyptotherium cylindricum by a review of the genus by American paleontologists David Gillette and Clayton Ray (1981). The specimen was sent to the American Museum of Natural History as well, where it was described by Brown in 1912 as a new genus and species of glyptodont, Brachyostracon cylindricum. In 1923, Oliver Perry Hay named a new species of Glyptodon, G. rivipacis, based on the fossils described by Leidy from DeSoto County, Florida. This species is now seen as a nomen nudum and synonymous with Glyptotherium cylindricum. Simpson referred all of the fossils previously described from Florida to B. floridanum and believed that all of the glyptodont fossils unearthed from North America were not of Glyptodon. The glyptodont fossils were originally referred to Glyptodon in 1928, but were not properly described until 1953. After later review, the former species was declared a junior synonym of G. texanum These include fossils previously referred to Glyptodon and Hoplophorus, as many fossils were hastily assigned to both by 19th century paleontologists.

Glyptotherium is a genus in the subfamily Glyptodontinae, an extinct clade of large, thoroughly armored armadillos that first evolved in the Late Eocene (ca. 33.5 mya) and went extinct in the Late Pleistocene Early Holocene extinctions. Glyptodontinae was classified in its own family or even superfamily until in 2016, when ancient DNA was extracted from the carapace of a 12,000 year old Doedicurus (a large, mace clubbed glyptodont) specimen, and a nearly complete mitochondrial genome was reconstructed (76x coverage). Comparisons with the DNA of modern armadillos revealed that glyptodonts diverged from tolypeutine and chlamyphorine armadillos approximately 33.5 million years ago in the late Eocene. This prompted moving them from their own family, Glyptodontidae, within the extant Chlamyphoridae as a subfamily, renamed Glyptodontinae. The internal phylogeny of Glyptodontinae is convoluted and in a flux, with many species and families erected on the basis of fragmentary or undiagnostic material that lacks comprehensive review. Glyptodontini is often recovered as more basal to most other glyptodonts like Doedicurus, Hoplophorus, and Panochthus. Glyptodontini is distinguishable from other groups for example in that it has large, conical tubercular osteoderms absent or only present on the caudal (tailward) notch on the posterior end of the carapace and different ornamentation of the armor on the carapace than the tail. The sister taxon, or closest relative(s) of another taxon, to Glyptotherium is the genus Glyptodon, which evolved in the Middle Pleistocene in Argentina. One specimen of G. cylindricum, AMNH 15548, preserved a carapace length of 1690 centimeters compared to just 1400 cm for MSM P4464, a G. texanum specimen. In both species, the central figures of the osteoderms get larger towards the margins of the carapace. Glyptotherium's zygoma are narrow, slender, almost parallel, and close to the sagittal plane in frontal view; in Glyptodon, this structure is broader, robust, divergent rather than parallel and more laterally placed. Glyptotherium and other glyptodonts preserve large nasal passages and sinuses that may have had nostrils adapted to breath in the cold arid climates of the Americas during the Pleistocene. In turn, the infraorbital foramina are narrow and not visible in anterior view in Glyptotherium, but in Glyptodon they are broad and clearly visible in anterior view. In lateral view, the dorso ventral height between the skull roof and the palatal plane in Glyptodon decreases anteriorly, contrary to Glyptotherium; the nasal tip is in a lower plane with respect to the zygomatic arch in Glyptodon, but in Glyptotherium is higher than the zygomatic arch plane. In Glyptotherium, the occlusal lateral profile is slightly curved, whereas it is strongly curved in Glyptodon. In Glyptodon, the 1st molariform (abbreviated as mf1) is distinctly trilobate (three lobed) both lingually and labially, nearly as trilobate as the mf2; on the contrary, Glyptotherium shows a very low trilobation of mf1, which is elliptical in cross section, the mf2 is weakly trilobate, and the mf3 is trilobate. In both genera, the mf4 to mf8 are fully trilobate and serially identical. In Glyptodon the top bottom height of the carapace represents 60% of its total length, whereas in Glyptotherium it is taller at ca. 70%. The ventral margins of the carapace in Glyptotherium is much more rectangular and less convex than in Glyptodon. In Glyptotherium, the osteoderms in the antero lateral areas of the carapace are less ankylosed than in Glyptodon, suggesting that the antero lateral carapace regions of the former had more flexibility. The osteoderms of the caudal aperture are more conical in Glyptodon and more rounded in Glyptotherium, though in the latter the anatomy of the caudal aperture osteoderms varies by sex Although frequently used to differentiate the two taxa, Glyptotherium and Glyptodon have very similar osteoderm morphologies that differ only in several areas. Both genera have very thick osteoderms compared to those of many South American glyptodonts like Hoplophorus and Neosclerocalyptus, but Glyptotherium always preserve a "rossette" pattern, where the osteoderm's central figure is surrounded by a row of peripheral figures. Some Glyptodon specimens preserve these "rossettes", but others lack them. The central and radial sulci are deeper and broader in Glyptodon (ca. 4–6 mm) than in Glyptotherium (ca. 1–2.4 mm). initially by British paleontologist Richard Owen in 1841 using comparative anatomy. Owen theorized that the phalanges were weight bearing due to their short and broad physiology, in addition to the evidence provided in the postcranial skeleton. The patellar articulation with the femur suggests rotation of the crus during knee extension and potentially even knee locking were feasible.

Glyptotherium is traditionally thought to consume wet, riparian herbs. The genus was mainly a grazer but also had a mixed diet of C3 and C4 plants based on isotope analyses of dental specimens recovered from the Late Pleistocene Cedral locality in San Luis Potosí, México. The locality preserves C4 plants from the families Poacea, Amaranthacea and Quenopodiacea, meaning that they were possible food sources for Glyptotherium. Additional isotopic evidence from Brazil suggests that fruits were also part of Glyptotherium diets, though only around 20% total. Glyptotherium and all other glyptodonts had hypsodont teeth, high crowned teeth with rough, flat surfaces adapted for grinding and crushing, that were adapted to break down gritty, fibrous material like grasses. This diet for Glyptotherium contrasts with those surmised for their relatives Pampatheres, which have been considered insectivores or grazers. Like most other xenarthrans, glyptodonts had lower energy requirements than most other mammals. They could survive with lower intake rates than other herbivores with similar mass.

Many extant species of armadillo have digging capabilities, with large claws adapted for scraping dirt to make burrows or forage for food underground. Also, much of their diet consists of insects and other invertebrates that live underground, in contrast to the herbivorous diets of Glyptotherium. Being from the armadillo family, glyptodont fossorial capabilities have been researched on several occasions. The trabecular core was made up of struts used for support with an average thickness of 0.25 mm, these struts making up the central support of the osteoderm. Mechanical analyses revealed that smaller load areas, representing sharper objects, cause higher stresses than those caused by large, blunt objects. This can be understood as the natural structure evolved to withstand blunt impact from large objects such as tail clubs and not as protection against sharp objects such as teeth. On several osteoderms that were also found in Brazil, ectoparasitism, lesions, and growths were found, some of these infections were likely caused by fleas.

Glyptotherium was primarily a grazer in forested grasslands and arboreal savannahs, though they may have preferred grasslands near water sources based on fossils localities from Mexico. The carnivores include the unusual "bone crushing" dog relative Borophagus and the "running hyena" Chasmaporthetes, in addition to the "saber toothed" cat Smilodon gracilis. Some isolated bird fossils have also been found consisting of vultures, falcons, and possibly corvids. Fossils from Guatemala were found from high altitudes, showing that Glyptotherium was highly adaptable and could live in a variation of environments. In the Brazilian Intertropical Region (BIR) in eastern Brazil, Glyptotherium was a mixed grazer in arboreal savannahs, tropical grasslands, and other grassy areas near water sources. Large, mesoherbivore mammals in the BIR were widespread and diverse, including the cow like toxodontids Toxodon platensis and Piauhytherium, the macraucheniid litoptern Xenorhinotherium and equids such as Hippidion principale and Equus neogaeus. Toxodontids were large mixed feeders as well and lived in forested areas, while the equids were nearly entirely grazers. Other xenarthran fossils are present in the area as well from several different families, like the giant megatheriid ground sloth Eremotherium, the scelidotheriids Catonyx and Valgipes, the mylodontids Glossotherium, Ocnotherium, and Mylodonopsis. Smaller ground sloths such as the megalonychids Ahytherium and Australonyx and the nothrotheriid Nothrotherium have also been found in the area. Eremotherium was a generalist, while Nothrotherium was a specialist for trees in low density forests, and Valgipes was an intermediate of the two that lived in arboreal savannahs. Other glyptodonts and cingulates like the grazing glyptodont Panochthus and the omnivorous pampatheres Pampatherium and Holmesina were present in the open grasslands. A proboscidean species has also been found in the BIR, Notiomastodon platensis, was also present and was a mixed grazer on the open grasslands. Carnivores included some of the largest known mammalian carnivores, like the giant felid Smilodon populator and the bear Arctotherium wingei. Two crab eating types of extant mammals are also known from the BIR, the crab eating raccoon and the crab eating fox, indicating that crabs were also present in the region. It is possible that the region alternated between dry open savanna and closed wet forest throughout the climate change of the Late Pleistocene.

South America, the continent where glyptodonts originated, was isolated after the breakup of the landmass Gondwana at the end of the Mesozoic era. This period of separation from the rest of the Earth's continents led to an age of unique mammalian evolution, with the dominance of groups such as marsupials, xenarthrans, and notoungulates in contrast to the North American mammal fauna. Marsupials likely got to South America prior to its separation from the rest of Gondwana in the Late Cretaceous or Paleogene, although the origins of mammalian orders like Xenarthra and Notoungulata ended up on the continent remains a mystery. There were several movements of outside mammals to South America prior to the formation of the Isthmus of Panama, such as with primates and rodents which may have rafted to the continent from Africa and the movement of bats via flight. As for the fauna of North America, contemporary groups like canids, felids, ursids, tapirids, antilocaprids, and equids populated the region in addition to extinct families like gomphotheres, amphicyonids, and mammutids. This intensified movement of glyptodonts, ground sloths, capybaras, pampatheres, terror birds, and marsupials to North America via the Central America route and a reverse migration of ungulates, proboscideans, felids, canids, and many other megafauna groups to South America. The period following the Isthmus' foundation witnessed the extinction or extirpation of many groups, including the South American terror birds, toxodonts, macraucheniids, pampatheres, ground sloths, and glyptodonts. Glyptotherium itself was part of this interchange, evolving in the Blancan of the Mexico & the USA after the formation of the Isthmus and its immigration. This is also connected to ecological segregation, with mountain barriers in Colombia possibly separating Glyptodon and Glyptotherium. The re entrance of a group to South America from North America has also been observed in the related cingulate family Pampatheriidae,

Smilodon may have occasionally preyed upon Glyptotherium, based on a skull from one Glyptotherium texanum individual recovered from Pleistocene deposits in Arizona bearing the distinctive elliptical puncture marks that best match those of the machairodont cat, indicating that the predator successfully bit into the skull through the armored cephalic shield. The Glyptotherium in question was a juvenile, with a still developing head shield, making it far more vulnerable to the cat's attack. Although originally theorized by George Brandes to be possible in 1900, Smilodon canines could not pierce the thick carapace osteoderms of glyptodonts. Brandes hypothesized that the evolution of thick glyptodont armor and long machairodont canines was an example of coevolution,

The first report of possible human consumption or interaction with Glyptotherium or its fossils came in 1958, where several osteoderms that were possibly consumed by humans were described from the Clovis site in Lewisville, Texas. This idea of human consumption has little evidence to back it, however. and many fossil discoveries from the Late Pleistocene have been unearthed since that exhibit human predation on glyptodonts. During this period, a wide array of Xenarthrans inhabited the Pampas were hunted by humans, with evidence demonstrating that the small (300–450 kg) glyptodont Neosclerocalyptus, the armadillo Eutatus, and the gigantic (2 ton) glyptodont Doedicurus, the largest glyptodont known, were hunted. The only other record of human predation from outside the Pampas was a partial carapace, found also in Venezuela, that was eviscerated by humans. The discoveries in the localities in Falcón showed the first signs of human hunting on the skulls of glyptodonts, but Glyptotherium also was more defenseless than glyptodonts like Doedicurus.

Glyptotherium is the only known North American glyptodont and is known from several regions of the continent from different periods. During the Blancan stage of the Early Pliocene, Glyptotherium texanum inhabited only central Mexico based on the discovery of a single osteoderm of Glyptotherium texanum from the early Pliocene strata of Guanajuato, central Mexico, dating to approx. 3.6 million years ago. In the Blancan Irvingtonian stages of the Early Pleistocene, G. texanum fossils are known from most of Mexico as well as the U. S. states of Arizona, Texas, Oklahoma, Florida, and possibly South Carolina. Costa Rica, Honduras, El Salvador, and Panama. The fossils from Central America are usually isolated and fragmentary, with the majority being osteoderms or isolated molariforms. In 2023, an associated skeleton of G. cylindricum, including skull and limb elements, from Guatemala was described, the most complete specimen from the region. It is most likely that the first Glyptotherium populations started in Central America during the Great American Biotic Interchange in the Late Pliocene based on their paleobiogeography. Although commonly regarded as an exclusively North American genus, In the United States, the last reliable direct radiocarbon date for Glyptotherium is 23,230 ± 490 BP, from Laubach Cave No. 3, Texas. However, statistical analyses suggest that a later survival until the terminal Pleistocene of the United States is possible, based on sampling biases associated with uncommon fauna, and a lack of reliable dates from the humid Atlantic plain due to poor preservation. although a minimum date of the entire assemblage (~15,780 cal. BP, 12,980 ± 85 radiocarbon BP) is more recent. As with other extinct Pleistocene megafauna, potential causes of extinction include human hunting, and climate change associated with the Younger Dryas cold interval.