Glyptodon

The word ‘Glyptodon’ has been derived from Greek words and imply ‘carved or grooved tooth’. Glyptodon was a genus, now extinct, and composed of giant mammals that resemble the present-day armadillos. Glyptodons are mostly found as fossil deposits in South and North America. They are estimated to have lived from Pliocene to the Pleistocene epochs (between 5.3 million and 11,700 years ago). Glyptodons belonged to the subfamily Glyptodontinae (glyptodontines or glyptodonts) and their body was heavily armoured. 

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Glyptodont

One is often confused between the terms ‘Glyptodon’ and ‘Glyptodont’. The seemingly similar terms, yet however, do not imply the same. While ‘Glyptodon’ is a genus, ‘Glyptodont’ is a subfamily that is now extinct. The Glyptodont sub-family consisted of large-bodied relatives of armadillos with heavy armour. The sub-family Glyptodont is a member of the mammalian superorder Xenarthra mostly seen in South America. They are estimated to have originated in South America, roughly 20 million years ago and then eventually spread to the southern part of North America after the merger of the continents. The family is also referred to as Glyptodontinae or Glyptodontines. The sub family’s best-known genus is Glyptodon. 

Structure and Morphology

The body armour of glyptodonts is tortoise-like with their skin consisting of bony deposits known as scutes or osteoderms. The shell type and osteoderm pattern of each Glyptodon species were unique. Glyptodonts were not able to withdraw their heads. Instead, their skull was enclosed by a bony cap formed by their armoured skin. The tails of Glyptodonts had a ring of bones meant for protection. The physical appearance of glyptodonts resembled superficially the dinosaurian ankylosaurs alive much earlier. It has been estimated that the largest glyptodons could have weighed up to 2000 kilograms.

Glyptodon and other members of the sub-family Glyptodont were encased in protective, thick armour. The entire body of the mammal from head to tail was encased in the armour which bore resemblance to the shape of a turtle’s shell. However, the armour consisted of bony plates as seen in the covering of armadillos. The length of the body shell alone was around 5 feet or 1.5 metres. The armour-clad tail could serve the purpose of a lethal club. It is believed that the tails of Glyptodon may have been used in competing for resources and as an accessory organ to provide a reproductive advantage.

The massive shell along with the long tail needed considerable support. The Glyptodons thus, had fused vertebrae, a broad shoulder girdle and short but massive limbs as evidenced by fossil records.

The major advantage of Glyptodonts was their large body size. The genus Glyptodon included within the sub-family were as large as the size of modern-day automobiles. Their heavy armour and defences were suggestive of the fact that Glyptodonts were indeed prey to an effective and large predator. Evolutionary history indicates that during the time the glyptodons evolved, phorusrhacids in the South American continental island were the apex predators. The phorusrhacids were a family of flightless large birds, carnivorous in nature. 

Glyptodon Anatomy

The length of the species Glyptodon was about 11 ft or 3.3 metres, height was about 4.9 ft or 1.5 metres and are believed to have weighed up to 2000 kilograms. 

Skull Anatomy

The anatomy of the Glyptodon skull reveals that their nasal passage was reduced and also bore heavy muscle attachments. While the exact purpose of the muscle attachments is not relatively known, it has been speculated that attachments were fr a trunk or proboscis akin to the tapir of elephants. The Glyptodons had very deep lower jaws which supported the massive chewing muscles enabling them to chew fibrous coarse plants. The teeth of Glyptodons bore resemblance to armadilloes but deep grooves on either side furrowed them. The cylindrical posterior teeth were contrasted from the compressed anterior teeth. Down the cheek of the Glyptodon, ran a bar of bone, distinctive. This bone extended over the lower jaw and is thought to have provided anchorage for the powerful snout muscles although some have attributed the large nasal sinuses to the arid and cold climate of South America in the Pleistocene 

Carapace - Osteoderm Anatomy

The carapace of Glyptodon bore resemblance to the shell of a turtle. The protective shell of glyptodon consisted of thick bony plates, each about 2.5 cm thick. These plates were called scutes or osteoderms and the shell comprised more than 1000 of them. The shell type along with the pattern of osteoderm was unique to each species. The osteoderms of Glyptodon were attached by syntoses prior to the Pleistocene. Also, osteoderms were present in double or triple rows on the sides or the front of the carapace’s edges along with the cephalic shield and the tail armour. The osteoderms on the carapace were conical and had a rounded point. The tail osteoderms were just conical. 

It was confirmed by fossil records from the Pleistocene that several species of the Glyptodon also had osteoderms on the hind legs, face and underside regions. These ossicles embedded in the dermis ranged between small and medium sizes, however, did not form a pattern. The emergence of this novel trait is coincident with the arrival of North-American predators during the Great American Interchange, in South America, as the two continents became adjoined. This led to the hypothesis the development of osteoderms was a defensive/offensive mechanism. The discovery of the fractured dorsal armour implicative of the physical conflict between the Glyptodon and other species only furthered this hypothesis. 

Tail Anatomy

The tail of Glyptodon clavipes was covered in free bony rings. The dermal sutures in the rings of the tail made it strong as well as flexible and motile. The Glyptodon was thus able to use the muscles of the tail and swing it powerfully. 

The caudal ring 1 or accessory ring consisted of small scutes in a short double row. The several scutes in the proximal row were small, pentagonal in shape. The scutes in the distal row, although pentagonal, were large as compared to the caudal row. The proximal row scutes have a convex shape. Each scute in the proximal row provides support to a pair of hair follicles. 

The first complete caudal ring is ring 2 and it is also the largest ring. Firmly sutured scutes in two complete rows constitute this ring. In this ring, the end or distal scutes are larger. The free margins of these scutes are rounded which gives rise to a fan-like shape. 

The second complete ring is ring 3. It is almost similar to Ring 2 with the exception of its smaller size and some of the distal row scutes reaching the proximal margin. The crowding of the proximal scutes makes the proximal row incomplete although the number of cutes in both rows is 20. 

The diameters of rings 4 to10 have gradually decreased, which increases the maximum length at the back (4 to 10 onwards). These rings are characterised by double rows with the number of scutes decreasing in each row from 4 to 10.

Spine Anatomy

The number of vertebrae in Glyptodon was 13 which were present consecutively. Of the thirteen vertebrae, four are so close together that they are almost indiscernible. The other vertebrae, barring these 4, are connected by means of sutures. As they approach the posterior, these vertebrae are spaced further apart. 

Each centrum of the vertebrae forms a hollow cylinder by means of curvature in the thin bony plate. The diameter of the cylinder is much larger in the front as compared to the hinder vertebrae. The width of the foremost vertebrae is comparable to the hind part of the tri vertebral bone. The vertebrae that follow suit are consecutively narrower until the 4th vertebra, whose width only reaches up to three-fifths of the first. 

Habitat

The Glyptodons originated in South America with their remains being found in Argentina, Uruguay and Brazil. As per the fossilised records of Brazil, the species of Glyptodons with the largest range is G. clavipes, having ranged from the northeast, north to southeast Brazil. On the other hand, remains of G. reticulatus have been found only in Southern Brazil. 

The exact range of habitat of the sub-family Glyptodonts had not been accurately determined given the poor taxonomic and morphological assessments. Only recently, the habitat range of Glyptodonts in western Uruguay, Paraguay and Bolivia has been confirmed. 

The habitat ranged from forested to sub-forested areas while some even became accustomed to open areas. They mostly thrived in areas where the climate was warm and humid while some have also been discovered in cold areas such as grasslands. The genus Glyptodon has also been found to have occurred in the southwestern region of the Amazon basin. This is suggestive of the wide diversity of the genus owing to varied climates within the range of its habitats. 

Behaviour

It is believed that the various genus within the Glyptodont sub-family engaged in intraspecific fighting. Given the very flexible nature of the tail of the Glyptodonts combined with the rings of bony plates, zoologists believe that the tail was utilised as a weapon in fights. The tail could have also been employed as a defence against predators, however, evidence points towards the offensive nature of the tail, for attacking its own kind. 

Calculations performed by a group of zoologists on the amount of force required to destroy the Glyptodon carapace showed that the tail was capable of doing so. It is likely that Glyptodons fought each other over the settlement of mating or territorial disputes as seen in the male-to-male combat among deers by means of their antlers. 

Diet

The Glyptodonts were primarily grazing herbivores. This is evidenced by their jaw morphology. This is supported by the lack of incisor or canine teeth and the presence of several cheek teeth enabling the mammals to chew on tough vegetation like grasses. The jaws were also distinctively deep with bony projections running downwards as a means of providing anchorage to the strong chewing muscles. 

Glyptodonts, on the basis of their feeding habits, can be characterised into two main groups. The early Miocene propalaehoplophorids which were of smaller size had narrow muzzles. The post-Miocene glyptodonts, which were larger, had wider muzzles. The glyptodonts of the Miocene era were selective feeders as opposed to the larger bulk-feeding glyptodons. 

In both cases, however, given the cervical vertebrae fusion and body form, all the Glyptodon members would have been required to forage close to the ground. The side-to-side movement of their jaw was limited by the craniomandibular joint. 

In the species, Glyptodon, the elaboration of their jaw’s osteodentine ridges provided them with effective grinding ill. This caused a constant pushing and shearing of the food particles through the mandible’s motion which allowed for consumption of the daily dietary needs. The musculature was well-developed and snout, which combined with a mobile neck region helped them in securing food. The primary grazing area for Glyptodon species was near water bodies such as lakes and rivers. As revealed by stable isotope analysis, their diet mainly seemed to have consisted of monocotyledonous grasses and dicotyledonous trees. 

The energy requirements of the glyptodonts were smaller than most other mammals which allowed them to survive even with intake rate rates that were smaller than herbivores with a smaller mass. 

Eyesight

The glyptodonts are believed to have a rare condition called rod monochromacy, characterised by the absence of the photoreceptor cells in the eye. This results in blindness in conditions of bright light, low acuity vision in conditions where light is dim and color blindness. 

It has been hypothesized that glyptodonts used vision most likely during twilight, at night, and while in burrows. The rain forests of South America are also likely to have been dark enough during the day allowing for the facilitation of limited eyesight in glyptodonts during the day. The tough carapace, as well as the large body size of glyptodonts, are likely to have compensated for their inability to see the approaching predators. 

Predation of Glyptodonts 

The sabre-toothed cat Smilodon, as well as Homotherium, were the most likely predators of the Glyptodon sp. The other notable predators include terror birds, dire wolves and the short-faced giant bear Arctotherium. Evidence of predation by humans on Glyptodonts is very rare. 

Glyptodon Extinction

The extinction of Glyptodonts can be traced back to the end of the last ice age. This also marked the extinction of a large number of other species such as the giant ground sloths, the Macrauchenia and the pampatheres. They were survived by their flexible and more lightly armoured armadillo relatives. The arrival of early humans in either Americas is also coincident with the extinction of the glyptodonts. 

Certain evidence is suggestive of the fact that the Glyptodon extinction event was driven by humans. As suggested by archaeological evidence, humans most likely made use of the armoured shells of these animals. In inclement weather, hunters are likely to have made use of the dead animals’ shells as shelters. Models have predicted that the Glyptodon extinctions were likely caused by a combination of anthropogenic causes and climatic change. 

Conclusion

In this article, we have provided a detailed picture of Glypton along with clarification on Glyptodon vs Glyptodonts. We have seen their morphology, anatomy, habitat and feeding habits. These large armoured mammals which once inhabited earth are now extinct which we have highlighted under the Glyptodon extinction.