Fossilized armour of Edmontonia, specimen AMNH 5665
Armour or armor in animals is a rigid cuticle or exoskeleton that provides exterior protection against attack by predators, formed as part of the body (rather than the behavioural utilization of external objects for protection) usually through the thickening and hardening of superficial tissues, outgrowths or skinsecretions. It is therefore mostly developed in prey species that are too slow or clumsy to outrun predators, or those that would stand their ground and fight, thus needing to shield vital organs against claw, talon or bite injuries.
Armour is evident in numerous animal species from both current and prehistoric times. Dinosaurs such as Ankylosaurus, as well as other Thyreophora (armoured dinosaurs such as Ankylosauria and Stegosauria), grew thick plate-like armour on their bodies as well as offensive armour appendages such as the thagomizer or a tail club. The armour took many forms, including osteoderms, spikes, horns, and plates. Other dinosaurs such as ceratopsian dinosaurs as well as some sauropods such as Saltasaurus, grew armour to defend themselves, although armour in sauropods overall is uncommon.
Numerous mammals employ the use of spines and body armour, although not as sturdy as reptilian armour, like the spines of the echidnas and of porcupines and hedgehogs. The bony shell of the armadillos and the extinct Glyptodon were very much like Ankylosaurus' armour and some modern armadillos curl up into a ball when threatened, making them unexposed due to their armour. Similarly, the hairy plate-like scales of the pangolin are employed in the same way and are constructed of the same material used in the offensive armour, the horn, of the rhinoceros.
Usage
Armour, although all used for the sole intent to ward off attackers, can be split into defensive and offensive armour. Examples of offensive armour are horns, hooves, antlers, claws and beaks, clubs and pincers, as developed in some mammals, birds, reptiles (including dinosaurs, such as the dromaeosaurid claw and the ceratopsian horn) and arthropods. Offensive armour is often used in conjunction with defensive armour and in some cases makes an animal almost unassailable.
An exoskeleton is a skeleton that is on the exterior of an animal to both support the body shape and protect the internal organs, in contrast to an internal endoskeleton which is enclosed underneath other soft tissues. Some large, hard and non-flexible protective exoskeletons are known as shell or armour.
Saltasaurus is a genus of saltasaurid dinosaur of the Late Cretaceous period of Argentina. Small among sauropods, though still heavy by the standards of modern creatures, Saltasaurus was characterized by a short neck and stubby limbs. It was the first genus of sauropod known to possess armour of bony plates embedded in its skin. Such small bony plates, called osteoderms, have since been found on other titanosaurians.
Ankylosauria is a group of herbivorous dinosaurs of the clade Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. They are known to have first appeared in the Middle Jurassic, and persisted until the end of the Cretaceous Period. The two main families of Ankylosaurs, Nodosauridae and Ankylosauridae are primarily known from the Northern Hemisphere, but the more basal Parankylosauria are known from southern Gondwana during the Cretaceous.
Ankylosaurus is a genus of armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period, about 68–66 million years ago, in western North America, making it among the last of the non-avian dinosaurs. It was named by Barnum Brown in 1908; it is monotypic, containing only A. magniventris. The generic name means "fused" or "bent lizard", and the specific name means "great belly". A handful of specimens have been excavated to date, but a complete skeleton has not been discovered. Though other members of Ankylosauria are represented by more extensive fossil material, Ankylosaurus is often considered the archetypal member of its group, despite having some unusual features.
A scute or scutum is a bony external plate or scale overlaid with horn, as on the shell of a turtle, the skin of crocodilians, and the feet of birds. The term is also used to describe the anterior portion of the mesonotum in insects as well as some arachnids.
Euoplocephalus is a genus of very large, herbivorous ankylosaurid dinosaurs, living during the Late Cretaceous of Canada. It has only one named species, Euoplocephalus tutus.
Scelidosaurus is a genus of herbivorous armoured ornithischian dinosaur from the Jurassic of England.
Zuul is a genus of herbivorous ankylosaurine dinosaur from the Campanian Judith River Formation of Montana. The type species is Zuul crurivastator. It is known from a complete skull and tail, which represents the first ankylosaurin known from a complete skull and tail club, as well as the most complete ankylosaurid specimen thus far recovered from North America. The specimen also preserved in situ osteoderms, keratin, and skin remains.
Agathaumas is a dubious genus of a large ceratopsid dinosaur that lived in Wyoming during the Late Cretaceous. The name comes from Ancient Greek: αγαν - 'much' and θαυμα - 'wonder'. It is estimated to have been 15 metres (49 ft) long and weighed 17.5 tonnes, and was seen as the largest land animal known at the time of its discovery.
Edmontonia is a genus of panoplosaurin nodosaurid dinosaur from the Late Cretaceous Period. It is part of the Nodosauridae, a family within Ankylosauria. It is named after the Edmonton Formation, the unit of rock where it was found.
Ankylosauridae is a family of armored dinosaurs within Ankylosauria, and is the sister group to Nodosauridae. The oldest known Ankylosaurids date to around 122 million years ago and went extinct 66 million years ago during the Cretaceous–Paleogene extinction event. These animals were mainly herbivorous and were obligate quadrupeds, with leaf-shaped teeth and robust, scute-covered bodies. Ankylosaurids possess a distinctly domed and short snout, wedge-shaped osteoderms on their skull, scutes along their torso, and a tail club.
Panoplosaurus is a genus of armoured dinosaur from the Late Cretaceous of Alberta, Canada. Few specimens of the genus are known, all from the middle Campanian of the Dinosaur Park Formation, roughly 76 to 75 million years ago. It was first discovered in 1917, and named in 1919 by Lawrence Lambe, named for its extensive armour, meaning "well-armoured lizard". Panoplosaurus has at times been considered the proper name for material otherwise referred to as Edmontonia, complicating its phylogenetic and ecological interpretations, at one point being considered to have existed across Alberta, New Mexico and Texas, with specimens in institutions from Canada and the United States. The skull and skeleton of Panoplosaurus are similar to its relatives, but have a few significant differences, such as the lumpy form of the skull osteoderms, a completely fused shoulder blade, and regularly shaped plates on its neck and body lacking prominent spines. It was a quadrupedal animal, roughly 5 m (16 ft) long and 1,600 kg (3,500 lb) in weight. The skull has a short snout, with a very domed surface, and bony plates directly covering the cheek. The neck had circular groups of plates arranged around the top surface, both the forelimb and hindlimb were about the same length, and the hand may have only included three fingers. Almost the entire surface of the body was covered in plates, osteoderms and scutes of varying sizes, ranging from large elements along the skull and neck, to smaller, round bones underneath the chin and body, to small ossicles that filled in the spaces between other, larger osteoderms.
In zoology, a tail club is a bony mass at the end of the tail of some dinosaurs and of some mammals, most notably the ankylosaurids and the glyptodonts, as well as meiolaniid turtles. It is thought that this was a form of defensive armour or weapon that was used to defend against predators, much in the same way as a thagomizer, possessed by stegosaurids, though at least in glyptodonts it is hypothesized it was used in fighting for mating rights. Among dinosaurs, the club was present mainly in ankylosaurids, although sauropods like Shunosaurus also possessed a tail club. The tail club is most often depicted on Ankylosaurus, especially in encounters with larger predators such as Tyrannosaurus. Victoria Arbour has established that ankylosaurid tails could generate enough force to break bone during impacts. In a separate study, Arbour suggested tail clubs as well as large armoured herbivores as a whole evolve when animals are too large to hide and too small to avoid predation by size alone.
The physiology of dinosaurs has historically been a controversial subject, particularly their thermoregulation. Recently, many new lines of evidence have been brought to bear on dinosaur physiology generally, including not only metabolic systems and thermoregulation, but on respiratory and cardiovascular systems as well.
Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls, various groups of dinosaurs, phytosaurs, aetosaurs, placodonts, and hupehsuchians.
Arthropods are covered with a tough, resilient integument, cuticle or exoskeleton of chitin. Generally the exoskeleton will have thickened areas in which the chitin is reinforced or stiffened by materials such as minerals or hardened proteins. This happens in parts of the body where there is a need for rigidity or elasticity. Typically the mineral crystals, mainly calcium carbonate, are deposited among the chitin and protein molecules in a process called biomineralization. The crystals and fibres interpenetrate and reinforce each other, the minerals supplying the hardness and resistance to compression, while the chitin supplies the tensile strength. Biomineralization occurs mainly in crustaceans. In insects and arachnids, the main reinforcing materials are various proteins hardened by linking the fibres in processes called sclerotisation and the hardened proteins are called sclerotin. The dorsal tergum, ventral sternum, and the lateral pleura form the hardened plates or sclerites of a typical body segment.
Diania is an extinct genus of lobopodian panarthropod found in the Lower Cambrian Maotianshan shale of China, represented by a single species - D. cactiformis. Known during its investigation by the nickname "walking cactus", this organism belongs to a group known as the armoured lobopodians, and has a simple worm-like body with robust, spiny legs. Initially, the legs were thought to have a jointed exoskeleton and Diania was suggested to be evolutionarily close to early arthropods, but many later studies have rejected this interpretation.
This glossary explains technical terms commonly employed in the description of dinosaur body fossils. Besides dinosaur-specific terms, it covers terms with wider usage, when these are of central importance in the study of dinosaurs or when their discussion in the context of dinosaurs is beneficial. The glossary does not cover ichnological and bone histological terms, nor does it cover measurements.
A plate in animal anatomy may refer to several things:
Osteoderms are dermal bone structures that support the upper layer of skin and serve as protection against the elements in a large variety of extinct and extant organisms, especially reptiles. This structure is commonly called "dermal armor" and serves to protect the organism, while also helping with temperature regulation. Osteoderms represent hard tissue components of the integument, making them easy to identify in fossil examination. This dermal armor is found prominently in many lizards. Some early amphibians have this armor, but it is lost in modern species with the exception a ventral plate, called the gastralia.
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