Thyreophorans are characterized by the presence of body armor lined up in longitudinal rows along the body. Primitive forms had simple, low, keeled scutes or osteoderms, whereas more derived forms developed more elaborate structures including spikes and plates. Most thyreophorans were herbivorous and had relatively small brains for their body size.
Thyreophora includes various subgroups, including the suborders Ankylosauria and Stegosauria. In both the suborders, the forelimbs were much shorter than the hindlimbs, particularly in stegosaurs. The clade has been defined as the group consisting of all species more closely related to Ankylosaurus than to Triceratops. Thyreophora is the sister group of Cerapoda within Genasauria.
|Skeletal mount of Gastonia burgei, BYU Museum of Paleontology|
|Skeletal mount of Stegosaurus stenops, Natural History Museum, London|
Ankylosaurids are noted by the presence of a large tail club composed of distended vertebrae that have fused into a single mass. They were heavy-set and heavily armored from head to tail in bony armor, even down to minor features such as the eyelids. Spikes and nodules, often of horn, were set into the armor. The head was flat, stocky, with little or no "neck", roughly shovel-shaped and characterized by two spikes on either side of the head approximately where the ears and cheeks were. Euoplocephalus tutus is perhaps the best-known ankylosaurid.
Nodosaurids, the other family in the Ankylosauria, may actually include the ancestors of the ankylosaurids. They lived during the middle Jurassic (approx 170 mya) on up through the late Cretaceous (66 mya) and, while armored as the ankylosaurids, did not have a tail club. Instead, the bony bumps and spikes that covered the rest of their body continued out to the tail and/or were augmented with sharp spines. Two examples of nodosaurs are Sauropelta and Edmontonia, the latter most notable for its formidable forward-pointing shoulder spikes.
The suborder Stegosauria comprises Stegosauridae and Huayangosauridae. These dinosaurs lived mostly from the Middle to Late Jurassic, although some fossils have been found in the Cretaceous. Stegosaurs had very small heads with simple, leaf-like teeth. Stegosaurs possessed rows of plates and/or spikes running down the dorsal midline and elongated dorsal vertebra. It has been suggested that stegosaur plates functioned in control of body temperature (thermoregulation) and/or were used as a display to identify members of a species, as well as to attract mates and intimidate rivals. Well known stegosaurs are Stegosaurus and Kentrosaurus.
While ranked taxonomy has largely fallen out of favor among dinosaur paleontologists, a few 21st century publications have retained the use of ranks, though sources have differed on what its rank should be. Most have listed Thyreophora as an unranked taxon containing the traditional suborders Stegosauria and Ankylosauria, though Thyreophora is also sometimes classified as a suborder, with Ankylosauria and Stegosauria as infraorders.
Thyreophora was first named by Nopcsa in 1915. Thyreophora was defined as a clade by Paul Sereno in 1998, as "all genasaurs more closely related to Ankylosaurus than to Triceratops". Thyreophoroidea was first named by Nopcsa in 1928 and defined by Sereno in 1986, as "Scelidosaurus, Ankylosaurus, their most recent common ancestor and all of its descendants". Eurypoda was first named by Sereno in 1986 and defined by him in 1998, as "Stegosaurus, Ankylosaurus, their most recent common ancestor and all of their descendants". The cladogram below follows a 2011 analysis by paleontologists Richard S. Thompson, Jolyon C. Parish, Susannah C. R. Maidment and Paul M. Barrett.
Ankylosauria is a group of mainly herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. They are known to have first appeared in the early Jurassic Period, and persisted until the end of the Cretaceous Period. They have been found on every continent. The first dinosaur discovered in Antarctica was the ankylosaurian Antarctopelta, fossils of which were recovered from Ross Island in 1986.
Ankylosauria was first named by Henry Fairfield Osborn in 1923. In the Linnaean classification system, the group is usually considered either a suborder or an infraorder. It is contained within the group Thyreophora, which also includes the stegosaurs, armored dinosaurs known for their combination of plates and spikes.Averostra
Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.Avetheropoda
Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.Barremian
The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 125.0 ± 1.0 Ma). It is a subdivision of the Early Cretaceous epoch (or Lower Cretaceous series). It is preceded by the Hauterivian and followed by the Aptian stage.Bienosaurus
Bienosaurus (meaning "Bien's lizard") is a genus of thyreophoran dinosaur from the Lower Jurassic (probably Sinemurian) Lower Lufeng Formation in Yunnan Province in China.Cerapoda
Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.Emausaurus
Emausaurus is a genus of thyreophoran or armored dinosaur from the Early Jurassic. Its fossils have been found in Germany. The type and only species, Emausaurus ernsti, was formalized by Harmut Haubold in 1990. The generic name is composed of an acronym of Ernst Moritz Arndt University of Greifswald and Greek sauros/σαυρος (lizard). The specific name is derived from the name of geologist Werner Ernst, who found the fossil, holotype SGWG 85, in the summer of 1963 at a loampit near Grimmen, in strata dating from the Toarcian.Genasauria
Genasauria is a clade of extinct beaked, primarily herbivorous dinosaurs. Paleontologist Paul Sereno first named Genasauria in 1986. The name Genasauria is derived from the Latin word gena meaning ‘cheek’ and the Greek word saúra (σαύρα) meaning ‘lizard.’ Genasauria is the most inclusive clade within the order Ornithischia. According to Sereno (1986), Genasauria represents all ornithischians except for the most primitive ornithischian, Lesothosaurus. Sereno’s formal definition is, “Ankylosaurus, Triceratops, their most recent common ancestor and all descendants.” It is hypothesized that Genasauria had diverged from Lesothosaurus by the Early Jurassic. Cranial features that characterize Genasauria include a medial offset of the maxillary dentition, a sprout-shaped mandibular symphysis, moderately sized coronoid process, and an edentulous (without teeth) anterior portion of the premaxilla. A distinguishing postcranial feature of Genasauria is a pubic peduncle of the ilium that is less robust than the ischial peduncle.
Genasauria is commonly divided into Neornithischia and Thyreophora. Neornithischia is characterized by asymmetrical distributions of enamel covering the crowns of the cheek teeth, an open acetabulum, and a laterally protruding ischial peduncle of the ilium. Neornithischia includes ornithopods, pachycephalosaurs, and ceratopsians. Thyreophora is characterized by body armor and includes stegosaurs, ankylosaurs, Scelidosaurus, and Scutellosaurus.Invictarx
Invictarx is a genus of herbivorous nodosaurid dinosaur from New Mexico dating from the early Campanian epoch of the Late Cretaceous.Laquintasaura
Laquintasaura is a genus of Venezuelan ornithischian dinosaur containing only the type species Laquintasaura venezuelae. The species is the first dinosaur to have been discovered in Venezuela. Found in the Lower Jurassic, Hettangian, La Quinta Formation from which it takes its name, the bipedal species was about a meter long and 25 centimeters high. L. venezuelae, which is believed to have lived in herds, was primarily herbivorous, although it may have also eaten large insects and other small animals.A phylogenetic analysis by Baron et al. (2017) recovered Laquintasaura as the sister-taxon to Scutellosaurus, within the clade Thyreophora.Lusitanosaurus
Lusitanosaurus (meaning "Portuguese lizard") is a genus of basal thyreophoran dinosaur from the Early Jurassic of Portugal.
The genus was first described by Albert-Félix de Lapparent and Georges Zbyszewski in 1957. The type species is Lusitanosaurus liasicus. The generic name is derived from Lusitania, the ancient Latin name for the region. The specific name refers to the Lias.
The holotype is part of the collection of the Museu de História Natural da Universidade de Lisboa. The exact location of the find and the date of collection are unknown, which makes a correct geological dating difficult, but it can be inferred from the matrix rock that it has been discovered near São Pedro de Moel, in strata from the Sinemurian (Early Jurassic). This would make it the oldest known dinosaur from Portugal. The fossil consists of a single partial left maxilla, an upper jaw bone, with seven teeth.
Originally assigned to the Stegosauria by de Lapparent, Lusitanosaurus is today considered a basal member of the Thyreophora, perhaps belonging to the Scelidosauridae. Some authors consider it a nomen dubium.Minmi paravertebra
Minmi is a genus of small herbivorous ankylosaurian dinosaur that lived during the early Cretaceous Period of Australia, about 119 to 113 million years ago.Neornithischia
Neornithischia ("new ornithischians") is a clade of the dinosaur order Ornithischia. They are the sister group of the Thyreophora within the clade Genasauria. Neornithischians are united by having a thicker layer of asymmetrical enamel on the inside of their lower teeth. The teeth wore unevenly with chewing and developed sharp ridges that allowed neornithischians to break down tougher plant food than other dinosaurs. Neornithischians include a variety of basal forms historically known as "hypsilophodonts", including the Parksosauridae; in addition, there are derived forms classified in the groups Marginocephalia and Ornithopoda. The former includes clades Pachycephalosauria and Ceratopsia, while the latter typically includes Hypsilophodon and the more derived Iguanodontia.Orionides
Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.Ornithischia
Ornithischia () is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure similar to that of birds. The name Ornithischia, or "bird-hipped", reflects this similarity and is derived from the Greek stem ornith- (ὀρνιθ-), meaning "of a bird", and ischion (ἴσχιον), plural ischia, meaning "hip joint". However, birds are only distantly related to this group as birds are theropod dinosaurs.Ornithischians with well known anatomical adaptations include the ceratopsians or "horn-faced" dinosaurs (e.g. Triceratops), armored dinosaurs (Thyreophora) such as stegosaurs and ankylosaurs, pachycephalosaurids and the ornithopods. There is strong evidence that certain groups of ornithischians lived in herds, often segregated by age group, with juveniles forming their own flocks separate from adults. Some were at least partially covered in filamentous (hair- or feather- like) pelts, and there is much debate over whether these filaments found in specimens of Tianyulong, Psittacosaurus, and Kulindadromeus may have been primitive feathers.Scelidosaurus
Scelidosaurus (; with the intended meaning of "limb lizard", from Greek skelis/σκελίς meaning 'rib of beef' and sauros/σαυρος meaning 'lizard') is a genus of herbivorous armoured ornithischian dinosaur from the Jurassic of England.
Scelidosaurus lived during the Early Jurassic Period, during the Sinemurian to Pliensbachian stages around 191 million years ago. This genus and related genera at the time lived on the supercontinent Laurasia. Its fossils have been found near Charmouth in Dorset, England, and are known for their excellent preservation. Scelidosaurus has been called the earliest complete dinosaur. It is the most completely known dinosaur of the British Isles. Scelidosaurus is currently the only classified dinosaur found in Ireland. Despite this, a modern description is still lacking. After initial finds in the 1850s, comparative anatomist Richard Owen named and described Scelidosaurus in 1859. Only one species, Scelidosaurus harrisonii named by Owen in 1861, is considered valid today, although one other species was proposed in 1996.
Scelidosaurus was about 4 metres (13 ft) long. It was a largely quadrupedal animal, feeding on low scrubby plants, the parts of which were bitten off by the small, elongated head to be processed in the large gut. Scelidosaurus was lightly armoured, protected by long horizontal rows of keeled oval scutes that stretched along the neck, back and tail.
One of the oldest known and most "primitive" of the thyreophorans, the exact placement of Scelidosaurus within this group has been the subject of debate for nearly 150 years. This was not helped by the limited additional knowledge about the early evolution of armoured dinosaurs. Today most evidence indicates that Scelidosaurus is the sister taxon to the two main clades of Thyreophora, the Stegosauria and Ankylosauria.Scutellosaurus
Scutellosaurus ( skoo-TEL-oh-SOR-əs) is an extinct genus of thyreophoran ornithischian dinosaur that lived approximately 196 million years ago during the early part of the Jurassic Period in what is now Arizona, USA. It is classified in Thyreophora, the armoured dinosaurs; its closest relatives may have been Emausaurus and Scelidosaurus, another armored dinosaur which was mainly a quadrupedal dinosaur, unlike bipedal Scutellosaurus. It is one of the earliest representatives of the armored dinosaurs and the basalmost form discovered to date. Scutellosaurus was a small, lighly-built, ground-dwelling, herbivore, that could grow up to an estimated 1.2 m (3.9 ft) long.Tatisaurus
Tatisaurus is a genus of ornithischian dinosaur from the Early Jurassic from the Lower Lufeng Formation in Yunnan Province in China. Little is known as the remains are fragmentary.Thyreophora cynophila
Thyreophora cynophila, commonly known as the bone skipper is a species of fly, once thought to be the first fly to be driven to extinction by humans, but rediscovered in 2009. It has a bright orange head, and is associated with animal carcasses where the bones are broken open.