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| Thyreophorans | |
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| Skeletal mount ofGastonia burgei,BYU Museum of Paleontology | |
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| Skeletal mount ofStegosaurus stenops,Natural History Museum, London | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Genasauria |
| Clade: | †Thyreophora Nopcsa, 1915 |
| Subgroups[1] | |
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| Thyreophorans distribution map | |
Thyreophora ("shield bearers", often known simply as "armored dinosaurs") is a group ofarmoredornithischiandinosaurs that lived from the EarlyJurassic until the end of theCretaceous.
Thyreophorans are characterized by the presence of body armor lined up in longitudinal rows along the body. Primitive forms had simple, low, keeled scutes orosteoderms, whereas more derived forms developed more elaborate structures including spikes and plates. Most thyreophorans wereherbivorous and had relatively small brains for their body size.
Thyreophora includes two major subgroups,Ankylosauria andStegosauria. In both clades, the forelimbs were much shorter than the hindlimbs, particularly in stegosaurs. Thyreophora has been defined as the group consisting of all species more closely related toAnkylosaurus andStegosaurus than toIguanodon andTriceratops. It is thesister group ofCerapoda withinGenasauria.[2]
Members of Thyreophora are characterised by the presence ofosteoderms (bony growths within the skin), with these osteoderms having lateral keels. Characters of the skull and jaws distinctive (synapomorphic) of thyreophorans include "absence of a deep ellipticfossa along thesutural line of thenasals, presence of a widejugal, remodeling of skulldermal bone, down-turneddentary tooth row".[3] Among primitive thyreophorans,Scutellosaurus was likely primarily bipedal, while the more quadrupedally adaptedScelidosaurus may have been bipedal for some of the time, particularly as a juvenile. Stegosaurs and ankylosaurs are thought to have been obligately quadrupedal.[4]
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 byNopcsa in 1915.[5] Thyreophora was defined as aclade byPaul Sereno in 1998, as "allgenasaurs more closely related toAnkylosaurus than toTriceratops". 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".[6] 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".[7]
In 2021, an international group of researchers led by Daniel Madzia registered almost all of the most commonly used ornithischian clades under theInternational Code of Phylogenetic Nomenclature, with the intent of standardizing their definitions. According to Madziaet al., Thyreophora is defined as the largest clade containingAnkylosaurus magniventris andStegosaurus stenops but notIguanodon bernissartensis andTriceratops horridus.[2] They also defined the less inclusiveEurypoda as "the smallest clade containingAnkylosaurus magniventris andStegosaurus stenops" to include the ankylosaurs and stegosaurs to the exclusion of basal thyreophorans. A later study conducted by André Fonseca and colleagues in 2024 gave a formal definition forThyreophoroidea in thePhyloCode as "the smallest clade containingAnkylosaurus magniventris,Scelidosaurus harrisonii, andStegosaurus stenops".[1]
The followingcladogram shows the results of thephylogenetic analysis Soto-Acuñaet al. (2021).[8] In their description ofJakapil the following year, Riguettiet al modified the same matrix and found it to occupy a position as thesister taxon to the Eurypoda.[9] A similar result was found by Fonseca et al. in 2024.[1]
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In 2020, as part of his monograph onScelidosaurus,David Norman revised the relationships of early thyreophorans, finding that Stegosauria was the most basal branch, withScutellosaurus,Emausaurus andScelidosaurus being progressivestem groups to Ankylosauria, rather than to Stegosauria+Ankylosauria. A cladogram is given below:[10]
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