Baiyinosaurus Temporal range: Middle Jurassic, late | |
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Skeletal reconstruction | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | † Ornithischia |
Clade: | † Thyreophora |
Clade: | † Stegosauria |
Genus: | † Baiyinosaurus Ning et al., 2024 |
Species: | †B. baojiensis |
Binomial name | |
†Baiyinosaurus baojiensis Ning et al., 2024 | |
Baiyinosaurus (meaning "Baiyin reptile") is an extinct genus of stegosaurian dinosaurs from the Middle Jurassic Wangjiashan Formation of China. The genus contains a single species, B. baojiensis, known from a partial skeleton including cranial bones. The skeletal anatomy of Baiyinosaurus demonstrates transitional features between basal thyreophorans and stegosaurs. While many stegosaurs are known from China, Baiyinosaurus is the only one currently named from Gansu Province.
The Baiyinosaurus holotype specimen, IVPG-D021, was discovered in 2016 by Li Daqing and his crew during excavations in sediments of the Wangjiashan Formation (Straw-yellow Sandstone Member). These outcrops are in the Pingchuan District of the city of Baiyin in Gansu Province, China. Following their discovery, the bones were collected and prepared by the Gansu Zhendan Dinosaur Culture Communication Co. Ltd., and reposited at Gansu Agricultural University. [1]
The holotype specimen consists of a partial skeleton, comprising fragmentary bones of the cranium (left premaxilla and maxilla, frontals, probable right jugal and squamosal, and left dentary) and several vertebrae (the atlas, seven dorsal vertebrae, and a caudal vertebra). [1]
In 2024, Ning et al. described Baiyinosaurus baojiensis as a new genus and species of stegosaurian dinosaurs based on these fossil remains. The generic name, Baiyinosaurus, combines a reference to Baiyin—the city where the holotype was found—with with the Greek "σαῦρος" ("sauros"), meaning "reptile". The specific name, baojiensis, references the Baiyinosaurus type locality in the Baojishan Basin in the Qilian Mountains. [1]
Baiyinosaurus is the only stegosaur taxon currently named from Gansu Province. The remains of a Cretaceous stegosaur, tentatively referred to Stegosaurus sp., were described earlier in 2024 from the Hekou Group but not assigned to a novel species. [2]
As a stegosaur, Baiyinosaurus would have been a quadrupedal herbivore with a paired row of a combination of large plates and spines running along the top of the animal from the neck to the tail tip. [1] The purpose of these armor pieces is debated, but the plates have been suggested to play a role in display, species recognition, and/or thermoregulation, and the spikes were likely served as defensive structures. [3]
While the Baiyinosaurus fossil material generally resembles stegosaurs in morphology, several features are also reminiscent of basal thyreophorans such as Scelidosaurus and Emausaurus , indicating that Baiyinosaurus had both plesiomorphic thyreophoran traits as well as derived stegosaurian traits. [1] Bashanosaurus , one of the basalmost stegosaurs from older rocks in China, also exhibits a similar blend of features, demonstrating the transitional states from early armored dinosaurs to the divergent body plans of stegosaurs and ankylosaurs. [4]
The holotype specimen of Baiyinosaurus belongs likely belongs to an adult individual. This can be determined as the neurocentral sutures on the dorsal vertebrae are fused and not visible, while they would be open and unfused in a juvenile. [1]
Baiyinosaurus is known from several skull bones. The posterior subnarial process of the left premaxilla (upper jaw bone at the tip of the snout) is preserved and has an expanded surface where it would contact the nasal. The front and middle part of the left maxilla (primary tooth-bearing bone of the upper jaw) is known, and indicates that this tooth row is inset medially (toward the middle of the skull), a feature expected in most ornithischian dinosaurs. A partial bone—likely the right jugal—is known, and has a triradiate form with a very expanded dorsal process. Another fragment—tentatively identified as the dorsal part of the right squamosal—includes visible sutures where it would be overlapped by the parietal and postorbital.
The paired frontals (large bones of the skull roof) are generally broad and shorter from front to back when compared to other stegosaurs besides Tuojiangosaurus . This shape is also similar to the basal non-stegosaurian thyreophorans Scelidosaurus and Emausaurus. The describing authors identified this structure of the frontal—being wider than long and contributing significantly to both the medial and anterior margins of the supratemporal fenestrae—as an autapomorphy (unique derived trait) of Baiyinosaurus. [1]
The left dentary (tooth-bearing bone of the lower jaw) is largely complete. It curves down and inward at the front. While a predentary (lower beak bone) is not preserved, there are visible facets for it on both sides of the tip of the dentary. Similar to many basally-branching stegosaurs like Huayangosaurus , Gigantspinosaurus , and Kentrosaurus , the first dentary tooth is immediately behind the predentary, without the wide diastema (gap) present in later taxa like Stegosaurus and Jiangjunosaurus . The dentary preserves eighteen alveoli (tooth sockets), some of which have partially erupted teeth visible. For both of the two teeth that are entirely preserved, the crown shows two denticles at the tip and seven denticles on both the front and back edges. This might be the condition for all of the dentary teeth, although the number of denticles for some other stegosaur species varies depending on the side. [1]
The postcrania of Baiyinosaurus comprises only bones from the axial skeleton. No osteoderms are known. The intercentrum of the atlas (first cervical vertebra) is the only cervical vertebra preserved, and it notably lacks the two ridges seen on the underside in Stegosaurus. [1]
The seven dorsal vertebrae (two anterior, five mid-posterior) have a typical combination of features. In most stegosaurs, the neural arches are very expanded dorsally, but like the more basal taxa Huayangosaurus and Gigantspinosaurus the arches are not significantly elongated. In the middle/posterior dorsals, the parapophyses (processes that articulate with the ribs) are elevated on short stalks, similar to the anatomy seen in Bashanosaurus and Scelidosaurus. The neural spines are comparatively broad from front to back in lateral view compared to other stegosaurs, but generally similar to Gigantspinosaurus and the non-stegosaurs Scelidosaurus, Laquintasaura and Lesothosaurus . The neural canal is ovate in cross-section. [1]
One anterior caudal vertebra is known. It is missing the zygapophyses (articular processes) and neural spine. There is a facet for a chevron at the base of the centrum. The neural canal is round in cross-section. [1]
In their phylogenetic analyses, Ning et al. (2024) recovered Baiyinosaurus as an early member of the Stegosauria, in a clade with the slightly older Argentinian Isaberrysaura and the younger Chinese Gigantspinosaurus . Their results are displayed in the cladogram below: [1]
Baiyinosaurus is known from the Straw-yellow Sandstone Member of the Wangjiashan Formation, which dates to the late Bathonian age of the Middle Jurassic period. The remains of undescribed possible mamenchisaurid sauropods and large theropods (including teeth) were found nearby by the same expedition that discovered Baiyinosaurus, as well as trackways of theropod footprints assigned to the ichnogenus Grallator pingchuanensis . [5] Some fossilized plants are also known from these outcrops. [1]
Stegosaurus is a genus of herbivorous, four-legged, armored dinosaur from the Late Jurassic, characterized by the distinctive kite-shaped upright plates along their backs and spikes on their tails. Fossils of the genus have been found in the western United States and in Portugal, where they are found in Kimmeridgian- to Tithonian-aged strata, dating to between 155 and 145 million years ago. Of the species that have been classified in the upper Morrison Formation of the western US, only three are universally recognized: S. stenops, S. ungulatus and S. sulcatus. The remains of over 80 individual animals of this genus have been found. Stegosaurus would have lived alongside dinosaurs such as Apatosaurus, Diplodocus, Camarasaurus and Allosaurus, the latter of which may have preyed on it.
Kentrosaurus is a genus of stegosaurid dinosaur from the Late Jurassic in Lindi Region of Tanzania. The type species is K. aethiopicus, named and described by German palaeontologist Edwin Hennig in 1915. Often thought to be a "primitive" member of the Stegosauria, several recent cladistic analyses find it as more derived than many other stegosaurs, and a close relative of Stegosaurus from the North American Morrison Formation within the Stegosauridae.
Hesperosaurus is a herbivorous stegosaurian dinosaur from the Kimmeridgian age of the Jurassic period, approximately 156 million years ago.
Scelidosaurus is a genus of herbivorous armoured ornithischian dinosaur from the Jurassic of England.
Dacentrurus, originally known as Omosaurus, is a genus of stegosaurian dinosaur from the Late Jurassic and perhaps Early Cretaceous of Europe.
Huayangosaurus is a genus of stegosaurian dinosaur from the Middle Jurassic of China. The name derives from "Huayang" (華陽), an alternate name for Sichuan, and "saurus", meaning "lizard". It lived during the Bathonian to Callovian stages, around 165 million years ago, some 20 million years before its famous relative, Stegosaurus appeared in North America. At only approximately 4 metres (13 ft) long, it was also much smaller than its famous cousin. Found in the Lower Shaximiao Formation, Huayangosaurus shared the local Middle Jurassic landscape with the sauropods Shunosaurus, Datousaurus, Omeisaurus and Protognathosaurus, the ornithopod Xiaosaurus and the carnivorous Gasosaurus.
Tuojiangosaurus is a genus of herbivorous stegosaurian dinosaur from the Late Jurassic Period, recovered from the Upper Shaximiao Formation of what is now Sichuan Province in China.
Paranthodon is a genus of stegosaurian dinosaur that lived in what is now South Africa during the Early Cretaceous, between 139 and 131 million years ago. Discovered in 1845, it was one of the first stegosaurians found. Its only remains, a partial skull, isolated teeth, and fragments of vertebrae, were found in the Kirkwood Formation. British paleontologist Richard Owen initially identified the fragments as those of the pareiasaur Anthodon. After remaining untouched for years in the British Museum of Natural History, the partial skull was identified by South African paleontologist Robert Broom as belonging to a different genus; he named the specimen Palaeoscincus africanus. Several years later, Hungarian paleontologist Franz Nopcsa, unaware of Broom's new name, similarly concluded that it represented a new taxon, and named it Paranthodon owenii. Since Nopcsa's species name was assigned after Broom's, and Broom did not assign a new genus, both names are now synonyms of the current binomial, Paranthodon africanus. The genus name combines the Ancient Greek para (near) with the genus name Anthodon, to represent the initial referral of the remains.
Stegosaurides is a genus of herbivorous thyreophoran dinosaur. It lived during the Cretaceous. Its fossils were found in the Xinminbao Group near Heishan in Gansu Province in China. These fossils consist of fragmentary material, including dermal spine elements. The genus is occasionally misspelled as "Stegosauroides".
Stegosauria is a group of herbivorous ornithischian dinosaurs that lived during the Jurassic and early Cretaceous periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere, Africa and possibly South America. Their geographical origins are unclear; the earliest unequivocal stegosaurian, Bashanosaurus primitivus, was found in the Bathonian Shaximiao Formation of China.
Emausaurus is a genus of thyreophoran or armored dinosaur from the Early Jurassic. Its fossils have been found in Mecklenburg-Vorpommern, northern Germany. Emausaurus is the only known Toarcian thyreophoran, as well as the only dinosaur from the zone of the same age with a formal name.
Gigantspinosaurus is a genus of herbivorous ornithischian dinosaur from the Late Jurassic. It was a stegosaur found in China.
Jiangjunosaurus is a genus of herbivorous stegosaurian dinosaur from the Oxfordian-age Shishugou Formation of the Junggar Basin, Xinjiang, China.
Hypsirhophus is a genus of stegosaurian dinosaurs. It contains a single species, Hypsirhophus discurus, which is known only from a fragmentary specimen. The fossil consists of partial vertebrae from the back, three from the tail, and a piece of rib.
Miragaia is a long-necked stegosaurid dinosaur. Its fossils have been found in Upper Jurassic rocks in Portugal and possibly also Wyoming, United States. Miragaia has the longest neck known for any stegosaurian, which included at least seventeen vertebrae. Some researchers consider this taxon to be a junior synonym of Dacentrurus.
Isaberrysaura is a genus of stegosaurian ornithischian dinosaur from the Middle Jurassic Los Molles Formation of Patagonia, Argentina. The genus contains a single species, I. mollensis, described by Salgado et al. in 2017 from a single specimen. Although initially classified as a basal neornithischian, subsequent analysis has allied it with the Stegosauria; the morphology of its skull resembles those of other members of the group.
Mongolostegus is a genus of stegosaur from the Early Cretaceous (Aptian-Albian) Dzunbain Formation of Mongolia. The type and only species is M. exspectabilis, known from a single specimen previously under the nomen nudumWuerhosaurus mongoliensis.
Adratiklit is an extinct genus of herbivorous stegosaurian dinosaur that lived on the supercontinent Gondwana during the Middle Jurassic period. The genus contains a single species, Adratiklit boulahfa. Its remains were found in the El Mers III Formation (Bathonian–?Callovian), near Boulahfa, south of Boulemane, Fès-Meknès, north Morocco.
Bashanosaurus is an extinct genus of stegosaurian dinosaur from the Middle Jurassic Shaximiao Formation of Yunyang County, China. The genus contains a single species, Bashanosaurus primitivus, known from incomplete skeletons belonging to three individuals. It is one of the basalmost stegosaurs, as well as one of the oldest known stegosaurs, along with Adratiklit, Isaberrysaura, and Thyreosaurus.
Yanbeilong is an extinct genus of stegosaurian dinosaur from the Early Cretaceous (Albian) Zuoyun Formation of Shanxi, China. The type and only species is Y. ultimus. It is considered one of the youngest definitive records of the group, alongside Mongolostegus from Mongolia and possible Stegosaurus remains from the Hekou Group of China, both of which date to the Aptian–Albian.