Bashanosaurus

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Bashanosaurus
Temporal range: Middle Jurassic (Bathonian), 167.5–164.5  Ma
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Bashanosaurus Skeletal.svg
Skeletal reconstruction
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Ornithischia
Clade: Thyreophora
Clade: Stegosauria
Genus: Bashanosaurus
Dai et al., 2022
Type species
Bashanosaurus primitivus
Dai et al., 2022

Bashanosaurus (meaning "Bashan lizard") 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 and Isaberrysaura .

Contents

Discovery and naming

China edcp location map.svg
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Bashanosaurus type locality in Yunyang County, China

In 2016, a quarry of dinosaur fossils belonging to the lower Shaximiao Formation was found in Laojun Village of Pu’an Township in Yunyang County, Chongqing Municipality, China. The Bashanosaurus fossil material was among the bones found in the outcrops, consisting of three specimens found in the same horizon. [1]

The holotype specimen, CLGPR V00006-1, includes one dorsal and two caudal vertebrae, the right scapulocoracoid, a partial left hindlimb (femur, tibia, fibula, and a metatarsal), several fragmentary ribs, and three dermal armor pieces (two plates and one spine). A second specimen was referred, CLGPR V00006-2, consisting of five dorsal vertebrae, the right tibia and fibula, partial ribs, and an incomplete dermal plate. The third specimen, CLGPR V00006-3, is represented by a single dorsal vertebra. [1]

In 2022, Dai et al. described Bashanosaurus primitivus as a new genus and species of basal stegosaurian based on these fossil remains. The generic name, "'Bashanosaurus", combines "Bashan"—the ancient name of Chongqing, where the fossils were discovered—with the Greek "sauros", meaning "lizard". The specific name, "primitivus", references the fact that Bashanosaurus is among the earliest diverging stegosaurians. [1]

Dai et al. (2022) also described a fourth stegosaurian specimen, CLGPR V00006-4, found in stratigraphic layers about 900 metres (3,000 ft) away and 50 metres (160 ft) above those of the Bashanosaurus locality. It includes a partial cranium (the frontals, parietals, and a braincase), a dorsal vertebra, and a small broken dermal spine. While similarities were noted between the dorsal vertebrae of this specimen and those referred to Bashanosaurus, it was not referred to this genus as it does not share unique traits with the holotype. [1]

Bashanosaurus is notable for a stegosaur because of its early age, having been found in rocks dating to the Bathonian age (166.0±1.5 Ma) of the Middle Jurassic epoch. [2] This makes it the oldest named stegosaur known from Asia. [3] Few other stegosaurians approach it in age. Isaberrysaura , an Argentinian stegosaur originally described in 2017 as a basal ornithopod within the Neornithischia, may date to the earlier Bajocian age. [4] [5] Another early stegosaur is Adratiklit , described in 2020 based on remains from the Bathonian-aged El Mers II Formation. [6] [7]

The high diversity of stegosaurs found in the Middle Jurassic rocks of China suggests that this clade may have originated in Asia before dispersing throughout Africa and South America, and eventually Europe and North America. [7]

Description

Life restoration Bashanosaurus primitivus.png
Life restoration

As a stegosaur, Bashanosaurus 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. These armor pieces—especially those on the end of the tail—could have served as defensive structures against predators. [1] [7]

While the Bashanosaurus fossil material generally resembles stegosaurs in morphology, several features are also reminiscent of the basal thyreophoran Scelidosaurus , indicating that Bashanosaurus had both plesiomorphic thyreophoran traits as well as derived stegosaurian traits. [1]

Skeleton

A small portion of the skeleton of Bashanosaurus is known from three different specimens, including vertebrae from the back and tail, ribs, bones from the shoulder and hind limbs, and armor pieces. [1]

In total, seven dorsal vertebrae are known from Bashanosaurus. One of these, CLGPR V00006-3, is nearly complete, missing only the tip of the neural spine. The centrum of this bone is amphiplatyan, meaning that it is flat on both ends. This contrasts with its close relative Chungkingosaurus , where one side of the centrum is curves outward strongly. Like most stegosaurs, the centrum length, width, and height are all similar (except for Dacentrurus , where the width is greater than the length). The vertebral centra of the basal stegosaur Gigantspinosaurus have large fossae (depressions), but these are not seen in Bashanosaurus. Like many early stegosaurs, the neural arch pedicle is not dorsally expanded; an expanded pedicle is common in later-diverging taxa in this clade. The parapophyses are more greatly elevated than in other stegosaurs, similar to the Scelidosaurus , an early thyreophoran. [1]

Two partial caudal vertebrae are known from Bashanosaurus, both from the holotype specimen. These have clear facets for chevrons to articulate with, indicating that these vertebrae are not from the posterior end of the tail. The prezygapophyses significantly hang over the anterior end of the centrum. In the contemporary Huayangosaurus , they only over hang slightly.

Many ribs are associated with the holotype and one of the referred specimens but have not been described in depth. [1]

The Bashanosaurus holotype includes a well-preserved right scapulocoracoid, missing part of the distal end of the scapula and the dorsal edge of the coracoid. The acromial process of the scapula is unusual, being poorly developed. In the majority of stegosaurs, this process is prominent and rectangular. However, in Bashanosaurus, it is small and triangular—more similar to the non-stegosaurian Scelidosaurus than its closer relatives. The blade of the scapula is generally slender, but with a notable flared expansion at the base. In other stegosaurs, the blade is deeper, without this distal expansion. Like in Huayangosaurus, there is no coracoid foramen. [1]

Several hindlimb bones have been assigned to Bashanosaurus. These include the left femur, tibia, fibula, and a metatarsal of the holotype, and a referred right tibia and fibula. The femur is poorly preserved, and only observable in posterior view. The fourth trochanter of the femur is incomplete, but visible as a ridge with a distinct process. It is unique in being positioned below the middle of the shaft of the femur, rather than at the midpoint, as in other stegosaurs. In some stegosaurs, like Dacentrurus, Kentrosaurus , and Stegosaurus , the fourth trochanter is absent or only poorly developed. The distal end of the femur is divided into two epicondyles by a deep groove. The tibiae and fibulae are generally similar in morphology to other stegosaurs. The cnemial crest of the tibia is visible as a sharp ridge. The left metatarsal III is well-preserved, with strongly expanded ends. [1]

Dermal armor

Illustration of armor pieces known from Bashanosaurus: a single spine (A) and three plates (B-D) Bashanosaurus Dermal Armor.svg
Illustration of armor pieces known from Bashanosaurus: a single spine (A) and three plates (B–D)

Four incomplete pieces of dermal armor are known from Bashanosaurus, consisting of one spine and three plates. The spine is tall and thin. It is unknown where the spine would have been located in life; spines at the end of the tail—forming a structure called a thagomizer—are common in stegosaurians, with some taxa also bearing a parascapular spine near the shoulder. [8] The plates appear broadly rectangular. The plate bases are thickened, with a groove separating the base from the anterior and posterior plate margins. This dermal plate morphology is considered to be an autapomorphy of Bashanosaurus. [1]

Ontogenetic stage

The fossil material of Bashanosaurus demonstrates a unique blend of features typically seen in both adult and immature animals. For example, in adult Stegosaurus specimens, the scapula and coracoid, as well as the tibia and fibula, are fused together. However, in Bashanosaurus, the scapula and coracoid are fused, but the tibia and fibula are not. Furthermore, the anterior and greater trochanters of the femur are fused in Bashanosaurus. In the femora of Stegosaurus specimens, this fusion is only seen in adult individuals. [1]

Size

Size of Bashanosaurus compared to a human Bashanosaurus Size Comparison.svg
Size of Bashanosaurus compared to a human

Bashanosaurus seems to have been a small stegosaur. Based on the proportions of Huayangosaurus , Dai et al. (2022) estimate that Bashanosaurus may have been about 3 metres (9.8 ft) long. However, it is unclear if the fossil specimens belonged to fully grown animals, so it may have been able to grow larger. [1] [7] In comparison, the closely related Chungkingosaurus was moderately-sized, with specimens ranging from around 4–5 metres (13–16 ft) in length. [9] Huayangosaurus was similar in size, around 4 metres (13 ft) in length and 500 kilograms (1,100 lb) in body mass. [10]

Classification

In the phylogenetic analyses in their 2022 description of Bashanosaurus, Dai et al. recovered it in the basalmost clade within the Stegosauria, as the sister taxon to the Late Jurassic Chungkingosaurus . [1] Later publications built upon this phylogenetic dataset and found very similar results to the original description. In their 2024 description of the Early Cretaceous stegosaur Yanbeilong , Jia et al. recovered the results displayed in the cladogram below: [11]

Stegosauria
Bashanosaurus
Bashanosaurus primitivus.png
Chungkingosaurus
Chungkingosaurus jiangbeiensis.png
Huayangosaurus
Huayangosaurus taibaii.png
Isaberrysaura
Isaberrysaura mollensis.png
Gigantspinosaurus
Gigantspinosaurus sichuanensis.png
Alcovasaurus
Alcovasaurus longispinus.png
Jiangjunosaurus
Jiangjunosaurus junggarensis.png

Tuojiangosaurus Tuojiangosaurus multispinus life restoration.jpg

Paranthodon
Paranthodon africanus.png
Kentrosaurus
Kentrosaurus aethiopicus.png
Adratiklit
Adratiklit boulahfa.png
Dacentrurus
Dacentrurus armatus.png
Hesperosaurus
Hesperosaurus mjosi.png
Miragaia
Miragaia longicollum.png
Loricatosaurus
Loricatosaurus priscus.png
Yanbeilong
Yanbeilong ultimus.png
Wuerhosaurus
Wuerhosaurus homheni.png
Stegosaurus stenops
Stegosaurus stenops.png

In 2023, Raven et al. performed a thorough analysis of thyreophoran relationships, including most of the named species within this clade. They commented that Bashanosaurus can confidently be considered to be an early-diverging stegosaurian. However, because its description was so recent, they did not include it in their phylogenetic analyses. [12]

Paleoecology

Palaeoenvironment

Using analyses of sedimentology and elemental geochemistry, the Shaximao Formation has been interpreted as representing a semi-arid to semi-humid region with meandering rivers and an intricate seasonal lake system. During the wet, flooding season, the lake level was high, surrounded by a small alluvial plain. During the drier season, there would have been small ephemeral lakes throughout a much larger alluvial plain. [13]

Contemporary fauna

Shunosaurus life restoration.jpg
Gasosaurus constructus.png
Hexinlusaurus.jpg
Huayangosaurus BW.jpg
Life restorations of various dinosaurs known from the Lower Member of the Shaximiao Formation. In clockwise order from the top left: Shunosaurus , Gasosaurus , Huayangosaurus , and Hexinlusaurus

The Bashanosaurus fossil material was discovered in the "Dinosaur Fossil Wall" locality of the Shaximiao Formation (Lower Member) of Yunyang County, China, which dates to the Bathonian age of the Middle Jurassic. [2] Several other dinosaur fossils, predominantly belonging to sauropods, have also been found in this bonebed, including Omeisaurus puxiani (a mamenchisaurid), [14] Shunosaurus (a basal eusauropod), [15] and Yuzhoulong (a basal macronarian). [16] [7]

Many other fossil taxa have been found in other localities of the lower Shaximiao Formation, so they may not have been exactly contemporaneous with Bashanosaurus. The dinosaurs discovered include sauropods ( Abrosaurus , Bashunosaurus , Dashanpusaurus , Datousaurus , Omeisaurus spp., and Protognathosaurus ), [16] theropods ( Chuandongocoelurus , Gasosaurus , Kaijiangosaurus , Szechuanosaurus , Xuanhanosaurus , and an indeterminate megalosaurid), neornithischians ( Agilisaurus , Hexinlusaurus , and Xiaosaurus ), [17] and the stegosaurian Huayangosaurus . [2] The non-dinosaurian fauna includes pterosaurs ( Angustinaripterus ), turtles ( Chengyuchelys spp., Plesiochelys , and Trionyx ), crocodyliforms ( Teleosaurus , Sunosuchus , and Hsisosuchus ), pliosaurid plesiosaurs, therapsids ( Bienotheroides and Polistodon ), fish ( Hybodus , Yuchoulepis , Lepidotes , and Ceratodus ), and amphibians ( Sinobrachyops ). [18]

The upper layers of the formation, which date to younger ages, have also yielded a similar dinosaur fauna, including several stegosaurs ( Chialingosaurus , Tuojiangosaurus , Chungkingosaurus , and Gigantspinosaurus ) and various sauropods, theropods, basal ornithischians. [18]

See also

Related Research Articles

<i>Stegosaurus</i> Thyreophoran stegosaurid dinosaur genus from Late Jurassic period

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.

<i>Kentrosaurus</i> Extinct genus of dinosaurs from late Jurassic in Lindi Region, Tanzania

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.

<i>Huayangosaurus</i> Extinct genus of dinosaurs

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.

<i>Xuanhanosaurus</i> Extinct genus of dinosaurs

Xuanhanosaurus is a genus of theropod dinosaur that lived during the Middle Jurassic (Bathonian) of the Sichuan Basin, China, around 166 million years ago. This taxon represents one of the various non-coelurosaurian tetanuran taxa found on the Middle Jurassic of the region, uncovered in the Lower Shaximiao Formation. Although it has been known for more than 40 years, this taxon has been the subject of very few studies, although most seem to agree that it is a tetanuran, possibly a basal allosauroid, highlighting the fact that it has a vestigial fourth metacarpal.

<i>Tuojiangosaurus</i> Extinct genus of dinosaurs

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.

<i>Paranthodon</i> Stegosaurian dinosaur genus from Early Cretaceous South Africa

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.

<i>Omeisaurus</i> Extinct genus of dinosaurs

Omeisaurus is a genus of sauropod dinosaur from the Middle Jurassic Period of what is now China. Its name comes from Mount Emei, where it was discovered in the lower Shaximiao Formation of Sichuan Province.

Bashunosaurus is a genus of potentially macronarian sauropod dinosaur from the Middle Jurassic Shaximiao Formation of Kaijiang, China. The type and only species is Bashunosaurus kaijiangensis.

<span class="mw-page-title-main">Stegosauria</span> Extinct clade of dinosaurs

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, predominantly in what is now North America, Europe, Africa, South America and Asia. Their geographical origins are unclear; the earliest unequivocal stegosaurian, Bashanosaurus primitivus, was found in the Bathonian Shaximiao Formation of China.

<span class="mw-page-title-main">Stegosauridae</span> Extinct family of dinosaurs

Stegosauridae is a family of thyreophoran dinosaurs within the suborder Stegosauria. The clade is defined as all species of dinosaurs more closely related to Stegosaurus than Huayangosaurus. The name ‘Stegosauridae’ is thus a stem-based name taken from the well-represented genus – Stegosaurus. Fossil evidence of stegosaurids, dating from the Middle Jurassic through the Early Cretaceous, have been recovered from North America, Eurasia and Africa.

<span class="mw-page-title-main">Huayangosauridae</span> Family of dinosaurs

Huayangosauridae is a family of stegosaurian dinosaurs from the Jurassic of China. The group is defined as all taxa closer to the namesake genus Huayangosaurus than Stegosaurus, and was originally named as the family Huayangosaurinae by Dong Zhiming and colleagues in the description of Huayangosaurus. Huayangosaurinae was originally differentiated by the remaining taxa within Stegosauridae by the presence of teeth in the premaxilla, an antorbital fenestra, and a mandibular fenestra. Huayangosaurinae, known from the Middle Jurassic of the Shaximiao Formation, was proposed to be intermediate between Scelidosaurinae and Stegosaurinae, suggesting that the origins of stegosaurs lay in Asia. Following phylogenetic analyses, Huayangosauridae was expanded to also include the taxon Chungkingosaurus, known from specimens from younger Late Jurassic deposits of the Shaximiao Formation. Huayangosauridae is either the sister taxon to all other stegosaurs, or close to the origin of the clade, with taxa like Gigantspinosaurus or Isaberrysaura outside the Stegosauridae-Huayangosauridae split. Huayangosauridae was formally defined in 2021 by Daniel Madzia and colleagues, who used the previous definitions of all taxa closer to Huayangosaurus taibaii than Stegosaurus stenops, and chose the 2020 phylogeny of Susannah Maidment et al. to illustrate the relationships of the clade:

<i>Gigantspinosaurus</i> Extinct genus of dinosaurs

Gigantspinosaurus is a genus of herbivorous ornithischian dinosaur from the Late Jurassic. It was a stegosaur found in China.

<i>Yingshanosaurus</i> Extinct genus of dinosaurs

Yingshanosaurus is a genus of stegosaurian dinosaur from the Late Jurassic, around 155 million years ago. It was a herbivore that lived in what is now China. The type species is Yingshanosaurus jichuanensis.

<span class="mw-page-title-main">Shaximiao Formation</span> Late Jurassic geological formation in China

The Shaximiao Formation is a Middle to Late Jurassic aged geological formation in Sichuan, China, most notable for the wealth of dinosaurs fossils that have been excavated from its strata. The Shaximiao Formation is exposed in and around the small township of Dashanpu, situated seven kilometres north-east from Sichuan's third largest city, Zigong, in the Da'an District.

<i>Loricatosaurus</i> Extinct genus of dinosaurs

Loricatosaurus is a Stegosaurid genus from Callovian-age rocks of England and France.

<i>Miragaia longicollum</i> Extinct species of dinosaur

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.

<i>Isaberrysaura</i> Extinct genus of dinosaurs

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.

<i>Adratiklit</i> Extinct genus of dinosaurs

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 Group, probably in the El Mers II Formation (Bathonian), near Boulahfa, south of Boulemane, Fès-Meknes, north Morocco.

<i>Sanxiasaurus</i> Extinct genus of dinosaurs

Sanxiasaurus is a genus of neornithischian dinosaur from the Middle Jurassic Xintiangou Formation in the Chongqing Municipality of China. The type and only species is S. modaoxiensis. The holotype is a partial postcranial skeleton consisting of "55 bones including two cervical vertebrae, 11 dorsal vertebrae, 4 sacral vertebrae, 18 caudal vertebrae, both humeri, radii and ulnas, partial right ilium, partial right ischium, both femora and tibiae, left fibula, 3 metatarsi and 4 phalanges." In a phylogenetic analysis, it was found to be a basal neornithischian, more derived than Lesothosaurus and less derived than Hexinlusaurus.

Yunyangosaurus is a genus of possible megalosauroid dinosaur from the Xintiangou Formation in Chongqing, China. The type and only species is Yunyangosaurus puanensis. The name was first published in the 2019 SVP abstract book by Dai (2019) before it was formally described by Dai et al. (2020).

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