Spicomellus | |
---|---|
Illustration of the holotype. | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | † Ornithischia |
Clade: | † Thyreophora |
Clade: | † Ankylosauria |
Genus: | † Spicomellus Maidment et al., 2021 |
Species: | †S. afer |
Binomial name | |
†Spicomellus afer Maidment et al., 2021 | |
Spicomellus is an extinct genus of early ankylosaurian dinosaur from the El Mers III Formation (Bathonian-Callovian) of Morocco. The genus contains a single species, S. afer, known from a single rib with fused osteoderms. Spicomellus represents the oldest named ankylosaur.
The Spicomellus holotype specimen, NHMUK PV R37412, was discovered in layers of the El Mers III Formation near Boulahfa in Boulemane, Fès-Meknès region, Morocco. It was later acquired by London's Natural History Museum from a commercial fossil dealer. The specimen consists of a single rib with four co-ossified spines. The holotype was CT scanned and histologically sectioned to confirm that it was an ankylosaurian. [1]
In 2021, Maidment et al. described Spicomellus afer as a new genus and species of ankylosaurian thyreophoran based on these fossil remains. The generic name, Spicomellus, combines the Latin words "spicus", meaning "spike" and "mellus", which refers to a collar of spikes. The specific name, afer, is a Latin word referring to something inhabiting Africa. [1]
Abundant diverse eurypodan dinosaurs have been found in Jurassic Laurasian sediments, but their remains are rarer in Gondwanan deposits. Spicomellus is the second described eurypodan taxon from North Africa, after Adratiklit . [1] [2]
The preserved dermal spikes of the holotype were fused directly to the bone, a trait unique to Spicomellus and not known from any other vertebrate. Some prehistoric animals, including Protuberum (a cynodont) and Euscolosuchus (a pseudosuchian), have superficially similar modified ribs. In all other known ankylosaurs, the osteoderms are embedded into the muscle tissue, rather than fused to underlying bone. [1] [3]
Preliminary assessments of the holotype led researchers to consider stegosaurian relationships for the species. [3] In their 2021 description of Spicomellus, Maidment et al. discussed several lines of evidence supporting the placement of Spicomellus a basal ankylosaurian. They had considered the possibility that the rib was actually part of the jaw of an osteichthyan fish, since some members have teeth fused to their jaws. However, since there is no evidence of orthodentine—an important component of fish teeth—they considered this classification unsupported. Based on the T-shaped cross section of the rib, Spicomellus can reasonably be assigned to the Eurypoda. Furthermore, the structural fibers of the osteoderms are interwoven, with a plywood-like arrangement, which is seen in ankylosaurs but not other thyreophorans. [1]
Spicomellus is the oldest known ankylosaur that has currently been named from anywhere in the world. Few other ankylosaurs are known from a similar time. Sarcolestes , known from a partial lower jaw, was found in England's Oxford Clay Formation, which dates to the Callovian age. [1] An unnamed thyreophoran from the Bajocian-aged Bearreraig Sandstone Formation of the Isle of Skye, Scotland, could be older than Spicomellus, but it is unclear if these fragmentary remains belonged to a stegosaur or an ankylosaur. [4]
Spicomellus is known from the El Mers III Formation (El Mers Group) of Morocco. This would have been part of the supercontinent Gondwana during the Middle Jurassic. It coexisted with the sauropod "Cetiosaurus" mogrebiensis and the stegosaurs Adratiklit and Thyreosaurus . [2] [5] Predators of the ecosystem consisted of indeterminate theropods (possible megalosaurids). [6] The sauropod Atlasaurus is also known from the contemporaneous terrestrial Guettioua Formation. [7]
The discovery of Spicomellus also shows that the two major thyreophoran groups (Ankylosauria and Stegosauria) coexisted for over 20 million years, and implies that the putative extinction of the stegosaurs in the Early Cretaceous may have happened for reasons other than an increased diversity of anyklosaurs at that time. [1]
Studies by the describing authors of the sedimentology and stratigraphy of the locality suggested a shallow marine depositional environment with continental mixed clastic, evaporitic and carbonate sediments. [2]
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.
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.
Polacanthus, deriving its name from the Ancient Greek polys-/πολύς- "many" and akantha/ἄκανθα "thorn" or "prickle", is an early armoured, spiked, plant-eating ankylosaurian dinosaur from the early Cretaceous period of England.
Scelidosaurus is a genus of herbivorous armoured ornithischian dinosaur from the Jurassic of England.
Tianchisaurus, also invalidly called Tianchiasaurus and "Jurassosaurus", is a genus of ankylosaurian dinosaur from the Late Jurassic (Oxfordian–Kimmeridgian)-aged Toutunhe Formation of China. It is one of the oldest ankylosaurs, being slightly younger than the Moroccan Spicomellus. While many later-diverging ankylosaurids had bony clubs at the tips of their tails, Tianchisaurus likely lacked such a structure.
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.
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.
Sarcolestes is an extinct genus of ankylosaurian ornithischian dinosaur from the Oxford Clay of England. The current type and only species is S. leedsi, and the holotype is a single partial left mandible. The genus and species were named in 1893 by Richard Lydekker, who thought they belonged to a theropod.
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.
Dracopelta is a monospecific genus of ankylosaur dinosaur from Portugal that lived during the Late Jurassic in what is now the Lourinhã Formation. The type and only species is Dracopelta zbyszewskii, which is represented by a partial skeleton including unpublished material.
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.
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.
The El Mers Group is a geological group in the Middle Atlas of Morocco. It is subdivided into three formations named the El Mers I, II, and III Formations, respectively. It is a marine deposit primarily consisting of marl, with gypsum present in the upper part of unit 3. It is the lateral equivalent of the terrestrial Guettioua Sandstone. Dinosaur remains are among the fossils that have been recovered from the group, most notably those of sauropods and the unusual thyreophorans Adratiklit, Thyreosaurus, and Spicomellus.
Susannah "Susie" Catherine Rose Maidment is a British palaeontologist at the Natural History Museum, London. She is also an honorary Professor at the University of Birmingham. She is internationally recognised for her research on ornithischian dinosaur evolution, and was awarded the 2016 Hodson Award of the Palaeontological Association and the 2017 Lyell Fund of the Geological Society of London. She was featured as a 2019 National Geographic Women of Impact.
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.
Parankylosauria is a group of basal ankylosaurian dinosaurs known from the Cretaceous of South America, Antarctica, and Australia. It is thought the group split from other ankylosaurs during the mid-Jurassic period, despite this being unpreserved in the fossil record.
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.
Thyreosaurus is an extinct genus of stegosaurian dinosaur from the Middle Jurassic El Mers III Formation of Morocco. The genus contains a single species, Thyreosaurus atlasicus, known form a partial disarticulated partial skeleton consisting of several dorsal vertebrae, ribs, a limb bone, and dermal bones. Thyreosaurus is characterized by a unique dermal armor with an asymmetrical texture, indicating that it may have been recumbent. Alongside Adratiklit, Thyreosaurus increases the diversity of unique stegosaurs occurring in the Middle Jurassic of Africa.
Baiyinosaurus 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.
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