Ahshislepelta Temporal range: Late Cretaceous, | |
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Restoration as a nodosaurid | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | † Ornithischia |
Clade: | † Thyreophora |
Clade: | † Ankylosauria |
Genus: | † Ahshislepelta Burns & Sullivan, 2011 |
Species: | †A. minor |
Binomial name | |
†Ahshislepelta minor Burns & Sullivan, 2011 | |
Ahshislepelta (meaning "Ah-shi-sle-pah Wash shield") is a monospecific genus of ankylosaur dinosaur from New Mexico that lived during the Late Cretaceous (late Campanian stage, 74.5 Ma) in what is now the Hunter Wash Member of the Kirtland Formation. [1] The type and only species, Ahshislepelta minor, is known only from an incomplete postcranial skeleton of a small subadult or adult individual. [1] It was named in 2011 by Michael Burns and Robert M. Sullivan. [1] Based on the size of the humerus, Ahshislepelta is larger than Pinacosaurus mephistocephalus but smaller than Talarurus and Pinacosaurus grangeri . [1]
In 2005, a partial postcranial skeleton of an ankylosaur was discovered from the Hunter Wash Member in the lower part of the Kirtland Formation, New Mexico at the Ah-shi-sle-pah Wilderness Study Area. The specimen was later collected over consecutive field seasons from 2005 to 2009 and was subsequently described in 2011 by Michael Burns and Robert M. Sullivan. The holotype specimen, SMP VP-1930, consists of a partial girdle, partial scapulocoracoid, a proximal portion of the radius, numerous cervical and/or dorsal vertebrae fragments, complete and fragmentary thoracic osteoderms, and other unidentifiable postcranial fragments. The holotype specimen is currently housed at the State Museum of Pennsylvania, Harrisburg. [1]
The generic name, Ahshislepelta, is derived from Ah-shi-sle-pah Wash, the locality from which the holotype came, and the Ancient Greek word "peltè" (shield). The specific name, minor, is in reference to its small adult size relative to other North American ankylosaurids. [1]
The holotype specimen represents a subadult or adult individual based on the complete fusion of the scapulocoracoids, centra and neural arches of the vertebrae, and the re-modelled osteoderm cores. The holotype falls within the same size range as adult specimens of other ankylosaurid taxa outside of North America and represents an individual that was larger than juvenile specimens of Pinacosaurus grangeri and Pinacosaurus mephistocephalus but smaller than Talarurus and adult specimens of P. grangeri based on humeral size; however, the scapulocoracoid is larger than that of Talarurus. [1]
Burns & Sullivan (2011) diagnosed Ahshislepelta based on the dorsolateral overhang of the scapular acromion process to 25% of the dorsoventral width of the scapula. Ahshislepelta differs from other ankylosaurids, with the exception of Euoplocephalus , by the superficial osteodermal surface texture, characterized by uniformly distributed pitted rugosity, and sparse distribution of reticular neurovascular grooves with neurovascular foramina extending perpendicularly to obliquely into the bone. [1]
The right scapula preserves osteoderms on the lateral side at the most distal portion and is associated with fragments of ribs that are mostly visible on the medial side. The scapula is fully fused to the coracoid and has a blunt, rugose process along the anterodorsal margin for the attachment of muscles. The coracoid is roughly 16 cm long and the coracoid foramen is anterodorsal to the glenoid cavity. The glenoid cavity forms an arc that projects the scapular margin posteroventrally at an 80° angle relative to the coracoid margin. As in nodosaurids, the scapula does not narrow towards the upper surface and sides relative to the coracoid and does not exhibit a scapular neck. A rugose, ridge-like structure that is identified as the acromion is present along the dorsal margin of the scapula opposite the glenoid cavity. The acromion attains its front most extension towards the back and sides to the most anterior extent of the glenoid cavity. Due to taphonomic shearing, the prominent overhang of the acromion on the left scapula is absent, although this feature is not a taphonomic artefact on the right scapulocoracoid. However, the right scapulocoracoid is cracked, its junction with the scapular blade is visible, well-preserved, and verifies its natural projection towards the lower edge and sides. Towards the sides of the acromion, the borders of the infraspinous fossa are prominent and creates an area or the attachment of muscles. The left forelimb is more than 50% complete. As in ankylosaurids, the left humerus is massive and has a length of 31 cm. The left humerus preserves a deltopectoral crest that is well-developed and measures 15 cm across the widest portion of the humerus. The lateral margin of the deltopectoral crest forms a 23° angle in posterior view with the long axis of the humerus. Bounded by the deltopectoral crest and humeral head is a broad, bicipital fossa that is present on the anterior face of the humerus. On the anterior face of the humerus is a hemispherical radial condyle. The proximal articular surface of the left radius is oval in proximal view and is concave. The articular surface is 8 cm long, proportionally twice the diameter of the diaphysis. [1]
Numerous vertebrae fragments that probably represent parts of the cervicals and/or dorsals were recovered and the position of the vertebrae are based on their association with elements of the pectoral girdles and forelimb. A few vertebrae were dorsoventrally tall dorsal vertebrae, based on a few of the more complete vertebrae appearing to have laterally compressed neural canals. All other vertebrae lack open sutural facets for the neural arches. [1]
Numerous osteoderms and associated osteoderm fragments were associated with the holotype specimen. Most osteoderms pertain to the thoracic region while others might pertain to the pelvic region and forelimbs. All osteoderms are either keeled or circular with an off-center apex. The distal portion of the right scapula preserves an in situ osteoderm and numerous ossicles. The osteoderm and ossicles of the right scapula and another series of osteoderms preserved in situ display a rosette arrangement of small ossicles surrounding the osteoderms. The largest osteoderm pertains to the thoracic region behind the cervical region based on the similar morphology to the median thoracic osteoderms of the holotype specimen of Scolosaurus. The osteoderm has a length of 15 cm, a width of 12 cm and a height of 10 cm. The smallest ossicle has a diameter of 1 cm. The surface texture of the osteoderms are smooth to uniformly pitted with a sparse patterns of grooves as in Euoplocephalus. One osteoderm has a histological condition typical of that of ankylosaurids. [1]
Burns & Sullivan (2011) originally placed Ahshislepelta as an ankylosaurid within the clade Ankylosaurinae, although this was not based on the result of a phylogenetic analysis. [1] Likewise, Arbour & Currie (2015) placed Ahshislepelta as sister taxon to Gastonia at the base of Ankylosauridae, and Wiersma and Irmis (2018) placed it in a polytomy consisting of Euoplocephalus , Oohkotokia , Scolosaurus , Ziapelta , Anodontosaurus , Ankylosaurus and Dyoplosaurus . [2]
On the other hand, several other studies have favored a nodosaurid position. Arbour et al. (2016) recovered it in a polytomy with Niobrarasaurus and a juvenile nodosaurid from the Paw Paw Formation, [3] [4] while Zheng et al. (2018) positioned Ahshislepelta in a polytomy containing Tatankacephalus , Silvisaurus , Niobrarasurus, Nodosaurus and more deeply nested taxa. Rivera-Sylva et al. (2018) placed it as sister taxon to Niobrarasurus. [5] [6]
A phylogenetic analysis conducted by Rivera-Sylva et al. (2018) is reproduced below, favoring a nodosaurid position. Clade names have been added following Madzia et al. (2021). [6] [7]
Nodosauridae |
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In contrast, an earlier analysis by Arbour & Currie (2015) favors an ankylosaurid position. Their results are reproduced below. [3]
Ankylosauridae |
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Ahshislepelta is known from the Hunter Wash Member of the Kirtland Formation which has been dated to the upper Campanian stage, 74.5 Ma. [1] [8] The Kirtland Formation consists of interbedded sandstone, siltstone, mudstone, coal and shale. [9] The Kirtland Formation lies on the western margin of the Western Interior Seaway and represents a floodplain that was abundant with ferns, conifers and flowering plants. [10] Based on the abundance of angiosperms with leaves that have entire or nearly entire margins and drip points, the Kirtland Formation may have had a warm temperate to subtropical climate. [10] The Kirtland Formation was better drained than the underlying Fruitland Formation due to the lack of coal swamps. [10]
Ahshislepelta coexisted with the pachycephalosaurid Stegoceras , [11] the chasmosaurine ceratopsids Navajoceratops and Terminocavus , [12] the ankylosaurine ankylosaurid Ziapelta , [8] the eutyrannosaur tyrannosauroid Bistahieversor , [13] and the azhdarchid pterosaur Navajodactylus . [14]
Ankylosaurus is a genus of armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period, about 68–66 million years ago, in western North America, making it among the last of the non-avian dinosaurs. It was named by Barnum Brown in 1908; it is monotypic, containing only A. magniventris. The generic name means "fused" or "bent lizard", and the specific name means "great belly". A handful of specimens have been excavated to date, but a complete skeleton has not been discovered. Though other members of Ankylosauria are represented by more extensive fossil material, Ankylosaurus is often considered the archetypal member of its group, despite having some unusual features.
Euoplocephalus is a genus of large herbivorous ankylosaurid dinosaurs, living during the Late Cretaceous of Canada. It has only one named species, Euoplocephalus tutus.
Edmontonia is a genus of panoplosaurin nodosaurid dinosaur from the Late Cretaceous Period. It is part of the Nodosauridae, a family within Ankylosauria. It is named after the Edmonton Formation, the unit of rock where it was found.
Pinacosaurus is a genus of ankylosaurid thyreophoran dinosaur that lived in Asia during the Late Cretaceous, mainly in Mongolia and China.
Saichania is a genus of herbivorous ankylosaurid dinosaur from the Late Cretaceous period of Mongolia and China.
Gastonia is a genus of herbivorous ankylosaurian dinosaur from the Early Cretaceous of North America, around 139 to 134.6 million years ago. It is often considered a nodosaurid closely related to Polacanthus. Gastonia has a sacral shield and large shoulder spikes.
Aletopelta is a monospecific genus of basal ankylosaurid dinosaur from Southern California that lived during the Late Cretaceous in what is now the Point Loma Formation. The type and only species, Aletopelta coombsi, is known from a partial skeleton preserving osteoderms. It was originally described in 1996 by W. P. Coombs, Jr. and T.A. Deméré before being named in 2001 by Tracy Ford and James Kirkland. Aletopelta has an estimated size of 5 metres and weight of 2 tonnes. The holotype formed a miniature reef and was scavenged upon by invertebrates and sharks.
Dyoplosaurus is a monospecific genus of ankylosaurid dinosaur from Alberta that lived during the Late Cretaceous in what is now the Dinosaur Park Formation. Dyoplosaurus represents a close relative of Scolosaurus and Anodontosaurus, two ankylosaurids known from the Horseshoe Canyon and Dinosaur Park Formation.
Texasetes is a genus of ankylosaurian dinosaurs from the late Lower Cretaceous of North America. This poorly known genus has been recovered from the Paw Paw Formation near Haslet, Tarrant County, Texas, which has also produced the nodosaurid ankylosaur Pawpawsaurus.
Tianzhenosaurus is a monospecific genus of ankylosaurid dinosaur from the Shanxi Province that lived during the Late Cretaceous in what is now the Huiquanpu Formation. Tianzhenosaurus may represent a junior synonym of Saichania, an ankylosaurine known from the Barun Goyot and Nemegt Formation.
Panoplosaurus is a genus of armoured dinosaur from the Late Cretaceous of Alberta, Canada. Few specimens of the genus are known, all from the middle Campanian of the Dinosaur Park Formation, roughly 76 to 75 million years ago. It was first discovered in 1917, and named in 1919 by Lawrence Lambe, named for its extensive armour, meaning "well-armoured lizard". Panoplosaurus has at times been considered the proper name for material otherwise referred to as Edmontonia, complicating its phylogenetic and ecological interpretations, at one point being considered to have existed across Alberta, New Mexico and Texas, with specimens in institutions from Canada and the United States. The skull and skeleton of Panoplosaurus are similar to its relatives, but have a few significant differences, such as the lumpy form of the skull osteoderms, a completely fused shoulder blade, and regularly shaped plates on its neck and body lacking prominent spines. It was a quadrupedal animal, roughly 5 m (16 ft) long and 1,600 kg (3,500 lb) in weight. The skull has a short snout, with a very domed surface, and bony plates directly covering the cheek. The neck had circular groups of plates arranged around the top surface, both the forelimb and hindlimb were about the same length, and the hand may have only included three fingers. Almost the entire surface of the body was covered in plates, osteoderms and scutes of varying sizes, ranging from large elements along the skull and neck, to smaller, round bones underneath the chin and body, to small ossicles that filled in the spaces between other, larger osteoderms.
Talarurus is a genus of ankylosaurid dinosaur that lived in Asia during the Late Cretaceous period, about 96 million to 89 million years ago. The first remains of Talarurus were discovered in 1948 and later described by the Russian paleontologist Evgeny Maleev with the type species T. plicatospineus. It is known from multiple yet sparse specimens, making it one of the most well known ankylosaurines, along with Pinacosaurus. Elements from the specimens consists of various bones from the body; five skulls have been discovered and assigned to the genus, although the first two were very fragmented.
Nodocephalosaurus is a monospecific genus of ankylosaurid dinosaur from New Mexico that lived during the Late Cretaceous in what is now the De-na-zin member of the Kirtland Formation. The type and only species, Nodocephalosaurus kirtlandensis, is known only from a partial skull. It was named in 1999 by Robert M. Sullivan. Nodocephalosaurus has an estimated length of 4.5 metres and weight of 1.5 tonnes. It is closely related and shares similar cranial anatomy to Akainacephalus.
Shanxia is a monospecific genus of ankylosaurid dinosaur from the Shanxi Province that lived during the Late Cretaceous in what is now the Huiquanpu Formation. Shanxia may possibly represent a junior synonym of Tianzhenosaurus, an ankylosaurine also known from the Huiquanpu Formation of China.
Oohkotokia is a genus of ankylosaurid dinosaur within the subfamily Ankylosaurinae. It is known from the upper levels of the Two Medicine Formation of Montana, United States. The discovery of Oohkotokia supports that Ankylosaurine dinosaurs existed and flourished continuously in Montana and/or Alberta throughout the late Campanian and early Maastrichtian stages in the Late Cretaceous period. It was a large, heavily built, quadrupedal, herbivore, that could grow up to 5 metres (16 ft) long and weigh up to 2 metric tons.
Europelta is a monospecific genus of nodosaurid dinosaur from Spain that lived during the Early Cretaceous in what is now the lower Escucha Formation of the Teruel Province. The type and only species, Europelta carbonensis, is known from two associated partial skeletons, and represents the most complete ankylosaur known from Europe. Europelta was named in 2013 by James I. Kirkland and colleagues. Europelta has an estimated length of 5 metres and weight of 1.3 tonnes, making it the largest member of the clade Struthiosaurini.
Chuanqilong is a monospecific genus of basal ankylosaurid dinosaur from the Liaoning Province, China that lived during the Early Cretaceous in what is now the Jiufotang Formation. The type and only species, Chuanqilong chaoyangensis, is known from a nearly complete skeleton with a skull of a juvenile individual. It was described in 2014 by Fenglu Han, Wenjie Zheng, Dongyu Hu, Xing Xu, and Paul M. Barrett. Chuanqilong shows many similarities with Liaoningosaurus and may represent a later ontogenetic stage of the taxon.
Ziapelta is an extinct genus of ankylosaurid. Its fossils have been found in the Hunter Wash and De-na-zin members of the Kirtland Formation of Upper Cretaceous (Campanian) New Mexico. It was named in 2014, in a research paper led by ankylosaur researcher Victoria Arbour. There is a single species in the genus, Ziapelta sanjuanensis. The genus is named after the Zia sun symbol, a stylized sun with four groups of rays, having religious significance to the Zia people of New Mexico, and the iconic symbol on the state flag of New Mexico, and pelta (Latin), a small shield, in reference to the osteoderms found on all ankylosaurids. The specific name is in reference to San Juan County and the San Juan basin, where the fossils were found. Multiple specimens have been described to date, though the fossils are mostly from the front part of the animal. Its closest relative appears to be either Scolosaurus or Nodocephalosaurus, depending on what cladistic model is used.
Crichtonpelta is a genus of extinct herbivorous ankylosaurid dinosaur from the Late Cretaceous (Cenomanian) of China.
Akainacephalus is a monospecific genus of ankylosaurid dinosaur from southern Utah that lived during the Late Cretaceous in what is now the Horse Mountain Gryposaur Quarry of the Kaiparowits Formation. The type and only species, Akainacephalus johnsoni, is known from the most complete ankylosaur specimen ever discovered from southern Laramidia, including a complete skull, tail club, a number of osteoderms, limb elements and part of its pelvis, among other remains. It was described in 2018 by Jelle P. Wiersma and Randall B. Irmis. It is closely related and shares similar cranial anatomy to Nodocephalosaurus.