''Ahshislepelta'' (meaning "Ah-shi-sle-pah Wash shield") is a monospecific

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

ankylosaur Ankylosauria is a group of herbivorous dinosaurs of the order 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. ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

from

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ker ...

that lived during the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

(late Campanian stage, 74.5 Ma) in what is now the Hunter Wash Member of the Kirtland Formation. The type and only species, ''Ahshislepelta minor'', is known only from an incomplete postcranial skeleton of a small subadult or adult individual. It was named in

2011 File:2011 Events Collage.png, From top left, clockwise: a protester partaking in Occupy Wall Street heralds the beginning of the Occupy movement; protests against Libyan dictator Muammar Gaddafi, who was killed that October; a young man celebrate ...

by Michael Burns and

Robert M. Sullivan Robert Michael "Bob" Sullivan (born August 4, 1951) is a Vertebrate_paleontology, vertebrate paleontologist, noted for his work on fossil lizards and Dinosaur, dinosaurs. Sullivan discovered the second and most complete skull of the Hadrosaurid ...

. Based on the size of the humerus, ''Ahshislepelta'' is larger than '' Pinacosaurus mephistocephalus'' but smaller than ''

Talarurus ''Talarurus'' ( ; meaning "basket tail" or "wicker tail") 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 19 ...

'' and ''

Pinacosaurus grangeri ''Pinacosaurus'' (meaning "Plank lizard") is a genus of ankylosaurid thyreophoran dinosaur that lived in Asia during the Late Cretaceous (Santonian-Campanian, roughly 75 million to 71 million years ago), mainly in Mongolia and China. The first ...

''.

Discovery and naming

In 2005, a partial postcranial

skeleton A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

of an

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

. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

specimen, SMP VP-1930, consists of a partial girdle, partial scapulocoracoid, a proximal portion of the

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

, numerous

cervical In anatomy, cervical is an adjective that has two meanings: # of or pertaining to any neck. # of or pertaining to the female cervix: i.e., the ''neck'' of the uterus. *Commonly used medical phrases involving the neck are **cervical collar **cervic ...

and/or dorsal vertebrae fragments, complete and fragmentary thoracic

osteoderms Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct ...

, and other unidentifiable postcranial fragments. The holotype specimen is currently housed at the

State Museum of Pennsylvania The State Museum of Pennsylvania is a non-profit museum at 300 North Street in downtown Harrisburg, Pennsylvania. It is run by the state through the Pennsylvania Historical and Museum Commission and was created to preserve and interpret the region ...

Harrisburg Harrisburg is the capital city of the Pennsylvania, Commonwealth of Pennsylvania, United States, and the county seat of Dauphin County, Pennsylvania, Dauphin County. With a population of 50,135 as of the 2021 census, Harrisburg is the List of c ...

. The generic name, ''Ahshislepelta'', is derived from Ah-shi-sle-pah Wash, the locality from which the holotype came, and the

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...

word "''peltè''" (shield). The specific name, minor, is in reference to its small adult size relative to other

North American North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Ca ...

ankylosaurids. The holotype specimen represents a

subadult A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles can look very different from the adult form, particularly in colour, and may not fill the same niche as the adult form. In many org ...

or adult individual based on the complete fusion of the scapulocoracoids, centra and

neural arches The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

of the vertebrae, and the re-modelled osteoderm cores. The holotype This new specimen 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''.

Description

Distinguishing traits

Burns & Sullivan (2011) diagnosed ''Ahshislepelta'' based on the dorsolateral overhang of the scapular acromion process to 25% of the dorsoventral width of the

scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eithe ...

. ''Ahshislepelta'' differs from other ankylosaurids, with the exception of ''

Euoplocephalus ''Euoplocephalus'' ( ) is a genus of very large, herbivorous ankylosaurid dinosaurs, living during the Late Cretaceous of Canada. It has only one named species, ''Euoplocephalus tutus''. The first fossil of ''Euoplocephalus'' was found in 1897 i ...

'', 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.

Postcrania

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 fuse 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 fossa of the scapula or the glenoid cavity is a bone part of the shoulder. The word ''glenoid'' is pronounced or (both are common) and is from el, gléne, "socket", reflecting the shoulder joint's ball-and-socket form. It is a sha ...

. 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 In human anatomy, the acromion (from Greek: ''akros'', "highest", ''ōmos'', "shoulder", plural: acromia) is a bony process on the scapula (shoulder blade). Together with the coracoid process it extends laterally over the shoulder joint. The acro ...

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 Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov t ...

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 The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

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

is oval in proximal view and is concave. The articular surface is 8 cm long, proportionally twice the diameter of the diaphysis. Numerous

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

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.

Osteoderms

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.

Classification

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. 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 ''

'', ''

Oohkotokia ''Oohkotokia'' ( ) is a genus of ankylosaurid dinosaur within the subfamily Ankylosaurinae. It is known from the upper levels of the Two Medicine Formation (late Campanian stage, about 74 Ma ago) of Montana, United States. The discovery of ''O ...

'', '' Scolosaurus'', ''

Ziapelta ''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 ankyl ...

'', '' Anodontosaurus'', ''

Ankylosaurus ''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 n ...

'' and ''

Dyoplosaurus ''Dyoplosaurus'' (meaning “double-armoured lizard”) is a monospecific genus of ankylosaurid dinosaur from Alberta that lived during the Late Cretaceous (middle Campanian, ~76.5–75 Ma) in what is now the Dinosaur Park Formation. ''Dyoplosau ...

''. 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 The Paw Paw Formation is a geological formation in Texas whose strata date back to the late Albian stage of the Early Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.Weishampel, David B; et al. (200 ...

, while Zheng ''et al.'' (2018) positioned ''Ahshislepelta'' in a polytomy containing ''

Tatankacephalus ''Tatankacephalus'' is a basal genus of nodosaurid dinosaur that lived during the Early Cretaceous. Its length has been estimated at 7 meters (23 ft). Its fossil has been collected from the Cloverly Formation (Aptian-Albian) of central Mon ...

'', ''

Silvisaurus ''Silvisaurus'', from the Latin silva "woodland" and Greek sauros "lizard", is a nodosaurid ankylosaur from the Early to Late Cretaceous period. Discovery and species A fossil of the species was discovered in the fifties by rancher Warren H. ...

'', ''Niobrarasurus'', ''

Nodosaurus ''Nodosaurus'' (meaning "knobbed lizard") is a genus of herbivorous nodosaurid ankylosaurian dinosaur from the Late Cretaceous, the fossils of which are found exclusively in the Frontier Formation in Wyoming. Description ''Nodosaurus'' grew ...

'' and more deeply nested taxa. Rivera-Sylva ''et al.'' (2018) placed it as sister taxon to ''Niobrarasurus''. A phylogenetic analysis conducted by Rivera-Sylva ''et al.'' (2018) is reproduced below, favoringa nodosaurid position. Clade names have been added following Madzia ''et al.'' (2021). In contrast, an earlier analysis by Arbour & Currie (2015) favors an ankylosaurid position. Their results are reproduced below.

Paleoenvironment

''Ahshislepelta'' is known from the Hunter Wash Member of the Kirtland Formation which has been dated to the upper Campanian stage, 74.5 Ma. The Kirtland Formation consists of interbedded

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dea ...

and

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

. The Kirtland Formation lays on the western margin of the Western Interior Seaway and represents a

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

that was abundant with ferns,

conifers Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All extan ...

and

flowering plants Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

. 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. The Kirtland Formation was better drained than the underlying Fruitland Formation due to the lack of coal swamps. ''Ahshislepelta'' coexisted with the pachycephalosaurid '' Stegoceras'', the

chasmosaurine Chasmosaurinae is a subfamily of ceratopsid dinosaurs. They were one of the most successful groups of herbivores of their time. Chasmosaurines appeared in the early Campanian, and became extinct, along with all other non-avian dinosaurs, during t ...

ceratopsids Ceratopsidae (sometimes spelled Ceratopidae) is a family of ceratopsian dinosaurs including ''Triceratops'', ''Centrosaurus'', and ''Styracosaurus''. All known species were quadrupedal herbivores from the Upper Cretaceous. All but one species are k ...

Navajoceratops ''Navajoceratops'' (meaning "Navajo horned face") is a genus of ceratopsid dinosaur from the late Cretaceous Period of what is now North America. The genus contains a single species, ''N. sullivani'', named after Robert M. Sullivan, leader of the ...

'' and ''

Terminocavus ''Terminocavus'' is a genus of ceratopsid dinosaur from the late Cretaceous Period of what is now North America. The genus contains a single species, the type species ''Terminocavus sealeyi'', known from a parietal and some other associated fragm ...

'', the

ankylosaurine Ankylosaurinae is a subfamily of ankylosaurid dinosaurs, existing from the Early Cretaceous about 105 million years ago until the end of the Late Cretaceous, about 66 mya. Many genera are included in the clade, such as ''Ankylosaurus'', ''Pinacos ...

ankylosaurid ''

'', the eutyrannosaur

tyrannosauroid Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent b ...

Bistahieversor ''Bistahieversor'' (meaning "Bistahi destroyer"), also known as the "Bisti Beast", is a genus of eutyrannosaurian tyrannosauroid dinosaur; the genus contains only a single known species, ''B. sealeyi'', described in 2010, from the Late Cretaceo ...

'', and the azhdarchid

pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 to ...

Navajodactylus ''Navajodactylus'' (meaning "Navajo finger") is an extinct genus of pterodactyloid pterosaur from Late Cretaceous (late Campanian stage) deposits of the San Juan Basin in New Mexico, United States. Discovery The holotype specimen of ''Navajoda ...

''.

References

{{Taxonbar, from=Q1705974 Late Cretaceous dinosaurs of North America Ankylosaurs Fossil taxa described in 2011 Paleontology in New Mexico Campanian genus first appearances Campanian genus extinctions Ornithischian genera

Discovery and naming

Description

Distinguishing traits

Postcrania

Osteoderms

Classification

Paleoenvironment

See also

References