''Aletopelta'' (; meaning 'wanderer shield') is a

monospecific In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of basal ankylosaurid

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

from Southern

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

that lived during the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...

(upper

Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...

stage, 75.5 Ma) in what is now the Point Loma Formation. The type and only species, ''Aletopelta coombsi'', is known from a partial

skeleton A skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal fra ...

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 (16 feet) and weight of 2 tonnes (4,409 lbs). The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

formed a miniature

reef A reef is a ridge or shoal of rock, coral, or similar relatively stable material lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic component, abiotic (non-living) processes such as deposition (geol ...

and was scavenged upon by

invertebrates Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordate subphylum ...

and

sharks Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the ...

Discovery and naming

In 1987, construction work was done on the College Boulevard near Carlsbad at the Californian coast. While paleontologically surveying the work, Bradford Riney noted that a skeleton had been uncovered by a ditch dug for a sewage pipe. Within days, the specimen was secured by the San Diego Natural History Museum. It was dubbed the "Carlsbad Ankylosaur".W.P. Coombs, Jr. and T.A. Deméré, 1996, "A Late Cretaceous nodosaurid ankylosaur (Dinosauria: Ornithischia) from marine sediments of coastal California", ''Journal of Paleontology'' 70(2): 311-326 The skeleton was later described, but not named, in 1996 by Thomas Deméré and Walter Preston Coombs before being named in 2001 by Tracy Lee Ford and James Kirkland.T.L. Ford and J.I. Kirkland, 2001
"Carlsbad ankylosaur (Ornithischia, Ankylosauria): an ankylosaurid and not a nodosaurid"
In: ''The Armored Dinosaurs''. Indiana University Press, Bloomington pp 239-260 The skeleton originated from a layer of the marine Point Loma Formation which dates to the upper

stage, 75.5 Ma. The formation has yielded specimens pertaining to calcareous nannoplankton, foraminifers, scaphopods, pelecypods, gastropods, cephalopods, ostracods, decapods, echinoids, elasmobranchs, and actinopterygians, with the addition of a

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

, right

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

containing

teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

and cervical

vertebrae Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

of a

hadrosaur Hadrosaurids (), also hadrosaurs or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod fami ...

. The type and only known specimen of ''Aletopelta'' was once a bloated carcass that had been washed out to sea, likely by a stream, which sank to the bottom with its underside facing upwards and became a miniature

, as evidence by Pelecypoda such as '' Ostrea sp.'' and '' Spondylus sp.'' being attached to the bones and the presence of

ammonites Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

and gastropods found in association with the skeleton. The carcass was also scavenged upon by marine invertebrates and sharks such as '' Squalicorax'' and ''

Scapanorhynchus ''Scapanorhynchus'' (from , 'shovel' and 'snout') is an extinct genus of shark belonging to the family Mitsukurinidae, that lived during the Cretaceous period, from the Aptian to the end of the Maastrichtian. It is a close relative of the li ...

'', which resulted with most of the long bones being hollow and many shallow pits on the osteoderms and ribs. The

specimen, SDNHM 33909, consists of

, fragmentary

scapula The scapula (: 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 either side ...

e, partial

humerus The humerus (; : humeri) 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 (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

, partial

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

, possible fragment of right

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

, partial left and possibly right

ischium The ischium (; : is ...

, femora,

tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

fibula The fibula (: fibulae or fibulas) or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. ...

e, four or five partial

, dorsal neural arch, neural arches of the

sacrum The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...

, fragmentary

rib In vertebrate anatomy, ribs () are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the ...

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

including

pelvic The pelvis (: pelves or pelvises) is the lower part of an anatomical trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis or pelvic skeleton). ...

shield and cervical half ring. The type specimen may represent an immature individual based on the unfused

astragalus Astragalus may refer to: * ''Astragalus'' (plant), a large genus of herbs and small shrubs *Astragalus (bone) The talus (; Latin for ankle or ankle bone; : tali), talus bone, astragalus (), or ankle bone is one of the group of foot bones known ...

, partly fused scutes and unfused neural spines. The generic name, ''Aletopelta'', is composed of the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

words "''aletes''" (wanderer) and "''pelte''" (small shield), in reference to its armour and the fact that the

tectonic plate Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

containing the Peninsular Ranges Terrane was somewhere opposite the middle of

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

in the Cretaceous, only moving northward due to

plate tectonics Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

, carrying the holotype specimen with it. The specific name, coombsi, honours the vertebrate palaeontologist Walter Preston Coombs, Jr., for their work and years of research.

Description

Size and distinguishing traits

Ford & Kirkland (2001) originally gave ''Aletopelta'' an estimated length of 6 metres (19.7 feet). However,

Gregory S. Paul Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology. He is best known for his work and research on theropoda, theropod dinosaurs and his detailed illustrations, both l ...

gave a lower estimate of 5 metres (16 feet) long and weight of 2 tonnes (4,409 lbs) in 2010. Ford and Kirkland (2001) originally diagnosed ''Aletopelta'' based on the teeth being wider than tall; the femur being much longer than both the tibia and fibula; the presence of three metatarsals; a pelvic shield composed of polygonal, low-peaked osteoderms; a large short-pointed spike in the shoulder region; the presence of hollow cap-like osteoderms across dorsum; the presence of hollow pup-tent-like osteoderms over neck and shoulders; triangular, dorsally compressed caudal osteoderms that are highly asymmetrical from top to bottom; and hollow and thin osteoderms. However, Arbour & Currie (2015) later diagnosed Aletopelta based on the presence of hexagonal pelvic osteoderms that form a semi-continuous sheet over the pelvis; the pelvic osteoderms lack a dendritic surface texture; the first cervical half ring is composed of osteoderms fused to an underlying bony band rather than being closely appressed adjacent osteoderms.

Classification

Deméré & Coombs (1996) originally interpreted SDNHM 33909 as an indeterminate nodosaurid that showed similarities with '' Edmontonia'', '' Panoplosaurus'' and '' Stegopelta'' but refrained from naming it as they considered it to be undiagnostic. Ford (2000) considered that SDNHM 33909 formed the clade Stegopeltinae, along with ''Stegopelta'' and '' Glyptodontopelta'', within

Ankylosauridae Ankylosauridae () is a family of armored dinosaurs within Ankylosauria, and is the sister group to Nodosauridae. The oldest known ankylosaurids date to around 122 million years ago and went extinct 66 million years ago during the Cretaceous–Pal ...

based on the presence of a pelvic shield composed of co-ossified hexagonal osteoderms.T.L. Ford. (2000). "A review of ankylosaur osteoderms from New Mexico and a preliminary review of ankylosaur armor", In: S. G. Lucas and A. B. Heckert (eds.), ''Dinosaurs of New Mexico. New Mexico Museum of Natural History and Science Bulletin'' 17: 157-176 Ford & Kirkland (2001) also reinterpreted it as an ankylosaurid and considered it to be taxonomically distinct enough to be warranted as a new genus and species. Vickaryous et al. (2004) considered ''Aletopelta'' as a ''

nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium,'' it may be impossible to determine whether a ...

'' due to the lack of diagnostic characteristics. Arbour & Currie (2015), however, considered it as a valid genus based on new characteristics and found Stegopeltinae to not be a valid clade. Arbour & Currie (2015) additionally recovered ''Aletopelta'' within a polytomy containing '' Liaoningosaurus'', '' Cedarpelta'', '' Chuanqilong'' and more derived ankylosaurids. A similar position was recovered by Arbour & Evans (2017) and Rivera-Sylva et al. (2018) but also placed '' Hylaeosaurus'', '' Crichtonpelta'', '' Gobisaurus'' and '' Shamosaurus'' within the polytomy. Park et al. (2019) also placed ''Aletopelta'' within a polytomy but with the inclusion of '' Jinyunpelta'', '' Nodosaurus'' and ''

Kunbarrasaurus ''Kunbarrasaurus'' (meaning "shield lizard") is an extinct genus of small ankylosaurian dinosaur from the Cretaceous of Australia. The genus contains a Monotypic taxon, single species, ''K. ieversi''. Discovery In November 1989, at Marathon ...

''. Although most often being recovered as a basal ankylosaurid, Frauenfelder et al. (2022) found it to be the basalmost nodosaurid. The results of a phylogenetic analysis conducted by Arbour & Currie (2015) is reproduced below.

References

External links