Extinct genus of ornithischian dinosaur
Mymoorapelta (Meaning "Shield from the Mygatt-Moore Quarry" after a combination of the names of the discoverers of the Mygatt-Moore Quarry that fossils were originally collected from, and the Greek word πέλτα, meaning "shield") is a nodosaurid ankylosaur from the Late Jurassic (Kimmeridgian-Tithonian, around 155 to 150 million years ago) Morrison Formation (Brushy Basin Member) of western Colorado and central Utah, USA. The animal is known from a single species, Mymoorapelta maysi, and few specimens are known. The most complete specimen is the holotype individual from the Mygatt-Moore Quarry, which includes ;dfn id="" ;osteoderms ;/dfn ;, a partial ;dfn id="" ;skull ;/dfn ;, ;dfn id="" ;vertebrae ;/dfn ;, and other bones. It was initially described by James Kirkland and Kenneth Carpenter in 1994. Along with "Gargoyleosaurus", it is one of the earliest known nodosaurids.
"Mymoorapelta" is one of the smaller known nodosaurids, with the estimated length of the largest specimen only reaching . It had a narrow snout and almost triangular skull in dorsal view, with two large horns pointing backwards from the brow and two horns below these that pointed backwards and down on the ;dfn id="" ;jugal ;/dfn ;. Five different armor types have been observed in "Mymoorapelta", ranging from elongated, sharp spines on the side of the body to a giant ;dfn id="" ;sacral ;/dfn ; shield composed of tiny osteoderms, called "ossicles", that covered the top of the pelvis. In contrast to the club-tailed ankylosaurids, the tail bore spikes that "Mymoorapelta" likely used for defense. 
"Mymoorapelta" was a low browser in the Morrison ecosystem, feeding on cycads and conifers, in contrast to the high-browsing "Apatosaurus" known from the same quarries. Other dinosaur groups were also present, including the large theropods "Allosaurus" and "Ceratosaurus" and possibly the ornithischian "Nanosaurus". Both of the theropods have also been found in association with the animal, and we have evidence that the former preyed on "Mymoorapelta." 
Discovery and naming.
The Mygatt-Moore Quarry was first discovered in March of 1981 by hikers Vanetta Moore and Pete and Marilyn Mygatt in Mesa County, west-central Colorado. The quarry's strata come from the Brushy Basin Member of the Morrison Formation, which dates to the Upper Jurassic. Fossils of "Mymoorapelta" were first discovered in the quarry in 1990, and since then over 160 elements have been found scattered over of the quarry. A few of these elements are part of a single adult individual and were described by American paleontologists James Kirkland and Kenneth Carpenter in 1994. This specimen (MWC 1815) would be designated the holotype of the species and includes a left ;dfn id="" ;ilium ;/dfn ; (hip bone) with preserved bitemarks. Kirkland and Carpenter named the species "Mymoorapelta maysi", the generic name deriving from the names of Marilyn Mygatt and the Moores, who had discovered the quarry, and the Greek root "pelta", meaning "shield", due to the preserved armor. The specific name is after Chris Mays, the president of the Dinamation International Corporation and Society, who funded the initial excavation of the Mygatt-Moore Quarry. "Mymoorapelta" was the first Jurassic ankylosaur named from North America, with the closely related "Gargoyleosaurus" being named four years later in 1998. Other parts of the type specimen that were excavated from the quarry include several ;dfn id="" ;dorsal ;/dfn ; (back) and ;dfn id="" ;caudal ;/dfn ; (tail) vertebrae, ;dfn id="" ;ribs ;/dfn ;, isolated limb bones, and many osteoderms, including the signature triangular cervical spine of basal ankylosaurs. Some osteoderms which have been found in the quarry and referred to "Mymoorapelta" come from a higher stratigraphic layer, suggesting that a second individual is preserved.
In 1998, a partial skeleton referred to "Mymoorapelta" was described by Kirkland "et al" from Cactus Park, Colorado, though at the time the fossil was still undergoing fossil preparation. The skeleton preserved natural molds and body fossils of the sacrum, caudal vertebrae, ;dfn id="" ;chevrons ;/dfn ; (bones attached to the underside of the tail vertebrae in dinosaurs), ;dfn id="" ;pes ;/dfn ; (foot), and many pieces of the dermal armor, including parts of the sacral shield, which was a type of armor that would cover the top of the pelvis. Though skull material was mentioned to be preserved it is still in preparation and undescribed. Some of the material, namely from the pes and sacral shield, was preserved in articulation making it the only known articulated specimen of the taxon. In a 2010 abstract, Kirkland and colleagues mentioned the discovery of many more elements of "Mymoorapelta" at Mygatt-Moore Quarry including a nearly complete skull and every postcranial element except the pubis and femur. All of the fossils found at Mygatt-Moore Quarry and Cactus Park are currently deposited in the Dinosaur Journey Museum of Western Colorado in Fruita. 2015 saw the presentation of an abstract by Katie Tremaine "et al" that mentions a new "Mymoorapelta" specimen unearthed at Hanksville-Burpee Quarry near Hanksville, Utah. The specimen includes one individual preserving: 24 osteoderms, three ribs, one vertebra, and a femur, though more material has yet to be excavated. The discovery of a single, dorsal osteoderm that had been collected from the Peterson Quarry outside of Albuquerque, New Mexico was described in 2016. The osteoderm is morphologically (based on external anatomy) similar to "Mymoorapelta", however it is stratigraphically (based on rock layers) closer to "Gargoyleosaurus."
Description.
"Mymoorapelta" is one of the smallest ankylosaurs known and the smallest known quadrupedal dinosaur from the Morrison Formation. However, few individuals have been found and only a portion of the known material has been described in detail. The Cactus Park specimen is the largest described individual, with its length being estimated at around long in 1998. Body mass estimates based on the type specimen give a weight of around .
Skull and dentition.
The ;dfn id="" ;skull ;/dfn ; specifically has not been described in detail, but the preserved morphology (external anatomy) is very similar to that of "Gargoyleosaurus", which also hails from the Morrison Formation. It had a narrow snout and almost triangular shaped skull in dorsal (top) view, with two large horns pointing backward from the back of the brow, and two horns below these that pointed backward and down from the ;dfn id="" ;jugal ;/dfn ; (cheek bone). A preserved jugal described in 1998 has a wedge-shaped, armored morphology and projects ventrolaterally (down and outwards) like in ankylosaurids. The ;dfn id="" ;premaxillae ;/dfn ; (bones at the tip of the snout) probably possessed a narrow, toothed, and trapezoidal muzzle like in "Gargoyleosaurus". In the back of the skull, the ;dfn id="" ;quadrate ;/dfn ;-articular area (place of contact between the skull and lower jaw) faces slightly medially (towards the midline of the body), and is subtly lengthened anteroposteriorly (front to back). The distal surface of the quadrate, especially on the medial condyle, is robust and elongated anteroposteriorly. In all ankylosaurs, the jaw joint (joint connecting the skull to the jaw bone) is placed ventrally to the occlusal plane (contact surface between teeth). The ;dfn id="" ;coronoid process ;/dfn ; (bony projection on the lower jaw) is very well developed in nodosaurids, and the jaw joint is well depressed in turn, which corresponds to a higher relative bite force. 
Most ankylosaurs have heterodont dentition (variation in tooth morphology), but not in "Gargoyleosaurus," which shows only subtle morphological differences in the premaxillary, maxillary, and dentary teeth. Ankylosaur teeth are compressed labiolingually and are phylliform (leaf-shaped), with an apical cusp and secondary cusps along the mesial and distal edges. Nodosaurid teeth are blade-like, larger, and usually more complex than the basic cusps of ankylosaurids, having a larger crown, a rough enamel surface, confluent fluting with grooves of the marginal cusps, and a crenelated ;dfn id="" ;cingulum ;/dfn ; (shelf-like bulge surrounding the base of a tooth crown). The wear facets on Ankylosaur teeth vary greatly, but in nodosaurids they are usually more extensive and steeply inclined than in ankylosaurids, demonstrating underlying patterns of shape-constrained function. In early nodosaurids like "Gargoyleosaurus" and "Gastonia", the ;dfn id="" ;pterygoid ;/dfn ; (a dermal, paired bone of the palate) is not yet well developed anteroposteriorly and mediolaterally, but in later species they are much wider, with more robust lateral wings, and they are more expanded anteroposteriorly than in basal forms, reaching the level of the distal quadrate condyles. This suggests more developed pterygoid muscles in later nodosaurids than in ankylosaurids, reflecting a more efficient jaw adductor system in nodosaurids. The mandibular adductor chamber and the coronoid process are generally taller in nodosaurids than in ankylosaurs, suggesting differences in the size and attachment of muscles.
Postcranial skeleton.
A large part of the postcranial (behind the skull) skeleton of "Mymoorapelta" is known. For instance, many ;dfn id="" ;cervical vertebrae ;/dfn ; (vertebrae of the neck) are known, though many of them have not been fully researched or excavated. In the cervicals, the faces (ends) of the ;dfn id="" ;centra ;/dfn ; are wider than they are tall and display a heart-shaped morphology. The centra overall are anteroposteriorly short with lengths that are around equal to their width. The ;dfn id="" ;neural spines ;/dfn ; are short and thick,and possess round, circular neural canals. A deep, tear-shaped fossa (small opening in bone) is present between the ;dfn id="" ;postzygapophyses ;/dfn ; (backwards projections of the vertebral arch). Several dorsal (back, sometimes referred to as thoracic) vertebrae are known from "Mymoorapelta," and they are unique when compared to those of Cretaceous nodosaurids. The centra are cylindrical, longer posteriorly, and less laterally compressed than those of other, later nodosaurids like "Sauropelta" and "Dracopelta". The anterior dorsals are unique in that they bear a triangular pit between the ;dfn id="" ;prezygapophyses ;/dfn ; (forwards projections of the vertebral arch), which are also much more elongate at the anterior end of the vertebra. Meanwhile, the postzygapophyses are truncated at the posterior end, with the left and right postzygapophyses divided by a large groove. The mid dorsal vertebrae differ in that they are rounded ventrally and have a weak keel at the bottom. The transverse processes of the dorsal vertebrae do not ascend steeply and are instead gradually heightened, similar to the condition in basal ankylosaurs, and differing from that of nodosaurids. "Mymoorapelta" has 13 ribs, all of which have triangular cross-sections and a weak T-shape, in contrast to other ankylosaurs. "Mymoorapelta" is also one of the few ankylosaurs with 4 sacral ribs, a trait it shares with only 3 other taxa. 
The caudal (tail) vertebrae of "Mymoorapelta" and other nodosaurids are longer than they are wide, and dorsoventrally (top-bottom) flattened with a reduction of the neural spines when compared to the anterior caudals. The haemal spine takes on a rounded, hatchet-shaped appearance. The prezygapophyses are short and extend past the anterior edge of the centra by only 25% or less. This trait is only present in nodosaurids and basal anklosaurs, but in taxa like "Liaoningosaurus" and more derived ankylosaurids they overlap by at least 50% of its length, making them more fused together. "Mymoorapelta" lacks tail club handles or tail club knobs, as in other nodosaurids, giving them less ankylosis. The transition from anterior to posterior caudal vertebrae is less abrupt compared to ankylosaurids, which have an abrupt transition at the midcaudals, the lack of this abrupt transition would give the tail more flexibility, which is unique to nodosaurids when compared to the strongly fused tails of ankylosaurids. The vertebral centra and neural spines are much shorter when compared to "Gargoyleosaurus." "Mymoorapelta," like other dinosaurs, preserves chevrons along the undersides of the caudal vertebrae, and just like in many other ankylosaurs, the chevrons are strongly fused to the lower posterior part of the centra, and the haemal arches extend parallel to the elongate vertebral centra. The extension of these arches is greater anteriorly than posteriorly, forming a continuous bony structure underneath the haemal canal. One of the preserved chevrons measures and is strongly recurved posteriorly.
The scapular spine forms a vertical ridge opposite the glenoid in "Mymoorapelta," as in other ankylosaurids and in an indeterminate ankylosaur scapula found in the nearby Dry Mesa Quarry. In the pelvic region, "Mymoorapelta" displays an intermediate between some features of basal and more derived ankylosaurs. The ischium is bent as in other nodosaurids and polacanthines, indicating that a