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 osteoderms, a partial skull, vertebrae, 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 3 metres (9.8 ft). 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 jugal. Five different armor types have been observed in Mymoorapelta, ranging from elongated, sharp spines on the side of the body to a giant sacral 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.
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.[1][2] Fossils of Mymoorapelta were first discovered in the quarry in 1990, and since then over 160 elements have been found scattered over 25 metres (27 yd) of the 150-square-metre (1,600 sq ft) quarry.[3][1] 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 ilium (hip bone) with preserved bitemarks.[1] 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.[1] 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.[1][3] Mymoorapelta was the first Jurassic ankylosaur named from North America, with the closely related Gargoyleosaurus being named four years later in 1998.[4][1] Other parts of the type specimen that were excavated from the quarry include several dorsal (back) and caudal (tail) vertebrae, ribs, isolated limb bones, and many osteoderms, including the signature triangular cervical spine of basal ankylosaurs.[5][3][1] 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.[3]