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Ziapelta is an extinct genus of Ankylosauridae. Its 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 Ankylosauria 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 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.
In 2014 Victoria Arbour, Michael Burns, Robert Sullivan, Spencer Lucas, Amanda Cantrell, Joshua Fry and Thomas Suazo named the type species Ziapelta sanjuanensis. The genus ( Ziapelta) was named after the Zia sun symbol, a religious image for the Zia people and an element of the flag of New Mexico, and the Latin word ("shield"), referring to ankylosaurids' osteoderms. The specific name ( sanjuanensis) comes from San Juan County, where the fossils were discovered.
From the Kirtland Formation a second ankylosaur is known from limited remains, Nodocephalosaurus. Ziapelta differs from Nodocephalosaurus in several traits. The edge on the squamosal horns is sharper. The points of these horns are more curved to the front instead of to below. The osteoderm peaks above the eye sockets are sharper. The caputegulae are more irregular in form, at best lightly convex instead of cone-shaped, have a more rectangular outline, instead of a rounded one, and are separated by deeper grooves.
At the rear of the skull, the paroccipital processes are fused with the quadrates. The contact with the neck, the occipital condyle, is kidney-shaped with a smooth surface surrounded by a groove. In Ziapelta, the bones of the upper rear skull sides, the exoccipitalia, do not contribute to this condyle which is fully formed by the basioccipital, the lower rear braincase element. More to below this basioccipital shows three deep parallel grooves, bordered by four rims. The middle groove has the opening of the foramen basioccipitale. To the front the basioccipital contacts the triangular basisphenoid of the underside of the braincase. The two elements are not fully fused but in side view show a clear suture, obliquely running to below.
At the underside of the skull, the paired front praemaxillae form a bony secondary palate, with a concave surface. Each praemaxilla is pierced by two foramina. Both elements are at the snout tip separated by a gap, ending about thirty-five millimetres in front of the tip of the narrow and flat at the midline. Behind the praemaxillae, the internal wings of the maxillae form the edges of the , the internal nostrils. To the rear of the vomers, triangular are located. These are not pierced by large fenestrae, though a triangular depression is present at their undersides.
The cervical halfrings of ankylosaurids typically consisted of six fused segments each, that were paired per side: one at the top, a second segment at the upper side and a third one at the lower side. These segments were fused to an underlying continuous bone ring. In Ziapelta the segments consisted of osteoderms that were in-between an oval and a rectangular shape. These osteoderms were keeled, featuring a high cutting edge. The osteoderms were between 146 and 169 millimetres long, between 58 and 104 millimetres wide and their keels varied between and tall. Where the middle segments touched each other on the midline, an irregular punctuated row of small trapezium-shaped "interstitial" osteoderms was present within the suture. At the front of the suture of the first cervical halfring, a small cone-shaped interstitial osteoderm protruded. Such interstitial elements were absent with the side segments.
Specimen NMMNH P-66930, a first cervical halfring, shared several traits with its counterpart of the holotype: high narrow keels, interstitial osteoderms in the middle and a lower side osteoderm that does not wrap around the lower edge. It was therefore referred to Z. sanjuanensis.
Several unconnected osteoderms have been discovered. One of these might originally have been part of a halfring. A second one was seen as originating from the pectoral, upper breast, region. A third, measuring 118 by 68 millimetres, had a narrow keel and the shark fin shape typical of the ankylosaurian side spikes and was thus identified as a lateral rump osteoderm. Some small ossicles were discovered also, round scutes of between two and four centimetres in cross-section, with a conical or flat shape and featuring a pitted surface. Their original position cannot be determined.
The following cladogram is based on a 2015 phylogenetic analysis of Ankylosaurinae conducted by Arbour and Currie:
Since, Ziapelta and other Late Cretaceous North American ankylosaurids are grouped with Asian genera, in a tribe which the authors dubbed Ankylosaurini, Arbour and Currie suggested that earlier North American ankylosaurids had gone extinct by the late Albian or Cenomanian ages of the Middle Cretaceous. They propose that ankylosaurids subsequently recolonized North America from Asia during the Campanian or Turonian ages of the Late Cretaceous, and there diversified once more, leading to genera such as Euoplocephalus, Scolosaurus and Ziapelta
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