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 ankylosaur 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 osteoderms 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.
Discovery
An expedition from the New Mexico Museum of Natural History and Science and the State Museum of Pennsylvania, led by Robert Michael Sullivan, discovered a number of Z. sanjuanensis fossils in the Kirtland Formation in 2011. The specimens were found in the Hunter Wash and De-na-zin Members of the formation in the Bisti/De-Na-Zin Wilderness in New Mexico. Z. sanjuanensis was identified as a new species from a number of fossils including the holotype NMMNH P-64484 found from the De-na-zin Member and consisting of a complete skull lacking the lower jaws, parts of the first two cervical half-rings, and a number of partial osteoderms; and a referred specimen NMMNH P-66930 from the older Hunter Wash Member, consisting of a first cervical half-ring. By argon dating of ash layers the age of the holotype skull has been determined at between 72.98 and 72.62 million years old, the late Campanian. It was initially prepared by Amanda K. Cantrell and Thomas L. Suazo; later by Larry Rinehart. In 2014 Victoria Megan 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 pelta ("shield"), referring to ankylosaurids' osteoderms. The specific name (sanjuanensis) comes from San Juan County, where the fossils were discovered.
Description
Ziapelta is known from a complete skull and specimens of first cervical half ring, so its head and cervical armor may have been separated from the body before the specimen was buried.
Distinguishing traits Ziapelta sanjuanensis showed three unique derived traits or autapomorphies. The caputegulum (middle bone plate), of the snout was large, prominent and roughly triangular in shape. Ziapelta had deep, anteriorly curved squamosal horns (measuring 10.2 centimetres (4.0 in) from the base to the tip). The rear base of the skull featured three deep grooves. A further possible distinguishing trait is the mixture of concave, flat and convex caputegulae on the skull top. 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.
Skull
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