NEW MATERIAL OF THE HEDGEHOG AMPHECHINUS (ERINACEIDAE, EULIPOTYPHLA) FROM THE OLIGOCENE OF THE PACIFIC NORTHWEST, USA

Oligocene hedgehog material is poorly known west of the Rocky Mountains in the United States, with only isolated teeth or partial jaws identified. These specimens cannot be confidently identified to the species level. To better understand Oligocene hedgehog ecology in what is now known as the western United States, additional fieldwork was necessary to recover new material. A nearly complete hedgehog skull with two dentaries (JODA 18944) was recovered from the JDNM-269, Rudio Creek 4 locality on Bureau of Land Management-administered land in 2019. The site includes exposures of the Kimberly Member of the John Day Formation between the Tin Roof Tuff (25.33 Ma) and the Haystack Valley Member Tuff (23.79 Ma). The specimen was found in a concretion and was misidentified as a gopher skull until further preparation was completed (fall 2022). The site is known for a high density of concretions with gopher skulls and jaws with damage to the base of the skulls contained within, suggesting the site may contain the remnants of a bird-of-prey roost. Mechanical preparation with an airscribe uncovered both the completeness of the specimen and its delicate nature. However, the diagnostic features in the dentition could not be safely exposed using mechanical means, so, JODA 18944 was scanned using microtomography (voxel size = 33.861 µm) to nondestructively reveal these structures, and the scan was segmented to produce a 3D model for further analysis. These 3D images reveled hidden morphology and allowed for measurements of features and structures to be made. The following characteristics were identified on JODA 18944: the i1 terminates below p4 and the P4 is under the orbit. The m3 has a single root with a length of 0.9 mm, is rounded, and pointing posteriorly. The mental foramen is anterior to the p4. The p4 talonid is the same width as the trigonid. These characters suggest a genus-level diagnoses of Amphechinus, though the exact affinities are still to be determined. This complete skull and two associated jaws allows for a better understanding of morphology of this taxon. The only other specimen from this genus to be recovered in this region is an isolated tooth, making JODA 18944 the most complete hedgehog specimen known from this region and the first know from this locality.