this may at least partially be an artifact of post-mortem compression. Helicoprion had an autodiastylic jaw suspension, meaning that the inner edge of the palatoquadrate was firmly attached (but not fused) to the chondrocranium at two separate points. These two attachment points are the dome-shaped ethmoid process at the front of the palatoquadrate, and the flange-like basal process at its upper rear corner. Autodiastylic jaws are common in early euchondrocephalans, though in modern animals they can only be found in embryonic chimaeriforms. Another well-preserved specimen, USNM 22577+494391 (the "Sweetwood specimen"), has demonstrated that the inner surface of the palatoquadrate was covered with numerous small (~2 mm wide) teeth. The palatoquadrate teeth were low and rounded, forming a "pavement" which scraped against the tooth whorl. When seen from behind, the palatoquadrate forms a paired jaw joint with the Meckel's cartilage. There is no evidence for an articulation between the palatoquadrate and the hyomandibula. Meckel's cartilage has an additional projection right before the joint with the palatoquadrate. This extra process, unique to Helicoprion, likely served to limit jaw closure to prevent the whorl from puncturing the chondrocranium. Another unique characteristic of Helicoprion is that the preserved labial cartilage forms a synchondrosis (fused joint) with the upper surface of the Meckel's cartilage. This joint is facilitated via a long facet on the upper edge of Meckel's cartilage. The labial cartilage provides lateral support for the tooth whorl, widening near the root of each volution. By wedging into the palatoquadrate while the mouth is closed, the upper edge of the labial cartilage helps to spread out the forces used to limit the extent of the jaw closure. The rear portion of the labial cartilage has a cup-like form, protecting the developing root of the last and youngest volution. Scales Tooth-like chondricthyan scales, specifically known as odontodes, have been found associated with H. bessonowi remains in Kazakhstan. They are broadly similar to scales of other eugeneodonts such as Sarcoprion and Ornithoprion. The scales have a cap-shaped base with a concave lower surface. The crowns are conical and covered with serrated longitudinal ridges. The scales may be monodontode (with one crown per base) or polyodontode (with a bundle of multiple crowns resulting from the fusion of several odontodes into a larger structure). Compared to other eugeneodonts, the scales of Helicoprion are more strongly pointed. Paleobiology The unusual saw-like tooth whorl and the lack of wear on