Myledaphus: a Cretaceous ray with a newly revealed skeleton

Myledaphus bipartitus was a Late Cretaceous ray from western North America, recorded in freshwater and marginal-marine deposits. For decades, researchers knew it mainly from small crushing teeth and vertebral centra. A nearly complete specimen from Alberta has now supplied the first detailed skeletal description, placing the animal among rhinopristiform rays in several analyses, although one strict consensus tree leaves its order unresolved. The combination of tooth, growth and body evidence makes it a distinctive entry in the ancient fish catalogue.

Quick facts

From a tooth pavement to a body plan

Edward Drinker Cope named Myledaphus bipartitus in 1876 from the western North American fossil record. The genus became familiar through isolated teeth in Late Cretaceous deposits. Their low, wide crowns interlock into a pavement rather than forming the pointed grasping row of a typical predatory shark. An articulated dental portion described from Chile later helped document variation within the genus and extended its known record into the Southern Hemisphere.

A specimen discovered in 1998 at Dinosaur Provincial Park changed what can be said about the animal. The fossil, catalogued as TMP1998.062.0001 and displayed at the Royal Tyrrell Museum, comes from alluvial and estuarine sediments of the middle to late Campanian Dinosaur Park Formation. The 2026 description documents the right half of a ray preserved in ventral view. It is the first nearly complete skeleton assigned to both the genus and species and supplies anatomical characters that loose teeth could not provide.

The slab preserves parts of the rostrum, nasal capsules, jaws, branchial skeleton, pectoral disc, pelvic girdle, fins, ribs and vertebral series. Ultraviolet examination helped distinguish some skeletal structures. The dorsal surface was left unprepared to protect this rare specimen, and available CT equipment could not accommodate its size. The anatomy is therefore unusually informative but not a complete, equally visible record of both sides of the body.

A freshwater-tolerant ray among rhinopristiforms

Older studies placed Myledaphus in several different ray groups, including stingray and guitarfish lineages. The new skeletal description supports placement within Rhinopristiformes, the order that includes living guitarfishes and sawfishes. Most parsimony, maximum-likelihood and Bayesian results recover that relationship, but the strict consensus of the parsimony search collapses the order-level relationships into a polytomy. The authors therefore leave its family uncertain and treat the order assignment as a well-supported working interpretation rather than a settled point in every analysis.

The skeletal record is consistent with a ray able to use freshwater and estuarine environments. It is the oldest known freshwater-tolerant representative of Rhinopristiformes in the 2026 study. This does not mean that all fossils came from a single salinity regime or that the species was restricted to rivers. Fluvial, estuarine and other marginal-water deposits record different parts of the Late Cretaceous landscape and can include transported remains.

Its broad tooth crowns remain useful for identifying isolated fossils. Their pavement-like arrangement suggests crushing or processing of firm food, but shape alone cannot specify a regular prey list. The 2019 Chilean material and later tooth studies also show why older names attached to isolated ray teeth need close comparison: similar crowns can vary with position in the mouth and across species.

Growth is recorded in the vertebrae

A separate study examined 117 fossil centra from the Oldman and Dinosaur Park formations of Alberta; 74 were sectioned for growth analysis. The researchers interpreted the visible bands as annual and estimated that the oldest sampled fish had lived about 16 years. The band pattern suggests that growth slowed after the early years, but the result describes a collected sample, not a proven maximum lifespan for every individual or population.

Centrum radius is not the same measurement as total body length. Without a reliable conversion for Myledaphus, the growth study cannot turn a count of rings into an exact adult length. The new skeleton gives body anatomy, while the centra provide a life-history estimate; together they improve the profile without removing the limits of either evidence set.

What a reconstruction can show

The articulated specimen supports a broad ray disc, a rostrum and the preserved arrangement of fin and girdle elements. It does not preserve the original colour, skin texture, full soft fin margins or a witnessed swimming posture. A reconstruction can use the observed skeleton and cautious comparison with living guitarfishes, but the family-level uncertainty means that fine details borrowed from one modern species should remain clearly interpretive.

Myledaphus is no longer merely a tooth name attached to a presumed guitarfish. Its near-complete skeleton gives researchers a basis for testing that relationship and for comparing freshwater-tolerant rays through time. The precise placement may change with additional specimens and analyses; the direct anatomy now available is the firmest starting point.

Explore related evidence in the ancient fish catalogue.