Kryoryctes

Kryoryctes is a genus of prehistoric monotreme mammal from the Early Cretaceous (Albian) Eumeralla Formation[1] of Victoria, Australia, from the Otway Group of Dinosaur Cove. It is known only from a partial right humerus, estimated at 106 million years old, and contains one species, K. cadburyi. The holotype, NMV P20894, was described in 2005 and is currently housed in the Museum Victoria Palaeontological Collection.

Etymology
The genus name derives from Greek "kryo", meaning low temperature, in reference to the seasonal coldness common to the paleo-environment of Dinosaur Cove, and from the Greek "oryktes", meaning one who digs, referring to the robust humerus from which a fossorial lifestyle has been inferred. The species is named in honor of Cadbury chocolates, referring to the dark color of the holotype, as well as for the "recognition and support provided" by Cadbury chocolates during the field work that resulted in discovery of the specimen.

Morphology
K. cadburyi is distinguished by the authors from all extant monotremes, as well as from fossil tachyglossids, by the presence of a broad, marginated, shallow bicipital sulcus on the proximal humerus, which extends distally onto the waist of the bone. It is also distinguished by the presence of a trochlear-form ulnar articulation and a distal olecranon fossa. Pridmore et al find these features sufficient enough to distinguish it from Steropodon as well as other non-tachyglossid but similar monotremes such as Obdurodon, Kollikodon, Teinolophos and Monotrematum. The bone itself measures a total length of 46 mm, though the authors point out that it is likely missing around an eighth of its true length and suffers from some amount of abrasion, and estimate the original length at around 50 mm in life.[2]

Pridmore et al determined on the basis of the expanded distal and proximal ends of its humerus that the animal was likely adapted for a burrowing lifestyle.[2] In an analysis of the burrows made by prehistoric animals in 2009, Martin concluded that Kryoryctes, though the largest mammal known from the Lower Cretaceous of Victoria, was probably too small for most of the burrows in this area. They do point out that on the basis of its assignment by the authors as a burrowing animal, K. cadburyi may be postulated as a tracemaker for other fossilized burrow-like structures.