''Kryoryctes'' is a genus of prehistoric monotreme mammal from the Early Cretaceous (

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/ Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0 ...

)

Eumeralla Formation The Eumeralla Formation is a geological formation in Victoria, Australia whose strata date back to the Early Cretaceous. It is Aptian to Albian in age. Dinosaur remains are among the fossils that have been recovered from the formation, particularl ...

Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seychelle ...

, Australia from the Otway Group of

Dinosaur Cove The Dinosaur Cove in Victoria, Australia is a fossil-bearing site in the south-east of the continent where the Otway Ranges meet the sea to the west of Cape Otway, adjacent to Great Otway National Park (''map''). The inaccessible ocean-front clif ...

. It is known only from a partial right humerus, estimated at 106 million years old, and contains one species, ''K. cadburyi''. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

, NMV P20894, was described in 2005 and is currently housed in the

Museums Victoria Museums Victoria is an organisation which operates three major state-owned museums in Melbourne, Victoria: the Melbourne Museum, the Immigration Museum and Scienceworks Museum. It also manages the Royal Exhibition Building and a storage faci ...

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 honour of Cadbury

chocolate Chocolate is a food made from roasted and ground cacao seed kernels that is available as a liquid, solid, or paste, either on its own or as a flavoring agent in other foods. Cacao has been consumed in some form since at least the Olmec civ ...

s, referring to the dark colour 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

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

r articulation and a distal

olecranon fossa The olecranon fossa is a deep triangular depression on the posterior side of the humerus, superior to the trochlea. It provides space for the olecranon of the ulna during extension of the forearm. Structure The olecranon fossa is located on ...

. Pridmore ''et al'' find these features sufficient to distinguish it from ''

Steropodon ''Steropodon'' is a genus of prehistoric monotreme, or egg-laying mammal. It contains a single species, ''Steropodon galmani'', that lived about 105 to 93.3 million years ago (mya) in the Early to Late Cretaceous period. It is one of the oldest m ...

'' as well as other non-tachyglossid but similar monotremes such as '' Obdurodon'', ''

Kollikodon ''Kollikodon'' is an extinct species of mammal, it is usually considered to be a member of Australosphenida and closely allied with monotremes, but is alternatively suggested to be a haramiyidan. It is known only from an opalised dentary fragment ...

'', ''

Teinolophos ''Teinolophos'' is a prehistoric species of monotreme, or egg-laying mammal, from the Teinolophidae. It is known from four specimens, each consisting of a partial lower jawbone collected from the Wonthaggi Formation at Flat Rocks, Victoria, Aus ...

'' 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. 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. 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 Lower may refer to: *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is situated about five miles south west of Dursley, eig ...

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 fossilised burrow-like structures.

Evolution

The authors note that the humerus appears to be similar in morphology to extant tachyglossids, but have not explicitly allied it with echidnas based on a number of important elements which differ between it and all known members of the family. They conclude that if ''K. cadburyi'' is in fact a monotreme, it is likely a stem-monotreme. This affinity was disputed in 2009 by Canens ''et al'', which allied ''K. cadburyi'' more closely with echidnas. This analysis was rejected in turn by a further analysis by Phillips, Bennett and Lee in 2010, which found it again to be distinct from tachyglossids, though they do reiterate that there is some possibility that the humerus attributed to ''K. cadburyi'' could belong to the contemporaneous stem-monotreme ''Steropodon'', which is similarly-sized.

References

{{Taxonbar, from=Q6439677 Prehistoric monotremes Cretaceous mammals of Australia Prehistoric mammal genera Fossil taxa described in 2005