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Kryoryctes
Holotype humerus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Monotremata
Family:	†Kollikodontidae (?)
Genus:	†Kryoryctes Pridmore, Rich, Vickers-Rich & Gambaryan, 2005
Species:	†K. cadburyi
Binomial name
†Kryoryctes cadburyi Pridmore et al., 2005

Kryoryctes is a genus of prehistoric monotreme mammal from the Early Cretaceous (Albian) Eumeralla Formation 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, Kryoryctes cadburyi. The holotype, NMV P208094, was described in 2005 and is currently housed in the Museums 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 honour of Cadbury chocolates, 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

Kryoryctes 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 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 (1.8 in), 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 (2.0 in) 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 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.

Taxonomy

The humerus was first noted to be similar in morphology to extant tachyglossids, but Kryoryctes is not allied it with this clade based on a number of important elements which differ between it and all known members of the family. As such, it can more appropriately be interpreted as 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. More recently, researchers have suggested a possible synonymy of Kryoryctes with the coeval Sundrius, a putative kollikodont. While this can not be proven due to a lack of fossil material, close affinities of Kryoryctes with Sundrius and Kollikodon are not implausible.

References

1. Kear, Benjamin A.; Hamilton-Bruce, Robert J. (2011), Dinosaurs in Australia: Mesozoic Life from the Southern Continent, CSIRO Publishing, p. 134, ISBN 978-0643100459
2. ^ Pridmore, Peter A.; et al. (December 2005), "A Tachyglossid-Like Humerus from the Early Cretaceous of South-Eastern Australia", Journal of Mammalian Evolution, 12 (3–4): 359–378, doi:10.1007/s10914-005-6959-9, S2CID 22931124
3. Martin, Anthony J. (June 2009), "Dinosaur burrows in the Otway Group (Albian) of Victoria, Australia, and their relation of Cretaceous polar environments", Cretaceous Research, 30 (5): 1223–1237, doi:10.1016/j.cretres.2009.06.003
4. Camens, AB (2009), "Were early Tertiary monotremes really all aquatic? Inferring palaeobiology and phylogeny from a depauperate fossil record.", Proc Natl Acad Sci USA, 107 (4): E12, doi:10.1073/pnas.0912404107, PMC 2824403, PMID 20133883
5. Phillips, Matthew J.; et al. (2010), "Reply to Camens: How recently did modern monotremes diversify?", Proc Natl Acad Sci USA, 107:E13 (4): E13, Bibcode:2010PNAS..107E..13P, doi:10.1073/pnas.0913152107, PMC 2824408
6. Flannery, Timothy F.; Rich, Thomas H.; Vickers-Rich, Patricia; Ziegler, Tim; Veatch, E. Grace; Helgen, Kristofer M. (2022-01-02). "A review of monotreme (Monotremata) evolution". Alcheringa: An Australasian Journal of Palaeontology. 46 (1): 3–20. doi:10.1080/03115518.2022.2025900. ISSN 0311-5518.
7. Poropat, Stephen F.; Bell, Phil R.; Hart, Lachlan J.; Salisbury, Steven W.; Kear, Benjamin P. (2023-04-03). "An annotated checklist of Australian Mesozoic tetrapods". Alcheringa: An Australasian Journal of Palaeontology. 47 (2): 129–205. doi:10.1080/03115518.2023.2228367. hdl:20.500.11937/96166. ISSN 0311-5518.

v t e Mammalia
Kingdom: Animalia Phylum: Chordata Clade: Synapsida Clade: Therapsida Clade: Cynodontia Clade: Mammaliaformes Synapsida see Synapsida Cynodontia see Cynodontia Mammalia see below↓
Mammalia Australosphenida? †Ambondro †Tendagurutherium? Monotremata? †Henosferidae Asfaltomylos Henosferus †Ausktribosphenidae Ausktribosphenos Bishops? Kryoparvus? Monotremata †Kollikodontidae? Kollikodon Kryoryctes? Sundrius †Steropodontidae Parvopalus? Steropodon †Teinolophidae Stirtodon? Teinolophos Ornithorhynchoidea †Opalios Ornithorhynchidae †Dharragarra? †Monotrematum? †Obdurodon Ornithorhynchus †Patagorhynchus? Tachyglossidae †Megalibgwilia †Murrayglossus Tachyglossus Zaglossus †Allotheria? see Allotheria includes multituberculates Theriimorpha see below↓
Theriimorpha Theriimorpha †Acinacodus †Amphidon †Amphilestes †Aploconodon †Chaoyangodens †Comodon †Condorodon †Dyskritodon? †Fruitafossor? †Hakusanodon †Indotriconodon †Juchilestes †Jueconodon †Kemchugia †Kryptotherium †Liaoconodon †Liaotherium †Manchurodon †Nakunodon †Phascolotherium †Sangarotherium †Tendagurodon †Allotheria? Monotremata? †Gobiconodontidae Fuxinoconodon Gobiconodon Hangjinia Huasteconodon? Meemannodon Repenomamus Spinolestes †Jeholodentidae Jeholodens Yanoconodon †Klameliidae? Ferganodon Klamelia †Triconodontidae Alticonodon Arundelconodon Astroconodon Corviconodon Eotriconodon Jugulator Meiconodon Priacodon Triconodon Trioracodon Victoriaconodon Volaticotheria? †Volaticotheria Argentoconodon Ichthyoconodon Triconolestes? Volaticotherium †Tinodontidae Gobiotheriodon? Tinodon Trishulotherium Yermakia Trechnotheria Monotremata? †Zhangheotheriidae Anebodon Kiyatherium Maotherium Ningchengodon Origolestes Zhangheotherium †Spalacotheriidae Akidolestes Aliaga Cifellitherium Heishanlestes Infernolestes Lactodens Shalbaatar Spalacolestes Spalacotheridium Spalacotherium Spalacotheroides Symmetrodontoides Symmetrolestes Yaverlestes Cladotheria see below↓
Cladotheria †Dryolestida Brancatherulum? Dorsetodon Drescheratherium Euthlastus Henkelotherium Paurodon Tathiodon Dryolestidae Achyrodon Amblotherium Anthracolestes Beckumia Crusafontia Dryolestes Groebertherium? Guimarotodus Hercynodon Krebsotherium Lakotalestes? Laolestes Minutolestes Phascolestes Portopinheirodon Treslagosodon †Meridiolestida Amarillodon Austrotriconodon Bondesius Casamiquelia Cronopio Groebertherium? Lakotalestes? Leonardus Necrolestes Paraungulatum Quirogatherium Solanutherium Mesungulatoidea Coloniatherium Mesungulatum Orretherium Peligrotherium Reigitherium †Donodontidae Amazighodon Anoualestes Donodon Stylodens Prototribosphenida †Abelodon †Amphibetulimus †Amphitherium †Arguimus †Brancatherulum? †Chunnelodon †Magnimus †Minimus †Mozomus †Nanolestes †Palaeoxonodon †Vincelestes Monotremata? †Peramuridae Afriquiamus? Kouriogenys Peramuroides Peramus Tendagurutherium? Tribosphenida / Boreosphenida †Aegialodon †Argaliatherium †Brasilestes †Carinalestes †Eomaia †Holoclemensia †Hypomylos †Juramaia †Kermackia †Kielantherium †Pappotherium †Picopsis †Tirotherium †Tribactonodon Theria †Patagomaia Eutheria see Eutheria includes placentals Metatheria see Metatheria includes marsupials
Other taxa Incertae sedis †Atlasodon †Chronoperates †Microderson †Thereuodon †Tingamarra Saint Bathans Mammal UA 8699 Other taxa Prototheria Yinotheria Eutriconodonta Amphilestidae Theriiformes Pantotheria Symmetrodonta Eupantotheria Paurodontidae Amphitheriidae Marsupionta

• Prehistoric monotremes
• Cretaceous mammals of Australia
• Prehistoric mammal genera
• Fossil taxa described in 2005
• Monotypic prehistoric mammal genera