''Teinolophos'' is a

prehistoric Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the beginning of recorded history with the invention of writing systems. The use of ...

species of

monotreme Monotremes () are prototherian mammals of the order Monotremata. They are one of the three groups of living mammals, along with placentals (Eutheria), and marsupials (Metatheria). Monotremes are typified by structural differences in their brain ...

, or egg-laying

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

, from the

Teinolophidae Teinolophidae is an extinct family of small, carnivorous mammals that were the earliest known monotremes and were endemic to what would become Australia. Two genera are known: ''Teinolophos'', and possibly also '' Stirtodon''. ''Teinolophos'' is ...

. It is known from four specimens, each consisting of a partial lower jawbone collected from the Wonthaggi Formation at Flat Rocks, Victoria,

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

. It lived during the late Barremian age of the Lower Cretaceous. The species name honours the artist

Peter Trusler Peter Trusler (born 1954) is an Australian artist known for his work on wildlife art, as well as for his scientifically rigorous reconstructions of prehistoric fauna. Trusler's artwork is featured in numerous books and scientific publications, a ...

. The genus name, ''Teinolophos'', means "extended ridge", a reference to its tooth structure. Originally, ''Teinolophos'' was thought to be a eupantothere. Further research revealed similarities to '' Steropodon'', except in size: the animal was around 10 cm long. It is often listed as a steropodontid, though it may be more basal.Thomas H. Rich, James A. Hopson, Pamela G. Gill, Peter Trusler, Sally Rogers-Davidson, Steve Morton, Richard L. Cifelli, David Pickering, Lesley Kool, Karen Siu, Flame A. Burgmann, Tim Senden, Alistair R. Evans, Barbara E. Wagstaff, Doris Seegets-Villiers, Ian J. Corfe, Timothy F. Flannery, Ken Walker, Anne M. Musser, Michael Archer, Rebecca Pian and Patricia Vickers-Rich (2016). "The mandible and dentition of the Early Cretaceous monotreme Teinolophos trusleri". Alcheringa: An Australasian Journal of Palaeontology. in press. doi:10.1080/03115518.2016.1180034. ''Teinolophos'' is deeply divergent within monotreme evolution, so in 2022 it was proposed to move it into its own family, Teinolophidae. '' Stirtodon'' may be close relative of ''Steropodon'' within Teinolophidae. The holotype is a partial left dentary known as NMV P208231. An age of approximately 123 million years makes this the earliest known monotreme. The lower molar is broadly similar in morphology to the m2 of ''Steropodon''. The trigonid is compressed and the talonid has no basin. The dentary is about one sixth the size of ''Steropodon'', and wear facets indicate an "orthal" occlusion with the upper molars.

Description

Jaw

The construction of the lower jaw differs from existing monotremes. Among the contrasts are the condyle, which is well above the tooth row (instead of at about the same height); and the ascending

ramus Ramus can refer to: * A branch (botany) * A portion of a bone (from Latin ''ramus'', "branch"), as in the Ramus of the mandible or Superior pubic ramus * A nerve ramus such as the Dorsal ramus of spinal nerve * A taxonomic rank ("branch" in English ...

, which is also higher. Also different is that ''Teinolophos'' probably had a strong bite. A unique feature for known toothed monotremes is that the trigonid is tall, while the talonid is set much lower. This is more like the general mammalian arrangement. The molar is double-rooted, which is plesiomorphic when compared to ornithorhynchids, but is a shared characteristic with ''Steropodon'' and '' Kollikodon''. Subsequent monotreme molars are multi-rooted. Unlike modern monotremes, ''Teinolophos'' lacked a beak.

Ears

Unlike modern monotremes, which have suspended ear bones much like placentals and marsupials, ''Teinolophos'' still had them connected to the jaw via the Meckel's cartilage. This reinforces the idea that the modern ear condition evolved independently among monotremes and therians.

Evolution

One study interpreted ''Teinolophos'' as a basal platypus.Rowe, T., Rich, T. H., Vickers-Rich, P., Springer, M., & Woodburne, M. O. (2008). The oldest platypus and its bearing on divergence timing of the platypus and echidna clades. Proceedings of the National Academy of Sciences, 105(4), 1238-1242. doi:10.1073/pnas.0706385105

References

Bibliography

* Rich ''et al.'' "Early Cretaceous Mammals from Flat Rocks, Victoria, Australia". Records of the Queen Victoria Museum, Launceston (1999). * Rich, T. H., ''et al.'' "Monotreme nature of the Australian Early Cretaceous mammal Teinolophos". ''Acta Palaeontologica Polonica'' 46(1). 2001 Pages 113–118. * Rowe, T., ''et al.'' "The oldest platypus and its bearing on divergence timing of the platypus and echidna clades". ''Proceedings of the National Academy of Sciences'' 105(4). 2008 Pages 1238–1242.

External links

Life in the Shadows, Non-reptilian life in Mesozoic Australia

"Prehistoric jawbone reveals evolution repeating itself"
10 February 2005
"The oldest platypus and its bearing on divergence timing of the platypus and echidna clades"
2008 {{Taxonbar, from=Q133024 Prehistoric monotremes Prehistoric mammal genera Aptian life Cretaceous mammals of Australia Fossils of Australia Fossil taxa described in 1999 Taxa named by Tom Rich