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 us ...
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
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 brai ...
, 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 ...
, 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'' i ...
. It is known from four specimens, each consisting of a partial lower jawbone collected from the
Wonthaggi Formation
The Wonthaggi Formation is an informal geological formation in Victoria, Australia whose strata date back to the Early Cretaceous. It is part of the Strzelecki Group within the Gippsland Basin. Dinosaur remains are among the fossils that have be ...
at Flat Rocks,
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
Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
. It lived during the late
Barremian
The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is preceded ...
age of the Lower
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
.
The
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
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
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
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
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 seve ...
is a partial left
dentary
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
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
The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone ...
is compressed and the
talonid
The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone ...
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
A condyle (;Entry "condyle" in ramus, 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
plesiomorph
In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades.
Plesiomorphy, symplesiomorphy, apomorphy, ...
ic 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
placental
Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguishe ...
s and
marsupial
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in ...
s, ''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
theria
Theria (; Greek: , wild beast) is a subclass of mammals amongst the Theriiformes. Theria includes the eutherians (including the placental mammals) and the metatherians (including the marsupials) but excludes the egg-laying monotremes.
...
ns.
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
See also
*
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.