| Kuehneotherium Fossil range: Norian - Sinemurian | |
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| Scientific classification
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Kuehneotherium | |
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Kuehneotherium was an early symmetrodont whose fossils have been found in Greenland, France and Luxembourg. It is known only from an upper molar as well as nine additional teeth and four dentary fragments.
Species[]
Remains of Kuehneotherium praecursoris have been found in the Pontalun Quarry in a single fissure pocket in South Wales. The deposit found in limestone is from the Late Triassic. (Whiteside and Marshall 2008) Additional Kuehneotherium fossils have been found in rock formations of the Early Jurassic of Britain (Somerset), and the Late Triassic of France (Saint-Nicolas-de-Porte), Luxembourg, and Greenland; the Kuehneotherium specimens for Saint-Nicolas-de-Porte have been named K. stanislavi.
Phylogeny[]
The phylogenetic position for Kuehneotherium has been widely debated. Kuehneotherium was once classified as a therian mammal (the common ancestor of marsupials, placentals, and their descendants). However, additional fossils of basal mammals have been found that predate the Kuehneotherium on the geological timescale and the relationships of early mammals were re-evaluated. Kuehneotherium is now placed in the more basal clade called Holotheria. Kuehneotherium preacursoris is the earliest mammal categorized as holotherian. Holotheria includes species in which the main and accessory molar cusps are arranged in a triangle. Kuehneotherium’s place in Holotheria is considered unstable, as it is difficult to determine a species characteristics based upon only mandible and dental fragments.
Phylogeny (Zofia Kielan-Jaworowska et al., 2002)
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Significance to the evolution of mammalian dentition[]
Study of the initial development of molar cusp triangulation in Kuehneotherium preacursoris was key in the early understanding of the transition between triconodont and crown therian molars.
Kuehneotherium dentition shows a significant link between mammaliaform triconodont shaped teeth used for in a puncture-crushing pattern, to modern crown therian molars that chew vertically and chew horizontally. Therian mammals such as marsupials and placentals shared a common ancestor that was characterized by an upper molar with three main cusps arranged in a triangle that fits into the lower molar that has a reversed triangle and basin-like heel. Later discovery of the earlier more basal mammal Woutersia, provided additional information on this dental transition. Kuehneotherium, like other mammals had 2 sets of teeth during its life. It is speculated that they may have had up to 6 lower molars with the last molar being added to the back later in life. The evidence for this is that the post canine tooth row shifts backwards as the animal grew. They had 5-6 premolars; the first four premolars are single rooted. Anterior premolars would have been shed in late adulthood and not replaced. The lower jaw is a more basal morphology with a prominent postdentary groove where more developed postdentary bones would attach. The enamel microstructures of Kuehneotherium teeth were synapsid columnar enamel characterized by a pattern of columnar, prism-less structures.
Metabolism[]
External links[]
Further Reading[]
- Zofia Kielan-Jaworowska, Richard L. Cifelli, and Zhe-Xi Luo, Mammals from the Age of Dinosaurs: Origins, Evolution, and Structure (New York: Columbia University Press, 2004), 361-362.