Sinoconodon rigneyi is an ancient proto-mammal that appears in the fossil record in the late Triassic period, about 208 million years ago. Although the animal seems more related to Morganucodon than anything else, it differed substantially from other Mammaliaformes in its dental and growth habits. Similar to reptiles, it replaced many of its teeth (its incisors, canines, and postcanines) throughout its lifetime (polyphydont), and it seems to have grown slowly but continuously until its death.

Therefore, Sinoconodon is generally considered more primitive (less mammalian) than related Mammaliaformes, including docodonts and morganucodonts, which appear a few million years later. Some label it the most primitive mammal taxon, while others do not label it a mammal at all.

[edit] References

• Luo, Z.-X., Z. Kielan-Jaworowska, and R.L. Cifelli (2001). In quest for a phylogeny of Mesozoic mammals. Acta Palaeleon. Pol. 47:1-78

[edit] External links

• Abstracts from Publications by Dr. Luo
• Mammaliformes from Palaeos
• Mammals of the Mesozoic: The least mammal-like mammals

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