Temporal range: Upper Jurassic
Its fossil was found in lakebed sediments of the Daohugou Beds of Inner Mongolia. Castorocauda was highly specialized, with adaptations like those of modern semi-aquatic mammals such as beavers, otters, and the platypus (convergent evolution). It is the earliest animal found with fur.
Although Castorocauda was not a crown group mammal, it is important in the study of how mammals evolved. It was the first find with an almost complete skeleton. Also it is not a "small nocturnal insectivore".
- It was larger than most Mesozoic mammaliaform fossils – about 17 in (43 cm) from its nose to the tip of its 5-inch (130 mm) tail, and may have weighed 500–800 g (18–28 oz).
- It is the earliest absolutely certain evidence of hair and fur. Previously the earliest was Eomaia, a crown group mammal from about 125M years ago.
- It had aquatic adaptations including flattened tail bones and remnants of soft tissue between the toes of the back feet, suggesting that they were webbed. Previously the earliest known semi-aquatic mammaliaforms were from the Eocene, about 110 million years later.
- Castorocauda's powerful forelimbs look adapted for digging. This feature and the spurs on its ankles make it resemble the platypus, which also swims and digs.
- Its teeth look adapted for eating fish: the first two molars had cusps in a straight row, which made them more suitable for gripping and slicing than for grinding. These molars are curved backwards, which helps in grasping slippery prey.
References[change | change source]
- "Jurassic "beaver" found; rewrites history of mammals".
- Ji, Q.; Luo Z-X, Yuan C-X, and Tabrum A.R. (2006). "A swimming mammaliaform from the Middle Jurassic and ecomorphological diversification of early mammals". Science 311 (5764): 1123. doi:10.1126/science.1123026. PMID 16497926. http://www.sciencemag.org/cgi/content/abstract/311/5764/1123.