Diminutive Dinosaur Era Mammal

Part and Counterpart Specimen

Mammalia indet

Geologic Time: Late Jurassic/Early Cretaceous

Size (25.4 mm = 1 inch): Vertebral Column (30 mm) limbs: 20 mm (if straight) Matrix 90 mm by 65 mm and 85 mm by 65 mm pair

Fossil Site: Yixian Formation, Shangheshou, Chaoyang, Liaoning Province, China

Code: CF490

Price: Sold

Dinosaur Era Mammal FossilDescription: The conventional view of mammals during the Mesozoic has been of tiny shrew-like animals that scurried at the feet of the dinosaurs, relegated to coming out only at night when “the coast was clear”. In 2000, the discovery of a new mammal from the Yixian Formation of Liaoning Province, China known as Repenomamus belied that tiny scurrying animal paradigm. Two species were discovered: Repenomamus giganticus, a dog-sized animal, and Repenomamus robustus, about the size of a modern-day Opossum. R. robustus weighed some 5 kg, and was 50 cm or so in overall length. In 2005, a specimen was found in which the remains of a hatchling Psittacosaurus were contained within the body cavity. This one is more in keeping with the original concept of dinosaur era, mammals: a small shrew –sized representative. When I first saw photos of this specimen, I was unsure whether it showed the remains of a small mammal or a lizard. The distinction was easily made by the phlangeal formula of the digits in that here there are no more than 3 phalanges per digit (formula 2,3,3,3,3) while reptiles have 2, 3, 4, or 5 in the formula 2,3,4,4,5. At any rate, the fact that these were preserved pretty much in the natural articulation shows that the specimen was buried rapidly. Preservation of such a small specimen is a truly rare event. I have never been able to offer its like in thirteen years.

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