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
Description:
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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