Science Literature

Over the years, samples of amber recovered from numerous sites around the world have been found to contain petrified insects, plants and a variety of other exotic inclusions. Invariably, we get an insight into a past world where the flora and fauna look very modern. A recent discovery has identified mammalian hair in amber, whose original owner was a contemporary of dinosaurs.

The shape and structure of mammal hair has remained unchanged since the Cretaceous (Source here)

The dimensions and topography of the two fossilised hairs were analysed carefully, because the find provides the first opportunity to look at Mesozoic mammal hairs preserved in 3D. The result:

"With such features, the cuticular surface of the Archingeay-Les Nouillers hairs shows a modern aspect, implying that the morphology of hair cuticula has remained unchanged throughout most of mammalian evolution."

The New Scientist report says this is the first time researchers have been able to study the pattern of scales on their surface:

"It turns out that the pattern is identical to that found on modern mammalian hair: rows of overlapping scales stacked on top of each other in an orderly fashion, with each row roughly 2 to 8 micrometres high. This discovery is "wonderful progress", says Zhe-Xi Luo, Curator of Vertebrate Paleontology at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania. "It shows the microstructure of hairs of mammals have always been the same.""

Why is this find worthy of comment? Many people have been brought up to think that the earlier we go back in the fossil record, the more strange the flora and fauna become. Whilst something can be said in favour of this view, it tends to hide the phenomenon of stasis. We do find animal radiations, diversification and extinction, but accompanying this change are pervasive evidences of continuity. The first mammals are thought to have appeared in the Late Triassic, and the first fossilised animal hair is dated as Late Jurassic (preserved as carbonized filaments). Now we find that the Early Cretaceous hair is essentially modern. It is an example of continuity across the geological Periods. It is an example of stasis. It is also an example of the abrupt appearance of complexity.

Mammals lived through the "Age of the Dinosaurs". As time goes on, it is apparent that the diversity of Mesozoic mammals is greater than used to be thought. An example is Castorocauda, from the Middle Jurassic Jiulongshan Formation of Inner Mongolia. This animal is well-preserved and shows specialisation in the fur:

"Castorocauda is preserved with a pelt (guard hairs and under furs), making it the most primitive-known mammal to be preserved with hairs. Carbonized in the fossil, the short and dense under-furs were to keep water from the skin; the longer guard hairs are preserved as impressions on the fossil slab." (Source here)

Mammals are now recognised to have occupied more varied ecological niches than was previously recognised. Castorocauda had specialized skeletal and soft-tissue features for swimming and teeth for eating fish. It is thought that many were ground-living, and a recent discovery is of mammals living in burrows and being prey to digging dinosaurs:

"Two fossilized burrows were spotted nearby. When compared with other burrows researchers have uncovered over the years, the size and complexity of these newfound ones suggest they belonged to mammals - the smaller burrow to a mouse-sized creature, the larger one to a guinea-pig-sized animal. The fact these fossils are so close together suggests they are evidence of dinosaurs scrabbling down to prey on mammals, the researchers suggested." (Source here)

It was a different world - but much that was present is still found today and a gradualist origin of complexity is not confirmed.

Mammalian hairs in Early Cretaceous amber
Romain Vullo, Vincent Girard, Dany Azar and Didier Neraudeau
Naturwissenschaften, 97(7), July 2010, 383-387 | doi 10.1007/s00114-010-0677-8

Abstract: Two mammalian hairs have been found in association with an empty puparium in a 100-million-year-old amber (Early Cretaceous) from France. Although hair is known to be an ancestral, ubiquitous feature in the crown Mammalia, the structure of Mesozoic hair has never been described. In contrast to fur and hair of some Jurassic and Cretaceous mammals preserved as carbonized filaments, the exceptional preservation of the fossils described here allows for the study of the cuticular structure. Results show the oldest direct evidence of hair with a modern scale pattern. This discovery implies that the morphology of hair cuticula may have remained unchanged throughout most of mammalian evolution. The association of these hairs with a possible fly puparium provides paleoecological information and indicates peculiar taphonomic conditions.