Jurassic mammals

The tiny lower jawbones from three different kinds of mole-sized mammals were also found in the Stonesfield Oolites of Oxfordshire. Although biologically important, the discovery of these mammal fossils and any publicity associated with them was largely eclipsed by greater interest in the much more exotic extinct reptiles. The small size of the mammal fossils contributed to their lack of allure. Subsequent discoveries of early mammals have verified the fact that the first mammals were all small, shrew to hedgehog-sized creatures. Like the poet Robert Burns's 'wee, sleekit, cow'rin, tim'rous beastie', these tiny Jurassic mammals would probably also have suffered the 'panic in thy breastie', and would need to be able to 'start awa sae hasty', considering the company they kept. Their world was populated by an enormous diversity of reptiles, not only dinosaurs of all sizes.

Cuvier also cast his expert eye over these fossils during his Oxford visit of 1818 and thought that they belonged to marsupial mammals, but noted that they differed from living marsupials and all known mammals in having 10 molar cheek teeth. One of the specimens was illustrated and described as a fossil marsupial with the name Thylacotherium by the French palaeontologist Constant Prévost in 1825. Richard Owen pointed out that the jawbone must belong to an extinct genus because of the number of molars. He also claimed that it might have an affinity with the newly discovered numbat, a squirrel-shaped, termite-eating marsupial technically known as Myrmecobius, which was first found in a hollow tree, surrounded by anthills, near the Swan River in southeast Australia. The mid-nineteenth century was a great period of biological discovery, with new animals and plants being found all over the world and brought back to fill the new natural history museums of the great metropolitan centres of the western world.

When another, better-preserved fossil jaw was found at Stonesfield, Richard Owen was able to show that Thylacotherium was not a marsupial but rather a placental insectivore. He renamed it Amphitherium in 1846, although it does

Constant Prévost, 1787-1856, French student of medicine who, encouraged by Brongniart Sr., turned palaeontologist and professor of geology at the Sorbonne, collaborated with Lyell and was co-founder of the Geological Society of France in 1830.

preserve some features similar to the marsupials. The other Stonesfield specimen, Phascolotherium, seemed to him to be a genuine marsupial.

Charles Lyell, in 1853, was so impressed by the occurrence of 'these most ancient memorials of the mammiferous type ... in so low a member of the oolitic series. (They) ... should serve as a warning to us against hasty generalisations, founded solely on negative evidence.' He eventually gets to the point:

it seems fatal to the theory of progressive development, or to the notion that the order of precedence in the creation of animals, considered chronologically, has precisely coincided with the order in which they would be ranked according to perfection or complexity of structure.

Remember that this was before the Darwin/Wallace theory of evolution and Lyell was, at this stage, arguing against any idea of progressive development. He thought that the fossil record of most groups of animals and plants would eventually be found to extend back to some common starting point (act of creation) in the earliest Transition strata, which were later named as Cambrian by Adam Sedgwick.

However, what had been clearly established in the early decades of the nineteenth century was that although life on land during Jurassic times was dominated by the dinosaurs, the mammals were also present. This important discovery tended to be overlooked until relatively recent times, partly because the mammals were very small and their fossils extremely rare, and partly because the dinosaurs and their reptilian relatives were much larger and, perhaps more importantly, much more spectacular. As we shall see, this view of prehistoric life was reinforced by the creation in London in 1851 of the world's first theme park with life-size models of dinosaurs.

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