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Recensione sul libro: WHAT BUGGED THE DINOSAURS ? (Cosa morse i dinosauri ?)
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ITA: What bugged the Dinosaurs ?, Ordina da IBS Italia



November 7, 2008

Flies in the Cretaceous ointment

Did bloodsucking insects do for the dinosaurs?

Textbooks of fifty years ago contained imaginative reconstructions of mid-Cretaceous landscapes, with tree ferns, cycads and primitive conifers. Wandering through these were happy browsing bands of herbivorous dinosaurs with, in the background, a tyrannosaur picking off the stragglers and, in the foreground, a lurking small mammal and a few primitive angiosperms waiting to inherit the Earth. This simplistic and two-dimensional image was reasonable. Our knowledge of the period was based on, for the most part, fossils of large and robust organisms – big vertebrates, big plants with big leaves, molluscs and things with hard shells. The smaller and softer an organism is, the more elusive become the chances of its fossilization in a recognizable form. That is, if we are considering fossilization in mud or silt to yield the familiar rock-based fossils. But a different form of fossilization does preserve the small and the weak. The oozing resins and sap of certain coniferous and leguminous trees act as a sticky-trap, enveloping and preserving pollen, small flowers, fungi, insects and a host of organic minutiae in what, over time, will eventually become amber. Amber fossils can sometimes be almost as good as having the actual specimen under the microscope. The most familiar amber is Baltic amber, which dates from 55 million years ago, well this side of the K-T boundary. It is the familiar amber used in jewellery. Baltic amber is abundant and its fossil inclusions give an extensive picture of the biota that collided with or fell into resin at the time. Cretaceous amber is much rarer and there are three major sources. The oldest is Lebanese amber, from 130–135 million years ago; the mid-Cretaceous deposits are Burmese (100–105 mya), and the youngest Cretaceous amber is Canadian (72–78 mya). Knowledge of the fossils of Cretaceous ambers is recent compared with that of Baltic amber, and has been enhanced greatly by modern advances in optics, microscopy and digital image processing. The fossil record is, of course, an incomplete sample. Compared with the potential number of species that may have inhabited the Cretaceous forests, we have fossils of very, very few. Not only is the fossil record incomplete, but it needs to be treated with scepticism, for much of it, especially that involving very small organisms, is flawed. That said, careful examination of the amber fossils of the Cretaceous allows extrapolation with some degree of authority. George and Roberta Poinar work on Cretaceous amber and the organisms that are preserved in it. And their ambitious foray in What Bugged the Dinosaurs? is to flesh out the simple picture of Cretaceous life and look at the possible interrelationships between dinosaurs, plants, insects and pathogens, using evidence from amber and other fossils. Much of our knowledge of the smaller organisms that did or could have interacted with dinosaurs is very recent, and some is startling in its detail. The excellent colour pictures of fossil insects in Cretaceous amber are spectacular and evocative. This book makes clear that a host of invertebrates competed with dinosaurs for food, were no doubt preyed upon in turn, and acted as camp followers. Large herds of dinosaurs would have provided extensive and complex microhabitats for invertebrates – Cretaceous beetles almost certainly would have rolled dinosaur dung. With a large sauropod producing one and a half tons a day (extrapolating from elephant and rhinoceros), there would have been no shortage. And dead dinosaurs would have provided carcasses for flies and carrion beetles; there are plenty of these in the fossil record, and there is fossil evidence of dermestid beetles feeding on dead dinosaurs. Living dinosaurs would have been prey – the Cretaceous had very much the same diversity of insects, mites and ticks that bit, gouged, scratched, scraped and jabbed to feed on skin and blood as would attack a herd of buffalo today. And the few large reptiles that we have left on the Earth are models for other examples of the possible victimhood of Cretaceous reptiles at the mercy of invertebrate pests, parasites and diseases. Many of the biting insects – midges, sandflies, mosquitoes, blackflies and horseflies – that targeted the vertebrates of the Cretaceous are familiar to us, at least at family or subfamily level; but others are not – the remarkable long-legged flealike Saurophthirus has been suggested to have fed on blood sucked from the membrane of pterosaur wings, but the Poinars suggest it may well have been adapted to straddle the scales of dinosaurs and drive the proboscis into the skin between pairs of scales. This book shows that bloodsucking insects were well-established in the age of dinosaurs, and they were the groups of insects that we think of today as vectors of a wide range of diseases. It is in the area of parasites and pathogens that this book startles. The vector insects to transmit these were there, a fact undisputed. And it is easy to assume that dinosaurs had diseases and parasites much as large vertebrates do today, but proving it is another matter. Yet the Poinars and their collaborators have done so. Their pièce de résistance is the demonstration of Leishmania, a minute parasitic worm that infects vertebrates (including, nowadays, man) in Cretaceous sandflies, together with a reptile-blood meal. This observation, unlike many in palaeontology, proved repeatable, as there were multiple examples of sandflies fossilized in amber. The Poinars’ current score is twenty-one fossil sandflies, ten of which were carrying and potentially transmitting Leishmania. Further, a biting midge has been shown to be carrying a malaria-like organism, and another contains the characteristic minute polyhedra that are clumped reo-viruses, a group that includes the pathogenic arboviruses. Dinosaurs were diseased. What Bugged the Dinosaurs? concludes with a careful but speculative discussion of faunal change, extinction, and the importance of the evolutionary arms race between predators, parasites, pathogens and their prey. The underlying question is whether the dinosaurs (those that were not destined to become today’s birds) were wiped out in a flash with the asteroid impact at the K-T boundary or whether, losers in the arms race, their decline had begun long before, and that a combination of factors, of which the asteroid impact was just one, were the last straws. Occasionally guilty of Jurassic Park hyperbole, especially in the imaginary scenarios narrated at the beginning of many chapters, and guilty of perhaps a little too much speculation and extrapolation, this book nevertheless succeeds in its aims. It opens doors and invites questions, as speculation should do. And the accounts of the scientific endeavours cannot fail to impress. I should like to have learned more of the observational techniques used, for the Poinars have seen through an amber window into a long-vanished world. They have seen a slice of long-gone time frozen in orange-brown resin. They have seen tiny, magical things. And we should be told how the trick is done. George Poinar Jr and Roberta Poinar WHAT BUGGED THE DINOSAURS? Insects, disease, and death in the Cretaceous 294pp. Princeton University Press. £17.95 (US $29.95). 978 0 691 12431 5 Gaden S. Robinson researches small tropical moths at the Natural History Museum, London. His latest monograph, on the genus Edosa in South-East Asia, is published in the current issue of Systematics and Biodiversity. He is the winner of the Karl Jordan Medal, 2008, awarded by the Lepidopterists’ Society for a lifetime’s contribution to research on Lepidoptera. source:  Support the blog, buy the book on my amazon associated shops: USAUK


novembre 10, 2008 - Posted by | - R. Dinosauri, Libri / Books, Paleontology / Paleontologia | , , , , , , , ,

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