New theory about the mass extinction of dinosaurs
The trend of putting a new spin on mass extinction theories continues unabated with the publication of a series of new books on the subject. One of these books suggests that stinging insects may have been the cause of the demise of the dinosaurs.
Extinction event sixty-five million years ago
When it comes to mass extinctions, the events that took place 65 million years ago and led to the eradication of dinosaurs, pterosaurs, marine reptiles, and about 65% of all life on Earth, undoubtedly garner the most attention. .
Recently, the Chicxulub impact theory first put forth in 1980 by the father and his team of Luis and Walter Alvarez was challenged by new evidence of volcanic activity in India: the effect of the Deccan Traps.
Now a number of new theories have been put forward regarding the cause or causes of the mass extinction event that took place at the end of the Cretaceous. For example, some scientists have postulated that changing terrestrial ecosystems, the diversification of angiosperms, and the rise of disease-carrying biting and sucking insects might have played a role in the downfall of the dinosaurs.
The rise and evolution of insects
A major contributor to the extinction of the dinosaurs might have been the rise and diversification of Insecta, especially the slow but overwhelming threat posed by new disease carriers. Midges and mosquitoes could have traveled long distances spreading diseases and other pathogens among dinosaur populations. These small sucking and biting insects could have played a significant role in the demise of these terrestrial vertebrates. Evidence of the rapid diversification of insects and other invertebrates such as arthropods has been preserved in fossilized tree sap: amber.
Problems with Sudden Extinction Theories of Dinosaurs
Commentators have stated that there are serious problems with sudden shock theories of dinosaur extinction. Although no dinosaur fossils have been found in younger rocks deposited in strata above the Cretaceous-Tertiary geologic boundary (the famous KT boundary of approximately 65 million years ago); scientists still debate the speed of the disappearance of the dinosaurs. There is evidence to suggest that the dinosaurs became extinct over a period of millions of thousands, even millions of years. This evidence conflicts with the theory of a sudden extinction caused by an alien impact event.
Researchers have spent many years studying microfossils and remains of insects and arthropods preserved from the Late Cretaceous. They theorize that although there were dramatic geological and climatic changes in the famous “KT Limit”these events alone do not explain what may have been a slow and gradual demise of Dinosauria.
Animal populations under stress
However, perhaps with animal populations under severe stress from such events, they may have weakened to such an extent that diseases and parasites spread by stinging/sucking insects and arthropods could have finally sent them off.
Scientists are not suggesting that the appearance of stinging insects and the spread of disease are the only things linked to the extinction of dinosaurs and pterosaurs. Other geological and catastrophic events certainly played a role. But such events alone do not explain a process that may actually have taken a long time, several million years, perhaps. Insects and disease provide that explanation, helping to wipe out the dinosaurs over an extended period of geological time.
Fossil amber has provided a number of Cretaceous insect fossils, perhaps these are to blame for the mass extinction event.
In the Late Cretaceous Period, often symbiotic or parasitic associations between members of the order Insecta and other small organisms and disease pathogens were just forming. Study of a species of biting insect (sand fly), discovered preserved in fifty-million-year-old amber, found traces of leishmania protozoa in the insect’s body cavity. This protozoan causes diseases in vertebrates by weakening the immune system, dinosaurs would surely have been affected if this type of protozoa had entered their bodies through insect bites.
In other insect specimens that have been preserved in fossilized tree resin, scientists have identified a form of the malaria parasite, one that readily infects lizards and birds today. As birds are thought to be the closest living relatives to dinosaurs, the evidence for Avian (bird) pathogens found in association with fossilized biting insects is particularly significant.
exploring coprolites
Microscopic analysis of fossilized dinosaur excrement (known as coprolite) has provided evidence of significant levels of parasites and bacteria living within the guts of these animals. Although some bacteria may have been helpful, forming a symbiotic relationship between themselves and the host, helping to break down cellulose in the stomach, for example, other organisms would have introduced disease.
In the lush jungles and rainforests of the late Cretaceous, insects, lice, and other parasites would have thrived, and perhaps these animals caused disease epidemics that helped weaken megafauna populations.
Several authors have given examples of vertebrate populations being decimated by the introduction of new pathogens. Many writers cite the case of avian malaria which, when introduced to the island of Hawaii, killed many of the native bird species. Although from our perspective this is a case of isolated animal communities being exposed to new pathogens, new diseases that they had not been exposed to before, with the consequence that they cannot develop any immunity within the species. Dinosaurs coexisted for millions of years with parasites and biting insects; the fossil record of animals from the Mesozoic is testimony to this.
The scientists propose that in addition to the parasitic effects on the dinosaurs, the ecosystem was being radically altered due to the rapid expansion of Angiosperms (flowering plants); partly due to the pollination activities of insects. Flowering plants seem to have been an evolutionary success story at the end of the Mesozoic with cycads, gingkoes and other gymnosperms being eclipsed by their more colorful plant competitors. But again, this process would have been quite gradual, giving herbivores a chance to adapt and exploit these new food sources. For example, some scientists have speculated that pachycephalosaurs may even have specialized as nibblers and foragers of flowering plants and shrubs, like many African gazelles today.
Insects have had a tremendous impact on the entire ecology of Earth, certainly shaping evolution and causing the extinction of terrestrial organisms. The largest of land animals, the dinosaurs, would have been engaged in a life and death struggle with them for their survival. Although it is quite a dramatic statement, a weakened population could have declined further due to the activities of parasites and other pathogens brought on by the increase in insects and arthropods. But then again, all organisms are in competition with each other, and it’s hard to believe that all of the large land fauna, including pterosaurs, could have succumbed to pests and diseases.
Insects have been linked to the demise of the dinosaurs numerous times. There was a book called “Before the Ark” published by the British Broadcasting Corporation (BBC) in 1975. The authors were Dr Alan Charig, Curator of Fossil Amphibians, Reptiles and Birds at the Natural History Museum, London, and Brenda Horsfield, television producer. The book accompanied a television documentary series on paleontology. In Chapter 13, titled “Fall of the Dinosaurs” Then, current theories about the extinction of the dinosaurs were discussed.
Did moths and butterflies kill off the dinosaurs?
One idea that was raised was that the rise and rapid expansion of the order Lepidoptera (moths and butterflies) wiped out the dinosaurs. The larval stages, the caterpillars with their voracious appetites consumed a lot of vegetation, causing the sudden collapse of food webs and the extinction of the megafauna on top of these food webs. A leafless ecosystem caused by caterpillars is a bit hard to stomach (no pun intended), after all, why did marine reptiles and ammonites also disappear? The birds would no doubt have detected a new food source and helped reduce caterpillar numbers, unless, of course, the larvae had already evolved complicated defenses to scare the birds away, like modern hawk moths, or had become nasty, like the cinnabar moths of the UK and Europe.
Had birds diversified and filled many ecological niches, they would surely have quickly exploited this new food source, and anyway Dr Charig and Ms Horsfield continue to cast considerable doubt on the validity of this theory, for example, the massive defoliation on such a scale would have left some sort of evidence within the fossil record. Palynomorphs: organic microfossils with walls, such as plant spores and pollen, indicate a dramatic change in vegetation at the KT boundary, the “fern spike”, but this adds credibility to the impact of a major environmental disaster such as an asteroid impact or massive volcanic activity. Ferns are often the first group of plants to recover, hence the large increase in fern spores that make up the microfossil record from about 65 million years ago.