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Did insects take down T. rex?

Jan. 4, 2008
Courtesy Oregon State University
and World Science staff

Most lead­ing the­o­ries on how di­no­saurs died out fo­cus on as­ter­oid im­pacts or mas­sive vol­can­ism. But a new book blames a much less thun­der­ous force: in­sects.

The rise and evo­lu­tion of these bugs—the bit­ing dis­ease-carriers, in par­ti­cu­lar—co­in­cided fate­fully with the mighty rep­tiles’ lat­er days, write George Po­inar Jr. of Or­e­gon State Un­ivers­ity and his wife Ro­ber­ta in the book, “What Bugged the Di­no­saurs? In­sects, Dis­ease and Death in the Cre­ta­ceous.” 

A Cretaceous-era insect preserved in amber (courtesy G. & R. Poinar)


The Poinars say the ev­i­dence is pre­served in life­like detail, in the form of var­ied in­sects trapped in an­cient am­ber. 

“There are se­ri­ous prob­lems with the sudden-im­pact the­o­ries of di­no­saur ex­tinc­tion, not the least of which is that di­no­saurs de­clined and dis­ap­peared over a pe­ri­od of hun­dreds of thou­sands, or even mil­lions of years,” said George Poi­nar. 

He didn’t deny that there is ev­i­dence for cat­a­stroph­ic events such as an as­ter­oid strike or la­va flows around that time. These “cer­tain­ly played a role” in the die­off, but don’t ac­count for its slow­ness, said Poi­nar, an en­to­mo­log­ist. 

On the oth­er hand, he added, “com­pe­ti­tion with in­sects, emerg­ing new dis­eases and the spread of flow­er­ing plants over very long pe­ri­ods of time is per­fectly com­pat­ible with ever­ything we know about di­no­saur ex­tinc­tion.” Pests and ill­ness may have sub­jected T. rex and its scaly kin to a slow­er tor­ment, but pos­sibly the fa­tal one ul­tim­ate­ly, ac­cord­ing to the au­thors.

The grad­u­al down­fall of the di­no­saurs came around a pe­ri­od known as the K-T Bound­a­ry, be­tween the so-called Cre­ta­ceous and Ter­tiary pe­ri­ods some 65 mil­lion years ago. But some di­no­saurs sur­vived for thou­sands of years there­af­ter, Poi­nar not­ed; a num­ber of lin­eages lived even long­er and evolved in­to modern-day birds.

Poinar and his spouse have spent much of their ca­reers stu­dy­ing plants and an­i­mals found pre­served in am­ber, us­ing them to re-cre­ate en­vi­ron­ments of yore. A semi-precious gem that orig­i­nates as sap ooz­ing from a tree, am­ber has a un­ique abil­ity to trap ti­ny crea­tures or oth­er ma­te­ri­als and pre­serves them al­most per­fectly in nat­u­ral dis­play cases for mil­lions of years. The phe­nom­e­non has been in­val­u­a­ble in re­search; it al­so formed the prem­ise for the film Ju­ras­sic Park, in which fiction­al sci­en­tists ex­tracted di­no­saur DNA from am­ber-trapped mosquitoes.

In­sects are be­lieved to have orig­i­nat­ed more than 400 mil­lion years ago from worms, but un­der­went a ma­jor flour­ish­ing in the Cre­ta­ceous era, when the lat­er di­no­saurs lived. The spread of new in­sect lin­eages went hand-in-hand with that of flow­ers, which had mu­tu­ally de­pend­ent rela­t­ion­ships with many in­sects. 

This rise of flow­ering plants was itself bad news for di­no­saurs, which tra­di­tion­ally fed on oth­er types of greens, said Poi­nar. Mean­while, in­sects came to com­pete for some foods with the great rep­tiles.

But things got worse, Poinar went on. By the late Cre­ta­ceous “the as­socia­t­ions be­tween in­sects, mi­crobes and dis­ease trans­mis­sion were just emerg­ing,” he said. “We found in the gut of one bit­ing in­sect, pre­served in am­ber from that era, the path­o­gen that causes leish­ma­ni­a—a se­ri­ous dis­ease still to­day, one that can in­fect both rep­tiles and hu­mans. In anoth­er bit­ing in­sect, we disco­vered or­gan­isms that cause ma­lar­ia, a type that in­fects birds and lizards to­day.

“In di­no­saur fe­ces, we found ne­ma­todes, trema­todes and even pro­to­zoa that could have caused dys­en­tery and oth­er ab­dom­i­nal dis­tur­bances. The in­fective stages of these in­tes­ti­nal par­a­sites are car­ried by filth-visiting in­sects.”

In the Late Cre­ta­ceous, Poinar said, the world was co­vered with warm-tempe­rate to trop­i­cal zones that swarmed with blood-sucking in­sects car­ry­ing leish­ma­nia, ma­lar­ia, in­tes­ti­nal par­a­sites, ar­bo­vi­ruses and oth­er path­o­gens. These caused re­peat­ed epi­demics that slowly but surely wore down di­no­saur popula­t­ions, Poi­nar ar­gued. Ticks, mites, lice and bit­ing flies would have tor­mented and weak­ened them. 

“S­maller and sep­a­rat­ed popula­t­ions of di­no­saurs could have been re­peat­edly wiped out, just like when bird ma­lar­ia was in­tro­duced in­to Ha­waii, it killed off many of the hon­ey­creep­ers” Poi­nar said. “After many mil­lions of years of ev­o­lu­tion, mam­mals, birds and rep­tiles have evolved some re­sist­ance to these dis­eases. But back in the Cre­ta­ceous, these dis­eases were new and in­va­sive, and ver­te­brates had lit­tle or no nat­u­ral or ac­quired im­mun­ity.”

A pos­si­ble rea­son why some di­no­saurs lived on to make a come­back as modern-day birds, Poi­nar sug­gested, is that these smaller an­i­mals had a shorter life­span. That might have helped them evolve faster to adapt to the in­sect men­ace, since ev­o­lu­tion oc­curs on a genera­t­ion-to-genera­t­ion ba­sis.

“In­sects have ex­erted a tre­men­dous im­pact on the en­tire ecol­o­gy of the Earth, cer­tainly shap­ing the ev­o­lu­tion and caus­ing the ex­tinc­tion of ter­res­tri­al or­gan­isms,” the au­thors wrote in their book. “The larg­est of the land an­i­mals, the di­no­saurs, would have been locked in a life-or-death strug­gle with them for sur­vival.”


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Most leading theories on how dinosaurs died out focus on asteroid impacts or massive volcanism. But but a new book blames a tiny, much less thunderous force: insects. Their rise and evolution—the biting disease-carriers in particular—coincided fatefully with the later days of the mighty reptiles, write George Poinar Jr. of Oregon State University and his wife Roberta in the book, “What Bugged the Dinosaurs? Insects, Disease and Death in the Cretaceous.” The Poinars say their evidence is captured in almost lifelike-detail, in the form of varied insects preserved in amber dating to the extinction era. “There are serious problems with the sudden-impact theories of dinosaur extinction, not the least of which is that dinosaurs declined and disappeared over a period of hundreds of thousands, or even millions of years,” said George Poinar. There is evidence for catastrophic events such as an asteroid strike or lava flows around that time. These “certainly played a role” in wiping out the dinosaurs, Poinar continued, but he insisted they don’t account for the slowness of the process. On the other hand, he added, “competition with insects, emerging new diseases and the spread of flowering plants over very long periods of time is perfectly compatible with everything we know about dinosaur extinction.” Insects and disease may have subjected the reptiles to a much slower torment, but it might have ultimately been the fatal one, according to the authors. The gradual downfall of the dinosaurs came around a period known as the K-T Boundary, between the so-called Cretaceous and Tertiary periods some 65 million years ago. But some dinosaurs survived for thousands of years thereafter, Poinar noted; a number of lineages lived even longer and evolved into modern-day birds. Poinar and his spouse have spent much of their careers studying plants and animals found preserved in amber, using them to re-create the environments of yore. A semi-precious gem that originates as sap oozing from a tree, amber has a unique ability to trap tiny creatures or other materials and preserves them almost perfectly in a natural display case for millions of years. The phenomenon has been invaluable in research; it also formed the premise for the film Jurassic Park, which related a tale of scientists extracting dinosaur DNA from amber-trapped mosquitoes. Insects are believed to have originated more than 400 million years ago from worms, but underwent a major flourishing in the Cretaceous era, when the later dinosaurs lived. The spread of new insect lineages went hand-in-hand with that of flowers, which had mutually dependent relationships with many insects. Flowers themselves were bad news for dinosaurs, which had traditionally fed on other sorts of plants, said Poinar. Meanwhile, insects came to compete for some foods with the great reptiles. But things got worse, Poinar went on. By the late Cretaceous “the associations between insects, microbes and disease transmission were just emerging,” he said. “We found in the gut of one biting insect, preserved in amber from that era, the pathogen that causes leishmania—a serious disease still today, one that can infect both reptiles and humans. In another biting insect, we discovered organisms that cause malaria, a type that infects birds and lizards today. “In dinosaur feces, we found nematodes, trematodes and even protozoa that could have caused dysentery and other abdominal disturbances. The infective stages of these intestinal parasites are carried by filth-visiting insects.” In the Late Cretaceous, Poinar said, the world was covered with warm-temperate to tropical zones that swarmed with blood-sucking insects carrying leishmania, malaria, intestinal parasites, arboviruses and other pathogens. These caused repeated epidemics that slowly but surely wore down dinosaur populations, Poinar argued. Ticks, mites, lice and biting flies would have tormented and weakened them. “Smaller and separated populations of dinosaurs could have been repeatedly wiped out, just like when bird malaria was introduced into Hawaii, it killed off many of the honeycreepers,” Poinar said. “After many millions of years of evolution, mammals, birds and reptiles have evolved some resistance to these diseases. But back in the Cretaceous, these diseases were new and invasive, and vertebrates had little or no natural or acquired immunity.” A possible reason why some dinosaurs lived on to make a comeback as modern-day birds, Poinar suggested, is that these smaller animals had a shorter lifespan. That might have helped them evolve faster to adapt to the insect menace, since evolution occurs on a generation-to-generation basis. “Insects have exerted a tremendous impact on the entire ecology of the Earth, certainly shaping the evolution and causing the extinction of terrestrial organisms,” the authors wrote in their book. “The largest of the land animals, the dinosaurs, would have been locked in a life-or-death struggle with them for survival.”