The Cretaceous A Time of Change

The sun rose and set over 29 billion times during the Cretaceous. Each succeeding dawn and nightfall saw the birth and death of billions of organisms, and in every passing millennium, species arose or became extinct. Dramatic physical and biological changes molded the evolution of insects, plants, and dinosaurs during that period in the planet's history. Differences in insect taxa are evident in the amber fossils found in Lebanon in the Early, Burma in the mid, and Canada in the Late Cretaceous. Other fossil deposits tell us that similar changes also occurred in dinosaurs and plants.

Geographic and Climatic Changes

In the 25-30 million years separating each amber site, continents drifted hundreds of miles, mountains formed, sea levels changed, volcanoes erupted and died, climates shifted, and earthquakes fractured the land. All of these physical transformations in the earth's architecture were the consequences of what is known as plate tectonics.

Geologists have made great strides deciphering the mysteries of the planet's history with the study of plate tectonics. They have established that the earth's surface is composed of a complex of continental and oceanic plates that are being continuously pushed apart in some areas and forced together in others, so that they are constantly slipping and sliding over, under, or against each other. Even today the earth continues to shift and in the most active areas of plate movement, earthquakes and volca noes are a daily reminder of its restlessness. Although this movement does not appear to have been uniform over geological time, and long periods of near-stasis have been interspersed with periods of rather intense activity, the end result was that the geography of the Early, mid and Late Cretaceous worlds was significantly different.

When we are presented with a map of 130 to 135 million years ago, the most obvious difference from one of today would be the very close association of continents situated in the Southern and Northern Hemispheres.9 The landmasses joined in the supercontinent Gondwanaland (Africa, South America, Antarctica, Australia, and India) were beginning to separate from each other. Africa and South America were still contiguous and remained in contact with the other southern continents via land bridges and island chains (fig. 6). In the northern regions the continents forming the Laurasian complex (North America, Greenland, and Eurasia) were also still closely interconnected. The flora and fauna were free to migrate over the entire conjoined landmasses, thus potentially allowing for the distribution of a specific genus or species of insect, plant, or dinosaur to become quite extensive.

Moving forward to 97 to 105 million years ago, another map would show that as the continents separated, a rise in sea levels had placed the interior of Burma and its amber-forming forest close to the water's edge (fig. 7). While the rising sea level inundated the interior of North America with a vast epicontinental ocean and reduced much of Europe to large islands, it also further opened the Tethys Seaway between the northern and southern continents. Antarctica had almost reached the position it occupies today at the South Pole.

By the time the Canadian amber was being formed some 77-79 million years ago, western and eastern North America were still separated by that large interior sea (fig. 8). The continents had continued moving and now resided close to their present locations. Such an extended period of geological isolation would have resulted in endemic species occurring on the eastern and western sides of continental North America.

Cretaceous Period World Map

Figure 6. This map illustrates the putative positions of the continents when amber was being deposited in Lebanon (asterisk) during the Early Cretaceous. The probable extent of the land masses are in white, oceans are in light gray, epicontinental seas are in dark gray, and black lines delineate present-day continental perimeters. The dotted lines indicate theoretical tropical, subtropical, and warm climatic zones on land. The dotted areas indicate mountain ranges. (Modified from Smith et al.9 for paleocoast-lines and Vakhrameev10 for climatic belts based on fossil plant distribution.) The horizontal and vertical lines intersect at 0° longitude and latitude.

Figure 6. This map illustrates the putative positions of the continents when amber was being deposited in Lebanon (asterisk) during the Early Cretaceous. The probable extent of the land masses are in white, oceans are in light gray, epicontinental seas are in dark gray, and black lines delineate present-day continental perimeters. The dotted lines indicate theoretical tropical, subtropical, and warm climatic zones on land. The dotted areas indicate mountain ranges. (Modified from Smith et al.9 for paleocoast-lines and Vakhrameev10 for climatic belts based on fossil plant distribution.) The horizontal and vertical lines intersect at 0° longitude and latitude.

We are left with the knowledge that geological changes over the course of the Cretaceous created an increasingly smaller terrestrial world as continents separated and sea levels rose. A team of scientists has estimated that from the beginning to near the end of the Cretaceous, there was a net loss of approximately 14% of non-marine areas on the globe so that at 80 million years ago, the world had the least amount of exposed land seen over the last 245 million years and an astonishing 28% less then it had 5 mya.9

Figure 7. This map illustrates the putative positions of the continents when amber was being deposited in Burma (asterisk) during the mid-Cretaceous. The probable extent of the land masses are in white, oceans are in light gray, epicontinental seas are in dark gray, and black lines delineate present-day continental perimeters. The dotted lines indicate theoretical tropical, subtropical, and warm climatic zones on land. The dotted areas indicate mountain ranges. (Modified from Smith et al.9 for paleocoast-lines and Vakhrameev10 for climatic belts based on fossil plant distribution.) The horizontal and vertical lines intersect at 0° longitude and latitude.

Figure 7. This map illustrates the putative positions of the continents when amber was being deposited in Burma (asterisk) during the mid-Cretaceous. The probable extent of the land masses are in white, oceans are in light gray, epicontinental seas are in dark gray, and black lines delineate present-day continental perimeters. The dotted lines indicate theoretical tropical, subtropical, and warm climatic zones on land. The dotted areas indicate mountain ranges. (Modified from Smith et al.9 for paleocoast-lines and Vakhrameev10 for climatic belts based on fossil plant distribution.) The horizontal and vertical lines intersect at 0° longitude and latitude.

Climate is another physical factor that influenced the lifestyles of past biota. Climatic changes have many causes, but landmass size and topography, along with wind patterns and ocean currents, contribute just as much as ozone layers and continental positions in relation to the solar energy gradient that extends from the equator to the poles. Since most of these can be correlated with changes brought about by plate tectonics, it follows that during the Cretaceous, the climate fluctuated somewhat. In general however, the Cretaceous was thought to have been con-

Cretaceous Snout Beetle

Figure 8. This map illustrates the putative positions of the continents when amber was being deposited in Canada (asterisk) during the Late Cretaceous. The probable extent of the land masses are in white, oceans are in light gray, epicontinental seas are in dark gray, and black lines delineate present-day continental perimeters. The dotted lines indicate theoretical tropical, subtropical, and warm climatic zones on land. The dotted areas indicate mountain ranges. (Modified from Smith et al.9 for paleocoast-lines and Vakhrameev10 for climatic belts based on fossil plant distribution.) The horizontal and vertical lines intersect at 0° longitude and latitude.

Figure 8. This map illustrates the putative positions of the continents when amber was being deposited in Canada (asterisk) during the Late Cretaceous. The probable extent of the land masses are in white, oceans are in light gray, epicontinental seas are in dark gray, and black lines delineate present-day continental perimeters. The dotted lines indicate theoretical tropical, subtropical, and warm climatic zones on land. The dotted areas indicate mountain ranges. (Modified from Smith et al.9 for paleocoast-lines and Vakhrameev10 for climatic belts based on fossil plant distribution.) The horizontal and vertical lines intersect at 0° longitude and latitude.

siderably warmer than today, and it is unlikely that there were freezing temperatures for most of those 80 million years.

Various disciplines have methods to garner information about past climates, such as detecting the distribution of climatically sensitive mineral deposits in the earth's surface or examining the dispersion of past biota indicative of particular temperature preferences. Since our three amber deposits were found in coal strata, we can infer that their associated forests thrived in a moist to humid environment. We also know that the araucarian trees that produced the Cretaceous amber predominately prefer tropical to subtropical wet zones today. The shapes, edges, sizes, and thickness of fossil leaves often indicate whether a plant grew in a cold, hot, wet, or dry environment. Using these characteristics, the paleobotanist V. A. Vakhrameev created phytogeographic maps to delineate Cretaceous climatic belts10 (figs. 6, 7, 8). Combining the available data leads us to portray the Lebanese and Burmese amber-forming habitats as lush hot and steamy tropical rainforests where the seasons were only marked by the amount of rain that fell each succeeding month. The Canadian amber forest flourished in verdant moist subtropical environs, and short mild winter days followed on the heels of long scorching summer days. All three forests grew near the sea, so they experienced a marine influence. Dense morning fog may have obscured the inhabitants, blanketed the trees, and deposited condensed beads of moisture on exposed surfaces. Periodic cyclones whipping across the vast tropical seas undoubtedly pounded the shores and wrecked havoc on the forests.

Alterations in global geography and climate over the course of the Cretaceous were accompanied by changes in the flora and fauna. The reasons for new plants and animals appearing while others died out are complex. The demise of each individual species had a unique set of causes and effects that were linked in an intricate web with the competition and survival of other organisms in their habitat or even the entire biome. Many of these biotic changes have been recorded in fossil deposits.

Biotic Changes

As the predawn light began to infuse the Early Cretaceous skies over Lebanon, the creatures of the night sought shelter. Hunters and gatherers crept under leaves, sidled into crevices or caves, climbed toward the treetops, or scurried underground. For a brief moment, the forest was in repose. The coming blaze of sunrise would illuminate an almost alien plant world, quite different from what it is today.

The archaic plants that covered the land then were predominately gymnosperms such as conifers, ginkgos, and cycads (fig. 9). An important conifer from our perspective would have been the amber-forming araucarian, Agathis levantensis. Ancient ferns, liverworts, lycopods, equisetums, and mosses grew everywhere. Flowering plants, the angiosperms, were rare, diminutive, and inconspicuous, and mainly consisted of types with primitive archetypical flowers. The exotic seed ferns were reduced to almost relictual circumstances. Primitive shrubs like Caytonia with its cupule-covered seeds and related cycadeoids with barrel-like trunks dotted with reproductive organs lent a strange, mysterious atmosphere to the landscape.

The world was an unfamiliar evergreen place where wind-carried pollen and spores drifted through the forest ensuring successive generations. There were no showy displays of fragrant flowers to festoon open spaces with multicolored floral tapestries or dot the canopy with brilliant splashes of color. The few plants fossils that have been found at the amber site certainly do not represent the diversity of flora that must have been present.11-13 There in Lebanon and throughout the globe were the last survivors of plant communities, the likes of which would disappear from the face of the earth by the mid-Cretaceous.

The composition of the flora of the entire planet was about to undergo a transformation as the angiosperms began to blossom and initiate the meteoric growth in diversity that would culminate in their dominance of the plant world (fig. 9). Already by the mid-Cretaceous, there were significant differences. Obvious changes in the 30-million-year span were that new genera and species of plants had evolved. Emerging habitats were replete with more modern conifers. In the Burmese amber-forming arau-carian forests, aromatic cedars touched slender pines, lofty sequoias grew next to elegant dawn redwoods, and expansive cypresses made contact with compact junipers.14-20 Ferns (fig. 10) and club mosses still dominated the undergrowth.

Those ascending stars, the angiosperms, were now aggressively competing for space everywhere, and their increasing

145.5 mya

Conifers

Ginkgos Lycopods

Cycadophytes

Angiosperms Seed ferns

Ferns Sphenopsids

Figure 9. The composition of global flora changed considerably over the 80-million-year span of the Cretaceous. Most significant was the radiation of the an-giosperms. This was accompanied by a decline in diversity of the other plant groups. The letters L, B, and C indicate the approximate times that the amber forests were flourishing at the Lebanese, Burmese, and Canadian sites, and illustrate in a very general way the proportions of plant types that could have occurred at those locations.

diversity appeared to be accompanied by a decline in diversity of other plants.18348 Infrequent clusters of delicate pale flowers peeked out from verdant growth and palm nuts accumulated with conifer cones on the forest floor. At least two grasses (fig. 11) with affinities to present-day bamboos prospered,17 possibly even forming ever-expanding thickets that threatened to overgrow the vast expanses of ferns and horsetails. Club and bracket fungi decorated decaying trunks while puffball and pinwheel mushrooms flourished on the forest floor91345 (fig. 12, color plates 12A, 12D).

By the time the Canadian amber was being formed, the forests, shrub lands, and meadows more closely resembled those of the present. Our knowledge of the plants growing in Alberta during

Figure 10. Tip of a fern leaf in

Burmese amber.

the Campanian Stage of the Late Cretaceous is actually quite extensive due to the concerted efforts of many paleontologists working over decades.21-27 In the forests, podocarps probably now mingled with the resin-producing kauri (araucarian) trees. The numbers of angiosperms increased significantly, and almost certainly some of the plants growing in the northern latitudes were now deciduous. The size and habits of those ancient flowering plants and how they may have contributed to the ecosystem is open to debate. Had some developed into trees by this time or were they only ground cover or low shrubs? As Dennis Braman and Eva Koppelhus remarked about Late Cretaceous fossil angiosperms in Canada, "If they had tree-like habits, one would expect to find large pieces of fossilized wood. However, angiosperm wood is presently unknown".21 So we can only guess how they contributed to the strata in these forests.

There are many factors that determine where a plant will grow, including temperature, water availability due to precipitation and evaporation, soil type, drainage, light, latitude, terrain, and elevation. In any of the amber sites these parameters changed with time, affecting the plants that were able to flourish there in succeeding millennia. While the distribution and relative importance of the various plant types throughout the Cretaceous gradually changed with some families, genera, and species

Figure 11. Spikelet of the primitive grass Programinis burmi-tis in Burmese amber.17

ft M

Figure 12. A group of puffballs in Burmese amber.

dying out and others converting into more modern forms, the animals that utilized them for food and shelter were also undergoing transformations.

We know that dinosaur species came and went. In fact, in the 25 to 30 million years separating each amber deposit, the fauna would have been replaced by new species and genera a multiplicity of times. Peter Dodson believes that individual dinosaur species lasted only between 1 and 2 million years, while their mean generic longevity averaged about 7.7 million years.28 This suggests that the entire dinosaur fauna may have turned over with every geological stage, or approximately ten times in the Cretaceous.29 With a high turnover rate, relatively few fossil sites, and the entire global distribution of dinosaurs over a vast time period to be considered, only some general patterns of the changes can be accessed.30-32 Unfortunately, while the presence of a fossil tells us what lineage existed in a particular time and place, the absence of other organisms does not mean they did not exist during that period.

In the Cretaceous, a gradual shift in the overall size of plant-eating dinosaurs from the gigantic multiton behemoths once dominant in the Jurassic to relatively smaller and faster herbivores occurred in the Northern Hemisphere (fig. 13). The or-nithopods in particular proliferated and spread. Perhaps the best known of these in the Early Cretaceous were the iguanodons, which were quite common in the northern hemisphere, while closely related ornithopods roamed the southern continents. Ponderous ankylosaurs, embellished with heavy dorsal bony plates decorated with an array of horny studs and spikes and armed with a clubbed tail, became prominent components of early Cretaceous fauna in the areas once comprising Laurasia, but were rare in Africa. Stegosaurs, those plated dinosaurs with ridiculously tiny heads and two rows of spines jutting from their backs, became extinct or scarce in some regions. In those habitats where they managed to survive, they did not appear to maintain a very significant presence. The small psittacosaurs, primitive ceratopsians with parrot-like beaks, became a successful group

herbivorous/omnivorous dinosaur morphotypes that could have lived in or near one or more of the amber sites are shown here. By far the largest land animals known were the sauropods. Examples of these were brachiosaurids (1) and titanosaurids (2), as well as diplodocids and cetiosaurids. Other massive four-legged herbivores, but having horny "beaks," included stegosaurids (3), ankylosaurids (4), nodosaurids (5), and ceratopsids (6). A small quadruped group of dinosaurs were the protoceratopsids (7). Walking on two legs or sometime four were the ornithopods, which ranged in size from very large to comparatively small and also possessed beak-like structures. These included iguan-odontids (8), hadrosaurids (9), dryosaurids (10), and thescelosaurids (11), intermediate-size ornithopods. Psittacosaurids (12) were small ceratopsids that probably walked on hind legs. Pachycephalosaurids (13) also walked on their hind legs and varied in size from small to intermediate.

in Asia. Herds of sauropods, the largest of the quadruped herbivores, with incongruously small heads perched on long necks, bodies the size of a house, and legs like telephone poles, continued to lumber with earth-shaking footsteps across the horizons of South America. These behemoths, 80 to 100 feet long, are estimated to have weighed up to 50 tons. They were seen, however, with ever-decreasing frequency in other parts of the globe.

By the Late Cretaceous new groups of dinosaurs begin to make their appearance for the first time in the Northern Hemisphere. Small pachycephalosaurs, many with prominent thick-roofed skulls crowned with rows of bony knobs, and a variety of ceratopsians with horns, frills, and oversized heads now joined herds of armored ankylosaurs and bipedal/quadrupedal hadro-saurs that could reach 40 feet long and weigh over 4 tons. Surprisingly, it appears that the southern continents retained mostly Early Cretaceous dinosaur types.

As the herbivores moved from large and slow to smaller and faster, and some became armed with defensive horns, the carnivores that fed on them changed also (fig. 14). The first part of the Cretaceous saw a burst in theropod diversity. These fierce, two-legged meat-eating machines became larger and if possible more formidable. Deinonychosaurs armed with capacious sickle-shaped claws appeared in the Northern Hemisphere. Members of this group included the dromaeosaurs and troodons that possessed relatively large brains and eyes, and were equipped with retractable second toes ending in a curved claw that could be flicked forward to slash their victims. The therizinosaurs, also in this group but apparently confined to Asia, were not only large but each hand terminated in three terrifying scythe-like claws.

By the late Cretaceous, the largest of all terrestrial carnivores now ruled the earth—the tyrannosaurs. Every child can easily envision T. rex with its characteristic immense jaws, 10-inch curved fangs, 4- or 5-foot-long head, and 45-foot-long body. Their overwhelming stature was somewhat offset by curiously short arms ending in tiny two-fingered hands. Other more obscure but equally foreboding theropods were the carcharodon-

Ribbon Drawing

Figure 14. Cretaceous theropods, showing their relative sizes. This figure illustrates some of the theropod morphotypes that could have frequented one or more of the amber forest sites. Theropods were a group of bipedal dinosaurs that included ferocious predators but also contained omnivores, insectivores, and perhaps even herbivores. They ranged in size from no bigger than a chicken to forty feet long. Some were small and armed with sharp teeth and curved claws, such as the coelurids (1) and deinony-chosaurs such as dromaeosaurids (2) and troodontids (3). These were considered swift hunters that traveled in packs. Other small- to intermediate-size theropods but with toothless beak-like structures were oviraptors (4), garudimimids (5), and ornithomimids (6). All of these resembled the ratite birds of today. Dominating the land were the large theropods. Spinosaurids (7) were unique in that they had a skin sail supported by tall spines along their back. Abelisaurids (8) had deep snouts and flat horns over their eyes. Therizinosaurids (9) had long forelegs, and based on their teeth type and beak, were probably herbivores. The best known of all theropods, the tyrannosaurids (10) epitomize the flesh-eating top predator of the Cretaceous.

Figure 14. Cretaceous theropods, showing their relative sizes. This figure illustrates some of the theropod morphotypes that could have frequented one or more of the amber forest sites. Theropods were a group of bipedal dinosaurs that included ferocious predators but also contained omnivores, insectivores, and perhaps even herbivores. They ranged in size from no bigger than a chicken to forty feet long. Some were small and armed with sharp teeth and curved claws, such as the coelurids (1) and deinony-chosaurs such as dromaeosaurids (2) and troodontids (3). These were considered swift hunters that traveled in packs. Other small- to intermediate-size theropods but with toothless beak-like structures were oviraptors (4), garudimimids (5), and ornithomimids (6). All of these resembled the ratite birds of today. Dominating the land were the large theropods. Spinosaurids (7) were unique in that they had a skin sail supported by tall spines along their back. Abelisaurids (8) had deep snouts and flat horns over their eyes. Therizinosaurids (9) had long forelegs, and based on their teeth type and beak, were probably herbivores. The best known of all theropods, the tyrannosaurids (10) epitomize the flesh-eating top predator of the Cretaceous.

tosaurs and the gigantosaurs. Although sometimes considered scavengers, all of these megacarnivores may have had to compete for food with roaming packs of dromaeosaurs or troodons. Two other emerging groups of theropods, however, may have fed on considerably different food. The ornithomimids and ovi-raptorosaurs eschewed rows of pointed fangs for prominent toothless beaks that nevertheless retained considerable shearing power. The unique, somewhat relictual dinosaur fauna of the Southern Hemisphere included the abelisaurs, large horned theropods. While large thundering herds of heavy herbivores and huge cunning carnivores are most frequently fossilized, small dinosaurs ranging from the size of chickens to large dogs also abounded, and their importance shouldn't be overlooked.

Insects

There are some 762 families of insects today.33 If you multiply that number by a factor of four, you will probably have an idea of insect diversity in the Cretaceous, since considering how few Cretaceous insect fossil sites there are, already some 490 families are known from that period (appendix A).

Changes in insect diversity can be demonstrated by comparing fossils from the Early, mid, and Late Cretaceous. Many Early Cretaceous insects retained archaic characters, physical attributes unique to each species, from their Jurassic forebearers, and this is reflected in representatives from Lebanese amber. These include primitive weevils34 that developed in conifer cones (fig. 15), bristly walking sticks, giant katydid-like insects, and stem-boring sawflies, all of which fed on gymnosperm leaves or pollen.35 They shared their world with spiny cicadas feeding on ginkgos and primitive moths whose caterpillars consumed moss.36 Small thrips37 with mouthparts modified for piercing and scraping devoured pollen and even defoliated some of the arau-carians, while long-beaked aphids38 sucked the juices of conifers, horsetails, ferns, and cycads.

It was just about this time when some insects developed a

Found Oak Island Treasure Chest
Figure 15. Larvae of this small weevil could have developed in the male cones of Agathis levantensis, the Lebanese amber-producing tree.34

taste for vertebrate blood. By the Early Cretaceous, horseflies, blackflies, mosquitoes,35 biting midges, sand flies, and a host of lesser-known hovering insects were all on the lookout for the fresh blood of everything from small frogs to gigantic dinosaurs.13 The diversification of the flowering plants in the mid-Cretaceous spelled extinction for many archaic insects. In fact, there were more hexapod extirpations at this time than even at the K/T boundary.35 The mid-Cretaceous was a time when older, established insects competed with modern ones for the same habitats. Some of the primitive types were inconspicuous beetles so small that hungry lizards patrolling the bark would have probably ignored them (fig. 16). One such beetle fed on mites and possessed an extra segment that provided its front legs with an added degree of flexibility to help snatch prey.39 Sharing the same habitat was a strange beetle with cuticular modifications on the head and body rivaling the frills, horns, and plates of any dinosaur. Not only did this insect have shield-like projections that protected bulging eyes, but also a fin-like protrusion on the top of the head plus a series of frills that ran the length of the back.347 A third beetle was so archaic it had to be described in a new family.40 With reduced mouthparts, this insect could only have fed on fungi, moss, or algae. Other beetles used chemicals for defense.349

Figure 16. Three fascinating beetles from Burmese amber. In the upper right is an extinct subfamily of ant-like stone beetles (Scydmaenidae).39 The unique character of this little mite predator is the extra segment in its front legs. The upper left shows an extinct silvanid beetle with head and body protrusions that could rival most dinosaurs. Its large bulging eyes were protected by triangular projections.347 In the center, hiding in a hollow and partly covered by a moss leaf, is the only known member of the extinct flightless beetle family Haplochelidae.40

Figure 16. Three fascinating beetles from Burmese amber. In the upper right is an extinct subfamily of ant-like stone beetles (Scydmaenidae).39 The unique character of this little mite predator is the extra segment in its front legs. The upper left shows an extinct silvanid beetle with head and body protrusions that could rival most dinosaurs. Its large bulging eyes were protected by triangular projections.347 In the center, hiding in a hollow and partly covered by a moss leaf, is the only known member of the extinct flightless beetle family Haplochelidae.40

Larger insects, which had evolved millions of years earlier and were near the end of their reign, included creatures that looked like a cross between a grasshopper and cricket (color plate 8A). These sturdy elcanids, with protruding eyes and long antennae, probably fed on gymnosperms. They would have interacted directly with dinosaurs by providing a food source, as well as competing with them for dwindling plant resources. However, their tiny cousins, pygmy mole crickets and pygmy grasshoppers, would have attracted the attention of hungry geckos and amphibians (color Plate 7B).

Evidence of more modern insect lineages at the mid-Cretaceous Burmese amber site included a weevil with elbowed antennae similar to those that feed on flowering plants today (color plate 5E).41 Insect damage to angiosperm flowers in Burmese amber shows that herbivores had already adjusted to a diet of flowering plants1819 (color plate 14A). Perhaps the injury was from a small, slender thrips or the larvae of a gall midge (color plates 3A, 3C). Certainly there would have been a horde of insects, including planthoppers and aphids, feeding on primitive grasses, and they competed with dinosaurs for that delicacy17,42. Some of those aphids survived very well with only two wings instead of the four found on plant lice today.43 These sucking insects could have been carrying plant viruses then. A surprise find was a small bee that was certainly pollinating some of the angiosperms at the site44 (color plate 14B).

Aside from the typical bloodsuckers, ticks also occurred at the Burmese amber site45 (color plate 11E). It is a challenge to imagine what other arthropods with piercing mouthparts were feeding on in that amber forest and whether they played an important role in the transmission of disease-causing pathogens46, 47(color plate 10). An unexpected surprise were two-winged scorpion flys with beaks containing dagger-like mandibles with serrated edges (color plates 11A, 11B). We can only guess how many other types of biting arthropods were present in those Cretaceous forests.

By the Late Cretaceous, more of the insects resembled those found today, including a palm-feeding beetle at the Canadian amber site26 (color plate 5A). There must also have been a considerable number of new herbivorous insects related to those that feed currently on maples and sycamores, alders and elms, or lilies and sedges, all plants present at that time (color plate 12B). Countless leaves were probably covered with the sweet deposits and shed skins of plant lice. The high number of aphids in Canadian amber, amounting to about 40% of the total animal fossils, indicates that they were one of the dominant groups of insect herbivores49 (color plate 2C). By then some females had developed the ability to eject squirming young directly on the plant and forego an egg stage, an advantage their ancestors lacked. Since extant aphids carry approximately 50% of insect-transmitted plant viruses, perhaps they were responsible for the rapid turnover of Late Cretaceous plant lineages. A mosquito in Canadian amber indicates that these bloodsuckers were thick at that particular location, possibly breeding in salt marshes near the amber site191 (color plate 11D), while the mouthparts of biting midges suggests that they fed on dinosaurs.51

Insect lineages came and went throughout the Cretaceous, and most of them had either a direct or indirect association with dinosaurs. Some bugs simply provided a food source, while others ate away at the dinosaur's plants or spread blights or other plant diseases. Scavengers recycled dinosaur waste and cadavers, and the bloodsuckers, at the top of the food chain, not only feasted on dinosaurs but also introduced pathogens into their bodies. What follows is an intriguing story about the struggle between plants, insects, pathogens, and dinosaurs that took place millions of years ago.

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