Herbivory

The sun beat down on the canopy of the freshly washed forest, causing steam to rise like puffs of smoke from the wet vegetation. Emerging through this leafy roof were the foliage crowns of the dominant trees, the kauri trees (araucarians). Massive trees with bases up to 40 feet in diameter, they reached skyward 120 or even 200 feet. Their flattened, elliptical leaves fluttered in the sunshine, displaying tapered ends, prominent longitudinal veins, and insect damage. A kauri cone infested with small caterpillars released its hold high in the branches, fell spiraling down through the canopy, dislodging leaves, ricocheting off the trunk, and coming to rest in the copious pile of duff built up around the base of the centuries-old tree.

The noise alerted a group of juvenile pachycephalosaurs that were foraging in the dimly lit recesses on the forest floor'. One moved to the area where the cone had landed to poke and paw through the debris. He picked at the infested cone and was rewarded with several juicy larvae to eat. The pachycephalosaurs were dwarfed by the surrounding trees and lush greenery. Elegant confers towered above the forest's floor like cathedral spires looming over a cityscape, while other species of archaic gymnosperms formed the dense canopy. Their narrow, pointed, and frequently prickly foiiage was qutte different from the exotic vein-ribbed leaf fans of the surrounding ginkgos, which also pushed upwards to share the light illuminating the canopy layer. Their mingling leaves carved by insect bites into strange sculptures fluttered in the wind and created a symphony of green hues delicately shaded with occasional glints of russets, browns, and yellows.

The young bipedal dinosaurs moved from the dim recesses of gloom-filled aisles into sunlit pools of open spaces created by fallen giants and along the bank of a dissecting stream, through an under-story flora of evergreen trees mingled with wooly tree ferns and coarse paJms. They feasted on ferns, which grew everywhere in a profusion of sizes and shapes with leaves as delicate as Jace or as stiff as bristles. Some, like the rugged climbing ferns that festooned the Jimbs of the mighty trees or sprouted from trunks, were too high to reach. But the smaller types crowded along the riverbank or flourishing in meadows were a delicacy. Male and female cycads, looking like stubby paJms, vied for space with large ferns, squat conifers, and the primitive relatives of bushy magnolias with smaJJ fleshy fruits, and aJJ offered up some tidbits to eat. Any habitable space on the forest floor was covered in a luxuriant undergrowth of ferns, equise-tums, smaJJ herbaceous plants, and hopefuJ seedlings providing habitats and food for a multitude of smaJJ vertebrates and invertebrates. Moist unduJating pockets of shade carpeted with a fabric woven of delicate bracken ferns, paJe ghostly lichens, and dark velvety mosses were home to mites, springtaiJs, and spiders.

Lianas and epiphytes festooned every layer in the forest. These effectively transformed the canopy into a roof garden where they cJung to the moss-covered branches and peeked through the Jeafy cover. The trunk and Jimbs of trees were draped with swaths of delicate mosses, sheets of liverworts, and veils of filmy ferns. Ropy lianas stretched across and around trunks and Jimbs, binding together every level in the forest and serving as highways for cockroaches and crickets. They intertwined with masses of tangled roots to form a meshwork on the forest floor, and twisted and looped out over the top layers of the canopy. Epiphytes perched in every stratum, weighing down Jimbs, creating dense Juxuriant growth over every avaiJabJe surface, and providing cover for frogs and birds. Even sedges grew in the forks of the trees, while feathery bamboo-Jike grasses flourished in the open areas. At ground JeveJ, a Jitter of discarded leaves, cones, twigs, Jogs, bark, and primitive fruits made an ideaJ home for saprophytic fungi of aJJ descrip tions, as well as centipedes, millipedes, and scorpions. And deep down in the loamy soil, the conifers of the forest spread stabilizing roots that coexisted with the rhizoids of symbiotic fungi and provided food for nematodes, beetles, and isopods.

This verdant jungle was teeming with hidden life. The pachy-cephalosaurs were not the only animals feeding there, only one of the more visible forms. Thousands of species of insects along with a sizable contingent of other arthropods crawled over every tree and bush, munching and crunching their way through a lavish feast. Beetles burrowed secretively under bark or browsed on pollen. Caterpillars grazed concealed on the underside of leaves while planthoppers covertly sucked plant juices. Camouflaged crickets sang and the calls of unseen strident grasshoppers permeated the air. Herbivorous insects subsisted on practically every plant surface at every level throughout the forest. Foliage was devastated as leaf beetles skeletonized, small moth larvae mined, crickets ate holes, and caterpillars gouged out the leaves. Lizards, frogs, and small mammals ran over the branches and crossed the lianas in search of prey while other warm-blooded vertebrates combed the plants for nutritious seeds and edible leaves.

On the forest floor, the group of small pachycephalosaurs continued to search for mushrooms, fallen fruits, and open seed cones to devour. One broke open a rotten log and the exposed fat white beetle grubs were gobbled down by these opportunistic omnivores. Suddenly cautious, they paused and looked in unison towards the cracking sounds now emanating from ahead. Like silent ghosts, a large herd of forest-dwelling ceratopsians had moved unnoticed through the undergrowth and were now using their massive heads to push over succulent saplings and partake of their leafage. Disturbed by the hubbub, a solitary male anky-losaur that had been feeding quietly on a patch of equisetum crashed angrily through the tangled underbrush in a rush to get away. A flock of ostrich-like ornithomimids striding along a pathway forged by the daily movements of countless large herbivores stepped off into the undergrowth and used their beaks to strip leaves and insects from the surrounding shrubs and low-growing herbaceous plants. Their movements had been shadowed by several juvenile troodons forced from the pack by a new leader. They hadn't eaten in almost a week and the ornithomimids looked like an easy meal. Creeping closer, a stronger more aggressive troodon, emboldened by hunger, leapt out to snatch the closest victim. The two dinosaurs leapt into the air, kicking out at each other with their hind legs. But the ornithomimid was larger and more experienced than the attacker, and his longer legs armed with toe claws carved a bloody swath down the chest of the inexperienced carnivore, forcing him to retreat along with his companions. Later the immature theropods would settle for a meal of insects and a few mouthfuls each of a snake they had fortuitously encountered. None of the herbivores went hungry because this lush tropical rainforest provided a cornucopia of plants to feast upon.

Signs of the feeding activities of insects were everywhere. Horsetails were turning pale and shriveling up because of the beetle larvae in their stems. Ginkgos had been denuded of florets and leaves due to an infestation of moth and sawfly caterpillars. Cy-cads and cycadophytes showed insect feeding activity with gaping holes in their leaves, and their brown-stained stems were filled with succulent moth and beetle larvae. The fronds of stunted tree ferns had died back as weevil larvae surreptitiously tunneled through their tissues. Smaller ferns had been stealthily defoliated by leaf-feeding sawflies and moths. Some leaves of the giant kauri trees were twisted and discolored from numerous leaf mines caused by small moth larvae, while huge holes in the leaves testified to the presence of giant weevils bristling with clusters of erect hairs that crept furtively along the branches. Fallen limbs exposed honeycombed wood, which served as brood chambers for bark beetles and weevils. In fact, entire areas of the forest contained dying kauri trees. The needles of Metasequoia trees had turned yellow due to the feeding of multitudes of scale insects and aphids even while stout leaf beetles and long-horned grasshoppers fed on the foliage. Patches of needles on various conifers had been covered and bound together with webbing made by gregarious sawfly larvae, and the activities of voracious sawflly caterpillars, walking sticks, and grasshoppers had partially denuded large branches.

Flowering plants had not escaped notice by the insects. Notches along the edges of many small flowers on both herbs and shrubs indicated that chewing insects had added them to their diet. Leaves on some had been "sewn" together with threads secreted from the silk glands of small caterpillars, creating a safe refuge where they could feed unmolested. Rolled up palm leaves with their inner epidermis scraped away and older leaves with huge incisions extending from their edges to the midvein were evidence of the activities of different stages of white-lined green caterpillars. Weakened by large white weevil larvae chomping through their tissues, toppled palm stems lay scattered on the forest floor. In a nearby pond, many water-lily leaves had been consumed by populations of leaf beetles. Ancient bamboos climbing up the trunks of the araucarians showed extensive leaf damage from large brown scarab beetles, and their roots suffered from attacks of small caterpillars. The hidden hordes of insects were gradually consuming their share of the forest's abundant flora.

Green plants are the most important organisms in any terrestrial ecosystem and have been since they first evolved. In terms of diversity, they are second only to insects and represent about one quarter of the total known species. They capture the energy from the sun and convert it into the plant tissues that sustain all animals. Herbivores transfer that energy directly into their tissues when eating plants, and carnivores indirectly obtain the energy when feeding on herbivores. For this reason plants comprise the very basis of the food chain.

There are many factors that determine where a particular insect or dinosaur lived, but food supply is the most important. The quantity of plants and their food quality determines how

Figure 17. An ecological pyramid can be created based on inferred numbers, biomass, or energy utilization in the Cretaceous. The actual size and proportions of the pyramid would be unknown, but insects and other invertebrates definitely dominated any ecosystems then as they do now. Dinosaurs would have represented a much smaller percentage and would also have had competition from all the other vertebrates. Ecological pyramids are not static, and contract and expand continuously due to many biotic and abiotic factors. Different pyramids can be created for large and small, more specialized habitats.

Figure 17. An ecological pyramid can be created based on inferred numbers, biomass, or energy utilization in the Cretaceous. The actual size and proportions of the pyramid would be unknown, but insects and other invertebrates definitely dominated any ecosystems then as they do now. Dinosaurs would have represented a much smaller percentage and would also have had competition from all the other vertebrates. Ecological pyramids are not static, and contract and expand continuously due to many biotic and abiotic factors. Different pyramids can be created for large and small, more specialized habitats.

many and what types of herbivores and ultimately carnivores reside where. Biologists have constructed ecological pyramids to illustrate this principle (fig. 17). There are several variations: the numbers pyramid (how many organisms), the biomass pyramid (total weight of all organisms present), and the energy pyramid (how much energy is produced, used, and stored in organisms). The pyramids are divided into several levels. The basal and largest contains the producers, the plants. The succeeding ones are devoted to the consumers, the animals. The consumers are further subdivided into types or orders. The first type or primary consumers are herbivores (plant predators), the second type are carnivores (animal predators) that feed on herbivores, and the third type are carnivores that feed on other carnivores, and so on until you reach a top predator. Omnivores fit into a ubiquitous category that extends across all the consumer levels.

Most people don't realize that insects dominate the typical consumer levels of any ecological pyramid, whether it denotes numbers, biomass, or energy, and they have probably occupied that position since they first walked the earth. They represent up to 60% of the herbivorous consumers in most ecosystems. In addition, insects and other small arthropods consume significantly greater amounts of plant tissues than all the vertebrates in any habitat (except grasslands) studied, and this prevalence has existed since the earliest of times.5355 This means that the remaining 40% of the consumer portion in a pyramid of 100 mya would have been subdivided between the dinosaurs and all other Cretaceous animals such as mammals, reptiles, amphibians, birds, and invertebrates (fig. 17). The exact proportions that each of these would share is not answerable. But however large the piece of the pyramid that dinosaurs would get, we know that it would be significantly less than that of the insects!

An ecological pyramid should be viewed as a continuously expanding and contracting entity. Its configuration changes from one ecosystem to the next. A tropical rainforest with the greatest diversity of species anywhere on earth would represent the consummate pyramid. This type of environment certainly covered more of the globe in the Cretaceous. Half of the known species in our world reside in tropical rainforests, which presently cover some 6% of the earth's land surface.66 Insect species there are estimated to number between 5 and 10 million. Since a larger portion of the earth was tropical rainforest habitat in the Cretaceous, it follows that greater insect diversity occurred then. The opposite end of the pyramid spectra would be one with sparse vegetation, such as a desert or tundra. There is in fact a 75-fold difference in plant biomass between a rain forest and tundra, and a 20-fold difference between a rain forest and a marsh.

Smaller, specialized pyramids can be applied to different levels in the biome, from communities to niches. Within each ecological pyramid there are one or more keystone species whose presence is crucial to its stability. All other species within an ecosystem have different levels of importance. The interrelationships can change overnight and a pyramid can collapse at any time. Any collapse would then be followed by a recovery period, and the pyramid would expand until equilibrium between plants and animals was once again obtained. But recovery may not result in the same populations of flora and fauna. Contraction and expansion of an ecological pyramid is normally cyclical or seasonal, but can be catastrophic due to fire, drought, floods, overgrazing by transients, and so on.

Within each ecosystem there are a variety of habitats with specialized niches. The animals compete within these for food, space, and shelter. In a forest these habitats are distributed throughout vertical strata. The rain forest has the open air space above, and inside the forest, the emergent layer, the canopy, the understory, the shrub layer, the herbaceous layer, the litter zone, and the soil are usable habitats. To reconstruct a scenario from ancient landscapes, the paleoecologist tries to fit the fauna into these levels (fig. 18). The air above the forest would have been home to gliding pterosaurs and archaic birds (feathers have floated down through the trees to be entombed in amber at all three amber deposits: color plates 15B, 15C). The birds pursued insects soaring above the crowns of the trees in the hot humid air or alighted on the branches to snatch insects feeding there, while plant-eating birds fed on seeds, pollen, and fruits. Small pterosaurs chased dragonflies and large ones may have swooped down and yanked unsuspecting mammals from the treetops.

Scampering throughout all levels of the forest and leaving hairs behind in the resin were small mammals, multitubercu-lates, and marsupials that had developed a scansorial lifestyle. Most of these were herbivores, omnivores, or insectivores. Joining them, moving along the lianas or among the leaves and even hiding in epiphytes, would have been a myriad of other animals such as tree frogs, lizards, snakes, geckos, hundreds of thousands of insects, and innumerable other small arthropods (color plate 15A). Each species of animal would find its own particular niche, a physical, environmental and biological space suited to their specific needs. At the ground level for example, there

Figure 18. Forests in the Cretaceous would be divided into strata where animals and plants lived and competed. Based on extant kauri forests, the layers would be: soil, litter, herbaceous (up to 3 ft), shrub (3-25 ft), understory (25-70 ft), canopy (70-120 ft.), emergent (above 120 ft), and free airspace. The structure of the forest differed in the Early to mid-Cretaceous from that of the Late Cretaceous due to changes in plant community composition and the radiation of the angiosperms. Also, the dinosaurs were smaller and fed at lower strata in the Late Cretaceous as shown by the columns indicating their estimated feeding levels. Insects exploited all strata from the soil to the air, but competition with dinosaurs for food was confined to the lower levels. The large trees with open foliage represent the amber-producing araucarian trees.

Figure 18. Forests in the Cretaceous would be divided into strata where animals and plants lived and competed. Based on extant kauri forests, the layers would be: soil, litter, herbaceous (up to 3 ft), shrub (3-25 ft), understory (25-70 ft), canopy (70-120 ft.), emergent (above 120 ft), and free airspace. The structure of the forest differed in the Early to mid-Cretaceous from that of the Late Cretaceous due to changes in plant community composition and the radiation of the angiosperms. Also, the dinosaurs were smaller and fed at lower strata in the Late Cretaceous as shown by the columns indicating their estimated feeding levels. Insects exploited all strata from the soil to the air, but competition with dinosaurs for food was confined to the lower levels. The large trees with open foliage represent the amber-producing araucarian trees.

would be insects, mammals, and even dinosaurs adapted to a fossorial life style. These would root around in the leaf litter, scratching in the soil or digging burrows. Mites and millipedes, springtails and crickets, annelids and nematodes, snails and scorpions, as well as cockroaches would have been creeping or slithering through the leaves, eating and being eaten. Insects moved and fed in every layer of the forest. They devoured the foliage, flowers, fruits, seeds, wood, pollen, nectar, and even resins. Perhaps three hundred or more insects fed on a single tree, but many of these probably included only three or fewer plant species in their diet.

Fitting dinosaurs into the forest takes a little imagination. We assume that many of the dinosaurs living in forests were restricted to feeding in the lower strata. No one currently seems to believe that non-avian dinosaurs resided in or even climbed trees. Size might have limited the extent to which extremely large dinosaurs entered the forest, and these may have been relegated to feeding along the fringes or in more open woodlands. Certainly small to intermediate bipedal and quadrupedal dinosaurs moved quietly through the dark, dense humid rain forests searching for food.

Animals that did not fly or climb had to feed within a vertical range dictated by their height or find some other method to extend that range. It has been suggested that some quadruped dinosaurs adapted a tripedal position and balanced on their tails and hind legs to achieve a feeding stance that extended their height.52 Sauropods, already outfitted with extremely long necks, and stout stegosaurs were suggested as likely candidates (fig. 19). The feeding strata of dinosaurs therefore had a wide potential (fig. 18); however, we will never know the true extent. Most earthbound animals today spend the majority of their time feeding at eye level or below, with some very few exceptions. Overall, the megaherbivores of the Late Cretaceous fed at a lower level than those of the Early Cretaceous, at least in the Northern Hemisphere. An Early Cretaceous sauropod could compete with insects feeding well into the understory. A Late Cretaceous cer-

Figure 19. An Early Cretaceous landscape. In the foreground two juvenile coelurids search for insects among the ferns, a dragonfly rests on ginkgo leaves, and an insect scurries up the trunk of an Agathis tree. In the middle, an iguanodontid feeds on cy-cads under the watchful eye of a spinosaurid hidden among some tree ferns. In the background, two diplodocids feed on Agathis foliage at the edge of an amber forest. The trunk of the resinous Agathis tree shows its cones and leaves.

Figure 19. An Early Cretaceous landscape. In the foreground two juvenile coelurids search for insects among the ferns, a dragonfly rests on ginkgo leaves, and an insect scurries up the trunk of an Agathis tree. In the middle, an iguanodontid feeds on cy-cads under the watchful eye of a spinosaurid hidden among some tree ferns. In the background, two diplodocids feed on Agathis foliage at the edge of an amber forest. The trunk of the resinous Agathis tree shows its cones and leaves.

Figure 20.

atopsian would only look for food in the low shrub to ground level, and the protoceratopsians coexisted with insects in the herbaceous layer of the ecosystem. But in araucarian forests, all the space above the understory was left to the insects, other arthropods, and small vertebrates (fig. 20).

Herbivores are the most numerous and diverse animals in any ecosystem. So how did phytophagous insects and dinosaurs compete? Probably in much the same way that insects are known to compete with mammals (including ourselves). Since insects feed on plants at all levels, we surmise that whatever the dinosaurs ate, insects were also there dining on it. We know that insect herbivores have greater effects on both plant growth and reproduction than mammals,53 and there may be up to ten times more invertebrate plant eaters present in an ecosystem than mammals.54 These same observations undoubtedly applied to ancient ecosystems; the difference in impact of megaherbivores vs. insects on the plants lay in the greater size of the dinosaurs. However, remember that pound for pound, the insects in most ecosystems would have outweighed the dinosaurs.

Thus, one megaherbivore may have eaten as much as 100,000 insects or more, but the general impact of millions upon millions of insects would have been more gradual and widespread. Large herbivores with their greater body size tend to eat a wider range of plants, take larger bites, and move over a greater area, trampling, defecating, and urinating copious amounts. This cuts a swath of defoliation and destruction across a narrow section of the terrain in a short amount of time. Insects with their small size but incredible numbers may eat as much or more, but they are normally more evenly distributed throughout the ecosystem. Because they are small, insects can selectively feed on seeds and roots that have a cumulative impact on plant viability. Insects also carry plant pathogens that can devastate entire plant populations. So while small and inconspicuous, insects probably were serious competitors with dinosaurs, not only eating more of the plants but also affecting overall plant health and distribution.

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