Dinosaurs Competing with Insects

From the habits of present day herbivorous insects, we can infer how they would have competed with dinosaurs. We know that nemonychid weevils, like the one found in Lebanese amber, feed on pollen in the male cones of kauri trees and presume that they had similar habits in the Early Cretaceous. And it is quite likely that this source of protein was sought after by dinosaurs, just as birds and lizards feed on pollen today.56 The interfaces between insects and dinosaurs regarding conifer cones represent just one type of antagonism that would have occurred between these groups. Dinosaurs and insects competed in the understory and lower levels of the forest and were the most serious threats to saplings and other new plants. Insects also fed in the upper canopy and emergent layers of the forest where their damage affected the health, longevity, and reproductive capabilities of the trees.

While few insects are known to ingest horsetails, certainly an entire guild feasted on the diverse assemblage of these coarse plants in the Cretaceous. Some insects, such as stem-inhabiting beetles and leaf-feeding caterpillars, still utilize these primitive plants, and if their ancestors had similar habits, herbivorous dinosaurs could have suffered.

Throughout the Cretaceous, ginkgos, or maidenhair, trees were diverse and widespread, and the periodic appearance of their pungent, cherry-like fruits certainly attracted both insects and dinosaurs. Protoceratopsians and pachycephalosaurs probably never missed the opportunity to consume these luscious fruits, but they must have competed with a succession of beetles and flies.

Dinosaurs that ate the leaves, peg-like stems, and male flowers of ginkgos would have had to contend with moth and sawfly caterpillars that gobbled down the florets and leaves during the night, leaving denuded branches the next morning. Cretaceous aphids, scales, planthoppers, and those long-beaked cicada-like insects, the palaeontinids, might have sucked the juices from these plants, causing the leaves to wilt or drop prematurely.35 Small beetles that relished the pollen-rich male flowers had the ability to reduce the reproductive potential of these trees.

Cycadophytes and cycads were diverse groups in the Cretaceous and ranged from dwarf to colossal plants. Iguanodons and stegosaurs that indiscriminately grazed on the fronds probably disturbed scarab beetles devouring the leaf edges. The pollen and seed cones of these plants would be relished, although those that produced nuts with toxic chemicals may have been avoided—but not necessarily, since baboons in Africa have no problem dealing with the undesirable compounds in the nutritious cycad seeds.57 Dinosaurs undoubtedly competed with guilds of insects feeding in the male and female cones, including small weevil larvae in the seeds. The starchy stem of cycads unquestionably provided food for pachycephalosaurs and hyp-silophons, but they had to contend with longhorn beetle and moth larvae.58 Other insect competitors on these plants possibly included sap-sucking aphids or scale insects that left layers of sticky, whitish residue on the dying leaves. And by the mid-Cretaceous, ants were beginning to distribute these sapsuckers throughout the forest.

Another abundant group of dinosaur food plants were ferns. These varied in size from dwarf maidenhairs and medium-sized bracken ferns to towering tree and seed ferns. In fact, some of the tree ferns probably grew in such dense clusters that they concealed the dining dinosaurs. The stegosaurs were no doubt quite fond of the tender fronds of these plants, but probably competed with sawfly larvae, moth caterpillars, weevils, and gall midge larvae living in chambers along the leaf edges. Aphids, plant bugs, leafhoppers, and planthoppers possibly vied with dinosaurs for this resource. A dinosaur delicacy certainly was their soft stalks and starchy, pith-filled trunks, both developmental sites for weevils. Some of these primitive weevils still exist, and one Australian species caused considerable damage to tree ferns when accidentally introduced into Hawaii.59 Many of the Cretaceous ferns likely had edible rootstocks60 that represented a delicacy for both protoceratopsians and beetle larvae.

Dinosaurs feeding on conifers encountered a host of insect competitors. Pachycephalosaurs can be envisioned eagerly gathering around araucarians when the cones dropped. Both the pollen and seed cones are highly nutritious, with elevated levels of carbohydrates, proteins, fats, and trace elements. Here the dinosaurs vied with weevil larvae developing in the pollen cones34 and moth (Agathaphigidae) and beetle (Belidae) larvae in the seed cones61 (color plate 12C). Today, caterpillars of Agathiphaga can destroy up to 95% of kauri seeds in a cone.182 There may even have been gall wasps devouring the seeds62 (color plate 5B). Diplodocids and titanosaurs feeding on leaves of young araucar-ian trees no doubt shared their meals with both leaf-mining and foliar caterpillars, as well as thrips, aphids, and scale insects (color plates 3A, 3E, 3F). The ancestors of a small moth (Gracil-lariidae) whose immatures are found mining the leaves of New Zealand kauri trees,63 as well as those of giant weevil larvae that develop in araucarian trunks, may have been present at that time.64

There would have been fringe-winged thrips on the buds, flowers, leaves, and stems of all types of plants (color plate 3A). These small insects have mouthparts adapted for sucking and exhibit two basic feeding patterns, a shallow type mostly restricted to epidermal cells and a penetrating type that probes the deeper plant tissues. The feeding punctures, as well as the ovipo-sition slits, cause mechanical injuries to plant tissue, and if the insects are numerous, defoliation can occur. This type of damage is caused by thrips that attack kauri trees in northeastern Australia.

Other important conifer defoliators in the amber forests were sawflies, many of which are gregarious. Today, the widespread red-headed sawfly is quite destructive to pines, larches, cedars, and spruces.65 If the attacked trees are not killed outright, the damage can retard growth and kill off limbs and twigs. Other conifer sawflies that existed back then were leaf-feeding tenthre-dinids and web-spinning sawflies, as well as xyelids that bred in cones, buds, and developing shoots. Certainly, these insects were serious competitors with conifer-feeding dinosaurs.

All conifers as well as angiosperms were susceptible to attack by generalist feeders such as crickets, katydids, elcanids, monkey grasshoppers, shorthorn grasshoppers, wetas, and mountain crickets (haglids) (color plates 4A, 4B). From their fossil record, haglids were quite diverse in the Mesozoic, and their probable behavior can be determined in part from the species still existing in North America. One that feeds on conifer pollen has singing males that offer not just a song for the chance to mate, but their fleshy wing flaps as a tasty treat. The collective feeding habits of the Cretaceous grasshopper-like locustopseids and elcanids probably destroyed many plants, just as hordes of locusts strip crops now.65 And short-horned grasshoppers must have attacked a variety of plants back then just as they do today. Insect defoliation of the conifers may have killed off many trees since they cannot produce new leaves and recover like angiosperms.66

Saplings of Metasequoia were certainly another preferred dinosaur plant. As sauropods devoured the tender leaflets, they possibly encountered leaf beetle larvae concealed between the needles, mealybugs within their white paper-like cocoons, and small caterpillars hidden in the bud tips. And the dinosaurs that selected low branches of cypresses shared their dinners with small bud caterpillars, sawfly larvae, and scale insects with their attending ants. Sap-sucking mesozoicaphidids, which appear to be related to modern adelgid aphids, were likely responsible for the decline and death of many conifers in the amber forests. When the hemlock woolly adelgid was introduced into eastern North America, it spread through one-third of the forests, killing many hemlocks along the way.67 These xylem-feeding bugs inject toxins into plant tissues, causing the needles to turn yellow and fall. This makes the plants more susceptible to drought and attack by other insects and plant diseases. Because of the combination of wind dispersal (they are quite light) coupled with rapid population buildup by parthenogenetic forms, these insects were responsible for the widespread death of hemlocks in North America. Hemlocks die about four years after the initial attack, and when the mature trees are gone, the canopy gaps are taken over by the more rapidly growing angiosperms. A similar scenario is reasonable in the Cretaceous amber forests.

The enigmatic Brachyphyllum, an extinct Mesozoic gymno-sperm, was quite widespread in the Cretaceous. Dinosaurs dining on the leaves and fallen pollen cones of plants would have encountered bizarre, elongate grasshopper-like insects as well as eccentric walking sticks and erratic sawflies, all of which have been recovered with the remains of Brachyphyllum leaves and pollen in their alimentary tracts.35

In 1962 an entomologist proposed that dinosaurs could have been eliminated by caterpillars that destroyed their food sources.68 As their plants were consumed by hordes of moth larvae, dinosaurs died from starvation. While this theory emphasizes the competition that occurred between foliage-consuming insects and herbivorous dinosaurs, its impossible to envision it resulting in any type of dinosaur extinction event.

Did some dinosaurs have a taste for mushrooms and other fungi? Did some hunt truffles? That is difficult to say, but if fun-givorous dinosaurs existed, they certainly had their choice of food items. These included various types of mushrooms, bracket fungi, puffballs, and truffles (color plate 12A, fig. 12). A range of animals, from rodents and pigs to deer and banana slugs and even tortoises, lizards, and birds seek out fungi. But no matter what type was selected, whether gilled mushrooms, puffballs, or club mushrooms, they certainly came with an assortment of insect competitors, including a variety of beetles and flies.

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