Fossil insects with functional wings are first reported from Mid Carboniferous strata. These insects were extraordinary (Fig. 14.20); the dragonfly Meganeura had an incredible wingspan of 70 cm. Intense aerobic activity such as powered flight suggests that atmospheric oxygen levels at the time were unusually high. But how effective was Meganeura as a flyer? Robin Wootton and his colleagues (1998) have identified so-called smart features that capitalized on both upstroke and downstroke movements of the animal's large wings. This form of smart engineering helps depress the trailing edges of the wings, rather like an aircraft's flaps during takeoff and landing, and helps wing twisting. It is unlikely that the giant Mid Carboniferous dragonflies could actually hover like modern forms but they had good maneuvrability. These winged giants had already developed a predatory lifestyle and, being about the size of a seagull, would have made a highly visible addition to terrestrial life in the forests of the Carboniferous (see p. 488).
The cirripedes or barnacles have shells, or capitula (singular, capitulum), consisting of several plates and these animals are adapted to an encrusting lifestyle. Two groups, the acorn barnacles and goose barnacles, have contrasting life strategies. The acorn barnacles, such as Balanus, have capitula consisting of overlapping plates and they are attached to rocks and other shells. The group rapidly diversified from an origin during the Late Cretaceous and are locally common. The goose barnacles are pseudoplankton, living attached to floating debris, that have a relatively poor fossil record.
The malacostracans include two subclasses, the phyllocarids and the eumalacostracans. The phyllocarids have large bivalved carapaces, seven abdominal somites and a telson with a pair of furcae (forked extensions; singular, furca), extending posteriorly. Canadas-pis from the Burgess Shale may be one of the first crustaceans. Living phyllocarids are usually minute, in contrast to their larger Paleozoic ancestors. The eumalacostracans include decapods - shrimps, lobsters and crabs - together with the less common branchiopods. Some of the most spectacular Carboniferous eumalacostracans have been
Figure 14.21 Carboniferous shrimps: (a) Tealliocaris woodwardi from the Gullane Shrimp Bed, near Edinburgh (x4); (b) Waterstonella grantonensis from the Granton Shrimp Bed, near Edinburgh (x2); (c) Crangopsis socialis and Waterstonella grantonensis from the Granton Shrimp Bed (x2). (Courtesy of Euan Clarkson.)
described from the Granton Shrimp Bed by Euan Clarkson (University of Edinburgh) and his colleagues (Fig. 14.21).
Ostracodes are crustacean arthropods, abundant and widespread in aquatic environments. They have small bivalved carapaces, hinged along the dorsal margin (Fig. 14.22a). The carapace is perforate and completely covers the entire animal when closed. Most ostra-codes are benthic, swimming, crawling or burrowing at the sediment-water interface in muds or silts with abundant organic material. A few, such as the myodocopids, are planktonic and some are commensal or parasitic. They are very useful for environmental recon structions and, at some levels in the strati-graphic record, have been used for correlation.
Ostracodes have weak segmentation with a poorly defined head, thorax and abdomen; the animal is contained within the two shells, with the carapace united dorsally by an elastic ligament and a variably developed hinge. Growth is by periodic ecdysis or molting. Following each molt phase the carapace initially develops as a pair of chitinous valves enclosing the animal; most of the carapace is then calcified, except the dorsal margin that remains as a chitinous ligament forcing the valves apart when the internal adductor muscles relax. The central muscle scars vary across the class (Fig. 14.22b), from complex patterns in the Leperditicopida to a single scar in some members of the Palaeocopida.
dorsal muscle scar third thoracic leg mandible antennule
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