Page 392 - Introduction to Paleobiology and The Fossil Record

ECDYSOZOA: ARTHROPODS 379

Box 14.5 Fossil spider webs

Beautifully intricate but lethal spider webs are an integral part of terrestrial arthropod ecosystems.
But how old is this specialized and unique mode of predation? Arthropods trapped in spider silk
webs have, in fact, been recovered from Early Cretaceous amber (Fig. 14.17). Enrique Peñalver and
his colleagues (2006) have illustrated a remarkable mosaic of silk strands, some with sticky droplets,
which ambushed a fly and a mite, whereas another piece of amber shows a trapped wasp. The webs

were elastic and armed with glue droplets – no match for stray insects. Preservation of spider silk
in Lower Cretaceous amber from the Lebanon and from Spain suggests this form of predation was
already well established by the Cretaceous. The diversification of the insects during the later Meso-

zoic was tracked by a similar diversification in spiders; perhaps the evolution of aerial webs and

winged insects was linked, evidence of an arms race in the airways of the Cretaceous.

1 mm

(a)

(b)

Figure 14.17 Insects trapped in a Cretaceous spider’s web: (a) reconstruction and (b) actual
specimen. Strands of the web have been emphasized on the reconstruction together with droplets;

a fly (center left) and mite (top right) were both caught in the web. (Courtesy of Enrique
Peñalver.)

legs. The opisthosoma usually has 12 seg- pauropods. They first appeared during the

ments. Arachnids breathe mainly through so- Mid Silurian, when Kampecaris-like forms
called book lungs or tracheae or both. were responsible for a variety of terrestrial
trails (Box 14.6). Some of the largest forms,
for example the giant Arthropleura, nearly
SUBPHYLUM MYRIAPODA
2 m long, hoovered their way through the
The myriapods are a varied group comprising lush, green vegetation of the Late Carbonifer-
the millipedes, centipedes, symphylans and ous forests.