SHEAR, W. A., and KUKALOVA-PECK, J. 1990. The ecology of Paleozoic terrestrial arthropods: the fossil evidence. Can. J. Zool.68: 1807-1834. The available fossil evidence for the ecology of terrestrial arthropods in the Paleozoic is reviewed and reinterpreted. Some original data are provided, derived mainly from the detailed morphology of mouthparts, genitalia, cuticular vestiture, and body form. Paleozoic chelicerates were more diverse than their modem descendants and were probably dominant ground-level and arboreal predators. Web-building spiders and highly diversified mites appear to have been absent. Paleozoic myriapods include possibly the earliest land animals, and as abundant detritivores, provided a major conduit for primary productivity into higher trophic levels. Paleozoic insects present many difficulties of interpretation, but appear to have been extraordinarily diverse and may have played quite different ecological roles from today's insects, viewed as a whole. It is postulated that herbivory, defined as predation on living plants, may have been rare in early Paleozoic terrestrial ecosystems, and that most primary productivity was funneled through detritivores and decomposers. In the late Paleozoic, the evidence for herbivory by insects, except for feeding on fructifications, is rare. Insects seem to have played a major part as a selective force on plant fructifications. SHEAR, W. A., et KUKALOVA-PECK, J. 1990. The ecology of Paleozoic terrestrial arthropods : the fossil evidence. Can. J. Zool. 68 : 1807-1834. On trouvera ici une rkvision et une nouvelle interprktation des donnCes palContologiques (fossiles) sur 1'Ccologie des arthropodes terrestres du PalCozoi'que. Des donnCes originales sont ajoutCes et elles ont trait surtout a la morphologie dCtaillCe des pikces buccales, des organes gknitalaux, du rev6tement cuticulaire et de la forme gCnCrale. Les chilickrates du PalCozoi'que Ctaient plus diversifiks que leurs descendants actuels et dorninaient probablement la faune des prkdateurs du sol et des prkdateurs arboricoles. Les araignCes tisseuses de toiles ne semblent pas avoir exist6 a cette Cpoque et les acariens ne paraissent par avoir Ct C trks diversifiis. Les myriapodes palCozoi'ques contiennent peut-6tre les animaux terrestres les plus anciens; ditritivores presents en abondance, ils constituaient un maillon important entre la productiviti primaire et les niveaux trophiques supkrieurs. Les insectes du PalCozoi'que sont assez difficiles a interprkter, mais semblent avoir Ct C remarquablement diversifiis et ont peut-&re, dans leur ensemble, jouC des r6les Ccologiques totalement diffirents des insectes d'aujourd'hui. I1 semble que << I'herbivorisme B, dCfini comme la prkdation de plantes vivantes, ait Ct C relativement rare au sein des Ccosystkmes terrestres du PalCozoi'que infkrieur, et que la majeure partie de la productivitC primaire soit passCe par les dktritivores et les dCcomposeurs. L'Cvidence de phytologie des insectes du PalCozoique supCrieur, a I'exception de ceux qui se nourrissaient s...
a b s t r a c tMillipedes are some of the earliest examples of terrestrial animals, and fossils from the early Carboniferous Period indicate they were also some of the earliest prey. These fossils record ozopores, the openings of chemical defense glands, occurring along the length of the body. The secretions of these glands may consist of topical irritants, repellents, antifeedants, or, in the case of the large and widespread Order Polydesmida, hydrogen cyanide (HCN) gas that can be fatal to other arthropods or even small vertebrates in a confined environment. Müllerian mimicry rings may develop in which unrelated species of millipedes that co-occur closely resemble one another, while participating in a completely differently patterned ring in another part of their geographic range. Chemistry is not the only defense of millipedes. Polyxenids carry tufts of entangling setae, many species rely on crypsis and the ability to roll into a smooth, resistant sphere or coil, and still others have spikey projections that may deter soft-mouthed predators. Nevertheless, chemical defense has been of significance in helminthomorph millipedes at least since the Lower Carboniferous. The distribution of classes of chemical defense compounds follows major phylogenetic groupings. Evidence suggests that the defensive glands of Glomerida arose independently of those of the Helminthomorpha.
Mandibles are feeding appendages functioning as "jaws" in the arthropod groups in which they occur. Which part of this appendage is involved in food manipulation (limb tip versus limb base), has been used to suggest phylogenetic relationships among some of the major taxa of arthropods (myriapods, crustaceans, and insects). As a way to independently verify the conclusions drawn from previous morphological analyses, we have studied the expression pattern of the gene Distal-less (Dll), which specifies the distal part of appendages. Our results show, in contrast to the traditional view, that both insect and crustacean adult mandibles are gnathobasic, handling food with the basal portion of the appendage. Furthermore, as is evident by the reduction in the number of Dll-expressing cells in the later developmental stages, adult diplopod jaws are also gnathobasic. Thus, jaws of all mandibulates (myriapods, crustaceans, and insects) seem to have a similar gnathobasic structure. We have also found that Dll is expressed in the labra of all arthropod taxa examined, suggesting that this structure is of appendicular derivation. Additionally, the spinnerets and book lungs of spiders, long considered on other grounds to be modified appendages, express Dll, confirming this interpretation. This study shows that, in addition to their use in phylogenetic and population genetic studies, molecular markers can be very useful for inferring the origins of a particular morphological feature.
Fourteen oribatid mite fossils have been recovered from a terrestrial Devonian deposit near Gilboa, New York; they allow an approximate doubling of the known age of the group. Two species are represented by specimens complete enough to allow descriptions. Protochthonius gilboa n. gen. and sp. is the earliest derivative known member of the Enarthronota, and comprises the monobasic new family Protochthoniidae. Devonacarus sellnicki n. gen. and sp. also represents a monobasic new family, Devonacaridae; it may also be an early derivative enarthronote mite, but its relationships are uncertain. Two other species are represented at the site, but meaningful descriptions are not possible with available material.
Silk production from opisthosomal glands is a defining characteristic of spiders (Araneae). Silk emerges from spigots (modified setae) borne on spinnerets (modified appendages). Spigots from Attercopus fimbriunguis, from Middle Devonian (386 Ma) strata of Gilboa, New York, were described in 1989 as evidence for the oldest spider and the first use of silk by animals. Slightly younger (374 Ma) material from South Mountain, New York, conspecific with A. fimbriunguis, includes spigots and other evidence that elucidate the evolution of early Araneae and the origin of spider silk. No known Attercopus spigots, including the original specimen, occur on true spinnerets but are arranged along the edges of plates. Spinnerets originated from biramous appendages of opisthosomal somites 4 and 5; although present in Limulus, no other arachnids have opisthosomal appendage homologues on these segments. The spigot arrangement in Attercopus shows a primitive state before the reexpression of the dormant genetic mechanism that gave rise to spinnerets in later spiders. Enigmatic flagellar structures originally described as Arachnida incertae sedis, are shown to be Attercopus anal flagella, as found in Permarachne, also originally described as a spider. An arachnid order, Uraraneida, is erected for a plesion, including these two genera, based on this combination of characters. The inability of Uraraneida precisely to control silk weaving suggests its original use as a wrapping, lining, or homing material.Araneae ͉ Chelicerata ͉ Devonian ͉ Paleozoic ͉ silk
The discovery of six specimens of the enigmatic order Siphoniulida, including for the first time males, prompted a modern re‐analysis of current phylogenetic schemes for the class Diplopoda derived from traditional morphological and developmental characters. The data matrix was constructed and analysed using paup. The resulting phylogenetic hypotheses corroborated the longest standing, traditional classification, but also demonstrated clearly that more characters must be included to reach a better resolution. Recent alternative phylogenetic hypotheses and classifications are discussed in the light of the current analysis. The validity of a putative helminthomorph synapomorphy, the location of male gonopods on the 7th body ring, is discussed. Scanning electron microscopy corroborated morphological characters already described for the Siphoniulida: modified anterior legs, an apparently legless 3rd body ring, pyriform head, antennae with clavate setae, and absence of ozopores. The highly modified gonopods of the Siphoniulida are described for the first time; only the anterior legs of the 7th ring are modified into gonopods, the posterior legs of this ring are developed as normal walking legs. The gnathochilarium differs from the Colobognatha and consists of well‐developed stipites with palps, elongated lingual plates with palps and a narrow central sclerite, most likely the mentum. Structures on the epiproct may possibly be spinnerets. Despite the discovery of adult males, the Siphoniulida are still considered Helminthomorpha incertae sedis .
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