The key to understanding fossil ecosystems is to understand the life habits of long extinct organisms. Yet, as direct observations are no longer possible, morphological details are usually the only ...available data source. One important aspect of lifestyle is feeding strategies, which can be inferred from morphological structures in comparison with those of extant relatives. The Lower Devonian Rhynie and Windyfield cherts preserve even minute structures to a high degree of detail, which allows investigation of the functional morphology of structures possibly involved in feeding. In this contribution, the feeding structures of different arthropods from the Rhynie and Windyfield cherts are described and the corresponding feeding strategies of the animals are discussed. This overview illustrates that in this early non-marine biota, a wide range of feeding strategies already existed.
This article is part of a discussion meeting issue ‘The Rhynie cherts: our earliest terrestrial ecosystem revisited’.
When the evolution of Euarthropoda is discussed, often the lineage of Chelicerata s. str. is assumed to be the more ‘primitive’ or ‘basal’ part of the tree, especially when compared to the other ...major lineage, Mandibulata. This claimed primitiveness is (at least partly) based on the assumption that different morphological structures are still in an ancestral state and did not evolve any further. One of these sets of structures is the feeding apparatus, which has been stated to be highly advanced in Mandibulata, but not ‘properly’ developed, or at least not to such a high degree, within Chelicerata s. str. In this study, I reinvestigate the feeding apparatus of different ingroups of Euchelicerata, with a focus on assumed ‘primitive’ groups such as Eurypterida and Trigonotarbida. The basis of this study is a large amount of material from different museum collections, with fossils with the entire feeding apparatuses being exceptionally well preserved. Based on high-resolution micro-photography and three-dimensional imaging, it is possible to resolve fine details of the feeding apparatuses. The results make clear that the feeding apparatuses of different ingroups of Euchelicerata are highly specialised and often possess morphological structures comparable to those of the feeding apparatuses of representatives of Mandibulata, apparently convergently evolved. Though the reconstruction of the evolution of the feeding apparatus within Euchelicerata is to a certain degree hampered by unclear phylogenetic relationships, there was clearly a shortening of the feeding apparatus from posterior (i.e. only the anterior appendages being involved in the feeding apparatus), probably linked to the colonisation of land in Arachnida.
Larvae of the group Holometabola (beetles, wasps, flies, moths and others) differ significantly in their morphology from their corresponding adults. In most larvae, appendages and other structures ...protruding from the body (antennae, palps, legs, trunk processes) appear less elongate than in their corresponding adults, providing the impression that these larvae are restricted to a certain degree in developing more elongate structures. We provide here numerous counterexamples of larvae of lacewings (Neuroptera). These include different forms of elongated antennae, mandibles, maxillae, labial palps, legs, trunk processes and neck regions. Most of these examples are larvae preserved in different types of 100 million-year-old amber. The longest neck region was found in an extant specimen. All these examples demonstrate that certain branches of Neuroptera indeed had larval forms that possessed strongly elongated structures. Hence there is no principal constraint that hinders holometabolan larvae to develop such structures.
Abstract
Physogastry is a phenomenon occurring in Euarthropoda and describes an extreme inflation of (parts of) the trunk. It is best known from ticks, termite queens, or honey-pot ants, but can also ...be found in several other representatives of Euarthropoda. Physogastry has so far rarely been seen in the fossil record. We describe here an example of physogastry in two lacewing larvae (Neuroptera) enclosed in a single piece of Kachin amber (ca. 100 Ma old). We measured head and trunk ratios of different physogastric and non-physogastric representatives of Euarthropoda. Plotting these ratios shows that the new larvae, which display quite extremely inflated trunks, are very similar to ticks or honey-pot ants, but also to certain lacewing larvae of the group Berothidae (beaded lacewings). Outline analysis of head capsule and mouthparts (stylets) further suggests a position within Berothidae. Physogastry is presumed to be linked with living in confined spaces such as wood galleries or soil. Indeed, at least some larvae of Berothidae are known to live inside termite nests for part of their larval life phase, a habit the new larvae may also have had. The new record represents the oldest case of extreme physogastry in insects known to date.
Most morphological studies focus on adult specimens, or if developmental studies are pursued, especially in Euarthropoda, they focus on embryonic development. Araneae (spiders) is one of these ...groups, in consequence with understudied post-embryonic development. Here we present aspects of the post-embryonic stages of different species of Mesothelae, sister group to the remaining spiders (when fossil species are not taken into account). We used different imaging methods and measured different external morphological structures to detect possible ontogenetic changes. One structure exhibiting post-embryonic changes is the chelicera. Here the significant change occurs between the last immature stage and the adult, yet only in males. For the spinnerets, we could not detect ontogenetic changes, but instead a high variability in length and width, probably due to their lack of pivot joints between the elements. The strongest morphological change during ontogeny occurred on the sternum, which begins with a rather roundish shape in the first stage and changes to being fairly elongate in shape in the last immature stages and the adult. This specific sternum shape only occurs in adults of mesothelan spiders, while opisthothelan spiders have a broader sternum also in the adult. We discuss our results in an evolutionary context, also taking into account recent finds of fossil spiders.
The group Xiphosurida (horseshoe “crabs”) is today only represented by four species. However, in the fossil record, several dozen species have been described, especially from the Carboniferous (about ...300 million years ago). Several species have been interpreted as representatives of
Euproops
or
Belinurus
, but there is ongoing discussion which of these species are valid and how they can be differentiated. Recent studies suggested that differences in the timing of individual development could provide information for species distinction, exemplified by studies on
Euproops danae
(Mazon Creek, USA) and
Euproops
sp. (“Piesproops”; Piesberg, Germany). For this study, we reinvestigated all Carboniferous xiphosurids from the British Coal Measures stored in the collections of the Natural History Museum London. Size comparisons of the specimens revealed nine size groups; the smaller specimens were originally labelled as
Belinurus
, the larger ones as
Euproops
. The nine size groups exhibit five different morphotypes differing in structures surrounding the posterior shield (= thoracetron): spines of different lengths and, in larger specimens, a more or less developed flange. Two of these morphotypes show significantly longer spines than the remaining specimens and could be conspecific as
E. anthrax
. The remaining specimens are interpreted as growth series of another species, presumably of
E. rotundatus
. An ontogenetic flange formation is also known from
E. danae
and the “Piesproops”, but the timing differs between all three species. In
E. rotundatus
, the flange develops rather late, but then comparably abruptly, which makes this development more metamorphic in relation to development in the other species.
Loss of biodiversity and especially insect decline are widely recognised in modern ecosystems. This decline has an enormous impact due to the crucial ecological roles of insects as well as their ...economic relevance. For comparison, the fossil record can provide important insights on past biodiversity losses. One group of insects, for which a significant decline over the last 100 million years has often been postulated, but not demonstrated quantitatively, is Neuroptera (lacewings). Many adult lacewings are pollinators, while the larvae are mostly predators, which becomes very obvious from their prominent stylet-like mouthparts. We investigated the fossil record of larvae of all neuropteran lineages as well as a large share of extant neuropteran larvae. Based on these, we performed an outline analysis of the head with stylets. This analysis provides a quantitative frame for recognising the decline of lacewings since the Cretaceous, indicating also a severe loss of ecological roles.
Thylacocephalans are enigmatic arthropods with an erratic Palaeozoic and Mesozoic fossil record. In many of the few localities where they occur, they are quite abundant. This also holds true for the ...Famennian Thylacocephalan Layer in the Maider (eastern Anti-Atlas of Morocco), a small epicontinental basin hosting some strata with taphonomic properties of a conservation deposit yielding exceptionally preserved gnathostomes and non-vertebrates. In a thin argillaceous interval in the earliest middle Famennian, thylacocephalans occur in such great numbers that they became eponyms of this unit. Therein, we discovered a new taxon of thylacocephalans, Concavicaris submarinus sp. nov., which represent the oldest records of thylacocephalans from Africa. In the CT-imagery, the holotype of Concavicaris submarinus sp. nov. revealed anatomical details including its eyes, appendages and other soft parts. Sedimentary facies and faunal composition of the Thylacocephalan Layer suggest that these animals populated the water column above the low-oxygen sea floor. Thus, thylacocephalans likely represented an important component of the diet of chondrichthyans and placoderms, which are quite common as well. The abundance of thylacocephalans in other conservation deposits like the Cleveland Shale (USA) and the Gogo Formation (Australia) underline their pivotal role in Late Devonian pelagic food webs.
Brachyura and Anomala (or Anomura), also referred to as true and false crabs, form the species-rich and globally abundant group of Meiura, an ingroup of Decapoda. The evolutionary success of both ...groups is sometimes attributed to the process of carcinization (evolving a crab-like body), but might also be connected to the megalopa, a specific transitional larval phase. We investigate these questions, using outline analysis of the shields (carapaces) of more than 1500 meiuran crabs. We compare the morphological diversity of different developmental phases of major ingroups of true and false crabs. We find that morphological diversity of adults is larger in false crabs than in true crabs, indicating that taxonomic diversity and morphological diversity are not necessarily linked. The increasing morphological disparity of adults of true and false crabs with increasing phylogenetic distance furthermore indicates diverging evolution of the shield morphology of adult representatives of Meiura. Larvae of true crabs also show larger diversity than their adult counterparts, highlighting the importance of larvae for biodiversity studies. The megalopa phase of Meiura appears to be plesiomorphic, as it overlaps between true and false crabs and shows little diversity. Causes may be common evolutionary constraints on a developmental phase specialized for transitioning.
Centipedes are predatory representatives of the group Myriapoda and important components of the soil and leaf-litter fauna. The first pair of trunk appendages is modified into venom-injecting ...maxillipeds in all centipedes. The number of trunk appendage pairs varies between the different groups of centipedes, from 15 pairs as apparently ancestral (plesiomorphic) condition, up to 191 pairs. The last pair of trunk legs can be used for different tasks in centipedes, e.g. mechano-sensation, defense, or stridulation. Many morphological details are also known from fossil centipedes, but especially the oldest fossils are often fragmentary and the fossil record in general is rather scarce. Especially the late appearance of lithobiomorphans in Cenozoic ambers is notable, though some not formally described lithobiomorph-like specimens from Cretaceous amber from Myanmar have been published. We present here a new specimen from Cretaceous Kachin amber, Myanmar with a lithobiomorph-type of morphology,
Lithopendra anjafliessae
gen. et sp. nov. The very large ultimate leg appears to have been used for defence and is, in relative proportions, larger than in any known lithobiomorphan, only comparable to that in scolopendromorphans. With this, the specimen presents a mixture of characters, which are in the modern fauna only known from two different centipede groups. We discuss the implications of this new fossil, also concerning events of convergence in this lineage.
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