Heterochrony in Silurian phacopid trilobites as suggested by the ontogeny of Acernaspis

New material of early growth stages of the Silurian (Llandovery) trilobite Acernaspis is described. Pre-adult ontogenetic stages of this genus closely resemble adults of the post-Llandovery genus ***Ananaspis. A heterochronic descent of Ananaspis from Acernaspis is proposed. ***Ananaspis is interpreted as pae-domorphic, having arisen largely through neoteny. Neotenic changes already appear in the lineage in the last Acernaspis species, and Ananaspis then underwent continuous ncotcnic change throughout its known Silurian history. ▭ Heterochrony, neoteny, Silurian, Trilobita, Phacopidae, Acernaspis. Ananaspis.     

The preoral cavity of lower Hymenoptera (Insecta): comparative morphology and phylogenetic significance

The skeletal and muscular morphology of the preoral cavity, including the labrum, hypopharynx and labium, was examined in the imago in representatives of all the ‘symphytan’ families as well as the apocritan families Stephanidae, Megalyridae and Trigonalyidae. Xyelidae have complex modifications for masticating pollen, remarkably similiar to those of primitive Lepidoptera. These modifications, collectively termed the triturating basket complex, include an asymmetrical distal epipharyngeal wall with a microtrichial brush and an enlarged infrabuccal pouch with heavy cuticular armature that interacts with the mandibles during feeding. There were striking structural differences between the two subfamilies of Xyelidae in the ligular region; the reduced glossa and clubshaped paraglossae of Macroxyelinae resembles those of primitive Lepidoptera, while the well developed, flattened glossa and paraglossae in Xyelidae are similiar to those of most other ‘Symphyta’. A putative transformation series, leading from a relatively large labrum with unsclerotised distal epipharyngeal wall lying anterior to the mandibles, as seen in Xyelidae and enthredinoidea, to a small and heavily sclerotised labrum and distal epipharyngeal wall lying posterior to the mandibles, as seen in ‘Siricoidea’, Orussidae and the Apocrita, was revealed. These modifications may be adaptations to enable the adult of the families pupating in wood to emerge from the pupal chamber. The Anaxyelidae, Orussidae and Apocrita have similiar configurations of the glossa and nsertions of the ventral premental adductors. This indicates a close affinity of the Anaxyelidae to Orussidae + Apocrita, a hypothesis that is in conflict with other character systems. The Orussidae and Stephanidae share a unique condition in the development of a pair of large apodemes attached to the labrum; this renders the groundplan state of the labrum in the Apocrita uncertain. Twentyfive characters were defined in an attempt to eludicate the ‘Symphyta’–Apocrita transition. A numerical cladistic analysis of the characters was undertaken, resulting in 522 minimum length trees. The characters are also discussed with reference to a cladogram which resulted from an analysis of the characters derived from the present study and a survey of characters from literature.     

A revision of the genus Dinofelis (Mammalia, Felidae)

This paper consists of a taxonomic and systematic revision of the extinct felid genus Dinofelis (Felidae, Ma-chairodontinae) and an analysis of its ecomorphology and evolution. Dinofelis has a broad distribution, with material from all northern continents and Africa, the latter of which was the apparent centre of evolution of the genus. We describe new material of Dinofelis from a number of sites in eastern Africa and reconsider all previously described material. We name two new species and identify several other distinct species-level taxa but refrain from naming these due to a paucity of well-preserved material. At the same time, we synonymize the two named Asian species, D. cristata and D. abeli , of which the former has priority. There are few characters useful in systematic analysis, but we can suggest at least one migration from eastern to southern Africa. Ecomorphological analysis of both craniodental and postcranial characters suggests that Dinofelis in many respects converged on modern pantherine cats in morphology and behaviour, a trend culminating in the South African D. barlowi and the Asian D. cristata , which are the most pantherine-like of all machairodont felids. This trend is reversed in the evolution of the youngest species, D. piveteaui , which is also the most machairodont in its ecomorphology. The timing of the extinction of Dinofelis is difficult to determine. Outside Africa material is scarce at all times, while in Africa the apparent extinction of Dinofelis at about 1.4 Mya coincides with the end of the good, semi-continuous fossil record present in eastern Africa from about 4 Mya onwards. Dating of Kanam East (with D. piveteaui) to the Jaramillo Subchron (1.070-0.990 Mya) suggests possible survival considerably later. Thus, the extinction datum for Dinofelis cannot at present be firmly established.     

Nitrate leaching from three afforestation chronosequences on former arable land in Denmark

In regions dominated by agricultural activities, nitrogen (N) is recognized as a major pollutant in aquatic environments. In north‐western Europe, afforestation of agricultural land is part of a strategy to improve water quality. In Denmark, former arable land has been afforested during the past 40–50 years. This study evaluated the effect of afforestation of former arable land on nitrate leaching, based on three afforestation chronosequences. Precipitation, canopy throughfall and soil water were collected and soil moisture was monitored at two Danish locations, Vestskoven (nutrient‐rich, medium deposition) and Gejlvang (nutrient‐poor, high deposition). Afforestation was performed using Norway spruce [Picea abies (Karst.) L.] and common oak (Quercus robur L.) at Vestskoven and Norway spruce at Gejlvang. The results suggest that afforestation of former arable land initially leads to lower nitrate leaching than that occurring under the former agricultural land use, and largely below the standard of 50 mg NO⁻₃ L⁻¹ for groundwater to be utilized as drinking water. Nitrate concentrations became almost negligible in forest stands of 5–20 years of age. However, after canopy closure (>20 years) nitrate concentrations below the root zone and nitrate leaching tended to increase. This was attributed to increased N deposition with increasing canopy development and decreased N demand once the most N‐rich biomass compartments had been built up. Nitrate leaching started to increase at a throughfall deposition level of about 10 kg N ha⁻¹ yr⁻¹. Compared with nutrient‐poor sandy soils, nutrient‐rich clayey soils appeared more vulnerable to disturbance of the N cycle and to increased N deposition, leading to N saturation and enhanced nitrate leaching. In approximately the first 35 years after afforestation, nitrate leaching below the root zone was generally higher below oak than below Norway spruce.     

Studies of fossil hyaenids: the genera Ictitherium Roth & Wagner and Sinictitherium Kretzoi and a new species of Ictitherium

Samples of the Miocene hyaenid Ictitherium from China and Pikermi, Greece, are analysed statistically. Ictitherium viverrinum Roth & Wagner, 1854 and Ictitherium gaudryi Zdansky, 1924, are found to be conspecific. Ictitherium sinense Zdansky, 1924 is also reduced to synonymy with Ictitherium viverrinum. Ictitherium kurteni sp. nov. differs from 1. viverrinum particularly in its large C^s and large and broad P³.     

The old wasp and the tree: fossils, phylogeny and biogeography in the Orussidae (Insecta, Hymenoptera)

The phylogenetic relationships of the fossil orussid taxa Mesorussus taimyrensis and Minyorussus luzzi are examined by analysing them together with a large data set compiled previously for the extant Orussidae. The fossils are placed in an unresolved trichotomy with the extant Orussidae. The phylogeny is used for evaluating the hypothesis that the ancestors of the family had reduced body size; the results of this analysis are inconclusive. The biogeographical history of the Orussidae is explored. The common ancestor of the family was probably widespread, the initial splitting events taking place prior to or coinciding with the separation of Laurasia from Gondwana. Later putative vicariance events can be correlated with the gradual breakup of Gondwana. However, the biogeographical history of the Orussidae is dominated by speciation within regions and dispersal. The minimum age of the common ancestor of the Orussidae is >180 Myr when estimated from the biogeographical pattern, >95 Myr when estimated from the phylogenetic position of the fossils; the earlier date is considered to be the most likely.  © 2004 The Linnean Society of London , Biological Journal of the Linnean Society , 2004, 82 , 139–160.