Succession of late Wenlock graptolites in the Kursala Formation, Tien Shan (Kirghizia), documents of the early recovery phase after the global C. lundgreni Event. Pristiograptus dubius was the only survivor among monograptids. After displaying a mass occurrence and an increased variation, the P. dubius stem lineage splits into two main trends: line A, represented by Pristiograptus idoneus and line B, represented by Colonograptus? praedeubeli. The former leads to Lobograptus? sherrardae, a generalized forerunner of such diverse trends as linograptids, cucullograptids and possibly also neocucullograptids (via Bohemograptus). The latter initiates the Colonograptus-Saetograptus line. The P. idoneus - L.? sherrardae lineage shows distinct gracilization, an apomorphic feature, while the other one preserves ancestral robustness, a plesiomorphic character. Hence, the bulk of the later monograptids of Gorstian and Ludfordian age may be derived from the P. dubius stem lineage. In respect of this conservative lineage a non-cladistic approach is prefered, because its morphological spectrum and evolutionary potential, and as we believe its specific identity, were preserved, in spite of numerous speciation events, until the early Pridoli.
An assemblage of animal remains, the oldest from undoubted nonmarine beds, with structures attributable to at least one possible terrestrial animal, has been recovered in deposits of Early Silurian, Rhuddanian age, from the Central Appalachians. Other elements of a terrestrial ecosystem are plants at a nonvascular, possible liverwort-like, level of organization, and ascomycetes, predominantly terrestrial saprophytic and parasitic fungi (the oldest known). Together they provide evidence that pre-tracheophytic land plants and fungi, in association with invertebrates, occupied continental habitats by at least the earliest Silurian. While no evidence suggests that these organisms existed in a single community, they provide the earliest fossil record for the coexistence of varied organisms in the nonmarine ecosystem. Terrestrial invertebrates may have co-occurred with the earliest mid-Ordovician embryophytes although no fossil evidence for invertebrates exists before the Late Ordovician/Early Silurian. In view of the limited embryophytic dependence of many soil invertebrates, a preembryophytic evolution for them is consistent with the postulated significance of the soil habitat in terrestrialization and the evolution of feeding strategies among nonpredatory terrestrial invertebrates from microphytophagy to detritivory to herbivory as some emerged from within soils to soil litter to the soil surface. Detritivory can be regarded as a derivative extension of microphytophagy, since detritivores only consume detritus ‘processed’ by microorganisms and may be selecting microorganisms from detrital substrates as the basis of their nutrition.
A new record of the phosphate microbrachiopod genus Acrotretella Ireland, 1961 from the Lower Ordovician of the Baltic syneclise, in north-east Poland is the oldest known species of the genus. Acrotretella goldapiensis sp. n. co-occurs with conodonts in shallow-water facies of Late Llanvirn age. The new data from Poland extend the statigraphical range of the genus from the Llanvirn to the middle Silurian (Ludlow); during the later Ordovician and Early Silurian Acrotretella apparently migrated westwards to sequentially occupy shallow-water facies on the palaeocontinents of Baltoscandia (Poland and Sweden), Avalonia (England), Laurentia (North America) and Australasia (Australia) with relatively little morphological change.
An abundant early Silurian brachiopod assemblage of 14 species, with strong affinities to the early Rhuddanian faunas of Britain and Baltoscandia, was recovered from the Akkerme Peninsula, on the western side of Lake Balkhash, southern Central Kazakstan. The occurrence of Stricklandia lens mullochensis, which is ttre earliest member of the Stricklandia-Costistricklandia lineage, dates this brachiopod assemblage as early Rhuddanian, within a stratigraphic interval from the Akidograptus acuminatus to the lower part of the Monagraptus cyphus graptolite biozones. This is the first well documented record of early Rhuddanian brachiopods in Kazakhstan. The assemblage also includes Meifodia tulkulensis sp. nov. and Eospirifer cinghizicus with well preserved spiralia. The co-occurrence of Stricklandia lens mullochensis and Eospirifer cinghizicus has not been recorded previously and is regarded here as the most signiffcant difference between the early Rhuddanan brachiopod faunas of the Baltic (East-European) Plate and Britain; in contrast Eospirifer first appears in the two latter areas in the late Llandovery.
Glacial erratic boulders of the Ostseekalk type, late Caradoc in age, contain spumellarian radiolarians with their skeleton substituted by iron minerals secondarily oxidized to goethite. Species of both the Inaniguttidae, characterized by the presence of a small spherical central shell, and Entactiniidae, with a transverse central bar, have been identified. A similar radiolarian assemblage, but with original siliceous skeletons preserved, has been identified in a graptolitic lirnestone boulder, early Ludlow in age.
The question of whether branching and budding in halysitid tabulate corals was regulated by the availability of nutrients or exposure to waste products is important for taxonomy. Moreover, such regulation could have implications for paleoenvironmental interpretation. Although the statistical and morphological evidence presented here is not unequivocal, it is suggested as a working hypothesis that halysitid astogeny was indeed regulated. This would be in accordance with current theories on the growth of Recent corals and sponges. The simulation results are used to reevaluate functional advantages of the regulation of the halysitid colony.
Oligophyly may be defined as a restrictive factor in evolution leading to minimization of the number of phyletic lines owing to an occasional reduction by means of mass extinction as well as to their recovery from scanty survivors. The monophyletic origin of the vast majority of taxa finds its explanation in this succession of events, namely in the diversity reduction (DR) - rediversification (RD) sequence. In turn, the recovery from a few or a single ancestral species (near-monophyly or monophyly) causes a number of consequences for the evolution of emerging new taxa. They produce a particular class of systematic groups called genealogical domains. Such groups display an exceptionally close affinity and a similar evolutionary potential exhibited i-.e. an abundant parallelism. In other words, the paucity of ancestry (oligophyly) explains why both the monophyletic origin and evolutionary parallelism are such common features of the phylogeny in most fossil groups. Parallelism is caused by the similarity of apomorphic tendencies (known as 'underlying synapomorphy' in phylogenetic systematics), which are among the most characteristic features of evolution within a genealogical domain. It is now evidenced that the vast majority of Late Silurian monograptid faunas are descendants of only two species - survivors from the severe lundgreni Event. Numerous cases of heterochronic parallelism and evolutionary repetitions observed within the repertoire of the Late -Silurian monograptid faunas may be explained as a far reaching effect of oligophyly. Each ancestral species established its own genealogical domain displaying certain apomorphic tendencies. The same is true for the monophyletic origin and early radiation of Llandovery monograptids. Whilst graptolites provide numerous graphic examples substantiating the oligophyly concept, it is clear that the phenomena discussed are of a much more general nafure.