Ecological disruption close to the Ordovician‐Silurian boundary

Following a long period of stability there was substantial ecological disruption in the late Ordovician, accompanied by widespread extinction. The ecological upheaval was spread over a period of time (1 My?) and varied in intensity between different groups.

The greatest change in brachiopod faunas occurred in the tropics, where there were widespread extinctions. In temperate regions the community structure, although disrupted, was not destroyed. The deep shelf associations (Benthic Assemblages 4–5) of the Rawtheyan persisted in an attenuated form into the Hirnantian when they were supplemented by genera of the ”Hirnantia fauna” and then became strongly re‐established in the Llandovery.

Trilobites, in contrast to brachiopods, suffered a worldwide extinction in the late Ashgill. Approximately 40% of trilobite genera became extinct at, or near, the Rawtheyan‐Hirnantian boundary.

Analysis of the distribution of Rawtheyan trilobite and brachiopod genera supports a correlation between geographical distribution and survival. Global range charts for brachiopod and trilobite genera, incorporating ecological and palaeogeographical data, have been compiled for this study.     

A new species of eastmanosteid arthrodire (Pisces: Placodermi) from Gogo, Western Australia

A new species of Eastmanosteus Obruchev is described from the Upper Devonian Gogo Formation of Western Australia as E. calliaspis sp. nov. It is at the pachyosteomorph level of organization having no contact between the plates of the flank and those of the ventral shield behind the pectoral fin. Well preserved material of the parasphenoid and scapulocoracoid throws further light on the structure of these elements in arthrodires. The genus Eastmanosteus is reviewed.     

The late Devonian trilobite crises

Mid‐Devonian to end‐Late Devonian trilobites of different taxonomic categories are updated as to their actual stratigraphical range with respect to the internationally defined stage boundaries. The main palaeogeographical and ecological occurrences are summarized. Numerical analyses emphasize the clear relationship between fluctuations in diversity and global eustatic events. Already declining in diversity from the early mid‐Devonian, shallow‐water communities became most restricted during the mid‐Givetian Taghanic transgression. After a phase of adaptive radiation, off‐shore trilobite communities were severely affected during the mid‐ and end‐Late Devonian crises. From an initial 5 orders 3 were lost at the end‐Frasnian Kellwasser crisis while only 1 from the remaining 2 orders survived the Devonian‐Carboniferous boundary Hangenberg event. In both cases extinction was preceded by a unidirectional evolutionary trend in eye reduction accompanied by impoverishment of lower rank taxa. This phenomenon is obviously a result of selective adaptation under constant long‐lasting environmental influences. Specialization to obligate epi‐ or even endo‐benthic life habit, however, led fatally to extinction when stable conditions became substantially perturbed. Sudden sea‐level changes with subsequent break in the REDOX‐equilibrium took place at the Kellwasser and Hangenberg events, which were most probably responsible for trilobite mass extinctions.     

澳大利亚泥盆纪皱纹珊瑚生物地层及生物地理研究展望

通过对澳大利亚泥盆纪皱纹珊瑚属级分布的分析,认为泥盆纪珊瑚在该区经历了两大繁盛期,尤以Ｌｏｃｈｋｏｖｉａｎ－Ｅｍｓｉａｎ最盛,有大量新属产生,内板珊瑚和菲力甫珊瑚科分子要Ｐｒａｇｉａｎ期开始出现,绳珊瑚科的分子也在Ｅｍｓｉａｎ大量出现,这些分子继而通过洋流逐渐扩散到华南及老世界域其他省区。     

Punctuated equilibrium excused: the original examples fail to support it

The four original stipulations of the definition of punctuated equilibrium (PE; Eldredge & Gould, 1972) are shown to be unsupported, and even contradicted, by the two evidential examples these authors supplied: the trilobite Phacops rana of the Middle Devonian, and the land snail Poecilozonites bermudensis of Late Pleistocene Bermuda.
The additional, much-discussed example of Bellamya unicolor and the accompanying suite of molluscan species of Pliocene-Recent African Lake Turkana, studied by Williamson, also fails to exemplify PE. In particular, the data produced for these cases appear to represent counterexamples to Mayr's paradigm of peripatric speciation , embraced by Eldredge and Gould as the central effective mechanism of PE. The data actually illustrate instead a prevailingly centrifugal pattern of speciation that will accommodate and explain episodic aspects of microevolution in a more realistic way.     

New durophagous arthrodires from Gogo, Western Australia

Three new monotypic genera of eubrachythorarid arthrodires with crushing toothplates are described from the Upper Devonian Gogo Formation of Western Australia as Bruntonichthys multidens gen. et sp. nov., Bullerichthysfascidens gen. et sp. nov. and Kendrickkhthys cavemosus gen. et sp. nov. Their structure and relationships are discussed within the framework provided by a sketch cladogram. All three are interchangeable with Coccosteus spp. but their phylogenetic relationships are not known in any detail. However, Kendrickkhthys does appear to be immediately related to Dinomylostoma from North America.     

Eubrachythoracid arthrodires with tubular rostral plates from Gogo, Western Australia

Two monotypic genera of tubular-snouted eubrachythoracid arthrodires are described from the Upper Devonian Gogo Formation of Western Australia as Rolfosteur gen nov. and Tubonnsus gen. nov. They are most closely related to Camuropiscis Dennis & Miles, also from the Gogo Formation, and all three are therefore placed in the family Camuropiscidae nov. Rolfosteus and Tubonasus are jointly the sister-group of Camuropiscis .