. Bulletin of the British Museum (Natural History), Geology. Asb Bri Pnd Am Cho Alp Kin Mrd Yea Lan Due Bol WeDCan Bar SIB SIC Aul Stages — Laveineopteris + Neuralethopteris * Neurocallipteris -•-Neuropteris X Paripteris "? Sphenoneuropteris Fig. 20 Stratigraphical diversity of six of the more abundant neuropteroid form-genera, showing complexity hidden by generalized graph in Figure 19a. analysis is based only show it as far back as the Langsettian). It then undergoes a significant decline in the lower Duckman- tian. Only one of the species extends much beyond the middle Duckmantian, and
. Bulletin of the British Museum (Natural History), Geology. Asb Bri Pnd Am Cho Alp Kin Mrd Yea Lan Due Bol WeDCan Bar SIB SIC Aul Stages — Laveineopteris + Neuralethopteris * Neurocallipteris -•-Neuropteris X Paripteris "? Sphenoneuropteris Fig. 20 Stratigraphical diversity of six of the more abundant neuropteroid form-genera, showing complexity hidden by generalized graph in Figure 19a. analysis is based only show it as far back as the Langsettian). It then undergoes a significant decline in the lower Duckman- tian. Only one of the species extends much beyond the middle Duckmantian, and that is what is referred to in the chart as the N. obliqua group. This pattern seems to be in general agreement with what is seen in areas other than the Franco-Belgian Basin. As with the other neuropterids, N. obliqua sensu stricto undergoes a marked decline in the lower Duckmantian. However, in the upper Duckmantian there is the start of a progressive change in the venation, which becomes more flexuous and eventually culminates in the anastomosed- veined form known as Reticulopteris Gothan. Details of this gradual change in venation through the Duckmantian and Bolsovian have been documented by Josten (1962), and the possible adaptive advantage of this style of venation is discussed by Zodrow & Cleal (1993). This morphological change is accompanied by a proliferation of the group of species, especially in the Bolsovian. The abundance of the N. obliqua group then undergoes a dramatic collapse in the topmost Bolsovian and it eventually becomes extinct in the upper Westphalian D. This collapse in abundance coincides approximately with the appearance of the second group of neuropterids at the base of the Westphal- ian D. In the Franco-Belgian Basin, this consists of just one species, namely N. ovata, but elsewhere in Europe there are other, very similar species which come in at about the same level (N. flexuosa, N. plicata and N. ervedosensis). This is near the top of the
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