Carr, R. K., 1995a. - Biological Sciences

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pressed during preservation. Little information is obtainable from other petalichthyids, concerning
body form, other than the partial shift of the orbits onto the head shield. Rhenanids disappeared
from the North American craton during the Frasnian-Famennian extinction episode (Upper
Frasnian last appearance) well after the Middle-Upper Devonian facies transition from shallow
water carbonates to anoxic clastic deposits. Petalichthyids survived into the Famennian. However,
petalichthyid and rhenanid low global diversities argue against the attachment of any particular
significance to their final disappearance.
The order Phyllolepida (Figs. 3C, 4-5) was clearly present in the Frasnian and survived,
until the end of the Devonian. They reached their highest specific diversity after the Frasnian­
Famennian extinction episode. An earlier Eifelian first appearance may be indicated if Antarctaspis
(whose stratigraphic range is unclear, i.e. Middle or Upper Devonian) is considered as a
member of Phyllolepida (family Antarctaspidae is considered here Arthrodira incertae sedis).
Phyllolepida were thought to be restricted to freshwater by DENISON (1978; BENDIX-ALMGREEN,
1976), al though LERICHE (1931) concurred, he noted the lateral association between Belgian
marine' Schistes de la Famerule and Psammites et Schistes d'Evieux which now suggests the
possibility that these latter phyllolepid deposits are potentially marginal marine. Recent analyses
also have called into question a non-marine interpretation for some Old Red Sandstone style
sediments (see discussion below). Phyllolepids survived the Frasnian-Famennian extinction
(table 1) with a specific increase, but a without generic change; however, low specific diversity
limits analysis.
The order Antiarcha (Figs. 3D, 4-5) first appeared in the Silurian of China and possibly
survived to the Lower Carboniferous (seven of the eight species recorded from the Carboniferous
are resolved temporally to series-level, i.e. Lower Carboniferous, suggesting that diversity plots
for antiarchs, figures 1, 2, 5, and 10, may artificially extend their range through the Visean).
Diversity during the Lower Devonian remained stable with successive increases seen in the
Eifelian, Givetian, and Frasnian when they finally reached their peak. Again, many species are
known from Old Red Sandstone facies. Antiarch extinction across the Frasnian-Famennian boundary
was between 30-58% (table I).
The order Ptyctodontida (Figs. 3E, 4-5) first appeared in the Siegenian with their last appearance
in the Famennian (Tollodus brevispinus is recorded from the Siegenian of the Soviet
Arctic, 0RVJG, 1980b, with other genera first appearing in the Eifelian). After the Eifelian, specific
diversity continued to increase until the Frasnian-Famennian extinction episode when 75-77%
of ptyctodont species went extinct (table 1). Generic diversity remained level from the Eifelian
through the Frasnian with a 71 % decline of known genera at the Frasnian-Famennian boundary.
FIG. 3. - Representative reconstructions for members of the placoderm orders discussed in the text. A, Lunaspis broilii, dorsal
view. A, a petalichthyid. B, Gemuendina stuertzi, dorsal view, a rhenanid. C, Phyllolepis orvini, dorsal view of head and
Ihoracic shields, a phyllolepid; D, Ctenurella gladbachensis, a ptyctodont, lateral view. E, Bothriolepis calladensis, an antiarch.
lateral view. F, Coccosteus cuspidalus, a brachythoracid, lateral view. A-F taken from STENSIO, 1963.
Recollstitutiolls de divers taxons d'ordres de Placodermes presentes dans Ie texte. A, un phalichthyide, Lunaspis broilii, vue
dorsale. B, un rhenanide, Gemundina stuerzi ell vue dorsale. C, un phyllolepide, Phyllolepis orvini, vue dorsale des cuirasses
cranienne et thoracique. D, Ull ptyctodollte, CtenureJla gladbachensis ell vue latera/e. E, un al1tiarche, BOlhriolepis canadensis
ell vue laterale. F, un brachythoracide, Coccosteus cuspidatus en vue laterale. Figures A-F reprises de STENSIO, 1963.