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TRILOBITE BIOGEOGRAPHY OF GONDWANA 61

Fig. 3. (b) Neseuretus subclade from second strict consensus cladogram generated by removing N. attenuatus,
N. chaschuilensis and N. sexangulus from the dataset.


between the consensus tree and the known

stratigraphic ranges of the ingroup taxa. As

Neseuretus represents a derived member of the

Reedocalymeninae in the consensus tree, all of

the major subclades are constrained to have

evolved by the Arenig. This necessitates ghost

ranges during the Arenig for N. sanlucasensis

and the Reedocalymene-Calymenesun subclade

only, providing fairly good correlation at series

level, although the stratigraphic occurrence of

Neseuretinus, Sarrabesia and Vietnamia remains

poorly understood for many Asian localities

and little confidence can be placed on strati-

graphic ranges within this subclade (e.g. Dean

1967b; Pillet & de Lapparent 1969; Hammann

& Leone 1997; Zhou et al. 1998a).

Cladistic biogeography

The consensus cladogram in Figure 3a was con-

verted into an area cladogram for biogeographic

analysis by substituting the names of the

different ingroup taxa with the Early Ordovician

geographic area(s) from which they have been

recorded (Fig. 4). The area cladogram is simpli-

fied, as area redundancy has been corrected. For

the non-Neseuretus reedocalymenine taxa, the

combined biogeographic area occupied by all

representatives of the genus recognized herein

was recorded on the area cladogram.

Area delimitation in some cases requires

explanation. France+Spain are regarded as rep-

resenting a single biogeographic area, following

the strong faunal similarities between these

regions noted by previous authors (e.g. Paris

1998). Sengor (1984, 1987) proposed that

Turkey, the Sibumasu and Indo-China terranes

and areas of Central Asia represented a

peri-Gondwanan continent called Cimmeria.

However, Turkey represents a complex region,

with northern and southern Turkey now inter-

preted as having occupied separate palaeogeo-

graphic positions during the Ordovician.

Southern Turkey, source of the Turkish material

of Neseuretus and Neseuretinus, was tentatively

assigned to a high-latitude position on the

margin of Gondwana at the eastern end of the

present-day Mediterranean (Dean et al, 2000;

Cocks 2001), the eastern region of the North

Gondwanan Province of Paris (1998). Following

these authors, southern Turkey is here pro-

visionally interpreted as having been separate

from Cimmeria during the Ordovician, and is

grouped with Sardinia, another eastern Mediter-

ranean component of Paris' (1998) North

Gondwanan Province. As noted above. Early

Ordovician faunas from South China, Tarim and

Indo-China also share strong similarities (e.g.

Zhou & Dean 1989), with the two South Chinese

Neseuretus species N. elegans Yin in Yin & Lee,

1978 and N. tungtzuensis Sheng, 1958 also

recorded from Indo-China by Zhou et al. (1998a,
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