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TRILOBITE BIOGEOGRAPHY OF GONDWANA 55

Fig. 1. Early Ordovician (Arenig) palaeogeography, showing the Arenig-basal Caradoc geographic
distribution of the 22 Neseuretus species included in the cladistic analysis. Key: 1, South China (Yangtze
Platform): N. concavus (Arenig), N. elegans (Arenig-Llanvirn), N. intermedius (Arenig), N.planus (Arenig),
N. shensiensis (Arenig); 2, Indo-China: N. elegans (Arenig-Llanvirn), N. turveyi (Llanvirn); 3, Arabia: N.
tristani (Llanvirn); 4, South Turkey: N. sexangulus (Arenig); 5, Libya: N. tristani (Llanvirn); 6, France
(Armorica, Montagne Noire); N. arenosus (Arenig), N. tristani (Llanvirn); 7, Spain (Iberia): N. avus
(Llanvirn), N. henkei (Llanvirn), N. leonensis (?Arenig/Llanvirn), N. tristani (Llanvirn-basal Caradoc); 8, Anti-
Atlas, Morocco: N. attenuatus (Llanvirn), N. tristani (Llanvirn); 9, Eastern Avalonia: N. caerhunensis (Arenig),
N. monensis (Arenig), N. murchisoni (Arenig), N. parvifrons (Arenig), N. ramseyensis (Arenig); 10, Western
Avalonia: N. vaningeni (Arenig); 11: South America: N. chaschuilensis (Arenig, Argentina), N. lipanensis
(Arenig-Llanvirn, Argentina), N. sanlucasensis (Llanvirn, Bolivia). Map generated by David Lees (Natural
History Museum, London).

China and the Central Andean basin of South

America, and is regarded as one of the more

reliable indicators of the former extent of

Gondwana (although species assigned to

Neseuretus or its junior synonym Synhomalono-

tus from various Central Asian regions, some of

which were listed by Fortey & Morris (1982) and

Rabano (1990) as valid representatives of the

genus, represent different reedocalymenine

genera) (Fig. 1). As early as 1937, Kobayashi

noted that the genus (as Synhomalonotus] was

characteristic of the 'Euro-Meridional' Province

in the Early Ordovician, and later established

the term 'Asaphopsis-Taihungshania-Neseure-

tus Fauna' to describe the Early and Middle

Ordovician southern faunal province

(Kobayashi 1976, 1987). The association is

interpreted as typically occurring in shallow

inner-shelf environments (Fortey & Morris

1982). However, various species of Neseuretus

have also been recorded in shallow outer-shelf

deposits across much of the geographic range of

the genus, in faunas composed of slightly

deeper-water trilobite taxa such as Colpo-

coryphe, Salterocoryphe, Placoparia, Zelis-

zkella, Ectillaenus and Hanchungolithus,

indicating that the genus had a wider palaeo-

bathymetric tolerance than has previously been

suggested (Dean 1966; Yin & Lee 1978;

Courtessole et al. 1981; Beckly 1989; Henry

1989; Rabano 1990; Zhou et al. 1998a). The

Neseuretus Association was originally regarded

as an indicator of cold water, circumpolar shelf

seas (Fortey & Morris 1982). This interpretation

has been revised due to the occurrence of the

association in Early Ordovician tropical regions
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