This second part follows and completes a first monograph (Ref. 845) on
the Lower Permian brachiopods from the Tarim Basin (CHEN & SHI 2006),
extending the analyses to the other orders of brachiopods there
recorded and to their palaeobiogeographical implications.
The biogeographic affinities of the Lower Permian Tarim brachiopods
have been established by comparison with those of other regions such
as South China, Tibet, Thailand, Karakorum and the Urals/Russian
Platform. It should be noted that the Tarim Basin faunas share about
13 species with the Wordian (Guadalupian) brachiopod assemblages of
the Rat Buri Limestone (Thailand). These, however, are younger, based
on conodonts and fusulinids, so that the second interpretation
proposed by the authors, i.e. that the shared species may be holdovers
of the Tarim fauna, is more likely. The Artinskian-Kungurian Tarim
brachiopod fauna has links to South China, Tibet and the Karakorum,
but it is different from the brachiopods of the Urals and the Russian
Platform, in contrast with the similarity they shared at the beginning
of the Early Permian (CHEN 2004). This is supported by the
palaeobiogeographical affinities of associated fusulinids and
floras. Such palaeobiogeographic features are explained by the authors
by the position of the tectonic block of Tarim which was at that time
in the northern Palaeotethys, but not yet accreted to the Angara Plate
and moving southeastward towards South China at the Artinskian/
Kungurian transition.
In the Systematic Paleontology section 29 brachiopod species in 20
genera are described based on the study of slightly less than 200
specimens; of these seven species and three genera are new.
Among the new species, Acosarina grandis sp. nov. is characterized by
a large size and a strong biconvexity; Larispirifer balikelensis
sp. nov., based on two specimens, is described as having a convex umbo
and a broad sulcus with a deep sulcal groove, which, however, is not
evident in the photos of the specimens; Orbicoelia elongatiformis
sp. nov. has a very distinct outline which differentiates it from
other species of the genus; Tarimathyris hotanensis sp. nov. is based
on slightly deformed specimens and it is not easily distinguishable
from Tarimathyris postambigua (USTRISKI, 1960).
Baliqliqia gen. nov. with type-species B. baliqliqensis sp. nov. is
very close to Cleiothyridina BUCKMAN, 1906 from which it differs only
by a more elongate outline and a parasulcate W-shaped anterior
commissure. However, this feature is not evident from the photos of
the specimens; furthermore, a low dorsal myophragm, said to be absent
in Baliqliqia, is in fact well recorded in the serial sections of
fig. 20. The erection of a new genus is not strongly supported.
Tarimathyris gen. nov. is placed in the subfamily Spirigerellinae
GRUNT, 1965, without any comments to the revision of the
classification of the athyridids performed by SHEN et
al. (2004). Judging from the internal characters (i.e. subparallel
dental plates, thin cardinal plate, absence of cardinal flanges) the
genus is better placed in the Subfamily Janicepsinae POSENATO,
2001. Also its similarity to Juxathyris LIANG, 1990 – as recently
revised by SHEN et al. (2004) – is very strong.
Ustriskia gen. nov. is distinguished more by the shape of the inner
hinge plates which are fused to a median septum than by the lack of
dental plates. The twelve plates and the text figures are of good
quality and they well display the external and internal features the
Lower Permian brachiopod fauna of the Tarim Basin.
L. ANGIOLINI
Zentralblatt Geo. Pal. T. II Jg. 2008, H. 3/4
