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Late Cretaceous Marine and non-Marine Invertebrates
A large amount of information has been collected on the
macroinvertebrates of the Late Cretaceous in Australia, comprehensive
data on the overall diversity of the fauna as well as the relationships
in several assemblages that have been well preserved. Marine deposits
have provided the vast majority of the fossils, though the Winton
Formation contained a few freshwater bivalves - Pledgia,
Hyridella, Megalovirgus, Alathyria, and gastropods (Melanoides)
and insects - a dragonfly (Aeschnidopsis flindersiensis),
and a mecopteran fly, have been identified.
The Walangarlu Mudstone and the Moonkinu Formation, both parts of
the Bathurst Island Group, are sites were the best known
macroinvertebrates of the Cenomanian are found, including about 25
genera and species of molluscs that include - bivalves, gastropods,
scaphopods and cephalopods. Some common forms that are present in the
Bathurst Island Group have also been found in deposits from the Lower
Cretaceous, bivalves such as Panopea, Nuculana
and Inoceramus. The bivalve
Nemocardium and the gastropod Arrhoges
make their first appearance in these deposits. Ammonite assemblages are
rich in the Bathurst Island Group deposits, that include a number of
genera that have a global distribution that include
Acanthoceras, Euomphaloceras, Hamites, Scaphites, Sciponoceras
and Turrilites. It is suggested by the
authors3 that as some
species from North Australian have been found in North Africa,
Madagascar (such as Scaphites dailyi) and
Europe Turrilites costatus), it is probable
this indicates open sea connections.
The limited number of outcrops of rocks from the Coniacian and
Turonian has meant that assemblages from these time periods are not well
known but they include ammonites such as Collingnoniceras.
This genus from the Turonian, widespread in the Northern Hemisphere, is
present in the Moonkinu Formation. There is virtually no knowledge of
the benthic invertebrates of the Turonian-Coniacian. Up to 8 genera of
bivalves are present in the Molecap Greensand and Gingin Chalk, including the
widespread Gryphaea and Inoceramus
(well-known in the
Northern Hemisphere), the extant oyster Ostrea,
and what the authors3 suggest may be the earliest specimens known of the
present-day scallop Spondylus. There are also
sponges, Porosphaera, brachiopods,
Boucharidella, Kingena and
Inopinarticula, ammonites such as
Baculites, sea urchins, Cidaris,
and crinoids lacking stalks, Uintacrinus and
Marsupites. According to the authors3
age ranges for the Gingin Chalk are provided by the latter genus as they
correlate with Europe and North America. The assemblages of the Molecap
Greensand and Gingin Chalk, in spite of their cosmopolitan nature, are
suggested by the authors3 to
herald the appearance of southern high-latitude kossmaticeratid
ammonites that are distinctive such as Kossmaticeras,
also suggesting it could indicate the onset of lower temperatures, a
trend that continued in the southern part of the
Perth Basin, at least,
into the latest part of the Cretaceous.
In these deposits the macroinvertebrate assemblages are among the
richest known from Australia. The situation is very different in the
fossil record of the Campanian where they are almost unknown. More than 44
benthic mollusc genera have been found in the Miria Formation, including
gastropods, bivalves and scaphopods, nearly all have been reported from
the Tethyan Ocean realm to the north, suggested by the authors3
to indicate the presence of warmer waters. A high proportion of infaunal
or burrowing bivalves has been reported from the Miria Formation, such
as Trigonia and Panopea,
as well as free-swimming pectinids, scallops such as Chlamys
and Giraliapecten suggested to probably
indicate shallow water. There is a high level of diversity among the
ammonites of the Miria Formation with more than 30 genera and 88
species, including a mixture of southern high-latitude genera such as
Kossmaticeratids, Gunnerites, as well as
elements that are known from northern warm waters,
Pachydiscus and Eubaculites and
Baculites, that both had strait shells. The
authors3 suggest the latter
appear to have been derived from assemblages in southeastern Africa, and
in particular India that were of contemporary ages. The presence of
these cephalopods together with other cosmopolitan cephalopods such as
Cimomia, a nautiloid, the authors3
suggest they support the view that the marine faunas of the latest
Cretaceous in Australia were latitudinally transitional, being comprised
of forms from the cooler waters in the south and warmer waters to the
north.
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