Australia: The Land Where Time Began |
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The
Toolebuc Formation
and the Allaru Mudstone both of upper Albian age in the northern section
of the
Eromanga Basin
in central western Queensland, as well as other deposits from the Lower
Cretaceous have produced shark and bony fish faunas. Aptian deposits,
such as the Bulldog Shale, have produced rare chondrichthyan fossils -
sharks, rays and skates, and osteichthyan (bony fish) remains.
Edaphodon, the earliest known chimaerid (rat fish) was found in
the Bulldog Shale in deposits near
Lake Eyre. Opal mines at Coober Pedy
and Andamooka have produced isolated bones, mainly vertebrae, of small
teleost fish. The Darwin Formation near Darwin, Northern Territory, of
upper Aptian age, has produced large vertebrae up to 125 mm in diameter
of lamniform sharks, the group including makos, tiger sharks, etc.,
specimens that are huge when compared to those of white pointers (great
white sharks) of the present, suggesting that at more than 6 m long they
were probably top predators in the marine environments of the Australian
continental margin.
In the Toolebuc Formation and Allaru Mudstone, as well as the Gearle
Siltstone, of upper Albian age, from Western Australia, fish assemblages
from the Albian have been documented. In the Coorikiana Sandstone, South
Australia, there are sporadic finds in the form of isolated teeth,
vertebral centra and accumulations of scales from the Albian suggest,
according to
the authors1, cosmopolitan affinities.
The authors3 have listed a number of these taxa:
In the Gearle Siltstone, continental margin sediments,
Notorhynchus aptiensis, a hexanchoid (cow shark) was very
common; Paraorthacodus, a widespread form that was known
from the European Late Cretaceous; Anomotodon or
Scapanorhynchus, a mitsukurinid; Cretalamna appendiculata;
Carcharias striatula, Paraisurus, Archaeolamna, Leptostyrax, and
possibly Cretoxyrhina; Microcorax, Squalicorax primaevus
and Pseudocorax australis, of which the commonest genus of
shark in Queensland deposits during the Albian was P. australis.
In the Toolebuc Formation tooth plates and fin spines have been found
that correspond to at least 1 genus and species of endemic chimaeroid,
Ptykoptychion tayyo.
The authors1 suggest
it is significant that isolated rostral teeth of Pristiophorus
tumidens, a sawshark, representing the oldest known specimen of
this widespread taxon as well as the only specimen known from the
Cretaceous of the Southern Hemisphere is present in this formation.
In the Toolebuc Formation bony fish fossils from the Albian are
extremely common. Also common are large articulated skeletons, though
isolated teeth and bones comprise much of the material from this
deposit. Among the described taxa are a number of primitive forms such
as Richmondichthys sweeti, a 1.5 m long armoured
aspidorhynchid that was a filter feeder entirely lacking teeth and a
predatory fish Australopachycormus hurleyi, a swordfish
like pachycormid. Among the teleosts present are :
Flindersichthys denmeadi,
an elopiform, Cooyoo australis, a predatory ichthyodectid
that was large, the skull measuring up to 400 mm, and 'Cladocyclus
sweeti';
Pachyrhizodus marathonensis,
that was closely related to forms that were well known in the Northern
Hemisphere;
Dugaldia emmilta,
a small neoteleost.
The authors1
say these fish have important
palaeobiogeographical links to 3 other continents, both the Americas and
Europe.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |