232
THE BIOLOGY OF FISHES
and head, but retained càlcied arches in the caudal region.
,
Many other
“
Sharks
”
of a similar type must have ranged
'
=
over the whole northern hemisphere from the Carboniferous
,
right on to the Chalk period, but it is curious that they have
_
not been noted from Australia.
From the latter as well as
__
the northern hemisphere, Europe and America, we have
'
=:
'
the peculiar form Pleuracanthus, which can hardly be
considered a pelagic sh. Its paddle—like ns and appa—
rently autostylic mouth, as well as the long caudal region,
'
show that it was a sedentaiy form and place it near to the '
'Ï
Dipnoi ; all the endoskeletal structures were partially
.
î
calCied.
As it occurred rst in the Carboniferous period,
,
it may have been a wanderer from the north before Australia
separated from South Africa.
It is possible, of course, that the Pacic 1 of those early
days was the home of “ Sharks
”
just as it is so at the present
…
time, but it is evident that they had a free range right
across the northern hemisphere. Quite a large number of
forms (Scyllidæ, Lamnidæ, Rhinidæ, Rhinobatidæ, and —
even the Rajidæ) have been found in the Cretaceous deposits
of Mount Lebanon.
_
"
The impression given by both of these pelagic types,
!
Palæofscùs and Acanthodes, as well as by the Ganoids and
.
Ç
other Sedentary shes, is that the waters in which they
'
moved may have been of greater density or salinity than we
.
.
'
’
'
nd in the waters of the present day.
_
From the distribution of the fossil shes it is possible ,
to obtain some general idea of the distribution of land and
on
during the Palæozoio and MesoZoiC ’
:
,
per10dsup
'of: the great, Chalk deposits
_,
(Big.
certain that the Southern Atlantic
'
,
the whole,_d£thait time,‘,whilstç Australia
_
i
was near South Africa _«at__ any;rate not separated— by
f
Onÿthe other
no
if— the_Moori
.
,
had” it‘s'_oïigin
SiÎr"G60rgé Darw1n süggæœd‘. '
The
depart—um of
thé.ehdof "the —
,
.Meso'zoic period,_wouldïprovidesufcientcause, for the_upheavalSthen
,
'
a_nd
_Accord—i‘ng "CO. S1_iÿh Woodwardlalsor—the deep-sea
-.
further backthanthè
'
_
'
THE BIOLOGY OF FISHES
and head, but retained càlcied arches in the caudal region.
,
Many other
“
Sharks
”
of a similar type must have ranged
'
=
over the whole northern hemisphere from the Carboniferous
,
right on to the Chalk period, but it is curious that they have
_
not been noted from Australia.
From the latter as well as
__
the northern hemisphere, Europe and America, we have
'
=:
'
the peculiar form Pleuracanthus, which can hardly be
considered a pelagic sh. Its paddle—like ns and appa—
rently autostylic mouth, as well as the long caudal region,
'
show that it was a sedentaiy form and place it near to the '
'Ï
Dipnoi ; all the endoskeletal structures were partially
.
î
calCied.
As it occurred rst in the Carboniferous period,
,
it may have been a wanderer from the north before Australia
separated from South Africa.
It is possible, of course, that the Pacic 1 of those early
days was the home of “ Sharks
”
just as it is so at the present
…
time, but it is evident that they had a free range right
across the northern hemisphere. Quite a large number of
forms (Scyllidæ, Lamnidæ, Rhinidæ, Rhinobatidæ, and —
even the Rajidæ) have been found in the Cretaceous deposits
of Mount Lebanon.
_
"
The impression given by both of these pelagic types,
!
Palæofscùs and Acanthodes, as well as by the Ganoids and
.
Ç
other Sedentary shes, is that the waters in which they
'
moved may have been of greater density or salinity than we
.
.
'
’
'
nd in the waters of the present day.
_
From the distribution of the fossil shes it is possible ,
to obtain some general idea of the distribution of land and
on
during the Palæozoio and MesoZoiC ’
:
,
per10dsup
'of: the great, Chalk deposits
_,
(Big.
certain that the Southern Atlantic
'
,
the whole,_d£thait time,‘,whilstç Australia
_
i
was near South Africa _«at__ any;rate not separated— by
f
Onÿthe other
no
if— the_Moori
.
,
had” it‘s'_oïigin
SiÎr"G60rgé Darw1n süggæœd‘. '
The
depart—um of
thé.ehdof "the —
,
.Meso'zoic period,_wouldïprovidesufcientcause, for the_upheavalSthen
,
'
a_nd
_Accord—i‘ng "CO. S1_iÿh Woodwardlalsor—the deep-sea
-.
further backthanthè
'
_
'