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Evolutionary dynamics of Permian-Triassic fishes and Early Triassic seawater temperature changes


Romano, Carlo. Evolutionary dynamics of Permian-Triassic fishes and Early Triassic seawater temperature changes. 2013, University of Zurich, Faculty of Science.

Abstract

The Permian and Triassic were critical
times for marine and continental life on
Earth. These periods saw the transition from
the typically Palaeozoic faunas and fl oras to
the more modern communities of the Mesozoic
and Cenozoic and witnessed profound
climatic and oceanographic changes due to
the assembly of the supercontinent Pangaea
and other environmental factors. A series of
important extinction events are known from
this time interval, amongst others the largest
mass extinction of all time near the Permian-
Triassic boundary. The study of the mechanisms
and patterns of extinctions and subsequent
recoveries has attracted a wealth of
research interest during the last decades. Most
publications are focussed on marine invertebrates
or on terrestrial vertebrates. However,
the effects of the various biotic crises of the
Permian-Triassic interval on fi shes (primary
aquatic vertebrates) are still poorly understood.
In addition, patterns of recovery after
the end-Permian mass extinction are not yet
well resolved. Carbon isotope excursions as
well as changes in spore-pollen ratios and the
palaeogeographic distribution of taxa during
the Early Triassic have been interpreted as
evidence for severe climatic changes, but little
was known about an important component
of climate: temperature.
The present dissertation is based on new
fi eld data and provides new insights into the
reconstruction of relative temperature changes
during the Early Triassic but also into the turnover
and recovery of fi shes (Chondrichthyes,
Osteichthyes) during the Permian-Triassic.
The thesis is organised in two parts, focussing
on (1) changes in seawater temperature during
the Early Triassic (Chapter 1), and (2) descriptions
of new Early Triassic fi sh material
and evaluation of evolutionary trends within
Permian and Triassic fi shes (Chapters 2–6).
In Chapter 1, a new Early Triassic temperature
record is presented based on oxygen
isotope values from biogenic apatite (conodonts,
actinopterygian teeth). The new data
from mid-palaeolatitudes (northern Pakistan)
suggests severe temperature changes during
the Early Triassic, thus confi rming previous
hypotheses. The trends in the oxygen isotope
record correlate well with those of the carbon
isotope record, and the latter have been shown
to be of global signifi cance. Cooler climatic
conditions coincide with early recovery pulses
in ammonoids, conodonts and other marine
taxa, whereas a phase of increased temperatures
in the middle-late Smithian is associated
with a severe turnover among nekto-pelagic
clades (e.g. ammonoids, conodonts). The results
suggest that climatic changes in the aftermath
of the end-Permian event are largely
responsible for the observed recovery patterns.
An important driver for the observed
climatic and biotic upheavals during the Early
Triassic is eruptive activity of the Siberian
Traps Large Igneous Province, which already
played a major role during the end-Permian
extinctions.
Chapter 2 is an extensive literature report
on Early Triassic and some Anisian fi shes
(Chondrichthyes, Osteichthyes) and provides
an overview of their global diversity and palaeobiogeography.
In Chapter 3 a new specimen of the rare
hybodontoid chondrichthyan Palaeobates polaris
is described from the Smithian of Spitsbergen
(Svalbard, Norway). The new specimen
is more complete than the type material
of P. polaris and allows the reconstruction of
the lower jaw and the determination of a few
potential apomorphies of this durophagous
fi sh.
In Chapter 4 new fi sh material from the
Early Triassic (late Smithian) of Bear Lake
County (SE Idaho, USA) is presented, which
amongst others includes a three-dimensionally
preserved skull of the garfi sh-like actinopterygian
Saurichthys. Due to its very peculiar
morphology, which allows even fragmentary
skeletal remains to be identifi ed at genus level,
the Triassic Saurichthys has a well-known
fossil record. The following trends are noted
in Saurichthys: (1) a change from cosmopolitan
distribution and high species richness in
the Early Triassic to restricted palaeogeographic
distribution and low species diversity
in the Late Triassic, and (2) disappearance of
plesiomorphic bauplans early in the Triassic
(in the marine realm) and successive anatomical
specialisations to increase predatory effi -
ciency.
Chapter 5 deals with the diversity dynamics
and body size changes of Permian and
Triassic bony fi shes based on a new data matrix
adapted from the available literature. The
results are compared to already existing data
on Permian-Triassic Chondrichthyes. Genus
diversity trends in Osteichthyes proceed from
generally low levels in the Permian to higher
values in the Triassic in combination with increased
diversity and abundance of more derived
taxa near the Permian-Triassic boundary
and onwards. Exceptionally high extinction
rates at genus level are absent during the
Permian and Triassic, but peaks in origination
rates for bony fi shes are observed in the Early
and Middle Triassic. Signifi cant body size
changes are noted at the Middle-Late Permian
boundary (size increase) and again at the Early
Triassic-Anisian boundary (size decrease).
The former is related with the appearance of
new taxa of larger body sizes within palaeopterygians
and the latter with the emergence of
numerous small taxa, mainly within neopterygians
and derived palaeopterygians (‘Subholostei’).
Strikingly, diversity trends in osteichthyans
are opposed to those in chondrichthyans
– the latter experienced a dramatic decline
in genus diversity during the Middle and Late
Permian. Hence, the Permian-Triassic marks
an important turnover between the chondrichthyan-
dominated communities of the Permocarboniferous
to the osteichthyan-dominated
(mainly actinopterygians) ichthyofaunas of
the Mesozoic and Cenozoic. During the Triassic,
basal groups of actinopterygians (palaeopterygians)
were subsequently replaced
by neopterygians, which include the bulk of
modern-day fi shes.
Chapter 6 is a review of marine predator
diversity (Chondrichthyes, Osteichthyes,
Tetrapoda) in the Early Triassic and Anisian
and aims at elucidating trophic complexity in
the wake of the end-Permian mass extinction
event. This review shows that large marine
predators (>1 metre) were present throughout
the investigated interval and that they also
had a wide palaeogeographic distribution. In
the earliest Triassic (Griesbachian, Dienerian,
Smithian), marine apex predators were
composed of temnospondyl ‘amphibians’
(trematosaurids), chondrichthyans (e.g. hybodontoids,
eugeneodontids) and osteichthyans
(e.g. Birgeria, Saurichthys). In the early
Spathian, sauropterygian reptiles and largesized
ichthyosaurs were added. Although fossils
of ichthyosaurs are still not known from
older strata, these early forms already show
a derived, fi sh-like body shape and it can be
inferred that representatives of these predators
were already present earlier in the Triassic.
Eugeneodontids disappear from the fossil
record and trematosaurids become much rarer
near the Smithian-Spathian boundary, suggesting
that they were possible victims of the
end-Smithian event. Later in the Triassic, ma-
rine apex predators were mainly represented
by ichthyosaurs, sauropterygians, and some
fi shes.
In conclusion, the Permian and Triassic
were evidently important intervals for fi shes
as well as many other groups. During these
periods, once dominant taxa disappeared and
newer clades emerged and diversifi ed, many
of which are still important in present-day
faunas. This transition was, however, not sudden
but took millions of years. Nevertheless,
mass extinction events in combination with
severe climatic and environmental changes
played an important role during these turnovers
near the Palaeozoic-Mesozoic boundary.

The Permian and Triassic were critical
times for marine and continental life on
Earth. These periods saw the transition from
the typically Palaeozoic faunas and fl oras to
the more modern communities of the Mesozoic
and Cenozoic and witnessed profound
climatic and oceanographic changes due to
the assembly of the supercontinent Pangaea
and other environmental factors. A series of
important extinction events are known from
this time interval, amongst others the largest
mass extinction of all time near the Permian-
Triassic boundary. The study of the mechanisms
and patterns of extinctions and subsequent
recoveries has attracted a wealth of
research interest during the last decades. Most
publications are focussed on marine invertebrates
or on terrestrial vertebrates. However,
the effects of the various biotic crises of the
Permian-Triassic interval on fi shes (primary
aquatic vertebrates) are still poorly understood.
In addition, patterns of recovery after
the end-Permian mass extinction are not yet
well resolved. Carbon isotope excursions as
well as changes in spore-pollen ratios and the
palaeogeographic distribution of taxa during
the Early Triassic have been interpreted as
evidence for severe climatic changes, but little
was known about an important component
of climate: temperature.
The present dissertation is based on new
fi eld data and provides new insights into the
reconstruction of relative temperature changes
during the Early Triassic but also into the turnover
and recovery of fi shes (Chondrichthyes,
Osteichthyes) during the Permian-Triassic.
The thesis is organised in two parts, focussing
on (1) changes in seawater temperature during
the Early Triassic (Chapter 1), and (2) descriptions
of new Early Triassic fi sh material
and evaluation of evolutionary trends within
Permian and Triassic fi shes (Chapters 2–6).
In Chapter 1, a new Early Triassic temperature
record is presented based on oxygen
isotope values from biogenic apatite (conodonts,
actinopterygian teeth). The new data
from mid-palaeolatitudes (northern Pakistan)
suggests severe temperature changes during
the Early Triassic, thus confi rming previous
hypotheses. The trends in the oxygen isotope
record correlate well with those of the carbon
isotope record, and the latter have been shown
to be of global signifi cance. Cooler climatic
conditions coincide with early recovery pulses
in ammonoids, conodonts and other marine
taxa, whereas a phase of increased temperatures
in the middle-late Smithian is associated
with a severe turnover among nekto-pelagic
clades (e.g. ammonoids, conodonts). The results
suggest that climatic changes in the aftermath
of the end-Permian event are largely
responsible for the observed recovery patterns.
An important driver for the observed
climatic and biotic upheavals during the Early
Triassic is eruptive activity of the Siberian
Traps Large Igneous Province, which already
played a major role during the end-Permian
extinctions.
Chapter 2 is an extensive literature report
on Early Triassic and some Anisian fi shes
(Chondrichthyes, Osteichthyes) and provides
an overview of their global diversity and palaeobiogeography.
In Chapter 3 a new specimen of the rare
hybodontoid chondrichthyan Palaeobates polaris
is described from the Smithian of Spitsbergen
(Svalbard, Norway). The new specimen
is more complete than the type material
of P. polaris and allows the reconstruction of
the lower jaw and the determination of a few
potential apomorphies of this durophagous
fi sh.
In Chapter 4 new fi sh material from the
Early Triassic (late Smithian) of Bear Lake
County (SE Idaho, USA) is presented, which
amongst others includes a three-dimensionally
preserved skull of the garfi sh-like actinopterygian
Saurichthys. Due to its very peculiar
morphology, which allows even fragmentary
skeletal remains to be identifi ed at genus level,
the Triassic Saurichthys has a well-known
fossil record. The following trends are noted
in Saurichthys: (1) a change from cosmopolitan
distribution and high species richness in
the Early Triassic to restricted palaeogeographic
distribution and low species diversity
in the Late Triassic, and (2) disappearance of
plesiomorphic bauplans early in the Triassic
(in the marine realm) and successive anatomical
specialisations to increase predatory effi -
ciency.
Chapter 5 deals with the diversity dynamics
and body size changes of Permian and
Triassic bony fi shes based on a new data matrix
adapted from the available literature. The
results are compared to already existing data
on Permian-Triassic Chondrichthyes. Genus
diversity trends in Osteichthyes proceed from
generally low levels in the Permian to higher
values in the Triassic in combination with increased
diversity and abundance of more derived
taxa near the Permian-Triassic boundary
and onwards. Exceptionally high extinction
rates at genus level are absent during the
Permian and Triassic, but peaks in origination
rates for bony fi shes are observed in the Early
and Middle Triassic. Signifi cant body size
changes are noted at the Middle-Late Permian
boundary (size increase) and again at the Early
Triassic-Anisian boundary (size decrease).
The former is related with the appearance of
new taxa of larger body sizes within palaeopterygians
and the latter with the emergence of
numerous small taxa, mainly within neopterygians
and derived palaeopterygians (‘Subholostei’).
Strikingly, diversity trends in osteichthyans
are opposed to those in chondrichthyans
– the latter experienced a dramatic decline
in genus diversity during the Middle and Late
Permian. Hence, the Permian-Triassic marks
an important turnover between the chondrichthyan-
dominated communities of the Permocarboniferous
to the osteichthyan-dominated
(mainly actinopterygians) ichthyofaunas of
the Mesozoic and Cenozoic. During the Triassic,
basal groups of actinopterygians (palaeopterygians)
were subsequently replaced
by neopterygians, which include the bulk of
modern-day fi shes.
Chapter 6 is a review of marine predator
diversity (Chondrichthyes, Osteichthyes,
Tetrapoda) in the Early Triassic and Anisian
and aims at elucidating trophic complexity in
the wake of the end-Permian mass extinction
event. This review shows that large marine
predators (>1 metre) were present throughout
the investigated interval and that they also
had a wide palaeogeographic distribution. In
the earliest Triassic (Griesbachian, Dienerian,
Smithian), marine apex predators were
composed of temnospondyl ‘amphibians’
(trematosaurids), chondrichthyans (e.g. hybodontoids,
eugeneodontids) and osteichthyans
(e.g. Birgeria, Saurichthys). In the early
Spathian, sauropterygian reptiles and largesized
ichthyosaurs were added. Although fossils
of ichthyosaurs are still not known from
older strata, these early forms already show
a derived, fi sh-like body shape and it can be
inferred that representatives of these predators
were already present earlier in the Triassic.
Eugeneodontids disappear from the fossil
record and trematosaurids become much rarer
near the Smithian-Spathian boundary, suggesting
that they were possible victims of the
end-Smithian event. Later in the Triassic, ma-
rine apex predators were mainly represented
by ichthyosaurs, sauropterygians, and some
fi shes.
In conclusion, the Permian and Triassic
were evidently important intervals for fi shes
as well as many other groups. During these
periods, once dominant taxa disappeared and
newer clades emerged and diversifi ed, many
of which are still important in present-day
faunas. This transition was, however, not sudden
but took millions of years. Nevertheless,
mass extinction events in combination with
severe climatic and environmental changes
played an important role during these turnovers
near the Palaeozoic-Mesozoic boundary.

Additional indexing

Item Type:Dissertation
Referees:Brinkmann Winand, Bucher Hugo
Communities & Collections:07 Faculty of Science > Paleontological Institute and Museum
Dewey Decimal Classification:560 Fossils & prehistoric life
Language:English
Date:2013
Deposited On:19 Feb 2014 13:30
Last Modified:05 Apr 2016 17:42
Number of Pages:303

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