Table Of ContentFreshwater Fishes
Vertebrate Palaeobiology and Palaeoenvironments Set
coordinated by
Eric Buffetaut
Freshwater Fishes
250 Million Years of Evolutionary History
Lionel Cavin
First published 2017 in Great Britain and the United States by ISTE Press Ltd and Elsevier Ltd
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as
permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced,
stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers,
or in the case of reprographic reproduction in accordance with the terms and licenses issued by the
CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the
undermentioned address:
ISTE Press Ltd Elsevier Ltd
27-37 St George’s Road The Boulevard, Langford Lane
London SW19 4EU Kidlington, Oxford, OX5 1GB
UK UK
www.iste.co.uk www.elsevier.com
Notices
Knowledge and best practice in this field are constantly changing. As new research and experience
broaden our understanding, changes in research methods, professional practices, or medical treatment
may become necessary.
Practitioners and researchers must always rely on their own experience and knowledge in evaluating and
using any information, methods, compounds, or experiments described herein. In using such information
or methods they should be mindful of their own safety and the safety of others, including parties for
whom they have a professional responsibility.
To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any
liability for any injury and/or damage to persons or property as a matter of products liability, negligence
or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in
the material herein.
For information on all our publications visit our website at http://store.elsevier.com/
© ISTE Press Ltd 2017
The rights of Lionel Cavin to be identified as the author of this work have been asserted by him in
accordance with the Copyright, Designs and Patents Act 1988.
British Library Cataloguing-in-Publication Data
A CIP record for this book is available from the British Library
Library of Congress Cataloging in Publication Data
A catalog record for this book is available from the Library of Congress
ISBN 978-1-78548-138-3
Printed and bound in the UK and US
Foreword
Since the pioneering work of Louis Agassiz at the beginning of the 19th
century, fossil fishes have been the subject of many scientific works. Their
evolutionary history has been reconstructed with a fair degree of accuracy,
although welcome new discoveries are constantly emerging, providing new
information and challenging our ideas. However, contrary to other groups
like mammals or dinosaurs, this history has not often been discussed in a
comprehensive summary that would allow us to situate it within the broader
framework of the geography and environments of our planet, and one might
well wonder why, because fishes are excellent material for such studies.
Lionel Cavin’s book addresses this gap by presenting the reader with a
summary of the evolutionary history of freshwater fishes over the last 250
million years since the start of the Triassic period. This long interval of time
was characterized by major events in the evolution of these animals
including the appearance of new groups and the succession of various faunal
assemblages, as well as major events in the history of the Earth and living
organisms including the break up of Pangaea, significant climate change, sea
level variation and large-scale biological crises. It was during this period that
the modern ichthyological world developed, an event that is no less
biologically significant than the evolutionary radiations of mammals or
birds. With such particular habitats and lifestyles determining the possibility
of geographical dispersal, the history of freshwater fishes during the
Mesozoic and Cenozoic eras generally reflects the major changes to the
geography and environment over time. With his vast experience in
x Freshwater Fishes
paleoichthyology, Lionel Cavin retraces a history that is no less eventful
than that of other groups of organisms that have attracted more attention.
This makes this book quite a unique addition to the genre, of interest to fossil
fishes experts as well as readers who are more generally interested in major
evolutionary phenomena.
Eric BUFFETAUT
Director of Research Emeritus at the CNRS
Ecole Normale Supérieure de Paris
Introduction
Today, freshwater fishes account for one quarter of the total number of
vertebrate species and half of the number of fish species. However, the
volume of the environment that they occupy represents only one ten-
thousandth of the total volume of water on Earth. How long has this massive
diversity existed and how did it come to be? The increased fragmentation of
continental environments, the isolation of river systems and latitudinal and
altitudinal climatic variations that characterize these areas are just a few of
the causes of this diversity. These features have varied over time, but it is
likely that the fragmentation of freshwater ecosystems was already
significant by the Mesozoic and Cenozoic eras. Among the important factors
for the evolution of freshwater fishes, three have varied consistently since
the beginning of the Mesozoic era: the global paleogeography structured by
tectonic movements, climate and sea levels. In a very general sense, the first
of these factors is associated with the fragmentation of Pangaea, the
foremost tectonic event of the last 250 million years. At the start of the
Triassic period, the supercontinent was an almost complete land mass that
gradually broke apart to form the continental arrangement we know today.
During that time, continental fragmentation was scarcely more significant
than it is today. Only at the end of the Cretaceous, when India was still an
island and Africa had not yet made contact with Eurasia, may our planet
have displayed a more fragmented geography than it has now. This period
was also a fruitful time for tetrapods, especially dinosaurs. The two other
factors, climate and sea level, are probably more significant than the general
positions of tectonic plates for understanding the evolutionary history of
freshwater fishes because they influence the capacity for life and dispersal in
xii Freshwater Fishes
shorter time frames. However, they are more difficult to characterize
precisely, especially in the ancient periods that concern us here.
In this book, we will examine, on a global scale, the groups of freshwater
fishes that have a fossil record dating from the Mesozoic and Cenozoic eras,
a period covering the last 250 million years of the Earth’s history. We will
focus on the paleogeographical and paleoenvironmental contexts that
surround the fossils and attempt to situate these discoveries within lengthy
evolutionary histories. In order to identify the biogeographical connections
that exist within a group of organisms, it is necessary to understand the
evolutionary relationships of the members in this group. To do this, we will
focus on the phylogenetic links within the clades under consideration. Over
the past few decades, molecular phylogenetic analyses have become
increasingly numerous and complete. Beyond the simple evolutive
relationships that they provide, these trees make it possible to construct
paleobiogeographical hypotheses. However, these models, which are based
on atemporal topologies, require calibrations provided by fossils. As we
shall see, the schemas obtained using these calibrations are often inconsistent
with paleontological data, but the differences seem to be decreasing in recent
publications. Often – too often even – this incompatibility between scenarios
based on molecular analyses and those based on fossil records is attributed to
the imperfection of the latter. As the saying goes, “The absence of evidence
is not evidence of absence”, which is true, but only within certain limits.
Presuming that the absence of a taxon predicted by a model in a given time
and space is exclusively linked to a lack of paleontological data is not
necessarily the most prudent hypothesis. For example, tracing the origin of
ostariophysans to the Paleozoic, as some calibrated molecular phylogenetics
suggest, is in complete contradiction with what we know from fossils. If the
fossil record is so incomplete, we would have to abandon the possibility that
it could teach us anything about the evolutionary history of these animals.
And so this book would be obsolete. Facing a similar problem concerning
the evolutionary history of osteoglossids fishes, Kumazawa and Nishida
[KUM 00] state: “We interpret this apparent discrepancy [between molecular
and fossil evidence] to be indicative of the paucity of osteoglossiform fossil
records rather than the inferiority of our molecular time estimates” (p. 1876).
Following instead from [FOR 10, p. 237] “we beg to differ” on this point, for
reasons that will be explained further on in this work.
Fossils of freshwater fishes are relatively rare. Paleontological sites
containing a large diversity of bony fishes, in both the number of individuals
Introduction xiii
and the number of species, are known in the Mesozoic and Cenozoic eras,
but they are primarily of marine origin. They are often concentration and
conservation Lagerstätten, of which the most well-known are as follows: for
the Triassic period, the Monte San Giorgio on the Swiss-Italian border and
Luoping in the Sichuan province of China; for the Jurassic period, Solnhofen
in Germany and Cerin in France; for the Cretaceous period, Haqil, Hgula
and En Namourra in Lebanon; and for the Cenozoic, Monte Bolca in Italy.
However, there are some Mesozoic and Cenozoic Lagerstätten that preserve
flora and fauna from fresh water environments. They generally correspond to
ancient lakes. The fish assemblages that they contain are less diverse than
the Lagerstätten of marine origin. Without describing them in detail in this
section, they include the following: the Triassic and Jurassic formations of
the Newark basin in the United States, the Jehol biota of the Lower
Cretaceous in China and the Eocene Green River Formation in the United
States. In addition to these exceptionally preserved sites, in which the
specimens are often preserved whole and anatomically connected, there are
several freshwater paleontological deposits where the fossils are preserved as
disjointed pieces. This kind of conservation corresponds to continental
environments where energy was higher than it is at the bottom of a lake. This
can include rivers, deltas or lagoons. In these environments, the fossils are
usually concentrated in the calmest areas, such as the turns of a river or the
channel bottoms of a delta. Lastly, the majority of the fossil sites of
continental origin are generally more difficult to date than marine sites since,
unlike marine sites, continental sites only rarely contain precise fossil
markers.
Despite the relative rarity and the low diversity of paleontological sites
preserving freshwater ichthyofauna compared to marine sites, the record is
sufficient to trace the broad evolutionary steps of groups of fish typical of
these environments. On a long time scale and without accounting for recent
anthropic action, it should be noted that the biodiversity of freshwater fishes,
as a whole, displays a very substantial diversification beginning in the
middle of the Mesozoic era. A recent study [GUI 15a] about the modalities
of this diversification, based on the fossil record and data using information
extracted from morphological and molecular phylogenetics, shows that the
diversity of freshwater fishes as a whole has increased exponentially during
the past 150 million years. This tendency contrasts with the dynamic of
increase in the global diversity of marine fishes, which seems to reach finite
capacity over time. This difference in the increase of the biodiversity of
fishes depending on their environment is discussed in section 5.2.1.
xiv Freshwater Fishes
It is now a question of examining how this extraordinary diversification
occurred. We will begin 250 million years ago in the Triassic, a period in
which the clades that made up the fauna of freshwater fishes were almost
entirely different from the current clades. Next, we will travel to the Jurassic,
which probably contains the least amount of information about ichthyofauna,
and then on to the Cretaceous, during which the transition from “primitive”
to “modern” ichthyofauna took place. Since the beginning of the Cenozoic,
the fauna of freshwater fishes has been essentially composed of extant
families, even extant genera, and studying them consists of analyzing the
establishment of modern fish assemblages. Above all, we are interested in
the introduction of freshwater wildlife on a continental scale and we will not
examine the factors responsible for the current intracontinental layouts that
have resulted from the climatic changes in the Neogene, such as the
aridification of North Africa and the Arabian plate, the closure of the Tethys
Sea and the Messinian Event, the ice ages and especially the retreat of large
glaciers from Europe and North America as well as the implementation of a
monsoon climate in Asia. Additionally, only the data based on skeletal
fossils are taken into account. I am aware that information gathered from
otoliths could provide slightly different scenarios for some lineages (the first
occurrences would be pushed back in time in some cases). However, the
approach based on the study of otoliths is distinct from this work and based
on different literature.
1
Freshwater Environments and Fishes
1.1. Environments of freshwater ichthyofauna
1.1.1. Areas and volumes of freshwater environments
Freshwater environments, which include all continental aquatic
environments, are difficult to define (Figure 1.1). As the name indicates,
freshwater is characterized by low concentrations of salt as opposed
to seawater (the term “sweetwater” is also used as a synonym for
“freshwater”). Generally, freshwater is defined as containing less than 0.05%
of dissolved salts. Freshwater only accounts for about 2.5–2.75% of all water
on Earth. However, 1.75–2% of freshwater is frozen in polar ice caps and
glaciers as ice, and 0.5–0.75% exists as groundwater. This leaves about
0.01% of freshwater on the surface where fish can live. Today, nearly three-
quarters of freshwater is concentrated in the Great Lakes region of Africa,
the Great Lakes in North America and the Baikal Lake in Siberia. Certain
continental aquatic environments do not contain freshwater, but still share
some characteristics that connect them to the environments we are interested
in, despite them having higher salt concentrations. These include sabkhas,
which are depressions in hot climates from which water evaporates which
increases the salt concentration.
Brackish water has an intermediate salt concentration between freshwater
and marine water, between 0.05 and 3%. There are several types of brackish
environments today. The most substantial in terms of area are estuaries and
