Table Of Contentm
JOHN G.MAIS
cum of Natural Hi:
*& V^^K
JOHN G. MAISEY
Department of Vertebrate Paleontology
American Museum of Natural History
Illustrations by
DAVID MILLER
IVY RUTZKY
Photography by
CRAIG CHESEK
DENIS FINNIN
FP^TT
F ^ H RS
a PETER N. NEVRAUMONT book
A Henry Holt Reference Book
HENRY HOLT AND COMPANY
New York
contents
1 AQUATIC ANCESTORS 8
2 A PARADISE FOR FISHES 16
3 FISHY ORIGINS 24
4 THE RISE AND FALL OF OUR ARMORED ANCESTORS 36
5 THE FIRST PREDATORS 58
6 EXTINCT RELATIVES OF MODERN FISHES 70
7 SHARKS: THE LORDS OF TIME
8 OSTEICHTHYANS: SO MUCH DIVERSITY, SO LITTLE CHANGE
9 THE FOSSIL FOREST OF RAY-FINNED FISHES 138
10 FISHES OUT OF WATER 192
11 THE WORLD OF FISHES
210
Glossary 216
Acknowledgments 221
Index 222
To Bobb Schaeffer,
colleague, mentor, and friend.
A Henry Holt Reference Book
Henry Holt and Company, Inc.
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Henry Holt ® is a registered trademark of Henry Holt and Company,
Copyright © 1996 John G. Maisey
Illustration (reconstructions) copyright © 199(1 David W. Miller
Illustrations (portraits) copyright © 1996 Ivy Rutzky
Photographs copyright © 1996 American Museum of Natural History
Line illustrations copyright © 1996 Patricia Wynne
Computer images copyright © 1996 Frank Ippolito
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i A Q U A TI
A N C E S T O RS
JList
5HH»r>\vii,jt's in .1 Niiim? HES have a unique evolutionary' history that stretches back in time
more than 450 million years. They are incredibly ancient, older than the
dinosaurs, and include the ancestors of all the limbed vertebrates living
on land, even humans. Human evolution is rooted in fishes; and scien
tists have discovered traces of 360-million-ycar-old fossils of transitional
aquatic creatures that had both gills and limbs. Not only are humans
and fishes related, some fishes are more closely related to humans than
they are to other fishes! We commonly think of ourselves as completely
separate from our aquatic ancestors when instead we should be mar
veling at the similarities.
PLATE 1 Let's see where we fit in. Humans are classified as tetrapods (four-
Cahmopkurus, an Early Cretaceous relative footed; more generally, having two pairs of limbs). This same designation
of the modern bowfin about im long,
applies to all the air-breathing land vertebrates with which we are famil
lunges from concealment at a passing
group of filter-feeding Vinclifer, members of iar: all other mammals, birds, reptiles, and amphibians. The tetrapods in
the extinct teleost group known as
turn are a highly specialized offshoot of a very ancient class of animals,
aspidorhynchids. These fishes lived in a
shallow inland sea covering parts of north the Sarcopterygii. The only other living members of this group are the
eastern Brazil about no million years ago.
coelacanths and the lungfishes. It seems that we have very important,
(see Plates 67 and 77)
and very fishy, ancestors!
We no longer look like fishes, of course, and that is because most
modern fishes evolved from different ancestors than did tetrapods. Our
tetrapod ancestors left the water and found a new environment on land.
In making this transition, they lost or without tetrapods. Why, then, write a book
modified many of their aquatic adapta about an incomplete group? Precisely
tions. Fishes stayed in the water, and because there is so much misunderstand
evolved new adaptations to this environ ing about the early evolution of craniates,
ment. [Plate 1] Both fishes and tetrapods, it is more convenient to discuss various
however, share common distant ancestors. issues under a blanket title of "fishes." And
These were highly mobile, aquatic creatures let's face it—few people would have read a
with a sophisticated brain, complex senso book entitled Discovering Primitive Fossil Non-
ry systems, and a muscular tail. These fea Tetrapodan Craniates]
tures, which first appeared more than 450
million years ago, characterize a group ■5HIW. -» I ishy Diversity
known as the craniates {having a cranium, From their ancient ancestors, the craniates,
the part of the skull that encloses the fishes evolved not once, in a single lin
brain). (Another name frequently used for eage, but multiple times, filling countless
the group is vertebrates, but, as we shall biological niches. The various classes of
see, the terms vertebrate and craniate are living and extinct fishes (for example
not strictly interchangeable.) Tetrapods sharks, lungfishes, coelacanths, ray-finned
have superimposed their adaptations to ter fishes, acanthodians and placoderms) are
restrial life upon their aquatic (craniate) fea as different from each other as mammals
tures; fishes have built more adaptations are from birds. Fishes are spectacularly
to aquatic life on top of theirs. [Figure 1] diverse, with around 25,000 living species
As we go back in time, we can trace described so far and untold thousands
our tetrapod lineage to a common ances more awaiting discovery. Fishes make up
try with fishes. When we try to trace the slightly more than half of the approxi
mately 48,500 described living species of
lineage forward from the earliest craniates,
vertebrates. The remaining known verte
however, we find that tetrapods have been
brate species, about 25,500, arc represented
segmented, by classificatory fiat, from the
by the tetrapods.
fishes. This poses a problem, for we see
that fishes do not form a natural group, Given their long evolutionary history,
because tetrapods have been excluded, but it is not surprising that so many species of
instead represent a heterogeneous assem fishes exist today; one new fish species
blage. The term "fish" is therefore generally evolving every 18,000 years, or about 55.5
used to refer to a life form that has many species evolving per 1 million years, would
different representatives. The basic form is account for the numbers. Such an orderly,
a craniate that has retained some primitive regular pace of evolution is unrealistic, of
features (evolved in the common ancestor course, for no living species has existed for
of all craniates), such as gills and a tail fin, 450 million years.
but may also have other features repre The sum total of fishy diversity
senting a long series of evolutionary adap through time is far greater than now, and
tations. Often the sense in which the word the evolutionary history of fishes is a vast
is used is merely conventional; from a and complex subject. It is impossible to
practical viewpoint, fishes are what we give an accurate estimate of how many
study in fish classes! Here is a paradox, for species of fishes have existed through
although most of us have no difficulty rec time, because the diversity of many groups
ognizing a fish, collectively fishes have no has waxed and waned, and because there
unique features by which they can be are significant gaps in the fossil record, but
classified. the total is likely to have been in the mil
Our first discovery, then, is that fishes lions. As more fossil fishes are uncovered,
do not represent an entire natural lineage we will know better what the ancient
world looked like and come to discover
of creatures that evolved from a common
more of our own ancestors.
ancestor, for the group is incomplete
AQUATIC ANCESTORS
FIGURE 1
©N0
Diagram to show the diversity of craniates. Groups
inside solid boxes are monophyletic (descended
from a single ancestor, the line leading to box).
Groups inside dashed boxes are unreal, because
they include members of more than one evolu
tionary line. For example, gnathostomes (craniates
with jaws, an advanced feature) form a mono
phyletic group, but "agnathans" (craniates lacking
jaws, a primitive condition) are unreal because
they include two separate evolutionary lineages:
hagfishes and lampreys. Similarly, tetrapods
(gnathostomes with limbs) are monophyletic, but
the group "fishes" (all craniates lacking limbs) is
unreal. (Lineages number 1-4 are extinct groups of
fishes discussed elsewhere in this book.)
Discovering Fossil Fishes
■5>imr*,\i-<' I islu-s I'rimitiw-.' the descendants of the ancestral species
Some fishes (sharks, for example) are clas provides a measure of evolutionary
sified as primitive, while others (such as change, and allows us to distinguish new
spiny-finned teleosts or lungfishes) are species. The greater the degree of anatom
classified as advanced. But scientists use- ical diversity within a given group,
words like "primitive" and "advanced," the more species we may recognize. A
(or "lower" and "higher") in an evolution species-rich (i.e. anatomically diverse)
ary sense only to provide a perspective group having only a short duration (in
on the hierarchy they have created. For terms of geologic time) presumably
example ray-finned fishes are intuitively underwent rapid speciation and had a
regarded by scientists as advanced high rate of anatomical change. Speciation
fishes (relative to sharks or extinct placo- rates among coelacanths (one living
derms), yel within ray-fins the reedfishes, species and about one hundred fossil
paddlefishes and sturgeons are all regard species over 350 million years) and acan-
ed as primitive. In Ihe sense that tetrapods thomorph teleosts (about 18,000 living
came later on the craniate evolutionary species plus innumerable fossil species
tree, and evolved many new adaptations over 100 million years) are clearly very
to a terrestrial environment, they have different. In essence, a creature that has
been considered more advanced than undergone a large number of evolutions,
fishes. While it is true that fishes (as they producing new species, in a defined time
are construed here) certainly include the is considered to be more evolved than a
earliest and most primitive of all craniale creature that has undergone few or no
animals, they nevertheless also include changes in a comparable or longer time.
groups (teleosts, for example) that possess Thus, the number of species can be taken
their own suites of unique advanced as a general indicator of a group's
features and which evolved much later in evolvedness-in a biological sense.
geologic time. Fishes did not stop evolving
Let's look at some examples to com
after tetrapods left the water some 350
pare the diversity and Ihe geological age
million years ago. Teleosts first appeared
of the spiny-rayed (acanthomorph) fishes
about 200 million years ago, and the
(the largest and most advanced group of
oldest fossil perchlike fish is now celebrat
living ray-finned fishes) with the diversity
ing only its 60 millionth birthday, along
and geological age of birds, which most
with the earliest ducks, frigate birds, and
people would place high on Ihe vertebrate
some mammalian groups such as horses
evolutionary tree. In other words, we will
and primates. In other words, the anatom
be comparing speciation rates-the num
ical features that define perchlike fishes,
ber of new species that have evolved over
frigate birds and horses appeared at
a defined time interval. The oldest fossil
roughly the same moment of geologic
bones from acanthomorph fishes are a
Lime.
mere 100 or so million years old, and
fossilized ear slones (otoliths) like those
One way to measure how evolved a
of acanthomorphs are known about 160
group is, in Ihe biological sense, is to look
million years old. Archaeopteryx, the oldest
al the number of species in that group
undisputed fossil bird, is about 150 million
relative to the length of lime the group
years old, so birds and acanthomorphs
has been around. Each new species repre
have virtually the same geological range.
sents a change in one or more characters
Acanthomorphs have close to 18,000
from the previous slate; if changes did
described living species, whereas there
not occur, there would be no new species!
are around 10,000 described species of
Hypothetically the original species had
birds. These numbers show, in a very
only original characters, which we call
crude way, that the phenomenal diversity
primitive. The appearance of new anatom
of modern acanthomorphs has arisen in
ical features (which we call advanced) in
AQUATIC ANCESTORS
about the same span of geologic time, as sun's warmth in the spring, the tribal
thai of birds. And based on the criterion gatherings at harvesl Lime.
of number of species, acanthomorphs are The origins of the human species are
more evolved than birds. We can see a more distant. They have been traced back
similar slory in virtually every group of in lime a few million years, to the dry
modern fishes, even among those suppos sands and muds of lakeshores in eastern
edly primeval creatures, the sharks (see Africa. There, unique and curious crea
Chapter 7). tures, our forebears, walked upright, used
crudely worked tools, and planned, in a
■sMVff* A I onj> Way Don 11! simple way, for the future. They looked
The human species is the only one on forward to shaping the new stone with its
Earth to have looked back over its shoul razor-sharp cutting edge, to the move
der, Lo see where it came from. No other ment of a pride of lions, to the ensuing
species has ever had this ability, for histo hunt. Farther back in time, the existence
ry and prehistory-like religion, politics, of primates, to which humans and our
and economics-are uniquely human simian cousins belong, is known from the
concepts. For a few millennia our history fragile bones of 60-million-year-old
is clear, because people wrote things down lemurs and tarsier-like animals from
and kept souvenirs of the past. What they Europe and North America, Morocco, and
wrote down and what they buried and Asia. Beyond that the fossil record reveals
discarded all form the tangible basis of no more traces of those peculiar traits by
human history. But what can we know of which we define humanity or the human
the time before writing, burial, and species, and we see only the relics of a
garbage? once living world.
Fortunately, some fragments of our Our mammalian origins are even
prehistoric ancestry still exist as fossils, more remote in the past, and we have
preserved by naturally occurring processes only fleeting glimpses of the earliest
on Earth. These fossils, painstakingly mammals, tiny fossilized bones of shrew-
extracted from the rocks, then reassem sized creatures that must have cowered
bled and reconstructed in the laboratory, in the shadows of early dinosaurs more
provide tantalizing glimpses into the than 200 million years ago. Beyond that
prehistory of humans, and beyond, into point, the fossil record reveals many
the unrecorded history of our biological bizarre extinct animals, large and small,
ancestors. Religious fundamentalists that to us seem increasingly reptilian
may deny that evolution exists, but in and share progressively fewer anatomical
the natural world it is religion that does features with modern mammals. Rarely,
not exist. we find the fossil bones of even earlier
Frequently our view into our prehis four-legged animals, primitive semi-
toric past is obscured by the mists of aquatic Letrapod amphibians, in strata
antiquity and the ravages of erosion. The that were laid down in lakes, swamps,
origins of humanity'-the totality of the cul and estuaries more than 360 million
tural and social relations that distinguish years ago.
humankind from other animals-can be Even these animals do not represent
followed into the past a few thousand the base of our evolutionary ladder, for
chilly years, to glacial and postglacial it stands in the water and extends deep
caves and rift valleys where small groups beneath the surface. Many of the most
of individuals lived who divided their fundamental physical features of humans,
labors, cared for their sick and elderly, even the legs that support us, first
cooked, painted, dreamed, and planned appeared in nascent form in an aquatic
for their future: the funeral of a loved one
environment. Our basic vertebrate
tomorrow, the bison returning with the
design-jaws, brain, nerves, internal
Discovering Fossil fishes i.l
