Should Everyone Know About Paleontology?”
Thomas R. Holtz, Jr.
The title question was recently asked by Roberto
Takata on the Dinosaur Mailing List
I think that is a good question. What really are the most important
elements of paleontology that the general public should understand? I took a
shot at coming up with a list of key concepts (http://dml.cmnh.org/2011Feb/msg00027.html and
based on experiences with teaching paleontology and historical geology and with
less-formally structured outreach to the public. I have offered this list (cross
posted at the Superoceras and
Musings blogs) as a way for it to reach a wider audience.
That this is Darwin Week makes it even more appropriate, as we should use this
occasion to encourage a better understanding of the changes of Earth and Life
through Time for the public at large.
Much as I might like to think otherwise,
the specific details of the hindlimb function of Tyrannosaurus rex or
the pneumatic features of brachiosaurid vertebrae really are not the most
important elements of the field. Understanding and appreciating the nitty gritty
details of the phylogeny and anatomy of any particular branch of the Tree of
Life are not really necessary for everyone to know, any more than we would
regard detailed knowledge of bacterial biochemistry or the partitioning of
minerals in a magma chamber to be significant general knowledge. (Indeed, these
latter two items are actually far more critical for human society than any
specific aspect of paleontology, and so from a certain point of view really more
important for people to know than the History of Life.)
That said, all human societies and many
individuals have wondered about where we have come from and how the world came
to be the way it is. This is, in my opinion, the greatest contribution of
paleontology: it gives us the Story of Earth and Life, and especially our own
I have divided this list into two
sections. The first is a list of general topics of paleontology, touching on the
main elements of geology that someone would need to know for fossils to make any
sense. The second is the more specific list of key points in the history of
(NOTE: as the idea of this list is that
it should be aimed at the general public, I have tried to avoid technical
terminology where possible.)
rocks are produced by various factors (erosion -> sedimentation;
metamorphism; volcanic activity; etc.)
rocks did not form at a single moment in time, but instead have been and
continue to be generated throughout the history of the planet.
fossils are remains of organisms or traces of their behavior recorded in
rocks (and the organisms that made the fossils) can be thousands, millions,
or even billions of years old.
the species discovered as fossils, and the communities of organisms at each
place and time, are different from the same in the modern world and from
despite these differences that there is continuity between life in the past
and life in the present: this continuity is a record of the evolution of
we can use fossils, in conjunction with anatomical, molecular, and
developmental data of living forms, to reconstruct the evolutionary pattern
of life through time.
fossils are incomplete remains of once-living things, and that in order to
reconstruct how the organisms that produced them actually lived, we can:
their anatomy (both gross external and with the use of CT scanning
internal), and compare them to the anatomy of living creatures in order to
estimate their function;
their chemical composition, which can reveal aspects of their
their microstructure to estimate patterns of growth;
their biomechanical functions using computers and other engineering
their footprints, burrows, and other traces to reveal the motion and other
actions of the species while they were alive;
collect information of the various species that lived together in order to
reconstruct past communities.
with all that, fossils are necessarily incomplete, and there will always be
information about past life which we might very much want to know, but which
has been forever lost. Accepting this is very important when working with
environments of the past were different from the present.
there have been episodes of time when major fractions of the living world
were extinguished in a very short period of time: such data could not be
known without the fossil record.
entire branches of the tree of life have perished (sometimes in these mass
extinction events, sometimes more gradually).
certain modes of life (reef formers, fast-swimming marine predators,
large-bodied terrestrial browsers, etc.) have been occupied by very
different groups of organisms at different periods of Earth History.
every living species, and every living individual, has a common ancestor
with all other species and individuals at some point in the History of Life.
Honestly, despite the fact the specific
issues about specific parts of the Tree of Life are the ones that
paleontologists, the news media, the average citizen, etc., are more concerned
with, they really are much less significant for the general public to know than
the points above. Sadly, documentary companies and the like keep on forgetting
that, and keep on forgetting that a lot of the public does not know the
Really, in the big picture, the
distinction between dinosaurs, pterosaurs, and crurotarsans are trivialities
compared to a basic understanding that the fossil record is our document of
Life’s history and Earth’s changes.
Summarizing the key points of the history
of life over nearly 4 billion years of evolutionary history is a big task. After
all, there is a tendency to focus on the spectacular and sensationalized rather
than the ordinary and humdrum. As Stephen Jay Gould and others often remarked,
from a purely objective external standpoint we have always lived in the Age of
Bacteria, and the changing panoply of animals and plants during the last
half-billion years have only been superficial changes.
But the question wasn’t “what should
a dispassionate outsider regard as the modal aspect of the History of Life?”;
it was “What should everyone know about paleontology?” Since we are
terrestrial mammals of the latest Cenozoic, we have a natural interest in events
on the land and during the most recent parts of Earth History. That is a fair
bias: it does focus on who WE are
and where WE come
That said, here is a list of key concepts
in the history of life. Other researchers might pick other moments, and not
include some that I have here. Still, I believe most such lists would have many
of the same key points within them.
first developed in the seas, and for nearly all of its history was confined
most of Life’s history, organisms were single-celled only. (And today,
most of the diversity remains single-celled).
evolution of photosynthesis was a critical event in the history of Earth and
Life; living things were able to affect the planet and its chemistry on a
life evolved independently several times.
animals were all marine forms.
major groups of animals diverged from each other before they had the ability
to make complex hard parts.
540 million years ago, the ability to make hard parts became possible across
a wide swath of the animal tree of life, and a much better fossil record
colonized land in a series of stages and adaptations. This transformed the
surface of the land, and allowed for animals of various groups to follow
the first 100 million years or so of skeletonized animals, our own group
(the vertebrates) were relatively rare and primarily suspension feeders. The
evolution of jaws allowed our group to greatly diversify, and from that
point onward vertebrates of some form or other have remained apex predators
in most marine environments.
forests of plants (mostly related to small swampland plants of today’s
world) covered wide regions of the lowlands of the Carboniferous.
of this vegetation before it could decay led to the formation of much of the
coal that powered the Industrial Revolution and continues to power the
most of the coal swamp plants required a moist ground surface on which to
propagate, one branch evolved a method of reproduction using a seed. This
adaptation allowed them to colonize the interiors, and seed plants have long
since become the dominant form of land plant.
the coal swamps, one group of arthropods (the insects) evolved the ability
to fly. From this point onward insects were to be among the most common and
diverse land animals.
terrestrial vertebrates were often competent at moving around on land as
adults, but typically had to go back to the water in order to reproduce. In
the coal swamps one branch of these animals evolved a specialized egg that
allowed them to reproduce on land, and thus avoid this “tadpole” stage.
new terrestrial vertebrates—the amniotes—diversified into many forms.
Some included the ancestors of modern mammals; others the ancestors of
today’s reptiles (including birds).
tremendous extinction event, the largest in the age of animals, devastated
the world about 252 million years ago. Caused by the effects and
side-effects of tremendous volcanoes, it radically altered the composition
of both marine and terrestrial communities.
the time after this Permo-Triassic extinction, reptiles (and especially a
branch that includes the ancestors of crocodilians and dinosaurs)
diversified and became ecologically dominant in most medium- to large-sized
the Triassic many of the distinctive lineages of the modern terrestrial
world (including turtles, mammals, crocodile-like forms, lizard-like forms,
etc.) appeared. Other groups that would be very important in the Mesozoic
but would later disappear (such as pterosaurs and (in the seas) ichthyosaurs
and plesiosaurs) evolved at this time.
were initially a minor component of these Triassic communities. Only the
tall, long-necked sauropodomorphs were ecologically diverse during this time
among the various dinosaur branches. However, a mass extinction event at the
end of the Triassic (essentially the Permo-Triassic extinction in miniature)
allowed for the dinosaurs to diversify as their competitors had vanished.
the Jurassic, dinosaurs diversified. Some grew to tremendous size; some
evolved spectacular armor; some become the largest carnivorous land animals
the world had seen by this point. Among smaller carnivorous dinosaurs, an
insulating covering of feathers had evolved to cover the body (possibly from
a more ancient form shared by all dinosaurs). Among the feathered dinosaurs
were the ancestors of the birds.
terrestrial groups such as pterosaurs, crocodile-ancestors, mammals, and
insects continued to diversify into new habits.
the Jurassic and (especially) the Cretaceous, a major transformation of
marine life occurred. Green-algae phytoplankton were displaced by red-algae
phytoplankton (which continue to dominate modern marine ecosystems). A wide
variety of new predators—advanced sharks and rays, teleost fish, predatory
snails, crustaceans with powerful claws, specialized echinoids,
etc.—appeared, and the sessile surface-dwelling suspension feeders that
dominated the shallow marine communities since the Ordovician became far
rarer. Instead, more mobile, swimming, or burrowing forms became more
the Cretaceous one group of land-plants evolved flowers and fruit and thus
tied their reproduction very closely with animals. Although not immediately
ecologically dominant, this type of plants would eventually come to be the
major land plant group.
impact of a giant asteroid—coupled with other major on-going environmental
changes—brought an end to the Mesozoic. Most large-bodied groups on land
and sea, and many smaller bodied forms, disappeared. The only surviving
dinosaurs were toothless birds.
beginning of the Cenozoic saw the establishment of mammals as the dominant
group of large-bodied terrestrial vertebrates. Early on mammals colonized
both the sea and the air as well.
its beginning the Cenozoic world was warm and wet, much like the Cretaceous.
However, a number of changes of the position of the continents and the rise
of mountain ranges caused the climates to cool and dry.
the world cooled and dried, great grasslands developed (first in
, and later nearly all other continents).
groups of animals adapted to the new grassland conditions. Herbivorous
mammals became swift runners with deep-crowned teeth, often living in herds
for protection. Mammalian predators became swifter as well, some becoming
new plant communities evolved, and new animal communities which inhabited
them. The rise of modern meadows (dominated by daisy-related plants and
grasses) saw the diversification of mouse-and-rat type rodents, many frogs
and toads, advanced snakes, songbirds, etc.
group of arboreal mammals with very big brains, complex social communities,
and gripping hands—the primates—produced many forms. In
one branch of these evolved to live at mixed forest-grassland margins, and
from this branch evolved some who became fully upright and moved out into
group of primates retained and advanced the ability to use stone tools that
its forest-dwelling ancestors already had. Many branches evolved, and some
developed even larger brains and more complex tools. It is from among these
that the ancestors of modern humans and other close relatives evolved, and
eventually spread out from
to other regions of the planet.
2.6 million years ago a number of factors led to ice age conditions, where
glaciers advanced and retreated. Various groups of animals evolved
adaptations for these new cold climates.
early humans managed to colonize much of the planet; shortly after their
arrival into new worlds, nearly all the large-bodied native species
some point before the common ancestor of all modern humans spread across the
planet, the ability to have very complex symbolic language evolved. This led
to many, many technological and cultural diversifications which changed much
faster than the biology of the humans themselves.
western Asia and northern
(and eventually in other regions), modern humans developed techniques to
grow food under controlled circumstances, leading to true agriculture.
(Other cultures are known to have independently evolved proto-agricultural
Neolithic revolution allowed for the development of more settled
communities, specialization of individual skills within a community
(including soldiers, metallurgists, potters, priests, rulers, and with the
rise of writing, scribes).
this point we begin to get a written record, and so the historians can take
up the story…
This list is obviously not comprehensive,
and there are many elements that I had to ignore to keep it relatively short.
Still, I hope this overview helps put where we as a species fit into the larger
perspective of Life’s long voyage, a voyage that could only have been traced
by the study of fossils.