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Re: Paleontology and Dinosaurology 101: What layperson MUST to know about?



On Sun, February 6, 2011 3:23 am, Roberto Takata wrote:
> Dear DMLers,
>
> Considering regular people, what are the facts and theories about
> paleontology (and dinosaurs) that they should to know?
>

Okay, I'll give it a brief shot:

GENERAL:
* That rocks are produced by various factors (erosion --> sedimentation;
metamorphism; volcanic activity; etc.)
* That fossils are remains of organisms or traces of their behavior
recorded in those rocks.
* That rocks (and the organisms that made the fossils) can be thousands,
millions, or even billions of years old.
* That the species discovered by fossils, and the communities of organisms
at each place and time, are different from the same in the modern world
AND from each other.
* That 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 life.
* That we can use fossils, in conjunction with anatomical, molecular, and
developmental data of living forms, to reconstruct the evolutionary
pattern of life through time.
* That environments of the past were different from the present.
* That 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.
* That entire branches of the tree of life have perished (sometimes in
these mass extinction events, sometimes more gradually)

SPECIFIC:
Honestly, despite the fact the specific issues are the ones that readers
here obsess over... er, are more concerned with, they 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 above points.
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.

Furthermore, while the readership here is understandably biased towards
dinosaurs, you could get an entirely different set of specific points if
you addressed a general vertebrate paleontology list, or an invert list,
or paleobotanists, or paleoanthropologists, or so on.

That said, here are some more specific points:
* Life first developed in the seas, and for nearly all of its history was
confined there.
* For most of Life's history, organisms were single-celled only. (And
today, most of the diversity remains single-celled).
* The evolution of photosynthesis was a critical event in the history of
Earth and Life; living things were able to effect the planet and its
chemistry on a global scale.
* Multicellular life evolved independently several times.
* Early animals were all marine forms
* The major groups of animals diverged from each other before they had the
ability to make complex hard parts
* About 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 happened.
* Plants 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 afterwards.
* For 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.
* Complex forests of plants (mostly related to small swampland plants of
today's world) covered wide regions of the lowlands of the Carboniferous.
Burial 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 modern world.
* While most of the coal swamp plants reproduced by means of spores, 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.
* In 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.
* Early 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 the
tadpole stage.
* These 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).
* A 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.
* In the time after this Permian-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 niches.
* During 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.
* DInosaurs 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.
* During 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.
* Other terrestrial groups such as pterosaurs, crocodile-ancestors,
mammals, and insects continued to diversify into new habits.
* During the Jurassic and (especially) the Cretaceous, a major
transformation of marine life occurred. Green-algae phytoplankton were
displaced by red- and brown-algae (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 common.
* During 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.
* The 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.
* The 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.
* During 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.
* As the world cooled and dried, great grasslands developed (first in
South America, and later nearly all other continents).
* Various 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 pack hunters.
* Other 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.
* A group of arboreal mammals with very big brains, complex social
communities, and gripping hands--the primates--produced many forms. In
Africa 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 the grasslands.
* This 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 Africa to other regions
of the planet.
* About 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.
* The early humans managed to colonize much of the planet; shortly after
their arrival into new worlds, nearly all the large-bodied native species
disappeared.
* At 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.
* In western Asia and northern Africa (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 techniques).
* This 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).
* From this point we begin to get a written record, and so the historians
can take up the story...

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661

Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA