Lecture 18: Macroevolution and the fossil record

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Lecture 18 Macroevolution and the fossil record
Readings read again Ch. 22.1, 25.1
Fossils kinds of fossils easy and hard
fossils more small fossils geological time
scale Stasis Punctuated equilibrium
foraminifera test sediments deep-sea drilling
project Everything is gradual
stickleback fish varved deposits
foraminifera again

Transition on a coarse scale
reptile to mammal transition, therapsid,
dentary bone Cool fossils
Mazon Creek, Illinois, 300 MYA
Pennsylvanian
2
Fig. 25.4 There are many kinds of fossils A
fossil is basically any kind of biological
material or trace that was deposited at some time
in the past. Some remains are unaltered, and
some are altered by e.g. mineralization. An
exceptional case is that of amber fossils.
3
Paleontologists prefer to find fossils that are
weathered out of a loose matrix (surrounding
material) if at all possible - getting fossils
out of hard rock is hard work!
Trilobite fossil in Ohio, weathered out - just
needs picking up.
http//nautiloid.net/fossils/sites/sylvania/sylvan
ia.html
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hundreds of micro-fossils (magnified)
5 or 6 of each kind of smaller clams
1 large clam
There are more small fossils than large ones.
Pliocene fossil clam showing microfossils in the
matrix (material in which the large fossil is
embedded)
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Table 26.1 The geological time scale. Memorize
the dates for the Eras. Also, read Fig. 26.7 on
radiometric dating of fossils on your own.
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What we would like the fossil record to be is a
sort of movie of the past, with a perfect view of
everything that happened. We are never going to
have such a perfect movie, because it would
require a complete record for all times and all
of the geographic range of the species of
interest. But we do have a surprisingly good
record in some cases, and one that is getting
better each year as more of the fossil record is
filled in.
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• So, what can we learn from our amazing but
  incomplete fossil record movie?
• Stasis - lack of change.
• Punctuated equilibrium - stasis interrupted by
  periods of rapid change.
• Everything seems to be gradual at a fine level.
• Intermediate fossils do exist between very
  different organisms.

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Stasis - lack of evolutionary change in a species
Living ginko tree, found naturally today only in
China. (But can be found planted on campus)
Fifty million year old fossil of ginko leaf from
Washington State.
www.washington.edu/.../images/ginkgo.gif
project.bio.iastate.edu/.../Ginkgo_leaf.jpeg
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• So, what can we learn from our amazing but
  incomplete fossil record movie?
• Stasis - lack of change.
• Punctuated equilibrium - stasis interrupted by
  periods of rapid change.
• Everything seems to be gradual at a fine level.
• Intermediate fossils do exist between very
  different organisms.

10
http//www.geol.ucsb.edu/faculty/lea/CurrentResear
ch.html
On the left is a living formaminiferan (note dark
test inside), and on the right is a scanning
electron micrograph (SEM) of a test (enlarged
compared to living specimen). Forams are 0.5 to
2 mm wide.
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Foraminifera provide excellent examples of the
phenomenon of punctuated equilibrium. In this
study, change in the size (and shape, as measured
by a compund statistic that reduces shape to a
few dimensions) of a formam is followed for some
6 million years of sediment.
Journal of the Geological Society, London, Vol.
154, 1997, pp. 295302, 3 figs. Printed in Great
Britain Stable isotopic evidence for the
sympatric divergence of Globigerinoides trilobus
and Orbulina universa (planktonic
foraminifera) P. N. PEARSON1, N. J. SHACKLETON2
M. A. HALL2
12
The main pattern in red.
13

• So, what can we learn from our amazing but
  incomplete fossil record movie?
• Stasis - lack of change.
• Punctuated equilibrium - stasis interrupted by
  periods of rapid change.
• Everything seems to be gradual at a fine level.
• Intermediate fossils do exist between very
  different organisms.

14
A stickleback, genus Gasterosteus
Fish from waters with predators are more spiny.
Pelvic spines
15
pubs.usgs.gov/of/2004/1216/tz/images/varve1.gif
Pelvic spines development can be measured on
fossil fish, and spine evolution can be studied
in varved deposits (deposits with annual layers).
Mike Bell site.
age life.bio.sunysb.edu/ee/belllab/
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spiny
not spiny
Spiny-ness of sticklebacks in about 20,000
years of a 7-8 million year old lake deposit in
Nevada. Samples represent 250 years worth of fish
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spiny
not spiny
Before the 0 time mark is 95,000 years of
stasis with a score of around 1.
Spiny-ness of sticklebacks in about 20,000
years of a 7-8 million year old lake deposit in
Nevada. Samples represent 250 years worth of fish
18
This point is actually 7 spiny (score 3) and 12
non-spiny (score 1) fish - no intermediates.
spiny
not spiny
So the jump is not an evolutionary event, but an
ecological one - a spiny species displaced a
non-spiny one by outcompeting it.
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The important point is that spinyness decreased
gradually over the next 14,000 years. There are
intermediates here.
spiny
not spiny
The big picture is that evolution seems to always
be gradual, if you look on a close enough scale.
20
A close-up of what really occurs during a
punctuation event.
Fig. 24.13 - modified
21
Now, an example of a larger scale change where we
can still see intermediates.
22
www.ucl.ac.uk/GeolSci/micropal/foram.html
Globigerinoides trilobus on the left has existed
for some 20 MYA, and still exists. Orbulina
universa on the left is a boring sphere - but
break it and there is a little G. triloba-like
test inside. It speciated from G. triloba about
16 MYA, in a period of about 1 MY.
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Gradual transition between Globigerinoides
trilobus (top left) and Orbulina universa (bottom
right)
Journal of the Geological Society, London, Vol.
154, 1997, pp. 295302, 3 figs. Printed in Great
Britain Stable isotopic evidence for the
sympatric divergence of Globigerinoides trilobus
and Orbulina universa (planktonic
foraminifera) P. N. PEARSON1, N. J. SHACKLETON2
M. A. HALL2
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In the great majority of cases, we dont have a
fine-scale fossil record. But for many cases we
still have a good record, which is adequate for
understanding the large-scale features of
evolution - and for revealing the basic pattern
of intermediate steps.
X
X
X
X
X
Fig. 24.13 - modified
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As an example, lets look at the transition from
reptiles to mammals. The unique (derived)
features of mammals that we think of first, hair,
milk production, the placental, dont fossilize,
but other mammalian features, like having a
single bone in the mandible (lower jaw), no ribs
on the cervical (neck) vertebrae, and
differentiated teeth, do fossilize. The
transition takes us from reptiles like
Dimetrodon, to therapsids like Lycaenops, to
modern mammals like us. We will focus mostly on
the mandible bones and the teeth.
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From A. S. Romer and T. S. Parsons, 1977, The
Vertebrate Body. Early to later (top to bottom)
mandible transitions in Dimetrodon to primitive
therapsid to advanced therapsid to modern mammal.
Note increasing differentiation of teeth and
also loss of all bones but dentary.
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Lycaenops, a therapsid (Berkeley Museum). Note
cervical (neck) ribs at right.
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A living transition - a platypus. Makes milk but
lays eggs, has hair but has cervical ribs, which
plancetal and marsupial mammals do not.
http//animaldiversity.ummz.umich.edu/site/resourc
es/Grzimek_mammals/Ornithorhynchidae/v12_id12_con_
burrow.jpg/view.html
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Mazon Creek fossils (near Kankakee), 300 MYA,
Pennsylvanian
Ironstone nodules
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The state fossil of Illinois The tully monster
http//www.museum.state.il.us/exhibits/mazon_creek
/
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Lecture 18 Macroevolution and the fossil record
Readings read again Ch. 22.1, 25.1
Fossils kinds of fossils easy and hard
fossils more small fossils geological time
scale Stasis Punctuated equilibrium
foraminifera test sediments deep-sea drilling
project Everything is gradual
stickleback fish varved deposits
foraminifera again

Transition on a coarse scale
reptile to mammal transition, therapsid,
dentary bone Cool fossils
Mazon Creek, Illinois, 300 MYA
Pennsylvanian