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Stephen Jay Gould & Niles Eldredge. 1993. Punctuated equilibrium comes of age. Nature: 366: 223-227. PowerPoint PPT Presentation


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We have no evidence that the species of 'living fossil' groups are particularly old. For example, the western Atlantic horseshoe crab, Limulus polyphemus --the 'type example' of the phenomenon--has no fossil record at all, whereas the genus can only be traced to the Miocene [about 20 mya].

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Stephen Jay Gould & Niles Eldredge. 1993. Punctuated equilibrium comes of age. Nature: 366: 223-227.

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Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

We have no evidence that the species of 'living fossil' groups are particularly old. For example, the western Atlantic horseshoe crab, Limulus polyphemus--the 'type example' of the phenomenon--has no fossil record at all, whereas the genus can only be traced to the Miocene [about 20 mya].

Stephen Jay Gould & Niles Eldredge. 1993. Punctuated

equilibrium comes of age. Nature: 366: 223-227.

Limulus polyphemus

Palaeolimulus (approx 300 mya)

http://www.ucmp.berkeley.edu


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

But extinction intensities vary greatly, and the geological record features episodes of high dying. during which extinction-prone groups are more likely to disappear, leaving extinction-resistant groups as life's legacy. Valentine concludes that "these clade-characteristic rates are of course not adaptations per se, but effects flowing from clade properties that were established probably during the early radiations that founded the clades."

Phyletic gradualism has been well documented, again across all taxa from microfossils to mammals. Punctuated equilibrium surely exists in abundance, but validation of the general hypothesis requires a relative frequency sufficiently high to impart the predominant motif and signal to life's history.

Stephen Jay Gould & Niles Eldredge. 1993. Punctuated

equilibrium comes of age. Nature: 366: 223-227.

the concept of widespread stasis essentially denies the existence of any kind of lineage evolution.

Michael J. Benton and Paul N. Pearson. 2001. Speciation in the fossil

record. Trends in Ecology & Evolution Vol.16 No.7: 405-411.


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

"Consider the lifetime testimonies of taxonomic experts on microfossils, on brachiopods and on beetles. Fortey has concluded for trilobites and graptolites 'that the gradualistic mode does occur especially in pelagic or planktic forms, but accounts for 10% or less of observations of phyletic change, and is relatively slow'."

"Opponents now accept that punctuated equilibrium was never meant as a saltational theory, and that stasis does not signify rock-hard immobility, but fluctuation of little or no accumulated consequence, and temporal spread within the range of geographic variability among contemporary populations—by Stanley's proper criterion, so strikingly validated in his classic study. We trust that everyone now grasps the centrality of relative frequency as a key criterion (and will allow, we may hope, that enough evidence has now accumulated to make a case, if not fully prove the point)."

Stephen Jay Gould & Niles Eldredge. 1993. Punctuated

equilibrium comes of age. Nature: 366: 223-227.


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

"It soon became clear that what was a gradual anagenetic pattern to one person was an obviously stepped, punctuational pattern to

another. Larger-scale studies from the 1980s and 1990s sometimes involved tens of thousands of assessed specimens, very fine-scale stratigraphies and subtle attempts to determine the nature of the

species involved (Box 1). Even in these massive exercises in data documentation, the objection could be raised that apparent speciation events might sometimes be simply ECOPHENOTYPIC rather than the result of evolutionary change."

Michael J. Benton and Paul N. Pearson. 2001. Speciation in the fossil

record. Trends in Ecology & Evolution Vol.16 No.7: 405-411.


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

"Thus, species are not special because their origin permits a unique moment for instigating change, but because they provide the only mechanism for protecting change. Futuyma writes: "In the absence of reproductive isolation, differentiation is broken down by recombination. Given reproductive isolation, however, a species can retain its distinctive complex of characters as its spatial distribution changes along with that of its habitat or niche. . . Although speciation does not accelerate evolution within populations, it provides morphological changes with enough permanence to be registered in the fossil record. Thus, it is plausible to expect many evolutionary changes in the fossil record to be associated with speciation."

Stephen Jay Gould & Niles Eldredge. 1993. Punctuated

equilibrium comes of age. Nature: 366: 223-227.


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

fossils of the Carribean bryozoan, Metrarabdotos spp.

A vs. B -

small difference

  • A) M. n sp. 10

  • B) M. tenue

  • C) M..lacryosum

  • D) M. unguiculatum

C vs. D -

large difference

Cheetham (1986) Tempo of evolution in a Neogene

bryozoan: rates of morphological change within

and across species boundaries. Paleobiology 12:190-202


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

Cheetham (1986) Tempo of evolution in a Neogene

bryozoan: rates of morphological change within

and across species boundaries. Paleobiology 12:190-202


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

"...some palaeontologists might argue that if a species lineage has evolved sufficiently in form (by ANAGENESIS) to be entirely distinct from its ancestor, it should constitute a different species; but by the definitions usually adopted, that can only be admitted if a cladogenetic event has occurred."

....and has been preserved

Rhizosolenia

bergonii

Rhizosolenia

praebergonii

Michael J. Benton and Paul N. Pearson. 2001. Speciation in the fossil

record. Trends in Ecology & Evolution Vol.16 No.7: 405-411.


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

Speciation is a consequence of reproductive isolation and thus the frequency of speciation in a group is likely to be related to the ease with which reproductive barriers appear. At one extreme, there are organisms such as planktonic protists that live in huge populations that seldom encounter barriers to dispersal, and which do not possess complex behaviours associated with reproduction. For these, genetic isolation of populations is a rare event, and speciation, which perhaps also occurs rarely, might be long term and gradual. At the other extreme are organisms such as freshwater fish that live in spatially structured and often transient environments. Here, speciation might be so common that every lake and river has its own reproductively isolated population of a particular type of fish, but these populations might neither be very distinctive nor last very long. In between might lie the majority of invertebrate and vertebrate groups, generally exhibiting stasis, but occasionally speciating in a punctuated manner following a major environmental perturbation.

Michael J. Benton and Paul N. Pearson. 2001. Speciation in the fossil

record. Trends in Ecology & Evolution Vol.16 No.7: 405-411.


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

the “K-T extinction”,

65 million years ago

total numbers

of different types of

animals over time

numbers of

different types of

animals going

extinct over time

numbers of

different types of

animals “appearing”

(as fossils) over

time

the “big five” mass extinctions


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

Dr. Ron Blakey

Cambrian period: 550 to 490 mya first appearance of practically every animal phylum with a decent fossil record

some animals (jellyfish, branched coral, comb jellies, sponges, peanut worms...) appeared before the Cambrian, but the Cambrian forms were endowed with significant hard parts for the first time

that includes coralline algae, which also made their first appearance in the Cambrian

dominant animal taxa included trilobites, certain lampshells, certain primitive echinoderms and sponges


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

Dr. Ron Blakey

The Ordivician period:490 to 443 mya

Very diverse marine invertebrates, including trilobites, a relative of acorn worms called "graptolites," lampshells, nautiloids, corals, sea mats and reef building sponges, as well as early verte-brates (conodonts) and red & green

algae. Also, the first spores appear, indicating the earliest land plants

The end-Ordivician mass extinction may have been caused by glaciation leading to major sea level drops in shallow seas. 60% of all marine invertebrate genera went extinct

William B. S. Berry

worst affected groups included the conodonts, graptolites and trilobites


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

Dr. Ron Blakey

The Devonian period:417 to 354 mya

Colonization of land by the insects, arachnids and amphibians. The first forests of ferns and seed plants. In the seas, lampshells, feather stars, corals & fish flourished. Ammonoids appear, trilobites in decline?

The Devonian mass extinction may actually have been a series of smaller extinctions lasting between 3 and 15 million years. The disproportionate impact on warmer water species suggests that global warming may have been a culprit.

There's also some evidence for a extraterrestrial impact.

Lampshells, ammo-

nites, jawless & armored fishes and reef corals suffered large losses. Trilo-bites too. Land critters did well.


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

Dr. Ron Blakey

The Permian period:290 to 248 mya

The warm shallow waters were productive reef systems, with sponges, corals, sea mats and sea moss, lampshells, algae and stromatolites. Also dominant were complex ammo-noids and nautiloids. Seed plants

diversified, ginkos and conifers appeared. But dry land climates caused problems for large trees and amphibians. Insects & reptiles diversified.

The end-Permian extinction is known as the "mother of all mass extinctions, with 90-95% of all marine species lost.

The cause is still unknown, but sea level changes associated with the formation of Pangaea is one possibility

The last trilobites went extinct, as did many corals, echinoderms, armored fish, all fin-backed reptiles, many sea mosses & sea mats, lampshells, ammonoids, ostracods (a bivalved arthropod) sharks and bony fish.


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

Dr. Ron Blakey

The Triassic period:248 to 206 mya

The age of the dinosaurs begins, large trees (especially cycads, ginkos and conifers) dominated the land. Nine orders of insects got wiped out in the Permian, but others, including beetles, survived and diversified. First

appearance of wasps/bees/ants, flies, caddis flies and walking sticks. Crocodiles and pterosaurs blossomed. In the seas, bivalves, ammonoids and lampshells recovered to dominate. Starfish and sea urchins appear. The first mammals appear, as do frogs.

The Triassic extinction (which may have been in 2 waves, about 15

million years apart) is poorly studied, and the

cause(s) is/are hence not well known.

Peabody Museum of Natural History

Still, up to a quarter of all families may have disappeared, including many sponges, cephalopods, lampshells, insects, the ancient fish-like "conodonts" and many vertebrates


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

Dr. Ron Blakey

The Jurassic period:206 to 146 mya

The age of the dinosaurs continues, with them reaching the peak of their dominance. Pterosaurs and birds appear, as do icthyosaurs and plesiosaurs. Also dominating the sea

are fish, squid, coiled ammonites. Mammals are still a relatively

minor groups. Seed plants dominate.

Peabody Museum of Natural History


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

Dr. Ron Blakey

The Cretaceous period:146 to 65 mya

The age of the dinosaurs continues, although their numbers are decreasing gradually throughout the cretaceous. Still some new forms appear, like the ceratopsians. Modern mammal groups appear, as do the first unequivocal flowering plants.

.......and then............


Stephen jay gould niles eldredge 1993 punctuated equilibrium comes of age nature 366 223 227

see this website for animations of plate tectonic movements:

http://www.ucmp.berkeley.edu/geology/tectonics.html


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