From:    Kathleen Hunt                          
To:      All                                    Msg #87, Sep-06-93 06:48PM
Subject: Refs for speciation in the fossil record

Organization: University of Washington, Seattle
From: jespah@carson.u.washington.edu (Kathleen Hunt)
Message-ID: <26gsq7$kpg@news.u.washington.edu>
Newsgroups: talk.origins

Hi all -- I've found some references for speciations that can be seen in the
fossil record.  Unfortunately I haven't had time to check out the refs myself,
but as it seems to be taking me forever to get to the library, I thought 
I'd tell you all about the refs so you can read 'em yourself if you're 
interested.

The following is all from Robert Carroll's _Vertebrate Paleontology
& Evolution_, chapter 22 (the section on evolution at the species level).
(copyright 1988, W.H. Freeman & Co., New York,)

It's clear from the text that most studies of speciation in the fossil record
have been done by scientists who are particularly interested in the *rate* of
evolution, e.g. does the speciation event follow the punk-eek model or
a more gradualistic model.  So if you look up the refs, keep in mind that 
that's the context in which the research was done, and that's the question
that's likely to be emphasized in the intro & discussion sections.

The studies Carroll mentions are:
1) Gingerich's 1976 study of the early Cenozoic mammals Hyopsodus, Haplomylus,
and Pelycodus.  (an early primate & 2 early ungulates, I think.) Both forms
of evolution (gradual "phyletic" evolution & sudden punk-eek speciation)
are seen.  Carroll calls this "the most detailed & extensive study" of
speciation in the fossil record.  He says, "All three genera are 
known from sequential series of species  
[stupid line editor!] 
showing gradual increase in size over time.  Most of the species had 
previously been recognized on the basis of a few, clearly distinct specimens
from widely separated horizons. Study of hundreds of specimens 
from intervening levels demonstrated several continuous morphological
series that can be divided into separate species only arbitrarily.
Divergence of lineages over time is observed in both Pelycodus and 
Hyopsodus."...[brief discussion of speciation requiring geographic
isolation...deja vu, another t.o. thread!]..."In these examples, speciation
does not appear to introduce factors of morphological change that are
different from those that occur through phyletic [gradual] evolution.....
Additional work by Gingerich (1980) in a wider area of western North
America that combines both late Paleocene & early Eocene sediments deposited
over approximately 12.5 million years documents 24 species that have arisen
by phyletic evolution, and 14 cases in which species appear 
suddenly in the fossil record; the latter events are attributed to 
immigration.  We should note that not all species exhibited progressive
change; some did exhibit stasis for variable periods of time."

Refs:
Gingerich, P.D.  1976.  Paleontology and phylogeny: Patterns of 
evolution at the species level in early Tertiary mammals.  Am. J. Sci.
276:1-28.

Gingerich, P.D.  1980.  Evolutionary patterns in early Cenozoic mammals.
Ann. Rev. Earth Planet. Sci. 8:407-424.

Gingerich, P.D. 1982.  Time resolution in mammalian evolution: Sampling,
lineages, and faunal turnover.  Third North Am. Paleont. Conv., Proc.,
1:205-210.

2) "Rose & Brown (1984) documented evidence of progressive change between
genera on the basis of over 600 specimens of primates collected from a 
700-meter-thick sequence representing approximately 4 million years of the
Eocene.  One example is provided by marked changes in the dentition between
_Tetonius homunculus_ and _Pseudotetonius ambiguus_.  There is no evidence
of a change in evolutionary rate across the transition; it is smoothly
gradational."

Rose, K.D., and Brown, T.M. 1984.  Gradual phyletic evolution at the 
generic level in early Eocene omomyid primates.  Nature 309:250-252.

"Other well-documented examples of progressive morphological change within 
species and genera are:" [Carroll then gives the following list, without
discussing them in detail]
3) Hurzeler (1962) - mid-Cenozoic rabbits
Hurzeler, J.  1962.  Kann die biologische Evolution, wie sie sich in der
Vergangengeit abgespielt hat, exakt erfasst werden?  Stud. Kath. Akad.
Bayern.  16:15-36.  [any German speakers out there want to summarize
this for the net?]

4) Chaline & Laurin (1986) - Plio-Pleistocene rodents
Chaline, J., and Laurin, B.  1986.  Phyletic graduatism in a European
Plio-Pleistocene _Mimomys_ lineage (Arvicolidae, Rodentia).  Paleobiology
12:203-216.

5) Fahlbusch (1983) - Miocene rodents
Fahlbusch, V.  1983.  Makroevolution. Punktualismus. Ein Diskussionsbeitrag
am Beispiel miozaner Eomyiden (Mammalia, Rodentia).  Palaont. Z. 57:213-230.
[English summary anyone?]

6) Harris & White (1979) - Plio-Pleistocene suids in Africa         
Harris, J., & White, T.D.  1979.  Evolution of Plio-Pleistocene African
Suidae.  Trans. Am. Phil. Soc. 69:1-128.

7) MacFadden (1985) - hipparion horses
MacFadden, B.J.  1985.  Patterns of phylogeny and rates of evolution in
fossil horses: Hipparions from the Miocene and Pliocene of North America.
Paleobiology 11:245-257.  [I have this paper & can summarize it if 
anyone wants.]

8) Krishtalka & Stucky (1985) - early Eocene artiodactyls
Krishtalka, L., and Stucky, R.K.  1985.  Revision of the Wind River Faunas.
Early Eocene of Central Wyoming.  Part 7.  Revision of _Diacodexix_
(Mammalia, Artiodactyla).  Am. Carnegie Mus. 54:413-486.

9) Elephants:  "It may be noted that the "sudden" appearance of the genera 
Loxodonta [African elephants], Elephas [Asian], and Mammuthus occurs after
a 500,000-year gap in the fossil record....[Loxodonta showed stasis in
dentition for 2 million years]...Within the genus Elephas, species 
demonstrate continuous change over a period of 4.5 million years. Maglio
(1973, p.81) stated:
..._Elephas recki_...can be traced through a progressive series of stages...
These stages pass almost imperceptibly into each other...In the late
Pleistocene a more progressive elephant appears which I retain as a 
distinct species, _Elephas iolensis_, only as a matter of convenience. 
although as a group, material referred to _E. iolensis_ is distinct from 
that of _E. recki_, some intermediate specimens are known and _E. iolensis_ 
seems to represent a very progressive, terminal stage in the _E. recki_
specific lineage.  [end of Maglio quote]
...the elephants provide excellent evidence of significant morphological
change within species, through species within genera, and through genera
within a family....There is considerable evidence from Tertiary mammals
that significant change does occur during the duration of species, as 
they are typically recognized, and this change can account for the
emergence of new species and genera."

Maglio, V.J.  1973.  Origin and evolution of the Elephantidae.  Trans.
Am. Phil. Soc., New Ser. 63:1-149.

****
Carroll also discusses the difficulties in finding a nice fossil record of a 
speciation event: "only rarely are geological process sufficiently regular
and continuous to lead to the preservation of numerous fossils that
are evenly distributed throughout the time range of the species."  It
does happen, but not very often.

Well, have fun at the library, everyone.

Kathleen