| Topic: |
Religions > Bible |
| User: |
"IKnowHimDoYou" |
| Date: |
14 Jan 2004 10:54:16 AM |
| Object: |
Sudden Appearences |
Sudden Appearences
"Each species of mammal-like reptile that has been found appears suddenly
in the fossil record and is not preceded by the species that is directly
ancestral to it. It disappears some time later, equally abruptly, without
leaving a directly decended species."
T.S. Kemp. "The Reptiles that Became Mammals," New Scientist, 92-583 Mar 4, 1982
Kemp is a specialist on "mammal-like reptiles and an avowed evolutionist.
If you think that there are transitional links extant showing the path of
evolution you would be mistaken. Even the experts on evolution say over
and over again they do not exist. This places the theroy of evolution in
the catagory of unfounded opinion-not reality.
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| User: "Zachriel" |
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| Title: Re: Sudden Appearences |
14 Jan 2004 11:35:59 AM |
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"IKnowHimDoYou" <IKnowHim@leavingsoon.com> wrote in message
news:IKnowHim-1401040854160001@pm6-20.kalama.com...
Sudden Appearences
"Each species of mammal-like reptile that has been found appears suddenly
in the fossil record and is not preceded by the species that is directly
ancestral to it. It disappears some time later, equally abruptly, without
leaving a directly decended species."
T.S. Kemp. "The Reptiles that Became Mammals," New Scientist, 92-583 Mar
4, 1982
Kemp is a specialist on "mammal-like reptiles and an avowed evolutionist.
If you think that there are transitional links extant showing the path of
evolution you would be mistaken. Even the experts on evolution say over
and over again they do not exist. This places the theroy of evolution in
the catagory of unfounded opinion-not reality.
Why would a single gap in our knowledge falsify the Theory of Evolution?
Just because we don't know everything doesn't mean we don't know anything.
The fossil record on the species level is necessarily rather spotty due to
the rarity of the process of fossilization. Nevertheless, paleontologists
have found ample fossil evidence of the transition from reptiles to mammals.
"The mammalian ear and jaw are instances in which paleontology and
comparative anatomy combine to show common ancestry through transitional
stages."
http://www.nap.edu/html/creationism/evidence.html
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| User: "Pastor Dave" |
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| Title: Re: Sudden Appearences |
14 Jan 2004 12:03:30 PM |
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On Wed, 14 Jan 2004 17:35:59 GMT, "Zachriel"
<angel@zachriel.com> spake thusly:
"IKnowHimDoYou" <IKnowHim@leavingsoon.com> wrote in message
news:IKnowHim-1401040854160001@pm6-20.kalama.com...
Sudden Appearences
"Each species of mammal-like reptile that has been found appears suddenly
in the fossil record and is not preceded by the species that is directly
ancestral to it. It disappears some time later, equally abruptly, without
leaving a directly decended species."
T.S. Kemp. "The Reptiles that Became Mammals," New Scientist, 92-583 Mar
4, 1982
Kemp is a specialist on "mammal-like reptiles and an avowed evolutionist.
If you think that there are transitional links extant showing the path of
evolution you would be mistaken. Even the experts on evolution say over
and over again they do not exist. This places the theroy of evolution in
the catagory of unfounded opinion-not reality.
Why would a single gap in our knowledge falsify the Theory of Evolution?
A single gap? That's a misrepresentation.
--
Pastor Dave Raymond
"As for me, I have not hastened from being a pastor
to follow thee: neither have I desired the woeful day;
thou knowest: that which came out of my lips was right
before thee." - Jeremiah 17:16
http://home.clear.net.nz/pages/bryanp/Evolution/Gre.Sci..htm
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| User: "Dave Oldridge" |
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| Title: Re: Sudden Appearences |
14 Jan 2004 06:01:33 PM |
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(IKnowHimDoYou) wrote in
news:IKnowHim-1401040854160001@pm6-20.kalama.com:
Sudden Appearences
"Each species of mammal-like reptile that has been found appears
suddenly in the fossil record and is not preceded by the species that
is directly ancestral to it. It disappears some time later, equally
abruptly, without leaving a directly decended species."
T.S. Kemp. "The Reptiles that Became Mammals," New Scientist, 92-583
Mar 4, 1982
Kemp is a specialist on "mammal-like reptiles and an avowed
evolutionist.
If you think that there are transitional links extant showing the path
of evolution you would be mistaken. Even the experts on evolution say
over and over again they do not exist. This places the theroy of
evolution in the catagory of unfounded opinion-not reality.
Yep...the transition in the fossil record is not fine-grained at the
species level. So what? It's still difficult to tell where to draw the
line. It was ultimately drawn arbitrarily based on jaw-to-ear
transitions.
--
Dave Oldridge
ICQ 1800667
Paradoxically, most real events are highly improbable.
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| User: "Adam Marczyk" |
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| Title: Re: Sudden Appearences |
14 Jan 2004 11:48:44 AM |
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IKnowHimDoYou <IKnowHim@leavingsoon.com> wrote in message
news:IKnowHim-1401040854160001@pm6-20.kalama.com...
Sudden Appearences
"Each species of mammal-like reptile that has been found appears
suddenly in the fossil record and is not preceded by the species that is
directly ancestral to it. It disappears some time later, equally
abruptly, without leaving a directly decended species."
T.S. Kemp. "The Reptiles that Became Mammals," New Scientist, 92-583 Mar
4, 1982
This is typical out-of-context quotation, of course.
http://members.cox.net/ardipithecus/evol/lies/lie013.html
--
"We have loved the stars too fondly | a.a. #2001
to be fearful of the night." | http://www.ebonmusings.org
--Tombstone epitaph of | e-mail: ebonmuse!hotmail.com
two amateur astronomers, | ICQ: 8777843
quoted in Carl Sagan's _Cosmos_ | PGP Key ID: 0x5C66F737
----------------------------------------------------------------------
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| User: "Elmer Bataitis" |
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| Title: Re: Sudden Appearences |
14 Jan 2004 03:42:02 PM |
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IKnowNothingDoYou wrote:
Sudden Appearences
"Each species of mammal-like reptile that has been found appears suddenly
in the fossil record and is not preceded by the species that is directly
ancestral to it. It disappears some time later, equally abruptly, without
leaving a directly decended species."
T.S. Kemp. "The Reptiles that Became Mammals," New Scientist, 92-583 Mar 4, 1982
Err, this is not what Kemp said. There was no period where you placed it
and he goes on at length about evolution: "Each species of mammal-like
reptile that has been found appears suddenly in the fossil record and is
not preceded by the species that is directly ancestral to it. It
disappears some time later, equally abruptly, without leaving a directly
decended species, although we usually find that it has been replaced by
some new, related species. The concept of punctuated equilibria - which
envisages evolutionary change occurring in a series of jumps, with
relatively little change between - was introduced in 1972 by Niles
Eldredge and Stepen Jay Gould, and accounts for this rather well.
According to this concept, intermediate stages between known species are
not found in the record because most evolutionary change occurs in very
small, geographically isolated parts of the main species population.
Such a peripheral isolate as it is termed can evolve very rapidly, for
three main reasons. It includes only a few individuals; it is isolated
from the main gene pool; and it inhabits an environment different from
that of the rest of the species. The large original population of the
species is at the same time highy susceptible to extinction; because its
population is large its potential rate of evolution is low and therefore
it cannot change quickly in response to a minor change in the
environment. In the course of time, such a species would become extinct
and its place in the habitat would be taken by a related species, newly
developed from one of the peripheral isolates. The fossil record shows
this as the sudden replacement of one species by another within a
lineage, rather than the gradual change of one species into another."
Kemp is a specialist on "mammal-like reptiles and an avowed evolutionist.
If you think that there are transitional links extant showing the path of
evolution you would be mistaken.
Not true, as just a wee bit of reading from your source shows:
"Each of the three phases of synapsid evolution - pelycosaur, therapsid,
and cynodont - shows basically a similar evolutionary pattern..."
And even the subtitle belies this claim:
"Biologists have considered that the fossil record is too incomplete to
contribute in detail to theories of evolution. But the fossil record of
the mammal-like reptiles is certainly convincing - and if taken at its
face value it gives rise to some quite new evolutionary concepts."
And there is a great illustration on the transistions of mammal - like
reptiles over time on page 582.
Even the experts on evolution say over
and over again they do not exist.
What they say is that there is really no way to determine exactly what
was the ancestor species and the descendant species. You could only do
that if you had DNA to test. Fossils are usually rock.
This places the theroy of evolution in
the catagory of unfounded opinion-not reality.
Heritable genetic change in reproducing populations over time is a fact.
**********************************************************
Elmer Bataitis "Hot dog! Smooch city here I come!"
Planetech Services -Hobbes
585-442-2884
"Proudly wearing and displaying, as a badge of honor,
the straight jacket of conventional thought." - C.
Cagle
**********************************************************
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| User: "Matt Silberstein matts2nopam@ix netcom.nospamcom" |
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| Title: Re: Sudden Appearences |
14 Jan 2004 08:49:31 PM |
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In alt.religion.christian I read this message from
IKnowHim@leavingsoon.com (IKnowHimDoYou):
Sudden Appearences
"Each species of mammal-like reptile that has been found appears suddenly
in the fossil record and is not preceded by the species that is directly
ancestral to it. It disappears some time later, equally abruptly, without
leaving a directly decended species."
T.S. Kemp. "The Reptiles that Became Mammals," New Scientist, 92-583 Mar 4, 1982
Why did you lie just then? You gave a false quote. Did you make
up the lie yourself? (That is, did your read that article and
change the quote.) Or did you copy from some creationist site? If
the latter you should repent your sin right now.
Kemp is a specialist on "mammal-like reptiles and an avowed evolutionist.
When did he vow he was an evolutionist? You seem to act as though
you have special dispensation from the sin of bearing false
witness. Jesus hates liars.
If you think that there are transitional links extant showing the path of
evolution you would be mistaken. Even the experts on evolution say over
and over again they do not exist. This places the theroy of evolution in
the catagory of unfounded opinion-not reality.
No, the experts say they are rare. And explain the rarity. They
sequences also exist. Sorry that the world does not conform to
your small minded notions.
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| User: "Alberich" |
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| Title: Re: Sudden Appearences |
14 Jan 2004 12:22:55 PM |
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On Wed, 14 Jan 2004 08:54:16 -0800,
(IKnowHimDoYou) wrote:
Sudden Appearences
"Each species of mammal-like reptile that has been found appears suddenly
in the fossil record and is not preceded by the species that is directly
ancestral to it. It disappears some time later, equally abruptly, without
leaving a directly decended species."
T.S. Kemp. "The Reptiles that Became Mammals," New Scientist, 92-583 Mar 4, 1982
Kemp is a specialist on "mammal-like reptiles and an avowed evolutionist.
If you think that there are transitional links extant showing the path of
evolution you would be mistaken. Even the experts on evolution say over
and over again they do not exist. This places the theroy of evolution in
the catagory of unfounded opinion-not reality.
Let me simply re-post something first put into talk.origins about four
years ago. (Apparently, that isn't enough time for a Creationist to
do his research.)
***
Okay. Your singling out of the reptile-mammal relationships is a
little
unfortunate since that particular transition happens to be
exceptionally
well-documented in the fossil record and well validated by genetic,
developmental, and morphological studies as well. Take, for example,
the
following fossil genera, going from the Permian clear to the
Cretaceous:
Paleothyris, Protoclepsydrops, Clepsydrops, Archaeothyris, Varanops,
Haptodus, Dimetrodon, Sphenacodon, Biarmosuchia, Procynosuchus,
Dvinia,
Thrinaxodon, Cynognathus, Diademodon, Probelesodon, Probainognathus,
Exaeretodon, Oligokyphus, Kayentatherium, Pachygenelus,
Diarthrognathus,
Adelobasileus, Sinoconodon, Kuehneotherium, Eozostrodon, Morganucodon,
Haldanodon, Peramus, Endotherium, Kielantherium, Aegialodon,
Vincelestes,
Kennalestes, Asioryctes, Cimolestes, Procerberus, and Gypsonictops -
you
remember these, they're all described in the standard texts and in the
t.o. transitions faq. Some more fossils have been described since the
faq
was last updated, but don't worry about those for now. And you
remember
how the fossils all occur in remarkable chronological-morphological
order,
using multiple independent dating methods, right? OK. Now, let's focus
on,
oh, the secondary palate, the maxilla, the lower jaw and the bones
around
the ear. (We'll put aside the gradual changes in tooth form &
replacement,
scapula, limb, pelvis, vertebrae, ribs, etc., just for now.) The
temporal
fenestra, as I'm sure you know, gradually enlarges, culminating with
complete exposure of the braincase dorsally and caudally - and of
course,
that parallels the remodeling of the synapsid reptile multiple jaw
muscles
for mammalian chewing. And of course, the development of the secondary
palate is also indisputable - I mean, just look at the little
protrusions
on the vomers in Biarmosuchia that then fuse in later genera to become
a
small bony palate that then extends further and further back. But to
me,
the most interesting story is the slow, gradual decrease in size of
the
articular and quadrate, and their eventual detachment and shift into
the
mammalian ear, as still occurs in mammalian embryos. Now, just look at
the
articular and quadrate in a crocodile and in a snapping turtle. You
see -
- oh, what's that?
- you don't know what a vomer is? or an articular or a quadrate?
- you've never examined the bones of a turtle's lower jaw?
- and you've never studied the anatomy of *any* of the above
fossils? Hmm, how odd. Really? Huh. From the way you were talking
about
reptiles and primates not showing any real relationship, it
seemed like you were implying that you knew something about vertebrate
biology. Well, why don't you start with these books and articles:
Benton, M.J. 1990. Vertebrate Palaeontology: biology and evolution.
Unwin Hyman, London.
Kemp, T.S. 1982. Mammal-like reptiles and the origin of mammals.
Academic Press, New York.
Kermack, D.M. & Kermack, K.A. 1984. The evolution of mammalian
characters. Croom Helm Kapitan Szabo Publishers, London.
(this is a great little book. Lay readers, start here.)
Rowe, T. 1988. Definition, diagnosis, and origin of Mammalia. J.
Vert. Paleont. 8(3): 241-264.
Szalay, F.S., M.J. Novacek, and M.C. McKenna. 1993. Mammal
Phylogeny,
vols 1 & 2. Springer-Verlag, New York.
Wible, J.R. 1991. Origin of Mammalia: the craniodental evidence
reexamined. J. Vert. Paleont. 11(1):1-28.
Plus you should *thoroughly* read any of the major books on vertebrate
biology or comparative vertebrate anatomy. There are five or six
available; really, any one will do to start with. You can usually
pick up
older editions cheaply at used book stores.
I can also post the brief summary descriptions of the fossils that I
wrote
up for the transitions faq, if you'd like. But be forewarned: it's
heavy
anatomy.
People who *have* studied the above fossils have concluded:
"When sampling artifact is removed and all available character data
analyzed [with computer phylogeny programs that do not assume anything
about occurrence or direction of evolution], a highly corroborated,
stable
phylogeny remains, which is largely consistent with the temporal
distributions of taxa recorded in the fossil record." (Rowe, quoted
in
Szalay et al. 1993)
and
"While living mammals are well separated from other groups of
animals
today, the fossil record clearly shows their origin from a reptilian
stock
and permits one to trace the origin and radiation of mammals in
considerable detail." - P.D. Gingerich, "Patterns of evolution in the
mammalian fossil record", from the 1977 book Patterns Of Evolution As
Illustrated By The Fossil Record (ed. A. Hallam), chapter 15, pp.
469-500.
Elsevier Scientific Pub. Co.
[Hint: In the future, don't pick the reptile-mammal transition to
argue
about. I used to recommend the reptile-bird transition to cheer up
depressed creationists, but gee, we've been finding more fossils from
that
transition recently too. There's some disagreement about turtle
origins,
though; maybe you could try those.]
Better luck next time,
Kathleen
just killing time until her lab volunteer arrives for the evening
Kathleen E. Hunt, Ph.D.
hunt@u.washington.edu
Woodland Park Zoo & University of Washington, Seattle
***
Alberich
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| User: "rogue" |
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| Title: Re: Sudden Appearences |
14 Jan 2004 05:42:28 PM |
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Alberich <Alberich@NoSpam.com> wrote in message news:<g52b00dffb0dk0ggqq3g5d8ual1lf152sq@4ax.com>...
On Wed, 14 Jan 2004 08:54:16 -0800,
YM1 (AKA IKnowHowToPlagiarizeOthers)
Sudden Appearences(sic)
<snipped intellectually dishonest quote that IDon'tKnowADamnedThing
posted without crediting the cretins at AiG>
ALBERICH
Let me simply re-post something first put into talk.origins about four
years ago. (Apparently, that isn't enough time for a Creationist to
do his research.)
JERRY
LOL. You are assuming that YM1 does research. This is a man who has
believes Abraham Lincoln was one of the Founding Fathers. He's
basically dumber than dirt and thinks that the rest of the world
around him is as dumb as he is, so he has to "preach" to us in the
newsgroup. He seems to think that this is his personal congregation
and no amount of heckling has made him realize otherwise. ;-)
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| User: "mvillanu" |
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| Title: Re: Sudden Appearences |
14 Jan 2004 08:40:54 PM |
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(rogue) wrote in message news:<6e14bcdc.0401141542.53207edb@posting.google.com>...
Alberich <Alberich@NoSpam.com> wrote in message news:<g52b00dffb0dk0ggqq3g5d8ual1lf152sq@4ax.com>...
On Wed, 14 Jan 2004 08:54:16 -0800,
[snip]
JERRY
LOL. You are assuming that YM1 does research. This is a man who has
believes Abraham Lincoln was one of the Founding Fathers.
If he wasn't a founding father then why is his face on Mount
Rushmore!?!?!?
And speaking of that...how could a natural rock formation like Mount
Rushmore bear such uncanny resemblances to the past presidents? Looks
like Design to me!
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| User: "Pastor Dave" |
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| Title: Re: Sudden Appearences |
14 Jan 2004 12:38:06 PM |
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On Wed, 14 Jan 2004 18:22:55 GMT, Alberich
<Alberich@NoSpam.com> spake thusly:
Okay. Your singling out of the reptile-mammal relationships is a
little
unfortunate since that particular transition happens to be
exceptionally
well-documented in the fossil record
Wrong.
and well validated by genetic,
developmental, and morphological studies as well. Take, for example,
the
following fossil genera, going from the Permian clear to the
Cretaceous:
Paleothyris, Protoclepsydrops, Clepsydrops, Archaeothyris, Varanops,
Haptodus, Dimetrodon, Sphenacodon, Biarmosuchia, Procynosuchus,
Dvinia,
Thrinaxodon, Cynognathus, Diademodon, Probelesodon, Probainognathus,
Exaeretodon, Oligokyphus, Kayentatherium, Pachygenelus,
Diarthrognathus,
Adelobasileus, Sinoconodon, Kuehneotherium, Eozostrodon, Morganucodon,
Haldanodon, Peramus, Endotherium, Kielantherium, Aegialodon,
Vincelestes,
Kennalestes, Asioryctes, Cimolestes, Procerberus, and Gypsonictops -
http://genesismission.4t.com/transition/reptiles-mammals.htm
--
Pastor Dave Raymond
"As for me, I have not hastened from being a pastor
to follow thee: neither have I desired the woeful day;
thou knowest: that which came out of my lips was right
before thee." - Jeremiah 17:16
http://home.clear.net.nz/pages/bryanp/Evolution/Gre.Sci..htm
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| User: "oz" |
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| Title: Re: Sudden Appearences |
16 Jan 2004 11:19:18 PM |
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PART ONE
Transition from amphibians to amniotes (first reptiles)
The major functional difference between the ancient, large amphibians and
the first little reptiles is the amniotic egg. Additional differences
include stronger legs and girdles, different vertebrae, and stronger jaw
muscles. For more info, see Carroll (1988) and Gauthier et al. (in Benton,
1988)
* Proterogyrinus or another early anthracosaur (late Mississippian) --
Classic labyrinthodont-amphibian skull and teeth, but with reptilian
vertebrae, pelvis, humerus, and digits. Still has fish skull hinge.
Amphibian ankle. 5-toed hand and a 2-3-4-5-3 (almost reptilian) phalangeal
count.
* Limnoscelis, Tseajaia (late Carboniferous) -- Amphibians apparently
derived from the early anthracosaurs, but with additional reptilian
features: structure of braincase, reptilian jaw muscle, expanded neural
arches.
* Solenodonsaurus (mid-Pennsylvanian) -- An incomplete fossil, apparently
between the anthracosaurs and the cotylosaurs. Loss of palatal fangs, loss
of lateral line on head, etc. Still just a single sacral vertebra, though.
* Hylonomus, Paleothyris (early Pennsylvanian) -- These are
protorothyrids, very early cotylosaurs (primitive reptiles). They were
quite little, lizard-sized animals with amphibian-like skulls (amphibian
pineal opening, dermal bone, etc.), shoulder, pelvis, & limbs, and
intermediate teeth and vertebrae. Rest of skeleton reptilian, with
reptilian jaw muscle, no palatal fangs, and spool-shaped vertebral centra.
Probably no eardrum yet. Many of these new "reptilian" features are also
seen in little amphibians (which also sometimes have direct-developing
eggs laid on land), so perhaps these features just came along with the
small body size of the first reptiles.
The ancestral amphibians had a rather weak skull and paired "aortas"
(systemic arches). The first reptiles immediately split into two major
lines which modified these traits in different ways. One line developed an
aorta on the right side and strengthened the skull by swinging the
quadrate bone down and forward, resulting in an enormous otic notch (and
allowed the later development of good hearing without much further
modification). This group further split into three major groups, easily
recognizable by the number of holes or "fenestrae" in the side of the
skull: the anapsids (no fenestrae), which produced the turtles; the
diapsids (two fenestrae), which produced the dinosaurs and birds; and an
offshoot group, the eurapsids (two fenestrae fused into one), which
produced the ichthyosaurs.
The other major line of reptiles developed an aorta on left side only, and
strengthened the skull by moving the quadrate bone up and back,
obliterating the otic notch (making involvement of the jaw essential in
the later development of good hearing). They developed a single fenestra
per side. This group was the synapsid reptiles. They took a radically
different path than the other reptiles, involving homeothermy, a larger
brain, better hearing and more efficient teeth. One group of synapsids
called the "therapsids" took these changes particularly far, and
apparently produced the mammals.
Some transitions among reptiles
I will review just a couple of the reptile phylogenies, since there are so
many.... Early reptiles to turtles: (Also see Gaffney & Meylan, in Benton
1988)
* Captorhinus (early-mid Permain) -- Immediate descendent of the
protorothryids.
Here we come to a controversy; there are two related groups of early
anapsids, both descended from the captorhinids, that could have been
ancestral to turtles. Reisz & Laurin (1991, 1993) believe the turtles
descended from procolophonids, late Permian anapsids that had various
turtle-like skull features. Others, particularly Lee (1993) think the
turtle ancestors are pareiasaurs:
* Scutosaurus and other pareiasaurs (mid-Permian) -- Large bulky
herbivorous reptiles with turtle-like skull features. Several genera had
bony plates in the skin, possibly the first signs of a turtle shell.
* Deltavjatia vjatkensis (Permian) -- A recently discovered pareiasaur
with numerous turtle-like skull features (e.g., a very high palate),
limbs, and girdles, and lateral projections flaring out some of the
vertebrae in a very shell-like way. (Lee, 1993)
* Proganochelys (late Triassic) -- a primitive turtle, with a fully
turtle-like skull, beak, and shell, but with some primitive traits such as
rows of little palatal teeth, a still-recognizable clavicle, a simple
captorhinid-type jaw musculature, a primitive captorhinid- type ear, a
non-retractable neck, etc..
* Recently discovered turtles from the early Jurassic, not yet described.
Mid-Jurassic turtles had already divided into the two main groups of
modern turtles, the side-necked turtles and the arch-necked turtles.
Obviously these two groups developed neck retraction separately, and came
up with totally different solutions. In fact the first known arch-necked
turtles, from the Late Jurassic, could not retract their necks, and only
later did their descendents develop the archable neck. Early reptiles to
diapsids: (see Evans, in Benton 1988, for more info)
* Hylonomus, Paleothyris (early Penn.) -- The primitive amniotes
described above
* Petrolacosaurus, Araeoscelis (late Pennsylvanian) -- First known
diapsids. Both temporal fenestra now present. No significant change in jaw
muscles. Have Hylonomus-style teeth, with many small marginal teeth & two
slightly larger canines. Still no eardrum.
* Apsisaurus (early Permian) -- A more typical diapsid. Lost canines.
(Laurin, 1991)
GAP: no diapsid fossils from the mid-Permian.
* Claudiosaurus (late Permian) -- An early diapsid with several
neodiapsid traits, but still had primitive cervical vertebrae & unossified
sternum. probably close to the ancestry of all diapsides (the lizards &
snakes & crocs & birds).
* Planocephalosaurus(early Triassic) -- Further along the line that
produced the lizards and snakes. Loss of some skull bones, teeth, toe
bones.
* Protorosaurus, Prolacerta (early Triassic) -- Possibly among the very
first archosaurs, the line that produced dinos, crocs, and birds. May be
"cousins" to the archosaurs, though.
* Proterosuchus (early Triassic) -- First known archosaur.
* Hyperodapedon, Trilophosaurus (late Triassic) -- Early archosaurs.
Some species-to-species transitions:
* De Ricqles (in Chaline, 1983) documents several possible cases of
gradual evolution (also well as some lineages that showed abrupt
appearance or stasis) among the early Permian reptile genera Captorhinus,
Protocaptorhinus, Eocaptorhinus, and Romeria.
* Horner et al. (1992) recently found many excellent transitional
dinosaur fossils from a site in Montana that was a coastal plain in the
late Cretaceous. They include:
1. Many transitional ceratopsids between Styracosaurus and Pachyrhinosaurus
2. Many transitional lambeosaurids (50! specimens) between Lambeosaurus
and Hypacrosaurus.
3. A transitional pachycephalosaurid between Stegoceras and Pachycephalosaurus
4. A transitional tyrannosaurid between Tyrannosaurus and Daspletosaurus.
All of these transitional animals lived during the same brief 500,000
years. Before this site was studied, these dinosaur groups were known from
the much larger Judith River Formation, where the fossils showed 5 million
years of evolutionary stasis, following by the apparently abrupt
appearance of the new forms. It turns out that the sea level rose during
that 500,000 years, temporarily burying the Judith River Formation under
water, and forcing the dinosaur populations into smaller areas such as the
site in Montana. While the populations were isolated in this smaller area,
they underwent rapid evolution. When sea level fell again, the new forms
spread out to the re-exposed Judith River landscape, thus appearing
"suddenly" in the Judith River fossils, with the transitional fossils only
existing in the Montana site. This is an excellent example of punctuated
equilibrium (yes, 500,000 years is very brief and counts as a
"punctuation"), and is a good example of why transitional fossils may only
exist in a small area, with the new species appearing "suddenly" in other
areas. (Horner et al., 1992) Also note the discovery of Ianthosaurus, a
genus that links the two synapsid families Ophiacodontidae and
Edaphosauridae. (see Carroll, 1988, p. 367)
Transition from synapsid reptiles to mammals
This is the best-documented transition between vertebrate classes. So far
this series is known only as a series of genera or families; the
transitions from species to species are not known. But the family sequence
is quite complete. Each group is clearly related to both the group that
came before, and the group that came after, and yet the sequence is so
long that the fossils at the end are astoundingly different from those at
the beginning. As Rowe recently said about this transition (in Szalay et
al., 1993), "When sampling artifact is removed and all available character
data analyzed [with computer phylogeny programs that do not assume
anything about evolution], a highly corroborated, stable phylogeny
remains, which is largely consistent with the temporal distributions of
taxa recorded in the fossil record." Similarly, Gingerich has stated
(1977) "While living mammals are well separated from other groups of
animals today, the fossil record clearly shows their origin from a
reptilian stock and permits one to trace the origin and radiation of
mammals in considerable detail." For more details, see Kermack's superb
and readable little book (1984), Kemp's more detailed but older book
(1982), and read Szalay et al.'s recent collection of review articles
(1993, vol. 1).
This list starts with pelycosaurs (early synapsid reptiles) and continues
with therapsids and cynodonts up to the first unarguable "mammal". Most of
the changes in this transition involved elaborate repackaging of an
expanded brain and special sense organs, remodeling of the jaws & teeth
for more efficient eating, and changes in the limbs & vertebrae related to
active, legs-under-the-body locomotion. Here are some differences to keep
an eye on:
------------------------------------------------------------------------
# Early Reptiles Mammals
------------------------------------------------------------------------
1 No fenestrae in skull Massive fenestra exposes all of braincase
2 Braincase attached loosely Braincase attached firmly to skull
3 No secondary palate Complete bony secondary palate
4 Undifferentiated dentition Incisors, canines, premolars, molars
5 Cheek teeth uncrowned points Cheek teeth (PM & M) crowned & cusped
6 Teeth replaced continuously Teeth replaced once at most
7 Teeth with single root Molars double-rooted
8 Jaw joint quadrate-articular Jaw joint dentary-squamosal (*)
9 Lower jaw of several bones Lower jaw of dentary bone only
10 Single ear bone (stapes) Three ear bones (stapes, incus, malleus)
11 Joined external nares Separate external nares
12 Single occipital condyle Double occipital condyle
13 Long cervical ribs Cervical ribs tiny, fused to vertebrae
14 Lumbar region with ribs Lumbar region rib-free
15 No diaphragm Diaphragm
16 Limbs sprawled out from body Limbs under body
17 Scapula simple Scapula with big spine for muscles
18 Pelvic bones unfused Pelvis fused
19 Two sacral (hip) vertebrae Three or more sacral vertebrae
20 Toe bone #'s 2-3-4-5-4 Toe bones 2-3-3-3-3
21 Body temperature variable Body temperature constant
------------------------------------------------------------------------
(*) The presence of a dentary-squamosal jaw joint has been arbitrarily
selected as the defining trait of a mammal.
* Paleothyris (early Pennsylvanian) -- An early captorhinomorph reptile,
with no temporal fenestrae at all.
* Protoclepsydrops haplous (early Pennsylvanian) -- The earliest known
synapsid reptile. Little temporal fenestra, with all surrounding bones
intact. Fragmentary. Had amphibian-type vertebrae with tiny neural
processes. (reptiles had only just separated from the amphibians)
* Clepsydrops (early Pennsylvanian) -- The second earliest known
synapsid. These early, very primitive synapsids are a primitive group of
pelycosaurs collectively called "ophiacodonts".
* Archaeothyris (early-mid Pennsylvanian) -- A slightly later
ophiacodont. Small temporal fenestra, now with some reduced bones
(supratemporal). Braincase still just loosely attached to skull. Slight
hint of different tooth types. Still has some extremely primitive,
amphibian/captorhinid features in the jaw, foot, and skull. Limbs,
posture, etc. typically reptilian, though the ilium (major hip bone) was
slightly enlarged.
* Varanops (early Permian) -- Temporal fenestra further enlarged.
Braincase floor shows first mammalian tendencies & first signs of stronger
attachment to rest of skull (occiput more strongly attached). Lower jaw
shows first changes in jaw musculature (slight coronoid eminence). Body
narrower, deeper: vertebral column more strongly constructed. Ilium
further enlarged, lower-limb musculature starts to change (prominent
fourth trochanter on femur). This animal was more mobile and active. Too
late to be a true ancestor, and must be a "cousin".
* Haptodus (late Pennsylvanian) -- One of the first known sphenacodonts,
showing the initiation of sphenacodont features while retaining many
primitive features of the ophiacodonts. Occiput still more strongly
attached to the braincase. Teeth become size-differentiated, with biggest
teeth in canine region and fewer teeth overall. Stronger jaw muscles.
Vertebrae parts & joints more mammalian. Neural spines on vertebrae
longer. Hip strengthened by fusing to three sacral vertebrae instead of
just two. Limbs very well developed.
* Dimetrodon, Sphenacodon or a similar sphenacodont (late Pennsylvanian
to early Permian, 270 Ma) -- More advanced pelycosaurs, clearly closely
related to the first therapsids (next). Dimetrodon is almost definitely a
"cousin" and not a direct ancestor, but as it is known from very complete
fossils, it's a good model for sphenacodont anatomy. Medium-sized
fenestra. Teeth further differentiated, with small incisors, two huge
deep- rooted upper canines on each side, followed by smaller cheek teeth,
all replaced continuously. Fully reptilian jaw hinge. Lower jaw bone made
of multiple bones & with first signs of a bony prong later involved in the
eardrum, but there was no eardrum yet, so these reptiles could only hear
ground-borne vibrations (they did have a reptilian middle ear). Vertebrae
had still longer neural spines (spectacularly so in Dimetrodon, which had
a sail), and longer transverse spines for stronger locomotion muscles.
* Biarmosuchia (late Permian) -- A therocephalian -- one of the earliest,
most primitive therapsids. Several primitive, sphenacodontid features
retained: jaw muscles inside the skull, platelike occiput, palatal teeth.
New features: Temporal fenestra further enlarged, occupying virtually all
of the cheek, with the supratemporal bone completely gone. Occipital plate
slanted slightly backwards rather than forwards as in pelycosaurs, and
attached still more strongly to the braincase. Upper jaw bone (maxillary)
expanded to separate lacrymal from nasal bones, intermediate between early
reptiles and later mammals. Still no secondary palate, but the vomer bones
of the palate developed a backward extension below the palatine bones.
This is the first step toward a secondary palate, and with exactly the
same pattern seen in cynodonts. Canine teeth larger, dominating the
dentition. Variable tooth replacement: some therocephalians
(e.gScylacosaurus) had just one canine, like mammals, and stopped
replacing the canine after reaching adult size. Jaw hinge more mammalian
in position and shape, jaw musculature stronger (especially the mammalian
jaw muscle). The amphibian-like hinged upper jaw finally became immovable.
Vertebrae still sphenacodontid-like. Radical alteration in the method of
locomotion, with a much more mobile forelimb, more upright hindlimb, &
more mammalian femur & pelvis. Primitive sphenacodontid humerus. The toes
were approaching equal length, as in mammals, with #toe bones varying from
reptilian to mammalian. The neck & tail vertebrae became distinctly
different from trunk vertebrae. Probably had an eardrum in the lower jaw,
by the jaw hinge.
* Procynosuchus (latest Permian) -- The first known cynodont -- a famous
group of very mammal-like therapsid reptiles, sometimes considered to be
the first mammals. Probably arose from the therocephalians, judging from
the distinctive secondary palate and numerous other skull characters.
Enormous temporal fossae for very strong jaw muscles, formed by just one
of the reptilian jaw muscles, which has now become the mammalian masseter.
The large fossae is now bounded only by the thin zygomatic arch (cheekbone
to you & me). Secondary palate now composed mainly of palatine bones
(mammalian), rather than vomers and maxilla as in older forms; it's still
only a partial bony palate (completed in life with soft tissue). Lower
incisor teeth was reduced to four (per side), instead of the previous six
(early mammals had three). Dentary now is 3/4 of lower jaw; the other
bones are now a small complex near the jaw hinge. Jaw hinge still
reptilian. Vertebral column starts to look mammalian: first two vertebrae
modified for head movements, and lumbar vertebrae start to lose ribs, the
first sign of functional division into thoracic and lumbar regions.
Scapula beginning to change shape. Further enlargement of the ilium and
reduction of the pubis in the hip. A diaphragm may have been present.
* Dvinia [also "Permocynodon"] (latest Permian) -- Another early
cynodont. First signs of teeth that are more than simple stabbing points
-- cheek teeth develop a tiny cusp. The temporal fenestra increased still
further. Various changes in the floor of the braincase; enlarged brain.
The dentary bone was now the major bone of the lower jaw. The other jaw
bones that had been present in early reptiles were reduced to a complex of
smaller bones near the jaw hinge. Single occipital condyle splitting into
two surfaces. The postcranial skeleton of Dvinia is virtually unknown and
it is not therefore certain whether the typical features found at the next
level had already evolved by this one. Metabolic rate was probably
increased, at least approaching homeothermy.
* Thrinaxodon (early Triassic) -- A more advanced "galesaurid" cynodont.
Further development of several of the cynodont features seen already.
Temporal fenestra still larger, larger jaw muscle attachments. Bony
secondary palate almost complete. Functional division of teeth: incisors
(four uppers and three lowers), canines, and then 7-9 cheek teeth with
cusps for chewing. The cheek teeth were all alike, though (no premolars &
molars), did not occlude together, were all single- rooted, and were
replaced throughout life in alternate waves. Dentary still larger, with
the little quadrate and articular bones were loosely attached. The stapes
now touched the inner side of the quadrate. First sign of the mammalian
jaw hinge, a ligamentous connection between the lower jaw and the
squamosal bone of the skull. Theoccipital condyle is now two slightly
separated surfaces, though not separated as far as the mammalian double
condyles. Vertebral connections more mammalian, and lumbar ribs reduced.
Scapula shows development of a new mammalian shoulder muscle. Ilium
increased again, and all four legs fully upright, not sprawling. Tail
short, as is necessary for agile quadrupedal locomotion. The whole
locomotion was more agile. Number of toe bones is 2.3.4.4.3, intermediate
between reptile number (2.3.4.5.4) and mammalian (2.3.3.3.3), and the
"extra" toe bones were tiny. Nearly complete skeletons of these animals
have been found curled up - a possible reaction to conserve heat,
indicating possible endothermy? Adults and juveniles have been found
together, possibly a sign of parental care. The specialization of the
lumbar area (e.g. reduction of ribs) is indicative of the presence of a
diaphragm, needed for higher O2 intake and homeothermy. NOTE on hearing:
The eardrum had developed in the only place available for it -- the lower
jaw, right near the jaw hinge, supported by a wide prong (reflected
lamina) of the angular bone. These animals could now hear airborne sound,
transmitted through the eardrum to two small lower jaw bones, the
articular and the quadrate, which contacted the stapes in the skull, which
contacted the cochlea. Rather a roundabout system and sensitive to
low-frequency sound only, but better than no eardrum at all! Cynodonts
developed quite loose quadrates and articulars that could vibrate freely
for sound transmittal while still functioning as a jaw joint, strengthened
by the mammalian jaw joint right next to it. All early mammals from the
Lower Jurassic have this low-frequency ear and a double jaw joint. By the
middle Jurassic, mammals lost the reptilian joint (though it still occurs
briefly in embryos) and the two bones moved into the nearby middle ear,
became smaller, and became much more sensitive to high-frequency sounds.
* Cynognathus (early Triassic, 240 Ma; suspected to have existed even
earlier) -- We're now at advanced cynodont level. Temporal fenestra
larger. Teeth differentiating further; cheek teeth with cusps met in true
occlusion for slicing up food, rate of replacement reduced, with
mammalian-style tooth roots (though single roots). Dentary still larger,
forming 90% of the muscle-bearing part of the lower jaw. TWO JAW JOINTS in
place, mammalian and reptilian: A new bony jaw joint existed between the
squamosal (skull) and the surangular bone (lower jaw), while the other jaw
joint bones were reduced to a compound rod lying in a trough in the
dentary, close to the middle ear. Ribs more mammalian. Scapula halfway to
the mammalian condition. Limbs were held under body. There is possible
evidence for fur in fossil pawprints.
* Diademodon (early Triassic, 240 Ma; same strata as Cynognathus) --
Temporal fenestra larger still, for still stronger jaw muscles. True bony
secondary palate formed exactly as in mammals, but didn't extend quite as
far back. Turbinate bones possibly present in the nose (warm-blooded?).
Dental changes continue: rate of tooth replacement had decreased, cheek
teeth have better cusps & consistent wear facets (better occlusion). Lower
jaw almost entirely dentary, with tiny articular at the hinge. Still a
double jaw joint. Ribs shorten suddenly in lumbar region, probably
improving diaphragm function & locomotion. Mammalian toe bones
(2.3.3.3.3), with closely related species still showing variable numbers.
* Probelesodon (mid-Triassic; South America) -- Fenestra very large,
still separate from eyesocket (with postorbital bar). Secondary palate
longer, but still not complete. Teeth double-rooted, as in mammals. Nares
separated. Second jaw joint stronger. Lumbar ribs totally lost; thoracic
ribs more mammalian, vertebral connections very mammalian. Hip & femur
more mammalian.
* Probainognathus (mid-Triassic, 239-235 Ma, Argentina) -- Larger brain
with various skull changes: pineal foramen ("third eye") closes, fusion of
some skull plates. Cheekbone slender, low down on the side of the eye
socket. Postorbital bar still there. Additional cusps on cheek teeth.
Still two jaw joints. Still had cervical ribs & lumbar ribs, but they were
very short. Reptilian "costal plates" on thoracic ribs mostly lost.
Mammalian #toe bones.
* Exaeretodon (mid-late Triassic, 239Ma, South America) -- (Formerly
lumped with the herbivorous gomphodont cynodonts.) Mammalian jaw prong
forms, related to eardrum support. Three incisors only (mammalian). Costal
plates completely lost. More mammalian hip related to having limbs under
the body. Possibly the first steps toward coupling of locomotion &
breathing. This is probably a "cousin" fossil not directly ancestral, as
it has several new but non-mammalian teeth traits.
GAP of about 30 my in the late Triassic, from about 239-208 Ma. Only one
early mammal fossil is known from this time. The next time fossils are
found in any abundance, tritylodontids and trithelodontids had already
appeared, leading to some very heated controversy about their relative
placement in the chain to mammals. Recent discoveries seem to show
trithelodontids to be more mammal- like, with tritylodontids possibly
being an offshoot group (see Hopson 1991, Rowe 1988, Wible 1991, and
Shubin et al. 1991). Bear in mind that both these groups were almost fully
mammalian in every feature, lacking only the final changes in the jaw
joint and middle ear.
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| User: "oz" |
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| Title: Re: Sudden Appearences |
16 Jan 2004 11:20:15 PM |
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PART TWO
Oligokyphus, Kayentatherium (early Jurassic, 208 Ma) -- These are
tritylodontids, an advanced cynodont group. Face more mammalian, with
changes around eyesocket and cheekbone. Full bony secondary palate.
Alternate tooth replacement with double-rooted cheek teeth, but without
mammalian-style tooth occlusion (which some earlier cynodonts already
had). Skeleton strikingly like egg- laying mammals (monotremes). Double
jaw joint. More flexible neck, with mammalian atlas & axis and double
occipital condyle. Tail vertebrae simpler, like mammals. Scapula is now
substantially mammalian, and the forelimb is carried directly under the
body. Various changes in the pelvis bones and hind limb muscles; this
animal's limb musculature and locomotion were virtually fully mammalian.
Probably cousin fossils (?), with Oligokyphus being more primitive than
Kayentatherium. Thought to have diverged from the trithelodontids during
that gap in the late Triassic. There is disagreement about whether the
tritylodontids were ancestral to mammals (presumably during the late
Triassic gap) or whether they are a specialized offshoot group not
directly ancestral to mammals.
* Pachygenelus, Diarthrognathus (earliest Jurassic, 209 Ma) -- These are
trithelodontids, a slightly different advanced cynodont group. New
discoveries (Shubin et al., 1991) show that these animals are very close
to the ancestry of mammals. Inflation of nasal cavity, establishment of
Eustachian tubes between ear and pharynx, loss of postorbital bar.
Alternate replacement of mostly single- rooted teeth. This group also
began to develop double tooth roots -- in Pachygenelus the single root of
the cheek teeth begins to split in two at the base. Pachygenelus also has
mammalian tooth enamel, and mammalian tooth occlusion. Double jaw joint,
with the second joint now a dentary-squamosal (instead of surangular),
fully mammalian. Incipient dentary condyle. Reptilian jaw joint still
present but functioning almost entirely in hearing; postdentary bones
further reduced to tiny rod of bones in jaw near middle ear; probably
could hear high frequencies now. More mammalian neck vertebrae for a
flexible neck. Hip more mammalian, with a very mammalian iliac blade &
femur. Highly mobile, mammalian-style shoulder. Probably had coupled
locomotion & breathing. These are probably "cousin" fossils, not directly
ancestral (the true ancestor is thought to have occurred during that late
Triassic gap). Pachygenelus is pretty close, though.
* Adelobasileus cromptoni (late Triassic; 225 Ma, west Texas) -- A
recently discovered fossil proto-mammal from right in the middle of that
late Triassic gap! Currently the oldest known "mammal." Only the skull was
found. "Some cranial features of Adelobasileus, such as the incipient
promontorium housing the cochlea, represent an intermediate stage of the
character transformation from non-mammalian cynodonts to Liassic mammals"
(Lucas & Luo, 1993). This fossil was found from a band of strata in the
western U.S. that had not previously been studied for early mammals. Also
note that this fossil dates from slightly before the known tritylodonts
and trithelodonts, though it has long been suspected that tritilodonts and
trithelodonts were already around by then. Adelobasileus is thought to
have split off from either a trityl. or a trithel., and is either
identical to or closely related to the common ancestor of all mammals.
* Sinoconodon (early Jurassic, 208 Ma) -- The next known very ancient
proto-mammal. Eyesocket fully mammalian now (closed medial wall).
Hindbrain expanded. Permanent cheekteeth, like mammals, but the other
teeth were still replaced several times. Mammalian jaw joint stronger,
with large dentary condyle fitting into a distinct fossa on the squamosal.
This final refinement of the joint automatically makes this animal a true
"mammal". Reptilian jaw joint still present, though tiny.
* Kuehneotherium (early Jurassic, about 205 Ma) -- A slightly later
proto-mammal, sometimes considered the first known pantothere (primitive
placental-type mammal). Teeth and skull like a placental mammal. The three
major cusps on the upper & lower molars were rotated to form interlocking
shearing triangles as in the more advanced placental mammals & marsupials.
Still has a double jaw joint, though.
* Eozostrodon, Morganucodon, Haldanodon (early Jurassic, ~205 Ma) -- A
group of early proto-mammals called "morganucodonts". The restructuring of
the secondary palate and the floor of the braincase had continued, and was
now very mammalian. Truly mammalian teeth: the cheek teeth were finally
differentiated into simple premolars and more complex molars, and teeth
were replaced only once. Triangular- cusped molars. Reversal of the
previous trend toward reduced incisors, with lower incisors increasing to
four. Tiny remnant of the reptilian jaw joint. Once thought to be
ancestral to monotremes only, but now thought to be ancestral to all three
groups of modern mammals -- monotremes, marsupials, and placentals.
* Peramus (late Jurassic, about 155 Ma) -- A "eupantothere" (more
advanced placental-type mammal). The closest known relative of the
placentals & marsupials. Triconodont molar has with more defined cusps.
This fossil is known only from teeth, but judging from closely related
eupantotheres (e.g. Amphitherium) it had finally lost the reptilian jaw
joint, attaing a fully mammalian three-boned middle ear with excellent
high-frequency hearing. Has only 8 cheek teeth, less than other
eupantotheres and close to the 7 of the first placental mammals. Also has
a large talonid on its "tribosphenic" molars, almost as large as that of
the first placentals -- the first development of grinding capability.
* Endotherium (very latest Jurassic, 147 Ma) -- An advanced eupantothere.
Fully tribosphenic molars with a well- developed talonid. Known only from
one specimen. From Asia; recent fossil finds in Asia suggest that the
tribosphenic molar evolved there.
* Kielantherium and Aegialodon (early Cretaceous) -- More advanced
eupantotheres known only from teeth. Kielantherium is from Asia and is
known from slightly older strata than the European Aegialodon. Both have
the talonid on the lower molars. The wear on it indicates that a major new
cusp, the protocone, had evolved on the upper molars. By the Middle
Cretaceous, animals with the new tribosphenic molar had spread into North
America too (North America was still connected to Europe.)
* Steropodon galmani (early Cretaceous) -- The first known definite
monotreme, discovered in 1985.
* Vincelestes neuquenianus (early Cretaceous, 135 Ma) -- A
probably-placental mammal with some marsupial traits, known from some nice
skulls. Placental-type braincase and coiled cochlea. Its intracranial
arteries & veins ran in a composite monotreme/placental pattern derived
from homologous extracranial vessels in the cynodonts. (Rougier et al.,
1992)
* Pariadens kirklandi (late Cretaceous, about 95 Ma) -- The first
definite marsupial. Known only from teeth.
* Kennalestes and Asioryctes (late Cretaceous, Mongolia) -- Small,
slender animals; eyesocket open behind; simple ring to support eardrum;
primitive placental-type brain with large olfactory bulbs; basic primitive
tribosphenic tooth pattern. Canine now double rooted. Still just a trace
of a non-dentary bone, the coronoid, on the otherwise all-dentary jaw.
"Could have given rise to nearly all subsequent placentals." says Carroll
(1988).
* Cimolestes, Procerberus, Gypsonictops (very late Cretaceous) --
Primitive North American placentals with same basic tooth pattern.
So, by the late Cretaceous the three groups of modern mammals were in
place: monotremes, marsupials, and placentals. Placentals appear to have
arisen in East Asia and spread to the Americas by the end of the
Cretaceous. In the latest Cretaceous, placentals and marsupials had
started to diversify a bit, and after the dinosaurs died out, in the
Paleocene, this diversification accelerated. For instance, in the mid-
Paleocene the placental fossils include a very primitive primate-like
animal (Purgatorius - known only from a tooth, though, and may actually be
an early ungulate), a herbivore-like jaw with molars that have flatter
tops for better grinding (Protungulatum, probably an early ungulate), and
an insectivore (Paranyctoides).
The decision as to which was the first mammal is somewhat subjective. We
are placing an inflexible classification system on a gradational series.
What happened was that an intermediate group evolved from the 'true'
reptiles, which gradually acquired mammalian characters until a point was
reached where we have artificially drawn a line between reptiles and
mammals. For instance, Pachygenulus and Kayentatherium are both far more
mammal-like than reptile-like, but they are both called "reptiles".
Transition from diapsid reptiles to birds
In the mid-1800's, this was one of the most significant gaps in vertebrate
fossil evolution. No transitional fossils at all were known, and the two
groups seemed impossibly different. Then the exciting discovery of
Archeopteryx in 1861 showed clearly that the two groups were in fact
related. Since then, some other reptile-bird links have been found. On the
whole, though, this is still a gappy transition, consisting of a very
large-scale series of "cousin" fossils. I have not included Mononychus (as
it appears to be a digger, not a flier, well off the line to modern
birds). See Feduccia (1980) and Rayner (1989) for more discussion of the
evolution of flight, and Chris Nedin's excellent Archeopteryx FAQ for more
info on that critter.
* Coelophysis (late Triassic) -- One of the first theropod dinosaurs.
Theropods in general show clear general skeletal affinities with birds
(long limbs, hollow bones, foot with 3 toes in front and 1 reversed toe
behind, long ilium). Jurassic theropods like Compsognathus are
particularly similar to birds.
* Deinonychus, Oviraptor, and other advanced theropods (late Jurassic,
Cretaceous) -- Predatory bipedal advanced theropods, larger, with more
bird-like skeletal features: semilunate carpal, bony sternum, long arms,
reversed pubis. Clearly runners, though, not fliers. These advanced
theropods even had clavicles, sometimes fused as in birds. Says Clark
(1992): "The detailed similarity between birds and theropod dinosaurs such
as Deinonychus is so striking and so pervasive throughout the skeleton
that a considerable amount of special pleading is needed to come to any
conclusion other than that the sister-group of birds among fossils is one
of several theropod dinosaurs." The particular fossils listed here are are
not directly ancestral, though, as they occur after Archeopteryx.
* Lisboasaurus estesi & other "troodontid dinosaur-birds" (mid-Jurassic)
-- A bird-like theropod reptile with very bird-like teeth (that is, teeth
very like those of early toothed birds, since modern birds have no teeth).
These really could be ancestral.
GAP: The exact reptilian ancestor of Archeopteryx, and the first
development of feathers, are unknown. Early bird evolution seems to have
involved little forest climbers and then little forest fliers, both of
which are guaranteed to leave very bad fossil records (little animal +
acidic forest soil = no remains). Archeopteryx itself is really about the
best we could ask for: several specimens has superb feather impressions,
it is clearly related to both reptiles and birds, and it clearly shows
that the transition is feasible.
* One possible ancestor of Archeopteryx is Protoavis (Triassic, ~225 Ma)
-- A highly controversial fossil that may or may not be an extremely early
bird. Unfortunately, not enough of the fossil was recovered to determine
if it is definitely related to the birds.
* Archeopteryx lithographica (Late Jurassic, 150 Ma) -- The several known
specimes of this deservedly famous fossil show a mosaic of reptilian and
avian features, with the reptilian features predominating. The skull and
skeleton are basically reptilian (skull, teeth, vertebrae, sternum, ribs,
pelvis, tail, digits, claws, generally unfused bones). Bird traits are
limited to an avian furcula (wishbone, for attachment of flight muscles;
recall that at least some dinosaurs had this too), modified forelimbs, and
-- the real kicker -- unmistakable lift-producing flight feathers.
Archeopteryx could probably flap from tree to tree, but couldn't take off
from the ground, since it lacked a keeled breastbone for large flight
muscles, and had a weak shoulder compared to modern birds. May not have
been the direct ancestor of modern birds. (Wellnhofer, 1993)
* Sinornis santensis ("Chinese bird", early Cretaceous, 138 Ma) -- A
recently found little primitive bird. Bird traits: short trunk, claws on
the toes, flight-specialized shoulders, stronger flight- feather bones,
tightly folding wrist, short hand. (These traits make it a much better
flier than Archeopteryx.) Reptilian traits: teeth, stomach ribs, unfused
hand bones, reptilian-shaped unfused pelvis. (These remaining reptilian
traits wouldn't have interfered with flight.) Intermediate traits:
metatarsals partially fused, medium-sized sternal keel, medium-length tail
(8 vertebrae) with fused pygostyle at the tip. (Sereno & Rao, 1992).
* "Las Hoyas bird" or "Spanish bird" [not yet named; early Cretaceous,
131 Ma) -- Another recently found "little forest flier". It still has
reptilian pelvis & legs, with bird-like shoulder. Tail is medium-length
with a fused tip. A fossil down feather was found with the Las Hoyas bird,
indicating homeothermy. (Sanz et al., 1992)
* Ambiortus dementjevi (early Cretaceous, 125 Ma) -- The third known
"little forest flier", found in 1985. Very fragmentary fossil.
* Hesperornis, Ichthyornis, and other Cretaceous diving birds -- This
line of birds became specialized for diving, like modern cormorants. As
they lived along saltwater coasts, there are many fossils known. Skeleton
further modified for flight (fusion of pelvis bones, fusion of hand bones,
short & fused tail). Still had true socketed teeth, a reptilian trait.
[Note: a classic study of chicken embryos showed that chicken bills can be
induced to develop teeth, indicating that chickens (and perhaps other
modern birds) still retain the genes for making teeth. Also note that
molecular data shows that crocodiles are birds' closest living relatives.]
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| User: "oz" |
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| Title: Re: Sudden Appearences |
16 Jan 2004 11:21:24 PM |
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Part Three
http://www.talkorigins.org/faqs/faq-transitional/part1b.html
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