There are no transitional fossils. Evolution predicts a continuum between
each fossil organism and its ancestors. Instead, we see systematic gaps
in the fossil record.
Morris, Henry M. 1985. Scientific Creationism. Green Forest, AR: Master
Watchtower Bible and Tract Society. 1985. Life--How Did It Get
Here? Brooklyn, NY, pp. 57-59.
- There are many transitional fossils. The only way that the claim of
their absence may be remotely justified, aside from ignoring the
evidence completely, is to redefine "transitional" as referring to a
fossil that is a direct ancestor of one organism and a direct
descendant of another. However, direct lineages are not required; they
could not be verified even if found. What a transitional fossil is, in
keeping with what the theory of evolution predicts, is a fossil that
shows a mosaic of features from an older and more recent organism.
- Transitional fossils may coexist with gaps. We do not expect to find
finely detailed sequences of fossils lasting for millions of years.
Nevertheless, we do find several fine gradations of fossils between
species and genera, and we find many other sequences between higher
taxa that are still very well filled out.
The following are fossil transitions between species and genera:
- Human ancestry. There are many fossils of human
and the differences between species are so gradual that it is not
always clear where to draw the lines between them.
- The horns of titanotheres (extinct Cenozoic mammals) appear in
progressively larger sizes, from nothing to prominence. Other head
and neck features also evolved. These features are adaptations for
head-on ramming analogous to sheep behavior (Stanley 1974).
- A gradual transitional fossil sequence connects the foraminifera
Globigerinoides trilobus and Orbulina universa (Pearson et
1997). O. universa, the later fossil, features a spherical test
surrounding a "Globigerinoides-like" shell, showing that a feature
was added, not lost. The evidence is seen in all major tropical
ocean basins. Several intermediate morphospecies connect the two
species, as may be seen in the figure included in Lindsay (1997).
- The fossil record shows transitions between species of Phacops (a
trilobite; Phacops rana is the Pennsylvania state fossil;
1972; 1974; Strapple 1978).
- Planktonic forminifera (Malmgren et al. 1984). This is an example
of punctuated gradualism. A ten-million-year foraminifera fossil
record shows long periods of stasis and other periods of relatively
rapid but still gradual morphologic change.
- Fossils of the diatom Rhizosolenia are very common (they are mined
as diatomaceous earth), and they show a continuous record of almost
two million years which includes a record of a speciation
event (Miller 1999, 44-45).
- Lake Turkana mollusc species (Lewin 1981).
- Cenozoic marine ostracodes (Cronin 1985).
- The Eocene primate genus Cantius (Gingerich 1976, 1980, 1983).
- Scallops of the genus Chesapecten show gradual change in one "ear"
of their hinge over about 13 million years. The ribs also change
(Pojeta and Springer 2001; Ward and Blackwelder 1975).
- Gryphaea (coiled oysters) become larger and broader but thinner
and flatter during the Early Jurassic (Hallam 1968).
The following are fossil transitionals between families, orders, and
- Human ancestry. Australopithecus, though its leg and pelvis bones
show it walked upright, had a bony ridge on the forearm, probably
vestigial, indicative of knuckle walking (Richmond and Strait 2000).
- Dinosaur-bird transitions.
- Haasiophis terrasanctus is a primitive marine snake with
well-developed hind limbs. Although other limbless snakes might be
more ancestral, this fossil shows a relationship of snakes with
limbed ancestors (Tchernov et al. 2000). Pachyrhachis is another
snake with legs that is related to Haasiophis (Caldwell and Lee
- The jaws of mososaurs are also intermediate between snakes and
lizards. Like the snake's stretchable jaws, they have highly
flexible lower jaws, but unlike snakes, they do not have highly
flexible upper jaws. Some other skull features of mososaurs are
intermediate between snakes and primitive lizards (Caldwell and Lee
1997; Lee et al. 1999; Tchernov et al. 2000).
- Transitions between mesonychids and whales.
- Transitions between fish and tetrapods.
- Transitions from condylarths (a kind of land mammal) to fully
aquatic modern manatees. In particular, Pezosiren portelli is
clearly a sirenian, but its hind limbs and pelvis are unreduced
(Domning 2001a, 2001b).
- Runcaria, a Middle Devonian plant, was a precursor to seed
plants. It had all the qualities of seeds except a solid seed coat
and a system to guide pollen to the seed (Gerrienne et al. 2004).
- A bee, Melittosphex burmensis, from Early Cretaceous amber, has
primitive characteristics expected from a transition between
crabronid wasps and extant bees (Poinar and Danforth 2006).
The following are fossil transitionals between kingdoms and phyla:
- The Cambrian fossils Halkiera and Wiwaxia have features that
connect them with each other and with the modern phyla of Mollusca,
Brachiopoda, and Annelida. In particular, one species of halkieriid
has brachiopod-like shells on the dorsal side at each end. This is
seen also in an immature stage of the living brachiopod species
Neocrania. It has setae identical in structure to polychaetes, a
group of annelids. Wiwaxia and Halkiera have the same
arrangement of hollow sclerites, an arrangement that is similar to
the chaetae arrangement of polychaetes. The undersurface of
Wiwaxia has a soft sole like a mollusk's foot, and its jaw looks
like a mollusk's mouth. Aplacophorans, which are a group of
primitive mollusks, have a soft body covered with spicules similar
to the sclerites of Wiwaxia (Conway Morris 1998, 185-195).
- Cambrian and Precambrain fossils Anomalocaris and Opabinia are
transitional between arthropods and
- An ancestral echinoderm has been found that is intermediate between
modern echinoderms and other deuterostomes (Shu et al. 2004).
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marine Cretaceous of the Middle East. Nature 386: 705-709.
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climatic modulation of evolution. Science 227: 60-63.
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sirenian. Nature 413: 625-627.
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to land. Reports of the National Center for Science Education
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(Green, 1832) and Phacops iowensis Delo, 1935 (Trilobita) from the
Middle Devonian of North America. Bulletin of the American Museum of
Natural History 147(2): 45-114.
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- Hallam, A., 1968. Morphology, palaeoecology and evolution of the genus
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The origin of snake feeding. Nature 400: 655-659.
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Species formation through punctuated gradualism in planktonic
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Cretaceous Burmese amber. Science 314: 614.
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from a knuckle-walking ancestor. Nature 404: 382-385. See also
Collard, M. and L. C. Aiello, 2000. From forelimbs to two legs.
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deposits of China. Nature 430: 422-428.
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new approach to an old problem. Evolution 28: 447-457.
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2010-2012. See also Greene, H. W. and D. Cundall, 2000. Limbless
tetrapods and snakes with legs. Science 287: 1939-1941.
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Pectinidae (Mollusca: Bivalvia) from the Miocene and Pliocene of
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created 2001-4-29, modified 2006-11-5