Claim CC215:
There is a great gulf between reptiles and mammals, with no transitional
fossils between them.
Source:
Watchtower Bible and Tract Society, 1985. Life--How Did It Get Here?
Brooklyn, NY, p. 80-81.
Response:
- The transition from reptile to mammal has an excellent record.
The following fossils are just a sampling.
In particular, these fossils document the transition of one type of jaw
joint into another. Reptiles have one bone in the middle ear and
several bones in the lower jaw. Mammals have three bones in the middle
ear and only one bone in the lower jaw. These species show
transitional jaw-ear arrangements (Hunt 1997; White 2002b). The
sequence shows transitional stages in other features, too, such as
skull, vertebrae, ribs, and toes.
- Sphenacodon (late Pennsylvanian to early Permian, about 270
million years ago (Mya)). Lower jaw is made of multiple bones; the
jaw hinge is fully reptilian. No eardrum.
- Biarmosuchia (late Permian). One of the earliest therapsids.
Jaw hinge is more mammalian. Upper jaw is fixed. Hindlimbs are
more upright.
- Procynosuchus (latest Permian). A primitive cynodont, a group of
mammal-like therapsids. Most of the lower jaw bones are grouped in
a small complex near the jaw hinge.
- Thrinaxodon (early Triassic). A more advanced cynodont. An
eardrum has developed in the lower jaw, allowing it to hear
airborne sound. Its quadrate and articular jaw bones could
vibrate freely, allowing them to function for sound transmission
while still functioning as jaw bones. All four legs are fully
upright.
- Probainognathus (mid-Triassic, about 235 Mya). It has two
jaw joints: mammalian and reptilian (White 2002a).
- Diarthrognathus (early Jurassic, 209 Mya). An advanced cynodont.
It still has a double jaw joint, but the reptilian joint functions
almost entirely for hearing.
- Morganucodon (early Jurassic, about 220 Mya). It still has
a remnant of the reptilian jaw joint (Kermack et al. 1981).
- Hadrocodium (early Jurassic). Its middle ear
bones have moved from the jaw to the cranium (Luo et al. 2001;
White 2002b).
Links:
Flank, Lenny, 1995. The Therapsid--mammal transitional series.
http://www.geocities.com/CapeCanaveral/Hangar/2437/therapsd.htm
Hunt, Kathleen, 1997. Transitional vertebrate fossils FAQ, part 1B.
http://www.talkorigins.org/faqs/faq-transitional/part1b.html#syn2mamm
Theobald, Douglas, 2004. 29+ evidences for macroevolution, part 1: The
unique universal phylogenetic tree.
http://www.talkorigins.org/faqs/comdesc/section1.html#morphological_intermediates_ex2
References:
- Hunt, K. 1997. (see above)
- Kermack, K. A., F. Mussett and H. W. Rigney, 1981. The skull of
Morganucodon. Zoological Journal of the Linnean Society 71:
1-158.
- Luo, Z.-X., A. W. Crompton and A.-L. Sun, 2001. A new mammaliaform
from the Early Jurassic and evolution of mammalian characteristics.
Science 292: 1535-1540.
- White, T., 2002a. Palaeos Vertebrates 420.500: Cynodontia: Probainognathia.
http://www.palaeos.com/Vertebrates/Units/410Cynodontia/410.500.html
- White, T., 2002b. Palaeos Vertebrates 420.300: Mammaliformes: Symmetrodonta.
http://www.palaeos.com/Vertebrates/Units/Unit420/420.300.html
Further Reading:
Benton, Michael J. 1991. The Rise of the Mammals.
New York: Crescent Books.
created 2003-6-13, modified 2004-3-18