TY  - JOUR
TI  - On the origin of pattern and form in early Metazoans
AU  - Cummings, FrederickW.
T2  - The International Journal of Developmental Biology
AB  - The 'Cambrian explosion', about 540 million years ago, may have occurred within 10 to 50 million years. Almost all of the modern phyla, a very restricted group and many groups that may represent extinct phyla, suddenly appear near that time in the fossil record. Numerous extensive periods of mass extinction since that time led to no new phyla. This is taken as an impetus to examine a possible source, beyond Darwinian adaptation, of the apparently restricted number of phyla. Such a postulated constraint or restriction beyond adaptation is proposed to be based on a mutation or mutations allowing single celled or colonial precursors to begin forming into epithelial sheets and gene activation patterns of a particular kind, those giving rise to the very earliest metazoans. The interaction of signaling pathways in pairs, with different pairs acting sequentially are proposed as key to this earliest patterning, such patterning being extensively elaborated over the last  approx.  550 million years. Restrictions on the very large set of possible forms and patterns on which adaptation acts are discussed.
PY  - 2006
DO  - 10.1387/ijdb.052058fc
VL  - 50
IS  - 2-3
SP  - 193
EP  - 208
J2  - Int. J. Dev. Biol.
LA  - en
SN  - 0214-6282
SN  - 1696-3547
UR  - https://ijdb.ehu.eus/article/052058fc
Y2  - 2024/11/21/17:17:21
ER  -