peter jay stein, md, ma
This 54 page synopsis of the evolution
of the Earth, the origin and progression of life, and the
emergence of humans as descendants of the hominin lineage, divides the last 4.57 billion years into progressively overlapping, imagistic, time segments, to outline our place in biological existence.
AMPHIBIAN - eggs require aquatic environment
running from time
Emergent Vertebrates I
4 legged animal, limbs derived from fish fins, that bridges vertebrate fish with vertebrate terrestrial animals
AMNIOTES! - eggs develop in an internal "pond", protected by amnion
conodont: an extinct marine, fish-like chordate, with gill arches, muscular segments, and fins, abundant from the Precambrian to the LateTriassic periods, having a long wormlike body, numerous small, hook-like teeth, and a pair of large eyes, believed to possibly be the earliest vertebrate (Biology, 10th ed., p. 680, G-10).
vertebrate: also called craniata, an animal derived from the phylum: chordates, sub-phylum vertebrata, having a backbone and bony skull that partly encloses a central nervous system. The hollow, dorsal nerve tube is now replaced by the spinal cord, which is now protected by a segmented vertebral, or spinal, column, composed of cartilage and/or bone. The head and brain house paired sense organs, that coordinate movement and sensation. Fish were the first vertebrates. Sub-phylum vertebrata includes 8 classes, including 4 classes of fish (including agnatha, chondrichthyes, and osteichthyes), and the additional classes: amphibia, reptilia, aves (birds), and mammalia (Anthro.Palomar.edu; Vertebrates, 2012, pp. 82-84).
coelacanth: thought to have become extinct 75 mya, rediscovered in the 1930's off the coast of southern Africa, this "living fossil", a sarcopterygian (fleshy-finned or lobe-finned) fish, also known as latimeria, its fins resembling limbs, represents an evolutionary transitional organism, linking the aquatic, vertebrate, bony fishes with tetrapod, terrestrial vertebrates. (Vertebrates, p. 46, 102).