Paleontologists suggest that " Tiktaalik " was an intermediate form between fish such as " Panderichthys ", which lived about 385 million years ago and early tetrapods such as " Acanthostega " and " Ichthyostega " that lived about 20 million years later.
42.
The femur of " Antlerpeton " is much more robust than that of " Ichthyostega ", and has prominent ridges like the fourth trochanter that are attachment points for well-developed leg muscles . " Antlerpeton " also has small scales covering its underside.
43.
The pustular ornamentation seen in " S . mirus " is in fact rare among early tetrapods ( plagiosaurid temnospondyls and the very early tetrapod " Ichthyostega " are some of the few to have them ), while the reticulate ornamentation of " S . pereger " is more typical.
44.
The "'uncinate processes of the ribs "'are extensions of bone that project caudally from the vertical segment of each rib . ( Uncinate means " hooked " from Latin " uncinatus ", from " uncinus ", barb, from " uncus ", hook . ) They are found in birds ( except for screamers ), reptiles, and the early amphibian Ichthyostega.
45.
Early groups like " Acanthostega " had eight digits, while the more derived " Ichthyostega " had seven digits, the yet-more derived " Tulerpeton " had six toes . or reptiliomorphs, retained the five-toe pattern still found in Amniotes, while further reduction had taken place on other Labyrinthodont lines, leaving the forefoot with four toes and the hind foot with five, a pattern still found in modern amphibians.
