. Chordate morphology. Morphology (Animals); Chordata. BIRD DIAPSID LIZARD (AND SNAKE) Figure 4-27. Evolution of the reptilian skull roof in terms of the temporal fenestroe or the loss of the cranial roof. Outlines of skulls are semidiogrammatic. fused postparietals, this type represents an early and primary branch of the reptiles. Goodrich (1916) cast some doubt on the idea of the rep- tiles being monophyletic, that is, all known reptiles stem- ming from a single primitive reptilian or prereptilian line. He proposed that the reptilian line giving rise to the mam- mals (this line as known now
. Chordate morphology. Morphology (Animals); Chordata. BIRD DIAPSID LIZARD (AND SNAKE) Figure 4-27. Evolution of the reptilian skull roof in terms of the temporal fenestroe or the loss of the cranial roof. Outlines of skulls are semidiogrammatic. fused postparietals, this type represents an early and primary branch of the reptiles. Goodrich (1916) cast some doubt on the idea of the rep- tiles being monophyletic, that is, all known reptiles stem- ming from a single primitive reptilian or prereptilian line. He proposed that the reptilian line giving rise to the mam- mals (this line as known now begins with the pelycosaurs) was distinct from that to which the other reptiles and birds belong, and that their basic difference in aortic arch plan must be traced back to separate amphibian lines. Watson has agreed with Goodrich and has suggested that the struc- ture of the ear region also identifies these two lines. It has also been proposed that the captorhinomorphs gave rise to the synapsids, whereas the diadectomorphs gave rise to the turtles and the other reptiles. Since the palatal struc- ture of lizards or birds denies a diadectomorph origin, it must be assumed that the earliest members of this line had a basipterygoid articulated palate. It is simpler to assume at this stage in our knowledge that there were several prim- itive reptilian types, not just two. For example, the eo- suchians (or Millerosauria) are no more modified than the others and could with equal verity be selected as an ances- tral type. Why should the captorhinomorphs be selected as ancestors of the pelecosaurs when these groups, as now known, are contemporary? General observations on the tetrapods The head skeleton of the tetrapod can now be considered in more general terms. There can be little doubt that there was a common ancestral pattern of bones from which the head skeletons of the various living lines have evolved. In each of the three evolutionary lines—mammal, reptile, and amphibian (the b
Size: 3477px × 719px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionameri, bookcollectionbiodiversity
