. Carnegie Institution of Washington publication. PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 43 ultimately distinguished by specific characters only, where the chain from ancestor to descendants nowhere lacks a single link. No character is ever more than varietal until it is fixed and isolated physiologically by heredity and time. One may be speculative and assume that Ophiacodon is really the beginning of the double-arched phylum, the beginning of a subclass, but there is not the slightest proof that such is the case. It will be many years before such an hypoth- esis can be proven or di
. Carnegie Institution of Washington publication. PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 43 ultimately distinguished by specific characters only, where the chain from ancestor to descendants nowhere lacks a single link. No character is ever more than varietal until it is fixed and isolated physiologically by heredity and time. One may be speculative and assume that Ophiacodon is really the beginning of the double-arched phylum, the beginning of a subclass, but there is not the slightest proof that such is the case. It will be many years before such an hypoth- esis can be proven or disproven, if it were ever possible, and classifications based upon hypotheses are unscientific. If the present form is merely a "mutation" or sport, then certainly the presence of a supratemporal vacuity has no taxonomic value, for we have no faith in the theory that species ever arise in such sudden ways. In other words, the most profound taxonomic characters must have had beginnings when they were merely varietal or specific; not till time and long descent have fixed them do they achieve a higher rank. In the present case we are con- vinced that, without further evidence to the contrary, the presence of two temporal vacuities and two temporal arches in Ophiacodon can not be assumed to have more than generic value. Vertebra and ribs: As has been stated, the vertebral column as collected was without break or even noticeable disturbance as far back as the sacrum, lying. Fig. 24.—Ophiacodon mints Marsh. Cervical vertebra.' from the side, the sixth also from in front, X li. ax. axis; an, atlantal neuropophysis; 0, odontoid; r, r, ribs; g, quadrate; pa, proatlas. with the skull and all or nearly all the ribs in natural articulation. Six or seven of the vertebrae may properly be called cervical, and twenty or twenty-one dorsal; the entire number, as in Dinietrodon, Varanosaurus, Theropleura,* and probably all other pelycosaurs in the narrower sense of the word, is twenty-
Size: 2124px × 1176px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorcarnegie, bookcentury1900, bookdecade1910, bookyear1913
