The evolution and distribution of fishes / by John Muirhead Macfarlane.

  • John Muirhead Macfarlane
Date:
1923
Catalogue details

Licence: In copyright

Credit: The evolution and distribution of fishes / by John Muirhead Macfarlane. Source: Wellcome Collection.

    20/584 page 6
    and 902 are marine, this by no means represents the prim- itive distributional relation. “We would therefore consider that all palaeontological, structural, and geographical evidence strongly favors the view that the primitive fishes have had a freshwater origin, and that derivative marine forms have evolved from these, which in the case of the anciently derived selacheans, and of the recent teleosteans, reached each to a high climax of species diversity, the former during the Cretaceous period, the latter in our own day.” If such conclusions are in harmony with the phylogeny and gradual distribution of fishes over freshwater and salt- water areas it should be highly probable that its correctness can be demonstrated by an appeal to the palaeontological record. Further, if that record is sufficiently complete, it should enable us to determine with fair accuracy the ap- proximate period when the main groups and even the smaller families of fishes migrated from a freshwater to a marine environment or vice versa. As a result an evolu- tionary sequence and exactness could thereby be obtained that would be in helpful contrast to the vague and un- certain record of the past. In now selecting the group of fishes for detailed treat- ment the writer has been guided by several considerations. First, it has been generally accepted as the group that con- nects the invertebrates with the more evolved vertebrates. Second, it shows several very distinct living divisions that can nevertheless be traced back through the greater extent of the palaeontological record to forms that strongly suggest community of origin and structure; Third, from its environal relations, and so from causes that will be fully discussed later, the group is one that is surprisingly well represented from later Silurian times up to the present day. Fourth, in spite of the great amount relatively of soft tissue that makes up each individual, the early for- mation, from at least Silurian times onward, of external scales and later of a resisting bony framework, ensured preservation of the remains in an exceptionally favorable manner. Fifth, owing to rare but remarkable combina- tions of geological conditions, that are fully discussed later
    digitised image 1
    digitised image 2
    digitised image 3