Earliest Discoveries—Footprints of Batrachians—Labyrinthodents of the Carboniferous—Microsauria of the Carboniferous—Other Types—Discoveries in Erect Trees—Invertebrate Air-breathers, Land Snails, Millipedes, Insects, Spiders And Scorpions—General Conclusions
Remains of Hylonomus Lyelli, Dawson, 1859.
Coal Measures, South Joggins; Nova Scotia.
Photograph of Type specimen somewhat enlarged, Geol. Magazine, 1891 ([p. 279]).
(1) Cranial bones and mandibles; (1a) Sternal and shoulder bones; (2) Mandible;
(3) Humerus, ribs and vertebræ; (4) Hind limb; (5) Pelvis; (6) Caudal vertebræ.
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[CHAPTER X.]
THE OLDEST AIR-BREATHERS.
A
Animal life had its beginning in the waters, and to this day the waters are the chief habitat of animals, especially of the lower forms. If we divide the animal kingdom into great leading types, the lowest of these groups, the Protozoa, includes only aquatic forms; the next, that of the coral animals and their allies, is also aquatic. So are all the species of the Sea Urchins and Star Fishes. Of the remaining groups, the Mollusks, the Crustaceans, and the Worms are dominantly aquatic, only a small proportion being air-breathers. It is only in the two remaining groups, including the Insects and Spiders on the one hand, and the Vertebrate animals on the other, that we have terrestrial species in large proportion.