Page:The Scientific Monthly vol. 3.djvu/327

 ORIGIN AND EVOLUTION OF LIFE 321

that of Lingula anatina, a species living to-day. Bepresentatives of the genoB Lingula (lAngulella) have persiBted from Cambrian to recent times. The great antiqui^ of the Brachiopods as a group is well illastrated by the persistence of Lingula (Cambrian — Ordovician — Re- cent), on the one hand, and of Terebratula (Devonian — Recent), be- longing to a widely differing family, on the other. These lamp-shells are thus characteristic of all geologic ages, ■- including the present Beaching their maximum radiation during the Ordovician and Silurian, they gradually lost their importance during the Devonian and Permian, and at the present time have dwindled into a relatively insigniticant group, members of which range from the oceanic shore-line to the deep- sea or abyssal habitat.

��Fia. 3. Bbacbiopoos, Cambbian and Recent. I.lngulella (Lingula) acuminata, Tangtng from Cambrian to Ordovician, and the ver; almllar Ungula anatina, peralat- Ing from Cambrian tJm«a down to the preBent day. LinguMla, CambtlaD to Ordo- vician, contraated with the widely differing Tertbratala which ranges from DcTonlan t« recent timei.

By the Middle Cambrian the continental seas covered the whole region of the present Cordilleras of the Pacific coast. In the present region of Mount Stephen, B. C, in the unusually favorable marine oily shales of the Burgess formation, the remarkable evolution of inverte- brate life prior to Cambrian time has been revealed through Walcotfs epoch-making discoveries between 1909 and 1912.** It is at once evi- dent (Figs- 2-9) that the seashore and pelagic life of this time ex- hibits types as widely divergent as those which now occur among the aquatic Invertebrata. Not only are the characteristic external features of these soft-trodied invertebrates evident in the fossil remains, but in some cases even the internal organs show through the imprint of the » Walcott, Charles D., 1911, 1912.

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