. Animal studies. 428 ANIMAL STUDIES But certain subdivisions of a principal group or class of animals often appear in an early epoch, become very abun- dant and highly specialized in a later one, and almost wholly or even totally disappear in a still later one. For ex- ample, a group of certain curious animals called Trilobites (Fig. 250), belonging to the great class Crustacea (which includes the crabs, crayfishes, and lobsters), first appeared in. Fig. 250.—Cambrian Trilobites. a, Paracloxides Bohemicus, reduced in size; b, Ellip- s cephalus Hoffi; c, Sao hirsuta; d, Conocoryphe Sultzeri (a
. Animal studies. 428 ANIMAL STUDIES But certain subdivisions of a principal group or class of animals often appear in an early epoch, become very abun- dant and highly specialized in a later one, and almost wholly or even totally disappear in a still later one. For ex- ample, a group of certain curious animals called Trilobites (Fig. 250), belonging to the great class Crustacea (which includes the crabs, crayfishes, and lobsters), first appeared in. Fig. 250.—Cambrian Trilobites. a, Paracloxides Bohemicus, reduced in size; b, Ellip- s cephalus Hoffi; c, Sao hirsuta; d, Conocoryphe Sultzeri (all the above, together with Fig. g, are from the Upper Cambrian or "primordial zone" of Bohemia); e, head-shield of Dikellocephalus Celticus, from the Lingula flags of Wales; /, head-shield of Conocoryphe Matthewi, from the Upper Cambrian (Acadian group) of New Brunswick; g, Agnostus rex, Bohemia; h, tail-shield of Dikello- cephalus Mnnesotensis, from the Upper Cambrian (Potsdam sandstone) of Minne- sota.—From Nicholson, after Barrande. Dawson, Salter, and Dale Owen. the Cambrian era, became very abundantly represented in the Silurian era, began to decline in the Devonian, and became extinct in the Carboniferous era. This was not the extinc- tion of a single kind or species of animal, but of a large. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Jordan, David Starr, 1851-1931; Kellogg, Vernon L. [from old catalog].
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Keywords: ., bookauthorjordanda, bookcentury1900, bookdecade1900, bookyear1903
