crinoids

• crinoids

59:3.11To­ward the close of the fi­nal Sil­urian sub­mer­gence there is a great in­crease in the echin­o­derms—the stone lilies—as is ev­i­denced by the crinoid lime­stone de­posits. The trilo­bites have nearly dis­ap­peared, and the mol­lusks con­tinue monar­chs of the seas; coral-reef for­ma­tion in­creases greatly. Dur­ing this age, in the more fa­vor­able lo­ca­tions the prim­i­tive wa­ter scor­pi­ons first evolve. Soon there­after, and sud­denly, the true scor­pi­ons—ac­tual air breathers—make their ap­pear­ance.

• secreted lime

59:5.8Two groups of echin­o­derms be­came es­pe­cially well de­vel­oped, and they are in re­al­ity the guide fos­sils of this epoch. The large shell-feed­ing sharks were also highly evolved, and for more than five mil­lion years they dom­i­nated the oceans. The cli­mate was still mild and equable; the ma­rine life was lit­tle changed. Fresh-wa­ter fish were de­vel­op­ing and the trilo­bites were near­ing ex­tinc­tion. Corals were scarce, and much of the lime­stone was be­ing made by the crinoids. The finer build­ing lime­stones were laid down dur­ing this epoch.

• crinoids

60:2.8The re­turn of the seas im­proved the weather. Corals spread to Eu­ro­pean wa­ters, tes­ti­fy­ing that the cli­mate was still mild and even, but they never again ap­peared in the slowly cool­ing po­lar seas. The ma­rine life of these times im­proved and de­vel­oped greatly, es­pe­cially in Eu­ro­pean wa­ters. Both corals and crinoids tem­porar­ily ap­peared in larger num­bers than here­to­fore, but the am­monites dom­i­nated the in­ver­te­brate life of the oceans, their av­er­age size rang­ing from three to four inches, though one species at­tained a di­am­e­ter of eight feet. Sponges were ev­ery­where, and both cut­tle­fish and oys­ters con­tin­ued to evolve.

• crinoids

60:4.5Bi­o­log­i­cally as well as ge­o­log­i­cally this was an event­ful and ac­tive age on land and un­der wa­ter. Sea urchins in­creased while corals and crinoids de­creased. The am­monites, of pre­pon­der­ant in­flu­ence dur­ing a pre­vi­ous age, also rapidly de­clined. On land the fern forests were largely re­placed by pine and other mod­ern trees, in­clud­ing the gi­gan­tic red­woods. By the end of this pe­riod, while the pla­cen­tal mam­mal has not yet evolved, the bi­o­logic stage is fully set for the ap­pear­ance, in a sub­se­quent age, of the early an­ces­tors of the fu­ture mam­malian types.