Middle Ordovician – Late Ordovician; Middle Silurian – Early Carboniferous
Diplobathrida is an extinct order of stationary upper-level epifaunal suspension feeders
Characteristics of the Order
- Calyx dicyclic
- Presence of two circlets of plates below the radials in the dorsal cup
- Symmetrical posterior plating and rigid plate sutures
Treatise on Invertebrate Paleontology, Part T, Vol. 2(2) (1978):
- Calyx dicyclic
- The order of camerate crinoids called Diplobathrida is distinguished by presence of two circlets of plates below the radials in the dorsal cup. This group comprises a minority of the Camerata which shows less evolutionary divergence and seems generally to have more archaic characters than a single-basal-circlet camerates called Monobathrida. Both orders make appearance in the Chazyan, but the Diplobathrida are more numerous and they have chief development in pre-Mississippian geologic time. Except in the Lower Devonian and Upper Mississippian. Diplobathrids are predominantly American crinoids. The peak of Diplobathrida development, represented by number of species, is in the Middle Silurian; approximately 90 percent of the known forms from these rocks are American.
- Distribution of diplobathrid crinoids, plotted by families, shows that only one family unit (Rhodocrinitidae) has any considerable development after the Silurian time; other families are exclusively Ordovician, Silurian, or have unimportant remnants persisting into the Devonian. Characteristic Silurian family assemblages are the Dimorocrinitidae, Lampterocrinidae, and Gazacrinidae. The Silurian genus Nyctocrinus, which has nearly perfect pentameral symmetry and lacks interradial plates in the dorsal cup, is judged to mark culmination of evolutionary trends in the order.
Moore & Laudon (1943):
- Camerate crinoids having 5IBB and 5BB. Ordovician to Mississippian. Most fundamental and long persisting among characters of camerate crinoids is structure of the base of the dorsal cup. Monocyclic and dicyclic stocks were evolved in pre-Ordovician times, and they ran parallel throughout most of Paleozoic time. Similar evolutionary trends are exhibited in both stocks.