Order Graptoloidea and Family Anisograptidae: Introduction, Morphology, and Systematic Descriptions

ZHANG Y.D.; TORO, B.A; MALETZ, J.

Treatise Online

Kansas University Paleontological Institute

Lugar: Lawrence; Año: 2017 vol. 85 p. 1 - 14

2153-4012

Graptoidea LAPWORTH, 1875, includes graptolites united by the retention of the nematophorous sicula in the adult stage as the defining synapomorphy. Ordovician (Tremadocian, Rhabdinopora flabelliformis preparabola Biozone)-Devonian (lower Emsian, Monograptus yukonensis Biozone): worldwide.In the past, all bithecae-bearing planktic taxa (family Anisograptidae) were included in the Dendroidea (BULMAN, 1955, 1970) or in the Graptodendroidea (MU & LIN in LIN, 1981) as they show close similarities to the construction of the bentic graptolites due the presence of a typical triad budding system with development of bithecae along the stipes. Early Graptoloidea share numerous tubarium characters with the Dendroidea, especially the stipe structure formed by triad budding (Wiman rule), in which each autotheca produces two doter thecae an autothecae and a bitheca. Dicalycal thecae are inserted at various distances to produce branching of the stipes. The most obvious difference the Graptoloidea has from the bentic taxa is the development of a free nema and the differentiation of the conus and cauda of the prosicula.Suborder Graptodendroidina MU & LIN, 1981 includes quadriradiate to biradiate planktic, nematophorous graptolites with a triad budding system of the thecae, bithecae reduced or even lost in stratigraphically younger taxa; colonies multiramous to biramous, pendent to reclined; dissepiments present in some taxa; autothecae simple, widening tubes with or without short ventral rutellu; thecal apertures may be isolated; prosicula with distinct differenciation of conus and cauda; origin of the th11 in the middle part of the conus; proximal end may posses one to three succesive (proximal) dicalycal thecae with th12 as the first dicalycal theca; later dicalycal thecae adventitiously or regurlarly distributed. Lower Ordovician (Tremadocian, Rhabdinopora flabelliformis praeparabola Biozone-Floian, Sagenograptus murrayi Biozone): wordwide.Family Anisograptidae BULMAN, 1950 are planktic nematophorous, multiramous graptoloids with a triad budding system; colony shape ranges from reclined through horizontal to declined and bell-shape or pendent; bithecae distinctly smaller than autothecae; bithecae initially regular, but in later taxa irregular and often reduced or absent; autothecae simple, widening tubes, sometimes apertrally isolated; ventral rutella common; disepiments present in a few taxa; proximal development type isograptid, quadriradiate to beradiate, variably dextral and sinistral; maeandrograptid type proximal symentry with inclined sicula; prosicula with distinct differentiation of conus and cauda; origin of the first theca in median part of the conus; th12 is first dicalycal theca, later dicalycal thaecae adventitiously or regularly distribuited. Lower Ordovician (Tremadocian, Rhabdinopora flabelliformis praeparabola Biozone-Floian, Sagenograptus murrayi Biozone): worldwide.