Topic
Harpetida
About: Harpetida is a research topic. Over the lifetime, 2 publications have been published within this topic receiving 47 citations.
Papers
TL;DR: Descendant lineages show increasing eye size, increased cephalic vaulting and effacement during the early Famennian, and the origin of post-event phacopids from shallow water environments is demonstrated for the first time.
Abstract: A diverse fauna of phacopid trilobites is described from the Late Devonian (middle Frasnian to early Famennian) of the northern Canning Basin, Western Australia. One new genus and four species in two genera are described from zones 11, 13a and 13b of the middle and late Frasnian: Trimerocephaloides sinevisus gen. nov. and sp. nov., T. ? linguiformis sp. nov., Acuticryphops acuticeps (Kayser, 1889) and A. klapperi sp. nov. Late Frasnian phacopines are either blind, as shown for the first time in Trimerocephaloides sinevisus, or show trends to decreasing eye size up to the Frasnian-Famennian 'Kellwasser' mass extinction event. This evolutionary trend in Acuticryphops is demonstrated to have been global at this time. One new genus and six species of early Famennian phacopids are described, from the Upper triangularis, crepida and rhomboidea zones: Houseops gen. nov. with the new taxa H. canningensis sp. nov., H. beckeri sp. nov. and H. sp. A, Babinops planiventer Feist & Becker, 1997, B. minor sp. nov., Trimerocephalus tardispinosus Feist & Becker, 1997 and T. mimbi sp. nov. In contrast to European sections where exclusively blind phacopids are known in earliest Famennian sites, initial recovery following the mass extinction event in Canning peri-reefal environments is characterized by oculated forms. These trilobites must have evolved from conservative ancestors with normal eyes that had succeeded in surviving the Kellwasser biocrises in reef-related shallow water niches. Thus the origin of post-event phacopids from shallow water environments is demonstrated for the first time. Descendant lineages show increasing eye size, increased cephalic vaulting and effacement during the early Famennian. Of the five orders of trilobites that are present during the Frasnian Stage at the beginning of the Late Devonian, only two, the Proetida and the Phacopida, survived into the Famennian. The presence of a conformable sequence of trilobite-bearing fore-reef limestones, the Virgin Hills Formation, that form part of the Late Devonian reef system in the northern part of the Canning Basin in Western Australia, allows the patterns of evolution and extinction of the late Frasnian and early Famennian trilobites to be assessed. In these deposits the three orders that became extinct during the Frasnian-Famennian biocrises were the Corynexochida (McNamara & Feist, 2006), the Lichida (Feist & McNamara, 2007) and the Harpetida (McNamara, Feist & Ebach, in press). Here we focus on one of the groups that survived this event, the Phacopida. Although, with a single exception, they are rare elements of the trilobite fauna in the Canning Basin, the phacopids are generically the most diverse of the
40 citations
TL;DR: The Eskoharpes lineage shows evolutionary trends that mirror changes seen in ontogenetic development of the youngest species, suggesting the operation of peramorphic processes in harpetids, marking the end of the trilobite order Harpetida worldwide.
Abstract: Late Devonian (Frasnian) harpetid trilobites have
hitherto only been described from the western side of the
Protethys Ocean, in what is now Europe and North Africa,
as well as from Gondwana-derived northwestern Kazakhstan
(Mugodjar). However, late Frasnian strata in the Canning
Basin, Western Australia, that were deposited on the eastern
side of this ocean, contain a rich harpetid fauna. Described
herein are two new harpetids: Eskoharpes gen. nov. and
Globoharpes gen. nov., within which are placed six species: E.palanasus sp. nov., E. wandjina sp. nov., E. boltoni sp. nov., E. guthae sp. nov., G. teicherti sp. nov. and G. friendi sp. nov.
The ontogenetic development of E. palanasus, E. wandjina
and G. teicherti are described, including the first unequivocal harpetid protaspis. Globoharpes exhibits evidence of sexual dimorphism in the development of a pronounced preglabellar boss in some specimens. This structure is thought to have functioned as a brood pouch. Such structures have previously only been described in Cambrian and Ordovician trilobites, and never before in harpetids. It is suggested that the characteristic harpetid fringe functioned as a secondary respiratory structure. The Eskoharpes lineage shows evolutionary trends that mirror changes seen in ontogenetic development of the youngest species, suggesting the operation of peramorphic
processes. This is the first record of heterochrony in
harpetids and the first documented example of peramorphosis
in Devonian trilobites. These harpetids demonstrate a
stepped pattern of extinction during the late Frasnian, probably related to the effects of the two Kellwasser biocrises that have been well documented in European Frasnian sections.
Highly vaulted species of Eskoharpes and the strongly vaulted Globoharpes became extinct at the Lower Kellwasser Event. The flatter species of Eskoharpes became extinct at the base of the Upper Kellwasser Event shortly prior to the Frasnian ⁄ Famennian boundary. The extinction of these harpetids, along with contemporaneous forms from Europe, which are also discussed herein, marks the end of the trilobite order Harpetida worldwide.
23 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2009 | 2 |