Topic
Cromus
About: Cromus is a research topic. Over the lifetime, 9 publications have been published within this topic receiving 118 citations.
Papers
TL;DR: The premise that derived similarities in early ontogeny reflect proximity of common ancestry provides a framework for evaluating relationships within the trilobite subfamily Encrinurinae Angelin and allied taxa on the basis of larval characters to corroborate a hypothesis of distant common ancestry and early divergence of this clade.
Abstract: r-The premise that derived similarities in early ontogeny reflect proximity of common ancestry provides a framework for evaluating relationships within the trilobite subfamily Encrinurinae Angelin and allied taxa on the basis of larval characters Protaspides for eight species of Ordovician and Silurian encrinurines are compared through cladistic analysis of character distributions; these are assigned to Encrinuroides Reed, Cromus? Barrande, Balizoma Holloway, and a new genus of the Encrinurus variolaris plexus Llandeilo Encrinuroides insularis Shaw, in which two metrically and morphologically distinct protaspid stages (instars) are rec- ognized, provides a standard for comparisons This two-stage division of the protaspid period is a synapomorphy of early encrinurines (Ordovician Encrinuroides), advanced cybelines (several species of Cybeloides Slocom), and early staurocephalids (Libertella Hu) The former groups further share a subtrapezoidal-subquadrate stage 1 instar with a single pair of protopygidial marginal spines, while stage 2 is broader with three pairs of marginal spines The two-stage protaspis in this clade, associated with several other evolutionary novelties (a torulus, prominent glabellar tubercle pairs, fixigenal "circumocular tubercles"), marks a reduction from the plesiomorphic state of numerous calcified larval instars (including small early "anaprotaspides") in pliomerids and early cybelines The conventional paraphyletic constructs of the Cybelinae and Encrinuroides obscure patterns of nested synapomorphy indicated by larval and adult character states Protaspides of Silurian Balizoma spp record a further shift in timing of calcification, with reduction to a single large instar with ontogenetically advanced character states (possibly allometric correlates of size increase) indicating homology with stage 2 of Encrinuroides and advanced cybelines Profound differences between protaspides of Llandovery Cromus? n sp (the first known for this genus) and those of other encrinurines corroborate a hypothesis of distant common ancestry and early divergence of this clade
52 citations
TL;DR: In this article, the Llandovery Encrinurinae from the Whittaker Formation in the central Mackenzie Mountains include Cromus canorus n. sp., Distyrax cooperi n.s. sp.
Abstract: Llandovery Encrinurinae from the Whittaker Formation in the central Mackenzie Mountains include Cromus canorus n. sp., Distyrax cooperi n. sp., Distyrax n. sp. A, Perryus bartletti n. sp., and Encrinurus n. sp. Additional diversity of Distyrax Lane, 1988, demands a revised generic diagnosis with emphasis on pygidial homologies; new species are described from the Llandovery of Newfoundland and Ontario. Several characters suggest a sister group relationship between Distyrax and Encrinurus s.s. A lectotype is designated for the Llandovery species Encrinurus elegantulus Billings, 1866. Cromus canorus n. sp. is closely allied to other northern Laurentian Llandovery species. Synapomorphies of Cromus are inclusive for Encrinuraspis as revised by Snajdr, 1985. The long stratigraphic range and morphological conservatism of Cromus are correlated with occurrence in distal mudstone facies. Ontogenetic material for Distyrax n. sp. A, Cromus canorus, and Perryus bartletti is described, with consideration of librigenal spine homologies in Encrinurinae. Humaencrinuroides Nan, 1985, is a pliomerid of the new subfamily Quinquecostinae, and not a subgenus of Encrinuroides Reed.
25 citations
Journal Article•
TL;DR: Webby et al. as discussed by the authors described a Late Ordovician trilobite fauna from mid-shelf deposits in the Gunningbland Formation near Gunningland, central-west New South Wales, including at least 13 species, among them the illaenid Eastonillaenus goonumblaensis gen.
Abstract: A Late Ordovician (latest Eastonian) trilobite fauna from mid-shelf deposits in the Gunningbland Formation near Gunningland, central-west New South Wales, includes at least 13 species, among them the illaenid Eastonillaenus goonumblaensis gen. et sp. nov., scutelluid Eokosovopeltis currajongensis sp. nov., lichid Amphilichas shergoldi sp. nov., remopleuridid Remopleurides cf. R. exallos Webby, asaphids Basiliella cf. B. fortis (Webby) and Basiliella? sp., encrinurids Cromus cf. C. optimus (Webby, Moors and McLean) and Erratencrinurus (Prophysemataspis) sp., and cheirurids Sphaerexochus sp. and Sphaerocoryphe sp. The new illaenid genus Eastonillaenus groups species from the Upper Ordovician of New South Wales. The trilobites of the Gunningbland Formation are mostly allied to those from other, coeval faunas of the New South Wales island-arc complex, and amplify affinities of eastern Australia to the eastern Gondwanan Eokosovopeltis-Pliomerina Province. Basiliella karmbergensis sp. nov. is described from the shelfal Karmberg Limestone (Middle Ordovician, Yapeenian) in the Florentine Valley, central Tasmania; three Tasmanian species form a group of effaced Basiliella species uniquely lacking genal spines.
14 citations
Journal Article•
TL;DR: The Gazelle formation in the Klamath Mountains is a eugeosynclinal suite of rocks from which well-preserved Silurian brachiopods and trilobites were discovered as discussed by the authors.
Abstract: The Gazelle formation in the Klamath Mountains is a eugeosynclinal suite of rocks from which well-preserved Silurian brachiopods and trilobites were discovered. A faunule containing the trilobites Leonaspis (Acanthalomina) minuta (Barrande), Dicranopeltis cf. C. decipiens (Weller), Trochurus sp. indet., Scutellum sp. indet., Proetus sp. indet., Cheirurus cf. C. insignis Beyrich, Encrinurus (Cromus) beaumonti (Barrande) is described. Encrinurus and Proetus are the only genera previously reported from the western states. Leptaena rhomboidalis Wilckens?, Atrypa reticularis Linnaeus var. orbicularis Sowerby?, Atrypella scheii (Holtedahl)?, and Gypidula sp. are brachiopods from this faunule. Gazelle trilobites are very closely related to the classical Bohemian fauna and some are conspecific. In addition the brachiopod assemblage more closely resembles the Alaskan and Asian faunas than those of the Great Basin and eastern North America.
12 citations
TL;DR: Fossiliferous localities within chloritoid slates of Upper Ludlow age from the West Asturian-Leonese Zone (NW Spain) in the Penalba and Sil synclines are reviewed in this paper.
9 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2009 | 1 |
| 2007 | 1 |
| 2006 | 1 |
| 2000 | 1 |
| 1993 | 1 |
| 1992 | 1 |