Search citation statements
Paper Sections
Citation Types
Year Published
Publication Types
Relationship
Authors
Journals
The Devonian–Carboniferous boundary beds in the Berchogur (Birshogyr) sections in the Mugodzhary (Mugalzhary) Mountains in western Kazakhstan, known to contain various fossil groups, including ammonoids, conodonts, foraminifers, corals, crinoids, and trilobites, are re-examined. The siliciclastic-carbonate succession of the Zhangana Formation reveals the presence of several ammonoid, conodont, and foraminiferal zones. The succession contains the Acutimitoceras ammonoid Genozone, equivalent to the level of the Stockum ammonoid fauna of Germany, with the conodont Siphonodella sulcata appearing within the Genozone. The same beds show mass occurrences of the foraminifer Tournayellina pseudobeata. The study of the Berchogur sections began in the 1980s; these sections are among very few successions globally with ammonoids of the Acutimitoceras Genozone in association with conodonts and foraminifers. At that time, several outcrops in a small area in the upper reaches of Burtybai (Zhangansai) Creek and two boreholes drilled near the sections were studied, and new taxa of ammonoids, foraminifers, ostracods, conodonts, algae, and spores were described. New excavations in 2018–2020, in conjunction with a search for a new definition of the Devonian–Carboniferous boundary, provided abundant new information on these taxa, on the lithology, and on crinoids, trilobites, and corals. The exact position of marker fossils and lithological changes are documented in several sections along Burtybai Creek allowing an amended correlation with sections of the D–C boundary beds in Western Europe.
The Devonian–Carboniferous boundary beds in the Berchogur (Birshogyr) sections in the Mugodzhary (Mugalzhary) Mountains in western Kazakhstan, known to contain various fossil groups, including ammonoids, conodonts, foraminifers, corals, crinoids, and trilobites, are re-examined. The siliciclastic-carbonate succession of the Zhangana Formation reveals the presence of several ammonoid, conodont, and foraminiferal zones. The succession contains the Acutimitoceras ammonoid Genozone, equivalent to the level of the Stockum ammonoid fauna of Germany, with the conodont Siphonodella sulcata appearing within the Genozone. The same beds show mass occurrences of the foraminifer Tournayellina pseudobeata. The study of the Berchogur sections began in the 1980s; these sections are among very few successions globally with ammonoids of the Acutimitoceras Genozone in association with conodonts and foraminifers. At that time, several outcrops in a small area in the upper reaches of Burtybai (Zhangansai) Creek and two boreholes drilled near the sections were studied, and new taxa of ammonoids, foraminifers, ostracods, conodonts, algae, and spores were described. New excavations in 2018–2020, in conjunction with a search for a new definition of the Devonian–Carboniferous boundary, provided abundant new information on these taxa, on the lithology, and on crinoids, trilobites, and corals. The exact position of marker fossils and lithological changes are documented in several sections along Burtybai Creek allowing an amended correlation with sections of the D–C boundary beds in Western Europe.
Shell-encrusting assemblages have uniquely high ecological fidelity among paleocommunities because adjacent epibionts coexisted in ecological time, and the abundances and spatial relationships of the various members are accurately preserved. This study presents a quantitative reconstruction of communities on brachiopod shells (Composita and alate spirifers) from the Carboniferous of North America. Thirty-one epibiont communities, comprised of a total of 1180 encrusted brachiopods, are analyzed in terms of epibiont abundance (e.g., percent areal cover), ecological diversity (e.g., Shannon-Wiener Index), and the role of larval recruitment and spatial competition in structuring the communities.Mississippian epibiont communities contain from seven to 14 encrusting taxa that occupy up to 25 percent of host shell surfaces. These communities are spatially dominated by trepostome bryozoans, but also include common lower Paleozoic epibionts, such as encrusting ctenostome bryozoans, hederellids, cornulitids, and edrioasteroids. Pennsylvanian epibiont communities contain between eight and 16 epizoan taxa that occupy up to 34 percent of shell surfaces. They are dominated by fistuliporoid or trepostome bryozoans and increasing proportions of erect bryozoans (e.g., fenestellids), encrusting foraminiferans, and articulate brachiopods.Carboniferous epibionts, like their modern counterparts, exist in loosely organized ecological communities that vary widely in abundance and composition in space and geological time. There is little evidence for tight controls on community structure. Much of the variation is attributed to vagaries in the magnitude and selective nature of larval recruitment. Evidence of competition between community members is rare, except where a high percentage of the shell surface is covered. In these cases, sheetlike bryozoans are usually most abundant. Solitary epibionts are surprisingly successful competitors in one-on-one encounters, but apparently lose areal cover to longer-lived colonial encrusters during ecological succession.
The Thoracica includes the ordinary barnacles found along the sea shore and is the most diverse and well-studied superorder of Cirripedia. However, although the literature abounds with scenarios explaining the evolution of these barnacles, very few studies have attempted to test these hypotheses in a phylogenetic context. The few attempts at phylogenetic analyses have suffered from a lack of phylogenetic signal and small numbers of taxa. We collected DNA sequences from the nuclear 18S, 28S, and histone H3 genes and the mitochondrial 12S and 16S genes (4,871 bp total) and data for 37 adult and 53 larval morphological characters from 43 taxa representing all the extant thoracican suborders (except the monospecific Brachylepadomorpha). Four Rhizocephala (highly modified parasitic barnacles) taxa and a Rhizocephala + Acrothoracica (burrowing barnacles) hypothetical ancestor were used as the outgroup for the molecular and morphological analyses, respectively. We analyzed these data separately and combined using maximum likelihood (ML) under "hill-climbing" and genetic algorithm heuristic searches, maximum parsimony procedures, and Bayesian inference coupled with Markov chain Monte Carlo techniques under mixed and homogeneous models of nucleotide substitution. The resulting phylogenetic trees answered key questions in barnacle evolution. The four-plated Iblomorpha were shown as the most primitive thoracican, and the plateless Heteralepadomorpha were placed as the sister group of the Lepadomorpha. These relationships suggest for the first time in an invertebrate that exoskeleton biomineralization may have evolved from phosphatic to calcitic. Sessilia (nonpedunculate) barnacles were depicted as monophyletic and appear to have evolved from a stalked (pedunculate) multiplated (5+) scalpelloidlike ancestor rather than a five-plated lepadomorphan ancestor. The Balanomorpha (symmetric sessile barnacles) appear to have the following relationship: (Chthamaloidea(Coronuloidea(Tetraclitoidea, Balanoidea))). Thoracican divergence times were estimated under ML-based local clock, Bayesian, and penalized likelihood approaches using an 18S data set and three calibration points: Heteralepadomorpha = 530 million years ago (MYA), Scalpellomorpha = 340 MYA, and Verrucomorpha = 120 MYA. Estimated dates varied considerably within and between approaches depending on the calibration point. Highly parameterized local clock models that assume independent rates (r > or = 15) for confamilial or congeneric species generated the most congruent estimates among calibrations and agreed more closely with the barnacle fossil record. Reasonable estimates were also obtained under the Bayesian procedure of Kishino et al. (2001, Mol. Biol. Evol. 18:352-361) but using multiple calibrations. Most of the dates estimated under the Bayesian procedure of Aris-Brosou and Yang (2002, Syst. Biol. 51:703-714) and the penalized likelihood method using single and/or multiple calibrations were inconsistent among calibrations and did not fit the fossil record.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.