Data di Pubblicazione:
2005
Citazione:
On the phylogeny of the late Albian genus Planomalina / M.R. Petrizzo, B.T. Huber. ((Intervento presentato al 2005. convegno Mesozoic Planktonic Foraminifera Working Group Meeting tenutosi a Université de Fribourg, Switzerland nel June 6-8, 2005.
Abstract:
The evolution of planktonic foraminifera in the late Albian is characterized by a high rate of turnover (extinction plus speciation) and by a high rate of diversification (speciation minus extinction) (see Leckie and others, 2002 and references herein). The accelerated speciation rate resulted in the appearance of new genera such as Biticinella, Rotalipora, Planomalina and Praeglobotruncana. Among these genera the planispiral and keeled genus Planomalina displays the shortest stratigraphic range, which is totally comprised within the uppermost Albian sediments.
There has been a general consensus among most authors that the late Albian Planomalina lineage was derived from the genus Globigerinelloides (Moullade, 1966, Pessagno, 1967; Longoria, 1974; Wonders, 1975). However, opinions have varied regarding what was the ancestral species. Citing morphological similarities, such as the planispiral coiling mode and the acquisition of keel and raised sutures, Moullade (1966) and Wonders (1975) concluded that Globigerinelloides caseyi (=G. eaglefordensis in Moullade’s study) is the ancestral species of the Planomalina lineage through the evolutionary series from G. caseyi – P. praebuxtorfi - P. buxtorfi. Later Moullade and others (2002) inferred that Globigerinelloides bentonensis gave rise to the planomalinids by progressive development of a peripheral keel and raised sutures through coalescence of muricae. The conclusions of Moullade and others (2002) are based on their studies of topotypes of G. caseyi (the ‘boreal’ species) from the Gault of England and specimens of G. bentonensis (the ‘Tethyan’ species) from various upper Albian levels of ODP Site 1050. These authors believe that the two species are distinct, with the former characterized by a smooth, probably microperforate wall texture that is totally devoid of muricae, whereas G. bentonensis yields a macroperforate wall with moderately developed muricae that are mostly confined to the first chambers of the last whorl.
Our re-examination of the primary type specimens of Planomalina caseyi (USNM 4869) and Anomalina bentonensis (USNM 65381) deposited at the Smithsonian Museum of Natural History (Washington, D.C.) reveal that both species have a smooth and macroperforate surface texture and an identical external morphology. For this reason the two species are considered synonymous, and G. bentonensis is designated as the senior synonym because of priority, as was observed previously by Leckie (1984).
A different origin for the Planomalina lineages was proposed by Radrianasolo and Aglada (1989). These authors considered a trochospiral form, Hedbergella wondersi, as the ancestor of the genus Planomalina through the evolutionary series from Hedbergella wondersi- Globigerinelloides praebuxtorfi - Planomalina pulchella - Planomalina buxtorfi. However, Radrianasolo and Aglada (1989) switched G. praebuxtorfi (a species restricted by their emendation to planispiral forms with globular chambers and therefore assigned to the genus Globigerinelloides) and P. pulchella, probably based on erroneous concepts of both holotypes (see also discussion in Moullade and others, 2002). The aim of this paper is to present an investigation of the ancestor-descendant relationships of the Planomalina lineage based on morphometric comparison of key morphological characters in order to more reliably differentiate the members of this lineage.
The taxonomic characters used in the classification of foraminifera are traditionally based on the external morphology of the adult shell such as (among other features) the mode of coiling of the test (i.e., trochospiral, planispiral), wall texture (smooth, totally or partially muricate) and pore size [microperforate (pores <1 μm), macroperforate (pores >1 μ
Tipologia IRIS:
14 - Intervento a convegno non pubblicato
Elenco autori:
M.R. Petrizzo, B.T. Huber
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