Application of numerical cladistic analyses to the Carnian-Norian conodonts: a new approach for phylogenetic interpretations
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Data di Pubblicazione:
2010
Citazione:
Application of numerical cladistic analyses to the Carnian-Norian conodonts: a new approach for phylogenetic interpretations / M. Mazza, A. Cau, M. Rigo. ((Intervento presentato al convegno New Developments on Triassic Integrated Stratigraphy tenutosi a Palermo nel 2010.
Abstract:
The high intraspecific variability of conodonts in the upper
Carnian-lower Norian interval and the proliferation of numerous
species in this relatively short stratigraphical time
generated many problems in the understanding of the Late
Triassic conodonts phylogeny, systematic and taxonomy.
The abundance of synonymies per species and the absence
of an established phylogenetic model contribute to
increase the issues concerning the conodonts systematic.
Unfortunately, being natural assemblages of the Late
Triassic conodont apparatuses still unknown, a multielement
approach to the problem would just introduce more
biases instead of solutions. The application of cladistic
methods to the platform elements, instead, may provide an
extremely valid methodology in the understanding of their
evolutionary relationships. Platforms are in fact the most
abundant conodont elements and they have well observable
evolutionary patterns and, thus, they can be considered as
the primary basis for the interpretation of the Late Triassic
conodont phylogeny.
We applied numerical cladistic analysis to the species belonging
to the five most widespread Late Triassic genera
(Paragondolella, Carnepigondolella, Metapolygnathus,
Epigondolella and Norigondolella) from the Pizzo Mondello
section (Sicani Mountains, Western Sicily, Italy),
GSSP candidate for the Norian (Mazza et al., 2010 and
references therein). This section provides several advantages
for these kind of taxonomic and cladistic studies
on conodonts: the section is a continuous succession of
pelagic carbonate sediments (Calcari con selce or Halobia
Limestone auctorum; Cherty Limestone, Muttoni et al.
2001, 2004; Guaiumi et al. 2007), characterized by uniform
facies, high sedimentation rates and, more important, it has
a rich conodont record which is representative of faunas
spread in the entire Tethys.
A taxon-character data matrix describing the distribution of
68 characters among 2 outgroup and 32 ingroup taxa was thus compiled and processed using PAUP* 4.1.
The analyses confirmed the validity of a series of evolutionary
trends among the platform elements, evidenced
the most important morphological characters for their
classification and led to a reinterpretation of the phylogenetic
position of the genera considered: Metapolygnathus
and Epigondolella resulted the only two monophyletic
groups and, thus, true phylogenetic genera; Paragondolella
a polyphyletic assemblage of basal members of
the ingroup; Norigondolella a paraphyletic series of taxa
bracketed by Paragondolella and Carnepigondolella a
paraphyletic group including all conodonts more derived
than Paragondolella and Norigondolella but outside the
Metapolygnathus and Epigondolella clades.
These results show the potentiality of applying cladistic
methods also to parataxonomic taxa. Parsimoniously
grouping by synapomorphies (shared derived characters)
provides a more informative classification than using
simple similarities (phenetics). A cladogram, in fact,
describing more of the character state changes than a phenogram,
gives a higher information content and provides
a more natural classification.
Tipologia IRIS:
14 - Intervento a convegno non pubblicato
Elenco autori:
M. Mazza, A. Cau, M. Rigo
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