Asteropyginae Research Papers - Academia.edu (original) (raw)

Three new Lower Devonian dalmanitid trilobite taxa are recognized from the Talacasto Formation in the Precordillera Basin, Argentina, which includes two monospecific genera (Ivanites leonorae n. gen., n. sp. and Aguaditaspis mediaspina n.... more

Three new Lower Devonian dalmanitid trilobite taxa are recognized from the Talacasto Formation in the Precordillera Basin, Argentina, which includes two monospecific genera (Ivanites leonorae n. gen., n. sp. and Aguaditaspis mediaspina n. gen., n. sp.), and one additional new genus and species left in open nomenclature. These taxa combine characters of the subfamilies Dalmanitinae Vogdes, 1890 and Synphoriinae Delo, 1935, challenging their taxonomic distinction. Forty percent of the dalmanitids from high paleolatitudinal basins from southwestern Gondwana (Malvinokaffric) exhibit non-homologous dorsal spinosity. Aguaditaspis mediaspina n. gen., n. sp. shares similar spines with Trypaulites calypso (Hall, 1861). The unnamed new genus resembles the spinosity of endemic Malvinokaffric dalmanitids, like Dalmanitoides Delo, 1935 and Fenestraspis Braniša & Vaněk, 1973. Considered defensive, the recorded spinosity along with putative sublethal-attack marks, suggest higher predation pressure...

Traditionally, the evolutionary scenarios of Asteropyginae have been organized in two major clades involving four pygidial patterns. The first cladistic analysis performed on the subfamily maintained the organization in two clades, though... more

Traditionally, the evolutionary scenarios of Asteropyginae have been organized in two major clades involving four pygidial
patterns. The first cladistic analysis performed on the subfamily maintained the organization in two clades, though the
phylogenetic relationships between genera were unexpected compared to the traditional scenarios. Moreover, the previous
systematic scheme based on pygidial segmentation was rendered obsolete. In this study, we performed a new phylogenetic
analysis from well-known taxa and recent discoveries. Sixty species assigned to 36 genera have been analysed from a
dataset of 72 characters. Three more species are used as the outgroup. The 79 most parsimonious trees have a length of
492 steps and a retention index of 0.735. Our analysis confirms the monophyly of Asteropyginae excluding the genus
Protacanthina. The phylogenetic pattern is unconventional in that a largely pectinate topology is resolved, rather than two
clades corresponding to formerly delimited pygidial morphs. Nevertheless, most relationships between genera suggested in
the traditional evolutionary scenarios of the subfamily have been recovered, the main differences being the origin of the
group. Whereas Treveropyge was usually considered as the origin of the remaining Asteropyginae, the present results instead
identify Destombesina as the sister group to all remaining members of the subfamily. From the new phylogenetic pattern,
the diagnoses of genera are rewritten in a standard way and to delimit clades more accurately. This work implies modified
generic assignments for some species and the erection of four new genera: Minicryphaeus gen. nov., Gandlops gen. nov.,
Morzadecops gen. nov. and Pennarbedops gen. nov. The systematic position of Erbenochile is also discussed, the genus no
longer being assigned to Asteropyginae.

During the Devonian the sedimentation on the continental shelves of Ardenne Massif and Boulonnais has changed from a mixed siliciclastic-carbonate ramp (Eifelian), through a carbonate barrier reef (Givetian) and then to a detritic influx... more

During the Devonian the sedimentation on the continental shelves of Ardenne Massif and Boulonnais has changed from a mixed siliciclastic-carbonate ramp (Eifelian), through a carbonate barrier reef (Givetian) and then to a detritic influx with local mud-mounds (Frasnian). Here we analysed the faunistic dynamics of the trilobite associations through the changing environment. We used multivariate analyses (clustering and ordering) to discriminate the trilobite associations within 67 different samples. Three previously known communities and one new were recognised: the Eifelian Mixed association, the Givetian Dechenella association and the two Frasnian Bradocryphaeus and Scutellum-Goldius associations. These trilobite faunas present a progressive ecological specialisation. The Mixed association occurs both in the ramp or carbonated (local reef developed on the ramp) facies without any significant difference in its composition. The Dechenella fauna occurs preferentially close to barrier reefs, but can also survive during short periods of detrital input. The two Frasnian communities show a strong relationship with their environment. The Scutellum-Goldius association is only found in reef systems, whereas the Bradocryphaeus flourishes exclusively in lateral facies.