Marcela Cichowolski | Universidad de Buenos Aires (original) (raw)

Papers by Marcela Cichowolski

Palaeontologia Electronica, 2023

Here we study the variation of the Paleozoic to Mesozoic ammonoid whorl profile shape (WPS, in p... more Here we study the variation of the Paleozoic to Mesozoic ammonoid whorl profile
shape (WPS, in previous contributions referred as the whorl cross-section shape)
employing a geometric morphometric approach, virtual modelling, and statistical tools
to assess possible biological phenomena. For this approach, a dataset covering 300
individuals (each belonging to a different genus) was generated from revised specimens and published literature data. From this dataset, we proposed several predictors (e.g., several size parameters) that could be applied in linear models using the principal components (resulting from the geometric morphometric analyses) as response variables. The whorl profile area from the specimens was calculated from virtual models of their original whorls. The results show that the variation in the whorl profile in this sample is resumed by 10 principal components, of which the first three cover 87% of the total variation. PC1 (54.5%) illustrates transformations mainly from the degree of compression and, to a lesser extent, the degree of whorl overlap. Furthermore, the statistical results indicate a significant association between PC1 with several ammonoid subtaxa and whorl size. A correlation between PC1 and the whorl area is also recognised. PC2 (24.8%) reflects morphological transformations that emulates stretching and compression of the whorl profile shape; it is likely related to the hydrodynamic performance of the resulting conch morphology. PC3 (7.4%) encompasses changes on the shape of the venter (from flat to rounded), and the curvature of the flanks, and it seems to be related to minor modifications required to achieve some extreme shapes.

Geological Society of America Abstracts with Programs

BMC Biology

Background Despite the excellent fossil record of cephalopods, their early evolution is poorly un... more Background Despite the excellent fossil record of cephalopods, their early evolution is poorly understood. Different, partly incompatible phylogenetic hypotheses have been proposed in the past, which reflected individual author’s opinions on the importance of certain characters but were not based on thorough cladistic analyses. At the same time, methods of phylogenetic inference have undergone substantial improvements. For fossil datasets, which typically only include morphological data, Bayesian inference and in particular the introduction of the fossilized birth-death model have opened new possibilities. Nevertheless, many tree topologies recovered from these new methods reflect large uncertainties, which have led to discussions on how to best summarize the information contained in the posterior set of trees. Results We present a large, newly compiled morphological character matrix of Cambrian and Ordovician cephalopods to conduct a comprehensive phylogenetic analysis and resolve ...

En este trabajo se describen Cymatoceras perstriatum (Steuer), del Cretacico Inferior de la cuenc... more En este trabajo se describen Cymatoceras perstriatum (Steuer), del Cretacico Inferior de la cuenca Neuquina (centro-oeste argentino) y C. patagonicum Cichowolski del Turoniano de la cuenca Austral (sur argentino), junto con otras formas de Cymatoceras indeterminadas de esta misma cuenca, cuya preservacion es regular y sus edades varian entre el Hauteriviano y el Campaniano. De la cuenca James Ross (Antartida) se describe material asignado a Eutrephoceras subplicatum (Steinmann) (que tambien se encuentra en la cuenca Austral), Eutrephoceras antarcticum Cichowolski et al. y un ejemplar de Eutrephoceras indeterminado. Todas estas especies tienen una edad cretacica tardia. Se incluyeron estas especies en un analisis filogenetico, junto con especies post-triasicas de otros generos, y mediante el metodo de pesos implicados se obtuvo un solo arbol con maximo ajuste, en el cual ni Cymatoceras, ni Eutrephoceras, son monofileticos. Tampoco resulta monofiletica la familia Cymatoceratidae en es...

Ordovician cephalopods from Western Gondwana are still poorly known and published data is in need... more Ordovician cephalopods from Western Gondwana are still poorly known and published data is in need of systematic and stratigraphical revision. In this work, the endocerid proterocameroceratid Protocyptendoceras from the Floian of the Eastern Cordillera of Argentina is revised using new material from La Ciénaga, 5 km upstream from Purmamarca. The species P. corvalani and P. teicherti are considered to be junior synonyms of P. fuenzalidae, which is redescribed in detail and reillustrated. Specimens preserve adapical parts of isolated siphuncles, related here to the presence of endocones in a posterior portion. Evidently P. fuenzalidae had a nektobenthic mode of life in a shallow water environment, oriented horizontally. Its palaeobiogeographical affinities are mainly with Floian proterocameroceratids from Eastern Gondwana, such as Anthoceras decorum and the related genera Lobendoceras, Ventroloboceras, and Notocycloceras.

Journal of Paleontology, 2005

... Ameghiniana, 31:291-297.[GeoRef]. Fernández, M. 1999. A new ichthyosaur from Los Molles Forma... more ... Ameghiniana, 31:291-297.[GeoRef]. Fernández, M. 1999. A new ichthyosaur from Los Molles Formation (Early Bajocian) Neuquén Basin, Argentina. ... 1996. Bone histology as a clue in the interpretation of functional adaptations in the Thalattosuchia (Reptilia, Crocodylia). ...

Ameghiniana, 2008

Fil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de... more Fil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina

Acta Palaeontologica Polonica, 2020

Based on three specimens assigned to Arthrophyllum sp., the family Lamellorthoceratidae is report... more Based on three specimens assigned to Arthrophyllum sp., the family Lamellorthoceratidae is reported from the Lower Devonian Talacasto Formation in the Precordillera Basin, central western Argentina. These Devonian cephalopods have been known only from low to mid palaeolatitudes and its presence in the cold water settings of southwestern Gondwana is notable. A nektonic mode of life, not strictly demersal but eventually pelagic, with a horizontal orientation of the conch is proposed for adults lamellorthoceratids, whereas a planktonic habit is suggested for juvenile individuals. These features would had allow their arrival to this southern basin, explaining their unusual presence in the Malvinokaffric Realm, and reinforcing the need of re-evaluate the distribution pattern of several groups of cephalopods.

Journal of Paleontology, 2018

Ascocerid cephalopods are described for the first time from high paleolatitudes of Gondwana. Stud... more Ascocerid cephalopods are described for the first time from high paleolatitudes of Gondwana. Studied material was collected from the Hirnantian?–Llandovery strata of the Eusebio Ayala and Vargas Peña formations, Paraná Basin, southeastern Paraguay. The specimens are poorly preserved and were questionably assigned to the subfamily Probillingsitinae Flower, 1941, being undetermined at genus and species rank because diagnostic characters are not visible. A particular feature seen in our material is the presence of both parts of the ascocerid conch (the juvenile or cyrtocone and the mature or brevicone) joined together, which is a very rare condition in the known paleontological record. The specimens are interpreted as at a subadult stage of development because fully grown ascocerids would have lost the juvenile shell. A planktonic vertical migrant mode of life with a subvertical attitude is proposed for the juvenile, and a horizontal demersal nektonic mode for the adult form, as has be...

Journal of Paleontology, 2017

Devonian bactritids are described for the first time from South America. They come from silicicla... more Devonian bactritids are described for the first time from South America. They come from siliciclastic rocks of the Talacasto Formation in the Precordillera Basin, west-central Argentina. The host strata span the Lochkovian–Emsian and contain other non-ammonoid cephalopods as well, thus refuting the alleged virtual absence of cephalopods in circumpolar Devonian basins from southwestern Gondwana (the Malvinokaffric Realm). We report Bactrites gracilis and Devonobactrites? sp., whose wide distribution contrasts with the endemic paleobiogeographic signature of some other taxonomic groups in these basins. Furthermore, new Lochkovian and Pragian records of Bactrites sp. provide new insights into the earliest bactritid records worldwide.

PALAIOS, 2016

Abstract Shell morphology affects multiple aspects of the biology of ectocochleate cephalopods (e... more Abstract Shell morphology affects multiple aspects of the biology of ectocochleate cephalopods (e.g., floatability, life habit, post mortem behavior of the shell, etc.), so it should impact the establishment and development of sclerobiont faunas as well. In this study, the sclerobiont faunas of Weavericeras vacaense (a spherocone) and Holcoptychites agrioensis (a discocone), two early Hauterivian ammonites from the Agrio Formation (Neuquén Basin, Argentina) were compared. The coeval nautilid Cymatoceras perstriatum (studied previously), was contrasted with both ammonites. Results show that the three sclerobiont faunas had similar abundance, taxonomic composition and distribution of individuals across the shells, but H. agrioensis showed a markedly reduced richness, with a fauna almost entirely composed by the oyster Amphidonte (Ceratostreon) sp. The more evolute and compressed H. agrioensis sank more quickly than W. vacaense and C. perstriatum, which may have undergone longer periods of flotation and exposure on the sea bottom. This agrees with the lower taxonomic richness of the sclerobiont fauna and a better overall preservation of H. agrioensis specimens. Differences in the sclerobiont faunas are greater across variations in shell inflation and coiling degree than across nautilids and ammonites; therefore, the latter are important parameters for the sclerobiont fauna as well since they impact how long shells will float and be exposed on the seafloor, and therefore on their time of exposure. The presence of an almost monospecific fauna in H. agrioensis, despite its rapid sinking and burial, indicates that Amphidonte (Ceratostreon) sp. was the earliest settler, and could abundantly colonize hard substrates in a short time.