Acta Palaeontologica Polonica 

About: Acta Palaeontologica Polonica is an academic journal published by Institute of Paleobiology. The journal publishes majorly in the area(s): Devonian & Cretaceous. It has an ISSN identifier of 0567-7920. It is also open access. Over the lifetime, 2052 publications have been published receiving 39177 citations.

Remarks on the evolution Of Ordovician conodonts

Abstract: Introduction Principles of taxonomy of conodonts The course of the phylogeny Organization of the "apparatus" of branching conodonts Affinities of Conodontophorida The outline of evolution of Conodontophorida Regularities in eyolution of conodont" Diagnoses of ne\v taxa List of synonymes References Frequency of conodonts in samples 395 :\95 396 398 413 416 417 420 421 42:") 447 454 Abstract. The phylogeny of Ordovician Conodontophorida from the Baltic region is reconstructed and homologization of elements of the natural assemblages is presented. A reconstruction of the apparatus of Spathognathodontidae indicates that it was a bilateral medial organ composed of 14 conodonts with dentides turned inwards. Attempts are made to homologize the tissue of conodonts Panderodontidac with enamel of dermal dentides of lower Ve,tebrata and the basal filling tissue with dentine. A common phenomenon in conodont evolution is the occurrence of morphological gradient within the apparatus. The evolutionary changes are introduced polarly, and successively spread from the most rapidly evolving element on the adjoining ones. Fifty six species and subspecies of Ordovician conodonts are illustrated and their synonymes given. Two new suborders, three genera, seven species and three temporal subspecies are proposed. The phylogeny of Ordovician Conodontophorida from the Baltic region is reconstructed and homologization of elements of the natural assemblages is presented. A reconstruction of the apparatus of Spathognathodontidae indicates that it was a bilateral medial organ composed of 14 conodonts with dentides turned inwards. Attempts are made to homologize the tissue of conodonts Panderodontidac with enamel of dermal dentides of lower Ve,tebrata and the basal filling tissue with dentine. A common phenomenon in conodont evolution is the occurrence of morphological gradient within the apparatus. The evolutionary changes are introduced polarly, and successively spread from the most rapidly evolving element on the adjoining ones. Fifty six species and subspecies of Ordovician conodonts are illustrated and their synonymes given. Two new suborders, three genera, seven species and three temporal subspecies are proposed.

In quest for a phylogeny of Mesozoic mammals

Abstract: We propose a phylogeny of all major groups of Mesozoic mammals based on phylogenetic analyses of 46 taxa and 275 osteological and dental characters, using parsimony methods (Swofford 2000). Mammalia sensu lato (Mammaliaformes of some authors) are monophyletic. Within mammals, Sinoconodon is the most primitive taxon. Sinoconodon, morganu− codontids, docodonts, and Hadrocodium lie outside the mammalian crown group (crown therians + Monotremata) and are, successively, more closely related to the crown group. Within the mammalian crown group, we recognize a funda− mental division into australosphenidan (Gondwana) and boreosphenidan (Laurasia) clades, possibly with vicariant geo− graphic distributions during the Jurassic and Early Cretaceous. We provide additional derived characters supporting these two ancient clades, and we present two evolutionary hypotheses as to how the molars of early monotremes could have evolved. We consider two alternative placements of allotherians (haramiyids + multituberculates). The first, supported by strict consensus of most parsimonious trees, suggests that multituberculates (but not other alllotherians) are closely re− lated to a clade including spalacotheriids + crown therians (Trechnotheria as redefined herein). Alternatively, allotherians can be placed outside the mammalian crown group by a constrained search that reflects the traditional emphasis on the uniqueness of the multituberculate dentition. Given our dataset, these alternative topologies differ in tree−length by only ~0.6% of the total tree length; statistical tests show that these positions do not differ significantly from one another. Simi− larly, there exist two alternative positions of eutriconodonts among Mesozoic mammals, contingent on the placement of other major mammalian clades. Of these, we tentatively favor recognition of a monophyletic Eutriconodonta, nested within the mammalian crown group. We suggest that the “obtuse−angle symmetrodonts” are paraphyletic, and that they lack reliable and unambiguous synapomorphies.

Cranial anatomy of tyrannosaurid dinosaurs from the Late Cretaceous of Alberta, Canada

Abstract: Beautifully preserved, nearly complete theropod skeletons from Alberta (Canada) allow re−evaluation of the taxonomic status of North American tyrannosaurids. It is concluded that the most parsimonious interpretation of relationships leads to the separation of the two species of Albertosaurus (sensu Russell 1970) into Gorgosaurus libratus from the Campanian Dinosaur Park Formation and Albertosaurus sarcophagus from the upper Campanian/lower Maastrichtian Horseshoe Canyon Formation. Albertosaurus and Gorgosaurus are closely related, but can be distinguished from each other by more characters than are known to justify generic distinction within another tyrannosaurid clade that includes Daspletosaurus, Tarbosaurus and Tyrannosaurus. Daspletosaurus is known from multiple species that cover extensive geographic, eco− logical and temporal ranges, and it is sensible to maintain its generic distinction from Tyrannosaurus. All tyrannosaurid species have consistent ontogenetic trends. However, one needs to be cautious in assessing ontogenetic stage because many characters are size−dependent rather than age−dependent. There are relatively few osteological differences that can distinguish tyrannosaurid species at any age. For example, Nanotyrannus lancensis is probably a distinct species from Tyrannosaurus rex because there is no evidence of ontogenetic reduction of tooth counts in any other tyrannosaurid spe− cies. Some characters that are good for separating mature tyrannosaurids, such as differences in the sizes and shapes of maxillary fenestrae, are not useful for identifying the species of juveniles.

Three-dimensional micro- and nanostructural characteristics of the scleractinian coral skeleton: A biocalcification proxy

Abstract: The contemporary “two-step model” of growth of the scleractinian skeleton is based mostly on transversely sectioned samples. According to this model, many skeletal elements e.g., septa are formed in two temporally distinct phases represented by (1) “centers of calcification” that are composed of homogenously distributed microcrystalline or/and organic components and serve as scaffolding for the further growth of (2) fibrous skeleton. Based on transverse and longitudinal sections and histochemical staining techniques, I demonstrate herein that in extant corals (i.e., Stephanocyathus, Flabellum, Desmophyllum, “Ceratotrochus”, Galaxea, Platygyra), the entire septal skeleton is composed of superimposed layers of mineral and organic-enriched phases. These may be interrupted in some directions of growth but in other directions there is continuity between “centers of calcification” and “fibers”, making any distinction between these two structures unclear. As an alternative to the “two-step model”, a “layered model” of skeletal growth is proposed, that explains the differences between “centers of calcification” and “fibers” in terms of differential growth dynamics between these regions. Instead of the traditional but inadequate “trabecular” and “centers of calcification” concepts, a distinction between deposits of the Rapid Accretion Front (dRAF; which in particular cases can be organized into Centers of Rapid Accretion (CRA), and Thickening Deposits (TD) is proposed. In the dRAF region, mineral components, ca. 50 nm in diameter, seem to match the size range of nodular structures recently interpreted as nascent CaCO3 crystals. Remarkable regularity of the mineral/organic phase alternations (microbanding) in the TD skeleton of zooxanthellate corals and lack of such regular microbanding in azooxanthellate coralla is a promising criterion for distinguishing these two ecological coral groups on a skeletal basis, and one that could be applicable to fossils.

Classification of fossil eggshells of amniotic vertebrates

Abstract: MIKHAILOV K. E.: Classification of fossil eggshells of amniotic vertebrates. Acta Palaeont. Polonica, 36, 2, 193-238. Fossil avian and reptilian eggs and eggshells, from the Cretaceous of Mongolia and USSR (Kazakhstan, Zaisan basin) as well as samples of dinosaurian and the Eocene avian eggshells from USA, China, France and Argentina were studied. Methodological, terminological and biomineralization aspects of eggshell structure are discussed. Considered are different classifications of eggshell according to the structural levels of eggshell matter organization (texture. general histostructure, superficial morphology). Basic types, morphotypes, types of pore system and types of surface ornamentation are the main structural categories employed in the systematic description of fossil material. About 18 groups of fossil eggshells referred to turtles, geckoes, crocodiles, and to 14 "families" or dinosaur and bird oological remains are described. Their composition, occurence, paleobiology and systematics are shortly presented.