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Urlichs M.,Staatliches Museum fur Naturkunde
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen | Year: 2017

Ammonoid species of the genera Arpadites, Klipsteinia, Muensterites, Protrachyceras, and Sirenotrachyceras from the Cassian Formation/Formazione di San Cassiano of the St. Cassian area/ Dolomites (latest Ladinian-Early Carnian, Triassic, Italy) are revised. Lectotypes are designated for Arpadites busiris, Protrachyceras ladinum, Sirenotrachyceras hadwigae, and Sirenotrachyceras rudolphi. Protrachyceras aequinodosum (KLIPSTEIN) is an older synonym of the late Ladinian Protrachyceras ladinum. In the canadensis Zone of the GSSP Stuoreswiesen/Prati di Stuores, Sirenotrachyceras is absent and the occurrence of Trachyceras is strongly questioned. Klipsteinia, Sirenotrachyceras, and Badiotites are typical ammonoid genera from the aon and aonoides zones of the St. Cassian area. They are missing in the subsequent austriacum Zone of the Dolomites and therefore, the extinction event at the base of this zone is also evident from the ammonoid record. In marlstones of the Cassian Formation mainly juvenile to subadult ammonoids occur; adults are rare. In claystones, mainly early juvenile ammonoids with normal-spaced sutures are present, which deceased premature due to unfavourable life conditions. The only exception is Lobites, where adults predominate both in marl- and claystones. The specimens from marlstones are normal-sized, whereas those from claystones are stunted. © 2017 E.

Schoch R.,Staatliches Museum fur Naturkunde
Paleobiology | Year: 2010

Recent studies have provided detailed insight into life cycles of early amphibians. These ontogenies were diverse and their evolution involved numerous kinds of change, which can now be addressed by comparison of ontogenetic trajectories. The plesiomorphic trajectory included (1) an early period in which a larval, aquatic predator was established, (2) an intermediate period in which the axial skeleton was strengthened, and (3) a final period during which the jaw joint, braincase, and limbs were ossified, producing an adult capable of terrestrial locomotion if completed. Heterochrony, among other factors, enabled the fine-tuning of the ontogenetic formation of ecologically important features (feeding, respiration, locomotion). Most common was a simple truncation of the trajectory that produced aquatic taxa of various kinds, while changes in the ontogenetic sequence often had a deeper impact on morphology. The most fundamental changes were accompanied by multiple heterochronies, resulting in the condensation or unpacking (stretch-out) of developmental events: metamorphosis evolved by an ever closer packing, whereas a novel larval feeding mechanism was established by a pull-apart of numerous critical events. © 2010 The Paleontological Society. All rights reserved.

The genus Trigonopterus Fauvel, 1862 is briefly diagnosed. At present, four junior subjective synonyms of the genus exist: Idotasia Pascoe, 1871, Eurysia Pascoe, 1885, Mimidotasia Voss, 1960 (syn. n.), and Microgymnapterus Voss, 1960 (syn. n.). Trigonopterus vossi nom.n. is proposed as a replacement name of the secondary homonym T. submetallicus (Voss, 1960) nec T. submetallicus Marshall, 1921, and T. micros nom.n. to replace T. minutus (Voss, 1960: 327) nec T. minutus (Voss, 1960: 341). Idotasia nasuta Pascoe is designated type species of Idotasia. Lectotypes are designated for the following names: Eurysia fulvicornis Pascoe, Idotasia ebriosa Pascoe, Idotasia elliptica Pascoe, Idotasia inclusa Pascoe, Idotasia nasuta Pascoe, Idotasia scaphioides Pascoe, and Microgymnapterus minutus Voss. The type species of Trigonopterus, Eurysia, Mimidotasia and Microgymnapterus, as well as the five species included in Pascoe's original description of Idotasia are redescribed: T. ebriosus (Pascoe), T. ellipticus (Pascoe), T. fulvicornis (Pascoe), T. inclusus (Pascoe), T. insignis Fauvel, T. micros nom.n., T. nasutus (Pascoe), T. scaphioides (Pascoe), and T. vossi nom.n. Trigonopterus egenus (Pascoe) is recognized as a junior synonym of T. scaphioides (Pascoe), syn.n. Trigonopterus oblitus sp.n., is described based on specimens labeled as paratypes of Microgymnapterus minutus. Douttia basimaculata Voss 1960 is transferred to Trigonopterus: T. basimaculatus (Voss) comb.n. Trigonopterus insignis Fauvel is endemic to New Caledonia, T. fulvicornis (Pascoe) to Sulawesi; the remaining species treated herein are restricted to parts of New Guinea and Maluku. The record of T. egenus (Pascoe) for New Zealand is incorrect. Copyright © 2011 · Magnolia Press.

Schoch R.R.,Staatliches Museum fur Naturkunde
Journal of Experimental Zoology Part B: Molecular and Developmental Evolution | Year: 2014

Despite their divergent morphology, extant and extinct amphibians share numerous features in the timing and spatial patterning of dermal skull elements. Here, I show how the study of these features leads to a deeper understanding of morphological evolution. Batrachians (salamanders and frogs) have simplified skulls, with dermal bones appearing rudimentary compared with fossil tetrapods, and open cheeks resulting from the absence of other bones. The batrachian skull bones may be derived from those of temnospondyls by truncation of the developmental trajectory. The squamosal, quadratojugal, parietal, prefrontal, parasphenoid, palatine, and pterygoid form rudimentary versions of their homologs in temnospondyls. In addition, failure to ossify and early fusion of bone primordia both result in the absence of further bones that were consistently present in Paleozoic tetrapods. Here, I propose a new hypothesis explaining the observed patterns of bone loss and emargination in a functional context. The starting observation is that jaw-closing muscles are arranged in a different way than in ancestors from the earliest ontogenetic stage onwards, with muscles attaching to the dorsal side of the frontal, parietal, and squamosal. The postparietal and supratemporal start to ossify in a similar way as in branchiosaurids, but are fused to neighboring elements to form continuous attachment areas for the internal adductor. The postfrontal, postorbital, and jugal fail to ossify, as their position is inconsistent with the novel arrangement of adductor muscles. Thus, rearrangement of adductors forms the common theme behind cranial simplification, driven by an evolutionary flattening of the skull in the batrachian stem. © 2014 Wiley Periodicals, Inc.

Schoch R.R.,Staatliches Museum fur Naturkunde
Palaeontology | Year: 2014

In the largest early tetrapod clade, the temnospondyls, ontogenies were diverse and quite distinct from the life cycles of extant amphibians. Three well-studied clades exemplify the diversity of these long-extinct ontogenies, here analysed with respect to their bearing on developmental plasticity, reaction norms and evolution. Sclerocephalus readily adjusted by means of developmental evolution to different lake environments. In addition, plasticity (reaction norm) played a significant role, apparent both morphologically and by altered developmental traits. Size increase and extension of the ontogenetic trajectory gave larger predators, a phenomenon also found in the dissorophoid Micromelerpeton. Whereas Sclerocephalus was throughout preying on the same fishes, Micromelerpeton was able to fit into different trophic levels. In the branchiosaurid Apateon, a biphasic life cycle was established, with metamorphosis producing a terrestrial morph in some species; truncation of the ontogenetic trajectory gave a sexually mature larva as an alternative morph (neoteny). Plasticity was high in the larval morphs, permitting neotenes to live as filter feeders or small carnivores. Fine-tuning of development permitted Apateon populations to adjust to specific lake properties and readily change from a filter-feeding to carnivorous mode of life. In the nonmetamorphosing Triassic Gerrothorax, morphology was extremely conserved, but histology reveals much plasticity at the microscopical level, correlating with fluctuating salinity and water energy. In responding to environmental fluctuations by enhanced plasticity, the studied temnospondyls managed to populate lakes inhabitable to other tetrapods and fishes. © The Palaeontological Association.

Schoch R.R.,Staatliches Museum fur Naturkunde
Historical Biology | Year: 2013

Evolutionary change does not proceed in every direction with equal probability. Evolutionary biases or constraints are limitations on the mode, direction and tempo of evolution. Early tetrapods provide interesting examples, especially Paleozoic and Mesozoic amphibians. (1) Body size had a strong impact on morphology and development in early amphibians, resulting in manifold convergences imposed by design limitations. Miniaturisation had similar effects in a wide range of Paleozoic tetrapods, which are consistent with observations on extant salamanders. Gigantism was a common feature of Triassic temnospondyls, correlating with slow developmental rates similar to those of gigantic salamanders and the convergent evolution of bone density. (2) Ontogeny imposes constraints on evolution by canalised (buffered) developmental sequences. In Paleozoic temnospondyls, ontogenetic trajectories evolved by several different modes (truncation of the trajectory, shifting of events or condensation of events). Metamorphosis is an extreme example of a condensed developmental sequence, which first evolved in Paleozoic temnospondyls, increased in salamanders and culminated in anurans. It imposes strong biases that may be broken by three conceivable modes: (1) loss of the adult period (neoteny), (2) loss of the larval period (direct development) and (3) 'unpacking' of metamorphosis by re-evolving the plesiomorphic trajectory. © 2013 Copyright Taylor and Francis Group, LLC.

Schoch R.R.,Staatliches Museum fur Naturkunde
Journal of Experimental Zoology Part B: Molecular and Developmental Evolution | Year: 2010

Rupert Riedl's concept of burden forms a causal hypothesis on organismic integration and evolutionary constraints. Defined as the hierarchically nested interdependence of characters within the organism, burden was seen as (1) defining and conserving body plans and (2) constraining and directing evolutionary trajectories. A review of the components of the burden concept reveals important consistencies with the modern tenets of evo-devo. This concept differs from the current consensus of evolutionary theory in that it (1) grants evolution less options for changing tightly integrated, "locked-in" characters and (2) in deducing from this an ever decreasing freedom for evolution, with cyclism and typostrophism as resulting macroevolutionary phenomena. Despite these differences, I show that the burden concept was consistent with most major tenets of the Modern Synthesis, and Riedl attempted to explain patterns of large-scale evolutionary trends exclusively by microevolutionary (gradualistic) processes. The burden concept is fruitful and unique in its focus on hierarchically nested constraints and resembles the hierarchical architecture of gene regulatory networks. However, such networks are more high-dimensional and most of their components appear to be easier to evolve than Riedl's burden. Yet in combination with evolvability, a modified concept of burden might contribute substantially to the understanding of organismic integration and the long-term evolution of body plans. © 2009 Wiley-Liss, Inc.

Urlichs M.,Staatliches Museum fur Naturkunde
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen | Year: 2012

Stunting occurs in several fossil assemblages of the Late Triassic Cassian Formation (Early Carnian, Dolomites). It can be shown for the bivalves Palaeonucula strigilata and Prosoleptus lineatus, the scaphopod Plagioglypta undulata, the gastropod Rhaphistomella radians, and for the brachiopods Koninckina leonhardi and Camerothyris subangusta. Previously, stunting had been investigated with statistical methods only in the ammonoid Lobites. Other small ammonoids represent normal-sized early juveniles. Stunting is also absent in sponges, corals, nautiloids, ostracods, and echinoderms. Normal-sized, intermediate, and stunted faunas alternate several times within the Cassian Formation. Hence, the small size is not genetically fixed and is explained as stunting depending on environmental factors. The high percentage of framboidal and finely dispersed pyrite in beds with stunting indicates restricted life conditions at the seafloor. Probably during poorly oxygenated intervals the toxic sulfoxide, which also retards growth and development in Recent marine invertebrates, caused the stunting in the Cassian Formation. The occurrence of stunting correlates with the ends of regressive cycles, when dysoxic conditions occurred more frequently at the termination of the progradation of the adjacent carbonate platforms into the St. Cassian Basin. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.

Maxwell E.E.,Staatliches Museum fur Naturkunde
Journal of Paleontology | Year: 2012

Ichthyosaurs represent one of the most highly specialized lineages of marine reptiles, but our understanding of the evolution of this group is based on specimens found at a surprisingly small number of stratigraphic intervals and localities. The Lower Jurassic (Toarcian) Posidonia Shale of southwestern Germany is one of the richest ichthyosaur-bearing formations in the world and has produced thousands of skeletons, including specimens with preserved soft tissue, and fetal remains inside the body cavity. The most abundant ichthyosaur genus in the Posidonia Shale is Stenopterygius. In spite of almost 200 years of research effort, the number of species in this genus is still a point of active disagreement in the literature. Here, bivariate and multivariate analyses are used to classify both articulated and disarticulated skeletons to the level of species, using measurement data from individual cranial and postcranial elements. Unlike previous classification attempts, this technique pinpoints ontogenetically conserved differences in size and proportion between the species, and so can be applied to adult, subadult, and neonatal specimens. Using this method, three species of Stenopterygius, S. quadriscissus, S. triscissus, and S. uniter are differentiated. © 2012 The Paleontological Society.

Schoch R.R.,Staatliches Museum fur Naturkunde
Neues Jahrbuch fur Geologie und Palaontologie - Abhandlungen | Year: 2011

Isolated bones of archosauriforms form regular finds in deposits of the Lower Keuper (Erfurt Formation: upper Middle Triassic) of southwestern Germany. In addition to the fairly well known 3-5 m long rauisuchian Batrachotomus kupferzellensis and the very fragmentary Zanclodon laevis, remains of further, 1-2 m long archosauriforms have been identified. Although the number of taxa represented by this incomplete material is unknown, the distinctness of these finds from Batrachotomus and Zanclodon is indicated by the following features: (1) a "rauisuchian" type maxilla with well-developed interdental plates, which forms a long suture with a posterodorsal process of the premaxilla, (2) relatively long cervical and anterior dorsal vertebrae, (3) a gracile humerus with a narrow proximal head and a weak deltopectoral crest, (4) a slender and markedly curved tibia, and (5) tear-drop shaped, keeled armour plates. These findings highlight the diversity of large predators in Middle Triassic land vertebrate faunas of Central Europe. ©2011 Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.

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