The Permian and Triassic palaeogeography of the Alpine region originated a peculiar geological situation, now well exposed in several sections, in which marine sediments, continental deposits, and volcanites interfinger. The study of the resulting mixed sections allowed to build a framework of biostratigraphic and chronological data in which tetrapod footprints play a key role (e.g., Avanzini & Mietto, 2008). Global track record is much more abundant than the skeletal record and, although suffering from problems related to a correct attribution to the trackmakers, provides data as reliable as those obtained from skeletal remains (Carrano & Wilson, 2001 and references therein). During the Permian and the Early-Middle Triassic, tetrapods, and especially reptiles, radiated and entire new land-dwelling groups originated (e.g., the archosaurs). Consequently, in this temporal interval the tetrapod track record shows a huge increase in variability reflecting the morphological diversity spanning from a stem-reptile to a 'mammalian' foot, from basal crocodilomorph to a dinosauromorph foot. How is this pattern documented in the Dolomites region and surrounding areas (Southern Alps, NE Italy)? In this geographical sector the recent discovery of many new tetrapod footprint-bearing outcrops has yield to a phase of renewed interest for ichnological data. As a result, the stratigraphical, palaeoecological and palaeogeographical importance of tetrapod footprints in this geographical sector is becoming more and more widely acknowledge. In this contribution we provide an overview of Permian and Triassic tetrapod faunal composition as deduced from the study of several ichnosites located in the Italian Southern Alps with special reference to the pattern exhibited around the PT boundary.
Abstract— We report the discovery of two large tridactyl footprints from the late Carnian (Tuvalian) of theSouthern Alps (NE Italy). The tracks can be confidently attributed to a dinosaur trackmaker with an estimatedbody length of about 5 meters. These specimens are part of a diverse ichnofauna testifying to the coexistence oflarge and small dinosaurs, dinosauriforms and crurotarsans. The track-bearing layers are well time-constrained, andprovide one of the earliest reliable evidence of dinosaurs in northern Pangea. INTRODUCTION The early diversification of dinosaurs is a long-standing debate invertebrate paleontology. The osteological record suggests that the dino-saur stem lineage (“Dinosauromorpha”) appeared in the latest Anisian(Nesbitt et al., 2010) and that “true” dinosaurs appeared in the earlyCarnian (Benton, 1983; Sereno and Arcucci, 1994; Sereno, 1999; Irmis etal., 2007; Brusatte et al., 2010; Ezcurra, 2010; Langer et al., 2010). Thetrack record, although known to be of problematic interpretation, hasyielded tracks attributed to dinosauromorph trackmakers from theOlenekian (Haubold, 1999; Haubold and Klein, 2002; Gand and Demathieu,2005; Klein and Haubold, 2007; Brusatte et al., 2010) and tridactyltracks referred to dinosaurs from the Ladinian (Marsicano et al., 2007).In the past, the Late Triassic was described as the period of thecompetitive replacement of faunas dominated by crurotarsan archosaursby those dominated by dinosaurs (Bakker, 1972; Charig, 1984). New,rigorous analysis of the body fossil record together with new discoverieshave, however, shown that during the Late Triassic, crurotarsans hadtwice the variety of body plans, lifestyles, and diets of dinosaurs duringthe first 25–30 million years of dinosaur history (Brusatte et al., 2008,2010, 2011; see also, Benton, 1983; Sereno, 1999). In addition tocrurotarsans, Triassic dinosaurs lived together with dicynodont synapsids(Dzik et al., 2008) and coexisted with dinosauromorphs for at least 20million years (Irmis et al., 2007) becoming dominant in Mesozoic terres-trial ecosystems only from the Jurassic (Brusatte et al., 2010, 2011).These studies have also shown that Late Triassic terrestrial vertebrateassemblages vary significantly in taxonomic composition, diversity andabundance (Irmis, 2011) thus highlighting the importance of local andregional studies to test current hypothesis on the early diversification ofdinosaurs (Irmis et al., 2007; Dzik et al., 2008; Nesbitt et al., 2009;Ezcurra, 2010).Here we describe new large tridactyl tracks that increase theichnofaunal diversity recently described by some of us (D’Orazi Porchettiet al., 2008) and document the co-occurrence of large and middle-sizeddinosaurs, dinosauriforms and crurotarsans in the late Carnian (Tuvalian)of the Southern Alps.
Vertebrate ichnology has proved to be a valuable tool for reconstructing tetrapod locomotion. Grounding on 1, the discovery of a new, exceptionally preserved Amphisauropus trackway (Permian Orobic Basin, Northern Italy), showing continuous tail and pedal scratch impressions; and 2, a comparative analysis of track and bony records, we provide a first synapomorphy-based attribution of Amphisauropus tracks to their most plausible producers, seymouriamorph reptiliomorphs, and propose a detailed reconstruction of the locomotion biomechanics in this group. The markedly sinuous and continuous tail impression with a relatively constant width, the curve arrangement of pedal scratches and the inferred position of head, trunk and tail during the locomotion suggest large lateral movements, while vertical movements were nearly absent, consistently with a primitive sprawling gait. We also document the functional prevalence of the hindlimbs and provide a detailed description of femur biomechanics during step cycle. Trackway parameters suggest that the speed was quite slow: a comparison with a large database of Amphisauropus trackways from Italy and Germany proves that this peculiar preservation was gait- and substrate-related, rather than trackmaker-related. In all, this study sheds light on the locomotion of Seymouriamorpha and aimed to contribute to a full integration of track and skeletal data in exploring locomotory biomechanics of extinct tetrapods.
Summary of counts of different categories of skeletal taxa, by tetrapod fauna and summary of counts of different categories of footprints, by ichnofauna
An Erpetopus trackway recorded in the Lower Permian Collio Formation (Orobic Alps, northern Italy) is investigated as a source of data to reconstruct ancestral patterns of locomotion in eureptiles. The inferred small-sized captorhinid-"protorothyridid" producer cut an inclined muddy surface dragging its front limb digits, tail, and belly on the ground. Integrating ichnological and anatomical data we suggest that small captorhinids ("protorothyridids") locomotion was performed with an obligatory, rigid sprawling posture with the trunk only slightly lifted from the substrate in a low, sprawled 'belly walk'.
Phylogenetic tree shape varies as the evolutionary processes affecting a clade change over time. In this study, we examined an empirical phylogeny of fossil tetrapods during several time intervals, and studied how temporal constraints manifested in patterns of tree imbalance and character change. The results indicate that the impact of temporal constraints on tree shape is minimal and highlights the stability through time of the reference tetrapod phylogeny. Unexpected values of imbalance for Mississippian and Pennsylvanian time slices strongly support the hypothesis that the Carboniferous was a period of explosive tetrapod radiation. Several significant diversification shifts take place in the Mississippian and underpin increased terrestrialization among the earliest limbed vertebrates. Character incompatibility is relatively high at the beginning of tetrapod history, but quickly decreases to a relatively stable lower level, relative to a null distribution based on constant rates of character change. This implies that basal tetrapods had high, but declining, rates of homoplasy early in their evolutionary history, although the origin of Lissamphibia is an exception to this trend. The time slice approach is a powerful method of phylogenetic analysis and a useful tool for assessing the impact of combining extinct and extant taxa in phylogenetic analyses of large and speciose clades.
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