Jerzy Dzik

A BEAKED HERBIVOROUS ARCHOSAUR WITH DINOSAUR AFFINITIES FROM THE EARLY LATE TRIASSIC OF POLAND

Abstract An accumulation of skeletons of the pre-dinosaur Silesaurus opolensis, gen. et sp. nov. is described from the Keuper (Late Triassic) claystone of Krasiejów in southern Poland. The strata are correlated with the late Carnian Lehrberg Beds and contain a diverse assemblage of tetrapods, including the phytosaur Paleorhinus, which in other regions of the world co-occurs with the oldest dinosaurs. A narrow pelvis with long pubes and the extensive development of laminae in the cervical vertebrae place S. opolensis close to the origin of the clade Dinosauria above Pseudolagosuchus, which agrees with its geological age. Among the advanced characters is the beak on the dentaries, and the relatively low tooth count. The teeth have low crowns and wear facets, which are suggestive of herbivory. The elongate, but weak, front limbs are probably a derived feature.

Anatomical information content in the ediacaran fossils and their possible zoological affinities.

Abstract Various modes of preservation of Ediacaran fossils in different sediments, quartz sand at Zimnie Gory in northern Russia and lime mud at Khorbusuonka in northern Yakutia, show that the sediment was liquid long after formation of the imprints and that its mineralogy did not matter. A laminated 2 mm thick microbial mat is preserved intact at Zimnie Gory. It stabilized the sediment surface allowing formation of imprints on it. The soft body impressions on the under surface of the sand bed and within it developed owing to formation of a less than 1 mm thin “death mask” by precipitation of iron sulfide in the sediment. Fossils of the same species or even parts of the same organism may be preserved differently. Internal organs either collapsed, their cavities being filled with sediment from above, or resisted compression more effectively than the rest of the body. This allows restoration of the original internal anatomy of Ediacaran organisms. At Zimnie Gory numerous series of imprints of Yorgia on the clay bottom surface with the collapsed body at their end represent death tracks. The environment of formation of the Ediacaran fossils was thus inhospitable to most organisms. Those adapted to it, namely the radially organized frondose Petalonamae (of possible ctenophoran affinities), anchored in the mat with their basal bulbs. They evolved towards sessile life possibly in symbiosis with photo- or chemoautotrophic microorganisms. Vagile Ediacaran organisms belong mostly to the Dipleurozoa (somewhat resembling chordates and nemerteans), characterized by a segmented dorsal hydraulic skeleton, intestine with metameric caeca, and serial gonads. Only a fraction of the actual Precambrian faunal diversity is represented in the Ediacaran biota.

Behavioral and anatomical unity of the earliest burrowing animals and the cause of the “Cambrian explosion”

Abstract All interpretable trace fossils from the Ediacarian–Cambrian transition strata of northern Siberia, Ukraine, and elsewhere represent shelters of infaunal animals feeding from the sediment surface. There is a gradation of forms ranging from (1) makers of horizontal galleries in soft sand with bilobed lower surface and proboscis extended to the surface, through (2) linear or zigzag series of short, widely U-shaped burrows in firm clay with bilobed or three-lobed lower surface, to (3) series of cylindrical chambers dug completely inside the sediment but opening to its surface. At the same time, protective skeleton originated in animals living above the sediment surface. Apparently, the diversification of predators in the earliest Cambrian forced other animals to invest energy either in digging or in a protective armor (“the Verdun Syndrome”). True mud-eaters appeared later, as documented by the late Tommotian horizontal spreite structures from central Siberia. Most, if not all, of those infaunal traces of activity were produced probably by relatives of priapulid worms. It appears that body cavities and segmentation in the Metazoa (diverse already in the Ediacarian) evolved independently of, and prior to, hydraulic burrowing.

A dicynodont-theropod association in the latest Triassic of Poland

It is generally accepted that during the Triassic the composi− tion of tetrapod faunas underwent a series of fundamental transformations, mainly as a result of diversification of archosaurs and decline of therapsids (Benton 1994, 2004, 2006). The last herbivorous basal synapsids, dicynodonts, disappeared from the record in the early Norian of the Americas, about 220 Ma (Langer et al. 2007), being un− known from the Late Triassic of Europe. Here, we report a partially articulated skeleton and isolated bones of a giant rhino−size dicynodont in the Upper Triassic fluvial sedi− ments at Lisowice (Lipie Śląskie clay−pit) in southern Po− land. Paleobotanical data indicate an early Rhaetian age for the fauna (Dzik et al. 2008; Niedźwiedzki and Sulej 2008). The dicynodont bones are associated with bones of carnivo− rous dinosaurs, pterosaurs, as well as capitosaur and plagio− saur amphibians. Dicynodonts were represented in the Ger− manic Basin throughout the Late Triassic, as proven by findings of smaller dicynodonts in older deposits in the same area, associated there with temnospondyl amphibians. It ap− pears, thus, that the fossil record of tetrapod succession in the Late Triassic was strongly controlled by ecological fac− tors and biased by uneven representation of particular envi− ronments. The Lisowice assemblage proves that faunas dominated by dicynodonts did not entirely disappear at least until the end of the Triassic.

A New Paleorhinus Fauna in the Early Late Triassic of Poland

A new locality in the middle Keuper marly clays with excellently preserved tetrapod skeletons was discovered at Krasiej?w near Opole, southern Poland (Dzik et al., 2000). It has yielded abundant cranial and postcranial material of metoposaur and capitosauroid labyrinthodonts, phytosaurs, aetosaurs, and undetermined archosaurs. Based on the position of the Krasiej?w fossiliferous horizon in the lithostratigraphic column, it seems to be coeval to the Lehrberg beds in Germany, which probably terminate the Carnian sedimentary cycle. The initial part of the cycle in Germany is the Schilfsandstein, a local rock equivalent of which is represented about 80 m below in boreholes drilled in the area. The labyrinthodont Metoposaurus found at Krasie j?w (Dzik et al., 2000) is conspecific with, or at least closely related to, M. diagnosticus, occurring in these strata in Germany. The phyto saurs from Krasiej?w (Fig. 1) confirm such age determination. They belong to a species of Paleorhinus, geologically the oldest and anatom ically the least derived of phytosaurs (Buffetaut, 1993; Long and Murry, 1995). In all phytosaurs the snout is strongly elongated but the Krasie j?w species is relatively short-snouted. In fact, it shows the shortest snout of known phytosaurs, except for Paleorhinus sawini, based on a single skull from the Colorado City Member of the Dockum Group of Texas and associated with numerous other specimens with longer snouts (Long and Murry, 1995). Although it was widely assumed (e.g., Greg ory, 1969; Gregory and Westphal, 1969; Chatterjee, 1978) that the de gree of its elongation in Paleorhinus expresses an evolutionary ad vancement of particular species, this character seems to vary in the genus. Anyway, the co-occurrence of Paleorhinus with Metoposaurus indicates that the Krasiej?w fauna chronologically belongs to the Late Carnian part of the Paleorhinus biochron of Hunt and Lucas (1991; Lucas, 1998). The basis of the age correlation of that part of the bioch ron (defined on the range of the nominal genus) is a finding of a species indeterminable specimen of Paleorhinus in marine strata of Late Car nian age in the Alps, supported by other tetrapod records and by pal ynological evidence (Lucas, 1998). The oldest specifically identifiable German phytosaur, the long-snouted Paleorhinus broili, represented by several skulls (Kuhn, 1933, 1936), comes from the Blasensandstein of Franconia. Strata presumably corresponding to that horizon terminate the Krasiej?w section. Paleorhinus is represented in the material from Krasiej?w by several skulls, more or less fragmentary articulated postcranial skeletons and numerous isolated bones. Individuals of various ontogenetic stages are represented, forming an ontogenetic series. This may help in evaluating the diagnostic importance of those skull structures which grew allo metrically. Thus, the most complete skeleton is a juvenile (skull length 40 cm) with still unfused centra and neural arches of the trunk vertebrae. Its antorbital fenestra and orbits are larger than in adult specimens (the best preserved skull is 64 cm long, some incomplete specimens are much larger). This may mean that the large size of orbits in the very small skull (27.5 cm long) of Arganarhinus magnoculus from the Iro halene Member of the Timesgadiouine Formation (?rgana Group) of Morocco (Dutuit, 1977; Long and Murry, 1995) is not necessarily of phylogenetic importance but may indicate an early ontogenetic stage. The extraordinary preservation of the Paleorhinus specimens from Kra siej?w supports the interpretation of the palate proposed in the classic works of Lees (1907) and Kuhn (1933, 1936). The palate is completely preserved in at least two skulls from Krasiej?w (Dzik et al., 2000:figs. 5, 6). The choanae are somewhat displaced backward in respect to the external nares in the Krasiej?w species of Paleorhinus, and a short secondary palate is present (Fig. 1A). This is not significantly different from the palate structure of P. bransoni from Texas (Lees, 1907) or the German Paleorhinus broili (see Kuhn, 1936), but not similar to that restored for the Indian Maleri Formation species classified as Parasu chus hislopi by Chatterjee (1978). The Krasiej?w fossil assemblage is dominated by skeletons of semi aquatic amphibians and reptiles, but less numerous bones of strictly terrestrial reptiles are also represented. Among them there is an aetosaur species with isolated scutes that are closely similar to those of Stagon olepis (Walker, 1961). An incomplete illium and two fragmentary den tarles have also been identified. Both dentaries show a toothless rostral

The axial skeleton of Silesaurus opolensis

ABSTRACT A recent find of an articulated skeleton of Silesaurus opolensis at its early Late Triassic type locality Krasiejów (Poland), with skull, neck, pectoral girdle, and thorax, supplemented by additional preparation of previously collected articulated specimens, enables complete restoration of the vertebral column and associated skeletal parts. Cervical ribs of Silesaurus, well preserved in their original disposition, are parallel to the neck and extend backward for a few vertebral lengths. There is a sudden change in their morphology behind the seventh vertebra, although otherwise the transition from the cervical to the dorsal vertebrae is very gradual. Parapophyses slowly migrate upward along the anterior margin of the centrum and leave the centrum at the sixth or seventh dorsal vertebra. Narrowing of the dorsal extremities of the neural spines of the fourth and neighboring vertebrae suggests the ability of this region of the vertebral column to bent upward. There is thus a disparity between the structural and functional neck-thorax transition. The presence of three sacrals firmly connected by their ribs with the ilia and the long tail of Silesaurus, providing a counterbalance to the weight of the body in front of the pelvis, suggests the ability for fast bipedal running. However, unusually long but gracile forelimbs of Silesaurus suggest that it represents a transition towards secondarily quadrupedal locomotion, characterizing most of the later herbivorous dinosaurs.

Organic membranous skeleton of the Precambrian metazoans from Namibia

Unlike the celebrated Ediacara fossils, those from the roughly coeval localities of the Kuibis Quarzite of Namibia are preserved not as imprints on the sandstone bedding plane, but three-dimensionally, within the rock matrix. The pattern of deformation and the presence of sand in lower parts of the bodies of Ernietta , the most common and typical of those organisms, indicate that their three-dimensional preservation is a result of a density-controlled sinking of sand-filled organic skeletons within hydrated mud layers. Specimens of Ernietta have preserved various stages of migration across the mud beds. Their wall material, as documented by the mode of deformation, was not only flexible, but also elastic, which makes it unlike chitin. The walls thus seem to be proteinaceous, built probably of a collagenous fabric. The Ernietta skeleton was built of series of parallel chambers, which excludes the possibility that these were external body covers. The chambers apparently represent walls of hydraulic skeleton units, resembling the basement membrane of chaetognaths or the notochord sheath of primitive chordates. Such chambers are widespread among the earliest fossil animals represented by fossils preserved in sandstone. The rise and fall of the Ediacaran faunas thus seem to be partially preservational artifacts. The range of its occurrence is a result of two successive evolutionary events: the origin of an internal hydraulic skeleton enclosed by a strong basement membrane, and the appearance of decomposers with abilities to disintegrate such collagenous sheaths.

Early Cambrian lobopodian sclerites and associated fossils from Kazakhstan

A low diversity fossil assemblage dominated by Mongolitubulus spines, from the Early Cambrian Geres Member of the Shabakhty Formation at Koksu, Malyi Karatau, Kazakhstan, enables identification of its sclerite variability within the scleritome. No other sclerotised structures could be matched with the spines, indicating that these were the only sclerotised part of the body and were periodically shed. The prominent spines of Mongolitubulus have a scale–like external ornamentation and fibrous internal structure. Possibly they armed the body of a lobopodian similar to Xenusion. The Mongolitubulus spines belong to a series of Cambrian phosphatic fossils, the other end members of which are sclerites of Microdictyon, the second most abundant component of the Koksu assemblage. The latter superficially resemble schizochroal trilobite eyes, but in life covered the dorso–lateral sides of the body segments, as is evident from complete specimens from the Chinese Chengjiang locality. A pair of sclerites of Microdictyon, representing uncompleted exuviation, from Koksu show that each hole originally contained a non–phosphatised lenticular body. This makes a compound eye nature of the Microdictyon sclerites likely, and even their homology with arthropod eyes cannot be excluded.

Ontogeny of Bactrotheca and related hyoliths

Abstract Orthothecid hyoliths Bactrotheca dens (Holm) and B. quadrangidaris (Holm) from the Ordovician of the Baltic province have relatively large, smooth embryonic shells indicating a lecithotrophic type of larval development, probably inside egg capsules. Their embryonic opercula are flat, subcircular in outline. Hatching is marked by the retardation of growth of both operculum and shell, and in the appearance of adult longitudinal sculpture on the shell surface. Juvenile post-embryonic opercula have fully developed structures on their internal side. Bactrotheca probably led a sub-sessile mode of life on its postlarval stages, similar to the Recent gastropod Turritella. Representatives of other hyolith genera, Circotheca stylus (Holm) and Decoritheca excavata (Holm) from the Baltic Cambrian, bear small initial shells with mucros, suggesting a planktotrophic mode of life for the larvae. Data presented here document a high diversity of larval development within particular groups of hyoliths (Monoplacopho...

Early Metazoan Evolution and the Meaning of Its Fossil Record

Much new data on late Precambrian and early Phanerozoic metazoan fossils have recently emerged as a result of discoveries of new fossil sites (Mikulic et al., 1985; Conway Morris, 1989; Hou et al., 1991), reinterpretation of earlier findings (Whittington, 1980; Conway Morris, 1985b; Conway Morris et al., 1987), and application of new paleontological techniques. Chemical extraction from the rock matrix of originally phosphatic or phosphatized skeletal fossils (Rozanov et al., 1969; Qian and Bengtson, 1989;Bengtson et al., 1990; Dzik et al., 1993), as well as finely phosphatized arthropod cuticles and soft tissues (Muller, 1979, 1983; Muller and Walossek, 1985; Andres, 1989) has appeared especially fruitful. The importance of this new source of evidence has been inadequately acknowledged not only in the zoological but even in the paleontological literature, partly because of diverging opinions on the significance of geological age in phylogenetic inference (Patterson, 1981; Briggs and Fortey, 1989).