Robert Niedźwiedzki

Trends in shell fragmentation as evidence of mid-Paleozoic changes in marine predation

Abstract Recent observations indicate that shell fragmentation can be a useful tool in assessing crushing predation in marine communities. However, criteria for recognizing shell breakage caused by durophagous predators versus physical factors are still not well established. Here, we provide data from tumbling and aquarium experiments to argue that physical and biotic processes lead to different patterns of shell damage, specifically that angular shell fragments are good indicators of durophagous predation. Using such angular shell fragments as a predation proxy, we analyze data from 57 European Paleozoic localities spanning the Ordovician through the Mississippian. Our results reveal a significant increase in angular shell fragments (either occurring as isolated valves or present in regurgitalites) in the Mississippian. The timing of this increase is coincident with the increased diversity of crushing predators as well as marked anti-predatory changes in the architecture and mode of life of invertebrate prey observed after the end-Devonian Hangenberg extinction (359 Ma). More specifically, the observed trend in shell fragmentation constitutes strong and independent confirmation of a recently suggested end-Devonian changeover in the primary method of fish predation from shearing to crushing. These results also highlight the important effect of extinction events, not only on taxonomic diversity, but also on the nature of predator-prey interactions.

Drill holes and predation traces versus abrasion-induced artifacts revealed by tumbling experiments.

Drill holes made by predators in prey shells are widely considered to be the most unambiguous bodies of evidence of predator-prey interactions in the fossil record. However, recognition of traces of predatory origin from those formed by abiotic factors still waits for a rigorous evaluation as a prerequisite to ascertain predation intensity through geologic time and to test macroevolutionary patterns. New experimental data from tumbling various extant shells demonstrate that abrasion may leave holes strongly resembling the traces produced by drilling predators. They typically represent singular, circular to oval penetrations perpendicular to the shell surface. These data provide an alternative explanation to the drilling predation hypothesis for the origin of holes recorded in fossil shells. Although various non-morphological criteria (evaluation of holes for non-random distribution) and morphometric studies (quantification of the drill hole shape) have been employed to separate biological from abiotic traces, these are probably insufficient to exclude abrasion artifacts, consequently leading to overestimate predation intensity. As a result, from now on, we must adopt more rigorous criteria to appropriately distinguish abrasion artifacts from drill holes, such as microstructural identification of micro-rasping traces.

Ophiuroids discovered in the middle triassic hypersaline environment.

Echinoderms have long been considered to be one of the animal phyla that is strictly marine. However, there is growing evidence that some recent species may live in either brackish or hypersaline environments. Surprisingly, discoveries of fossil echinoderms in non-(open)marine paleoenvironments are lacking. In Wojkowice Quarry (Southern Poland), sediments of lowermost part of the Middle Triassic are exposed. In limestone layer with cellular structures and pseudomorphs after gypsum, two dense accumulations of articulated ophiuroids (Aspiduriella similis (Eck)) were documented. The sediments with ophiuroids were formed in environment of increased salinity waters as suggested by paleontological, sedimentological, petrographical and geochemical data. Discovery of Triassic hypersaline ophiuroids invalidates the paleontological assumption that fossil echinoderms are indicators of fully marine conditions. Thus caution needs to be taken when using fossil echinoderms in paleoenvironmental reconstructions.

Oxygen isotope analysis of shark teeth phosphates from Bartonian (Eocene) deposits in Mangyshlak peninsula, Kazakhstan

Oxygen isotope analysis of shark teeth phosphates from Bartonian (Eocene) deposits in Mangyshlak peninsula, Kazakhstan We report the results of high-precision (±0.05‰) oxygen isotope analysis of phosphates in 6 teeth of fossil sharks from the Mangyshlak peninsula. This precision was achieved by the offline preparation of CO2 which was then analyzed on a dual-inlet and triple-collector IRMS. The teeth samples were separated from Middle- and Late Bartonian sediments cropping out in two locations, Usak and Kuilus. Seawater temperatures calculated from the δ18O data vary from 23-41°C. However, these temperatures are probably overestimated due to freshwater inflow. The data point at higher temperature in the Late Bartonian than in the Middle Bartonian and suggest differences in the depth habitats of the shark species studied.

Putative Late Ordovician land plants

The colonization of early terrestrial ecosystems by embryophytes (i.e. land plants) irreversibly changed global biogeochemical cycles (Berner & Kothavala, 2001; Berner et al., 2007; Song et al., 2012). However, when and how the process of plant terrestrialization took place is still intensely debated (Kenrick & Crane, 1997; Kenrick et al., 2012; Edwards et al., 2014; Edwards & Kenrick, 2015). Current knowledge suggests that the earliest land plants evolved from charophycean green algae (Karol et al., 2001) most probably during Early-Middle Ordovician times (Rubinstein et al., 2010; and references cited therein). They were represented by small nonvascular bryophyte-like organisms (Edwards & Wellman, 2001;Wellman et al., 2003; Kenrick et al., 2012). The oldest fossil evidence from dispersed spores of presumable bryophytic nature is known from aMiddle Ordovician locality (c. 470million years ago (Ma), Rubinstein et al., 2010; Fig. 1) from Argentina (Gondwana palaeocontinent). The dispersed spore fossil record also suggests that the first radiation of vascular plants probably occurred during Late Ordovician times (c. 450Ma, Steemans et al., 2009). However, unequivocal macrofossils of vascular plants appear much later, during mid-Silurian (c. 430Ma, Edwards et al., 1992). This macrofossil evidence comes from the fossil-genus Cooksonia, an early polysporangiophyte (i.e. a plant with bifurcating axes and more than one sporangium), which is considered the earliest vascular land plant (Edwards et al., 1992; Fig. 1). Further advances in knowledge about the origin and early dispersion of polysporangiophytes are needed for a better understanding of the initial plant diversification. Unfortunately, unravelling the initial steps of polysporangiophyte evolution is hindered by gaps in the fossil record of the earliest plants as well as by limitations of inference based on molecular clocks (Kenrick et al., 2012; Edwards & Kenrick, 2015). Assessing the affinities of fragmentary fossils is frequently only tentative. Most often, only partial evidence for land plant nature is visible on fossils of Silurian–Devonian age. Nevertheless, there are numerous examples in the deep-time fossil record of organisms that have been interpreted as early embryophytes even though unambiguous land plant characters were not demonstrated. For instance, Edwards & Feehan (1980) reported on some Silurian terminal sporangia and dichotomous axes interpreted as Cooksonia-type plantswith no evidence for in situ spores nor for tracheids.Wellman et al. (2003) described the first plant mesofossils with in situ spores from the Ordovician (Katian) fossil record, but the morphology of the parent plants remains unknown. More recently, Morris et al. (2011) reported on numerous fragments of LowerDevonian plants with terminal sporangia and dichotomous axes, some of them lacking preserved unambiguous land plant characters. Interestingly, some of the plants illustrated by Morris et al. (2011, pl. VI) appear closely similar to those reported in Fig. 2 (see later). Here, we document an Ordovician (Hirnantian, c. 445Ma) putative plant macrofossil assemblage. The specimens come from an Upper Ordovician locality at Zbrza in the southern Holy Cross Mountains (HCM, central Poland, SW peri-Baltica; Supporting Information Figs S1, S2, see also Notes S1). The fossils occur in mudstones of the uppermost Ordovician (Hirnantian) Zalesie Formation dated by trilobites, brachiopods and palynomorphs (Kielan, 1959; Temple, 1965; Masiak et al., 2003; Trela & Szczepanik, 2009). The age of the plant-bearing sediments is confirmed by acritarchs and chitinozoans (Notes S1). Reported evidence consists of dichotomously branched slender axes, some with terminal discoid or ovoid structures interpreted as sporangia, which could represent the earliest macrofossil occurrence of polysporangiophytes (Fig. 1). The plant fossils described herein are scattered among various fragments of coalifiedmaterial. Two branching axes broken at both ends (3 mm long9 0.1 mm wide and 2 mm long9 0.3 mm wide, respectively; Fig. 2a,b) are attributable to the fossil genusHostinella that includes vegetative isotomously branched axes. Another specimen shows a trichotomous axis division (3.2 mm long9 0.3 mm wide; Fig. 2c), a feature known to occur in some late Silurian–early Devonian plants (Gonez & Gerrienne, 2010a, b). The studied samples also yielded several probably fertile axes. A small, dichotomously branched, slender and leafless stem (1.5 mm long9 0.2 mmwide; Fig. 2d) bears terminal structures interpreted as sporangia (0.4 mm long9 0.3 mm wide; Fig. 2d). The two other fertile specimens are not branched.They consist of a short axis (1.1 mm long9 0.3 mm wide; Fig. 2e) ending either in a horizontally stretched, presumably cup-shaped, structure interpreted as a sporangium (0.8 mm long9 1.1 mm wide; Fig. 2e) or in an ovoid/hemispherical sporangium-like body (1.3 mm long9 1 mm wide; Fig. 2f). Their form, size and structure seem to be close to those observed fromCooksonia pertoni (Fig. 2e; Lang, 1937; Edwards & Feehan, 1980) and C. hemisphaerica (Fig. 2f; Edwards & Rogerson, 1979; Edwards & Feehan, 1980), respectively. Moreover, the specimen illustrated in Fig. 2(d) looks quite similar to the bifurcating axis showing the basal part of a sporangium described by Edwards et al. (2014, Fig. 3f). Within a macerated residue, we found rare trilete spores resembling the Ambitisporites avitus-dilutus (Steemans et al., 1996; Fig. 2g,h), a morphon interpreted as indicative of vascular plants (Fanning et al., 1988; Steemans et al., 2009); however the trilete marks of our specimens are not regularly formed, which casts doubts on their trilete spore nature. Interestingly, there are a variety of Ordovician spores with irregular trilete-like folds, such as Besselia nunaatica (Nøhr-Hansen & Koppelhus, 1988) that are well known from mosses and hornworts. The last important feature shown by our

Environmental control on shell size of Middle Triassic bivalve Plagiostoma

Fossil shells of the marine bivalve Plagiostoma striatum Schlotheim sampled from the Middle Triassic (so-called Muschelkalk) of Poland demonstrate that, under unfavourable environmental conditions, this species commonly occurring in Triassic German basins exhibits a dwarfed shell. As a consequence of a marine regression episode resulting in a significant increase of salinity and a partial emersion of seafloor these bivalves vanished. The next transgressive pulse caused a re-emergence of these bivalves. They were initially characterized by half-size shells than in the population living prior to the regression episode and, subsequently, during progressive transgression, their shells returned to normal size. Coincidence between eustatic curve and changes in bivalve shell size and their disappearance may be attributed also to biotic interactions, such as a biotic collapse in primary bioproductivity or/and a competition for space or any other resources due to shelf habitat loss during regressive periods.