Boreholes in Devonian blastoids and their implications for boring by platyceratids

Complete, circular holes found on the thecae of 51 specimens of Devonian nucleocrinid blastoids are interpreted as biogenic in origin. Their morphology, their stereotyped position on the theca, and the lack of multiple borings, suggest that they represent predation or parasitism. Platyceratid gastropods are presumed to be the borers because (1) they occur in the same localities as the bored blastoids, (2) they have been found on thecae of other blastoids, and (3) their boring abilities have been previously demonstrated. □ Paleozoic boreholes, platyceratids, blastoids, gastropod drilling.     

Bite traces on dicynodont bones and the early evolution of large terrestrial predators

Nied?wiedzki, G., Gorzelak, P. & Sulej, T. 2010: Bite traces on dicynodont bones and the early evolution of large terrestrial predators. Lethaia, Vol. 44, pp. 87–92. Dicynodont (Synapsida: Anomodontia) bones from the Late Triassic (late Norian/early Rhaetian) of Poland yield characteristic tooth marks that can be attributed to three ichnotaxa (Linichnus serratus, Knethichnus parallelum and Nihilichnus nihilicus). The general shape and dimension of these traces perfectly match the dental morphology of a co‐occurring carnivorous dinosaur. It is therefore concluded that early carnivorous dinosaurs were feeding on dicynodonts. This discovery constitutes one of the oldest evidence of dinosaur predator–prey interaction. It is suggested that an evolutionary increase in the size of dicynodonts across the Late Triassic may have been driven by selection pressure to reach a size refuge from early dinosaur predators. □Bite traces, dicynodonts, dinosaurs, predation, Triassic.     

The pterygotid telson as a biological rudder

Functional hypotheses for fossil organisms can be rigorously tested through the application of engineering principles and physical laws (paleobiomechanics). Alternative functional models for the telson (tail spine) of the large pterygotid eurypterids are examined in terms of the hydrodynamics of fish propulsion and of ship rudders. The telson probably served as a rudder for steering in the horizontal and vertical planes during swimming, rather than as a thrust producer. The aspect ratio of the telson may approach an 'optimum', for the production of rudder forces over a wide range of angles of attack. Pterygotids may have been highly agile, rather than rapidly swimming animals. Eurypterids, functional morphology, paleobiomechanics .     

Disarticulation patterns in Ordovician crinoids: Implications for the evolutionary history of connective tissue in the Crinoidea

Taphonomic information is examined to evaluate the early history of connective tissues in the Crinoidea. The pattern of stalk segmentation of Middle and Late Ordovician crinoids is consistent with the two-ligament (intercolumnal and through-going ligaments) pattern present in living isocrinid crinoids and interpreted for fossil isocrinids, holocrinids, and Lower Mississippian crinoids. A single rhombiferan was also examined; its taphonomic pattern is also indicative of this style of tissue organization. Furthermore, the taphonomy of all Middle and Late Ordovician crinoids may reflect that they lacked discretely organized muscles between arm brachials, which is consistent with the hypothesis that muscles evolved as a connective tissue between plates only once within the Crinoidea, during the Early Devonian. These data indicate that the two-ligament organization of the stalk is a primitive feature among the Crinoidea and perhaps even among stalked echinoderms. Therefore, the autotomy function of this column-tissue organization among living crinoids is an exaptation. On the other hand, discretely organized muscles as connective tissue in crinoid arms is a derived trait that first appeared during the middle Paleozoic; this adaptation proved very successful for the advanced cladid crinoids.     

Crinoid stalk flexibility: theoretical predictions and fossil stalk postures

Flexibilities in Lower Mississippian crinoid stalks were inferred from preserved postures and shown not to conform with predictions of a cantilever beam model. Flexibilities were not correlated with hard-part characters such as stalk diameter, stalk length, or columnal height. The lack of correspondence between the predictions of the cantilever model and observed flexibilities implies that the most likely control of stalk flexibility is the ligament, more specifically, its non-constant, mutable properties. Although a few Lower Mississippian crinoids, such as Gilbertsocrinus, Platycrinites , and Camptocrinus , have enhanced flexibility achieved by radical modifications of columnal facet morphology, this study has failed to identify any general morphological characters that consistently predict flexibility. It appears that skeletal morphology is a poor guide to stalk flexibility; mutable collagenous tissue is the key. Crinoidea, taphonomy, constructional morphology, Lower Carboniferous, connective tissues.     

Physical modeling of the batocrinid anal tube: functional analysis and multiple hypothesis testing

Baumiller, T. K. 1990 10 15: Physical modeling of the batocrinid anal tube: functional analysis and multiple hypothesis testing. Lethaia , VOL 23, pp. 399–408. Oslo. ISSN 0024–1164.
Three hypotheses related to the function of the batocrinid anal tube were tested using physical models: (1) the anal tube served as a 'rudder', allowing the crinoid to passively maintain an effective feeding posture in moving water, (2) the tube served as a splitter 'plate', reducing the drag on the organism while it was in its feeding posture, and (3) the anal tube functioned as a 'chimney' by moving the anus downstream of the arms and thus reducing the risk of the organism ingesting its own wastes and/or gametes. Results of experiments performed in a recirculating flow tank suggested that the tube was well suited for the 'chimney' function: it reduced the concentrations of excreted matter in the proximity of the feeding appendages. Differences in rotational torques between models with a tube versus those without a tube implied that a large tube may have increased the rotational stability of the feeding posture in environments with variable current directions. No differences were detected between drag measurements on models with and without the anal tube; thus the 'splitter-plate' function of the tube was rejected. ▭ Batocrinid anal tube, functional morphology, physical modeling .     

On the Question of Stem Polarity with Respect to Auxin Transport

The effect of section length and number of longitudinally contiguous cells upon polar transport of natural auxin from the pine stem cambial region was investigated with oat coleoptile curvature tests. Basipetal and acropetal efflux of auxin to agar declines with increasing length of the sections, but the polarity quotient varies little and is similar to the polarity of individual cells. An integrated system of cells produces a wave along the stem in the efflux of auxin from consecutive segments. The possible role of such waves in development of polarity gradients and of the morphogenic maps of orientation of cells in the stem cambial region is discussed.