none 10.1098/rstb.1987.0046 The Royal Society The Royal Society 175 24864386 378325 2026010205561472600 10.1098 2026-01-02T10:56:19Z 2006-12-18T17:49:02Z 56 Philosophical Transactions of the Royal Society of London. B, Biological Sciences 0080-4622 2054-0280 09 24 1987 317 1182 Harry Blackmore Whittington Department of Earth Sciences, Downing Street, Cambridge CB2 3EQ, U. K. J. E. Almond Department of Earth Sciences, Downing Street, Cambridge CB2 3EQ, U. K. Abstract Sixteen specimens from the classic locality quarried by C. E. Beecher, in the Frankfort Formation near Rome, New York State, U.S.A., have been examined. Pyrite has replaced the exoskeleton and lines or infills confined spaces such as within the doublure and appendages. Appendages are compressed beneath the flattened exoskeleton and retain their original relationship to one another; biramous appendages have in most cases been rotated, commonly showing the posterior face beneath the cephalon, the anterior face beneath thorax and pygidium. The specimens were collected and prepared by C. D. Walcott, most having been exposed from the ventral side and lie approximately parallel to the bedding, three are oblique-lateral in relation to bedding. Seven have been additionally prepared using a gas pressure abrasion machine, photographs taken in reflected light, the specimens submerged in alcohol, and explanatory camera-lucida drawings made. The antennae may not have had an originally lyriform configuration. Additional evidence supports the view that the cephalon bore three pairs of biramous appendages as J. L. Cisne claimed (Science, Wash. 186, 13-18 (1974); Fossils Strata 4, 45-63 (1975); Palaeontogr. Am. 9, 99-142 (1981)), but there is no indication that a metastome was present. Coxae are poorly preserved, the last-formed posterior coxa small, triangular, coxae becoming progressively elongate forward along the series, and deeper beneath the cephalon. Neither the ventral membrane nor the coxa-body junction has been observed. The interpretation of the form of the coxa, and attachment of leg branches, by Cisne (1975, 1981), is considered to have been based on misinterpretation of an X-ray stereograph; the leg branch is inserted into the full depth of the abaxial coxal margin. Endites of the podomeres of the leg branch are deep, acutely triangular in shape, on podomeres 1-4 of the posterior branches; podomeres become progressively more elongate forward along the series, endites less acutely triangular, and are present only on the proximal podomere anteriorly, as C. E. Beecher (Am. J. Sci. 1, 251-256 (1896)) showed. The tips of the endites were spinose. We consider that there was no `post-pygidial abdomen', as claimed by Cisne (1975, 1981), the structure so interpreted being the most posterior, six or seven tiny coxae and leg branches, preserved crowded together and overlapping, backwardly directed across and behind the pygidial doublure. The shaft of the exite was rigidly attached to the upper, posterior side of the coxa, was broad proximally, tapering, and obliquely subdivided. It bore about 50 filaments and a small, setose terminal lobe. The filaments are preserved as imbricated, flattened strips, closely spaced and parallel, always dorsal to the leg branches. The most posterior limb pair was the last-formed, differing growth rates between portions of the earlier-formed limbs led to the graded differentiation shown by the biramous limb series. The differences between coxae and leg branches in particular regions of the body were concerned with capture and ingestion of food. A new reconstruction is made, the exoskeletal convexity based on uncrushed, enrolled specimens of the similar species Triarthrus beckii. Exoskeletal structures show that T. eatoni could have enrolled to form an enclosed capsule, within which all the appendages must have been accommodated. The biramous limbs are restored in a hanging stance, the inner ends of the coxae close together. Both branches of the limbs projected well below the margins of the exoskeleton, but only the tips were visible in dorsal view. T. eatoni was a benthic animal that walked on the substrate, and could have launched itself off the bottom and drifted above it. It was probably a generalized deposit feeder, scavenger and predator, exploring the surface of the mud and digging into it for small organic fragments, and capable of catching and squeezing small prey in the formidable array of posterior endites and spines. Food was passed forward to the mouth by the interaction of the spinose mesial edges of pairs of coxae, larger cephalic coxae helped push food toward the mouth. T. eatoni is preserved predominantly in dark shales, that were formed in muddy environments of the outer continental shelf and upper slope. 09 24 1987 1 46 https://royalsociety.org/journals/ethics-policies/data-sharing-mining/ 10.1098/rstb.1987.0046 https://royalsocietypublishing.org/rstb/article/317/1182/1/17695/Appendages-and-habits-of-the-Upper-Ordovician http://journals.royalsociety.org/index/10.1098/rstb.1987.0046 https://royalsocietypublishing.org/rstb/article-pdf/317/1182/1/80702/rstb.1987.0046.pdf https://royalsocietypublishing.org/rstb/article-pdf/317/1182/1/80702/rstb.1987.0046.pdf https://royalsocietypublishing.org/doi/pdf/10.1098/rstb.1987.0046 10.2475/ajs.s3-46.276.467 Am. Geol. Beecher C. 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B. 1 59 1954 Silicified Middle Ordovican trilobites ahr articulating half-ring axf axial furrow a-z serial lettering of limb branches when anterior branches on body are not preserved c coxa ce cephalon ced doublure of cephalon cepb posterior border of cephalon cpm posterior margin of cephalon c St curved structures d doublure dpb doublure of posterior border of cephalon e exite el lobe at tip of exite es exite shaft ex. exsagittal a line parallel to but outside the sagittal line ey furrow at outer margin of eye lobe fil filaments of exite fr fracture gr longitudinal groove in exite shaft gs genal spine h hypostome limb lbf lateral border furrow L prefix denoting left side of animal or occipital ring pbf posterior border furrow pi pleura Pif pleural furrow pm posterior margin pyg pygidium R prefix denoting right side of animal s glabellar furrow numbered IS 2S etc. anteriorly from IS the furrow next to the occipital furrow sag. sagittal a median longitudinal line in the body sp spine St step in level stp stop in enrolment t thoracic segment tr. transverse a direction at right angles to the sagittal line used also for the direct along the axis of a limb branch to trough U.S.N.M. United States National Museum of Natural History V vincular depression w walking leg 1-72 serial numbering of thoracic segments pleurae or pleural furrows coxae branches of limbs when first in body is known and podomeres of leg branch