Search the Community
Showing results for tags 'gsa'.
Found 3 results
Catch up on the current trilobite research with the abstracts from the GSA Annual Meeting in Indianapolis, Indiana - November 4 - 7, 2018. Matthew K. Witte - University of Chicago ON THE PHYLOGENETICS OF THE TRILOBITE FAMILY PHACOPIDAE WITH SYSTEMATIC IMPLICATIONS FOR ELDREDGEOPS (GREEN, 1832). Paper Number 13-6 - Session No: 13 T130. Trilobites belonging to the family Phacopidae are of particular interest partly due to their unique schizochroal eyes. Work by Eldredge documenting cephalic and eye morphology within the Middle Devonian Phacops rana (=Eldredgeops) group helped shape early arguments on punctuated equilibrium. However, morphological similarity between taxa, genera, and tribes among members of Phacopidae result in polytomies, homoplasy, and paraphyly. Further, extensive taxonomic splitting in the last several decades has left phacopid systematics in a state of mild disarray. Work by Strüve (1990, 1992) has brought the identity of the Phacops rana-group into question. The process of erecting the genus Eldredgeops from Phacops rana has led to the following uncertainties: (1) which of the former Phacops rana subspecies are to be considered members of the genus of Eldredgeops; (2) what are the relationships among these members; (3) if Eldredgeops is to be considered a valid genus, what is the relationship of Eldredgeops to other members of the family Phacopidae? To answer these questions a suite of characters comprising all sclerites of the trilobite were coded for 41 species, representing 16 genera across the trilobite family Phacopidae, including all ‘subspecies’ formerly assigned to Phacops rana (=Eldredgeops). Parsimony analysis run on a subset of the data matrix reveal the following systematic implications for Eldredgeops: (1) the two African ‘subspecies’ described by Burton and Eldredge (1974) are nested within Eldredgeops and should be systematically considered Eldredgeops; (2) all 'subspecies' of Phacops rana are united in a monophyletic clade suggesting that Eldredgeops is a valid monophyletic genus; (3) Eldredgeops is a sister genus to Geesops (G. schlotheimi) as hypothesized by Eldredge (1972); (4) Together Geesops-Eldredgeops are sister to Phacops s.s. With a clearer picture of the relationship among members of Eldredgeops and of Eldredgeops to the rest of Phacopidae, we may better understand the morphological evolution of an enigmatic clade. Future work uniting morphology and phylogenetics could have important macroevolutionary consequences. Joanna Stebing - Purdue University Fort Wayne Minh Le - Purdue University Fort Wayne Donald G. Mikulic - Illinois State Geological Survey Benjamin Dattilo - Purdue University Fort Wayne Jonathan J. Havens - Irving Materials, Inc NEW SILURIAN (LUDLOW, GORSTIAN) TRILOBITE FAUNA FROM PIPE CREEK JUNIOR QUARRY, SWAYZEE, GRANT COUNTY, INDIANA. Booth No. 260 - Session No: 39 D25. Pipe Creek Junior is a quarry in a rare limestone Silurian reef in Grant County, Indiana. It features spectacular exposures of steeply dipping Silurian distal reef flank beds. Most Silurian rocks in the region were hydrothermally dolomitized which destroyed primary sedimentary fabrics and fine fossil details. Pipe Creek Junior was largely unaffected by these processes, so most of the original fabrics, cements and fossil textures were preserved- accomodating study of Silurian reef depositional systems and biota. A limited group of distal flank beds exhibits a highly diverse fauna of trilobites that differs from that seen in most Midwestern reefs. , and one of us (Havens) has been collecting trilobites from the quarry since 1992 and amassed a collection of over 900 trilobite fossils. A partial list of taxa includes Styginidae (including a bumastine and a scutelluid), Harpetidae (including Scotoharpes?), Lichidae (Genera Dicranopeltis and Hemiarges (?)), Odontipleuridae (including Dudleyaspis, Ceratocephala), Calymenidae (Genus Calymene), Cheiruridae (including Cheirurus?, Deiphon, Sphaerexochus, Youngia) Encrinuridae (Genus Struzia), Phacopiodae, and Proetidae. There appears to be several undescribed genera and species in this fauna which will be described at a future date. Most of the trilobites were collected from the proximal reef flank beds, and many of these were also found in a lateral bioherm. Phacopids are exceptional in being found farther from the reef core, always in very coarse grained rocks. One unusual Sphaerexochus pygidium came from distal flank beds. We are in the process of photographing and describing this large and unique collection. The goal of this project will to describe and quantify a rare and poorly known highly diverse late Silurian trilobite fauna from the Midwest. Shujian Qin - Peking University Lin Dоng - Peking University Bing Shen - Peking University ONTOGENETIC VARIATION ON CRANIDIAL SHAPE OF THE LATE MIDDLE CAMBRIAN (CAMBRIAN SERIES 3) TRILOBITE JIULONGSHANIA ACALLA. Booth No. 274 - Session No: 39 D25. A large number of complete cranidiums together with numerous disarticulated sclerites of the late middle Cambrian (Cambrian series 3) trilobite Jiulongshania acalla Walcott, 1905 were collected from the Gushan Formation at the Tangwangzhai section in Shandong Province, North China. Jiulongshania acalla is characterized by a subtrapezoidal cranidium with conical to triangular glabella, wide fixigenae and preglabellar field. The cranidial morphology shows a wide range of variation and can be divided into different morphotypes, but it is unclear whether the morphological variations were related to the ontogenetic change during growth. In this study, we analyzed the morphological and ontogentic changes in the cranidial shape of J. aculla to gain insight into the morphogenetic processes during the development of trilobites. Classic morphometrics and geometric morphometrics methods were used to evaluate the variability in the cranidium. Five variables of cranidium were measured for morphometric analysis, including the total cranidial length and width, the maximum glabellar length (including the occipital ring) and width, and the length of cranidial frontal area. In addition, 5 landmarks were selected to optimize the half shape of the cranidium and at the same time retain a reasonable sample size. In this study, we found the following observations: (1) allometric growth of the preglabellar and glabellar area, (2) elongation of cranidium during the developmental process, (3) gradual increase in the length of cranidial frontal area with respect to glabellar length, and (4) progressive expansion of the maximum glabellar width relative to the total cranidial width. Our results clearly show that the relative growth rates of different regions of cephalon was disparate during growth. Fortey and Owens (1999) have proposed that the variation of trilobite exoskeletal morphology, particularly the cephalon, might be related to the feeding mode of trilobites. Thus,we speculate that the natant trilobites may extend the preglabellar field during growth when the hypostome detaches from the doublure. It is likely that there was a change in feeding habit between larvals and adult stages in the development of Jiulongshania acalla. Loren E. Babcock - The Ohio State University PATHOLOGIES IN PALEOZOIC TRILOBITES. Booth No. 279 - Session No: 40 T135. Trilobites of Paleozoic age provide some of the earliest and most dramatic documentation of malformations known from the fossil record. Although once commonly treated as monstrosities or curiosities, advances in identification reveal specimens showing a history of trauma, disease, parasitism, and infection. Such interpretation provides valuable glimpses into the paleoecology and evolutionary history of trilobites. Accidents, especially those incurred in molting, sublethal predation, and teratological conditions account for a large percentage of malformed specimens. Trilobites retain a record of their wounds, and clues to the processes of wound response and tissue regeneration, in their biomineralized exoskeleton; this helps to distinguish pathological conditions from congenetic malformations. Wound response or other tissue response is key to distinguishing conditions that took place during life from post-mortem events such as scavenging, boring of exoskeletal sclerites, and attachment of larvae to sclerites. A high incidence of healed predation scars in Cambrian trilobites is consistent with the interpretation that predator-prey interactions were an important evolutionary driving force during the Cambrian radiation. Atrophy expressed on some trilobite exoskeletons suggests an origin with infection or parasites. Neoplasms, or nodular growths, on trilobite exoskeletons can sometimes be distinguished as healed, or encased, borings into the exoskeleton, thus recording interactions with microscopic parasites. Other nodular growths resemble tumors, and putatively provide some of the earliest documentation of uncontrolled cellular growth, or cancer, known from fossils. Reuben Y. Ng - University of Iowa Jonathan M. Adrain - University of Iowa PHYLOGENY AND MORPHOLOGY OF THE CAMBRIAN-ORDOVICIAN TRILOBITE GENUS CLELANDIA WITH NEW AND REVISED SPECIES. Booth No. 285 - Session No: 115 T130. The Laurentian trilobite genus Clelandia Cossman, 1902, presently contains 12 formally named species ranging from the late Cambrian (Furongian; Jiangshanian; Sunwaptan) to the Early Ordovician (early Tremadocian; Skullrockian). The genus as a whole has rarely been subject to detailed study and most of the species are inadequately known. Clelandia has never been subject to phylogenetic analysis, and even its phylogenetic affinity and familial assignment is unclear. In addition, much of the published work on the genus is in need of revision, especially the published images which are few in number and of poor resolution. Undescribed material from the Great Basin of North America represents four new species of Clelandia from the Skullrockian Stage of the Early Ordovician. The secondarily silicified nature of this material allows for detailed study of trilobite sclerites free of matrix and in three dimensions, following acid digestion. Species are represented by multiple examples of sclerites which often document different growth stages. The new Skullrockian species of Clelandia are each characterized by several diagnostic features of the cranidium. None of the new species appear to have the extended glabellar-occipital spine structure found in C. bispina or C. wilsoni, nor do they exhibit glabellar furrows as are seen in C. parabola, C. briscoensis, C. typicalis, C. texana, or C. albertensis. Two of the new species entirely lack an occipital spine, a condition rarely found in other species. These two species also have a dramatic reduction in furrow definition, especially of the occipital and posterior border furrows which are almost completely effaced. Phylogenetic analysis shows a subclade dominated by species with glabellar furrows, well-expressed axial furrows, and a curved preglabellar furrow. A second component consists of species with a unique glabellar-occipital spine. The most effaced species of Clelandia, with disjunct axial, posterior, and occipital furrows and limited or absent occipital spines, are resolved as a third subclade. Based on distinctive morphology of the cranidium, the species Desmetia annectans Walcott, 1925 is reassigned to Clelandia, and Desmetia is considered a junior synonym. Mary K. Pankowski Michael J. Pankowski Thomas Hegna - Western Illinois University LEGACY DATA IN PHYLOGENETICS AND A RE-ANALYSIS OF MID-PALEOZOIC PHACOPID PHYLOGENY. Paper Number 13-6 - Session No: 13 T130. Phylogenetic data is often presented in published papers in a table format. This table format is not immediately useful for testing the phylogenetic hypotheses, as it cannot be directly run by a phylogenetics computer program. By imputing legacy phylogenetic matrices into an online resource like MorphoBank, old phylogenetic datasets can be made accessible for easy testing and modification. In some cases, computing power at the time of the original analyses was insufficient for a comprehensive search of treespace, and hence better results can now be obtained. Through an initiative of importing old trilobite phylogenetic analyses into Morphobank, we reanalyzed the phylogenetic analysis of Silurian-Devonian phacopid trilobites of Ramsköld and Werdelin (1991). The hypothetical ancestor outgroup was replaced with an Ordovician pterygometopid, Calyptaulax callirachis. Several additional mid-Paleozoic phacopids were also added to the analysis. The resulting matrix was analyzed using both parsimony and Bayesian methodologies. Though the broad conclusions of the original paper remain intact, a surprising number of taxa shifted positions when compared to the original study. Rhiannon J. LaVine - University of Chicago PATTERNS OF MORPHOLOGICAL DIVERSIFICATION WITHIN THE SUBORDER AGNOSTINA (TRILOBITA). Booth No. 283 - Session No: 115 T130. Members of the Order Agnostida (Salter 1864) have a long and perplexing history of uncertain systematics. On all taxonomic levels, the extremely conserved morphologies of many agnostine arthropods make them the subject of ongoing systematic revision. Agnostina, the subclade of Agnostida that excludes Eodiscina, is a moderately diverse group comprised of 13 recognized families and over 100 genera. Taxonomic diversification of this clade is “bottom-heavy” in terms of generic origination rates, with a peak in the middle Cambrian and subsequent decline until its extinction in the Late Ordovician. It is expected that morphological diversity of this clade demonstrates a similar “bottom-heavy” pattern. Specimens from 13 families of Agnostina plus additional taxa classified as “Uncertain” and “Unassigned” were coded for a set of characters that describe cephalic, thoracic, and pygidial traits. A preliminary phylogenetic tree of Agnostina was constructed using parsimony-based methods, rooted on the stratigraphically oldest species, Eoagnostus roddyi. Cephalic sclerites from representative specimens were selected and subject to geometric morphometric analysis. Specimens were chosen based on the ability to apply a common landmark configuration that includes coverage of the cephalic margin and border, anterior glabella, posterior glabella, and basal lobes. For this reason, effaced genera were excluded. The resultant morphospace was then overlain with the phylogenetic tree in order to produce a phylomorphospace. This study is the first attempt to explore disparity of this enigmatic clade in a phylogenetic context. It serves as a foundation for ongoing research into developmental constraints that may shape patterns of morphological evolution in this very conservative group of arthropods. Steven M. Stanley - University of Hawaii GENAL SPINES FUNCTIONED TO ALLOW TRILOBITES TO RIGHT THEMSELVES AFTER BEING OVERTURNED. Paper Number 199-11 - Session No: 199 D23. The fact that about 80% of trilobites possessed genal spines indicates that these structures must have served at least one important function. The spines were not for predator deterrence because they extended nearly parallel to a trilobite’s body, and no other function for these structures seems previously to have been identified. Here I propose a common function for genal spines and enrollment by trilobites. (Of course, the primary role of enrollment was protection.) Being overturned on the seafloor would have been problematical for trilobites because their feet could not have righted them, but genal spines as well as enrollment made it possible for them to regain their normal position. Overturned trilobites could have used genal spines to stabilize themselves while they flexed their bodies and, in effect, undertook a backward somersault to stretch out in life position without turning sideways along the way because of their rounded pygidium. Instead, some trilobites could have used enrollment to do so. After enrolling, if fortunate, these forms could simply have allowed water movements to rotate them to a position in which unenrolling placed them in life position. Some trilobites that could enroll also possessed genal spines that were short enough to permit rolling, so they could have righted themselves by either method. (A few genera lacked roughly round cross-sections when enrolled and could not have rolled effectively on the seafloor.) The distribution of morphologic features among trilobites provides a test for these ideas. Species that could protect themselves by secure enrollment could do so only by virtue of their shapes. In fact, the outlines of trilobites that enroll are dictated by this behavior. One can predict that taxa with pygidia too narrow for protection by enrollment would have been required to possess genal spines to right themselves when overturned, whereas taxa that lacked genal spines would have been required to have pygidia wide enough for successful enrolling. Observations bear out these predictions. For trilobites that could not enroll for protection, partial enrollment in the presence of strong water movements would have provided the genal spines with a secondary function. Projecting out from the body and sticking in the sediment, they would have provided temporary stability. James D. Loch - University of Central Missouri John F. Taylor - Indiana University of Pennsylvania John E. Repetski - U.S. Geological Survey-Emeritus Justin V. Strauss - Dartmouth College Wesley T. Kamerer - Indiana University of Pennsylvania PALEOENVIRONMENTAL DISTRIBUTION OF THE LATE CAMBRIAN (FURONGIAN) AGNOSTOID ARTHROPOD LOTAGNOSTUS IN WESTERN LAURENTIA. Booth No. 173 - Session No: 257 D16. In excess of 1000 specimens of agnostoid arthropods from siliceous (spiculitic) basinal carbonates of the Windfall Formation in Nevada provided the first opportunity to assess the range of morphologic variation within species of Lotagnostus in Laurentian deposits. These non-compacted and non-sheared specimens from one horizon confirm the presence of at least two non-intergrading species: a strongly scrobiculate form with conspicuous trisection of the posteroaxis, and another with faint or no scrobiculae or trisection. The lack of transitional morphs, throughout the ontogeny of both species, reinforces arguments provided by Westrop and Landing (2016) against the broad species concept advocated for Lotagnostus americanus by Peng et al. (2015), which would encompass both Windfall species. The absence of transitional morphs dismisses the claim that L. americanus is a highly variable and globally distributed species whose First Appearance Datum should define the base of Cambrian Stage 10. Associated conodonts and trilobites allow fairly precise correlation of the Lotagnostus-dominated faunas from several horizons in the Windfall to coeval middle to upper Furongian strata elsewhere. These include shelfbreak to upper slope deposits of the Jones Ridge Formation in Alaska, and its off-platform equivalent, the Hillard Limestone. The lower slope carbonates of the Hillard have yielded only two specimens of Lotagnostus. No specimens of Lotagnostus have yet been identified within the 14 agnostoid-bearing collections of middle to upper Sunwaptan age (Proconodontus tenuiserratus through Eoconodontus Zones) recovered through over 145m of Furongian strata in the Jones Ridge Formation. The near to total absence of Lotagnostus from faunas from upper slope and platform facies severely limits the utility of that genus for correlation into the Laurentian platform and upper slope successions, making it a highly questionable choice for defining the base of Stage 10. Madison L. Armstrong - University of Oklahoma Stephen R. Westrop - University of Oklahoma Michael Engel - University of Oklahoma INTEGRATING TRILOBITE BIOSTRATIGRAPHY AND CARBON ISOTOPE STRATIGRAPHY OF THE CAMBRIAN (PAIBIAN; STEPTOEAN) SPICE EVENT IN CENTRAL TEXAS AND WESTERN UTAH. Paper Number 272-15 - Session No: 272 D15. The Steptoean Positive Carbon Isotope Excursion (SPICE) has been identified worldwide and is a significant feature for global correlation. Although the SPICE has been documented from several localities in Laurentian North America, biostratigraphic characterization has relied on paleontological work done decades earlier. A new program of sampling in Texas and Utah allowed us to analyze trilobite-bearing collections to provide direct links between the faunal succession and carbon isotope stratigraphy. The Steptoean (Paibian) Riley Formation of Texas is strongly condensed. Increasingly positive values of the rising limb of the SPICE are recorded in the skeletal carbonates of the Cap Mountain Member. Peak positive values reaching 2.5–2.99‰ (VPDB) occur in correlatives of the Dunderbergia Zone in the overlying lowstand sandstone succession of the Lion Mountain Member. The upper portion of the SPICE is not preserved due to the absence of skeletal carbonate lags in trough cross-bedding towards the top of the member. The Candland Shale Member of the Orr Formation at its type locality at Orr Ridge, Utah, is broadly correlative with the Texas succession. Our data from trilobite-rich skeletal carbonates forms a curve that closely matches one published by Saltzman et al. (1998) from the same locality. A steady rise to about 2.5‰ occurs in the Aphelaspis Zone and stabilizes in the Dicanthopyge and lower Prehousia zones. Values then rise rapidly in the upper Prehousia Zone, peaking between 4.5–5‰ in the overlying Dunderbergia Zone. The base of the lowstand succession in Texas correlates into the upper Candland Shale, an interval that has been variously interpreted by previous workers as either transgressive or regressive. The extinction interval at the base of the Steptoean Stage is exposed at both sections. The onset of extinctions (base of the Coosella perplexa Zone) is characterized by an unremarkable shift in the carbon isotope curve of no more than about 0.5‰. This suggests that, although physical environmental change might possibly act as a trigger for the extinction, there may be a significant role for ecological impact of biological factors, such as immigration of invasive species.
HI all, we are doing some research on gastropods in the permian, and have not had much luck finding this very important reference on line. Can any one point us in the right direction? Maybe you have a PDF? Supal Formation (Permian) of Eastern Arizona. Geological Society of America Memoir 89. Stephen S. Winters. Geological Society of America, New York, 1963. viii + 99 pp. Illus