Geological Society Trilobite Abstracts

[piranha]

For all my trilo-pals at TFF: Trilobite-related abstracts from the recent GSA symposium:

The Origins of Arthropod Diversity: Phylogenetic Insights from the Living and the Dead

LAMSDELL, James C., STEIN, Martin, OLESON, Jørgen, and SELDEN, Paul A.

Paper No. 30392-208169: TESTING THE ARACHNOMORPHA AND LAMELLIPEDIAN HYPOTHESES

The original Arachnomorpha hypothesis placed trilobites and a number of predominantly early Palaeozoic arthropod taxa, including megacheirans, in the chelicerate stem lineage. As an alternative hypothesis, Lamellipedia (Arachnomorpha excluding megacheirans) was originally interpreted as a paraphyletic grade of derivatives of the chelicerate stem lineage but,are increasingly being discussed as possible stem-lineage mandibulates under a modified lamellipedian hypothesis. Here, we present a broad analysis aimed at testing the Arachnomorpha hypotheses versus the modified lamellipedian hypothesis. Most of the over 80 included taxa are extinct, and the more than 170 characters coded focus on external morphology recognizable in the fossils. Euchelicerates are represented by three extant and 14 extinct species spanning synziphosurines, xiphosurids, chasmataspids, eurypterids, and scorpions. Three extant myriapods are included in acknowledgement of the Paradoxopoda versus Mandibulata controversy. Crustacea is represented by five extant and seven extinct taxa, including cephalocarids, branchiopods, mystacocarids, remipedes, and malacostracans, as well as four supposed derivatives of the crustacean stem lineage. Lamellipedians are represented by marrellomorphs, 16 artiopod species, three of which are trilobites, as well as Cheloniellon calmani, Sidneyia inexpectans, Squamacula clypeata, and Aglaspis spinifer. Five megacheirans were included. Also, several controversial or problematic taxa were included, such as Canadaspis perfecta, Agnostus pisiformis, Sanctacaris uncata, Kiisortoqia soperi, and Sarotrocercus oblita. The stem-lineage euarthropod Shankouia zhengei was selected as outgroup. The matrix was run in TNT. Results strongly support the position of all ingroup taxa except Fuxianhuia protensa within a well-supported Euarthropoda. Arthropods with a great appendage and Kiisortoqia are well supported as derivatives of the stem lineage of a monophyletic Chelicerata (Pycnogonida + Euchelicerata). Canadaspis is retrieved as an early derivative of the mandibulate stem lineage, and artiopods are rendered a paraphyletic grade giving rise to Crustacea. These results falsify the Arachnomorpha hypothesis, but are more in line with the modified lamellipedian hypothesis.

MCROBERTS, Christopher, HEGNA, Thomas, BURKE, Jeri, STICE, Morgan, MIZE, Steven, and MARTIN, Markus

Paper No. 30392-211132: ORIGINAL SPOTTED PATTERNS ON MIDDLE DEVONIAN PHACOPID TRILOBITES FROM WESTERN AND CENTRAL NEW YORK

Preserved color markings in Paleozoic fossils are extremely rare and have been hypothesized to reflect muscular attachment scars, diagenetic artifacts unrelated to biological features or the altered remains of biochromes (organic pigments) or sclerochromes (structural colors) embedded in fossilized skeletal remains. More than 25 exceptionally well-preserved phacopid trilobites with spotted patterns are described from the Middle Devonian western and central New York. The small (~0.24 mm) circular markings appear either brown on a lighter cuticle, or white on a darker cuticle. Spots are non-randomly distributed on the entire dorsal exoskeleton and the regions of occurrence are bilaterally symmetrical and are not correlated with the locations of tubercles or with other surface features (e.g., frontal auxiliary impressions, or facial sutures). Thin section, SEM imaging, and EDX and WDS elemental analyses show spots to be spheres embedded within the primary layer of the cuticle below the prismatic layer and composed of microcrystalline low-Mg calcite. Surrounding cuticle (also low-Mg calcite) exhibits coarser crystallinity, lamellar structures, pore canals, and likely organic matrix as expected for unaltered trilobite skeletons. Potential diagenetic mineralogies or microstructures were not observed making diagenesis an unlikely explanation. Spot distribution, morphology and position in cuticle rule out a relationship with sites of musculature attachment/insertion. We suggest that the spots represent original biologic structures manifest as either crystallographic/optical loci resulting in structural color spots or potentially clear spots embedded in the cuticle that contrasted with a pigmented exoskeleton and may have served as windows to an underlying epidermis. The spots likely served as camouflage by providing a disruptive pattern to their dorsal surfaces serving to break-up the trilobite’s visual outline and also to reduce the starkness of shadows caused by surface relief.

ADRAIN, Jonathan M., WESTROP, Steven R.

Paper No. 30392-212606: TOWARDS A PHYLOGENETIC CLASSIFICATION OF TRILOBITA: SYNAPOMORPHIES AND STRUCTURE OF THE ORDER OLENIDA ADRAIN, 2011

Despite progress at lower taxonomic levels, our understanding of higher trilobite phylogeny is surprisingly weak. Although peak global species richness was attained during the Cambrian, trilobites of this age are classified in a small number of orders widely considered either paraphyletic or polyphyletic. Very little modern phylogenetic work has been carried out on any of these groups. Post-Cambrian trilobites are classified in a greater number of orders, most of which are clearly monophyletic. The relationship of these groups to each other, or to any potential Cambrian sister taxa, is largely unknown and hence the basic structure of Trilobita remains unresolved. Our basic ignorance of higher trilobite phylogeny even has a name: Stubblefield, in 1959, introduced the term "cryptogenesis" to refer to the unknown origins of post-Cambrian orders. Secondarily silicified trilobites yield new data on ventral structures and developmental morphologies, and have revealed the surprising presence of a complex articulation of the librigenal anterior projection and the cranidium in several groups of trilobites, many of which have not been considered related to one another. We propose the term "stylidion" for this structure. It involves a series of tiny pillars running dorsally from the inner edge of the librigenal doublure and articulating in a series of small pits on the inner (ventral) surface of the cranidium. These pits are often expressed on the dorsal (external) surface of the cranidium as tiny tubercles. The pillars are matched on the outer (ventral) surface of the librigenal doublure by another series of small pits. This morphology has not previously been documented. Most trilobites have a simple inner doublural margin and no cranidial modifications in this region. We hypothesize that the stylidion is an unreversed synapomorphy of the recently proposed Order Olenida. While available data are scant, all firmly associated larvae and early growth stages of olenide species have a characteristic morphology involving transversely complete glabellar furrows (most trilobites have the furrows expressed only abaxially), anteriorly placed eye ridges, and tuberculate fixigenae. These will likely prove to be additional synapomorphies of the order, supplementing the stylidion, which is developed later in ontogeny.

MCADAMS, Neo E.B. and ADRAIN, Jonathan M.

Paper No. 30392-213058: IMAGING, MORPHOLOGICAL KNOWLEDGE OF SPECIES, AND PHYLOGENY RECONSTRUCTION: A CASE STUDY IN PLIOMERID TRILOBITES

Many invertebrate paleontological phylogenetic analyses rely on images of specimens from the published literature as coding sources. Species are typically represented by a handful of specimens which were imaged at low magnification in plan view. New digital technology enables publication of highly resolved images of numerous specimens. Here we use silicified Lower Ordovician pliomerid trilobites from the Great Basin to investigate whether the quality of information conveyed in traditional vs current illustrations affects phylogenetic precision or accuracy. The trilobites were originally described in mid-20^th century publications widely regarded as excellent, but our field-based revision of these faunas indicates that only about 1/3 of the common species were described, and that species which initially appeared well-known were often composites of several poorly known species. Simulations have shown that phylogenetic accuracy and resolution are reduced by inability to code characters for all taxa, not just the percentage of missing entries in any incomplete taxa. This is borne out in our analyses. Our primary dataset includes 29 species coded for 69 characters, from our photographs of specimens we collected at the type localities. Most characters are coded for all taxa. A second dataset consists of the 20 species now known to be represented in the literature (even if unrecognized at the time) coded only from the original illustrations. Dataset 2 is incomplete due to species that were known from few exoskeletal elements, or because the original illustrations did not show all relevant morphology. 25 uncodable or autapomorphic characters were removed from it. It contains no characters coded for all taxa. We analyzed both datasets using parsimony. Analysis of Dataset 1 resulted in six well resolved, well supported trees (CI 0.64, RI 0.89, average GC bootstrap support of 74.6). Analysis of Dataset 2 resulted in nearly 1500 poorly resolved, poorly supported trees (CI 0.77, RI 0.88, average GC support of 35.2). The strict consenses reflect similar broad relationships between genera, but the low resolution of the second analysis obscures relationships within genera. These preliminary data suggest that much greater species-level phylogenetic precision is possible with wider application of modern imaging techniques.

GAPP, Wesley I., HOLDER, Mark T., LIEBERMAN, Bruce S.

Paper No. 30392-211368: COMPARING AND CONTRASTING PARSIMONY AND MAXIMUM LIKELIHOOD APPROACHES TO PALEONTOLOGICAL PHYLOGENETICS USING TRILOBITES AS A MODEL SYSTEM

Traditionally, paleontologists have used parsimony analysis to estimate tree topology in their analyses of fossil taxa. However, complications do arise when applying parsimony due to factors such as missing data, long-branch attraction, and large clades whose taxonomic diversity exceeds the number of characters available for phylogenetic analysis; these can affect results and may limit resolution, suggesting that expanding the tool kit available to phylogenetically-minded paleontologists beyond the simple application of parsimony may lead to advances in phylogeny reconstruction. The use of maximum likelihood (ML) may help obviate some of these complications, but naïve application of the same ML methods used for molecules to morphology is problematic because of several differences between morphological and molecular data. In particular, modifications to likelihood models have been developed by Paul Lewis and others that accommodate some of the ascertainment biases implicit in morphological phylogenetic approaches that make these types of data so different from molecular data. These ascertainment biases include only sampling variable data or excluding autapomorphies. We have extended the GARLI software by implementing models that included extensions of Lewis' approach for correcting for ascertainment biases. These extension enable ML tree searching for fossil data sets. These modifications make the application of ML to phylogeny estimation with morphological data more tractable. Here we apply ML methods to phylogenetic analysis of an enigmatic collection of Ordovician cheirurid trilobites previously referred to the Eccoptochilinae. We especially focus on the differences between results from parsimony and ML, although each supports a paraphyletic “Eccoptochilinae” and suggests the group is nested within another subfamily, the Sphaerexochinae. We also consider differences between ML analyses of groups that differ substantially in size, using a previous analysis of Early Cambrian olenelloid trilobites as a comparison. ML phylogenetic methods applied to fossil taxa appear to provide great promise, but at this time analyses require substantial computational time. Further, thus far with large clades the degree of resolution is less than that attained by parsimony-based supertree approaches.

CONGREVE, Curtis R., KLOC, Gerald

Paper No. 30392-210086: PHYLOGENETIC AND TAXONOMIC REVISION OF CERAURID TRILOBITES

The genus Ceraurus Green 1835 is a speciose group of cheirurid trilobites from the Ordovician of North America. Despite being diverse and successful throughout the Late Ordovician, the group went extinct at the end Ordovician Mass Extinction Event. Over the years, taxonomists have split this large genus into various genera (Leviceraurus Hessin 1988, Gabricerarus Prybl Vanek and Pek 1985, Bufoceraurus Hessin 1988, etc.) suggesting “Ceraurus” might actually be better considered a tribe of related forms, however this hypothesis has not previously been tested phylogenetically. This study used specimen based phylogenetic analysis in order to elucidate the relationships between species within this potential “ceraurid tribe”. To this end, a larger scale phylogenetic analysis was first conducted on the subfamily containing the ceraurids, the Cheirurinae Hawle and Corda 1947, in order to understand the positions of the groups within the clade. Then, small phylogenies were conducted on the various clades of ceraurids in order to understand interspecific relationships, as well as to test the monophyly of the genera. Furthermore, new material collected from Wisconsin, Iowa, Missouri, New York, and Ontario were used to name several new species of ceraurid trilobites, as well as to revise established taxa, including the type species of the genus, Ceraurus pleurexanthemus Green 1835. This revision of the ceraurids is part of a larger, ongoing study of cheirurid trilobites that seeks to both revise the taxonomy of the cheirurids, as well as to generate phylogenetic hypotheses that can be used to better understand the macroevolutionary significance of the End Ordovician Mass Extinction on the evolution of the group as a whole.

[Caleb]

I can't wait to get my hands on that last paper!

[Missourian]

I hope they aren't the dreaded 'abstracts with programs', where there are presentations at the symposium, but the papers never see the light of day.

This happened with the 'paper' "KNOB NOSTER; A NEW UPPER CARBONIFEROUS (PENNSYLVANIAN) LAGERSTÄTTE IN MISSOURI CONTAINING MILLIPEDS (DIPLOPODA), INSECTS, CRUSTACEANS, VERTEBRATES, PLANTS, AND OTHER TERRESTRIAL AND BRACKISH WATER ORGANISMS", with an abstract here: https://gsa.confex.c...ract_50110.htm. It's been 10 years and counting....

[piranha]

I hope they aren't the dreaded 'abstracts with programs', where there are presentations at the symposium, but the papers never see the light of day.

This happened with the 'paper' "KNOB NOSTER; A NEW UPPER CARBONIFEROUS (PENNSYLVANIAN) LAGERSTÄTTE IN MISSOURI CONTAINING MILLIPEDS (DIPLOPODA), INSECTS, CRUSTACEANS, VERTEBRATES, PLANTS, AND OTHER TERRESTRIAL AND BRACKISH WATER ORGANISMS", with an abstract here: https://gsa.confex.c...ract_50110.htm. It's been 10 years and counting....

Sad but true...

...at least there is hope that a fraction of interest generates a few published papers. In any event, a good snapshot of some of the current research projects.

[pleecan]

I can't wait to get my hands on that last paper!

Gerald Kloc is a member of the Fossil Forum.

[piranha]

Another round of trilobite abstracts from the upcoming GSA conference in Kalamazoo, Michigan (May 2-3).

The last four abstracts are from a special session entitled:

T15: Paleontology as a Murder Mystery: How the Study of Predation and Taphonomy

Reveals the Means, Motives & Opportunities of Ancient Perpetrators and Their Victims

NEW INSIGHTS INTO THE TRILOBITE AND CONODONT BIOSTRATIGRAPHY OF THE

MIDDLE-UPPER DEVONIAN GENESEE GROUP IN EASTERN NEW YORK STATE

Paper No. 8-7 Presentation Time: 8:00 AM-12:00 PM

ZAMBITO, James J. IV, Department of Geology and Geography, West Virginia University

DAY, Jed, Geography & Geology, Illinois State Univ

During the Middle Devonian (Givetian) Global Taghanic Biocrisis, numerous trilobite families underwent extinction including the Homalonotidae. In northeastern North America, the last occurrence of homalonotid trilobites (Dipleura dekayi) has previously been reported in strata deposited during the final stages of the Taghanic Biocrisis (semialternans Zone –latest Middle Givetian) including the Tully Formation of the northern Appalachian Basin and the Petoskey and Thunder Bay formations of the Michigan Basin. Globally observed low-oxygen conditions associated with the Taghanic Biocrisis, represented by the Geneseo and Antrim black shales in the Appalachian and Michigan basins, respectively, have been interpreted to be at least in part responsible for the local extinction of the Homalonotidae and other trilobite families. Recent geologic mapping in eastern New York State (northern Appalachian Basin) has documented the occurrence of Dipleura dekayi in siliciclastic-dominated, nearshore post-Taghanic strata that were deposited below fair-weather wave base. Although these strata have been mapped as Genesee Group, they have yet to be assigned a formation-level designation. An integrated stratigraphic approach, including litho-, sequence-, and conodont biostratigraphy has provided new insight into the stratigraphic succession in the eastern Genesee Group, representing marine shelf through non-marine settings. Lithostratigraphic correlation places the occurrence of Dipleura dekayi above the level of the Fir Tree Limestone of western, offshore sections. Application of a sequence stratigraphic model has enabled the identification of time-rich intervals such as flooding surfaces and sequence boundaries that have yielded conodonts. Preliminary conodont biostratigraphic data suggests that Dipleura dekayi persisted into at least the latest Middle Devonian Lower subterminus Zone (=Lower disparilis Zone). Preliminary mapping further suggests that Dipleura dekayi may have even survived into the Late Devonian. Similar to other northern Appalachian Basin taxa that persisted through the Taghanic Biocrisis, Dipleura dekayi apparently found intra-basinal refuge in oxygenated, nearshore shelfal settings.

CARNIVOROUS TRILOBITES: MORPHOLOGIC, ICHNOLOGIC, AND TAPHONOMIC EVIDENCE

Paper No. 27-3 Presentation Time: 8:40 AM

BABCOCK, Loren E., School of Earth Sciences, The Ohio State University

BRANDT, Danita S., Department of Geological Sciences, Michigan State University

Mounting evidence from polymerid trilobites and their trace fossils suggests that many, and perhaps the majority, of taxa were active predators or scavengers. Morphologic evidence from the exoskeleton includes attachment mechanisms allowing active movement of the hypostome, and in some, hypostome morphology (e.g., forked serrated blades capable of slicing prey). Spiny appendages may have assisted in restraining prey. Numerous Rusophycus-Planolites trace fossil associations representing the interactions of trilobites and ‘worms’ provide clear documentation of trilobite attack strategy and prey manipulation. A large variety of Rusophycus predation traces are now known. The trilobites’ incursions into the sediment for purposes of feeding are remarkably precise, suggesting that chemosensory skills may have played a large role in locating prey that was concealed within sediment. Fossilized alimentary tracts, preserved through early diagenetic mineralization, provide another source of information about trilobite ‘paleogastronomy,’ the dietary habits of trilobites. Numerous trilobites are now known to preserve digestive tracts, and nearly all have mineralized (not sediment-filled or sclerite-filled) guts. This implies that the guts were fluid-filled at the time of death and burial, a condition common in extant carnivorous arachnomorph arthropods.

ICHNOLOGIC EVIDENCE FOR PREDATORY TRILOBITES: HOW LITERALLY CAN WE READ THE RECORD?

Paper No. 27-4Presentation Time: 9:00 AM

BRANDT, Danita S., Department of Geological Sciences, Michigan State University

Superimposition of trilobite trace fossils (Rusophycus) with “worm” burrows (e.g, Paleophycus) is used to support interpretations of trilobite predatory behavior. However, the stratigraphic range of these “trilobite hunting burrows” is not entirely coincident with the stratigraphic range of trilobite taxa presumed to have been predatory, based on the morphological criterion of having had spinose gnathobases. Trilobites with spinose gnathobases reportedly range from the Cambrian through the Permian; Rusophycus is also known over the same range. Trilobite/worm burrow associations are relatively rare. Specimens interpreted as showing this predator/prey interaction have been described from four different stratigraphic localities ranging from the Cambrian to the Silurian. If trilobites with spinose gnathobases were predatory, why are there no trilobite hunting burrows from post-Silurian strata? If the correlation of possession of spinose gnathobases with a predatory habit is causal, then a literal reading of the fossil record of trilobite hunting burrows suggests that our characterization of post-Silurian trilobite limbs is incomplete, and that, after the Silurian, trilobites did not occupy the predator niche. The elimination of this trophic option would have reflected the reduction of trilobite diversity through the Mid-to-Late Paleozoic.

DIETARY PREFERENCES OF THE CAMBRIAN TRILOBITE ELRATHIA KINGII: INFERENCES FROM FOSSILIZED DIGESTIVE TRACTS

Paper No. 27-5 Presentation Time: 9:20 AM

PETEYA, Jennifer A. and BABCOCK, Loren E., School of Earth Sciences, The Ohio State University

Specimens of the common trilobite Elrathia kingii from the Wheeler Formation (Cambrian Series 3) of western Utah were studied for their digestive tract contents using standard microscopic, computed tomographic (CT) imaging, and microtomographic (micro-CT) imaging techniques. Specimens showing fossilized alimentary tracts are complete dorsal exoskeletons retaining the librigenae, preserved in cone-in-cone calcite concretions. Examined specimens have collapsed glabellas that approximate the margins of the stomach cavity. Remains of the digestive system are outlined by a thin crust of pyrite, perhaps reflecting early mineralization of a biofilm associated with decay early in the taphonomic process. Similar pyritic crusts have been observed on the hypostome and near the exoskeletal margin. A circular stomach is located in the anterior part of the glabella, and it is followed by a thin, slightly tapering tube that extends the length of the axis. Neither sediment fill nor macerated sclerites have been found in the gut of E. kingii, which tends to rule out the possibility that this trilobite was either a sediment deposit-feeder or a sclerite-ingesting durophagous carnivore. Instead, the presence of an open, pyrite-lined gut suggests a fluid-filled alimentary tract at the time of death, and implies a carnivorous feeding strategy involving separation of the skeletal parts of prey prior to ingestion.

DEATH BY COMMON HOUSEHOLD TOOLS: MECHANICAL ANALOGY AND THE FUNCTIONAL MORPHOLOGY

OF THE HYPOSTOME IN GENUS ISOTELUS (DEKAY) EVIDENCE FROM ISOTELUS IOWENSIS (OWEN)

Paper No. 27-6 Presentation Time: 9:40 AM

DEVERA, Joseph, Illinois State Geological Survey, Prairie Research Institute, University of Illinois

The forked morphology of the hypostome in the Genus Isotelus (DeKay) is analogous to the common straight claw hammer. The claw portion of the hammer is strikingly similar in form and function to that of the isotelid hypostome. Cross-sections of both isotelid hypostome and claw hammer reveal a flat to slightly curved ventral surface and a beveled, dorsal surface on the inner side of each tine. The notch of the fork in the hypostome narrows toward the anterior end of the structure, identical to a claw hammer. This morphology implies a prying function for the isotelid hypostome. The forked morphology together with the partially arched, enrollment habit observed in Isotelus iowensis(Owen) fossils, suggests a dual prying/digging habit for feeding purposes. All isotelid cephalons are convex, spade-like and were well adapted for digging in soft, lime-mud environments where they are typically preserved. This idea supports the predatory habits for asaphid trilobites proposed by Forety and Owens. Isotelid species including I. maximus, I. gigas, I. rex and I. iowensis all attain a relatively large size compared to other trilobites. This relates to food intake that had high nutritional value. A number of specimens of I. iowensis have been found in association with Chondrites isp. burrows. In the Maquoketa Shale, a distal tempestite bed containing anoxic mud (now pyritic shale) yields trilobites “frozen” in time. They appear to have been feeding at the level of an abundance of Chondrites isp.burrows. The forked shape of the isotelid hypostome was an adaptation for infaunal polychete worm extraction. The flattened shovel-like cephalon was well adapted for digging into soft sediment. The morphological fits between common household tools i.e. claw hammer and spade and the hypostome and cephalon in the Genus Isotelus is remarkable. This strategy made the isotelids highly successful as predators on and in muddy infaunal environments.