Revision of the type species of the Early Ordovician (Tulean, late Tremadocian) bathyurid trilobite Licnocephala Ross, 1951 demonstrates that it has significantly different morphology than that ascribed to it in the earlier literature, which was based largely on species now assigned to a different genus. In addition to the type species, L. bicornuta Ross, 1951, which is fully revised on the basis of new material, four species, all apparently new, have been recovered, two of which, L. ngi n. sp. and L. bradleyi n. sp., are well enough known to formally name. The overall phylogenetic structure of bathyurids is yet to be determined, but several apparent clades can now be recognized and are discussed. Among these is what is termed the “Chapmanopyge group,” including Chapmanopyge Fortey and Bruton, 2013, Punka Fortey, 1979, Uromystrum Whittington, 1953, and Licnocephala. These genera are united in the occurrence of much of the anterior cephalic border on the librigenal anterior projection, with most of the anterior margin of the cranidium representing the suture, the possession of very short (exsag.) strap-like posterior cranidial projections, and extremely narrow visual surfaces. A fifth genus of the group, Ibexocephala n. gen., is represented by two new species, I. lossoae (type species) and I. dekosterae. The taxon features a remarkable cranidial morphology involving a strong deflection of the posteriormost part of the cranidium from the anterior part in sagittal profile.

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Differences in brachyuran morphology among and between juveniles and adults as well as sexual dimorphism are not well studied among extinct brachyuran crabs. Carapace dimorphism and morphological changes during growth have received little attention in fossil crabs. Tetracarcinus subquadratus Weller, 1905, Dakoticancer australis Rathbun, 1935, and Seorsus wadei Bishop, 1988 are herein synonymized on the basis of examination of dozens to hundreds of specimens of each from the same locality. Synoriacarcinus new genus is named to embrace two species previously referred to Seorsus Bishop, 1988, Synoriacarcinus millerae (Bishop, 1992), new combination, and Synoriacarcinus kauffmani (Feldmann et al., 2013), new combination. Both Dakoticancridae and Ibericancridae were well established on coastal North America during the Late Cretaceous but became extinct in the end-Cretaceous event.

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Obruchevodid petalodonts are rare small chondrichthyans known from nearly complete to partial skeletons from the Upper Mississippian (Serpukhovian) Bear Gulch Limestone of central Montana and isolated teeth from the Upper Mississippian Bangor Limestone of northern Alabama. New records of obruchevodid petalodonts are presented here from the Middle Mississippian (Viséan) Joppa Member of the Ste. Genevieve Formation at Mammoth Cave National Park, Kentucky. Obruchevodids are here represented by multiple teeth of a new taxon, Clavusodens mcginnisi n. gen. n. sp., and a single tooth referred to ?Netsepoye sp. Clavusodens mcginnisi n. gen. n. sp. is characterized by teeth with pointed mesiodistal and lingual margins and more robust chisel-like cusps on the anterolateral and distolateral teeth. The suggestion that obruchevodid petalodonts evolved to inhabit complex reef-like environments and other nearshore habitats with a feeding ecology analogous to extant triggerfish is explored and discussed.

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Identifying feeding interactions in the fossil record remains a key challenge for paleoecologists. We report the rare occurrence of a conical, perforative bite mark in a cervical vertebra of an azhdarchid pterosaur, which we identified as a juvenile individual of Cryodrakon boreas Hone, Habib, and Therrien, 2019 from the Campanian Dinosaur Park Formation in Alberta, Canada. Based on comparative analysis of the dentition and ecomorphology of potential trace makers in the Dinosaur Park Formation, as well as the morphology of the trace, the most likely candidate is a crocodilian, although whether it was made as a result of scavenging or predatory behavior is unknown. Feeding interactions involving pterosaurs are rare globally, whereas crocodilian bite marks are not uncommon in Cretaceous terrestrial ecosystems. Given the opportunistic feeding style and known range of food items for both extant and extinct crocodilians, pterosaurs can be counted as a rare, but not surprising, component of at least some Cretaceous crocodilian diets.

Fossil egg capsules of chimaeroids (holocephalian fishes), although rare, have been known for more than 150 years (Bessels, 1869; Meunier, 1891a) and have been found in rocks as old as Upper Triassic (Gottfried and Fordyce, 2014). Egg capsules of extant chimaeroids are spindle shaped, with a smooth central body where the embryo develops, an elongate anterior beak through which the hatchling emerges, and an elongate posterior pedicle. The capsules are flanked by a lateral membrane or web on both sides, and the web is reinforced with branching or unbranching rib-like costae that extend laterally from the central body, beak, and pedicle. Specimens are typically about 10–30 cm long. Egg capsules of extant chimaeroids are made of collagen (Hamlett et al., 2005) and as fossils, chimaeroid egg capsules are typically preserved as external casts (Fischer et al., 2014).

The existence of Ordovician Peruvian cephalopods has been known since at least the 1910s. However, they have not been effectively documented previously with only a few described taxa listed in open nomenclature. Here, we describe a cephalopod assemblage at the finest taxonomic level possible. The specimens were collected from the Floian section (Baltograptus minutus graptolite Zone) of the San José Formation from the Kimbiri area, northwest of Cuzco (= Cusco), and from a section along the Inambari River, southeastern Peru. The dark mudstone-siltstone of the San José Formation was deposited within the Central Andean Basin. The assemblage contains five species of small orthoceracones belonging to four families and three orders, consisting of one indeterminate dissidocerid, one bathmoceratid (Saloceras sp.), one rioceratid (Rioceras? sp.), and two baltoceratids belonging to Annbactroceras grecicostatum (Kobayashi, 1937), and Bactroceras cocafolium new species. The dominance of small orthoceracones is typical for early Paleozoic pelagic cephalopod assemblages. One species, A. grecicostatum, is known from elsewhere in the Central Andean Basin. The other taxa indicate a peri-Gondwana-Avalonia paleogeographical relationship of the cephalopod fauna, which is consistent with previously published data from brachiopods and trilobites.

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A small trilobite assemblage, including Parabolina (Neoparabolina) frequens, assignable to the Parabolina Fauna, has been recovered from the Furongian (Cambrian Stage 10) Sah Member of the Mila Formation in the Tuyeh–Darvar section, the eastern Alborz Mountains, north Iran. The assemblage includes eight genera and species; two of them, Niobella darvarensis n. sp. and Macropyge (Promacropyge) sahensis n. sp., are new to science. The incursion of a Parabolina fauna into Alborz is confined to a significant drowning event with associated dark-gray shale deposition, which most probably occurred in the lower part of the Cordylodus proavus conodont Zone. While the generic composition of the assemblage is mostly cosmopolitan with the exception of the endemic Alborsella, the occurrence of Indiligens, Macropyge (Promacropyge) sahensis n. sp., Agnostotes sp. aff. A. sulcatus, and Leiagnostus bexelli indicates faunal links with South China and Tarim. Parabolina (Neoparabolina) frequens is widespread mainly in offshore deposits from temperate Gondwana (Armorican terrane assemblage, Argentina) and Baltica of about that age.

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Predation is a behavior that is commonly unsuccessful, but the cause of failure is often difficult to determine in the fossil record. Here, we report on gastropod drill holes in two Plio- and Miocene bivalve specimens from the Netherlands created from the inner side of the bivalve prey's shell, which we call reverse drill holes. These holes are unequivocally caused by failure of the gastropod drilling predators to make effective use of their chemoreception and mechanoreception sensory adaptations. We hypothesize that the diffuse nature of chemical cues emanating from dense aggregations of living prey could have confused foraging predators and stimulated them to initiate the drilling process on empty valves. Poor decision making due to hunger is an alternative hypothesis. These traces represent the first reported examples of reverse gastropod drill holes from the fossil record, and the first attributed to Naticidae. Compared to other types of failed predation (incomplete drill holes and drill holes in multiply-drilled specimens) in the two assemblages studied, reverse drill holes are rare (< 1% of drill holes). This result implies that the driller's sensory and decision-making processes were generally reliable at distinguishing dead from live prey.

A new dalmanitid trilobite is described from the early Silurian (Telychian) Waukesha Biota in Wisconsin, USA, best known for its variety of exceptionally preserved arthropods. Waukeshaaspis eatonae new genus new species is the most common trilobite found in the Waukesha Biota, numbering ~200 specimens, allowing a thorough description of the dorsal exoskeleton. This new taxon has a combination of characters unique to the Dalmanitidae, including a distinct embayment on the posterior margin of the pygidium. Embayments are rare for dalmanitids, most species having instead a caudal spine. The lengthening of the genal spines might have served a similar function to that which a caudal spine would have served, allowing the embayment to fulfill a different function, related to keeping an opening when enrolled. The abundance at the preservation site suggests physiological tolerance at the habitation site.

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The ontogeny of two species of corynexochid trilobites from the middle Cambrian Mount Cap Formation of the eastern Mackenzie Mountains, northern Canada, is documented. Sahtuia carcajouensis (Dolichometopidae) and Mackenzieaspis parallelispinosa (Zacanthoididae) are both endemic to this formation and only known from one locality. They, along with several other corynexochid taxa, occur in a succession of mudstone with scattered carbonate interbeds, deposited in a weakly storm-agitated setting near the flank of a semi-enclosed basin. The ontogeny of both species is characterized by mainly normal cranidial development, but a unique distribution of segments in their thoraxes and pygidia. The number of trunk segments was typical for their respective families, whereas the final number of segments released into the thorax was reduced. This occurred in both species through timing modifications to segment release, indicating heterochrony. Sahtuia carcajouensis and Mackenzieaspis parallelispinosa are likely derived from two separate clades, and heterochrony probably arose separately but synchronously. The endemicity of both species probably reflects unique paleoecological conditions in this part of the basin. Preliminary results indicate that the fossil-bearing mudstone was deposited under well-oxygenated conditions that underwent high nutrient flux and possibly experienced varying salinity. These factors may have affected the organisms’ physiology, or perhaps provoked an adaptation to achieve early maturation.

Harpetid and trinucleid trilobites share a similar and unusual morphology, the most striking feature of which is a wide, flattened cephalic brim with many pits or holes. This similarity was once interpreted as a sign that these two groups of trilobites were closely related, but in recent years it has instead been assumed that the ‘harpiform’ brim arose in both groups independently. However, relatedness and similarity can be difficult to disentangle in fossil taxa without close living relatives, and this assumption about the harpiform brim has never been explicitly tested. Our study re-evaluates the relationship between Harpetida and Trinucleioidea in order to test a longstanding assumption about trilobite relationships and as a case study in evaluating different kinds of morphological similarity in extinct groups. We inferred a new phylogenetic tree using parsimony methods and discrete morphological character data from a broad sampling of harpetids, trinucleids, and their relatives. Despite their gross morphological similarities, we found that harpetids and trinucleids were readily distinguished in our analyses, a result consistent with a hypothesis of multiple origins for the harpiform brim. By mapping brim-related characters across our new phylogeny, we identified a sequence of morphological innovations that arose in parallel in both groups and led ultimately in each case to the evolution of the harpiform brim. These results indicate that harpiform brims are a prime example of parallel evolution—the similar development of a morphological trait in distantly related taxa that nevertheless share a similar original morphology. In addition, our phylogeny supports the idea that trinucleids are specialized, harpiform asaphids, rather than an independent order of trilobites. We also provide new information on the relationships of the putative ‘basal-most’ members of Trinucleioidea, the Liostracinidae, and confirm recent assessments that this family is more distantly related to trinucleids.

First-formed shells of several species of Dalmanellidae (Brachiopoda) from the Ordovician (Katian) of North America were measured and compared: Cincinnetina multisecta, Diceromyonia tersa, Diceromyonia storeya, Paucicrura corpulenta, Paucicrura rogata, and Paucicrura sillimani. Sizes and structures of the first-formed shells suggest that members of this family had planktotrophic subadults, with some species showing indications of only an unshelled larval stage and others showing both a larval stage and a shelled juvenile stage. This differs from modern rhynchonelliformean brachiopods, which all possess only a lecithotrophic larval stage. The range of sizes of first-formed shells of most studied species are similar, but P. sillimani of Baffin Island, Canada (middle Katian), has a significantly larger first-formed shell that formed during an extended juvenile stage. This may have enabled the species to colonize newly exploitable habitats during an interval of rapid sea level rise in Laurentia during the Katian. This plasticity of developmental modes in the Dalmanellidae shows not only that using distantly related modern brachiopods as an analog for extinct Paleozoic lineages may be misleading, but also that development can vary within a single lineage and that timing of developmental stages should not be considered a reliable character for use in phylogenetic studies of brachiopods.

Shape deformation during fossilization can prevent accurate reconstruction of an organism's form during life, hampering areas of paleontology ranging from functional morphology to systematics. Retrodeformation attempts to restore the original shape of deformed fossil specimens and requires an adequate knowledge of the deformation process. Although tectonic processes and retrodeformation are relatively well understood, research on quantifying the effect of compressive deformation on fossil morphology is scant. Here we investigate the factors that can cause changes in the shape of fossil specimens during compressive deformation. Three-dimensional (3D) models of trilobite cranidia/cephala are subjected to simulated deposition and compaction using rigid body simulation and scaling features of the open-source 3D software Blender. The variation in pitch and roll angle is lowest on flat surfaces, intermediate on tilted surfaces, and highest on irregular surfaces. These trends are reflected in the morphological differences captured by principal component scores in geometric morphometric analyses using landmarks. In addition, the different shapes of trilobite cranidia/cephala according to their systematic affinity influence the degree of angular variation, which in turn affects their posture—normal or inverted. Inverted cranidia/cephala show greater morphological variability than those with normal postures.

The Eager Formation (Cambrian Stage 4) of the Cranbrook area, British Columbia, contains abundant, sometimes beautifully preserved, trilobites and rare non-biomineralized taxa. Trilobites were first reported just over a century ago but have received little research attention, resulting in uncertainty in the number and identity of species within the assemblage and ambiguity in the age of the fauna. The trilobites of the Eager Formation in the Cranbrook area are described herein based largely upon material collected in 2015. A minimum of eight (and perhaps up to 11) trilobite species are recognized. The four species of olenelloids (Olenellus santuccii Webster n. sp., Olenellus? schofieldi, Mesonacis eagerensis, and Wanneria cranbrookense Webster n. sp.) are by far the most abundant elements of the fauna. At least two, and perhaps as many as five, species of dorypygid are present, as are two species of “ptychoparioids”. Paucity and poor preservational quality of specimens mean that the various dorypygid and “ptychoparioid” species are left in open nomenclature. Trilobite diversity in the Cranbrook Lagerstätte is comparable to that within other Lagerstätten from Cambrian Stage 4 (Series 2) of Laurentia. The diversity and abundance of trilobites, combined with biostratinomic and trace fossil data, suggest that the assemblage is autochthonous and/or parautochthonous, and that the local environment was at least periodically able to support a “typical” benthic trilobite community. The age of the Cranbrook Lagerstätte is constrained to lie within the middle Dyeran Stage of Laurentia, within what was a substantial stratigraphic gap in the distribution of Burgess Shale-type Lagerstätten.

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The Lower Ordovician (Floian) Al Rose Formation from the Inyo Mountains, California, is a deeper-water, graptolitic equivalent of the well-known and richly fossiliferous successions described from Utah and Nevada. It is considered to have been originally marginal to the Laurentian paleocontinent. It has yielded a low-diversity trilobite fauna that differs strikingly from contemporary faunas to the east in its abundance of raphiophorid, nileid, olenid, and agnostoid trilobites, resembling that of the Nileid Biofacies known from scattered locations marginal to Laurentia. Two new trilobite species are described: Globampyx sexsegmentatus (Raphiophoridae) and Protopresbynileus divergens (Nileidae). Carolinites genacinaca Ross, 1951 is a link with the Great Basin. Other trilobites include the olenid Cloacaspis cf. C. ceryx anataphra Fortey, 1974, metagnostid Geragnostus cf. G. (Novoagnostus) longicollis Raymond, 1925, and pliomerid Hintzeia sp.

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Fossils are rare in Cambrian strata of the Uinta Mountains of northeastern Utah, and are important because they can help integrate our understanding of laterally adjacent but discontiguous rock units, e. g., the Tintic Quartzite of Utah and the Lodore Formation of Utah-Colorado. New body fossils from strata previously mapped as Tintic or Cambrian Undifferentiated, but here interpreted as the Ophir Formation, include indeterminate hyoliths and hyolithids, brachiopods including a linguloid, and the trilobites Trachycheilus Resser, 1945 and Elrathiella Poulsen, 1927. The last two assign these strata to the Ehmaniella Biozone (uppermost Wuliuan Stage; Miaolingian Series) or traditional Laurentian middle Cambrian. These data, together with fossil occurrences elsewhere in Utah, require that the Tintic Quartzite was deposited prior to and/or during the early Wuliuan, and suggest that the unit could be correlative to much of the Lodore Formation of Utah and Colorado.

Here we describe the first articulated olenid trilobite specimens recovered from the lowermost Fezouata Shale Formation (lower Tremadocian, Ordovician) of Morocco. Prior to the discovery of this sample, only two partial olenid trilobite specimens had been found from this part of the rock record. The specimens are well preserved enough to confidently identify as Leptoplastides salteri (Callaway, 1877), extending the species geographic range from Avalonia into Gondwana. We argue that the Moroccan occurrences formerly referred to as “Beltella sp.” in the literature are likely to be those of L. salteri. This species is the only olenid trilobite known from African Gondwana.

Intense commercial exploitation of fossils in the famous El Qaid Errami area in the last 20 years has led to the discovery of the interesting Declivolithus Fauna in the Moroccan Anti-Atlas. This unusually large trinucleid trilobite, described originally from the Czech Republic, is the most conspicuous element of an assemblage mainly occurring in the Bofloss locality, a local biofacies development of pelagic mudstones and sandstones cropping out in a structurally isolated place in the Tizi n'Ounfite area. Here we revise this Declivolithus Fauna trilobite assemblage from Morocco, increasing the known trilobite diversity from four to 11 species: Ulugtella? biformis n. sp., Selenopeltis cf. S. vultuosa, Phacopidina quadrata, Eudolatites cf. E. bondoni, Prionocheilus cf. P. verneuili, Nobiliasaphus cf. N. kumatox, Cyclopyge cf. C. rediviva, Symphysops stevaninae, Heterocyclopyge sp., Dionide sp., and Declivolithus alfredi. The new data and the very good preservation of specimens in sandstones, clarify the specific identity of previously reported taxa. Although the stratigraphical correlation of the fossiliferous levels remains problematic, it probably corresponds to the upper part of the Lower Ktaoua Formation or to the lower half of the Upper Tiouririne Formation. Most taxa support previous assignment of the Moroccan assemblage to the late Berounian (ca. early Katian, Ka2), although a middle Berounian (ca. Sa2–Ka1) age cannot be excluded. Most of the identified species are known from the Czech Republic (eight out of 11), showing that the strong faunal link between Morocco and the Czech Republic still existed during the Late Ordovician, being stronger than the link with the coeval Ibero-Armorican domain faunas.

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