Conodont microfossils extracted from limestone at “Fossil Hill” in central Nevada about 60 years ago were the first of Middle Triassic age (ca. 243 My) discovered in North America. These canoe-shaped elements were named Neogondolella constricta, a species that subsequently has been reported worldwide. However, the scope of this species has remained uncertain because it was based on comparatively small early growth stages characterized by features lost during growth. Abundant specimens of the N. constricta group recovered from the original type locality form the basis for documenting changes in morphology during their accretionary growth and provide better definition of the species. This facilitates discrimination of similar species, 10 of which are distinguished in Nevada, including four new taxa; most of these are also identified in British Columbia. Successive associations through the Fossil Hill strata include elements with similar platform shapes but different relative lengths, the younger species being longer. This succession is calibrated with established ammonoid fossil zones and contributes to a parallel conodont biozonation. Eurasian occurrences of the Neogondolella constricta group are assessed and their correlation with the Nevadan scheme summarized.

Neogondolella constricta (Mosher and Clark, 1965) from the Prida Formation at Fossil Hill in central Nevada was the first conodont described from Middle Triassic strata in North America. The species has since been widely reported from elsewhere despite uncertainties about its taxonomic scope and that of similar related taxa. Poor definition of these taxa has spawned a diverse nomenclature and inhibited use of the group in biozonation. Starting with a growth series of topotype N. constricta, we reassess allied contemporaneous taxa from North America. In Nevada, 11 conodont taxa are identified: N. constricta, N. aldae Kozur, Krainer, and Mostler, 1994b, N. cornuta Budurov and Stefanov, 1972, N. ex gr. mesotriassica (Kozur and Mostler, 1982), N. postcornuta (Kovács, 1994), N. posterolonga Kozur, Krainer, and Mostler, 1994b, N. quasiconstricta n. sp., N. quasicornuta n. sp., and three subspecies of N. excentrica Budurov and Stefanov, 1972. Successive associations of taxa display symmetry transition in posterior platform configuration. Subdivision of the upper Anisian–lower Ladinian is provided by dominant N. constricta plus relatively uncommon N. quasiconstricta n. sp. and N. excentrica primitiva n. subsp. in the Rotelliformis ammonoid zone. This is followed in the Meeki through the Subasperum zones by dominant N. cornuta, associated N. posterolonga, plus relatively uncommon N. quasicornuta n. sp., and a variety of asymmetric elements: the Meeki Zone includes N. aff. N. cornuta; the Occidentalis Zone adds N. e. excentrica; and finally, N. e. sigmoidalis n. subsp. appears in the Subasperum Zone. In British Columbia, the three subspecies of N. excentrica are recognized in, respectively, the Deleeni, Chischa, and Matutinum (and younger) ammonoid zones.

Tropidoleptus was a genus of brachiopods that had a very peculiar morphology and occurred in the Devonian period (about 419–358 million years ago) throughout the world. Although there have been reports of the presence of this genus in the Paraná Basin (Brazil) since the nineteenth century, its actual occurrence has been the subject of much debate. The objective of this work was to clarify this situation. For that, dozens of specimens from the Brazilian state of Mato Grosso were analyzed. The studied samples have typical characteristics of Tropidoleptus, therefore this genus actually also occurred in the Paraná Basin. Tropidoleptus possibly arrived in the Paraná Basin 385 million years ago, at the moment when there was a marine connection among the Brazilian Paraná, Parnaíba, and Amazonas basins. The occurrence of Tropidoleptus can be used as a marker of shallower marine environments, and in the Paraná Basin in particular, it can indicate that the rocks, where they are present, are less than 390 million years old.

Tropidoleptus is a brachiopod genus with a very peculiar morphology that existed throughout the Devonian as a cosmopolitan taxon. Although there have been reports of the presence of this genus in the Paraná Basin since the nineteenth century, its actual occurrence has been the subject of much debate. The objective of this paper was to clarify this situation. For this purpose, dozens of specimens from Monjolo dos Padres and Juscimeira outcrops (São Domingos Formation, possibly Givetian) in the Brazilian state of Mato Grosso were analyzed. The samples studied here exhibit the typical characteristics of Tropidoleptus, confirming that this genus also occurred in the Paraná Basin. It is possible that Tropidoleptus entered the Paraná Basin during the Eifelian/Givetian from the Amazonas and/or Parnaíba basins (Brazil), during a period of warm-water transgression. When Tropidoleptus is found in situ, it can serve as an indicator of a shallower water environment (shoreface to shallower portions of transitional offshore). In the Paraná Basin, its presence can indicate rocks no older than the Eifelian–Givetian transition.

On the Sinai Peninsula, a thick pile of terrestrial to shallow-marine sediments accumulated during the Jurassic period. The sea floor at that time was colonized chiefly by brachiopods and bivalves. Among the latter, trigoniids were a comparatively rare but diverse faunal element, represented by very small to small individuals. They belong to 14 species and nine genera. One of these species is new to science, but five genera with species occurring also elsewhere in Jurassic seas were recognized as new, all of them characterized by a very small to small size.

The Jurassic trigoniid bivalves of Gebel Maghara, northern Sinai, Egypt are described and figured. They belong to 14 species, nine genera, and two families. The identified taxa occur in rocks ranging in age from the Toarcian (Lower Jurassic) to the lower Kimmeridgian (Upper Jurassic). Five genera and one species are new: Magharitrigonia asymmetrica new genus new species; Cotswoldella aff. C. hemisphaerica (Lycett, 1853); Cornbrashella pullus (J. de C. Sowerby, 1826); Parorthotrigonia lepidomorpha (Abdallah and Fahmy, 1969); and Retetrigonia imbricata (J. de C. Sowerby, 1826). Five species, Trigonia reticulata Agassiz, 1840, T. cf. T. castor d'Orbigny, 1849, Promyophorella tuberculata (Agassiz, 1840), Orthotrigonia exortiva (Kitchin, 1903), and O. gracilis (Kitchin, 1903) are recorded from the Jurassic rocks of Gebel Maghara for the first time.

Monstrocrinus is a most unusual crinoid from the Devonian of Germany. It has long, simple to complex spines attached to most calyx plates. A stem was not associated with the initial specimens on which this genus was named. Thus, it was assumed that Monstrocrinus was a stemless crinoid that sat directly on the sea floor and, when alive, rolled around on its spines. For a variety of reasons, this seems unlikely, but the rolling crinoid lifestyle interpretation has persisted in the literature. More thorough cleaning of historical specimens and, more importantly, a new specimen with an attached column clearly refute the classical lifestyle interpretation and demonstrate that Monstrocrinus was a typical crinoid attached to a long column that was presumably anchored to the sea floor. In addition to revising the lifestyle of this crinoid, the varieties of spine types are redefined with names that more accurately reflect their morphology. Monstrocrinus occurs in Europe and South America, and one previously described species is placed in synonymy so that the genus is now comprised of three species.

The diplobathrid camerate crinoid genus Monstrocrinus is morphologically reinterpreted on the basis of new finds from the upper Emsian (Lower Devonian) to lower Eifelian (Middle Devonian) of Germany (Rhenish Slate Mountains, North Rhine-Westphalia, and Rhineland-Palatinate). The most complete, new specimen has a long segment of column projecting outward from the basal concavity, which confirms that the Monstrocrinus crown was attached to a column as an adult. Thus, a free-living life mode of a passively rolling or drifting crinoid is refuted and Monstrocrinus is reinterpreted as an attached, stalked echinoderm. This finding is supported by re-examination of the historical type material. A column attachment with a central pentalobate axial canal was recognized for the first time in the calyx of the holotype of the type species Monstrocrinus securifer. The holotype of Monstrocrinus granosus is far more complete than previously thought. It is a partially disarticulated crown embedded together with an associated longer part of the column. The extraordinary spines on the calyx plates of Monstrocrinus can be divided into eight morphological types and into two superordinate categories: “Category A” is a physical part of the calyx plate, whereas “Category B” is an attachment onto the calyx plate. Taxonomically, M. aliformis from the upper Emsian of Spain is treated herein as a subjective junior synonym of M. securifer.

The new fossil eryopid amphibian Stenokranio boldi, a temnospondyl closely related to Eryops, is described here. The new crocodile-like amphibian is based on well-preserved cranial and postcranial material from ca. 300 million-year-old fluvio-lacustrine deposits of the Permo-Carboniferous (Gzhelian/Asselian) in the Saar–Nahe Basin of southwestern Germany. Phylogenetic analysis identifies Stenokranio as a sister taxon to Eryops. Stenokranio was among the largest predators of the Saar–Nahe Basin. Due to its semiaquatic lifestyle, Stenokranio was able to scour the river and lake shores for prey, but most likely fed on aquatic vertebrates. Stenokranio was part of a faunal assemblage of aquatic, semiaquatic, and fully terrestrial vertebrates, such as sarcopterygian and actinopterygian fishes, xenacanthid sharks, a dvinosaurian temnospondyl, and various other tetrapods (“lepospondyls”, diadectomorphs, and synapsids). This corresponds broadly to the vertebrate community from Permo-Carboniferous rocks in North America that are approximately the same age.

A new eryopid temnospondyl, Stenokranio boldi n. gen. n. sp. is described based on well-preserved cranial and postcranial material from fluvio-lacustrine deposits of the Permo-Carboniferous (Gzhelian/Asselian) Remigiusberg Formation at the Remigiusberg quarry near Kusel, Saar–Nahe Basin, southwest Germany. The new taxon is characterized by three autapomorphies within the Eryopidae: (1) the relatively narrow posterior skull table, therefore nearly parallel lateral margins of the skull; (2) the short postparietals and tabulars; and (3) the wide ectopterygoid. Phylogenetic analysis reveals a monophyletic Eryopidae with the basal taxa Osteophorus, Glaukerpeton, and Onchiodon labyrinthicus forming a polytomy. Actinodon may be either a basal eryopid or a stereospondylomorph, and the genus Onchiodon is not monophyletic. Stenokranio n. gen. is found as a more derived eryopid forming the sister taxon to Eryops. Stenokranio n. gen. was among the largest predators of the Saar–Nahe Basin. Its semiaquatic lifestyle enabled Stenokranio n. gen. to browse riverbanks and lake shorelines for prey, but most likely it fed on aquatic vertebrates. Stenokranio n. gen. was part of a faunal assemblage of aquatic, semiaquatic, and fully terrestrial vertebrates, such as sarcopterygian and actinopterygian fishes, xenacanthid sharks, a dvinosaurian temnospondyl, different “lepospondyls”, diadectomorphs, and synapsids. This is in general accordance with the vertebrate community from the Permo-Carboniferous of North America and from the early Permian localities of Manebach (Thuringian Forest Basin) and Niederhäslich (Döhlen Basin). It is notable that the occurrence of Stenokranio n. gen. and other eryopids in these localities excluded the presence of other large temnospondyls such as Sclerocephalus. However, a previously described isolated eryopid mandible from the Remigiusberg locality differs from that of Stenokranio n. gen. in several characters, implying that probably two different eryopid taxa lived at the same locality.

Multituberculates were rodent-like mammals that existed for some 130 million years and survived the mass extinction event that decimated the non-avian dinosaurs (Cretaceous–Paleogene boundary; 66 million years ago). Despite this lengthy record, multituberculates remain one of the more poorly understood mammalian groups, a situation resulting in part from their fossil record consisting largely of isolated teeth and jaws, which makes confident identification difficult. Fortunately, the blade-like lower fourth premolar (p4) of many multituberculates is frequently preserved, and has significant diagnostic power, allowing researchers to distinguish multituberculates, sometimes to species level. Various methods have been used in examining the p4, ranging from qualitative assessments and basic measurements to more sophisticated statistical methods that quantify form (called morphometrics). A recent study comparing the effectiveness of qualitative and quantitative methods for distinguishing the p4s of species of the Late Cretaceous–early Paleocene multituberculate genus Mesodma concluded that size is the most important contributor to morphological variation among the included species. To test this hypothesis, we applied the study methods to a novel dataset that included additional species of Mesodma, and to a second dataset consisting of unidentified p4s of Mesodma. Our results suggest that rather than size being the most important variable in distinguishing species of Mesodma, that shape and size are more informative when analyzed together. Our results confirm previous hypotheses that shape and size are intricately linked, and that biological significance is sometimes difficult to maintain when attempting to isolate each variable. The use of quantitative methods such as those proposed in the original study, with appropriate caution, were found to be useful in distinguishing among the p4s of the various species of Mesodma and have potential for use in studies on other multituberculates more broadly.

Although knowledge of their fossil record continues to improve, multituberculates nonetheless remain one of the more poorly understood mammalian clades, which can be attributed to a record comprised of isolated teeth and fragmentary jaws. Fortunately, the p4 of multituberculates is the most common form of remains for this group and is a principal source of diagnostic characters in systematic studies, the p4 of cimolodontan multituberculates is both common and a source of diagnostic characters in systematic studies. The results of a recent morphometric study on the neoplagiaulacid Mesodma suggest that p4 size may be more useful than shape in diagnosing the various species referred to this genus. We tested this hypothesis by applying two different morphometric methods (2D geometric morphometrics and linear measurements) to two samples: (1) one including the p4s of four known species of Mesodma (M. ambigua, M. thompsoni, M. formosa, and M. pygmaea), and (2) a sample of unidentified p4s of Mesodma from the Bug Creek Anthills locality of northeastern Montana. Our results indicate that while form explains most of the morphological variation in p4s of the various species of Mesodma, linear-measurement data support differences in p4 morphology that are not recovered by form data alone. Depending on the methods used, we found evidence for the presence of one or more species of Mesodma in the Bug Creek Anthills fauna. Although shape and size both contribute to morphological variation in the p4 of Mesodma, our results suggest that the diagnostic power of each varies with the type of methodology employed.

We describe new material of a small early rodent, Lophiparamys. The material includes the first ankle bones of Lophiparamys and indicates that it spent more time climbing than other early rodents. The new material is also the first record of its species, Lophiparamys debequensis, from north-central Wyoming. It helps to clarify how L. debequensis differs from other species of Lophiparamys. A phylogenetic analysis of the relationships of Lophiparamys does not confidently show what other rodents it was related to, but it may have been related to living dormice.

We report new material of the rare early Eocene rodent Lophiparamys debequensis Wood, 1962 from the Willwood Formation of the southern Bighorn Basin, north-central Wyoming. The new material constitutes the first record of L. debequensis from the Bighorn Basin and documents aspects of the anatomy of Lophiparamys that were previously unknown, including a portion of the maxilla and a portion of the tarsus. The maxillary fragment demonstrates that Lophiparamys has a small P3 and a relatively large infraorbital canal. The tarsus of Lophiparamys is similar to that of other early rodents but differs in a few features that suggest an arboreal locomotor repertoire, including an asymmetric astragalar trochlea, long astragalar neck, transverse astragalar sustentacular facet, short calcaneal tuber, elongate calcaneal ectal facet, and circular calcaneal cuboid facet. The presence of arboreally adapted features in the tarsus of Lophiparamys is consistent with a hypothesized relationship between small-bodied Eocene microparamyine rodents and extant Gliridae. Phylogenetic analysis fails to consistently support this relationship or monophyly of Microparamyinae, but both remain plausible. Comparison of L. debequensis with other species of the genus emphasizes the distinctiveness of L. debequensis and suggests the presence of multiple lineages of Lophiparamys.

The name eomysticetids refers to the “dawn” of the baleen whale, suggesting the critical role in understanding the origin and early evolution of baleen whales. Eomysticetids represent an early diverging lineage showing the baleen-assisted feeding mode—an essential feature for baleen whales, including giant animals such as the blue or fin whales. This paper describes a new eomysticetid species—Echericetus novellus—from the Oligocene of Mexico, about 28 million years old. Our discovery of a new species of Oligocene eomysticetids from Mexico shows a much broader global distribution and higher diversity than previously recognized. The existence of Echericetus novellus from Mexico indicates that eomysticetids also inhabited warmer waters in the Northern Hemisphere instead of primarily higher latitudinal regions. Last, our discovery of a new but extinct eomysticetid from the Oligocene of Mexico provides new insights into the distribution pattern and habitat use of Eomysticetidae, which helps to decipher the ultimate demise of this once-successful baleen whale lineage.

Among the several evolutionary lineages of the baleen whales (Mysticeti), the eomysticetids are an ancient successful family that retain possibly nonfunctional teeth and functional baleen, a transitional stage between toothed and baleen-assisted filter-feeding mysticetes. The patchy fossil record leaves gaps in eomysticetid paleobiology interpretations, but their diversity and widespread geographical distribution can be a relevant proxy to understanding the evolution of crown Mysticeti. Here we describe a new baleen whale, Echericetus novellus n. gen. n. sp., from the Oligocene of Mexico (slightly older than 27.95 million years ago). This new taxon has morphological features that show its affinity to Eomysticetidae, such as the intertemporal region longer than wide, the elongate and oval temporal fossa, and a well-developed and lobate coronoid process of the mandible. Similarly, our cladistic analyses confirm the inclusion of Echericetus in the Eomysticetidae. Echericetus reinforces our notion of the eomysticetid diversity and disparity. Geographically, the existence of Echericetus from Mexico also indicates that eomysticetid inhabited subtropical regions in the Northern Hemisphere. Last, our discovery of a new eomysticetid from the Oligocene of Mexico provides new insights into the distribution patterns and habitat use of Eomysticetidae, essential to further explain the demise of this transitional lineage between toothed and baleen-bearing whales.