The atrypide brachiopod Qilianotryma Xu in Jin et al., 1979 is an early member of the subfamily Spirigerininae initially described from the Katian (Upper Ordovician) Koumenzi Formation of the Qilian Mountains, Qaidam terrane, Northwest China. Qilianotryma suspectum (Popov in Nikiforova et al., 1982) is described for the first time from the Upper Ordovician of South China paleoplate. Serial sectioning in this study revealed the typical spiralia and other internal structures of early atrypides. The rephotographing of type material and discriminant analysis support that Qilianotryma and broadly similar Euroatrypa can be differentiated in terms of external morphology. The distribution of Qilianotryma across the South China paleoplate, Qaidam terrane, and a few Kazakh terranes (i.e., Chu-Ili, Boshchekul, and Chingiz-Tarbagatai) supports a low-latitude faunal province separate from that of Laurentia and Baltica during the Katian, but further work describing and reviewing additional fossil material from these plates and terranes may improve our understanding of the position of these plates and the role that paleogeography played in increasing biodiversity during the Ordovician Radiation.

Two species of Teiichispira Yochelson and Jones reported from the Early/Middle Ordovician marine deposits of the San Juan Formation in the Argentine Precordillera are described. The new species Teiichispira teresae n. sp. is a component of the Early/Middle Ordovician marine gastropod assemblage in the studied region; Teiichispira argentina (Kayser), previously known from the San Juan Formation, is described with a complete teleoconch and associated operculum. The opercula of both Teiichispira species are complete and preserved in life position associated with the shell of T. argentina. The unguiculate morphology of the operculum is here interpreted as a mechanism for increasing the shell weight and ensuring anchoring to the substrate in a more or less fixed mode of life for Teiichispira, and as protection. The new occurrence of Teiichispira provides new taxonomic data on early Paleozoic marine gastropods in Argentina and testifies to a wide paleobiogeographical distribution for the genus, restricted to tropical and subtropical regions during the Early/Middle Ordovician.

Patagorbitestella new genus is here proposed to include two extant and one fossil species: P. ponderi (Linse, 2002) new combination, P. patagonica (Simone and Zelaya, 2004) new combination, and P. leonensis new species, the last described from the Punta Entrada Member of Monte León Formation (50°21′25.4”S, 68°53′05.9″W, Aquitanian to lower Burdigalian, lower Miocene). A protoconch sculptured with distinctive microscopic spiral threads serves as a per se diagnostic shell character for the new genus. Patagorbitestella n. gen. constitutes a distinctive lineage of orbitestellid gastropods inhabiting exclusively the Magellanic Region at least since the early Miocene. This is the first fossil record of Orbitestellidae in South America.

The present contribution illustrates the type material of the Lower Cretaceous ammonoids Ptychoceras aequicostatus Gabb, 1864 (type species of Helicancylus Gabb, 1869) and Hamiticeras pilsbryi Anderson, 1938 (type species of Hamiticeras Anderson, 1938). The typification and taxonomic validity of both genera are clarified, and the affinities with coeval Acrioceratidae are discussed. Their stratigraphic range is investigated with implications for correlation between northern Pacific and European ammonoid scales.

The western Mongolian Lake Zone was a Neoproterozoic to early Paleozoic volcanic arc where tuffs, lavas, fossiliferous siliciclastics, and carbonates accumulated during the early Cambrian. An uppermost Cambrian Series 2 (upper Stage 4) trilobite assemblage is described here from the Burgasutay Formation representing a continuous lower Cambrian succession at the Seer Ridge of the Great Lake Depression. The new assemblage is dominated by dorypygids and consists of 13 trilobite genera belonging to nine families including Catinouyia heyunensis new species. These fossils comprise the youngest and richest lower Cambrian trilobite assemblage in Mongolia. The composition of the Lake Zone fauna suggests its biogeographic affinity with the Siberian Platform and Altay-Sayan Foldbelt, but the presence of inouyiids also implies a connection of this region with East Gondwana.

Trilobites from the upper Guzhangian of the southern Argentine Precordillera, preliminarily described by Carlos Rusconi in the 1950s, are revised herein. The specimens studied were collected from an allochthonous limestone block of La Cruz Olistoliths at 200 m northwest of Estancia San Isidro locality (San Isidro area, Mendoza). Taxa comprise Kormagnostus seclusus (Walcott, 1884), Cedaria prolifica Walcott, 1924, C. puelchana Rusconi, 1954, Tricrepicephalus texanus (Shumard, 1861), Meteoraspis metra (Walcott, 1890), Coosia conicephala (Rusconi, 1954) new combination, Coosella texana? Resser, 1942, Nasocephalus cf. N. nasutus Wilson, 1954, and Olenoides proa (Rusconi, 1954) new combination. The North American genera Meteoraspis Resser, 1935 and Nasocephalus Wilson, 1954 are reported confidently from South America for the first time. This assemblage is representative of the Cedaria prolifica Zone, which correlates with the lower Crepicephalus Zone of the traditional North American genus-based zonation. Most of the genera and species identified were previously described exclusively from Canada, the United States, and northwestern Mexico, a fact that provides new support to an allochthonous Laurentian origin of the Argentine Precordillera.

An early form of eurypterids (Chelicerata), Archopterus anjiensis n. gen. n. sp., is described from the uppermost Ordovician Wenchang Formation of Anji County, Zhejiang Province, South China. It is the earliest record of eurypterids in China and likely the oldest representative of the Adelophthalmidae. The species, represented by a single specimen, is diagnosed by a ventrally preserved prosoma with a parabolic carapace, Hughmilleria-type prosomal appendages, a short vase-shaped metastoma, and a three-segmented type A (female) genital appendage. The specimen is preserved, together with diverse sponges, graptolites and occasional nautiloids, in a 10 m thick shale of marine deep-water setting. This finding extends the stratigraphic range of adelophthalmids from the previously recorded early Silurian into the Late Ordovician (some 10 million years older) and supports an earlier cryptic phase of eurypterid evolution in Gondwana.

This work provides the detailed investigation (taxonomy, biostratigraphy, and paleoecology) of a nonmarine ostracod fauna from the Shinekhudag Formation in Gobi–Altai area, southwest Mongolia. The samples from two sections (Tsagaan Tsuvarga and Oshih Hollow East) yielded various ostracods assigned to nine species belonging to six genera: Cypridea verrucata Neustrueva, 1974, C. ihsienensis Hou, 1958, C. unicostata Galeeva, 1955, C. tumefacta Neustrueva, 1974, Yumenia cf. Y. oriformis Hou, 1958, Scabriculocypris subscalara Zhang and Chen in Ye et al., 2003, ?Trapezoidella sp., Candona sp., and Vlakomia ulanense Neustrueva, 1977. The biostratigraphic application of our taxonomic results suggests that the age of the Shinekhudag Formation is Barremian–Aptian. In addition, the ostracod fauna shows strong affinities to faunas from northeast China and potentially northwest China, providing evidence of faunal exchanges between these regions and southwest Mongolia. The new discovery of Vlakomia ulanense indicates that mid-Cretaceous (Albian) species in northeast China probably originated in Mongolia at the time of deposition of the Shinekhudag Formation. Two ostracod assemblages in the studied sections reflect that different paleoenvironment settings have existed during deposition; the Tsagaan Tsuvarga Section represents a shallow-littoral zone of athalassic (inland) saline lake under arid climate, and the dominance of cypridoideans of the Oshih Hollow East Section is indicative of ephemeral water bodies.

Pleurocystitid echinoderms are known to have consistent plating in the theca or body. However, many specimens with aberrant plating are known among glyptocystitoids (Glyptocystella, Hadrocystis, Tyrridiocystis, and so on) as well as the new Ordovician species Pleurocystites? scylla, described here from the Benbolt Formation near Thorn Hill, Tennessee, USA. The presence of an extra plate in the holotype of P? scylla is most likely teratological. While teratology is often misconstrued as parasitism and pathology, it is easily recognized among glyptocystitoid rhombiferans because of the conservative nature of plate arrangements found in these taxa. Teratologic features in stemmed echinoderm thecae appear only to alter suture positioning and not significantly change the thecal shape or diminish the diagnosability of a specimen taxonomically.

New specimens of Cyclocystoides scammaphoris Smith and Paul, 1982, are here reported from the Upper Ordovician Platteville Formation of northern Illinois, Plattin and Decorah groups of east-central Missouri, and Lebanon Limestone of central Tennessee. These fossils reveal skeletal details that provide insight into the anatomy of cyclocystoids. Of particular significance is a network of channels that likely originate near the center of the central disk and extend along the oral side of the radial plates, bifurcating distally two or three times before entering the radial facets on the proximal surface of each marginal ossicle. From here, the network enters a series of facet canals that extend upward through each marginal ossicle, exiting in a linear row of pores. The canals are very similar in size and distribution to the nerve canals in living echinoderms. The axes of the canals, which number up to 500 in some specimens, and those of the radial ducts project proximally away from the oral surface at an elevation angle of about 25°, apparently forming a network that could have converged within the upper part of the body cavity. This origin and function are made clear by the connection between the channel on each radial plate and the radial facet canal pores within each marginal ossicle.

Nine crinoids are described from the Wooster Shale Member of the Cuyahoga Formation from Wayne and Ashland counties, Ohio, USA. Identifiable elements of the fauna include five camerate crinoids, one flexible crinoid, and three other eucladid crinoids. Five new species are described, including Cactocrinus woosterensis n. sp., Cusacrinus brushi n. sp., Agaricocrinus murphyi n. sp., Decadocrinus laevis n. sp., and Decadocrinus inordinatus n. sp. Overall, the distribution of crinoid clades in the Wooster Shale is similar to that of the stratigraphically lower Meadville Shale Member of the Cuyahoga Formation, although less diverse and with only one species (Cyathocrinites simplex) in common. Many of the Wooster Shale Member crinoids are completely or partially preserved with siderite either in nodules or within siderite beds. These crinoids are commonly preserved in trauma postures, which is characteristic of burial in episodic high turbulence events. The paleoenvironments and taxa of the two Cuyahoga Formation crinoid faunas more closely resemble Viséan faunas in siliciclastic settings than typical carbonate faunas of the Tournaisian.

The recently discovered mass mortality of fishes from the Tanis Site in the North Dakota portion of the Late Cretaceous Hell Creek Formation contains many well-preserved, three-dimensional skeletons. Among these are representatives of two acipenseriform families, Acipenseridae (sturgeons) and Polyodontidae (paddlefishes). This paper describes two new monotypic polyodontid genera, expanding our knowledge of polyodontid diversity. The first of the new species described here is †Parapsephurus willybemisi n. gen. n. sp. It is distinguished from all other known species by having a combination of posteriorly elongate parietals, the middle fenestra longitudinalis bordered medially by the parietal and frontal and laterally by the dermopterotic, slender and numerous dorsal caudal fulcra, an elongate hyomandibula that is not hourglass shaped, and gill rakers that are short and widely spaced. The second polyodontid species described here is †Pugiopsephurus inundatus n. gen. n. sp. It is diagnosed by a combination of having stellate bones that are exceptionally poorly developed or absent and having a dermopalatine with a medial expansion and lacking an ectopterygoid process. The two species of paddlefishes described in this paper add to the morphological and taxonomic diversity of Polyodontidae. The presence of these taxa within the Hell Creek Formation hints at substantial diversity of polyodontids at this stage of their evolutionary history.

Chiniquodontidae is a family of nonmammaliaform probainognathian cynodonts with occurrences in the Middle to Late Triassic of Africa and South America (Brazil and Argentina). The history of the family is marked by changes in composition and revisions due to the poor preservation of the first discovered specimens. Currently, Chiniquodontidae includes two genera and six species. Here, we apply the computed tomography (CT-scan) method to describe and revise the morphology of one of the best-preserved chiniquodontid specimens (MCP 1600 PV, holotype of ‘Probelesodon’ kitchingi Sá-Teixeira, 1982) from Brazil, which allowed the visualization of sutures and the segmentation of each bone. The CT-scan data also revealed some previously undescribed traits due to the presence of matrix covering structures of the skull. In addition, the morphological comparisons revealed differences of MCP 1600 PV in relation to the other chiniquodontids, and eight discrete cranial features not related to ontogeny indicate that ‘Probelesodon’ kitchingi might not be included within Chiniquodon theotonicus Huene, 1936. Therefore, we consider the species valid but propose the new combination Chiniquodon kitchingi. Moreover, the results obtained highlighted the necessity of a reassessment of the family, as well as the description of new specimens, morphometric analyses, and use of CT-scan, when feasible.

A late Pliocene (3.36–3.06 Ma) exposure of the Tangahoe Formation on the North Island of New Zealand preserves close fossil relatives of many extant seabird clades. Here, we report an extinct member of the little penguin (Eudyptula Bonaparte, 1856) lineage from the Tangahoe Formation—the smallest extinct crown penguin yet known. Eudyptula wilsonae n. sp. is based on the nearly complete skulls of an adult and a fledged but immature individual. Both skulls show more slender proportions than modern little penguins and precede genome-derived estimates for the divergence between Eudyptula minor minor Forster, 1781 (endemic to New Zealand) and Eudyptula m. novaehollandiae Stephens, 1826 (native to Australia and recently established in New Zealand). This raises the possibility that the fossil taxon represents a lineage directly ancestral to extant little penguins. Our results support a Zealandian origin for little penguins, with subsequent Pleistocene dispersal to Australia and a more recent Holocene range expansion of Eudyptula m. novaehollandiae back into New Zealand.

Despite the recognition that bone histology provides much information about the life history and biology of extinct animals, osteohistology of extinct marsupials is sorely lacking. We studied the bone histology of the ca. 15-mil-lion-year-old Nimbadon lavarackorum from Australia to obtain insight into its biology. The histology of thin sections of five femora and five tibiae of juveniles, subadult, and adult Nimbadon lavarackorum was studied. Growth marks in the bones suggest that N. lavarackorum took at least 7–8 years (and likely longer) to reach skeletal maturity. The predominant bone tissue during early ontogeny is parallel-fibered bone, whereas an even slower rate of bone formation is indicated by the presence of lamellar bone tissue in the periosteal parts of the compacta in older individuals. Deposition of bone was interrupted periodically by lines of arrested growth or annuli. This cyclical growth strategy indicates that growth in N. lavarackorum was affected by the prevailing environmental conditions and available resources, as well as seasonal physiological factors such as decreasing body temperatures and metabolic rates.

We appraise the morphology and potential origin of two Neogene cricetodontine-like muroids, Pliotomodon primitivus from Late Miocene sediments in northern California and an undescribed muroid from the late Oligocene or Early Miocene of central Oregon. Superficial resemblance of the dentition of Pliotomodon with members of the North American galushamyinan neotominins is considered a result of parallel evolution, as shown by the large size and unreduced M3/m3 of the former. Dental features of Pliotomodon are similar to those of Eurasian genera such as Byzantinia, Hispanomys, and Ruscinomys, but the unusual morphology of M3/m3, with continuous enamel connections across their lingual surfaces closing the hypoflexus and posteroflexid, respectively, plus retention of only three roots on M1, suggests Pliotomodon arose from an ancestor distinct from the one that gave rise to the large late Neogene hypsodont cricetodontines of the Old World. In the absence of known ancestral taxa in North America, we postulate Pliotomodon dispersed to North America across Beringia during the Hemphillian (ca. 8.6 Ma, Hh-1). Another archaic cricetodontine-like rodent, from the Warm Springs region of the John Day Formation in Oregon, is named as a new species of Deperetomys, D. dingusi new species. Deperetomys dingusi n. sp. likely descended from a species of Deperetomys intermediate between archaic species such as D. calefactus and D. magnus and more dentally derived species such as D. intermedius and D. hagni, dispersing to North America during the late Oligocene or Early Miocene (Arikareean; ca. 23 Ma, Ar3 or Ar4).

Although the well-known Upper Jurassic Morrison Formation has yielded abundant fossil plants for nearly a century, relatively little is known about fossil fungi and their ecological relationships to the Morrison flora. The first mention of fungal decay in fossil wood was briefly made over three decades ago, and since then, a few more reports of fungal decay associated with Morrison plants have been published. However, up to now, detailed data on the fossil fungi themselves have not been given from the Morrison Formation. Here we describe in detail well-preserved fossil mycelia in a silicified log of Xenoxylon utahense Xie et Gee, 2021 from the Upper Jurassic Morrison Formation at Miners Draw, Blue Mountain, near Vernal in northeastern Utah, USA. The fungal hyphae are variable in form, ranging from straight to slightly curved to highly coiled to tubular; they measure ∼1.53 µm in diameter and possess clamp connections, septa, and occasional bifurcations. The occurrence of clamp connections typical of living Basidiomycota indicates a taxonomic affinity to this division of fungi. On the basis of the patterns of wood decay in the Xenoxylon log, the fossil fungi are interpreted here as pertaining to saprotrophic, white-rot wood fungi. These fossil mycelia represent a new record of ancient Basidiomycota from the Upper Jurassic Morrison Formation and provide further evidence for plant–fungus interactions in Jurassic terrestrial ecosystems.