Xiphosuran chelicerates, also known as horseshoe crabs, are a long-lived clade characterized by a highly distinctive morphology and are a classic example of supposed evolutionary stasis. One key feature of horseshoe crabs is the fusion of the opisthosomal segments into a single sclerite referred to as a thoracetron. There has been historical uncertainty as to whether the thoracetron originated once or multiple times within the clade. Here we review criteria for determining whether segments are fused and apply them to a broad census of taxa for which their ontogeny is known or the adult status of specimens can be reasonably asserted to explore the evolution of the thoracetron within a developmental framework. Our findings indicate that the thoracetron evolved once in the common ancestor to Xiphosura. However, subsequent independent loss of the thoracetron segment boundaries is identified and shown to be the result of heterochronic processes acting on a shared developmental pathway. The multiple cases of effacement of the thoracetron within Limuloidea are cases of peramorphically driven parallelism, while the effacement of the thoracetron in the pedomorphic Belinurina is a case of convergence. Xiphosurids therefore represent an interesting case study for recognizing parallelism and convergence on the same structure within closely related lineages. We also demonstrate that somite VII has been incorporated into the prosoma multiple times within the chelicerate lineage, which has implications for interpreting the ground pattern of the group.

Today, the range of the genus Euthria encompasses the Mediterranean and the eastern Atlantic, the region around southern Africa, and extends into the western Indo-Pacific. The genus, which has a geological history dating back to the Eocene of Europe, has recently undergone taxonomic revision in several European Neogene basins. These studies revealed a pronounced expansion during the Oligocene and Neogene in the Atlanto-Mediterranean region and the Paratethys, and these studies highlighted the overall diversity of the genus combined with a pronounced regional endemism. This paper reviews the fossil record of the genus in the western Iberian Pliocene of the Cainozoic Mondego Basin of Portugal. Two new species endemic to western Iberia with protoconchs showing non-planktotrophic developmental traits have emerged: Euthria galopimi n. sp. and Euthria lockleyi n. sp. These results reinforce the glocal character of Euthria, a genus that is both widespread and diversified, but simultaneously showing a high endemism. The contribution of nonplanktotrophic development to this scenario is discussed. Although well represented in the fossil record of Atlantic France, in present-day European waters, Euthria is represented by a single species, E. cornea (Linnaeus, 1758), and only in the Mediterranean and the northern shores of the Gulf of Cadiz. As with other warm-water molluscan taxa, the northern distribution limit of Euthria in the Atlantic has shifted southward since the Early to mid-Pliocene due to global cooling events and decreasing sea surface temperatures.

http://zoobank.org/2A64f041-8e17-491e-8782-a31a9c5dfd57

From re-examination of the type and additional specimens of Munida nishioi Karasawa, 1993 and Kazuoia ogaensis Hatai and Kotaka, 1970 from the Miocene deposits of Japan, both species are assigned to Grimothea Leach, 1821 [1820] of the squat lobster family Munididae Ahyong et al., 2010. The revised diagnosis and description are given for Grimothea nishioi (Karasawa, 1993) new combination and Grimothea ogaensis (Hatai and Kotaka, 1970) new combination. The monotypic genus Kazuoia Hatai and Kotaka, 1970 becomes a junior subjective synonym of Grimothea. Trapezionida chiyoensis new species is described from the lower Miocene of central Japan. These species represent the first records of Grimothea and Trapezionida Macpherson and Baba in Machordom et al., 2022 recognized as fossils.

UUID: http://zoobank.org/5917b8a9-2c16-443f-a64f-964cb78fce16

A new genus is established for species of late Paleozoic pterioid bivalves that have substantial ontogenetic change in hinge characters during growth. Juvenile shells have small cardinal and posterior lateral teeth on the hinge that are overgrown on the adult shell and the hinge become edentulous. The shell has a wide ligament plate with a clinovincular ligament (new term). Adjacent to the cardinal teeth on juvenile shell, ligament sheets tend to have small, low amplitude folding and wavy alignment of ligament grooves. A new genus and species, Willipteria nestelli, is described and the species Leptodesma falcata Boyd and Newell, is transferred to genus Willipteria n. gen. Comparison of Willipteria n. gen. to Leptodesma reveals a need to revise Leptodesma. A study of the type lot of genotype species Leptodesma potens Hall, provides a redescription for the genus, presented here. Definition of the new term, clinovincular ligament, is presented. Discussion of muti-sheet ligaments is presented for duplivincular, monovincular, and clinovincular configurations.

http://zoobank.org/014f32de-414d-4cda-a5d4-790c35d0bfa5

The allosauroid theropod dinosaurs of the clade Carcharodontosauridae were the apex predators in terrestrial ecosystems of the Early Cretaceous but were replaced in this ecological niche by Tyrannnosauridae in the Late Cretaceous. Details of this turnover are poorly known because only two transitional ecosystems, containing both carcharodontosaurids and tyrannosauroids, had been recognized to date (Cenomanian Cedar Mountain Formation of Utah, USA, and Turonian Bissekty Formation of Uzbekistan). Moreover, the presence of carcharodontosaurids in the Bissekty Formation, based on a maxilla fragment identified as Ulughbegsaurus uzbekistanensis Tanaka et al., 2021, has been recently questioned. Here we report on the third ecosystem containing both clades of apex predators, the Cenomanian Khodzhakul Formation in Uzbekistan. This new occurrence of Carcharodontosauridae is based on a newly identified maxilla that closely resembles the holotype maxilla of U. uzbekistanensis and is identified as Ulughbegsaurus sp. The revised morphological characters of both specimens support attribution of Ulughbegsaurus to Carcharodontosauridae. We report a novel neurovascular feature of the theropod maxilla—a medial alveolar canal that supplied the alveoli medially and contained tributaries of the palatine vessels in Ulughbegsaurus.

The Indo-West Pacific region serves as the primary habitat for the majority of extant hexapodid crabs. The hexapodids boast a rich evolutionary history dating back to the Cretaceous, marked by a significant radiation throughout the Cenozoic, while the Paleocene–Miocene of tropical America emerges as a pivotal center of radiation, evidenced by reported hexapodid species in Barbados, Panama, Peru, Trinidad, and Venezuela. Through an examination of the paleocarcinological collection at the Museu Paraense Emílio Goeldi, a new genus and species within Hexapodidae is described and illustrated. Rodneyellus feldmanni, the newly described taxon, is named in honor to Dr. Rodney Feldmann for his unwavering commitment to fossil crustacean research. This report marks the inaugural documentation of Hexapodidae in Brazil, encompassing both fossilized and extant representatives. Furthermore, the Pirabas Formation emerges as a critical locus for comprehending the contemporary distribution of decapod crustaceans across tropical America.

UUID: http://zoobank.org/9792bc1e-d06e-490b-a8e6-c23ee1c11fb1

Despite being a conspicuous group in many fossil-bearing beds from the Tepuel–Genoa Basin, the knowledge of bryozoans from Patagonia is scarce and outdated. The majority of bryozoan records are known from faunal components of the Lanipustula patagoniensis Biozone (Carboniferous, upper Serpukhovian–Moscovian), in lower to middle levels of the Pampa de Tepuel Formation, Tepuel Group. For the present contribution, we conducted a taxonomic study on bryozoan samples from the lower third of the Pampa de Tepuel Formation at the type section, Sierra de Tepuel, central-western Patagonia, Argentina. We found Paraptylopora gondwanica n. sp. along with species of Penniretepora, Polyporella, Septatopora, Levifenestella, Rectifenestella, Spinofenestella, and others still under study. Most studied fenestrate species are restricted to central-western Patagonia, indicating a degree of biogeographical isolation, while a few imply faunal migration between the western and eastern margins of southern Gondwana during the Late Paleozoic Ice Age. The bryozoan growth habits association and accompanying fauna suggests a mid-shelf to upper-slope environment characterized by deep, low-turbidity, euhaline waters and a soft to firm substrate.

UUID: http://zoobank.org/3bf56286-9fd7-43c2-b5f6-417e86994d08

Gnathodus pseudosemiglaber is an important conodont species for Lower Mississippian biostratigraphy, but differentiating it from morphologically similar species remains difficult due to uncertainties in the intraspecific, ontogenetic, and phylogenetic relationships between taxa. To clarify these uncertainties, a fauna from the Yudong Formation at the Yudong II section in Baoshan, southwestern China, that contains abundant G. pseudosemiglaber was analyzed using population thinking. Quantitative morphometric methods were employed to analyze G. pseudosemiglaber specimens. Six anatomical measurements were taken on specimens of different ontogenetic stages to conduct analyses on normal distribution, correlation, and regression. A geometric morphometric analysis based on 13 landmarks was also performed. The results demonstrated that all analyzed specimens belonged to a single population. The dorsal carina of G. pseudosemiglaber has a growth rate that far exceeds other features on the platform through ontogeny as well as exhibits a series of transverse ridges in adult individuals, which becomes the most prominent diagnostic characteristic of this species. Thus, an amended systematic description for G. pseudosemiglaber is presented. Gnathodus girtyi maxwelli, a previously named species, however, is regarded as a junior synonym of G. pseudosemiglaber. Based on the revised taxonomy of G. pseudosemiglaber, its possible phylogenetic lineages and biostratigraphic use were reviewed. The ancestor of G. pseudosemiglaber is probably G. semiglaber but its descendant is unknown. The range of G. pseudosemiglaber is from the Scaliognathus anchoralis–Doliognathus latus Zone of uppermost Tournaisian to the lower part of the G. bilineatus Zone of middle-upper Visean.

The first unequivocal fossil of a tupinambine in North America is described on the basis of a single thoracic vertebra from a middle Miocene (Barstovian 2) paleocoastal deposit in southwestern Georgia, USA. Wautaugategu formidus n. gen. n. sp. is a mid- to large-bodied taxon with a unique mosaic of tupinambine features. Vertebral position of the fossil was determined both by qualitative and quantitative methods. This record is coeval with the warmest part of the Neogene, the Middle Miocene Climatic Optimum, when increased temperatures would have made the southeastern United Sates more habitable for this hyperthermic group of lizards. Although the arrival time of tupinambines into North America is still unclear, an increasing number of endemic South American reptiles, including the large-bodied iguanid Ctenosaura, dispersed as far North as Panama by the early Miocene before formation of the Panamanian Isthmus.

http://zoobank.org/58ded940-9082-46ae-8023-4b5f1b01691e

A new pylochelid hermit crab, Cretatrizocheles rodfeldmanni new species, is recorded from a Lower Cretaceous (Aptian/Albian) olistolith reefal limestone block near the village of Velika Strmica, southeast Slovenia. It adds to the fossil record of the symmetrical pagurid subfamily Trizochelinae, whose members appear to have been successful inhabitants of shallow-marine reefal settings during at the least the Late Jurassic and Early Cretaceous across Europe. Given their exclusive occurrence in shallow-marine, reef-related facies of Mesozoic age and the present-day confinement to deep-marine settings, trizocheline paguroids may also illustrate the effect of the Mesozoic Marine Revolution.

UUID: http://zoobank.org/b3f862ca-3b4d-44c1-911c-820af4426029

The knowledge on decapod crustaceans considerably increased in recent years, including that of the glypheid lobsters, known from the Early Jurassic to the present. On the basis of known occurrences worldwide, we analyze the spatial and temporal distribution of 86 species of the family Glypheidae and provide a general description of their history since the Early Jurassic. The first records are from low- to mid-paleolatitude localities of central Europe, around the margins of northern Tethys. During the Early Jurassic they diversified fast, and by Pliensbachian/Toarcian times they already had a wide paleolatitudinal range in both hemispheres. After a short decline in late Toarcian–Aalenian, they reached the highest diversity of their history during Oxfordian times and can be regarded as Jurassic cosmopolitans. After a diversity decline and occurrence gap during the earliest Cretaceous, they recovered again in the Barremian, but they were clearly beginning to be less diverse than before in the Tethys, to the point that by the Campanian their known occurrences were confined to high paleolatitudes. They survived the Cretaceous/Paleogene crisis but in Paleocene and Eocene times remained restricted to cold waters, being seemingly absent from low paleolatitudes. For a long time, the group was thought to be extinct about 50 million years ago, until two extant species were discovered in the deep Pacific. We also add to the knowledge of the only South American Jurassic Glypheidae known so far, the Toarcian Paraglyphea eureka (Damborenea and Manceñido, 1987) on the basis of newly collected material, discussing its significance and taphonomy.

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.

UUID: http://zoobank.org/2eab7247-6235-435d-8eb1-b40d5a633e2b

Rare specimens of eldonioids recovered from the lower Cambrian (Series 2, Stage 4) Emu Bay Shale (EBS) Konservat-Lagerstätte represent the first record of the group for the Cambrian of East Gondwana. The disc-shaped body of the EBS taxon bears fine concentric corrugations on the dorsal surface and, ventrally, a series of internal lobes that have primary and secondary bifurcations, as well as a coiled sac. It appears to be most similar to Rotadiscus and Pararotadiscus of the Cambrian Chengjiang and Kaili biotas of South China, respectively. While the structure of the internal lobes would indicate that this occurrence in the EBS represents a new taxon within the Rotadiscidae, lack of detail regarding the precise number of internal lobes and the condition of the circumoral tentacles warrants a more conservative approach in leaving the genus and species under open nomenclature. The EBS specimens also host trace fossils, including the remains of a burrow, which are generally lacking in the body-fossil-bearing layers of the Konservat-Lagerstätte interval. These traces appear to have been made by small organisms and are similar to traces associated with the discs of Pararotadiscus guizhouensis Zhao and Zhu, 1994 from the Kaili Biota. The available taphonomic, paleoenvironmental, and ichnological evidence indicates that the EBS eldonioids are most likely vagrants that were transported or settled into the ‘preservational trap’ and subsequently exposed on the substrate for a brief period before burial, thereby allowing organisms to exploit their carcasses for nutrients or other purposes.