Osteology and phylogeny of Robustichthys luopingensis, the largest holostean fish in the Middle Triassic

A New Sinamiin Fish (Actinopterygii) from the Early Cretaceous of Thailand: Implications on the Evolutionary History of the Amiid Lineage

The Sinamiidae are a family of halecomorph fishes (Holostei) stratigraphically limited to the Lower Cretaceous and confined to East Asia. The first species of sinamiids were discovered in China, and then new occurrences were recorded in Thailand and Japan. The three recognized genera, Sinamia, Siamamia and Ikechaoamia, are notably characterized by an unpaired parietal. Here, we describe a new genus and species of sinamiid based on material from the Aptian Khok Kruat Formation of Ban Krok Duean Ha, Nakhon Ratchasima, Thailand. The new taxon known from preserved specimens in 3D is characterized by four pairs of extrascapular and tall cylindrical teeth with a conical enamel stalk topped by an arrowhead-shaped acrodine cap, among other characters. A phylogenetic analysis of the halecomorph fishes shows that the new taxon is the sister of the other Thai species, Siamamia naga, and that the two are grouped with two Chinese genera in a strongly supported clade, the Sinamiinae. This subfamily is here grouped with the Amiinae that contained the extant Amia. This new discovery is a clue that Southeast Asia may have been a center of diversification for this fish clade, and the phylogenetic analysis reveals that amiines may have originated somewhere in Asia during the Cretaceous before they spread throughout the northern hemisphere.

Taxonomic status of the caturid genera (Halecomorphi, Caturidae) and their Late Jurassic species

Caturids are among the best-known predatory ray-finned fishes of the Mesozoic. Although there is consensus about their sister-group relationship to Amiidae (Holostei, Amiiformes), their diversity, ingroup phylogenetic relationships and evolutionary history are still very poorly understood. Caturidae is currently restricted to Caturus and Amblysemius, each with two species. Among them, C. furcatus has become the wastebasket taxon for the group. Our revision of nearly 40 species based on the original descriptions, type and referred material led to significant results changing the picture of caturid diversity in the Late Jurassic. Four specific names are unavailable. Due to insufficient information in the original descriptions, lack of diagnostic features in the type material, or the complete lack of type material, 13 nominal species are nomina dubia. Two species currently considered junior synonyms represent distinct taxa. Strobilodus giganteus is removed from Caturidae. Caturus cliftoni, Thlattodus and Ditaxiiodus are tentatively referred to Strobilodus. The fossil record of Caturoidea is restricted to the Jurassic and earliest Cretaceous. The group apparently underwent significant diversification during the Late Jurassic, as indicated by the increase in the number of taxa and the dispersal of the group outside Europe, which had already begun in the Middle Jurassic.

A Permian fish reveals widespread distribution of neopterygian-like jaw suspension

The actinopterygian crown group (comprising all living ray-finned fishes) originated by the end of the Carboniferous. However, most late Paleozoic taxa are stem actinopterygians, and broadly resemble stratigraphically older taxa. The early Permian †Brachydegma caelatum is notable for its three-dimensional preservation and past phylogenetic interpretations as a nested member of the neopterygian crown. Here, we use computed microtomography to redescribe †Brachydegma, uncovering an unanticipated combination of primitive (e.g., aortic canal; immobile maxilla) and derived (e.g., differentiated occipital ossifications; posterior stem of parasphenoid; two accessory hyoidean ossifications; double jaw joint) dermal and endoskeletal features relative to most other Paleozoic actinopterygians. Some of these features were previously thought to be restricted to the neopterygian crown. The precise phylogenetic position of †Brachydegma is unclear, with placements either on the polypterid stem, or as an early-diverging stem neopterygian. However, our analyses decisively reject previous placements of †Brachydegma in the neopterygian crown. Critically, we demonstrate that key-endoskeletal components of the hyoid portion of the suspensorium of crown neopterygians appeared deeper in the tree than previously thought.

The oldest species of Peltoperleidus (Louwoichthyiformes, Neopterygii) from the Middle Triassic (Anisian) of China, with phylogenetic and biogeographic implications

The previously alleged ‘perleidid’ genus Peltoperleidus is a stem-neopterygian fish taxon with two or three horizontal rows of notably deepened flank scales. Until recently, members of this genus were known only from the Ladinian (late Middle Triassic) or near the Anisian/Ladinian boundary (~242 Ma) in southern Switzerland and northern Italy. Here, I report the discovery of a new species of the genus, Peltoperleidus asiaticus sp. nov., based on three well-preserved specimens from the Anisian (early Middle Triassic, ~244 Ma) of Luoping, eastern Yunnan, China. The discovery extends the geological range of Peltoperleidus by approximately two million years and documents the first record of the genus in Asia. Similar to its relatives (represented by P. macrodontus) from Europe, P. asiaticus sp. nov. is likely a small-sized durophagous predator with dentition combining grasping and crushing morphologies. Results of a cladistic analysis unite four species of Peltoperleidus as a monophyletic group within the Louwoichthyiformes, and suggest that the presence of two horizontal rows of notably deepened scales was independently evolved in Peltoperleidus and another stem-neopterygian taxon Altisolepis. P. asiaticus sp. nov. is nested at the base of Peltoperleidus, and a new family Peltoperleididae is proposed for the genus, contrasting the previous placement of Peltoperleidus in the poorly defined, paraphyletic ‘Perleididae’. Comparative studies of the basal peltoperleidid from China with its younger relatives from Europe provide new insights into the evolutionary origin and paleogeographic distribution of this clade.

The Making of Calibration Sausage Exemplified by Recalibrating the Transcriptomic Timetree of Jawed Vertebrates

Molecular divergence dating has the potential to overcome the incompleteness of the fossil record in inferring when cladogenetic events (splits, divergences) happened, but needs to be calibrated by the fossil record. Ideally but unrealistically, this would require practitioners to be specialists in molecular evolution, in the phylogeny and the fossil record of all sampled taxa, and in the chronostratigraphy of the sites the fossils were found in. Paleontologists have therefore tried to help by publishing compendia of recommended calibrations, and molecular biologists unfamiliar with the fossil record have made heavy use of such works (in addition to using scattered primary sources and copying from each other). Using a recent example of a large node-dated timetree inferred from molecular data, I reevaluate all 30 calibrations in detail, present the current state of knowledge on them with its various uncertainties, rerun the dating analysis, and conclude that calibration dates cannot be taken from published compendia or other secondary or tertiary sources without risking strong distortions to the results, because all such sources become outdated faster than they are published: 50 of the (primary) sources I cite to constrain calibrations were published in 2019, half of the total of 280 after mid-2016, and 90% after mid-2005. It follows that the present work cannot serve as such a compendium either; in the slightly longer term, it can only highlight known and overlooked problems. Future authors will need to solve each of these problems anew through a thorough search of the primary paleobiological and chronostratigraphic literature on each calibration date every time they infer a new timetree, and that literature is not optimized for that task, but largely has other objectives.

Feroxichthys panzhouensis sp. nov., a hump-backed colobodontid (Neopterygii, Actinopterygii) from the early Middle Triassic of Panzhou, Guizhou, China

Neopterygii is a taxonomically diverse clade of ray-finned fishes, including Teleostei, Holostei and closely related fossil taxa. The Colobodontidae is a stem group of large-sized neopterygians with a durophagous feeding adaption from the Middle to Late Triassic marine ecosystems in Europe and South China. Here, we report the discovery of a new colobodontid, Feroxichthys panzhouensis sp. nov., based on a well-preserved specimen from the early Middle Triassic (Anisian) of Panzhou (formerly known as Panxian), Guizhou, China. The discovery extends the geographical distribution of Feroxichthys from eastern Yunnan into western Guizhou, and demonstrates a more rapid diversification of early colobodontids than previously thought. The new species possesses diagnostic features of Feroxichthys (e.g., a fused lacrimal-maxilla), but it is easily distinguished from the type species Feroxichthys yunnanensis and other colobodontids by some derived features on the skull and, especially, the relatively short and deep body with a prominent postcranial hump. This body form, previously unknown in colobodontids, implicates a morphological adaptation to structurally complex habitats in light of ecological studies of modern ray-finned fishes with a similar body form. In addition, the feeding apparatus suggests a more obligate durophagous diet for F. panzhouensis sp. nov. than other colobodontids. Results of a cladistic analysis recover the new species as a sister taxon of F. yunnanensis within the Colobodontidae, and suggest that a hump-backed body form has independently evolved multiple times in Triassic neopterygians. As such, the new finding provides an important addition for our understanding of the morphological and ecological diversity of neopterygian fishes from the Triassic marine ecosystems in South China.

Feroxichthys yunnanensis gen. et sp. nov. (Colobodontidae, Neopterygii), a large durophagous predator from the Middle Triassic (Anisian) Luoping Biota, eastern Yunnan, China

Neopterygii is a large group of ray-finned fishes which underwent a rapid radiation in the Middle Triassic. Until recently, 11 stem neopterygians have been recovered from the early Middle Triassic Luoping Biota in eastern Yunnan, China, and they are small to medium-sized fishes. Here, I report the discovery of a new stem neopterygian, Feroxichthys yunnanensis gen. et sp. nov. from the Luoping Biota, which represents the first evidence of large-sized stem neopteygians in this biota with a total length of ~340 mm (290 mm in standard length). The skull of the new taxon is exceptionally well-preserved, showing some peculiar features rarely known in other stem neopterygians, for example fusion of paired premaxillae, fusion of lacrimal with maxilla, and a fused parieto-dermopterotic with a strong posterior process. Phylogenetic studies recover Feroxichthys as a basal colobodontid, and a revised diagnosis of this family is presented. The feeding apparatus indicates that Feroxichthys might have been predominantly durophagous, resembling other colobodontids. However, the anterior peg-like teeth in the jaws of Feroxichthys are much longer and stronger than other colobodontids, enabling a more powerful initial prey capture before food was passed posteriorly to molariform teeth for crushing in the oral cavity. As a mysterious large durophagous predator previously unknown from the Luoping Biota, the new finding is important not only for understanding the early diversification of neopterygians during this age but also for investigating the trophic structure in this marine ecosystem.

A new stem-neopterygian fish from the Middle Triassic (Anisian) of Yunnan, China, with a reassessment of the relationships of early neopterygian clades

Neopterygii is a taxonomically diverse group of ray-finned fishes, including Teleostei, Holostei and their closely related fossil taxa. Here, a new small-sized stem-neopterygian with extraordinarily long teeth, Louwoichthys pusillus gen. et sp. nov., is described based on 14 well-preserved specimens from the Middle Triassic (Anisian) marine deposits of Yunnan, China. Louwoichthys is closely related to Luopingichthys from the same fossil beds and Ctenognathichthys from the Middle Triassic of the Monte San Giorgio area in Europe; the three genera are grouped into the family Louwoichthyidae fam. nov., which is recovered as sister to the ‘perleidiform’ Pseudobeaconiidae. Given that ‘Perleidiformes’ is notoriously paraphyletic, a new order, Louwoichthyiformes ord. nov., is introduced to group both families. The louwoichthyiform monophyly is strongly supported by a series of derived features, such as a relatively short maxilla, an anteriorly inclined preopercle, a subopercle with a prominent anteroventral extension, and two or three pairs of branchiostegal rays. Louwoichthys is one of the smallest louwoichthyiforms, having a largest standard length of 39 mm. It is deduced to be a scavenger that might use its long and sharp teeth to grasp and tear the prey from the substrate or to bite a piece from a larger prey item.