Principal Rays Research Articles

A revision of the Late Jurassic fish Aphnelepis australis from the Talbragar Fossil Fish Bed of New South Wales, Australia

The discovery of an exceptionally preserved specimen of the Mesozoic teleost fish Aphnelepis australis from the upper Kimmeridgian (Upper Jurassic) Talbragar Fossil Fish Bed in New South Wales, together with historic confusion over its phylogenetic affinities, has prompted a detailed reassessment of the taxon. The new specimen of A. australis is skeletally complete and exhibits the dorsal fin with long principal dorsal fin rays and characteristic squamation comprising heavy rhombic scales anterior to insertions of the dorsal fin and anal fin, and much lighter and thinner weakly crenulate scales on the posterior half of the body. A cladistic analysis resolves A. australis as a member of Archaeomenidae, along with Archaeomene tenuis, Wadeichthys oxyops, Oreochima ellioti, Gurvanichthys mongoliensis, Zaxilepis quinglongensis, and Aphnelepis australis. Lynne B. Bean [lynne.bean@anu.edu.au ], Research School of Earth Sciences, 142 Mills Road, Australian National University, Acton, Australian Capital Territory 2601, Australia.

Mixed reality interfaces for achieving desired views with robotic X-ray systems

ABSTRACT Robotic X-ray C-arm imaging systems can precisely achieve any position and orientation relative to the patient. Informing the system, however, what pose exactly corresponds to a desired view is challenging. Currently these systems are operated by the surgeon using joysticks, but this interaction is not necessarily effective because users may be unable to efficiently actuate more than a single axis of the system simultaneously. Moreover, novel robotic imaging systems, such as the Brainlab Loop-X, allow for independent source and detector movements, adding complexity. To address this challenge, we consider complementary interfaces for the surgeon to command robotic X-ray systems effectively. Specifically, we consider three interaction paradigms: (1) the use of a pointer to specify the principal ray of the desired view, (2) the same pointer, but combined with a mixed reality environment to synchronously render digitally reconstructed radiographs from the tool’s pose, and (3) the same mixed reality environment but with a virtual X-ray source instead of the pointer. Human-in-the-loop evaluation with an attending trauma surgeon indicates that mixed reality interfaces for robotic X-ray system control are promising and may contribute to substantially reducing the number of images acquired solely during ‘fluoro hunting’ for the desired view or standard plane.

Generation of a large vortex Bessel solitary wave in an optical fiber winding around a curved path

A light fiber winding around a curved path model can generate a large vortex Bessel solitary wave (BSW). The spiral body structure BSW can carry orbital angular momentum (OAM) modes. We investigate the influence of curved path and the type of winding of the principal ray based on the OAM modes. The curve path corresponds to the intensity of the modes of the OAM beam. Our vortex BSW is different from traditional electromagnetic amplitude solitary waves. We calculate the propagating diffraction pattern in the optical fibers, and find that a fundamental BSW is an Airy spot. Along with increasing the order number, we also see that the vortex BSW decays gradually from the center to the exterior, and the BSW leaks more energy to the outer rings.

Platyfish bypass the constraint of the caudal fin ventral identity in teleosts.

The caudal fin of teleosts is characterized by dorsoventral symmetry. Despite this external morphology, the principal rays of this appendage connect to bones below the notochord, indicating the ventral (hypochordal) identity of this organ. Here, we report that this typical architecture of the caudal fin is not fully conserved in the platyfish (Xiphophorus maculatus) and the guppy (Poecilia reticulata), representatives of the Poeciliidae family. We show that in these species, 3-4 principal rays connect to bones above the notochord, suggesting an epichordal contribution. Consistently, as examined in platyfish, dorsal identity genes zic1/4 were highly expressed in these rays, providing molecular evidence of their epichordal origin. Developmental analysis revealed that the earliest rays above the notochord emerge at the 10-ray stage of fin morphogenesis. In contrast to zebrafish and medaka, platyfish and guppies display a mirrored shape of dorsal and ventral processes of the caudal endoskeleton. Our study suggests that an ancestral bauplan expanded in poeciliids by advancing its symmetrical pattern. The platyfish evolved a fin architecture with the epichordal origin of its upper principal rays and a high level of symmetry in the caudal endoskeleton. This innovative architecture highlights the adaptation of the teleost skeleton.

The outstanding suction-feeder Marcopoloichthys furreri new species (Actinopterygii) from the Middle Triassic Tethys Realm of Europe and its implications for early evolution of neopterygian fishes

Marcopoloichthys furrerisp. nov., a small scaleless fish from the Ladinian of Switzerland, is described based on ten well preserved specimens, which provide outstanding morphological information, allowing the re-study of the family and generic diagnoses that were solely based on a few Eurasian marcopoloichthyids. An exhaustive investigation of morphological features of M. furreri provides evidence of new morphological structures not previously known in Triassic neopterygians (e.g., supraneural carrier; two pairs of nasal bones; mesethmoid; series of three bony postcleithra) that are interpreted as autapomorphies of Marcopoloichthys, which occur together with some primitive features (e.g., lack of supramaxillae; presence of surangular and coronoid; aspondylous vertebral column; clavicle present). The combination of primitive and advanced characters proved to be critical when M. furreri was added to a previous hypothesis of neopterygian relationships, because it provided unquestionable support for Marcopoloichthys as a stem teleost or teleosteomorph. Some characters supporting this interpretation are the presence of a mobile premaxilla; an unpaired vomer; and first and last principal rays forming leading margins of caudal fin. Additionally, Marcopoloichthys furreri, due to a combination of teleostean synapomorphies (e.g., epineural processes; four pectoral radials; propterygium fused with first pectoral ray), stands in a polytomy with aspidorhynchiforms and more advanced teleosteomorphs in another phylogenetic analysis. Consequently, the combination of characters of Marcopoloichthys is relevant for understanding the taxonomy and systematics of crown neopterygians. Marcopoloichthyids were suction-feeding fishes, and the excellent preservation of the new species permits discussion of the anatomical modifications involved in the feeding and resting processes.

Silurichthys exortivus, a new catfish (Teleostei: Siluridae) from eastern Borneo, Indonesia.

Silurichthys exortivus, a new species of silurid catfish, is described from the Mahakam River drainage in eastern Borneo. The new species can be distinguished from congeners in lacking a dorsal fin, having 4 (vs. 67) principal rays on the upper caudal-fin lobe and a combination of: body depth at anus 14.0% SL, caudal peduncle depth 5.1% SL, pelvic fins absent, 54 anal-fin rays, caudal fin with asymmetrical lobes (upper lobe 1.1 times longer than lower), 48 vertebrae, 1 gill raker on the first branchial arch, and a mottled brown body. Based on the reduced number of principal caudal-fin rays, S. exortivus, S. ligneolus and S. sanguineus are hypothesized to form an exclusively Bornean clade.

INVESTIGATING SPHERICAL EPIPOLAR RECTIFICATION FOR MULTI-VIEW STEREO 3D RECONSTRUCTION

Abstract. Multi-view stereo (MVS) reconstruction is essential for creating 3D models. The approach involves applying epipolar rectification followed by dense matching for disparity estimation. However, existing approaches face challenges in applying dense matching for images with different viewpoints primarily due to large differences in object scale. In this paper, we propose a spherical model for epipolar rectification to minimize distortions caused by differences in principal rays. We evaluate the proposed approach using two aerial-based datasets consisting of multi-camera head systems. We show through qualitative and quantitative evaluation that the proposed approach performs better than frame-based epipolar correction by enhancing the completeness of point clouds by up to 4.05% while improving the accuracy by up to 10.23% using LiDAR data as ground truth.

Coordinated patterning of zebrafish caudal fin symmetry by a central and two peripheral organizers.

Caudal fin symmetry characterizes teleosts and likely contributes to their evolutionary success. However, the coordinated development and patterning of skeletal elements establishing external symmetry remains incompletely understood. We explore the spatiotemporal emergence of caudal skeletal elements in zebrafish to consider evolutionary and developmental origins of caudal fin symmetry. Transgenic reporters and skeletal staining reveal that the hypural diastema-defining gap between hypurals 2 and 3 forms early and separates progenitors of two plates of connective tissue. Two sets of central principal rays (CPRs) synchronously, sequentially, and symmetrically emerge around the diastema. The two dorsal- and ventral-most rays (peripheral principal rays, PPRs) arise independently and earlier than adjacent CPRs. Muscle and tendon markers reveal that different muscles attach to CPR and PPR sets. We propose that caudal fin symmetry originates from a central organizer that establishes the hypural diastema and bidirectionally patterns surrounding tissue into two plates of connective tissue and two mirrored sets of CPRs. Further, two peripheral organizers unidirectionally specify PPRs, forming a symmetric "composite" fin derived from three fields. Distinct CPR and PPR ontogenies may represent developmental modules conferring ray identities, muscle connections, and biomechanical properties. Our model contextualizes mechanistic studies of teleost fin morphological variation.

Toward Perception-based Anticipation of Cortical Breach During K-wire Fixation of the Pelvis.

Intraoperative imaging using C-arm X-ray systems enables percutaneous management of fractures by providing real-time visualization of tool to tissue relationships. However, estimating appropriate positioning of surgical instruments, such as K-wires, relative to safe bony corridors is challenging due to the projective nature of X-ray images: tool pose in the plane containing the principal ray is difficult to assess, necessitating the acquisition of numerous views onto the anatomy. This task is especially demanding in complex anatomy, such as the superior pubic ramus of the pelvis, and results in high cognitive load and repeat attempts even in experienced trauma surgeons. A perception-based algorithm that interprets interventional radiographs during internal fixation to infer the likelihood of cortical breach - especially early on, when the wire has not been advanced - might reduce both the amount of X-rays acquired for verification and the likelihood of repeat attempts. In this manuscript, we present first steps towards developing such an algorithm. We devise a strategy for in silico collection and annotation of X-ray images suitable for detecting cortical breach of a K-wire in the superior pubic ramus, including those with visible fractures. Beginning with minimal manual annotations of correct trajectories, we randomly perturb entry and exit points and project the 3D scene using a physics-based forward model to obtain a large number of 2D X-ray images with and without cortical breach. We report baseline results for anticipating cortical breach at various K-wire insertion depths, achieving an AUROC score of 0.68 for 50% insertion. Code and data are available at github.com/benjamindkilleen/cortical-breach-detection.

Osteology-focused redescription and description of the blood-feeding candirus Paracanthopoma parva and Paravandellia alleynei sp.n. (Trichomycteridae: Vandelliinae).

This study resolves a significant impediment to the taxonomy of the Neotropical endemic hematophagous candirus by providing the first high-resolution, CT-based osteological descriptions of type and nontype specimens of Paracanthopoma parva, type species of the genus. We also describe the distinctive new species Paravandellia alleynei based on specimens that were previously misidentified as Parac. parva in the only taxonomic study of that species since its 1935 description. Paracanthopoma parva is distinguished from all nominal congeners by its parietosupraoccipital and caudal skeleton morphology and by various meristics, including numbers of teeth on median premaxilla, vertebrae, and procurrent and principal caudal-fin rays. Paravandellia alleynei differs from both nominal congeners (Paravandellia oxyptera and Paravandellia phaneronema) by the unique morphology of its maxilla, mesethmoid and opercular apparatus, relative position of the pelvic- and anal-fin origins, orientation of the opercular odontodes, and various meristics, including numbers of vertebrae, median premaxillary teeth, medial teeth on premaxilla, branchiostegal rays, opercular and interopercular odontodes, distal claw-like premaxillary teeth, dorsal-fin rays and dentary teeth. This is the first species of Paravandellia recognized from Guyana and the Essequibo River basin. It is currently known only from two type specimens from the lower Essequibo River basin and 43 nontype specimens from the upper Branco River basin. By providing the first skeletal observations for type specimens of the type species Parac. parva and for topotypic specimens of all three nominal species of Paravandellia, we clarify and confirm the diagnosis of Parac. parva and establish a robust foundation for ongoing taxonomic revisions of these two small-sized and species-poor, yet trans-continentally distributed genera, both of which contain considerable unrecognized diversity.

Osteodiscus abyssicola, a new snailfish (Cottoidei: Liparidae) collected off the Pacific coast of northern Japan.

The snailfish Osteodiscus abyssicola sp. nov. is described from a single specimen collected off the Pacific coast of Hokkaido, northern Japan, at a depth of 4,6714,744 m. It is distinguished from all currently recognized congeners by the following combination of characters: vertebrae 49; dorsal-fin rays 44; anal-fin rays 39; principal caudal-fin rays 8; pyloric caeca 5; mouth horizontal; teeth on both jaws simple and sharp, without cusps; upper and lower jaw symphyses without diastema; cephalic pore sizes moderate, similar to or slightly larger than nostril; gill slit extending ventrally to 2nd pectoral-fin ray base; pectoral fin notched; mandibular symphysis to center of anus 101.6% head length (HL); posterior edge of pelvic disk to center of anus 15.5% HL; epural 1, reduced; epipleural ribs absent. An emended diagnosis and key to the species of Osteodiscus are provided.

Two new species of snailfishes of the genus emCareproctus/em (Cottoidei: Liparidae) from the western North Pacific Ocean with a range extension of emCareproctus brevipectoralis/em.

Three snailfish species of Careproctus (Cottoidei: Liparidae), including two new species, are described from the deep Pacific Ocean off northern Honshu Island, Japan. Careproctus cyanogladius sp. nov., collected from the depths of 2,698-3,223 m, can be distinguished from congeneric species by having the following combination of characters: vertebrae 63; dorsal-fin rays 57-58; anal-fin rays 50; principal caudal rays 7; pectoral-fin rays 29-31; pectoral fin without a notch; uppermost pectoral-fin base below a horizontal through posterior margin of maxillary; pelvic disk oval; chin pores well separated; teeth simple; pyloric caeca 6-10; body pale blue or gray when fresh. The other new species, Careproctus orri sp. nov., collected from depths of 640-808 m, can be distinguished from congeneric species by having the following combination of characters: vertebrae 58-60; dorsal-fin rays 52-53; anal-fin rays 47-49; pectoral-fin rays 34-35; pectoral fin with a distinct notch; cephalic pores 2-6-7-2, chin pores single, unpaired; gill slit extending ventrally to 5th or 6th pectoral-fin ray; teeth strongly trilobed; peritoneum dark, stomach white. In addition, one specimen of Careproctus brevipectoralis Chernova, Thiel Eidus, 2020 was newly collected from Japan, and is redescribed here in detail with comments on intraspecific variations.

Generation of a large orbital angular momentum beam via an optical fiber winding around a curved path and its application* *Project supported by the National Natural Science Foundation of China (Grant No. 11504074) and the State Key Laboratory of Quantum Optics and Quantum Optics Devices, Shanxi University (Grant No. KF202004).

Many papers have been published on the study of orbital angular momentum (OAM) of the laser modes based on the Laguerre–Gaussian (LG) beam and helical phase plate or rotating cylindrical lens, and the principal ray of the LG beam remains straight line. These ways are difficult to get a large OAM modes. In this paper, we propose a novel method to prepare a large OAM modes when the light propagates through a optical fiber winding around a curved path, and establish a theoretical framework based on the principal ray path changing. Firstly, we investigate three kinds of winding structure. Secondly, based on the analytical solutions and numerical calculations, we can find that the spiral body can achieve a large OAM temporal pulse. At the same time, based on the zero OAM diffraction diagram, we can obtain an improvement of resolving power beyond Rayleigh’s criterion. Finally, applying a large OAM diffraction pattern to realize 12-bitencodes, we can obtain a high-security optical information transfer system.

First record of the Deepsea pigfish Congiopodus coriaceus (Scorpaeniformes: Congiopodidae) in the Great Australian Bight with new data on morphology

The Deepsea pigfish Congiopodus coriaceus Paulin et Moreland, 1979 is recorded from the waters off the southern coast of Australia, Great Australian Bight for the first time, based on a juvenile specimen SL 64 mm collected in 1966. This is the westernmost known locality of the species, 3500 km from the type locality off New Zealand. The lack of published data after the original description of the species revealed the need to clarify a number of meristic and morphometric parameters. Based on x-ray images of 28 ZIN specimens of C. coriaceus from New Zealand, the range of individual variability in the number of vertebrae, the number of rays of the dorsal and anal fins is shown. The number of procurrent and principal rays in the caudal fin has been clarified. In some cases, the range of morphometric parameters published in the original description has been expanded, for example, the maximum body height and head length. The original description was supplemented with 16 new measurements. For the first time, data on the lengths of the ventral and caudal fins, the length and height of the caudal peduncle, and the interorbital distance were published. Because of contradictory published data on the number of gill rakers on the first branchial arch, their number was clarified; the diagnostic value of this parameter was confirmed.

On the radiation gauge for spin-1 perturbations in Kerr–Newman spacetime

We extend previous work (2020 Class. Quantum Grav. 37 075001) to the case of Maxwell’s equations with a source. Our work shows how to construct a vector potential for the Maxwell field on the Kerr–Newman background in a radiation gauge. The vector potential has a ‘reconstructed’ term obtained from a Hertz potential solving Teukolsky’s equation with a source, and a ‘correction’ term which is obtainable by a simple integration along outgoing principal null rays. The singularity structure of our vector potential is discussed in the case of a point particle source.

A new species of snailfish of the genus Paraliparis (Liparidae) from the western North Pacific, with a redescription of the poorly known species Paraliparis mandibularis.

A new snailfish, Paraliparis flammeus, is described on the basis of 18 specimens collected off the Pacific coast of Tohoku District, northern Japan at depths of 422–890 m. The new species is distinguished from 28 species of Paraliparis described from the North Pacific by the following combination of characters: mouth oblique; uppermost pectoral-fin base below horizontal through posterior margin of maxillary; 60–63 vertebrae, 54–58 dorsal-fin rays, 50 or 51 anal-fin rays, six principal caudal-fin rays, and 17–20 pectoral-fin rays. A maximum likelihood tree based on 106 COI gene sequences (492 bp) of Paraliparis recovered a monophyletic group comprising P. flammeus, Paraliparis cephalus, and Paraliparis dipterus. Paraliparis cephalus is similar to P. flammeus in having an oblique mouth, but it has four caudal-fin rays (vs six rays) and the uppermost pectoral-fin base above a horizontal through the maxillary posterior margin. Paraliparis dipterus differs from P. flammeus in having a horizontal mouth, 12–14 pectoral-fin rays, and lacking pyloric caeca (present in P. flammeus). Paraliparis flammeus is most similar to the eastern North Pacific Paraliparis mento in having an oblique mouth and the uppermost pectoral-fin base below a horizontal through the posterior margin of the maxillary. However, P. flammeus differs from P. mento in having six caudal-fin rays (vs five rays) and greater preanal length (29.9–35.3% SL vs 26.7–28.5% SL). A poorly known species, Paraliparis mandibularis, previously known from only two specimens collected from Tosa Bay, southern Japan, is redescribed based on the holotype and seven newly collected specimens. It is also similar to the new species but has 27–30 pectoral-fin rays and a shorter pectoral-fin lower lobe (13.8–15.9% SL in P. mandibularis vs 16.7–23.4% SL in P. flammeus).

A tholichthys‐like larva (Teleostei, Percomorpha) from the Eocene of Northern Caucasus, Russia

A morphologically bizarre fish larva is described based on a single specimen from Eocene (Bartonian) locality of Gornyi Luch, Krasnodar Region, Northern Caucasus, SW Russia. The fossil larva described here was collected form the Kuma Horizon and inhabited an open marine setting with bottom waters characterized by poorly oxygenated conditions, where it was associated with abundant pelagic fish taxa. This fossil fish larva exhibits a peculiar morphology, being characterized by remarkably expanded and thickened bones that form an armour-like protective covering, a strong and greatly elongate pelvic-fin spine and a unique head spination that comprises a conical and posterodorsally directed supraoccipital spine, a rostral spine formed by the nasals, and enormous spines on the preopercle and opercle. Moreover, this fish larva has an advanced insertion of the dorsal fin and 17 principal rays in the caudal fin thereby revealing its affinity to percomorph fishes. The hypertrophied bony plates encasing the head and forming a bony armour are shared with the so-called tholichthys larval stage of chaetodontid butterflyfishes, as well as with the larval stages of some other percomorphs. Comparison with selected percomorph larval morphotypes (e.g. families Chaetodontidae, Malacanthidae, Ostracoberycidae and Scatophagidae) suggests that the Eocene larva described herein exhibits a unique combination of characters that would support an attribution to a new, previously undescribed taxon.

Four new species of Careproctus (Cottoidei: Liparidae) from the deep-water vicinity of the southern Kuril Islands (Western North Pacific).

Four new species of Careproctus (Cottoidei: Liparidae) are described from the Bussol Strait (the deepest channel of the Kuril archipelago) and two neighboring abyssal basins of the Western North Pacific. Careproctus laperousei sp. nov. from the northern slope of the Kuril-Kamchatka Trench (depths of 4796-4803 m) has the following characters: vertebrae 57, pectoral-fin rays 26, principal caudal-fin rays 8 and pore pattern 2-6-7-1; it differs from the most similar congeners from the North Pacific in having a black peritoneum, short head (22.5 % of standard length, SL) and large disk (37.0 % of head length, lc). Careproctus brevipectoralis sp. nov. from the Kuril Basin of the Sea of Okhotsk (depths of 3301 m) has the following characters: vertebrae 55, pectoral-fin rays 26, caudal-fin rays 9, pore pattern 2-6-7-1 and peritoneum black; it differs from congeners by the absence of pleural ribs, deep and compressed leaf-like body (greatest depth 119 % lc, depth above anal-fin origin 113 % lc), small head (18 % SL), short pectoral fin (11 % SL) and cartilaginous-like tissue surrounding the dorsal fin. Careproctus pulcher sp. nov. and Careproctus globulus sp. nov., both having 46 vertebrae, are found on the Pacific side of the Bussol Strait at depths of 2350-2358 m. Careproctus pulcher sp. nov. is characterized by pectoral-fin rays 31-32, caudal-fin rays 10, pore pattern 2-6-7-1 and peritoneum pale; it differs from the most similar congeners in having a shorter head (25.5-26.3 % SL in adults) and gill opening reaching ventrally to 4th pectoral ray. Careproctus globulus sp. nov. has the following characters: pectoral-fin rays about 24, caudal-fin rays 8 and peritoneum black; it differs from other species in having a globular body, deep curve of vertebral column and pore pattern 2-5-6-1. Thus, based on these collections, the underwater sill of the Bussol Strait is inhabited by different species of Careproctus than the neighboring abyssal plains, Kuril-Kamchatka Trench and the Kuril Basin of the Sea of Okhotsk. Careproctus laperousei sp. nov. is the most deep-water Careproctus in the North Pacific.

A new, uniquely patterned spiny eel (Teleostei: Mastacembelidae) from southern Borneo, Kalimantan Tengah, Indonesia.

A new species of Macrognathus of the M. aculeatus species group is described from the Kahayan River drainage in southern Borneo, Kalimantan Tengah, Indonesia. Macrognathus kris, new species, is distinguished from all Asian congeners in having the following unique combination of characters: rim of anterior nostril with two fimbriae and two fimbrules; 43-45 rostral tooth plates; 24-25 dorsal spines; 46-55 dorsal-fin rays; 51-59 anal-fin rays; 20-23 principal caudal-fin rays; 76-78 total vertebrae; body depth at anus 11.8-15.9% SL; color pattern consisting of light brown stripe on dorsum and 11-14 irregular pentagonal dark brown blotches on sides of body.

Osteology of the posterior vertebral column and caudal skeleton of marine amphibious gobies (mudskippers) (Teleostei: Gobioidei)

Mudskippers are amphibious gobies (Teleostei: Gobioidei, Oxudercinae) that have served as models for the specialised physiology and behaviour of fishes out of water. In this study, a comparative analysis of the posterior vertebral column and the caudal skeleton of ten mudskipper species was conducted on the basis of X-ray imaging. The species considered were Apocryptes bato, Apocryptodon madurensis, Boleophthalmus dussumieri, Oxuderces dentatus, Periophthalmodon freycineti, Pn. schlosseri, Periophthalmus novemradiatus, Ps. waltoni, Pseudapocryptes borneensis, and Scartelaos tenuis. For the osteological description the new term 'modified caudal vertebra' is used for all those vertebrae that display visibly modified neural and/or haemal spines compared to the spines of a 'usual' caudal vertebra, but are not involved in the support of caudal rays. The results reveal that the most terrestrial forms (Pn. freycineti, Pn. schlosseri, Ps. novemradiatus, Ps. waltoni) possess distinct traits that are seldom found in the other species. Among these features are (a) the existence of at least two modified caudal vertebrae (also present in S. tenuis), (b) a particularly close, dovetailing association between the neural spines of the preural vertebrae two and three (restricted to Ps. novemradiatus and Ps. waltoni), and (c) thickening and shortening of the ventralmost principal caudal rays (also present in B. dussumieri and S. tenuis). These findings support the idea that the posterior caudal vertebrae and caudal skeleton of the mentioned species are modified to enhance locomotion on land. Moreover, a relationship between character development and degree of terrestrial adaptation is probable, as all three traits are most pronounced in Ps. waltoni, which correlates with its strikingly high level of adaptation to amphibious life. A further aspect of this study is that the newly recognized skeletal structures have good fossilization potential and could therefore facilitate recognition of fossil species of mudskippers, which are currently unknown.