The "elongate chelicera problem": A virtual approach in an extinct pterygotid sea scorpion from a 3D kinematic point of view.

Chelicerae, distinctive feeding appendages in chelicerates, such as spiders, scorpions, or horseshoe crabs, can be classified based on their orientation relative to the body axis simplified as either orthognathous (parallel) or labidognathous (inclined), exhibiting considerable diversity across various taxa. Among extinct chelicerates, sea scorpions belonging to the Pterygotidae represent the only chelicerates possessing markedly elongated chelicerae relative to body length. Despite various hypotheses regarding the potential ecological functions and feeding movements of these structures, no comprehensive 3D kinematic investigation has been conducted yet to test these ideas. In this study, we generated a comprehensive 3D model of the pterygotid Acutiramus, making the elongated right chelicera movable by equipping it with virtual joint axes for conducting Range of Motion analyses. Due to the absence in the fossil record of a clear indication of the chelicerae orientation and their potential lateral or ventral movements (vertical or horizontal insertion of joint axis 1), we explored the Range of Motion analyses under four distinct kinematic settings with two orientation modes (euthygnathous, klinogathous) analogous to the terminology of the terrestrial relatives. The most plausible kinematic setting involved euthygnathous chelicerae being folded ventrally over a horizontal joint axis. This configuration positioned the chelicera closest to the oral opening. Concerning the maximum excursion angle, our analysis revealed that the chela could open up to 70°, while it could be retracted against the basal element to a maximum of 145°. The maximum excursion in the proximal joint varied between 55° and 120° based on the insertion and orientation. Our findings underscore the utility of applying 3D kinematics to fossilized arthropods for addressing inquiries on functional ecology such as prey capture and handling, enabling insights into their possible behavioral patterns. Pterygotidae likely captured and processed their prey using the chelicerae, subsequently transporting it to the oral opening with the assistance of other prosomal appendages.

Unveiling the ventral morphology of a rare early Cambrian great appendage arthropod from the Chengjiang biota of China.

BACKGROUND: The early Cambrian arthropod clade Megacheira, also referred to as great appendage arthropods, comprised a group of diminutive and elongated predators during the early Palaeozoic era, around 518 million years ago. In addition to those identified in the mid-Cambrian Burgess Shale biota, numerous species are documented in the renowned 518-million-year-old Chengjiang biota of South China. Notably, one species, Tanglangia longicaudata, has remained inadequately understood due to limited available material and technological constraints. In this study, we, for the first time, examined eight fossil specimens (six individuals) utilizing state-of-the-art µCT and computer-based 3D rendering techniques to unveil the hitherto hidden ventral and appendicular morphology of this species. RESULTS: We have identified a set of slender endopodites gradually narrowing distally, along with a leaf-shaped exopodite adorned with fringed setae along its margins, and a small putative exite attached to the basipodite. Our techniques have further revealed the presence of four pairs of biramous appendages in the head, aligning with the recently reported six-segmented head in other early euarthropods. Additionally, we have discerned two peduncle elements for the great appendage. These findings underscore that, despite the morphological diversity observed in early euarthropods, there exists similarity in appendicular morphology across various groups. In addition, we critically examine the existing literature on this taxon, disentangling previous mislabelings, mentions, descriptions, and, most importantly, illustrations. CONCLUSIONS: The µCT-based investigation of fossil material of Tanglangia longicaudata, a distinctive early Cambrian euarthropod from the renowned Chengjiang biota, enhances our comprehensive understanding of the evolutionary morphology of the Megacheira. Its overall morphological features, including large cup-shaped eyes, raptorial great appendages, and a remarkably elongated telson, suggest its potential ecological role as a crepuscular predator and adept swimmer in turbid waters.

Just a matter of size? Evaluating allometry and intersexual heterometry in Pagurus bernhardus using ratios and indices (Decapoda, Anomura).

Heterochely denotes the presence of dissimilarly sized chelipeds on opposite sides of the body, a prevalent occurrence in diverse crustaceans. Conversely, heterometry pertains to the quantifiable disparities in size between these chelipeds. Both chelipeds hold pivotal roles in activities such as foraging, mating, and defense. Consequently, individuals of both genders in heterochelic species exhibit this morphological pattern. Previous studies have identified sexual dimorphism in cheliped size, with males displaying larger major chelipeds compared to females, albeit solely relying on propodus length as a size proxy and focusing solely on the major cheliped. In our study, we meticulously examined 190 specimens of the common European hermit crab Pagurus bernhardus from two collections. We sought to elucidate allometric relationships and assess whether heterometry exhibited sex-based differences when adjusting for body size by using ratios. Our findings revealed that male chelipeds displayed hyperallometric growth relative to females, and all three calculated heterometry indices exhibited significant disparities between the sexes. Consequently, male specimens exhibited larger major and minor chelipeds, even when theoretically matched for body size with females. This phenomenon may be attributed, among other factors, to male-male contests. Should indirect mate selection favor males with larger chelipeds in proportion to their body size, this dynamic could potentiate sexual selection in their favor.

Raptorial appendages of the Cambrian apex predator Anomalocaris canadensis are built for soft prey and speed.

The stem-group euarthropod Anomalocaris canadensis is one of the largest Cambrian animals and is often considered the quintessential apex predator of its time. This radiodont is commonly interpreted as a demersal hunter, responsible for inflicting injuries seen in benthic trilobites. However, controversy surrounds the ability of A. canadensis to use its spinose frontal appendages to masticate or even manipulate biomineralized prey. Here, we apply a new integrative computational approach, combining three-dimensional digital modelling, kinematics, finite-element analysis (FEA) and computational fluid dynamics (CFD) to rigorously analyse an A. canadensis feeding appendage and test its morphofunctional limits. These models corroborate a raptorial function, but expose inconsistencies with a capacity for durophagy. In particular, FEA results show that certain parts of the appendage would have experienced high degrees of plastic deformation, especially at the endites, the points of impact with prey. The CFD results demonstrate that outstretched appendages produced low drag and hence represented the optimal orientation for speed, permitting acceleration bursts to capture prey. These data, when combined with evidence regarding the functional morphology of its oral cone, eyes, body flaps and tail fan, suggest that A. canadensis was an agile nektonic predator that fed on soft-bodied animals swimming in a well-lit water column above the benthos. The lifestyle of A. canadensis and that of other radiodonts, including plausible durophages, suggests that niche partitioning across this clade influenced the dynamics of Cambrian food webs, impacting on a diverse array of organisms at different sizes, tiers and trophic levels.

Ventral Morphology of the Non-Trilobite Artiopod Retifacies abnormalis Hou, Chen & Lu, 1989, from the Early Cambrian Chengjiang Biota, China.

The artiopodans represent a diverse group of euarthropods with a typically flattened dorsal exoskeleton that covers numerous pairs of biramous ventral appendages, and which are ubiquitous faunal components of the 518-million-year-old Chengjiang Lagerstätte in South China. Despite their abundance, several Chengjiang artiopodans remain poorly known, such as the large euarthropoda Retifacies abnormalis, Hou, Chen & Lu, 1989, which is distinguished by the presence of mesh-like ornamentation on its dorsal exoskeleton. Although only a few ventral details were described in a single study in 25 years, it has been frequently featured in phylogenetic analyses that explore the relationships between Cambrian euarthropods. Here, we employ micro-CT and fluorescent microphotography to investigate the exceptionally preserved ventral morphology of R. abnormalis and explore its phylogenetic implications through maximum parsimony and Bayesian inference. Detailed morphology revealed here better supports R. abnormalis as a sister group to the diminutive artiopod Pygmaclypeatus daziensis, also known from Chengjiang, and strengthens the close relationship of these taxa that have been suggested by previous studies as early-branching representatives of Trilobitomorpha. Cephalic appendages suggest this animal might be a scavenger, possibly feeding on soft-bodied organisms. Different pairs of pygidial appendages suggest an anamorphic post-embryonic ontogeny, which adds to the understanding of the developmental mode of Cambrian artiopods, and further supports the statement that post-hatching segment addition occurred in the ancestor of Euarthropoda.

Before trilobite legs: Pygmaclypeatus daziensis reconsidered and the ancestral appendicular organization of Cambrian artiopods.

The Cambrian Stage 3 Chengjiang biota in South China is one of the most influential Konservat-Lagerstätten worldwide thanks to the fossilization of diverse non-biomineralizing organisms through pyritization. Despite their contributions to understanding the evolution of early animals, several Chengjiang species remain poorly known owing to their scarcity and/or incomplete preservation. Here, we use micro-computed tomography to reveal in detail the ventral appendage organization of the enigmatic non-trilobite artiopod Pygmaclypeatus daziensis-one of the rarest euarthropods in Chengjiang-and explore its functional ecology and broader evolutionary significance. Pygmaclypeatus daziensis possesses a set of uniramous antennae and 14 pairs of post-antennal biramous appendages, the latter of which show an unexpectedly high degree of heteronomy based on the localized differentiation of the protopodite, endopodite and exopodite along with the antero-posterior body axis. The small body size (less than 2 cm), the presence of delicate spinose endites and well-developed exopodites with multiple paddle-shaped lamellae on the appendages of P. daziensis indicate a nekto-benthic mode of life and a scavenging/detritus feeding strategy. Pygmaclypeatus daziensis shows that appendage heteronomy is phylogenetically widespread within Artiopoda-the megadiverse clade that includes trilobites and their relatives with non-biomineralizing exoskeletons-and suggests that a single exopodite lobe with paddle-like lamellae is ancestral for this clade. This article is part of the theme issue 'The impact of Chinese palaeontology on evolutionary research'.

Spines and baskets in apex predatory sea scorpions uncover unique feeding strategies using 3D-kinematics.

Megalograptidae and Mixopteridae with elongate, spinose prosomal appendages are unique early Palaeozoic sea scorpions (Eurypterida). These features were presumably used for hunting, an untested hypothesis. Here, we present 3D model-based kinematic range of motion (ROM) analyses of Megalograptus ohioensis and Mixopterus kiaeri and compare these to modern analogs. This comparison confirms that the eurypterid appendages were likely raptorial, used in grabbing and holding prey for consumption. The Megalograptus ohioensis model illustrates notable Appendage III flexibility, indicating hypertrophied spines on Appendage III may have held prey, while Appendage II likely ripped immobilized prey. Mixopterus kiaeri, conversely, constructed a capture basket with Appendage III, and impaled prey with Appendage II elongated spines. Thus, megalograptid and mixopterid frontalmost appendages constructed a double basket system prior to moving dismembered prey to the chelicerae. Such 3D kinematic modeling presents a more complete understanding of these peculiar euchelicerates and highlights their possible position within past ecosystems.

Kinematics of whip spider pedipalps: a 3D comparative morpho-functional approach.

Amblypygi are tropical and subtropical ambush predators that use elongated, raptorial pedipalps for different activities. Although pedipalp use in predation and courtship has been explored in videography in vivo analyses, kinematic ex vivo examination of these appendages has not been conducted. Here, we rectify this lack of data by using micro-CT scans to 3D-kinematically model the appendage morphology and the range of motion (ROM) of the joints for Damon medius and Heterophrynus elaphus. We illustrate the successful application of this technique to terrestrial euarthropods in determining the maximum ROM values for each pedipalp joint. We also note that, in life, these values would be lower due to motion restricting structures like tendons, arthrodial membranes, and muscles. We further compare our maximum values obtained here with data from video-based motion analyses. The ROM of each joint shows the greatest flexibility in the femur-tibia joint (140-150°), the lowest in the basitarsus-claw joint (35-40°). ROM in the tibia-basitarsus joint is markedly distinct (D. medius: 44°; H. elaphus: 105°). This disparity reflects how H. elaphus uses the joint in the capture basket, while D. medius uses the femur-tibia joint to form the capture basket. We further illustrate notable vertical motion of the H. elaphus pedipalp compared to D. medius. This difference reflects the retro-ventral trochanter apophysis of H. elaphus. Our study opens the possibility to further whip spider kinematic understanding. Examination of other taxa using this approach will result in a more comprehensive understanding of the ecological significance and ethological implications of this unique arachnid group.

Exites in Cambrian arthropods and homology of arthropod limb branches.

The last common ancestor of all living arthropods had biramous postantennal appendages, with an endopodite and exopodite branching off the limb base. Morphological evidence for homology of these rami between crustaceans and chelicerates has, however, been challenged by data from clonal composition and from knockout of leg patterning genes. Cambrian arthropod fossils have been cited as providing support for competing hypotheses about biramy but have shed little light on additional lateral outgrowths, known as exites. Here we draw on microtomographic imaging of the Cambrian great-appendage arthropod Leanchoilia to reveal a previously undetected exite at the base of most appendages, composed of overlapping lamellae. A morphologically similar, and we infer homologous, exite is documented in the same position in members of the trilobite-allied Artiopoda. This early Cambrian exite morphology supplements an emerging picture from gene expression that exites may have a deeper origin in arthropod phylogeny than has been appreciated.

Intraspecific variation in the Cambrian: new observations on the morphology of the Chengjiang euarthropod Sinoburius lunaris.

BACKGROUND: The Chengjiang biota from southwest China (518-million-years old, early Cambrian) has yielded nearly 300 species, of which more than 80 species represent early chelicerates, crustaceans and relatives. The application of µCT-techniques combined with 3D software (e.g., Drishti), has been shown to be a powerful tool in revealing and analyzing 3D features of the Chengjiang euarthropods. In order to address several open questions that remained from previous studies on the morphology of the xandarellid euarthropod Sinoburius lunaris, we reinvestigated the µCT data with Amira to obtain a different approach of visualization and to generate new volume-rendered models. Furthermore, we used Blender to design 3D models showing aspects of intraspecific variation. RESULTS: New findings are: (1) antennulae consist of additional proximal articles that have not been detected before; (2) compared to other appendages, the second post-antennular appendage has a unique shape, and its endopod is comprised of only five articles (instead of seven); (3) the pygidium bears four pairs of appendages which are observed in all specimens. On the other hand, differences between specimens also have been detected. These include the presence/absence of diplotergites resulting in different numbers of post-antennular appendages and tergites and different distances between the tip of the hypostome and the anterior margin of the head shield. CONCLUSIONS: Those new observations reveal intraspecific variation among Chengjiang euarthropods not observed before and encourage considerations about possible sexual dimorphic pairs or ontogenetic stages. Sinoburius lunaris is a variable species with respect to its morphological characters, cautioning that taxon-specific variabilities need to be considered when exploring new species.

Moving legs: A workflow on how to generate a flexible endopod of the 518 million-year-old Chengjiang arthropod Ercaicunia multinodosa using 3D-kinematics (Cambrian, China).

Understanding the functional morphology and mobility of appendages of fossil animals is important for exploring ecological traits such as feeding and locomotion. Previous work on fossils from the 518 million-year-old Chengjiang biota of China was based mainly on two-dimensional information captured from the surface of the specimens. Only recently, µCT techniques started to reveal almost the entire, though flattened and compressed, three-dimensionally preserved morphologies of the arthropods from Chengjiang. This allows more accurate work on reconstructing the possible movement of certain structures such as the appendages. Here, we present a workflow on how to reconstruct the mobility of a limb of the early Chengjiang arthropod Ercaicunia multinodosa from the famous Chinese fossil site. Based on µCT scans of the fossil, we rendered surface models of the 13th-15th right endopods using the 3D visualization and 3D-rendering software Amira. The 3D objects then were postprocessed (Collapse Hierarchy, Unify Normals) in SAP 3D Visual Enterprise Author before being imported into the 3D animation program Autodesk Maya 2020. Using the add-on tool X_ROMM in Maya, we illustrate step-by-step on how to make the articles of the limbs swing-in toward each other. Eventually, we propose several possible limb movements of E. multinodosa, which helps to understand how this early arthropod could have moved its endopods.

Kinematics and morphology: A comparison of 3D-patterns in the fifth pereiopod of swimming and non-swimming crab species (Malacostraca, Decapoda, Brachyura).

Swimming crabs of the taxon Portunoidea show specialized, paddle-shaped fifth pereiopods (P5), which play a role in these crabs' ability to swim. In this study, the morphology of the fifth pereiopod in swimming and non-swimming crabs was studied in detail and the mobility in the articulations between podomeres was calculated from reconstructed three-dimensional (3D)-models. This way, we aimed to provide new estimates of kinematic parameters, and to answer the question on a possible homology of the P5 within several portunoid clades. We measured and compared podomere length ratios, orientations of the joint axes, and modeled single range of motion (sROM) of each joint as well as the total range of motion (tROM) of all joints of the P5 as a whole. Seven Portunoidea species, four of them belonging to the P5-swimming crab morphotype (Liocarcinus depurator, Polybius henslowii, Callinectes sapidus, Portunus pelagicus) and three not belonging to this morphotype (Carcinus aestuarii, Portumnus latipes, and with uncertain status Carupa tenuipes) were compared with the non-portunoids Sternodromia monodi, Ranina ranina, Raninoides bouvieri, Eriocheir sinensis, Varuna litterata, Ashtoret lunaris, and Cancer pagurus. The study was carried out using a combination of microcomputer tomography (µCT)-techniques and 3D-reconstructions. The µCT-data were used to create surface models of the P5 in Amira, which were then 3D-animated and manipulated in Maya to qualitatively compare modeled kinematic parameters. Results show that the merus and carpus in swimming crabs are shorter than in non-swimming crabs, while sROM angles are generally larger. The tROM of all joints expressed as Euclidean distances is generally higher in the portunoids (except for Carcinus). Our comparison of the complete trajectory of the dactylus tip regarding all maximum joint positions of the studied species suggests that the P5-swimming leg might have evolved once in the Portunoidea and got lost afterward in certain clades.

[Dealing with Relatives of the Victims of the "Aktion T4" by the National Socialist Institutions as well as by Wuerttemberg Asylums]. / Der Umgang mit Angehörigen der Opfer der Aktion "T4" durch die NS-Behörden und die Anstalten in Württemberg.

The role of the relatives in the context of the "euthanasia" "Aktion T4" ("T4" campaign) has been controversially discussed in recent years. Based on documents of the National Socialist bureaucracy, statements of asylum psychiatrists in the year 1945 to the French occupation force as well as letters from relatives to Weissenau asylum in Wuerttemberg, these sources are analysed here in the light of the reactions of family members in respect to "Aktion T4". The results testify to a broad spectrum of responses of relatives, which are mainly characterised by fear, helplessness and protest.

[An acute psychiatric ward moves into the community. An empirical test of the satellite model]. / Eine psychiatrische Akut-Station zieht in die Gemeinde Das Satellitenmodell auf dem empirischen Prüfstand.

A satellite ward is a psychiatric ward at a general hospital settled within a catchment area that is administered by a distant psychiatric hospital. The objective of the satellite model is to close the gap between patients and their community on the one hand and between psychiatry and general medicine on the other. The essential size of the satellite ward that enables it to take care for the patients in its catchment area is discussed controversially. This study investigated admission rates and number of beds needed in two catchment areas distant to the psychiatric hospital from 6 months before opening until 12 months after the opening of a satellite ward with 21 beds in one of the two catchment areas. We registered an 81% increase of admission rates in this catchment area (from 130 admissions in the half-year before the opening of the satellite ward to 235 admissions in the 2nd half-year after it) and a 41% increase in beds needed (from 28.8 beds in the half-year before opening to 40.7 beds in the 2nd half-year following). This increase was significant in comparison to the increase in the controlled catchment area. Thus, only 168 (71%) patients of the catchment area (but 82% of the patients with schizophrenia) were treated in the satellite ward. The remaining patients were treated in the parent house. A selective admission of severely ill patients into the parent house was not observed.

[Reasons for Hospital Treatment of Psychiatric Patients before and after the Opening of a Satellite Ward]. / Anlässe zur Krankenhausbehandlung psychisch Kranker vor und nach der Eröffnung einer Satellitenstation.

A satellite ward is a psychiatric ward at a general hospital settled within the catchment area that is administered by a psychiatric hospital. The objective of the satellite model is to approach community treatment on the one hand and somatic medicine on the other hand, consequently diminishing the threshold for hospital treatment. This study investigated whether the diagnostic, psychopathologic and social reasons for admissions changed from this catchment area due to the lower threshold of a satellite ward. The results were controlled with another catchment area's admissions to the 30 km distant psychiatric hospital. The opening of the satellite ward was followed by an 81 % increase of admissions. In particular, admissions of patients with neuroses and personality disorders were more frequent. There was no change of the severity code of psychopathology at admission. From the catchment area of the satellite ward less patients were admitted involuntarily whereas more admissions happened due to social reasons and after patients' own decision.