Post-metamorphic ontogeny of Zoroaster fulgens Thomson, 1873 (Asteroidea, Forcipulatacea)

The complete ontogenetic development of an asteroid skeleton has never been described formally for any species. Here, we describe in detail the post-metamorphic ontogeny of Zoroaster fulgens Thomson, 1873. The major novelty of our work is the description of patterns of plate addition, the ontogeny of the internal ossicles, as well as the variability of ossicles according to their position along series. Seven specimens collected in the Rockall Basin (North Atlantic) were dissected with bleach and their anatomy was documented using a scanning electron microscope. The external anatomy was additionally observed on more than 30 specimens. We found that the overall structure of the skeleton does not change much between juveniles and adults, but the shape of individual ossicle changes during growth. Allometric scaling was particularly visible on the orals, ambulacrals and adambulacrals. The shape of an ossicle is more dependent of its position along the arm series than of its individual size. Many morphological features differentiate progressively during ontogeny, while others are expressed consistently among specimens. The study of this ontogenetic series allows discussing the homology between the structures present on the ossicles of Z. fulgens in particular and other forcipulatacean sea stars in general (i.e. muscles insertions and articulation areas). The new data obtained in this study provide a comprehensive framework of the anatomy and ontogeny of Z. fulgens that will help resolve taxonomic and phylogenetic controversies in the future

Assessing the Distribution of Water Ice and Other Volatiles at the Lunar South Pole with LUVMI-X: A Mission Concept

The search for exploitable deposits of water and other volatiles at the Moon’s poles has intensified considerably in recent years, due to the renewed strong interest in lunar exploration. With the return of humans to the lunar surface on the horizon, the use of locally available resources to support long-term and sustainable exploration programs, encompassing both robotic and crewed elements, has moved into focus of public and private actors alike. Our current knowledge about the distribution and concentration of water and other volatiles in the lunar rocks and regolith is, however, too limited to assess the feasibility and economic viability of resource-extraction efforts. On a more fundamental level, we currently lack sufficiently detailed data to fully understand the origins of lunar water and its migration to the polar regions. In this paper, we present LUVMI-X, a mission concept intended to address the shortage of in situ data on volatiles on the Moon that results from a recently concluded design study. Its central element is a compact rover equipped with complementary instrumentation capable of investigating both the surface and shallow subsurface of illuminated and shadowed areas at the lunar south pole. We describe the rover and instrument design, the mission’s operational concept, and a preliminary landing-site analysis. We also discuss how LUVMI-X fits into the diverse landscape of lunar missions under development

Comparative anatomy and phylogeny of the Forcipulatacea (Echinodermata: Asteroidea): insights from ossicle morphology

A new phylogenetic analysis of the superorder Forcipulatacea is presented. Forcipulatacea is one of the three major groups of sea stars (Asteroidea: Echinodermata), composed of 400 extant species. The sampled taxa are thought to represent the morphological diversity of the group. Twenty-nine forcipulate taxa were sampled belonging to Asteriidae, Stichasteridae, Heliasteridae, Pedicellasteridae, Zoroasteridae and Brisingida. Specimens were dissected with bleach. Detailed description of the skeleton and the anatomy of the ossicles were investigated using scanning electron microscopy. Comparative anatomy allowed the scoring of 115 phylogenetically informative characters. The consensus tree resulting from the analysis recovers Asteriidae, Stichasteridae, Zoroasteridae and Brisingida as monophyletic. All types of morphological features contribute to tree resolution and may be appropriate for taxon diagnosis. The synapomorphies supporting different clades are described and discussed. Brisingida and Zoroasteridae are the best- supported clades. The potentially challenging position of Brisingida in the tree may be explained by homoplastic changes, but also by the presence of numerous non- applicable characters

Révision du genre <i>Benthogenia</i> Fisher, 1911 (Asteroidea, Echinodermata), avec la description d’une nouvelle espèce et de l’anatomie des ossicules

Porcellanasteridae Sladen, 1883 est une famille d’étoiles de mer vivant ensevelie dans le sédiment dans des environnements bathyaux et abyssaux. Parmi les douze genres actuellement reconnus au sein de cette famille, Benthogenia Fisher, 1911 est le seul à avoir été signalé à des profondeurs inférieures à 1000 m. Benthogenia diffère de tous les autres porcellanastéridés par la présence d’organes cribriformes entre toutes ses plaques marginales, du disque à l’extrémité des bras. Benthogenia cribellosa Fischer, 1911 est signalée dans une localité aussi peu profonde que 111 m, et une nouvelle espèce, Benthogenia mahi n. sp., est décrite à partir de matériel conservé au Muséum national d’Histoire naturelle, Paris (MNHN). Benthogenia mahi n. sp. est représenté par douze spécimens, collectés au cours de quatre expéditions différentes à des profondeurs allant de 400 à 1200 m. Benthogenia cribellosa est représentée par deux spécimens du MNHN, plus l’holotype et deux autres spécimens conservés au National Museum of Natural History (Smithsonian Institution), Washington D.C. Benthogenia mahi n. sp. diffère de B. cribellosa principalement par ses bras plus robustes, moins de piquants oraux et adambulacraires, et par les organes cribriformes ne couvrant pas toute la surface des plaques supéromarginales du disque. Des données moléculaires (ADNR 16S) ont également été collectées pour tester la divergence entre les deux espèces. Benthogenia mahi n. sp. est présent en Nouvelle-­Calédonie, aux Îles Salomon et au Vanuatu, alors que B. cribellosa n’est connue qu’aux Philippines. Des descriptions détaillées des deux espèces sont fournies, ainsi qu’une description détaillée du squelette de la nouvelle espèce.Porcellanasteridae Sladen, 1883 is a family of mud-dwelling sea stars, living in bathyal and abyssal environments. Among the twelve currently recognized genera of this family, Benthogenia Fisher, 1911 is the only one known occurring at depth shallower than 1000 m. Benthogenia differs from all other porcellanasterids by having cribriform organs between all its marginals, from the disc to the tip of the arms. Benthogenia cribellosa Fisher, 1911 is reported from a locality as shallow as 111 m, and a new species, Benthogenia mahi n. sp., is described from material housed in the Muséum national d’Histoire naturelle, Paris (MNHN). Benthogenia mahi n. sp. is represented by twelve specimens, collected at depth ranging from 400 to 1200 m during four different expeditions. Benthogenia cribellosa is represented by two specimens from the MNHN, plus the holotype and two specimens from the National Museum of Natural History (Smithsonian Institution), Washington D.C. Benthogenia mahi n. sp. differs from B. cribellosa mostly by having more robust arms, fewer oral and adambulacral spines, and by the cribriform organs not covering the entire surface of the superomarginals of the disc. Molecular data (16S rDNA) were also used as an independent dataset to test for divergence between the two species. Benthogenia mahi n. sp. occurs in New Caledonia, Solomon Islands and Vanuatu, whereas B. cribellosa is only known from the Philippines. Detailed descriptions of both species are provided, as well as a detailed description of the skeleton of the new species.</p

https://github.com/gilles-didier/Diversification

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Photogrammetry for 3D digitizing bones of mounted skeletons: Potential and limits

International audienceSince the late 20th century, new technologies have provided powerful ways to digitize biological structures in three dimensions (3D). Among those, photogrammetry is a low cost and non-destructive method, which has become increasingly used since the development of the digital camera. Recent studies have demonstrated that reconstructions of isolated elements can be of as high quality as those obtained with laser scanners. Here, we wanted to test the performance of photogrammetry for the quantitative analysis of mounted specimens in museum exhibitions. Indeed, access to material can be an issue in comparative anatomy and, especially, in paleontology. This is notably the case for large, impressive specimens. We performed reconstructions based on acquisitions done under various conditions and also tested the reconstruction performance of two software programs. The resulting 3D models were then compared to a reference object corresponding to the bone of interest digitized with a cutting-edge surface scanner. Our results show that photogrammetry enables quality reconstruction of the almost entire surface of the mounted bone of interest. Photogrammetry thus appears a reliable method perfectly suited to study large specimens exposed in museum gallery. Mots clés : Photogrammétrie Squelettes montés Paléontologie 3D Digitalisation Agisoft photoscan VisualSF

Appendix

A pdf file with results and proofs referred in the article

Likelihood of tree topologies with fossils and diversification rate estimation

International audienceDiversification rates are estimated from phylogenies, typically without fossils, except in paleontological studies. By nature, rate estimations depend heavily on the time data provided in phylogenies, which are divergence times and (when used) fossil ages. Among these temporal data, fossil ages are by far the most precisely known (divergence times are inferences calibrated with fossils). We propose a method to compute the likelihood of a phylogenetic tree with fossils in which the only known time information is the fossil ages. Testing our approach on simulated data shows that the maximum likelihood rate estimates from the phylogenetic tree shape and the fossil dates are almost as accurate as the ones obtained by taking into account all the data, including the divergence times. Moreover they are substantially more accurate than the estimates obtained only from the exact divergence times (without taking into account the fossil record)