The first gladius-bearing coleoid cephalopods from the lower Toarcian "Schistes Cartons" Formation of the Causses Basin (southeastern France).

The fossil record of gladius-bearing coleoids is scarce and based only on a few localities with geological horizons particularly favourable to their preservation (the so-called Konservat-Lagerstätten), which naturally leads to strongly limited data on geographical distributions. This emphasizes the importance of every new locality providing gladius-bearing coleoids. Here, we assess for the first time the gladius-bearing coleoid taxonomic diversity within the lower Toarcian "Schistes Cartons" of the Causses Basin (southeastern France). The material includes two fragmentary gladii, identified as Paraplesioteuthis sagittata and ?Loligosepia sp. indet. Just with these two specimens, two (Prototeuthina and Loligosepiina) of the three (Prototeuthina, Loligosepiina and Teudopseina) suborders of Mesozoic gladius-bearing coleoids are represented. Thus, our results hint at a rich early Toarcian gladius-bearing coleoid diversity in the Causses Basin and point out the need for further field investigations in the lower Toarcian "Schistes Cartons" in this area. This new record of Paraplesioteuthis sagittata is only the second one in Europe and the third in the world (western Canada, Germany and now France). Based on these occurrences, we tentatively suggest that P. sagittata originated in the Mediterranean domain and moved to the Arctic realm through the Viking Corridor to eventually move even farther to North America.

'Arm brains' (axial nerves) of Jurassic coleoids and the evolution of coleoid neuroanatomy.

Although patchy, the fossil record of coleoids bears a wealth of information on their soft part anatomy. Here, we describe remains of the axial nerve cord from both decabrachian (Acanthoteuthis, Belemnotheutis, Chondroteuthis) and octobrachian (Plesioteuthis, Proteroctopus, Vampyronassa) coleoids from the Jurassic. We discuss some hypotheses reflecting on possible evolutionary drivers behind the neuroanatomical differentiation of the coleoid arm crown. We also propose some hypotheses on potential links between habitat depth, mode of life and the evolution of the Coleoidea. Supplementary Information: The online version contains supplementary material available at 10.1186/s13358-023-00285-3.

Comparative anatomy and functional implications of variation in the buccal mass in coleoid cephalopods.

In contrast to the well-studied articulated vertebrate jaws, the structure and function of cephalopod jaws remains poorly known. Cephalopod jaws are unique as the two jaw elements do not contact one another, are embedded in a muscular mass and connected through a muscle joint. Previous studies have described the anatomy of the buccal mass muscles in cephalopods and have proposed variation in muscle volume depending on beak shape. However, the general structure of the muscles has been suggested to be similar in octopuses, squids, and cuttlefish. Here we provide a quantitative analysis of the variation in the buccal mass of coleoids using traditional dissections, histological sections and contrast-enhanced computed tomography scans. Our results show that the buccal mass is composed of four main homologous muscles present in both decapodiforms and octopodiforms as suggested previously. However, we also report the presence of a muscle uniquely present in octopodiforms (the postero-lateral mandibular muscle). Our three dimensional reconstructions and quantitative analyses of the buccal mass muscles pave the way for future functional analyses allowing to better model jaw closing in coleoids. Finally, our results suggest differences in beak and muscle function that need to be validated using future in vivo functional analyses.

Corrigendum: The significance of cephalopod beaks as a research tool: An update.

[This corrects the article DOI: 10.3389/fphys.2022.1038064.].

The significance of cephalopod beaks as a research tool: An update.

The use of cephalopod beaks in ecological and population dynamics studies has allowed major advances of our knowledge on the role of cephalopods in marine ecosystems in the last 60 years. Since the 1960's, with the pioneering research by Malcolm Clarke and colleagues, cephalopod beaks (also named jaws or mandibles) have been described to species level and their measurements have been shown to be related to cephalopod body size and mass, which permitted important information to be obtained on numerous biological and ecological aspects of cephalopods in marine ecosystems. In the last decade, a range of new techniques has been applied to cephalopod beaks, permitting new kinds of insight into cephalopod biology and ecology. The workshop on cephalopod beaks of the Cephalopod International Advisory Council Conference (Sesimbra, Portugal) in 2022 aimed to review the most recent scientific developments in this field and to identify future challenges, particularly in relation to taxonomy, age, growth, chemical composition (i.e., DNA, proteomics, stable isotopes, trace elements) and physical (i.e., structural) analyses. In terms of taxonomy, new techniques (e.g., 3D geometric morphometrics) for identifying cephalopods from their beaks are being developed with promising results, although the need for experts and reference collections of cephalopod beaks will continue. The use of beak microstructure for age and growth studies has been validated. Stable isotope analyses on beaks have proven to be an excellent technique to get valuable information on the ecology of cephalopods (namely habitat and trophic position). Trace element analyses is also possible using beaks, where concentrations are significantly lower than in other tissues (e.g., muscle, digestive gland, gills). Extracting DNA from beaks was only possible in one study so far. Protein analyses can also be made using cephalopod beaks. Future challenges in research using cephalopod beaks are also discussed.

Exceptional soft-tissue preservation of Jurassic Vampyronassa rhodanica provides new insights on the evolution and palaeoecology of vampyroteuthids.

Although soft tissues of coleoid cephalopods record key evolutionary adaptations, they are rarely preserved in the fossil record. This prevents meaningful comparative analyses between extant and fossil forms, as well as the development of a relative timescale for morphological innovations. However, unique 3-D soft tissue preservation of Vampyronassa rhodanica (Vampyromorpha) from the Jurassic Lagerstätte of La Voulte-sur-Rhône (Ardèche, France) provides unparalleled opportunities for the observation of these tissues in the oldest likely relative of extant Vampyroteuthis infernalis. Synchrotron X-ray microtomography and reconstruction of V. rhodanica allowed, for the first time, a high-resolution re-examination of external and internal morphology, and comparison with other fossil and extant species, including V. infernalis. The new data obtained demonstrate that some key V. infernalis characters, such as its unique type of sucker attachment, were already present in Jurassic taxa. Nonetheless, compared with the extant form, which is considered to be an opportunistic detritivore and zooplanktivore, many characters in V. rhodanica indicate a pelagic predatory lifestyle. The contrast in trophic niches between the two taxa is consistent with the hypothesis that these forms diversified in continental shelf environments prior to the appearance of adaptations in the Oligocene leading to their modern deep-sea mode of life.

Underwater photogrammetry for close-range 3D imaging of dry-sensitive objects: The case study of cephalopod beaks.

Technical advances in 3D imaging have contributed to quantifying and understanding biological variability and complexity. However, small, dry-sensitive objects are not easy to reconstruct using common and easily available techniques such as photogrammetry, surface scanning, or micro-CT scanning. Here, we use cephalopod beaks as an example as their size, thickness, transparency, and dry-sensitive nature make them particularly challenging. We developed a new, underwater, photogrammetry protocol in order to add these types of biological structures to the panel of photogrammetric possibilities.We used a camera with a macrophotography mode in a waterproof housing fixed in a tank with clear water. The beak was painted and fixed on a colored rotating support. Three angles of view, two acquisitions, and around 300 pictures per specimen were taken in order to reconstruct a full 3D model. These models were compared with others obtained with micro-CT scanning to verify their accuracy.The models can be obtained quickly and cheaply compared with micro-CT scanning and have sufficient precision for quantitative interspecific morphological analyses. Our work shows that underwater photogrammetry is a fast, noninvasive, efficient, and accurate way to reconstruct 3D models of dry-sensitive objects while conserving their shape. While the reconstruction of the shape is accurate, some internal parts cannot be reconstructed with photogrammetry as they are not visible. In contrast, these structures are visible using reconstructions based on micro-CT scanning. The mean difference between both methods is very small (10-5 to 10-4 mm) and is significantly lower than differences between meshes of different individuals.This photogrammetry protocol is portable, easy-to-use, fast, and reproducible. Micro-CT scanning, in contrast, is time-consuming, expensive, and nonportable. This protocol can be applied to reconstruct the 3D shape of many other dry-sensitive objects such as shells of shellfish, cartilage, plants, and other chitinous materials.

Ontogenetic Data Analyzed As Such in Phylogenies.

Ontogeny is rarely included in phylogenetic analyses of morphological data. When used, the ontogenetic information is reduced to one character for two or three different ontogenetic stages. Several examples show that current methods miss a major part of the information. We here propose a new method for including the ontogenetic dimension in coding schemes of phylogenetic analyses. Our goal was to maximize the phylogenetic information extracted from ontogenetic trajectories. For discrete features, we recommend including precise timings of transformation(s) from one state to another in the ontogenetic trajectories. For continuously varying features, growth laws are modeled on raw data using least-square regressions. Then, parameters of models are included in the coding scheme as continuous characters. This method is employed to reconstruct phylogenetic relationships using the ammonite family Amaltheidae as a test subject. Based on the same data set, a second analysis has been performed only for characters of the adult stage. Comparisons of retention index, bootstrap support, and stratigraphic congruence between the two analyses show that the inclusion of ontogeny yields better phylogenetic reconstruction. Morphological traits in ammonites which are usually the most homoplastic show a better fit to most parsimonious trees by including the ontogenetic dimension. In several cases, growth rates and patterns of growth have better fit to phylogeny than adult shapes, implying that paths of ontogeny can be more relevant than its products.

The phylogeny of Hildoceratidae (Cephalopoda, Ammonitida) resolved by an integrated coding scheme of the conch.

Ammonite phylogeny has mainly been established based on a stratigraphic approach, with cladistics underconsidered. The main arguments against the use of cladistics are the supposed large amount of homoplasy and the small number of characters. Resolving the phylogeny of the Hildoceratidae (Early Jurassic) is especially challenging because of its large diversity and disparity. Many forms that have not been determined as closely related in previous studies exhibit very similar shapes. Moreover, some groups are morphologically very different, adding difficulties to building a unique coding scheme at a low taxonomic resolution (i.e. species). Here we propose an integrated coding scheme of the peristome shape and the ornamentation, allowing an increased level of comparison. The shape of the peristome is used as a new reference to locate ornamental features and propose new homology hypotheses. In total, 105 taxa have been analysed for 47 characters. We code continuous characters by their means and ranges ± one standard deviation. We test two weighting schemes: equal weights standardized by unit range and implied weighting with several concavity constants. This work has led to redefinition of the phylogenetic inclusivenesses of all the hildoceratid subfamilies. The new coding scheme based on peristome shapes provides the fewest homoplastic characters. The schemes appear promising to improve phylogenetic analyses in ammonoids as well as molluscs as a whole by creating a general coding framework.

Increasing the number of discrete character states for continuous characters generates well-resolved trees that do not reflect phylogeny.

Since the introduction of the cladistic method in systematics, continuous characters have been integrated into analyses but no methods for their treatment have received unanimous support. Some methods require a large number of character states to discretise continuous characters in order to keep the maximum level of information about taxa differences within the coding scheme. Our objective was to assess the impact of increasing the character state number on the outcomes of phylogenetic analyses. Analysis of a variety of simulated datasets shows that these methods for coding continuous characters can lead to the generation of well-resolved trees that do not reflect a phylogenetic signal. We call this phenomenon the flattening of the tree-length distribution; it is influenced by both the relative quantity of continuous characters in relation to discrete characters, and the number of characters in relation to the number of taxa. Bootstrap tests provide a method to avoid this potential bias.

The role of ammonites in the Mesozoic marine food web revealed by jaw preservation.

Ammonites are prominent in macroevolutionary studies because of their abundance and diversity in the fossil record, but their paleobiology and position in the marine food web are not well understood due to the lack of preserved soft tissue. We present three-dimensional reconstructions of the buccal apparatus in the Mesozoic ammonite Baculites with the use of synchrotron x-ray microtomography. Buccal mass morphology, combined with the coexistence of food remains found in the buccal mass, suggests that these ammonites fed on plankton. This diet may have extended to all aptychophoran ammonites, which share the same buccal mass morphology. Understanding the role of these ammonites in the Mesozoic food web provides insights into their radiation in the Early Jurassic, as well as their extinction at the end of the Cretaceous/early Paleogene.