Anatomy across the animal kingdom

Examining the anatomy of an organism opens up a whole world of exploration into the function of its body, its evolution, and how it interacts with the biotic and abiotic elements in its environment. On the cusp of new advances in technology that have furthered this exploration, the editors at Communications Biology have gathered a Collection of our exciting research in organismal anatomy to highlight the possibilities of this field yet to come.

Nuria Melisa Morales-García et al. analyze jaw shape and mechanical advantage of 70 small modern mammals and 45 Mesozoic mammals and find that these metrics can be used to distinguish dietary groups for most extant mammals, and to infer diet in Mesozoic taxa.

Fornai et al. present a geometric morphometric study of the sacrum in two alleged Australopithecus africanus specimens from Sterkfontein Member 4, South Africa. By comparing the two fossil hominins to a diverse sample of modern humans and great apes, the authors conclude that the observed morphological differences are unlikely to occur within a single species, supporting earlier claims of taxonomic heterogeneity within the Australopithecus africanus hypodigm.

Newton et al. use microCT data and geometric morphometric analyses to explore the processes underlying the convergently evolved skulls of thylacine and gray wolf. Similarities in growth trajectory are contrasted by differential developmental event timing, with origins of morphometric similarity constrained by developmental modules and embryonic tissue origins.

Bertrand and colleagues use virtual endocasts from a variety of living and extinct rodent species to assess the effect of locomotion, body mass and phylogeny on the size of the brain and three of its components. Their findings indicate that arboreal and fossorial locomotor types correlate with differential expansion of the neocortex, petrosal lobules, and relative brain size.

Frey and colleagues describe a new fossil shark from the Late Devonian of Morocco in which the specialized jaw articulation is unusually well preserved. Biomechanical modelling reveals that the mandible rolled throughout its movement arc, engaging more of its tooth battery in a clutching bite action.

Miller et al. present a disassociated rhamphotheca of a Cretaceous bird, which sheds light on the diet and developmental biology of some of the earliest birds. Exceptionally preserved fossils are rare but when soft tissue is preserved it can provide insight into the anatomy and behavior of extinct organisms.

Oku, Ide and Ogihara use forward dynamic simulation to virtually manipulate the foot posture of the Japanese macaque from a digitigrade to plantigrade posture for bipedal locomotion. This postural shift results in greater energetic economy despite the macaque not having anatomy adapted for bipedal movement. Structural changes in the foot are likely a key component of the acquisition of human-like bipedal locomotion.

Deng et al. report a new species of giant rhino, Paraceratherium linxiaense, from specimens of the upper Oligocene Jiaozigou Formation in China with an age of 26.5 Ma. Morphological analysis of the completely preserved skull with articulated mandible and atlas reveals a high level of specialization and the formation of a clade with P. lepidum with close ties to P. bugtiense.

Plateau and Foth use anatomical network analysis to study the evolution of avian skull anatomy. They report that the ontogenetic changes in the morphology and modularity of the avian skulls is comparable to evolutionary transformations from non-avian theropods to modern birds. Their work highlights the complexity of avian skull evolution.

Marcos Ercoli et al. present a reconstruction of masticatory muscles in two species of Pachyrukhinae, showing evidence that these are the first known case of sciuromorph non-rodent mammals. They propose that this innovative acquisition occurred along with hard-food consumption.

Figueirido et al. use a 3D geometric morphometric approach to study functional among-species disparity in the vertebral column of Carnivora, as well as assessing the effect of different sampling methods on homology. Disparity is generally higher in more caudal regions, compared to more cranial regions, but recruitment for locomotor function is pervasive throughout the whole studied column.

Daniel García-Martínez et al. report Neanderthal lung volume estimates based on measurements from rib bone fossils and lung capacity data from modern humans. They estimate that Neanderthal individuals had approximately 20% higher lung capacity than modern humans, possibly due to higher energy requirements.

Thomas Kaye et al. use Laser-Stimulated Fluorescence and fossil evidence from the oldest known bird, Archaeopteryx, to document the oldest record of molting, demonstrating that a sophisticated molting strategy developed unexpectedly early on in the evolution of avian flight. This discovery provides important insights into the flight capabilities of the earliest birds and predates other major flight adaptations.

Using microcomputed tomography, Ginzel, Martynov et al. provide a modernized exploration of the developing midgut in rat embryos. This study enables three-dimensional, spatial interpretations of key structures throughout development, including the umbilicus and umbilical coelom.

Craig Albertson et al. report a study of the genetic basis of scale shape variation in cichlids from Lake Malawi. They find 40 QTL for scale development, most of which are specific to distinct body locations, and a role for Fgf signaling in shaping cichlid scales.

Massen, Hartlieb, Martin et al. study the duration of yawns across mammals and birds to test the brain cooling hypothesis. Consistent with this hypothesis, their findings indicate that brain mass and neuron numbers influence yawn duration, and that mammals yawn longer than birds with similar brain and body masses.

Odise Cenaj et al. find that the fibrous interstitial spaces within and around organs may in fact be continuous networks throughout the human body. Using traceable particles injected into colon and skin interstitial spaces in human tissue samples, they demonstrate the interconnectedness of these fluid-filled spaces.

Byrnes et al. reconstruct the developing mesentery from digitized embryonic datasets and human and animal cadavers using 3D digital and printed models. They confirm the mesentery remains a continuous organ in and on which all abdominal digestive organs develop and that at the foundation level, the abdomen comprises a mesenteric and non-mesenteric domain.

Suzuki, Takaku, Hariyama and colleagues report on a crown-like structure found on the heads of midge larvae. This structure, analysed using scanning electron microscopy and experimental methods, enables subsurface adhesion and aids in control of locomotion in this region of the water column.

A new fossil of a vampire squid bridges a 120 million-year gap in their fossil record. Vampire squid today are adapted to low oxygen, deep sea environments and this new specimen provides evidence that the deep sea specialisation of vampire squid may have been triggered during the development of oxygen minimum zones in the oceans during the Cretaceous and Cenozoic.

Jean-Bernard Caron and Brittany Cheung provide new evidence that the rare Cambrian animal Amiskwia is closely related to gnathiferans, thereby resolving its ambiguous phylogeny. They describe new specimens from the Burgess Shale that preserve the complex jaw apparatus, which is most similar to gnathostomulids.

Schubnel, Nel and colleagues present the first Carboniferous representative of Titanoptera, Theiatitan azari. Specially modified wing zones suggest that Titanoptera were capable of wing-based communication using light or sound, as seen in modern species.

Lietz, Rajabi and colleagues investigate the physiological and structural components of damping in insect wings. Notably, flight muscles and hemolyph appear to have no direct involvement in wing damping, compared to the function of the wing hinge.

Cheryl L Ames, Anna Klompen et al. describe cassiosomes, stinging cell structures in the mucus of the upside-down jellyfish Cassiopea xamachana. They show that these motile cell masses consist of an outer epithelial layer largely composed of nematocytes surrounding centralized clusters of endosymbiotic dinoflagellates.

Christian Klug et al. have re-examined the Early Carboniferous coleoid Gordoniconus beargulchensis by Reflectance Transformation Imaging, various lights and synchrotron revealing new anatomical details. They discuss evolutionary scenarios of how conchs became internalized, as well as the timing of other important steps in early coleoid evolutionary.

Dayou Zhai et al. show marked variation in limb morphology and patterns in limb-tagmosis in three early Cambrian bradoriid arthropods. This suggests remarkable evolutionary convergence, either of fundamental body plans or appendage specialization patterns.