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The structural and bonding properties of liquid L-lactic acid were investigated through ab initio molecular dynamics simulations, leveraging on the agreement between the static structure factors obtained from high-energy X-ray diffraction (HEXRD) measurements. It has been demonstrated that predominant intermolecular interactions arise from hydrogen bonding. Hydrogen atoms in two hydroxy groups tend to form hydrogen bonds with two of the three oxygen atoms in neighboring molecules. This results in the presence of an oxygen atom in the hydroxy group of the carboxy group that does not significantly contribute to hydrogen bond formation with neighboring hydrogen atoms. This is consistent with the behavior observed in the crystalline phase. However, in the liquid state, four types of intermolecular hydrogen bonds are primarily formed, whereas in the crystal, only two types are observed. We show that the directionality of hydrogen bonds determines the intermolecular orientation. We thoroughly studied the structural properties and covalent bonding between atoms and charged states of atoms. [ABSTRACT FROM AUTHOR]

Studies have shown that there are two mineralization patterns of roots in multirooted teeth: one forms dentin islands (subpulpal lobes) independent of the crown, and the other does not form any subpulpal lobes. In this study, we found abnormal multirooted teeth in porpoise specimens and focused on the developmental process of its root furcation. To examine the features of the tooth in detail, we used scanning electron microscopy for the morphology of the surface and micro‐computed tomography (micro‐CT) for the structure of the pulp cavity. The micro‐CT scanning showed that a triple‐rooted tooth had only one pulp chamber and one horn. In addition, we observed the intermediate bifurcational ridge‐like structure and dentinal bulges on the subpulpal wall, both of which suggest the formation of the subpulpal lobes. To our knowledge, this study is the first report about teeth with supernumerary roots in Phocoenidae and also the first study to focus on the process of furcation of tooth roots in modern cetaceans. We concluded that the cause of the triple‐rooted tooth was not secondary adhesion of several teeth but rather the furcation of the root at the developmental stage. Additionally, the tooth could have formed lobes during the root furcation. [ABSTRACT FROM AUTHOR]

Bats are the second-most speciose group of mammals, comprising 20% of species diversity today. Their global explosion, representing one of the greatest adaptive radiations in mammalian history, is largely attributed to their ability of laryngeal echolocation and powered flight, which enabled them to conquer the night sky, a vast and hitherto unoccupied ecological niche. While there is consensus that powered flight evolved only once in the lineage, whether laryngeal echolocation has a single origin in bats or evolved multiple times independently remains disputed. Here, we present developmental evidence in support of laryngeal echolocation having multiple origins in bats. This is consistent with a non-echolocating bat ancestor and independent gain of echolocation in Yinpterochiroptera and Yangochiroptera, as well as the gain of primitive echolocation in the bat ancestor, followed by convergent evolution of laryngeal echolocation in Yinpterochiroptera and Yangochiroptera, with loss of primitive echolocation in pteropodids. Our comparative embryological investigations found that there is no developmental difference in the hearing apparatus between non-laryngeal echolocating bats (pteropodids) and terrestrial non-bat mammals. In contrast, the echolocation system is developed heterotopically and heterochronically in the two phylogenetically distant laryngeal echolocating bats (rhinolophoids and yangochiropterans), providing the first embryological evidence that the echolocation system evolved independently in these bats. [Display omitted] • Hearing apparatus development of 34 bat species and various mammals were compared • Non-bat mammals and non-laryngeal echolocating bats show identical development • Two distantly related laryngeal echolocating bats show divergent development • The findings suggest that the laryngeal echolocation evolved convergently among bats Whether laryngeal echolocation evolved only once in bats or evolved multiple times independently is one of the major unanswered questions in vertebrate evolution. Extensively comparing the prenatal development of bats and various mammals by high-resolution microCT, Nojiri et al. show that embryological evidence supports independent origins. [ABSTRACT FROM AUTHOR]

Although toothed whales have dentition peculiar to mammals, little attention has been paid to the periodontal tissues that support these characteristic teeth. In this study, we clarified the anatomical characteristics of the periodontal tissue in several species of Delphinidae through three-dimensional observation using micro-computed tomography, histological observations using decalcified sections, and immunohistochemical analysis. The results indicated that the teeth and the periodontal tissues of dolphins are morphologically unique among mammals. The alveolar bone was both crude and spongy. The lamina dura, a radiopaque line observed in the alveolar bone of common mammals, was thin in dolphins, and the teeth were attached to the trabeculae with the periodontal ligament (PDL). The alveolar sockets were massive for the size of the teeth. The PDL, a collagen fiber that fills the periodontal space, was well-developed and peculiarly divided into two layers. The inner layer fibers radially spread out from the cementum, similar to the PDL in common mammals. However, the outer layer fibers penetrate the spongy bone in a complicated manner. The interstitial space between the inner and outer layers contained nerve fiber bundles that were thicker than those found in the PDL of other mammals. Sensory receptor-like structures were observed at the terminal ends of the nerve fibers. These findings indicated that the dolphin PDL is more sensitive to dental stimuli than those of other mammals, suggesting that the dolphin dentition plays a functional role as a sensory receptor, similar to tactile hair., (© 2024 American Association for Anatomy.)

Turbinals are key bony elements of the mammalian nasal cavity, involved in heat and moisture conservation as well as olfaction. While turbinals are well known in some groups, their diversity is poorly understood at the scale of placental mammals, which span 21 orders. Here, we investigated the turbinal bones and associated lamellae for one representative of each extant order of placental mammals. We segmented and isolated each independent turbinal and lamella and found an important diversity of variation in the number of turbinals, as well as their size, and shape. We found that the turbinal count varies widely, from zero in the La Plata dolphin, (Pontoporia blainvillei) to about 110 in the African bush elephant (Loxodonta africana). Multiple turbinal losses and additional gains took place along the phylogeny of placental mammals. Some changes are clearly attributed to ecological adaptation, while others are probably related to phylogenetic inertia. In addition, this work highlights the problem of turbinal nomenclature in some placental orders with numerous and highly complex turbinals, for which homologies are extremely difficult to resolve. Therefore, this work underscores the importance of developmental studies to better clarify turbinal homology and nomenclature and provides a standardized comparative framework for further research., (© 2024 The Author(s). The Anatomical Record published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

Multiple corrugated cartilaginous structures are formed within the mammalian nasal capsule, eventually developing into turbinals. Due to its complex and derived morphology, the homologies of the bat nasal turbinals have been highly disputed and uncertain. Tracing prenatal development has been proven to provide a means to resolve homological problems. To elucidate bat turbinate homology, we conducted the most comprehensive study to date on prenatal development of the nasal capsule. Using diffusible iodine-based contrast-enhanced computed tomography (diceCT), we studied in detail the 3D prenatal development of various bat species and non-bat laurasiatherians. We found that the structure previously identified as "maxilloturbinal" is not the true maxilloturbinal and is only part of the ethmoturbinal I pars anterior. Our results also allowed us to trace the evolutionary history of the nasal turbinals in bats. The turbinate structures are overall comparable between laurasiatherians and pteropodids, suggesting that pteropodids retain the ancestral laurasiatherian condition. The absence of the ethmoturbinal I pars posterior in yangochiropterans and rhinolophoids has possibly occurred independently by convergent evolution., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Ito, Tu, Eiting, Nojiri and Koyabu.)

We compared the temporomandibular joint structure between species of the order Carnivora and investigated its variation among family lineages. We also investigated the effect of the masticatory muscle physiological cross-sectional area (PCSA) on temporomandibular joint structure. The masticatory muscle is composed of multiple muscles, which contract in different directions and exert pressure on the temporomandibular joint. We investigated the effect of the ratio of each muscle's PCSA-an indicator of muscle force-and muscle size relative to body size on temporomandibular joint structure. The temporalis PCSA relative to body size showed the highest correlation with temporomandibular joint structure. When the temporalis PCSA is large relative to body size, the preglenoid projects caudally, the postglenoid projects rostrally and the pre-postglenoid angle interval is small, indicating that the condyle is locked in the fossa to reinforce the temporomandibular joint. Most Carnivora use blade-like carnassial teeth when slicing food. However, dislocation occurs when the carnassial teeth are used by the temporalis muscle. Our results suggest that the temporomandibular joint is reinforced to prevent dislocation caused by the temporalis muscle. In Mustelidae, the temporomandibular joint with a rostrally projecting postglenoid is suitable for carnassial biting using the temporalis muscle. In Felidae, the force of the masseter onto the carnassial teeth is diverted to the canine by tightening the temporomandibular joint. In Canidae, the masticatory muscle arrangement is well-balanced, enabling combined action. Hence, reinforcement of the temporomandibular joint by bone structure is unnecessary.