Ontogeny of the Orbital Glands and Their Environs in the Pantropical Spotted Dolphin (Stenella attenuata: Delphinidae).

The nasolacrimal duct (NLD) connects the orbital (often associated with the Deep Anterior Orbital gland: DAOG, a.k.a. Harderian gland) and nasal regions in many tetrapods. Adult cetaceans are usually said to lack an NLD, and there is little agreement in the literature concerning the identity of their orbital glands, which may reflect conflicting definitions rather than taxonomic variation. In this study, we examined an embryological series of the pantropical spotted dolphin (Stenella attenuata), and report numerous divergences from other tetrapods. Underdeveloped eyelids and a few ventral orbital glands are present by late Stage (S) 17. By S 19, circumorbital conjunctival glands are present. In S 20, these conjunctival glands have proliferated, eyelids (and scattered palpebral glands) have formed, and a duct similar to the NLD has appeared. Subsequently, both the palpebral glands and the NLD are progressively reduced by S 22, even as the conjunctival glands exhibit regional growth. In most tetrapods examined, the ontogeny of the NLD follows a series of three stages: Inception of NLD, Connection of orbit and nasal cavity by the NLD and Ossification (i.e., formation of the bony canal surrounding the NLD, emerging into the orbit via the lacrimal foramen in the lacrimal bone). In contrast, the dolphin NLD originates at the same time as the lacrimal bone, and a lacrimal foramen fails to develop. The cetacean fossil record shows that a lacrimal foramen was present in the earliest ancestral amphibious, freshwater forms, but was soon lost as the lineage invaded the oceans. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 301:77-87, 2018. © 2017 Wiley Periodicals, Inc.

Development of the nasolacrimal apparatus in the Mongolian gerbil (Meriones unguiculatus), with notes on network topology and function.

The nasolacrimal apparatus (NLA) is a multicomponent functional system comprised of multiple orbital glands (up to four larger multicellular exocrine structures), a nasal chemosensory structure (vomeronasal organ: VNO), and a connecting duct (nasolacrimal duct: NLD). Although this system has been described in all tetrapod vertebrate lineages, albeit not always with all three main components present, considerably less is known about its ontogeny. The Mongolian gerbil (Meriones unguiculatus) is a common lab rodent in which the individual components of the adult NLA have been well studied, but as yet nothing is known about the ontogeny of the NLA. In this study, serial sections of 15 fetal and three adult Mongolian gerbil heads show that the development of the NLA falls into three fetal stages: inception (origin of all features), elongation (lengthening of all features), and expansion (widening of all features). No postnatal or juvenile specimens were observed in this study, but considerable growth evidently occurs before the final adult condition is reached. The development of the orbital glands and the VNO in the Mongolian gerbil is largely consistent with those in other mammals, despite a slight nomenclatural conundrum for the anterior orbital glands. However, the Mongolian gerbil NLD follows a more circuitous route than in other tetrapods, due mainly to the convoluted arrangement of the narial cartilages, the development of a pair of enlarged incisors as well as an enlarged infraorbital foramen. The impact of these associated features on the ontogeny and phylogeny of the NLA could be examined through the approach of network science. This approach allows for the incorporation of adaptations to specific lifestyles as potential explanations for the variation observed in the NLA across different tetrapod clades.

Breathing in a box: constraints on lung ventilation in giant pterosaurs.

Pterosaurs were the first vertebrates to achieve active flight, with some derived forms reaching enormous size. Accumulating fossil evidence confirms earlier indications that selection for large size in these flying forms resulted in a light, yet strong skeleton characterized by fusion of many bones of the trunk. However, this process also added mechanical constraints on the mobility of the thorax of large pterosaurs that likely limited the options available for lung ventilation. We present an alternative hypothesis to recent suggestions of an avian-like mechanism of costosternal pumping as the primary means of aspiration. An analysis of the joints among the vertebrae, ribs, sternum, and pectoral girdle of large pterosaurs indicates limited mobility of the ribcage and sternum. Comparisons with modes of lung ventilation in extant amniotes suggests that the stiffened thorax, coupled with mobile gastralia and prepubic bones, may be most consistent with an extracostal mechanism for lung ventilation in large pterodactyloids, perhaps similar to a crocodile-like visceral displacement system.

Towards a comprehensive model of feather regeneration.

Understanding of the regeneration of feathers, despite a 140 year tradition of study, has remained substantially incomplete. Moreover, accumulated errors and mis-statements in the literature have confounded the intrinsic difficulties in describing feather regeneration. Lack of allusion to Rudall's (Rudall [1947] Biochem Biophys Acta 1:549-562) seminal X-ray diffraction study that revealed two distinct keratins, beta- and alpha-, in a mature feather, is one of the several examples where lack of citation long inhibited progress in understanding. This article reviews and reevaluates the available literature and provides a synthetic, comprehensive, morphological model for the regeneration of a generalized, adult contour feather. Particular attention is paid to several features that have previously been largely ignored. Some of these, such as the beta-keratogenic sheath and the alpha-keratogenic, supra-umbilical, pulp caps, are missing from mature, functional feathers sensu stricto because they are lost through preening, but these structures nevertheless play a critical role in development. A new developmental role for a tissue unique to feathers, the medullary pith of the rachis and barb rami, and especially its importance in the genesis of the superior umbilical region (SUR) that forms the transition from the spathe (rachis and vanes) to the calamus, is described. It is postulated that feathers form through an intricate interplay between cyto- and histodifferentiative processes, determined by patterning signals that emanate from the dermal core, and a suite of interacting biomechanical forces. Precisely regulated patterns of loss of intercellular adhesivity appear to be the most fundamental aspect of feather morphogenesis and regeneration: rather than a hierarchically branched structure, it appears more appropriate to conceive of feathers as a sheet of mature keratinocytes that is "full of holes.

"A new lachrymal gland with an excretory duct in red and fallow deer" by Johann jacob Harder (1694): English translation and historical perspective.

The Harderian gland is an enigmatic orbital gland that has been described for many tetrapods, although a consistent definition of this structure has remained elusive. In particular, an unambiguous distinction between the Harderian gland and the nictitans gland, which may both occur in the anterior aspect of the orbit of mammals, remains problematic. These glands were first distinguished in 1694 by Johann Jacob Harder, a Swiss physician and anatomist. To facilitate a renewed examination of the anatomical and developmental relationships of the anterior orbital glands, we review the historical context of Harder's discovery, and provide Harder's original Latin text as well as an English translation.

The evolution of endothermy in terrestrial vertebrates: Who? When? Why?

Avian and mammalian endothermy results from elevated rates of resting, or routine, metabolism and enables these animals to maintain high and stable body temperatures in the face of variable ambient temperatures. Endothermy is also associated with enhanced stamina and elevated capacity for aerobic metabolism during periods of prolonged activity. These attributes of birds and mammals have greatly contributed to their widespread distribution and ecological success. Unfortunately, since few anatomical/physiological attributes linked to endothermy are preserved in fossils, the origin of endothermy among the ancestors of mammals and birds has long remained obscure. Two recent approaches provide new insight into the metabolic physiology of extinct forms. One addresses chronic (resting) metabolic rates and emphasizes the presence of nasal respiratory turbinates in virtually all extant endotherms. These structures are associated with recovery of respiratory heat and moisture in animals with high resting metabolic rates. The fossil record of nonmammalian synapsids suggests that at least two Late Permian lineages possessed incipient respiratory turbinates. In contrast, these structures appear to have been absent in dinosaurs and nonornithurine birds. Instead, nasal morphology suggests that in the avian lineage, respiratory turbinates first appeared in Cretaceous ornithurines. The other approach addresses the capacity for maximal aerobic activity and examines lung structure and ventilatory mechanisms. There is no positive evidence to support the reconstruction of a derived, avian-like parabronchial lung/air sac system in dinosaurs or nonornithurine birds. Dinosaur lungs were likely heterogenous, multicameral septate lungs with conventional, tidal ventilation, although evidence from some theropods suggests that at least this group may have had a hepatic piston mechanism of supplementary lung ventilation. This suggests that dinosaurs and nonornithurine birds generally lacked the capacity for high, avian-like levels of sustained activity, although the aerobic capacity of theropods may have exceeded that of extant ectotherms. The avian parabronchial lung/air sac system appears to be an attribute limited to ornithurine birds.

TURBINATES IN THERAPSIDS: EVIDENCE FOR LATE PERMIAN ORIGINS OF MAMMALIAN ENDOTHERMY.

The structure and function of the nasal conchae of extant reptiles, birds, and mammals are reviewed, and the relationships to endothermy of the mammalian elements are examined. Reptilian conchae are relatively simple, recurved structures, which bear primarily sensory (olfactory) epithelium. Conversely, the conchae, or turbinates, of birds and mammals are considerably more extensive and complex, and bear, in addition, nonsensory (respiratory) epithelium. Of the mammalian turbinates, only the exclusively respiratory maxilloturbinal has a clear functional relationship with endothermy, as it reduces desiccation associated with rapid and continuous pulmonary ventilation. The other mammalian turbinates principally retain the primitive, olfactory function of the nasal conchae. The maxilloturbinates are the first reliable morphological indicator of endothermy that can be used in the fossil record. In fossil mammals and mammallike reptiles, the presence and function of turbinates are most readily revealed by the ridges by which they attach to the walls of the nasal cavity. Ridges for olfactory turbinals are located posterodorsally, away from the main flow of respiratory air, whereas those of the respiratory maxilloturbinals are situated in the anterolateral portion of the nasal passage, directly in the path of respired air. The maxilloturbinal is also characterized by its proximity to the opening of the nasolacrimal canal. Posterodorsal ridges, for olfactory turbinals, have long been recognized in many mammallike reptiles, including early forms such as pelycosaurs. However, ridges for respiratory turbinals have not been identified previously in this group. In this paper, the presence of anterolateral ridges, which most likely supported respiratory turbinals, is reported in the primitive therocephalian Glanosuchus and in several cynodonts. The presence of respiratory turbinals in these advanced mammallike reptiles suggests that the evolution of "mammalian" oxygen consumption rates may have begun as early as the Late Permian and developed in parallel in therocephalians and cynodonts. Full mammalian endothermy may have taken as much as 40 to 50 million yr to develop.