Ontogeny and Microanatomy of the Nasal Turbinals in Lemuriformes

Evolutionary constraint and innovation across hundreds of placental mammals

Zoonomia is the largest comparative genomics resource for mammals produced to date. By aligning genomes for 240 species, we identify bases that, when mutated, are likely to affect fitness and alter disease risk. At least 332 million bases (~10.7%) in the human genome are unusually conserved across species (evolutionarily constrained) relative to neutrally evolving repeats, and 4552 ultraconserved elements are nearly perfectly conserved. Of 101 million significantly constrained single bases, 80% are outside protein-coding exons and half have no functional annotations in the Encyclopedia of DNA Elements (ENCODE) resource. Changes in genes and regulatory elements are associated with exceptional mammalian traits, such as hibernation, that could inform therapeutic development. Earth's vast and imperiled biodiversity offers distinctive power for identifying genetic variants that affect genome function and organismal phenotypes.

Ontogenetic transformation of the cartilaginous nasal capsule in mammals, a review with new observations on bats

The nasal capsule, as the most rostral part of the chondrocranium, is a critical point of connection with the facial skeleton. Its fate may influence facial form, and the varied fates of cartilage may be a vehicle contributing to morphological diversity. Here, we review ontogenetic changes in the cartilaginous nasal capsule of mammals, and make new observations on perinatal specimens of two chiropteran species of different suborders. Our observations reveal some commonalities between Rousettus leschenaultii and Desmodus rotundus, such as perinatal ossification of the first ethmoturbinal. However, in Rousettus, ossification of turbinals is demonstrated as either perichondrial or endochondral. In Desmodus, perichondrial and endochondral ossification of the posterior nasal cupula is observed at birth, a part of the nasal capsule previously shown to persist as cartilage into infancy in Rousettus. Combined with prior findings on cranial cartilages we identify several diverse transformational mechanisms by which cartilage as a tissue type may contribute to morphological diversity of the cranium. First, cartilage differentiates in an iterative fashion to increase nasal complexity, but still retains the capacity for later elaboration via de novo bone emanating outward before or after cartilage ossifies. Second, cartilage acts as a driver of growth at growth centers, or via interstitial growth (e.g., septal cartilage). Finally, cartilage as a tissue may influence the timing of ossification and union of the facial and basicranial skeleton. In particular, cartilage at certain points of ontogeny may "model" via selective resorption, showing some similarity to bone.

Survey anatomy and histological observation of the nasal cavity of Tupaia belangeri chinensis (Tupaiidae, Scandentia, Mammalia)

This study aimed to provide researchers with an atlas of the survey anatomy, histology, and imaging of the nasal cavity of Tupaia belangeri chinensis. Seven T. b. chinensis adult males were euthanized and scanned using micro-computed tomography (CT). The nose was separated, and tissue sections were made on the coronal and axial planes to observe the survey anatomy and histological and imaging characteristics of the nose. T. b. chinensis contains one maxilloturbinal and three ethmoturbinals, one nasoturbinal, one interturbinal, two frontoturbinals, and one lamina semicircularis in the unilateral nasal cavity. Other identified structures were the ostiomeatal complex, vomeronasal organ, superior nasal vault, maxillary sinus, and frontal recess. The drainage pathways of the sinuses and nasal airflow in T. b. chinensis were confirmed. The vault epithelium consisted of the squamous epithelium, respiratory epithelium, transitional epithelium, and olfactory epithelium. Micro-CT confirmed our findings of the coronal tissue sections. The nasal cavity anatomy of T. b. chinensis is similar to that of some strepsirrhine primates. However, the airflow and olfactory function are quite different from that of humans. Our gross and histological atlas of the nasal septum, turbinals, maxillary sinus, and frontal recess provides a reference for researchers to use T. b. chinensis for nasal cavity functional research.

Anatomy of the Nasal and Auditory Regions of the Fossil Lagomorph Palaeolagus haydeni: Systematic and Evolutionary Implications

Palaeolagus, a late Eocene to early Miocene North American lagomorph genus, represented by numerous and well-preserved specimens, has been long considered a basal leporid, although it is currently understood as a stem lagomorph. Based on micro-computed tomography (μCT) data and 3D reconstructions, here we present the first description of intracranial structures of the nasal and auditory regions of a complete skull of Palaeolagus haydeni from the early Oligocene of Nebraska. Although Palaeolagus haydeni shows a puzzling mixture of extant leporid and ochotonid characters, it helps to polarize and re-evaluate already known lagomorph intracranial characters based on outgroup comparison with Rodentia and Scandentia. Common derived features of Palaeolagus haydeni and extant Lagomorpha are the dendritic maxilloturbinal and the excavated nasoturbinal that contacts the lamina semicircularis. Generally, Palaeolagus haydeni and Leporidae have several characters in common, some of which are certainly plesiomorphic (e.g., thin wall of bulla tympani and flat conic cochlea). Palaeolagus haydeni resembles Leporidae in having an interturbinal between the two frontoturbinals, and three ethmoturbinals plus one interturbinal between ethmoturbinal I and II. Now, this should also be regarded as a plesiomorphic grundplan pattern for Leporidae whereas ochotonids are derived from the lagomorph grundplan as concerns the number of frontoturbinals. Concerning the middle ear, Palaeolagus haydeni significantly contributes to the polarization of the anterior anchoring of the malleus in extant lagomorphs. Palaeolagus haydeni resembles the pattern observed in early ontogenetic stages of Ochotonidae, i.e., the attachment of the malleus to the ectotympanic via a short processus anterior. The patterns in adult ochotonids and leporids now can be regarded as two different and apomorphic character states. Autapomorphic characters of Palaeolagus haydeni are the reduced frontoturbinal 2 and the additional anterolaterally oriented process of the lamina semicircularis. Interestingly, among the investigated intracranial structures the loss of the secondary crus commune is the only apomorphic grundplan character of crown Lagomorpha.

Inward collapse of the nasal cavity: Perinatal consolidation of the midface and cranial base in primates

Living primates show a complex trend in reduction of nasal cavity spaces and structures due to moderate to severe constraint on interorbital breadth. Here we describe the ontogeny of the posterior end of the primate cartilaginous nasal capsule, the thimble shaped posterior nasal cupula (PNC), which surrounds the hind end of the olfactory region. We used a histologically sectioned sample of strepsirrhine primates and two non-primates (Tupaia belangeri, Rousettus leschenaulti), and histochemical and immunohistochemical methods to study the PNC in a perinatal sample. At birth, most strepsirrhines possess only fragments of PNC, and these lack a perichondrium. Fetal specimens of several species reveal a more complete PNC, but the cartilage exhibits uneven or weak reactivity to type II collagen antibodies. Moreover, there is relatively less matrix than in the septal cartilage, resulting in clustering of chondrocytes, some of which are in direct contact with adjacent connective tissues. In one primate (Varecia spp.) and both non-primates, the PNC has a perichondrium at birth. In older, infant Varecia and Rousettus, the perichondrium of the PNC is absent, and PNC fragmentation at its posterior pole has occurred in the former. Loss of the perichondrium for the PNC appears to precede resorption of the posterior end of the nasal capsule. These results suggest that the consolidation of the basicranial and facial skeletons happens ontogenetically earlier in primates than other mammals. We hypothesize that early loss of cartilage at the sphenoethmoidal articulation limits chondral mechanisms for nasal complexity, such as interstitial expansion or endochondral ossification.

The dog-human connection

This special issue of The Anatomical Record is the end result of a rare convergence of researchers scattered around the globe who came together to explore the mystery of the dog-human connection. Many of the discussions at the 12th International Congress of Vertebrate Morphology in Prague (July 23, 2019) are echoed within this issue. The enigmatic origins of dog domestication (as well as feralized descendants such as the dingo) are discussed, including phases of domestication that we might infer, and our historical knowledge of dog breeding. Emphasized by the morphological and genetic data are the forces of selection, both unintentional and intentional. In our modern life with dogs, we enjoy their companionship and benefit from the utility of many breeds, but we encounter unintended health care issues that are often breed-specific. Dogs are so different in their sensory specializations (especially olfaction), but have uniquely (among other domestic mammals) developed highly sophisticated means of interspecific communication with humans. In sum, the manuscripts within this issue discuss anatomical, paleontological, genetic, and behavioral evidence bearing on the antiquity of the domestic dog, the process of domestication, and the many ways in which dogs continue to affect human life.

Fissures, folds, and scrolls: The ontogenetic basis for complexity of the nasal cavity in a fruit bat (Rousettus leschenaultii)

Mammalian nasal capsule development has been described in only a few cross-sectional age series, rendering it difficult to infer developmental mechanisms that influence adult morphology. Here we examined a sample of Leschenault's rousette fruit bats (Rousettus leschenaultii) ranging in age from embryonic to adult (n = 13). We examined serially sectioned coronal histological specimens and used micro-computed tomography scans to visualize morphology in two older specimens. We found that the development of the nasal capsule in Rousettus proceeds similarly to many previously described mammals, following a general theme in which the central (i.e., septal) region matures into capsular cartilage before peripheral regions, and rostral parts of the septum and paries nasi mature before caudal parts. The ossification of turbinals also generally follows a rostral to the caudal pattern. Our results suggest discrete mechanisms for increasing complexity of the nasal capsule, some of which are restricted to the late embryonic and early fetal timeframe, including fissuration and mesenchymal proliferation. During fetal and early postnatal ontogeny, appositional and interstitial chondral growth of cartilage modifies the capsular template. Postnatally, appositional bone growth and pneumatization render greater complexity to individual structures and spaces. Future studies that focus on the relative contribution of each mechanism during development may draw critical inferences how nasal morphology is reflective of, or deviates from the original fetal template. A comparison of other chiropterans to nasal development in Rousettus could reveal phylogenetic patterns (whether ancestral or derived) or the developmental basis for specializations relating to respiration, olfaction, or laryngeal echolocation.

"Forever young"-Postnatal growth inhibition of the turbinal skeleton in brachycephalic dog breeds (Canis lupus familiaris)

In short snouted (brachycephalic) dogs (Canis lupus familiaris), several genetic mutations cause postnatal growth inhibition of the viscerocranium. Thus, for example, the pug keeps a snub nose like that observed in neonate dogs in general. However, little is known how far intranasal structures like the turbinal skeleton are also affected. In the present study, we provide the first detailed morphological and morphometric analyses on the turbinal skeleton of pug, Japanese chin, pekingese, King Charles spaniel, and Cavalier. In order to elucidate how a shortened snout affects turbinal shape, size, and density, our sample covers different degrees of brachycephaly. Macerated skulls of 1 juvenile and 17 adult individuals were investigated by μCT and virtual 3D reconstructions. In addition, histological serial sections of two prenatal and one neonate whippet were taken into account. All investigated postnatal stages show three frontoturbinals and three ethmoturbinals similar to longer snouted breeds, whereas the number of interturbinals is reduced. The shape of the entire turbinal skeleton simplifies with decreasing snout length, that is, within a minimized nasal cavity the turbinals decrease proportionally in surface area and surface density due to a looser arrangement. We interpret these apparent reductions as a result of spatial constraint which affects postnatal appositional bone growth and the position of the turbinals inside the nasal cavity. The turbinal skeleton of brachycephalic dogs arrests at an early ontogenetic stage, corresponding with previous studies on the dermal bones. Hence, we assume an association between the growth of intranasal structures and facial elongation.

Nasal airflow in the pygmy slow loris (Nycticebus pygmaeus) based on a combined histological, computed tomographic and computational fluid dynamics methodology

'Macrosmatic' mammals have dedicated olfactory regions within their nasal cavity and segregated airstreams for olfaction and respiratory air-conditioning. Here, we examined the 3D distribution of olfactory surface area (SA) and nasal airflow patterns in the pygmy slow loris (Nycticebus pygmaeus), a primate with primitive nasal cavities, except for enlarged eyes that converge upon the posterodorsal nasal region. Using the head of an adult loris cadaver, we co-registered micro-computed tomography (CT) slices and histology sections to create a 3D reconstruction of the olfactory mucosa distribution. Histological sections were used to measure olfactory surface area and to annotate CT reconstructions. The loris has a complex olfactory recess (∼19% of total nasal SA) with multiple olfactory turbinals. However, the first ethmoturbinal has a rostral projection that extends far anterior to the olfactory recess, lined by ∼90% non-olfactory epithelium. Only one (of three) frontoturbinals bears olfactory mucosa. Computational fluid dynamics simulations of nasal airflow and odorant deposition revealed that there is some segregation of respiratory and olfactory flow in the loris nose, but that it is not as distinct as in well-studied 'macrosmats' (e.g. the dog). In the loris, airflow is segregated medially and laterally to vertically elongated, plate-like first ethmoturbinals. Thus, lorises may be said to have certain macrosmatic anatomical characteristics (e.g. olfactory recess), but not segregated nasal airflow patterns that are optimized for olfaction, as in canids. These results imply that a binary 'microsmatic/macrosmatic' dichotomy does not exist. Rather, mammals appear to exhibit complex trends with respect to specialization of the turbinals and recesses.

A digital collection of rare and endangered lemurs and other primates from the Duke Lemur Center

Scientific study of lemurs, a group of primates found only on Madagascar, is crucial for understanding primate evolution. Unfortunately, lemurs are among the most endangered animals in the world, so there is a strong impetus to maximize as much scientific data as possible from available physical specimens. MicroCT scanning efforts at Duke University have resulted in scans of more than 100 strepsirrhine cadavers representing 18 species from the Duke Lemur Center. An error study of the microCT scanner recovered less than 0.3% error at multiple resolution levels. Scans include specimen overviews and focused, high-resolution selections of complex anatomical regions (e.g., cranium, hands, feet). Scans have been uploaded to MorphoSource, an online digital repository for 3D data. As captive (but free ranging) individuals, these specimens have a wealth of associated information that is largely unavailable for wild populations, including detailed life history data. This digital collection maximizes the information obtained from rare and endangered animals with minimal degradation of the original specimens.

Internal nasal morphology of the Eocene primate Rooneyia viejaensis and extant Euarchonta: Using μCT scan data to understand and infer patterns of nasal fossa evolution in primates

Primates have historically been viewed as having a diminished sense of smell compared to other mammals. In haplorhines, olfactory reduction has been inferred partly based on the complexity of the bony turbinals within the nasal cavity. Some turbinals are covered in olfactory epithelium, which contains olfactory receptor neurons that detect odorants. Accordingly, turbinal number and complexity has been used as a rough anatomical proxy for the relative importance of olfactory cues for an animal's behavioral ecology. Unfortunately, turbinals are delicate and rarely preserved in fossil specimens, limiting opportunities to make direct observations of the olfactory periphery in extinct primates. Here we describe the turbinal morphology of Rooneyia viejaensis, a late middle Eocene primate of uncertain phylogenetic affinities from the Tornillo Basin of West Texas. This species is currently the oldest fossil primate for which turbinals are preserved with minimal damage or distortion. Microcomputed tomography (μCT) reveals that Rooneyia possessed 1 nasoturbinal, 4 bullar ethmoturbinals, 1 frontoturbinal, 1 interturbinal, and an olfactory recess. This pattern is broadly similar to the condition seen in some extant strepsirrhine primates but differs substantially from the condition seen in extant haplorhines. Crown haplorhines possess only two ethmoturbinals and lack frontoturbinals, interturbinals, and an olfactory recess. Additionally, crown anthropoids have ethmoturbinals that are non-bullar. These observations reinforce the conclusion that Rooneyia is not a stem tarsiiform or stem anthropoid. However, estimated olfactory turbinal surface area in Rooneyia is greater than that of similar-sized haplorhines but smaller than that of similar-sized lemuriforms and lorisiforms. This finding suggests that although Rooneyia was broadly plesiomorphic in retaining a large complement of olfactory turbinals as in living strepsirrhines, Rooneyia may have evolved somewhat diminished olfactory abilities as in living haplorhines.

Ontogeny of the Postorbital Region in Tarsiers and Other Primates

Bony structure of the postorbital region is a key trait distinguishing major clades of primates. Strepsirrhines share a postorbital bar, and anthropoids share a complete postorbital septum. At issue is whether the partial postorbital septum of tarsiers unites living tarsiers more closely with anthropoids than with certain large-eyed Eocene fossils. Previously we reported incomplete postorbital closure in tarsiers at birth. In this article, we document comparative analyses of the postorbital region in a broad range of perinatal primates. Virtual reconstructions of microCT data were used to study three-dimensional structure of the perinatal cranium in these taxa. We also describe and illustrate formation of the tarsier partial postorbital septum through the perinatal period using a growth series of Tarsius syrichta. Our results support the hypothesis that partial postorbital septation in the tarsier is secondary to eye hypertrophy. Based on these observations, we propose a structural hypothesis for phylogenetic differences observed in the primate postorbital region. Specifically, we propose that key postorbital traits, including the frontal spur in strepsirrhines and the posterior lamina of the zygomatic in anthropoids, develop as a result of the spatial relationships of brain, eyes, and teeth. Haplorhines are united by expansion of the anterior cranial fossa and loss of the frontal spur. Anthropoids are further united to the exclusion of tarsiers by expansion of the temporal lobes and associated formation of the posterior lamina of the zygomatic. Mechanical forces related to these spatial relationships may be modulated by deep fascia of the orbit to induce formation of the postorbital septum. Anat Rec, 299:1631-1645, 2016. © 2016 Wiley Periodicals, Inc.