The Core Concepts, Competencies, and Grand Challenges of Comparative Vertebrate Anatomy and Morphology.

Core concepts offer coherence to the discourse of a scientific discipline and facilitate teaching by identifying large unifying themes that can be tailored to the level of the class and expertise of the instructor. This approach to teaching has been shown to encourage deeper learning that can be integrated across subdisciplines of biology and has been adopted by several other biology subdisciplines. However, Comparative Vertebrate Anatomy, although one of the oldest biological areas of study, has not had its core concepts identified. Here, we present five core concepts and seven competencies (skills) for Comparative Vertebrate Anatomy that came out of an iterative process of engagement with the broader community of vertebrate morphologists over a 3-year period. The core concepts are (A) evolution, (B) structure and function, (C) morphological development, (D) integration, and (E) human anatomy is the result of vertebrate evolution. The core competencies students should gain from the study of comparative vertebrate anatomy are (F) tree thinking, (G) observation, (H) dissection of specimens, (I) depiction of anatomy, (J) appreciation of the importance of natural history collections, (K) science communication, and (L) data integration. We offer a succinct description of each core concept and competency, examples of learning outcomes that could be used to assess teaching effectiveness, and examples of relevant resources for both instructors and students. Additionally, we pose a grand challenge to the community, arguing that the field of Comparative Vertebrate Anatomy needs to acknowledge racism, androcentrism, homophobia, genocide, slavery, and other influences in its history and address their lingering effects in order to move forward as a thriving discipline that is inclusive of all students and scientists and continues to generate unbiased knowledge for the betterment of humanity. Despite the rigorous process used to compile these core concepts and competencies, we anticipate that they will serve as a framework for an ongoing conversation that ensures Comparative Vertebrate Anatomy remains a relevant field in discovery, innovation, and training of future generations of scientists.

Implementing Fabrication as a Pedagogical Tool in Vertebrate Anatomy Courses: Motivation, Inclusion, and Lessons.

Increasing course structure by incorporating active learning and multimodal pedagogical strategies benefits all learners. Students of vertebrate anatomy can especially benefit from practicing fabrication, or "making", incorporating skills such as 3D digital modeling, 3D printing, and using familiar low-tech materials to construct informed replicas of animal anatomy. Student perceptions of active learning projects are shaped by motivation theories such as the expectancy-value theory and self-directed learning, both of which are briefly reviewed here. This paper offers inspiration and resources to instructors for establishing a makerspace in an anatomy lab and leveraging community partners to stimulate students to construct their own versions of nature's designs. Learning science in informal environments and specifically in makerspaces has been shown to promote equity and increase motivation to study science. Examples here emphasize accessibility for diverse learners, including strategies for instructors to ensure ease of student access to 3D technology. Scaffolding formative assessments builds student confidence and expertise, further closing opportunity gaps. Two specific cases are detailed where fabrication and the use of 3D digital models are used to augment student learning of vertebrate anatomy at a small liberal arts college. In a semester-long research project in an introductory biomechanics course, students investigate, write about, and build models of animal anatomy of their choice. They use simple materials, crafting supplies, household tools, and/or 3D printing to demonstrate structures of interest, enhancing understanding of the physical principles of animal form and function. Given increased availability of CT data online, students can download, analyze, and 3D print skeletal models of both common and endangered animals. Comparative anatomy students reported that they had increased motivation to study intricate skeletal anatomy simply by manipulating bones in a 3D software assignment. Students in both classes reported enjoying the use of fabrication in learning vertebrate anatomy and this may establish a pattern of lifelong learning.

Bottom Feeding and Beyond: How the Premaxillary Protrusion of Cypriniforms Allowed for a Novel Kind of Suction Feeding.

While much of the functional work on suction feeding has involved members of Acanthopterygii, an earlier cypriniform radiation led to over 3200 species filling nearly every freshwater trophic niche. Within the great majority of acanthomorph clades that have been investigated suction feeding and the underlying morphology responsible for the generation of rapid suction have been largely conserved. This conserved feeding-apparatus is often associated with increasing the force experienced by the prey item, thus making a strike on elusive prey more effective. Cypriniforms' trophic anatomy is comprised of a number of novelties used for benthic feeding, which characterized early members of this clade. The modified cypriniform structure of the oral jaws represents a situation in which a particular type of suction feeding allowed for probing the benthos with a more functionally maneuverable anatomy. Requisite evolutionary modifications included origin and elongation of a median kinethmoid, duplications of certain divisions of the muscles of the adductor mandibulae, and origin of a dorsal, intra-buccal muscular palatal organ used in winnowing detritus. The elongated kinethmoid (coupled with modified adductor muscles) allowed for a type of premaxillary protrusion that decoupled the upper and lower jaws, enabled premaxillary protrusions with a closed mouth, and facilitated benthic feeding by increasing functional flexibility. The resultant flow of fluid generated by cypriniforms is also quite flexible, with multiple instances of peak flow in a single feeding event. This greatly modified morphology allowed for a degree of kinematic maneuverability not seen within most acanthomorphs. Later cypriniform radiations into piscivorous, insectivorous, or planktivorous feeding guilds were associated with shortening of the kinethmoid and with simplified morphology of the adductor, likely involving an emphasis on ram feeding. Although this suite of morphological novelties seemingly originated within the context of benthic feeding, with minimal modifications these anatomical features were later coopted during radiations into different functional niches.

The Teleost Intramandibular Joint: A mechanism That Allows Fish to Obtain Prey Unavailable to Suction Feeders.

Although the majority of teleost fishes possess a fused lower jaw (or mandible), some lineages have acquired a secondary joint in the lower jaw, termed the intramandibular joint (IMJ). The IMJ is a new module that formed within the already exceptionally complex teleost head, and disarticulation of two bony elements of the mandible potentially creates a "double-jointed" jaw. The apparent independent acquisition of this new functional module in divergent lineages raises a suite of questions. (1) How many teleostean lineages contain IMJ-bearing species? (2) Does the IMJ serve the same purpose in all teleosts? (3) Is the IMJ associated with altered feeding kinematics? (4) Do IMJ-bearing fishes experience trade-offs in other aspects of feeding performance? (5) Is the IMJ used to procure prey that are otherwise unavailable? The IMJ is probably under-reported, but has been documented in at least 10 lineages within the Teleostei. Across diverse IMJ-bearing lineages, this secondary joint in the lower jaw serves a variety of functions, including: generating dynamic out-levers that allow fish to apply additional force to a food item during jaw closing; allowing fish to "pick" individual prey items with pincer-like jaws; and facilitating contact with the substrate by altering the size and orientation of the gape. There are no consistent changes in feeding kinematics in IMJ-bearing species relative to their sister taxa; however, some IMJ-bearing taxa produce very slow movements during the capture of food, which may compromise their ability to move prey into the mouth via suction. Despite diversity in behavior, all IMJ-bearing lineages have the ability to remove foods that are physically attached to the substrate or to bite off pieces from sessile organisms. Because such prey cannot be drawn into the mouth by suction, the IMJ provides a new mechanism that enables fish to obtain food that otherwise would be unavailable.

Flexibility in starting posture drives flexibility in kinematic behavior of the kinethmoid-mediated premaxillary protrusion mechanism in a cyprinid fish, Cyprinus carpio.

Premaxillary protrusion in cypriniform fishes involves rotation of the kinethmoid, an unpaired skeletal element in the dorsal midline of the rostrum. No muscles insert directly onto the kinethmoid, so its rotation must be caused by the movement of other bones. In turn, the kinethmoid is thought to push on the ascending processes of the premaxillae, effecting protrusion. To determine the causes and effects of kinethmoid motion, we used XROMM (x-ray reconstruction of moving morphology) to measure the kinematics of cranial bones in common carp, Cyprinus carpio. Mean kinethmoid rotation was 83 deg during premaxillary protrusion (18 events in 3 individuals). The kinethmoid rotates in a coordinated way with ventral translation of the maxillary bridge, and this ventral translation is likely driven primarily by the A1ß muscle. Analyses of flexibility (variability between behaviors) and coordination (correlation between bones within a behavior) indicate that motion of the maxillary bridge, not the lower jaw, drives premaxillary protrusion. Thus, upper jaw protrusion is decoupled from lower jaw depression, allowing for two separate modes of protrusion, open mouth and closed mouth. These behaviors serve different functions: to procure food and to sort food, respectively. Variation in starting posture of the maxilla alone dictates which type of protrusion is performed; downstream motions are invariant. For closed mouth protrusion, a ventrally displaced maxillary starting posture causes kinethmoid rotation to produce more ventrally directed premaxillary protrusion. This flexibility, bestowed by the kinethmoid-maxillary bridge-A1ß mechanism, one of several evolutionary novelties in the cypriniform feeding mechanism, may have contributed to the impressive trophic diversity that characterizes this speciose lineage.

Independently evolved upper jaw protrusion mechanisms show convergent hydrodynamic function in teleost fishes.

A protrusible upper jaw has independently evolved multiple times within teleosts and has been implicated in the success of two groups in particular: Acanthomorpha and Cypriniformes. We use digital particle image velocimetry (DPIV) to compare suction feeding flow dynamics in a representative of each of these clades: goldfish and bluegill. Using DPIV, we contrast the spatial pattern of flow, the temporal relationship between flow and head kinematics, and the contribution of jaw protrusion to the forces exerted on prey. As expected, the spatial patterns of flow were similar in the two species. However, goldfish were slower to reach maximal kinematic excursions, and were more flexible in the relative timing of jaw protrusion, other jaw movements and suction flows. Goldfish were also able to sustain flow speeds for a prolonged period of time as compared with bluegill, in part because goldfish generate lower peak flow speeds. In both species, jaw protrusion increased the force exerted on the prey. However, slower jaw protrusion in goldfish resulted in less augmentation of suction forces. This difference in force exerted on prey corresponds with differences in trophic niches and feeding behavior of the two species. The bluegill uses powerful suction to capture insect larvae whereas the goldfish uses winnowing to sort through detritus and sediment. The kinethmoid of goldfish may permit jaw protrusion that is independent of lower jaw movement, which could explain the ability of goldfish to decouple suction flows (due to buccal expansion) from upper jaw protrusion. Nevertheless, our results show that jaw protrusion allows both species to augment the force exerted on prey, suggesting that this is a fundamental benefit of jaw protrusion to suction feeders.

Comparative kinematics of cypriniform premaxillary protrusion.

Premaxillary protrusion has evolved multiple times within teleosts, and has been implicated as contributing to the evolutionary success of clades bearing this adaptation. Cypriniform fishes protrude the jaws via the kinethmoid, a median sesamoid bone that is a synapomorphy for the order. Using five cypriniform species, we provide the first comparative kinematic study of jaw protrusion in this speciose order. Our goals were to compare jaw protrusion in cypriniforms to that in other clades that independently evolved upper jaw protrusion, assess the variation in feeding kinematics among members of the order, and test if variation in the shape of the kinethmoid has an effect on either jaw kinematics or the degree of suction or ram used during a feeding event. We also examined the coordination in the relative timings of upper and lower jaw movements to gain insight on the cypriniform protrusile mechanism. Overall, speed of protrusion in cypriniforms is slower than in other teleosts. Protrusion speed differed significantly among cypriniforms but this is likely not due to kinethmoid shape alone; rather, it may be a result of both kinethmoid shape and branching patterns of the A1 division of the adductor mandibulae. In the benthic cypriniforms investigated here, upper jaw protrusion contributed up to 60% of overall ram of the strikes and interestingly, these species also produced the most suction. There is relatively little coordination of upper and lower jaw movements in cypriniforms, suggesting that previous hypotheses of premaxillary protrusion via lower jaw depression are not supported within Cypriniformes. Significant variation in kinematics suggests that cypriniforms may have the ability to modulate feeding, which could be an advantage if presented with the challenge of feeding on different types of prey.

Development of the cypriniform protrusible jaw complex in Danio rerio: constructional insights for evolution.

Studies on the evolution of complex biological systems are difficult because the construction of these traits cannot be observed during the course of evolution. Complex traits are defined as consisting of multiple elements, often of differing embryological origins, with multiple linkages integrated to form a single functional unit. An example of a complex system is the cypriniform oral jaw apparatus. Cypriniform fishes possess an upper jaw characterized by premaxillary protrusion during feeding. Cypriniforms effect protrusion via the kinethmoid, a synapomorphy for the order. The kinethmoid is a sesamoid ossification suspended by ligaments attaching to the premaxillae, maxillae, palatines, and neurocranium. Upon mouth opening, the kinethmoid rotates as the premaxillae move anteriorly. Along with bony and ligamentous elements, there are three divisions of the adductor mandibulae that render this system functional. It is unclear how cypriniform jaws evolved because although the evolution of sesamoid elements is common, the incorporation of the kinethmoid into the protrusible jaw results in a function that is atypical for sesamoids. Developmental studies can show how biological systems are assembled within individuals and offer clues about how traits might have been constructed during evolution. We investigated the development of the protrusible upper jaw in zebrafish to generate hypotheses regarding the evolution of this character. Early in development, the adductor mandibulae arises as a single unit. The muscle divides after ossification of the maxillae, on which the A1 division will ultimately insert. A cartilaginous kinethmoid first develops within the intermaxillary ligament; it later ossifies at points of ligamentous attachment. We combine our structural developmental data with published kinematic data at key developmental stages and discuss potential functional advantages in possessing even the earliest stages of a system for protrusion.

Using zebrafish to investigate cypriniform evolutionary novelties: functional development and evolutionary diversification of the kinethmoid.

Although the zebrafish has become a popular model organism for biomedical studies, we propose that the wealth of morphological novelties that characterize this cypriniform fish makes it well suited for investigating the development of evolutionary innovations. Morphological novelties associated with feeding in cypriniform fishes include: a unique structure of the pharyngeal jaws in which the lower pharyngeal jaws are enlarged and opposed to a pad on the basioccipital process; a palatal organ found on the roof of the buccal chamber that is thought to help process detrital food within the buccal chamber; and, the kinethmoid, a novel ossification that effects a unique means of premaxillary protrusion. We present new morphological and developmental data and review functional data regarding the role of the kinethmoid in premaxillary protrusion in the zebrafish. Premaxillary protrusion plays an important role in effective prey acquisition in teleosts and the evolution of a unique means of premaxillary protrusion within Cypriniformes may have led to a number of trophic radiations within this clade. Ontogenetic data from zebrafish show that substantial premaxillary protrusion is not seen until these fish have undergone metamorphosis at which point the adductor mandibulae musculature becomes divided and all ligamentous attachments become established. A comparative study of families within Cypriniformes shows diverse morphologies of the kinethmoid. The morphological diversification that characterizes the kinethmoid suggests that this feeding structure has played a role in trophic radiations within Cypriniformes, since the morphology of this feature is correlated with feeding habits.