Chondrichthyes possess a skeleton that differs considerably from other species in that their skeletons are made up of cartilage rather than bone. This project gives insight on the normal developmental pattern of the chondrocranium of a chondrichthyan, using the little skate, Leucoraja erinacea as a model organism. This is demonstrated by using histological techniques to visualize and describe this sequence of chondrocranium development, focusing on two stages of development. In the context of what is morphologically known from their relative taxas and other chondrichthyans, the developmental pattern that occurs in these two stages is given in detail. It’s suggested that from anterior to posterior, beginning with the earlier of the two …show more content…
Starting off as a pair of parachordal cartilage, the basal region, or basal plate will grow to surround the notochord and pair with prechordal cartilages, the trabeculae cranii, that form in front of the notochord to form the ethmoid plate. The occipital region will form at the posterior end of the chondrocranium and surround the descending notochord via a segmented occipital arch, which exhibits similarly to that of a vertebral column present in vertebrates having both a neural and hemal arch (3).
The little skate, Leucoraja erinacea, is a chondrichthyan that is a key model organism for chondrichthyan embryology studies. As an oviparous species, after internal fertilization its development is independent of its mother, encapsulated in a laid, moderately thin keratinized egg case during embryonic development. These embryos receive nourishment via a yolk sac located in the egg case and remain capsuled during development for approximately 6-9 months (Figure 2a-j). As an oviparous species, they are amenable to experimental embryological manipulation and therefore are important as a model organism.
Chrondrichthyans are an important lineage in that their studies can shed light onto evolutionary processes that can give key insights into both development of extinct early-jawed fishes and the evolution of higher
1. Many experiments were conducted during the 1950s and 1960s with chick embryos and they showed that two patches of tissue essentially controlled the development of the pattern of bones inside limbs. Describe at
It lacks a backbone, but has a nerve cord that runs down its back and a rod that runs the length of its body parallel to the nerve cord that supports the body (notochord). Humans have a notochord as an embryo, but it breaks up and becomes part of the disks that lie between our vertebrae. Also shared with Amphioxus are gill arches, the bar of cartilage associated with each arch and the cartilage that form jaws, ear bones and our voice box.
s Flat bones Irregular bone Sesamoid bones Anatomy of a Long Bone Epiphyses Metaphyses Epiphyseal growth plate Epiphyseal growth line Diaphysis Periosteum Medullary cavity Endosteum Articular cartilage Microscopic Anatomy Compact bone Osteons Spongy bone Trabeculae Bone Formation Intramembranous ossification Endochondral ossification Cells in Bone Osteogenic cells Osteoblasts Osteocytes Osteoclasts Hormonal Control of Bone Calcitonin Parathyroid hormone Osteology of the Axial Skeleton Frontal Parietal Temporal Zygomatic arch Mastoid process Occipital Foramen magnum Occipital condyles Sphenoid Sella turcica Greater wing Lesser wing Ethmoid Cribriform plate Crista galli Nasal Maxilla Alveolar process Palatine process Zygomatic Zygomatic arch Lacrimal Palatine Inferior nasal conchae
Obviously a very fierce animal, the skate, related to the ray, has special adaptations that can allow it to be protected from predators and to perform actions with ease. Seeking and consuming prey with ease, the skate has its mouth on its underside and it can eat prey that is hiding in the sand below it. Quickly swimming away from predators or to attack prey, the skate also has tiny teeth-like structures on its skin. The FLMNH Ichthyology Department reports, “The skin feels exactly like sandpaper
Our arches are the beginnings of gills in most fish, and shark species, but in humans they usually will close and form the usual structures. In most animals these same four arches can also be found, further showing their similarity to sharks. Also the arches create the same or similar structures in sharks and humans, the first arch creates the jaw, and trigeminal nerve in both humans, and sharks. The second arch creates one of the bones in the ear, but also the hyoid, a bone at the base of the skull. In sharks the second arch will create a similar bone that supports their jaws. All of these show how our heads, and many other animals heads, are all created from a similar structure.
Fish started to evolve during the Cambrian explosion. Early fish fossil records act for by a small group of fish that are jawless and that have armored scales, which are known as ostracoderms. Jawless fish lineages are mostly extinct. An extant clade, the lampreys may indefinite ancient pre-jawed fish. The first fish with jaws were found in Placoderm fossils. The range of jawed vertebrates may indicate the evolutionary advantage of a jawed mouth. It is not clear if the advantage of a hinged jaw has a stronger biting force, improved respiration, or a combination of
Significant changes in internal organs development can be revealed from larval and pupa stages in complete metamorphosis. According to  between day one to day thirteen, the chrysalis shows development of numerous aspects of morphology which include wing veins, midgut, flight
In the science of paleontology, the history of life is studied. Paleontologists study fossils to learn the past ecologies, evolution, and the origins of humans. In order to understand the processes that have led to both the origination and destruction of organisms since life began, paleontologists incorporate both scientific knowledge and studies. Fossil findings are critically important for confirming predictions of evolution theory. Of the many discoveries that are made yearly to add depth to the understanding of evolution, an example is a recent discovery of a creature they named Tiktaalik. The Tiktaalik was uncovered to be a transitional animal between shallow-water fishes and limbed animals. The creature supports the idea that it emerged from both mammals and reptiles, suggesting that the two are related. These findings support prediction of evolution, contradicting the belief that God
The following section was entitled “What Does Developement Tell Us,” and in it, Jeffery described the developmental phases of Astyanax because “evolutionary changes proceed through alterations in development.” By describing the different phases, Jeffery was able to point out the places where the development of the eyes in cavefish morphologies is different from the surface-dwelling fish. The first phase of eye development in both forms of the Astyanax is the appearance of optic vesicles, and with this appearance and other simultaneous mechanisms, the eye primordia, consisting of the lens vesicle, an optic cup with an inner retinal layer and an outer retinal pigment epithelium layer, and optic stalk, forms. I found it extremely important
Because of this body shape the skate’s eyes are positioned on the top of its head, while the mouth and gill slits are found on the bottom side. While the placement of the skate’s jaw and gills may look comical, this morphology has been expertly honed through thousands of years of evolution for the dietary needs of the ray. The rays mouth contains rounded teeth that that they use to grind food from the bottom of the ocean floor. Most fish have well discernable pectoral fins, the leopard skate’s fins resemble an elongation of the back. The pectoral fins run the full length of the skate’s body, where as a typical pectoral fin is much smaller and typically ends before the first dorsal fin. Along with comparatively large pectoral fins, skates
Through research of the embryonic development of the ascidians, scientists were able to better understand the vertebrate gene function and regulatory networks of several processes. The ascidia genes involved in the formation of the notochord, which were shown to be analogous to those of tadpoles, and were consequently mapped in order to obtain information regarding gene function in vertebrates. In addition, the developmental processes in ascidia embryogenesis were studied in great detail, leading to advances in the conception of the regulatory network's involvement in governing notochord differentiation and also the process leading to the formation of the tail (Corbo et al. 2001).