These two first chapters show an engaging continuity. Chapter three is about the cranium, cephalic muscles and homology in cyclostomes, with remarks on the development of the chondrocranium and the evolution of jaws. As cyclostomes constitute the sister clade of extant jawed vertebrates, comparison of their shared traits could help to unveil those present in their last common ancestor LCA. Chapter four is a detailed account of the evolution of Chondrichthyes, including a fascinating report on the development of their sense organs.
Chapter five is devoted to the actinopterygians and the sixth to sarcopterygians; both chapters include an overview of the groups composing these two big clades, with descriptions of the cranial skeletal and myological structures. Chapter seven is about the diversity of the head, jaws and cephalic muscles in amphibians, addressing topics such as heterochrony and evo-devo issues.
Reading of this chapter brings immediately to mind the truly amazing events that conform salamanders and frogs development in bones and muscles, along with the diversity in, for example, cranial morphology between the amphibian taxa. The chapter includes analyses about the homology and evolution of several anatomical structures such as the branchiohyoideus, depressores branchiales and cucullaris muscles, very useful to people seeking for the correct use of myologycal terms.
Subheadings devoted to Evo-Devo and Heterochrony are also a general synthesis of the points previously addressed. Chapter eight is about the evolution, diversity and development of the craniocervical system in turtles.
This section shows with accuracy the elusive issues related to the phylogeny and evolution of turtles by addressing their cranial and jaw musculature. They relate the neck with feeding and mobility, underlining its unique ability to retract it and the head inside the shell, and including an interesting report on the functional anatomy of jaw muscles and feeding.
Lancelets are suspension feeders that feed on phytoplankton and other microorganisms. Most tunicates live on the ocean floor and are suspension feeders. Which of the two invertebrate chordate clades is more closely related to the vertebrates continues to be debated. Vertebrata is named for the vertebral column, which is a feature of almost all members of this clade. The name Craniata organisms with a cranium is considered to be synonymous with Vertebrata. Figure Which of the following statements about common features of chordates is true?
Which of the following is not contained in phylum Chordata? Hagfish, lampreys, sharks, and tuna are all chordates that can also be classified into which group? The characteristic features of the phylum Chordata are a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. What is the structural advantage of the notochord in the human embryo?
Be sure to compare the notochord with the corresponding structure in adults. In the adults, the notochord has been replaced by the bony, rigid vertebral column. This loss of flexibility restricts the movement of adult humans, and would make it unlikely that the embryo would fit within the small space it is allotted inside the uterus. Skip to content Vertebrates.
Learning Objectives By the end of this section, you will be able to do the following: Describe the distinguishing characteristics of chordates Identify the derived characters of craniates that sets them apart from other chordates Describe the developmental fate of the notochord in vertebrates.
Deuterostome phylogeny. All chordates are deuterostomes possessing a notochord at some stage of their life cycle. Visual Connection. Chordate features. In chordates, four common features appear at some point during development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.
The endostyle is embedded in the floor of the pharynx. Link to Learning. Chordates and the Evolution of Vertebrates Two clades of chordates are invertebrates: Cephalochordata and Urochordata. Cephalochordate anatomy. In the lancelet and other cephalochordates, the notochord extends into the head region.
Adult lancelets retain all five key characteristics of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, an endostyle, and a post-anal tail. Urochordata The 1, species of Urochordata are also known as tunicates Figure. Urochordate anatomy. These colonial tunicates feed on phytoplankton.
Salps are sequential hermaphrodites, with younger female colonies fertilized by older male colonies. Subphylum Vertebrata Craniata A cranium is a bony, cartilaginous, or fibrous structure surrounding the brain, jaw, and facial bones Figure.
Anterior gill bars evolved into the jaw, which supports structures in vertebrates. The origin of gill slits in pre-vertebrate chordates and the major changes leading to gill bars becoming jaw elements in early vertebrates are described by Dr. DeLaurier describes detailed studies of the cellular and molecular signalling events surrounding the patterning of jaw and jaw support structures, with a particular focus on studies in lamprey and zebrafish.
She also highlights the contribution of neural crest cells and reviews key genetic pathways in development that may have driven jaw evolution including Hox genes, Endothelin signalling, and genes involved in the formation of a jaw joint. So the question was, how did they evolve, and what is their relationship to modern jawed animals? A paper published today in Science by Zhu Min and colleagues at the Institute of Vertebrate Palaeontology and Palaeoanthropology in Beijing, shows how placoderm jaws evolved and then rapidly changed.
It has an unusual set of jaws that is similar to both those of traditional placoderms and those of modern bony fishes, or osteichthyans. This is significant because we are all ultimately descended from osteichthyans, as this group includes the lobe-finned fishes Sarcopterygii , from which all four-limbed land animals arose. With this finding, we can now trace our dermal jaw bones dentary, maxilla and premaxilla to the most primitive jawed vertebrates.
The gnathal plates of conventional placoderms, such as the gigantic Dunkleosteus , are the homologues of the marginal jaw bones of bony fishes and tetrapods.
But the latest fossil is just the latest in a series of intriguing discoveries made over the past decade at Qujing. These include the oldest known complete bony fish, Guiyu , as well as the oldest known complete placoderms.
One of these, Entelognathus is arguably one of the most significant transitional fossils found in the past century, bridging a huge morphological gap between the extinct placoderms and the living bony fishes. Such discoveries have profound philosophical implications, as they finally link our tetrapod line directly back to placoderms, which were the first vertebrates to evolve the complex suite of anatomical features that are found in all living higher animals today.
0コメント