63: Phylogeny and development of the postcranial skeleton Flashcards
What is the structure of the notochord?
The notochord is an elastic, unsegmented longitudinal axis of mesodermal origin.
What is the function of the notochord in development?
The notochord initially provides structural support and is later replaced by vertebral bones.
What are cyclostomes?
Cyclostomes are primitive vertebrates that lack a distinct vertebral column but have cartilaginous structures near the notochord.
How does the vertebral column develop across evolution?
In advanced stages, the notochord is largely replaced by a structured vertebral column, with vertebrae design following a common plan but showing variations among vertebrate classes and different regions of the column.
Describe the skull-vertebrae connection in fish.
The skull-vertebrae connection in fish is immotile due to a lack of advantage in motility under water and constraints from the gill apparatus.
What are the regions of the fish vertebral column?
The regions are dorsal (regio dorsalis) and tail (regio caudalis).
What is the significance of the caudal vertebrae in fish?
Caudal vertebrae feature transverse processes and often connect to ribs, critical for locomotion, characterized by hemal arches.
How are ribs in fish different from those in modern sharks?
Ribs evolved first in fishes but are reduced in modern sharks to decrease skeletal weight.
What adaptations are seen in the cervical region of reptiles and other amniotes?
The cervical region is expanded to allow enhanced mobility of the head, including lateral rotation (“no” movement) facilitated by the atlas and axis vertebrae.
What are the thoracic adaptations in reptiles and other amniotes?
The thoracic region develops to support lung ventilation via intercostal muscles.
How is the vertebral column divided in reptiles and other amniotes?
The vertebral column is divided into cervical, thoracic, lumbar, sacral, and caudal regions.
Describe the rib development in reptiles and other amniotes.
Ribs are well-developed in the thoracic region to aid in respiration.
What is the function of sacral vertebrae in mammals?
Sacral vertebrae typically fuse to form the sacrum, facilitating connection with the pelvis.
How are the thoracic and lumbar regions distinct in mammals?
These regions are distinct due to the diaphragm, with ribs present only in the thoracic region.
What adaptations are present in aquatic mammals?
Aquatic mammals show a loss of the sacral region due to an aquatic lifestyle, as seen in species like whales and sirenians.
Describe the sternum structure in mammals.
The sternum consists of the manubrium, body, and xiphoid process, elongated to support mammalian respiratory mechanics.
What components make up the appendicular skeleton?
The appendicular skeleton includes the pectoral (shoulder) and pelvic girdles, and the extremities (fins in fishes and limbs in tetrapods).
What is the function of paired fins?
Paired fins (pectoral and pelvic) serve as stabilizers during swimming.
How do unpaired fins differ from paired fins in their development?
Unpaired fins (dorsal and anal) are older evolutionarily and developed close to the notochord, which influences their formation.
What is a significant developmental innovation in jawed vertebrates?
The development of paired fins is a significant innovation in jawed vertebrates (gnathostomes), with complex formation due to their distance from the notochord, limiting direct notochordal signaling influence.
What is the structure of the notochord?
The notochord is an elastic, unsegmented longitudinal axis of mesodermal origin.
What is the function of the notochord in development?
It provides initial structural support, later replaced by vertebral bones.
