The Vertebrates- Semester 2 First Year PDF

Preview

Summary

Life on Earth...

Description

The Vertebrates Phylum: Chordata TUNICATES Three major groups: - Sea squirts - Thaliaceans - Larvaceans ~2,800 species Pharynx enlarged into a basket that filters prey TUNICATES: LARVACEANS Particular species create Larvacean mucus nets. When nets get full they discard them and they become known as a sinker. Most larvaceans are less than 5mm long, but some spp are larger and build delicate mucus nets to snare organic particles built into these mucus ‘houses’. The house of Bathochordaeus species can be as large as 1 metre (3 feet) wide even though the animal itself is only about 3-5 centimetres (1-2 inches) long. When the old ‘house’ gets clogged with excess debris, the animal exits and builds a new one. This happens approx every 24 hrs. The old house deflate and sink to the bottom of the ocean where, in some locations, they are a significant source of nutrients for deep sea life. TUNICATES: THALIACEANS Thaliaceans - Salps and pyrosomes - Live singly or in chain-like colonies - Tropical and subtropical oceans down to 1,500 m LANCELETS (e.g. Branchiostoma sp.) Fish-like but not fish. Not vertebrates but are probably a precursor. No respiratory system – small enough for cutaneous gas exchange Gill slits used solely for filter feeding. Pharyngeal basket filters prey ~35 spp. Mainly sedentary, but can swim. 26 pairs of ductless gonads. Gonads rupture during reproduction to release gametes into body cavity and then into open water = external fertilisation VERTEBRATES Key characteristic  Notochord is replaced by a jointed, dorsal vertebral column Four more key features Anterior skull enclosing large brain Rigid internal skeleton Internal organs suspended in a coelom Well-developed circulatory system, driven by contractions of a ventral heart These characteristics allow evolution of large, highly active organisms.

Jawless Fish

   

Hagfish and Lamprey Evolutionary relationships are unclear Jawless Cylindrical, eel-like bodies

 No paired fins

Evolution of Jaws

CHONDRICHTHYES (sharks and rays) Emergence of paired fins  Pectoral and pelvic fins stabilize the fish’s position in the water Sharks move via side-to-side undulations of body and caudal fin

RAY-FINNED FISH  The majority of extant bony fish species belong to this group (class: Actinopterygii)  Evolution of swim bladders: allow near-effortless depth control  ~32,000 known species alive  Huge diversity  Exploit almost all known aquatic food sources  Complicated behaviours in some species: maintain schools, build nests, court mates, care for young Lobe-finned fish  Coelacanths and lungfish (and tetrapods)  Features:  Muscular paired fleshy fins  Teeth coated with enamel.  Lungfish – have lung-like structures instead of swim bladders which allow air-breathing TETRAPODS (four legs)  An early evolutionary split in tetrapod evolution:  Amphibians  Amniotes  Most modern amphibians are confined to moist environments due to permeable skin rapidly losing water.  ~7000 known amphibian species divided into three main groups DEVELOPMENT OF TETRAPOD LIMB

Evolution of the tetrapod limb skeleton. (a) Human arm shown as an archetypical tetrapod limb composed of three skeletal segments: the stylopod (red), zeugopod (yellow), and the autopod (blue). Fossil sarcopterygians as (b)Acanthostega, (c)Tiktaalik, and (d)Eusthenopteron, in addition to the extant sarcopterygian (e) coelacanth, show progressive elaboration of the distal endochondral skeleton and the appearance of digits in the tetrapod

lineage. (f) The zebrafish pectoral fin is shown to illustrate the actinopterygian fin. H, humerus; U, ulna; R, radius; u, ulnare; i, intermedium. AMPHIBIAN GROUPS Axolotl exhibits neoteny – the retention of juvenile features AMNIOTES  Able to successfully colonise dry environments due to development of the amnion – a membranous sac enclosing the developing embryo.  Amniote egg is relatively impermeable to water and stores yolk. This allows the embryo to attain a relatively advanced state before it hatches.

REPTILE KEY FEATURES  Covered in scales – makes cutaneous gas exchange impossible.  Breathe solely via lungs.  Most lay eggs. Some, like the boa constrictor, give birth to live young.  Almost all reptiles are ectothermic. One of the exceptions is the leatherback sea turtle, which can regulate its body temperature to some degree. AVIAN KEY FEATURES  Feathers – evolved prior to emergence of birds, original function as yet unclear (Insulation? Colouration?)  Pneumatic bones  Endothermic  Specialised sternum for wing muscles  Evolved from a branch of dinosaurs - saurischians...