Chp 34 Origin and Evolution of Vertebrates Flashcards
What are vertebrates?
Animals that have a backbone (vertebrae)
When did vertebrates colonize land?
365 MYA around the Cambrian period
What animals did vertebrates give rise to?
- amphibians
- reptiles (including birds)
- mammals
How many vertebrate species are there?
More than 57,000 species
What group comprise of all vertebrates and two invertebrates?
Chordates
What are chordates (phylum Chordata)?
Bilaterian animals that belong to the clade of animals known as Deuterostomia
What two groups of invertebrates are apart of Chordates?
- Urochordates
- Cephalochordates
What are the 4 key characteristics of chordates?
- Have a notochord
- dorsal, hollow nerve cord
- Pharyngeal slits or clefts
- Muscular, post-anal tail
What is special about chordates characteristics
- Only some species show these characteristics during embryonic development
What is the notochord?
Longitudinal, flexible rod between the digestive tube and nerve cord
What does the notochord provide?
Provides skeletal support throughout the length of a chordate
What is the dorsal, hollow nerve cord?
Developed from a plate of ectoderm that rolls into a tube dorsal to the notochord
What does the nerve cord develop into?
Developes into the central nervoue system: brain and spinal cord
What are pharyngeal slits/clefts?
Grooves in the pharynx that develops into slits that open to the outside of the body
What are the functions of the pharyngeal slits?
- Suspension-feeding structures in many invertebrate chordates
- Gas exchange in vertebrates (except vertebrates with limbs, the tetrapods)
- Develop into parts of the ear, head, and neck in tetrapods
What is the muscular, post-anal tail?
A tail posterior to the anus in chordates.
What are lancelets?
Invertebrates that are marine suspension feeders that retain characteristics of the chordate body plan as adults
What phylum are lancelets in?
Cephalochordata; named for their bladelike shape
What are tunicates?
Invertebrates that most resemble chordates during their larval stage (only last a few minutes)
What phylum are tunicates apart of?
Urochordata
Are tunicates more closely related to other chordates compared to lancelets?
Yes
What is special about turnicates?
Highly derived, and has fewer Hox genes than other vertebrates
What is significant about the Hox gene in early chordate evolution?
- Same Hox genes that organize the vertebrate brain are expressed in the lancelet’s simple nerve cord tip
What does the sequencing of tunicate genome indicates?
- Genes associated with the heart and thyroid are common to all chordates
- Genes associated with transmission of nerve impulses are unique to vertebrates
How are vertebrates and chordates related?
- Vertebrates are chordates that are related
What does the skeletal system and complex nervous system allow for vertebrates to do?
- Capture food
- Evade predators
How many Hox genes does vertebrates have compared to lancelets and tunicates?
Vertebrates: Have 2 or more sets of Hox genes
Lancelets & Tunicates: Have one cluster of Hox genes
What are the following derived characteristics of Vertebrates?
- Vertebrae enclosing a spinal cord
- An elaborate skull
- Fin rays, in the aquatic forms
What are the only two lineages of jawless vertebrates that are here today?
- Hagfishes
- Lampreys
Members of these groups also lacked a backbone
What does fossil evidence of the earliest vertebrates show?
- Lacked a jaw
What is the clade of living jawless vertebrates (hagfishes and lampreys)?
Cyclostomes
What is the clade of vertebrates with jaws?
Gnathostomes
What are hagfishes? (3)
Jawless vertebrates that have a cartilaginous skull, reduced vertebrae, and a flexible rod of cartilage derived from the notochord
What are some characteristics of hagfishes? (6)
- small brain
- small eyes
- small ears
- tooth like formations
- Are marine
- Bottom dwelling scavengers
What are lampreys (Petromyzontida)?
Parasites that feed by clamping their mouth onto a live fish
What are some characteristics of lampreys?
- Inhabit various maine and freshwater habitats
- Have cartilaginous segments that surrounds the notochord and arching partly over the nerve cord
What are the most primitive fossil from Cambrian explosion that shows transition to craniates?
Haikouella fossil that has well-formed brain, eyes, and muscular segments, but no skull or ear organs
What are conodonts?
- Earliest vertebrates in the fossil record, dating from 500 to 200 million years ago
What did conodonts have?
- Had mineralized skeletal elements in their mouth and pharynx
Where did mineralization of bone and teeth appear?
Appear with the vertebrate mouthparts
What did gnathostomes consists of? (6)
- sharks and relatives
- ray finned fishes
- lobe finned fishes
- amphibians
- reptiles (including birds)
- mammals
What are gnathostomes named for?
Named for their jaws, hinged structures that, especially with help of teeth, are used to grip food items firmly and slice them
What are placoderms?
- Earliest gnathostomes in the fossil record that are an extinct lineage of armored vertebrates
appeared 440 MYA
What are acanthodians?
Group of jawed vertebrates that radiated during the Silurian and Devonian periods
What 3 lineages of jawed vertebrates can we find today?
- chondrichthyans
- ray finned fishes
- lobe fins
What is the chondrichthyans (chondrichthyes) skeleton composed of?
Skeleton is composed of primarily cartilage
What is the largest and most diverse group of chondrichthyans?
- Sharks
- Rays
- Skates
What are the 3 different ways shark eggs can develop?
- Oviparous
- Ovoviviparous
- Viviparous
What is oviparous?
Eggs hatch outside the mother’s body
What is ovoviviparous?
- Embryo develops within the uterus and is nourished by the egg yolk
What is viviparous?
Embryo develops within the uterus and is nourished thru a yolk sac placenta from mother’s blood
What is cloaca?
Location of where reproductive tract, excretory system, and digestive tract empties into
What percentage of sharks are threatened by overfishing?
95%
What are some characteristics of sharks? (5)
- Have a streamlined body/swift swimmers
- Has short digestive tracts with a ridge called spiral valve
- Have acute senses
- Has the ability to detect electrical fields from nearby animals
- Most are carnivores but can be filter feeders
What do osteichthyans include?
Includes bony fishes and tetrapods
What are fishes?
Aquatic osteichthyans that are vertebrates
What do nearly all living osteichthyans have?
All have a bony endoskeleton
What is the operculum?
A layer that protects gills when water goes over them
What are actinopterygii?
Ray-finned fishes that include nearly all familiar aquatic osteichthyans
What are the characteristics of lobe fins (Sarcopterygii)?
- Have a muscular pelvic and pectoral fins that they use to swim and “walk” underwater across the substrate
What are the 3 lineages of lobe-finned fishes that survived?
- Coelacanths
- Lungfishes
- Tetrapods
What are tetrapods?
- A group that adapted to life on land
What is one of the most significant events in vertebrate history?
- When fins of some lobe fins evolved into limbs and feet of tetrapods
How are tetrapods and gnathostomes related?
Tetrapods are gnathostomes that have limbs
What are the 5 adaptations of tetrapods?
- Four limbs, and feet with digits
- A neck, which allows separate movement of the head
- Fusion of the pelvic girdle to the backbone
- The absence of gills (except some aquatic species)
- Ears for detecting airborne sounds
What did the Tikktaalik have?
- Fins, gills, lungs, and scales
- Ribs to breathe air and support its body
- A neck and shoulders
- Fins with the bone pattern of a tetrapod limb
What is a Tiktaalik?
An animal named a fishapod because it had both fish and tetrapod characteristics
What are the three clades in Amphibians (class Amphibia)?
- Urodela (salamanders)
- Anura (frogs)
- Apoda (caecilians)
How many species make up Amphibians?
6,150 species
What are salamanders (urodeles)?
Amphibians with tails
*some are aquatic but most live on land
What is paedomorphosis?
Retention of juvenile features in sexually mature organisms, is common in aquatic species
What are frogs?
Amphibians that lack tails and have powerful hind legs for locomotion on land
What are toads?
Frogs with leathery skin
What are caecilians?
Amphibians that are legless, nearly blind, and resemble earthworms
What is the secondary adaptation of caecilians?
- absence of legs
