BIOL360 Lecture Notes - Lecture 12: Biomineralization, Neural Crest, Apatite
12 May 2018
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Fishes and Early Tetrapods
VERTEBRATES
• Animals w/ backbones in Phylum Chordata
• Key features -> Bony skeleton and vertebrae
• Skeleton = backbone, skull (enclosing brain & sense organs) and bones
supporting limbs/fins
• Important because huge diversity, but not greatest (ie. insects, microbes
more diverse)
• Humans, represent very successful vertebrate
• Largest animals on land, sea, and in air
Two Key Characteristics:
Only vertebrates have heads that can be called “craniates” -> other have from ends
(mollusc, echinoderms). The head contains a brain, mouth and major sensory organs
Vertebrates also have a neural crest which appears in early embryo just below the
ectoderm where the backbone will develop. The neural crest later develops into
head, muscles, nerves and all other parts
** First vertebrates had no jaws; first fishes traced back to Cambrian
The skeleton
• Skeleton = bone (apatite) and cartilage
• Bone -> collagen fibers on which crystals of apatite and calcium phosphate
form; this makes bones flexible
• Cartilage -> flexible and unmineralized; collagen and elastic tissues
• First vertebrates -> fish with cartilaginous skeleton; but only on outside
• Mineralized versus unmineralized skeleton
• Rarely get soft tissue preserved
Two types of skeleton
Inner skeleton was a major innovation -> it can grow with the animal and get very
large. It is remodelled all the time
Fishes and Early Tetrapods
External skeleton shed and required a lot of energy -> cannot grow and so fast, it
is less able to support large mass and is vulnerable to damage. It can be repaired
by extending fleshy parts outside the shell (molluscs) or molting shell (arthropods)
Ostradocerms: Jawless Fishes
• First vertebrates had no jaws; slurped did not bite
• Most common during Devonian; armoured jawless fishes died out by end of
Devonian
• Armoured but no internal skeleton (only external thin bony skeleton)
• They have a lateral line (Series of sensory organs) that detect movement
• Had a single back fin that was not powerful -> They likely propelled
themselves through a series of rapid side to side movements
• Semi-circular head shield with openings for eyes and nostrils
• Mouth on underside which acted as sieve for organic matter
• Modern jawless fishes are lampreys and hagfishes; have tooth-bearing bones
for gripping onto prey
Conodonts
• Phosphatic tooth-like microfossils
• Abundant, well-preserved, and taxonomically recognizable
• Extinct chordate that resembled hagfish; conodonts show wear =one
set/lifetime
• Earliest Precambrian age; around 70% of conodonts wiped out in Devonian
Extinction event; good ones in Burgess Shale
• Valuable biostratigraphic indicator; good index fossils; marine and marine near-
shore environments
Placoderms: Jaw-bearing Fish
• Appeared during Ordovician into Devonian
• Jaws started from strengthening of cartilage between gill slits
Document Summary
Vertebrates: animals w/ backbones in phylum chordata, key features -> bony skeleton and vertebrae, skeleton = backbone, skull (enclosing brain & sense organs) and bones supporting limbs/fins. Important because huge diversity, but not greatest (ie. insects, microbes more diverse: humans, represent very successful vertebrate. Largest animals on land, sea, and in air. Only vertebrates have heads that can be called craniates -> other have from ends (mollusc, echinoderms). The head contains a brain, mouth and major sensory organs. Vertebrates also have a neural crest which appears in early embryo just below the ectoderm where the backbone will develop. The neural crest later develops into head, muscles, nerves and all other parts. ** first vertebrates had no jaws; first fishes traced back to cambrian. Inner skeleton was a major innovation -> it can grow with the animal and get very large.
