Gnathostomes

Question 1

Conodonta

Answer 1

Cambrian to Late Triassic
all fossils
known primarily from isolated elements- mainly used in biostratigraphy correlation
suggestion of paired elements that could be used for feeding- ‘conodont apparatus’

eg. Promissum pulchrum
notochord, v-shaped myomeres, eyes, conodont apparatus (believed to contain enamel, dentine)

Question 2

Conodont apparatus

Answer 2

aka Conodont assemblage
located in pharyngeal or gill arch region, posterior to oral cavity
used for feeding?
role in evolution of teeth?
But Murdock et al., 2013: patterning mechanisms for enamel and dentine found only in Euconodonta, and most basal Conodonts lack- Euconodonta evolved independently to teeth in jawed vertebrates

Question 3

Anaspida

Answer 3

Silurian to Devonian
dermal skeleton of larger scales
vertebral column, potential paired fins in Euphanoerops

Fossil evidence:
elongate scales
elongate diagonal gill arch, branchial openings
triradiate spines behind them, fins behind spines
elongate folds along body- fins?

Question 4

Euphanerops

Answer 4

Anaspid

elongate fold located under gill arch region along body = fins?. But has no supporting skeleton, and not a narrow base as in osteostraci
evidence of extensive vertebral column
first time mineralized internal skeleton seen
and potential evidence for regionalisation of vertebral column

Question 5

Thelodonti

Answer 5

Late Ordovician- Late Devonian
dermal skeleton made up of small scales, most commonly found dotted around, used for stratigraphy
elongate folds along body=fins. But has no supporting skeleton & not narrow based like that of osteostraci
more complete specimens found at MOTH locality, Canadian Arctic

Question 6

Arandaspida

Answer 6

Large dorsal and ventral plates of dermal bone, or elongate scales
restricted geographic locality- Australia and Bolivia only
early ordivician
fan-shaped arrangement of oral plates around mouth
dorsal bony plate and ventral body plates
multiple branchial openings
no elongate folds or fins

Question 7

Heterostraci

Answer 7

fan-shaped arrangement of oral plates around mouth
early Silurian - late Devonian
only 1 branchial opening, compared to several in Arandaspida
no elongate fins or folds

Question 8

Osteostraci

Answer 8

Early Silurian- Late Devonian
close to sister group to jawed vertebrates
characterised by cephalic shield on head
huge range in morphologies of the shield
extensive sensory fields around shield margin
has nasohypophyseal organ (also in cyclostomes) = sensory structure at top of head that opens into duct that goes into single nasal sac (olfactory chamber)

some have pectoral fins with internal fin radials and musculature, as in jawed vertebrates
but no pelvic fins (suggests pectoral evolved first)

pectoral fin in narrow-based with supporting girdle for fin skeleton/radials
insertion area for fin muscles
foramina for blood vessels and nerves
all comparable to shark pectoral fin