Reptiles, birds & fish cranial skeleton

Question 1

State some key features of reptiles, including the trait that makes it easier for them to live in warmer climates.

Answer 1

Poikilothermic = easier to live in warmer climates.
Dry scaled skin.
Internal fertilisation.
3 or 4 chambered heart.
Can be aquatic, semi-aquatic, terrestrial or arboreal.
Morphologically range from 1.3 inches to 33 feet.

Question 2

State the 4 extant reptile orders.

Answer 2

Squamata = lizards
Chelonia = turtles
Crocodylia = crocodilians
Rhynochocephalia = tuatara

Question 3

Describe distinguishing cranial features of reptilia.

Answer 3

Have smaller more simple cerebrum than mammals so smaller brain case.
Lower jaw is composed of multiple bones - a clear dentary bone to hold teeth as well as many other fused extra bones at the temporomandibular joint.
Dentition are simple and continuously being replaced.
They have only 1 occipital condyle for atlas articulation.
They have only one middle ear bone / ossicle, analogous to the stapes - the columella.

Question 4

Describe distinguishing cranial features of the rhynochocephalia

Answer 4

Common order amongst dinosaur and very few species surviving: family = sphenodontidae, genus = sphendon/tuatara, species = punctatus & guntheri.
Similar to sister lizard group externally but not internally: lack external ears, parietal eye more formed (absorb UV).
Rigid skulls, lower jaw pivots from end of quadrate and quadratojugal bones.

Question 5

Describe distinguishing features of the squamata

Answer 5

Lizards (lacertilian) and snakes (serpents).
(Squam = scale).
7000+ species.
Temperate > tropical climates so live everywhere but Antarctica.
Lizards: additional joint behind the eye (mesokinesis) which allows muzzle to flex up and down.

Snakes: joint lies in front of eyes (prokinesis).
Quadrate hinges in two places to mouth can open wide and swallow large prey.
Loose temporomandibular joint so freedom of movement and no occlusion.
Mandible not fused at midline.

Question 6

Describe distinguishing cranial features of the crocodilia

Answer 6

Approx 72 socketed teeth with fitted dentition so as not to damage teeth when snapping as well as being able to crush shred or tear.
Alligator = U shaped (eat turtles, upper jaw hides lower teeth).
Crocodile = V shaped (eat fish, jaws similar width with teeth exposed)
Gharial/Gavial = very thin long snout (eat fish, teeth exposed)
Caiman = Straight wide upper jaw which covers lower jaw (technically an alligator).
Skulls are robust and lined with muscles with weak antagonistic masticatory muscles.

Question 7

Define diapsids and what they are otherwise known as

Answer 7

Also known as temporal fenestrae, diapsid means “2 arches”.
300MYA, amniote tetrapods developed these two holes.
They occur in crocodiles, lizards, snakes, tuatara, birds and non-avian dinosaurs.
Lizards lost 1, snakes lost both, birds are different but still technically classed as diapsid.

Question 8

Name some key orders within the aves class

Answer 8

Anserine = ducks, geese, swans
Charadiinaceous = gulls, terns and other shore birds
Columbine = pigeons and doves
Falconine = eagles, hawks, kites, osprey, vultures, falcons
Gallinaceous = grouse, quail, partridge, pheasants, jungle fowl, pea fowl, turkeys
Passerine (82 families) = perching birds
Psittacine = lories, parrots, macaws etc
Strigine = owls

Question 9

What are the five major bones present in the aves skull?

Answer 9

5 major bones: frontal, parietal, premaxillary, nasal (top beak), mandible (bottom beak)

Question 10

Describe any distinguishing cranial features of aves/avifauna

Answer 10

1 occipital condyle.
Skull light (1% of body weight)
Beak is keratin on outside and is extremely diverse between species as it adapt very specifically to diet.
No dentition present, food is pecked, torn, and swallowed whole (also makes them lighter).
Gizzard present to “chew” after food is swallowed.
Sclerotic ring - moveable bony ring surrounding eyeball.
Salt glands present in sea birds to secrete excess ions in salty solution into nostrils.

Question 11

State distinguishing cranial features about Agnatha

Answer 11

Jaw absent, bony scales, skin plates were present in ancient species but no longer, cyclostomic (circular) mouth to suck blood e.g. hafish, lamprey.

Question 12

State distinguishing cranial features about chondrichthyes

Answer 12

cartilaginous fish, true bone, teeth calcified but rarely anything else e.g. sharks, skates, rays.

Question 13

State distinguishing cranial features about osteichthyes

Answer 13

bony fish, jaws present, gill arches to support the gills, protected by operculum.
protective scales, sharp eyesight.
e.g. coelacanth had a hinged joint in skull to allow front part of head to be lifted whilst feeding and eventually developed into early tetrapods.