CrocodiliansPart I

VERTEBRATE ZOOLOGY (VZ Lecture20 – Spring 2012 Althoff - reference PJH Chapter 16)

Rajasaurus narmadensis -extinct

?

• The Age of Reptiles = Mesozoic era

• ~ 251 MYA to 65 MYA

• Much radiation and diversification, resulting in diapsids occupying most of the “liveable” zones know today

• A large segment of that vertebrate fauna was represented by the large-bodied herbivorous and carnivorous tetrapod group known as the dinosaurs…of course, we have no extant representatives of that group

• The amount of diversity during that Mesozoic era is illustrated in the phylogenetic relationships diagram in Fig. 16-1, p389 in PJH

Early Days for Diapsida

• _____________ came and went, for the most part (“thecodont” refers to teeth set in sockets in general and to a set of now extinct reptiles)

• _____________ emerged….and stayed on

• Pterosauria, ornithischia, and saurischia came and went….with the saurischia currently suspected of being the most recent ancestral group to _________________

• ________________ (marine reptiles) came and went…they had recent “divergence” from line that represents modern day lepidosaurs (i.e., tuatara, lizards, and snakes)

• ________________ emerged…and stayed on

Summary of Fig. 16-1 for Mezosoic Era

Fig. 16-1, p389 PJH

DIAPSIDA

phylogeneticrelationships

Fig. 16-2, p391 PJHDIAPSIDA

ARCHOSAURS LEPIDOSAURSArchosauromorphs Lepidosauromorphs

Ruling reptile forms Scaled reptile forms

• From the “dinosaur” –Age of Reptile group—only the _____________ and ___________ remain (1)

• Thus, extant crocodiles and birds are modern day ________________ (2)

• Birds appear to have emerged earlier (3) than squamates yet we often consider them more advanced.

• Clearly, within the living archosaurs, birds are more advanced…but several groups diverged and vanished after the two lineages representing birds and crocodiles split (4)

Summary of Fig. 16-2 Cladogram

Fig. 16-2, p391 PJHDIAPSIDA

ARCHOSAURS LEPIDOSAURS

CROCODILES

BIRDS

Archosauromorphs Lepidosauromorphs

Ruling reptile forms Scaled reptile forms

• Generally, diapsid is a reference to the skull

• Translation: 2 arches

• Refers, again, to the presence of an upper and a lower fenestra in the temporal region of the skull (see next slide)

• Early forms had both these arches, but over time (i.e., radiation of species) many “diapsids” have lost the lower arch and the upper arch, in some forms, has been reduced or lost….with lizards and snakes providing examples of the most extreme reductions or losses in these arches (see Lecture 18 notes, also Fig. 13-6, pg 343 PJH)

Diapsids

• _____ temporal arch formed by postorbital bone (pb) and squamosal (sq)

• _____ temporal arch formed by jugal (j) and quadratojugal bone (qj)

• Also, derived diapsids have a fenestra anterior to the eye (orbit) – AF—known as _______________

sq

pb

Fig. 16-3, p392 PJH

qj

j

Now extinct Ornithosuchus

Rajasaurus narmadensis -extinct

• Earliest known diapsid is Petrolacosaurus…from Kansas….>_______ (during Paleozoic era)

a) 60-70 cm in total lengthb) long neck, large eyes, long

limbs c) probably fed on large insects

• “Split” thereafter resulted into 2 groups:Archosauromorpha (“ruling reptile form”)

(includes Archosaurs)

Lepidosauromorpha (“scaled reptile form”)(includes Lepidosaurs)

(see cladogram again)

Diapsids

Archosaurs

• Includes dinosaurs and perosaurs which were very distinctive:a) presence of antorbital fenestra (opening

in skull in front of eye)b) orbit of the eye shaped like inverted ________

rather than being circular

• Teeth are laterally compressed

• Trend towards ______________

• Femur shaft _________________

head

fourth trochanter

• Femur bone “mod”site of attachment for powerfulcaudiofermoral muscle that originated on the base of the tail and inserted on trochanter.

• When contracted, itretracted the thigh

Archosaurs gave rise to 2 aquatic fish eaters…

• ______________—radiated before crocodilians but extinct a) nostrils just anterior to eyes b) no secondary palate

• ______________a) nostrils are at the tip of the snoutb) secondary palate separates nasal

passages from the mouthc) first appeared in Triassic…and seemed

to have replaced the phytosaurs by theend of the Triassic

Crocodilians: adaptation to semi-aqautic existence

• Flap of tissue arising from _____ of tongue can form a watertight seal between the mouth and throatenables crocodilian to breathe while only its nostrils are exposed without inhaling H20

• Advantage: aids _______________…and

probably impacts thermoregulation

Extant Crocodilians: 3 families(see Fig. 16-4, p393 PJH for general forms)

• ____________: alligators (2 species) & caimansfreshwater forms (mostly New World only)

• ____________: mostly associated with saltwaterconditions but some species live in freshwater streams a) saltwater crocodile probably largest

of all (up to 7 meters)b) but some < 1 m as adults

• ____________: only 1 species….the gharial…confined to Burma/India region. Theyhave the narrowest snouts

Isisfordia

Fully formed

__________________

CROCODILIAN FORMS

Modern forms