Paleo 419 Lab 5

Clade Diapsida groups

• Carboniferous to Recent

• Archosauromorpha and lepidosauromorpha

Archosauromorpha stance

erect stance reflected in a triradiate pelvis and decreased lateral flexure of the vertebral column

Clade Archosauromorpha characteristics

• single rooted teeth

• premaxilla extends behind naris

• antorbital fenestrae (in most)

• postfrontal bone is reduced or lost

• tabulars absent

• neomorphic laterosphenoid bone forming the anterolateral surface of the braincase

• quadratojugal behind lower temporal fenestra

• lateral mandibular fenestra in the lower jaw

Groups in Archosauromorpha

Archosauriformes, Prolacertiformes, Rhynchosauria, Trilophosauria, and possibly the Choristodera

Choristodera (Archosauromorpha) characteristics

acoelous vertebrae with a characteristic hour-glass shaped neural canal floor on top of the centrum

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Champsosaurus (Choristodera, Archosauromorpha)

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Champsosaurus (Choristodera, Archosauromorpha) vertebrae

Clade Archosauriformes groups and characteristics

ossified laterosphenoid and serrated teeth

• Archosauria proper, Phytosauria and several basal taxa like Vancleavea and Euparkeria

Euparkeria characteristics (Archosauriformes)

• erect stance

• antorbital fenestra

• jugal-quadratojugal contact

• lateral mandibular fenestra

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Euparkeria (Archosauriformes)

Order Phytosauria (Archosauriformes)

• superficially resemble crocodilians

• primitive ankle joint

• external nares located near the orbits rather than at the tip of the snout

• dorsoventrally taller skulls

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Rutiodon (Order Phytosauria, Archosauriformes)

Clade Crocodylomorpha Groups

• Protosuchia (“first” crocodiles)

• Mesosuchia (“middle” crocodiles)

• Eusuchia (“true” crocodiles, including extant crocodiles)

• Thalattosuchia (“sea” crocodiles)

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Clade Crocodylomorpha

Red arrow?

subnarial gap

Blue arrow?

nasal and anteorbital fossa

Mesoeucrocodylia groups

mesosuchian, thalattosuchian, and eusuchian members

Clade Crocodylomorpha Synapomorphies

• subnarial gap between premaxilla-maxilla

• nasal forming part of the dorsal border of the antorbital fossa

• loss of both the clavicles in the pectoral girdle and the postfrontal bone on the skullroof

Suborder Notosuchia (Crocodylomorpha)

• fully terrestrial crocodilians

• erect limb posture

• heterodonty

• smooth, unsculptured surface of skull

• short preorbital region

• naris anteriorly oriented

• fewer than ten maxillary teeth

• large denticles on teeth

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Notosuchus, Suborder Notosuchia (Crocodylomorpha)

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Araripesuchus, Suborder Notosuchia (Crocodylomorpha)

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Simosuchus, Suborder Notosuchia (Crocodylomorpha)

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Simosuchus, Suborder Notosuchia (Crocodylomorpha)

Neosuchia (Crocodylomorpha) Synapomorphies

• overhanging bony rims surrounding the fenestrae, except for the anteromedial corner of supratemporal fenestra

• anterolateral projections from postorbital bar

• enlarged fourth and fifth maxillary teeth are largest maxillary teeth

• pubis excluded from acetabulum

• sigmoidal (s-shaped) humerus

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Leidyosuchus (Neosuchia, Crocodylomorpha)

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Crocodilaemus (Neosuchia, Crocodylomorpha)

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Alligatoroidea (Neosuchia, Crocodylomorpha)

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Alligatoroidea (Neosuchia, Crocodylomorpha)

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Crocodyloidea (Neosuchia, Crocodylomorpha)

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Gavialoidea (Neosuchia, Crocodylomorpha)

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Crocodyloidea Scutes (Neosuchia, Crocodylomorpha)

Main difference Gavialoidea, Alligatoroidea and Crocodyloidea

Gharials are characterized by a narrow, elongate snout that is well adapted for trapping and holding on to fish, alligatoroids have blunt, U-shaped snouts, and crocodyloids have tapering, triangular snouts

Groups in Neosuchia (Crocodylomorpha)

• Crocodilaemus

• Pholidosaurs

• Paralligator

• Alligatoroidea, Gavialoidea, and Crocodyloidea

Groups in Crocodilia (Neosuchia)

Alligatoroidea, Gavialoidea, and Crocodyloidea

2 types of Crurotarsan (Crocodilian) ankle

ball and socket joints between the astragalus and calcaneum

• “crocodile normal” - the astragalus bears a peg that fits into the socket of the calcaneum

• “crocodile reversed” - the calcaneum bears a peg that fits into the socket of the astragalus

Avemetatarsalians/Ornithodirans Joint

distinct hinge-like joints between the paired astragalus-calcaneum and more distal elements of the foot

Which joint do Avemetatarsalians/Ornithodirans have?

Hinge joint on the right

Which joint do Crurotarsan/Crocodylomorpha have?

Ball and socket on the left