MESOZOIC DIVERSIFICATION
- Terrestrial Invertebrates & Invasion of Soil
- Jurassic rocks have yielded a variety of insects
- flies, mosquitos, caddis flies, earwigs, hymenopterans -ants,
bees, and wasps
- Beetles are known from Cretaceous.
- Marine Invertebrates
- Experiences a lag in recovery of the marine biota after the Permian mass
extinction.
- Bivalvia (clams and oysters) become dominant benthos.
- In the Jr-K, conical rudists formed reefs .
- Scleractinian (modern) corals evolve
- Echinoids more abundant and diverse
- Cephalopods -Ammonoids & Belemnites (?squid Ancestor) most
prolific during Jr-K.
- Octopods known from late Cretaceous.
- Crustaceans abundant in Jurassic
- Reptile evolution
- Adaptive radiation with major classification of groups based on skull
anatomy:
- Anapsids - lacking temporal fenestrae; solid skull roof
- Synapsids - single temporal fenestrae low on back of skull (unique to
mammal-like reptiles and mammals)
- Diapsids - two temporal fenestrae (most reptiles: lizards, snakes,
crocodiles, pterosaurs, dinosaurs, birds)
- Eurapsids - derived character; single temporal high on skull
(marine reptiles; Perm)
- Saurians
- Lepidosaurs - snakes, lizards, Tuatara (Sphenodon)
- Archosaurs
- Thecodonts:
- Small, agile, lightly constructed bipedal with long tails & short
forelimbs.
- Ancestral stock of pterosaurs & dinosaurs.
- Quadrupedal armored terrestrial carnivores
- Quadrupedal crocodile-like aquatic forms known as Phytosaurs
(nostrils in front of eyes).
- Saurischia ("lizard-hipped")
- Primitive pelvic girdle with anterior oriented pubis
- •Elongate, S-shaped neck, asymmetrical hand with distinct
thumb
- •Bipedal carnivores and living birds
- Coelurosaurs (Tr) are bird-like in body-plan
- Theropods were carnivores that attained large sizes (>13 m; 4 tons)
- Allosaurus temporally restricted to Jurassic;
- Deinonychus and Tyrannosaurus temporally restricted to
Cretaceous.
- Sauropods were quadrupedal herbivores first found in Jurassic.
- Apatosaurus is temporally restricted to the Jurassic;
- Supersaurus & Ultrasaurus (80 tons) known only from the
Cretaceous.
- Ornithischia ("bird-hipped")
- Derived pelvic girdle with bifurcate pubis
- Additional bone at front of lower jaw
- predentary bone and cheek teeth
- Radiation of herbaceous dinosaurs into end of Cretaceous
- Bipedal and quadrupedal ornithiscians evolve as late Triassic
herbivores.
- Ornithopods are the bipedal group.
- Camptosaurus, Iguanodon in the Jurassic;
- Hadrosaurs in the Cretaceous (broad, flat, toothless skull
resembling a duck).
- Quadrupedals include
- Jurassic Stegosaurs
- Replaced in the Cretaceous by the armoured (bony plates)
Ankylosaurs and Ceratopsians (horned dinosaurs).
- Pterosaurs (Late Tr - Late K)
- First to achieve true flight
- Active fliers first known in Sharovipteryx (Tr)
- Possess mesotarsal joint like dinosaurs
- Foot hinged between 1st and 2nd row of ankle bones
- Hairy (Jr - Russia; Sordes pilosus) and probably endothermic.
- Two groups:
- Rhamphorhynchoids (long tails)
- Pterodactyloids (tail-less) such as Pteranodon (7 m
wingspan) and Quetzalcoatlus (15.5 m wingspan)
- Marine Reptiles I
- Archosaurs (Saurischians)
- The sea crocodile is the only group evolved into marine
habitat. Crocodiles are Extant.
- Sauropterygia (diapsids)
- Placodonts (Tr) - large comb-like teeth at front of jaw; bivalves
crused between flat, molar teeth in jaw
- Nothosaurs (Tr) - more advanced, ribs evolved far back along
body; strong forelimbs
- Plesiosaurs (Jr-K) - equally developed limbs, paddle-like
modifications for swimming
- Diapsid Marine Reptiles
- Ichthyosaurs (Jr-K; ?diapsid) - dophin-shaped with vertical tail flukes;
spine continued into lower tail fin; good vision based upon orbital
dimensions and placement
- Mosasaurs - (Late K) 10m monitor lizards; long heads on structurally
powerful neck and jaw hinged at midpoint
- Avian Reptiles
- Presently accepted hypothesis evolved from small Triassic bipedal
theropods
- Homologous evidence
- Reptilian anatomy (including curved claws) with feathers
first exemplified in Archaeopteryx of the Jurassic.
- Confuciusornis sanctus China (Jr) bird characteristics well
established.
- Bird skeletons, with teeth, known from the Cretaceous.
- Birds are a dead-end lineage.
- Primitive Mammals (Tr-K)
- True mammals are recognized on tooth anatomy.
- Late Triassic mammalian tooth pattern: incisors, canines, premolars,
molars.
- Lineage arose from advanced therapsids with mammalian features
including:
- Bony palate
- Single lower jaw.
- Recognized lineages based upon:
- occlusion of upper and lower teeth
- alternation of upper and lower molars & triangular teeth.