Focus on sauropods, specifically the macronaria, dominant during the Cretaceous.
Discussion includes aspects from the Jurassic period.
Macronaria
Branch of Neosauropoda:
Other branch: Diplodocidae, e.g., Diplodocus and Amargasaurus.
Features:
Notable for big nares (openings on skull, not actual nostrils).
Nares located on top of the skull, resulting in their name.
Early example: Camarasaurus.
Camarasaurus is considered a bit "boring": stubby face, equal limb proportions, thick neck, blocky head.
Evolutionary Adaptations
Nares:
Found above the eyes in all sauropods.
Evidence suggests nostrils located at the snout's end with cartilaginous tubes running down the skull.
Unclear why nares moved to the top of the head.
Hypotheses include: respiratory system repositioning to accommodate digestive system.
Significant Groups and Characteristics
Brachiosaurus:
Large inflated opening on skull, possibly related to large nares.
Notable for high shoulders, longer front legs than back, long necks held vertically.
Different from Camarasaurus in having smaller, denser air spaces in bones.
Saur Poseidon:
High-shouldered like Brachiosaurus, very large.
Known from multiple US states (Texas, Oklahoma, Utah).
Initially misidentified as different species (Polexy Source).
Lack of found skull typical among sauropods.
Evolutionary Tree and Divergence
Transition to Titanosauria:
Brachiosaur-like sauropods gave rise to Saur Poseidon and subsequently Titanosauria.
Characteristics include high-shoulderedness and spongy vertebrae.
Cretaceous Record and Extinction
Alamosaurus:
Found in late Cretaceous, representing the return of sauropods in North America.
Previously believed that sauropods went extinct in North America.
Global Sauropod Diversity:
South American (Argentinian) fossil discoveries highlight diverse Titanosauria.
Late Cretaceous titanosaur forms proliferated in Gondwana (e.g., South America).
Summary
The lecture covered the evolutionary trajectory and distinctive features of macronarian sauropods leading up to the diverse titanosaur forms in the late Cretaceous.
The understanding of sauropod evolution is enhanced by fossils from areas like Argentina, filling gaps in the North American fossil record.