Megafauna Coexistence & Extinction Chronology In Southwest Ecosystems

1. Pleistocene Megafaunal Assemblages of the Southwest

The Pleistocene ecosystems of Southwest Western Australia supported a diverse and formidable assemblage of extinct giant marsupials, birds, and reptiles that coexisted with ancestral Bibbullmun populations.¹ Keystone taxa included the massive herbivorous Diprotodon optatum (weighing up to 2.5 tonnes), the browsing marsupial Zygomaturus trilobus, short-faced giant kangaroos (Simosthenurus occidentalis), the giant wallaby (Protemnodon anak), and the apex marsupial carnivore Thylacoleo carnifex (the marsupial lion).² Southwest fossil records also preserve the giant flightless bird Genyornis newtoni and the massive monitor lizard Varanus priscus (Megalania).³ These megafaunal guilds shaped vegetation architectures, maintaining open forest pathways and dispersing large-seeded endemic floras prior to their terminal extinction.⁴

2. Karst Deposits: Mammoth Cave and Kudjal Yolgah Chronostratigraphy

The primary paleontological and taphonomic repositories for Pleistocene megafauna in the Southwest are the karstic limestone caves of the Leeuwin-Naturaliste ridge, particularly Mammoth Cave and Kudjal Yolgah Cave.⁵ Excavations initiated by Ludwig Glauert in the early 20th century and modernized by Merrilees and Dortch uncovered dense bone beds representing natural pitfall traps and subterranean sediment washes.⁶ At Mammoth Cave, thousands of fossilized elements from Zygomaturus, Simosthenurus, and Thylacoleo were preserved in calcified cave earth.⁷ Direct Electron Spin Resonance (ESR) and coupled Uranium-Series (U-series) dating of tooth enamel, combined with optical dating of surrounding sediment matrices, have placed the primary Mammoth Cave megafaunal horizons between 55,000 and 42,000 BP, directly overlapping with the earliest human occupation dates at nearby Devil's Lair.⁸

3. Temporal Overlap and Coexistence Dynamics (50,000–30,000 BP)

The chronological calibration of fossil deposits confirms a significant temporal overlap—spanning thousands of years—between megafauna and ancestral Bibbullmun populations.⁹ Basal cultural levels at Devil's Lair contain modified bone fragments from extinct macropod species alongside early quartz debitage, demonstrating direct interaction between humans and Pleistocene fauna.¹⁰ Unlike simplistic 'overkill' or 'blitzkrieg' models that posit rapid mass slaughter by incoming humans within a few centuries, the southwest empirical record demonstrates prolonged ecological coexistence.¹¹ Ancestral communities established complex totemic relationships and customary hunting protocols that governed interactions with these giant creatures across generations.¹²

4. Extinction Etiology: Evaluating Climate Change and Anthropogenic Factors

The eventual disappearance of the megafaunal guilds between 45,000 and 38,000 BP remains a subject of intense scientific debate, centered on the interplay between climatic aridification and human-mediated environmental change.¹³ High-resolution paleoclimatic records indicate that Marine Isotope Stage 3 experienced increasing aridity and unpredictable rainfall shifts that contracted the permanent wetlands upon which large-bodied browsing herbivores depended.¹⁴ Concurrently, the controlled application of mosaic fire regimes (karl) by Bibbullmun custodians altered vegetation structures, favoring fire-tolerant sclerophyllous plants over the dense, fleshy understorey required by species like Zygomaturus.¹⁵ The extinction of Southwest megafauna was thus the result of complex synergistic factors rather than indiscriminate human predation.¹⁶