Isthmian America (49,293 to 28,578 BCE) Upper Pleistocene I — Shelf Lowstands, Rainforest Refugia, and Kelp-Edge Seas

Geographic & Environmental Context

Isthmian America includes Costa Rica, Panama, Darién (Panama–Colombia), San Andrés Archipelago, Galápagos Islands, and the Ecuadorian Capelands (Cabos Manglares, San Francisco, Pasado, San Lorenzo, Punta Santa Elena; Manta; western Esmeraldas, Manabí, Guayas, Santa Elena).

Anchors: Panama isthmus and Azuero; Darién–Chocó rainforests; Costa Rica Central Valley and Nicoya; San Andrés banks; Galápagos volcanic outliers; Manta–Santa Elena capes and lagoons.

• Sea level ~100 m lower exposed Pacific & Caribbean benches; Azuero/Nicoya capes extended; Manta–Santa Elena had broader strand-plains; Galápagos remained far-oceanic.

• Darién–Chocó held humid forest refugia; Central American volcanic spine cooler/drier.

Climate & Environmental Shifts

• LGM: cooler, drier; monsoon weakened; upwelling strengthened along Humboldt contact; Caribbean trade winds intensified.

Subsistence & Settlement

• No secure evidence for people this early is expected in this corridor; any presence would hug refugia (Darién springs, Azuero coves), exploiting shellfish, reef fish, deer, peccary.

Technology & Material Culture

• Flake–core industries if present; expedient shell tools; organic nets/baskets (poorly preserved).

Movement & Interaction Corridors

• Pacific kelp-edge & Caribbean strandlines offered rich “highways” if used episodically; gap crossings shortest near Darién.

Cultural & Symbolic Expressions — Inferred only (ochre, shell beads) by analogy to nearby regions.

Environmental Adaptation & Resilience

• Refugial tethering (springs & coves) + mixed coast/inland foraging buffered LGM stress.

Transition

• Deglaciation will flood benches, build lagoons, and stabilize rainforest corridors for sustained occupation.