From chickens and eggs to a cosmological argument

Suppose we have an infinite regress of chickens and eggs, with no first item, and suppose that if there is any last item, it’s not a chicken. Plausibly, then: The plurality of the chickens explains the eggs. But also plausibly: If x has an explanation, then x has a fundamental explanation. However: No plurality of chickens and eggs fundamentally explains the eggs. So, something that is other than…