On my world, the equivalent of the Cambrian/Avalon explosion happened 5 byr (2 byr after formation) ago as opposed to 0.5 byr ago on Earth.
The planets rough parameters are:
mass between 0.4 and 0.25 Earth-masses
only 10 to 30 percent global ocean cover, water is mostly near the poles
orbits a 10.9 Jupiter-mass warm super-Jovian
extensive vulcanism and some plate tectonics
the global average temperature is 63 C, just shy of a runaway greenhouse effect given the local atmospheric pressure of 2,7 atm
only one atmospheric circulation cell due to slow rotation (the moon is tidally locked)
long days and nights (still need to do the math, assume one terra-week each)
the sun is an old F-type with only a few hundred million years left on the main sequence
So how would this planet's 5 byr old biosphere and environment be different from Earths young one in a broad sense?
I´m aware that this could easily be considered as too broad or opinion based, but I´m only looking for macro details. For example, I think that the planet would have very extensive fossil fuel deposits, a very diverse tree of life, an environment where life has adapted to very exotic niches (cloud-algae for example),... .