Cosmos In Collision is an excellent book about the formation of celestial objects. A small part is reserved for discussion regarding the anomalies encountered concerning the ability of most of the dinosaurs to exist on Earth.
The conclusion reached by the authors, Theodore A Holden and Troy D McLachlan, regarding the gravitational conditions at the time, clearly state that the gravity must have been attenuted to about 1/3 the present value.
The figure quoted after much detailed maths and analysis is (2.8 * gravity for dinosaur) = (gravity for an elephant)
My interpretation of this is 2.8 * 3.5m/s2 = 9.81m/s2
The authors give no indication as to how they think this could be possible. I think that at the time of the dinosaurs the planet was not rotating, or rotating minimally. The static gravity was probably about 2m/s2. As the planet increased rotational speed over a long period, the dynamic gravitational field created gradually forced the dinosaurs out of existance.