First of all it is a bit strange to express the change of Earths rotation in miles per second every 100 years, since the speed due to Earths rotation depends on your position on Earth. It would be better to express it as an angular deceleration, so for example in radians per second squared.
But lets assume you mean the velocity at Earths equator, which has a radius of $6378.1\ km$ ($3963.2\ miles$). However I am unable to find or derive your $4.7\times 10^{−4}$ miles per second every 100 years. It only states that:
Atomic clocks show that a modern day is longer by about 1.7
milliseconds than a century ago
Current angular velocity of Earth is $7.292115 \times 10^{−5} rad/s$, which means that its rotation period is equal to $8.616410 \times 10^{4} s$. So the average angular acceleration of Earth, $\alpha$, over the last 100 years is equal to:
$$
\alpha=7.292115 \times 10^{−5} - \frac{2\pi}{8.616410 \times 10^{4} - 1.7 \times 10^{-3}}={-2.0\times 10^{-12}\ rad/s}\ \text{per 100 years}
$$
Which is therms of change of equatorial velocity only yields $7.9\times 10^{−9}$ miles per second every 100 years
The angular velocity, $\omega$ which would be required to make dinosaurs fly off the Earth, assuming that the Earth would not change shape much (it probably would though, but is hard calculate), is equal to:
$$
\omega > \sqrt{\frac{GM}{r^3}} = 1.24 \times 10^{-3}\ rad/s
$$
This would make the duration of a day take less than 1 hour and 24 minutes. Using the average angular deceleration you would have to go back 58 billion years to reach those angular velocities. However Earth is only roughly 4.54 billion years old.
There is also geological and paleontological evidence that the Earth was rotating faster, namely by looking at sedimentary layers of sand and silt laid down offshore by tides:
This geological record is consistent with these conditions 620 million
years ago: the day was 21.9±0.4 hours, and there were 13.1±0.1 synodic
months/year and 400±7 solar days/year.
This means that the average angular acceleration of Earth the last 620 million years is equal to:
$$
\alpha=\left(7.292115 \times 10^{−5} - \frac{2\pi}{21.9 \times 60^2}\right)\frac{100}{620\times 10^6}={(-1.1\pm 0.2)\times 10^{-12}\ rad/s}\ \text{per 100 years}
$$
This means that Earths angular acceleration has decreased (the deceleration has increased). I did not expect this, since since the Moon was closer to Earth and the rotation was bigger, which both would lead to bigger tides and thus a larger torque slowing down Earth rotation. But perhaps the lower angular velocity lead to the Earth becoming more spherical and therefore have a lower moment of inertia, so initially making it harder to slow down its angular velocity.
PS: This does makes me wonder how close the Moon was to the Earth and how short a day would have been when the earliest life forms roamed the Earth about 3.6 billion years ago.
