By the time of Spinosaurus, ... more than eight times the forward thrust in water than the tails of the non-spinosaurid theropods Coelophysis and Allosaurus—and does so twice as efficiently. The T. Rex was also substantially heavier at 14,000 lbs compared to the allosaurus at 4,000 lbs. The average height of an allosaurus was 17ft (a little over 5m) while T. Rex was about 23ft (7m) tall on average. An allosaurus adult was between 8.5 and 12m in length (28-39 ft), while the average T. Rex adult was about 12-15m long (40-50 ft).