https://phys.org/news/2018-05-smallest-biggest-theropod-dinosaur.html

The striking similarities with the claw phalanges of the foot of Spinosaurus allowed palaeontologists Simone Maganuco and Cristiano Dal Sasso to identify the tiny bone to a very small and young specimen of the sail-backed Spinosaurus, the smallest individual reported up to today. "Besides the rarity of the fossils belonging to juvenile theropod dinosaurs, and the rarity of Spinosaurus bones, this finding is even more remarkable if we consider the dramatic size attained by some large specimens of Spinosaurus, which are possibly the longest, and among the largest predatory dinosaurs ever found"- says Maganuco.

Assuming the juveniles looked like smaller versions of the adults, the 21 mm-long claw phalanx from this small specimen would pertain to an early juvenile individual, 1.78 m-long, only just a little bit longer than the estimated length of the sole head of the largest adult Spinosaurus known to date, which is also housed at the Natural History Museum of Milan.