François Therrien and Donald Henderson, in a 2007 paper using scaling based on skull length, challenged previous estimates of the size of Spinosaurus, finding the length too great and the weight too small.
Based on estimated skull lengths of 1.5 to 1.75 meters (4.9 to 5.7 ft), their estimates include a body length of 12.6 to 14.3 meters (41 to 47 ft) and a body mass of 12 to 20.9 tonnes (11.8 to 20.6 long tons; 13.2 to 23.0 short tons).
The skull of Spinosaurus was long and narrow, similar to that of a modern crocodilian.
Spinosaurus is known to have eaten fish, and most scientists believe that it hunted both terrestrial and aquatic prey; evidence suggests that it lived both on land and in water as a modern crocodilian does.
Spinosaurus sails were unusual, although other dinosaurs, namely the ornithopod Ouranosaurus, which lived a few million years earlier in the same general region as Spinosaurus, and the South American sauropod Amargasaurus, might have developed similar structural adaptations of their vertebrae.
Estimates published in 2005, 2007, and 2008 suggested that it was between 12.6–18 metres (41–59 ft) in length and 7 to 20.9 tonnes (7.7 to 23.0 short tons) in weight.The Therrien and Henderson study has been criticized for the choice of theropods used for comparison (e.g., most of the theropods used to set the initial equations were tyrannosaurids and carnosaurs, which have a different build than spinosaurids), and for the assumption that the Spinosaurus skull could be as little as 1.5 meters (4.9 ft) in length.Very tall neural spines growing on the back vertebrae of Spinosaurus formed the basis of what is usually called the animal's "sail".Stromer's son donated Stromer's archives to the Paläontologische Staatssammlung München in 1995, and Smith et al.analyzed two photographs of the Spinosaurus holotype specimen BSP 1912 VIII 19 discovered in the archives in 2000.This specimen was destroyed in World War II, specifically "during the night of 24/25 April 1944 in a British bombing raid of Munich" that severely damaged the building housing the Paläontologisches Museum München (Bavarian State Collection of Paleontology).However, detailed drawings and descriptions of the specimen remain.The distinctive spines of Spinosaurus, which were long extensions of the vertebrae, grew to at least 1.65 meters (5.4 ft) long and were likely to have had skin connecting them, forming a sail-like structure, although some authors have suggested that the spines were covered in fat and formed a hump.Multiple functions have been put forward for this structure, including thermoregulation and display. (2005) assumed that Spinosaurus and Suchomimus had the same body proportions in relation to their skull lengths, and thereby calculated that Spinosaurus was 16 to 18 meters (52 to 59 ft) in length and 7 to 9 tonnes (6.9 to 8.9 long tons; 7.7 to 9.9 short tons) in weight. estimates were criticized because the skull length estimate was uncertain, and (assuming that body mass increases as the cube of body length) scaling Suchomimus which was 11 meters (36 ft) long and 3.8 tonnes (4.2 short tons) in mass to the range of estimated lengths of Spinosaurus would produce an estimated body mass of 11.7 to 16.7 tonnes (12.9 to 18.4 short tons).Stromer considered them different enough to belong to another species, and this has been borne out.With the advantage of more expeditions and material, it appears that they pertain either to Carcharodontosaurus Later authors have been split on this topic.