English: Restoration of a young tyrannosaurid (primarliy based on the specimen BMRP 2002.4.1, aka. "Jane" (attributed to Tyrannosaurus rex)) surprise and bring push down prey, an ornithomimid (mostly based on Ornithomimus), illustrating the hypothesis that juvenile Tyrannosaurus rex used their forelimbs to handle prey before the rest of their bodies "outgrew" the arms and the heads with jaws became powerful enough to take over as their main and/or sole weapon.^[1]

• The first complete tyrannosaurid forelimbs were described in Gorgosaurus holotype fossil (CMN 2120) by Lawrence Lambe in 1914 and 2017,^[2][3] with Barnum Brown shortly after describing tyrannosaurids as animals in which "the short, reduced frontlegs could have been used only in grasping prey".^[4] The idea, however, did not get serious attention until late 1980s/early 1990s, when the first complete forelimbs of Tyrannosaurus were discovered and began to be studied by Carpenter and Smith, who noted that the musculature would have been well developed.^[5] Such research have continued for decades.^[6]
• Some researchers have been skeptical and argued that the forelimbs of tyrannosaurids were still very small for their body size, and would therefore have been usuitable to grasp large prey. Absence of healed pathologies (i.e. fractures, breakage) have been seen as evidence that the forelimbs would not have been used very much,^[7] while signs of healed pathologies have been used both as evidence that they could not have been necessary (as the animals apparently could survive with broken arms) and that they served some function.
• Some researchers propose that the forelimbs in juvenile tyrannosaurids were longer relative to body size – and possibly more useful – than in their adult counterparts, but were “outgrown” by the rest of the body as they got larger.^[1]

References

1. ↑ ^{a b} Williams S et.al. (2011). "A new subadult tyrannosaurus rex and a reassessment of ontogenetic and phylogenetic changes in tyrannosauroid forelimb proportions". Geological Society of America Abstracts with Programs 43(1): p. 120
2. ↑ Lambe L.M. (1914). "On the forelimb of a carnivorous dinosaur from the Belly River Formation of Alberta, and a new genus of ceratopsia from the same horizon, with remarks on the integument of some Cretaceous herbivorous dinosaur". The Ottawa Naturalist 27(10): p. 129-135
3. ↑ Lambe L.M. (1917). "The Cretaceous theropodous dinosaur Gorgosaurus". Geological Survey of Canada Memoir 100: p. 1-85
4. ↑ Brown B (1919). "Hunting Big Game of Other Days: A Boating Expedition in Search of Fossils in Alberta, Canada". National Geographic Magazine 35: p. 407-429
5. ↑ Angier N. (July 2nd, 1990). "Researchers Challenge Ideas on Dinosaur Arms". The New York Times: section A: p. 13
6. ↑ Geggel L. "Hail the Lizard King. T. Rex's Puny Arms Were Useful After All". LiveScience 18-10-2018
7. ↑ Pappas S. "T. Rex Probably Didn't Use Its Tiny Arms Much". LiveScience 14-10-2016