Largest Triceratops skeleton
Big John
7.15 m, 2.7 m, 1.55 m dimension(s)
United States ()

The largest documented skeleton of a Triceratops dinosaur is that of "Big John", a Triceratops horridus dating to the Late Cretaceous period, which was discovered in 2014 in the Hell Creek Formation of South Dakota, USA. The mounted skeleton of Big John measures approximately 7.15 m (23 ft 5 in) long from snout to tail tip and stands 2.7 m (8 ft 10 in) high at the hips. The reconstructed skull measures 2.62 m (8 ft 7 in) long and 2 m (6 ft 6 in) wide with a basal skull length of 1.55 m (5 ft 1 in), making it 5–10% larger than any other Triceratops skull reported to date.

Skull size is widely used to assess the size of ceratopsian dinosaurs, such as Triceratops, owing to the fact that full skeletons are extremely rare making it difficult to compare total body length or stature like for like. The most consistent measurement to compare skull size is the basal skull length (BSL), from the tip of the snout to the back of the occipital condyle, as the frill is often damaged when discovered, plus frill and horn size/shape varied significantly among species.

Big John's skeleton is about 60% complete, with a 75% complete skull including two 1.1-m-long (3-ft 7-in) brow horns .

Big John was found at Mud Butte Ranch, Southwestern Perkins County, near Newell, South Dakota, and was excavated across 2014 and 2015. The specimen was assessed and measured by palaeontological preparation company ZOIC s.r.l. and natural history expert Iacopo Briano (both Italy). The skeleton is due to be sold by Drout auction house in Paris, France, in October 2021.