Sauroposeidon
The press release in 1999 immediately garnered international media attention, which led to many (inaccurate) news reports of "the largest dinosaur ever!". While "Sauroposeidon" likely represents the tallest known dinosaur taxon, it does not hold records for either the longest or most massive. "Patagotitan" or "Argentinosaurus" make better candidates for the title "World's Largest Dinosaur" (presuming to ignore, as is conventional, "Amphicoelias"), though incomplete fossil evidence makes exact rankings impossible.
Compsognathidae
Compsognathids are considered to be among the smallest dinosaurs ever discovered. "Compsognathus longipes" was largely acknowledged to the smallest dinosaur and was around the size of a chicken when fully grown. The specimens found indicate that this species was around 1 m long and weighed 2.5 kg. However, recently other adult dinosaur specimen have now been found that are smaller than Compsognathus, including the dinosaurs "Caenagnathasia", "Microraptor", and "Parvicursor", all of which are estimated to be less than 1m long. Most of these specimen are incomplete, so size determination is still just an estimate.