The pallid sturgeon is one of the largest freshwater fish species in North America. They are generally between in length and weigh as much as . The species is ancient and has remained virtually unchanged for 70 million years, since the Cretaceous period. The pallid sturgeon has a distinctive appearance that has been referred to as "primitive", "dinosaur-like" and even "ugly". Although visually similar, the shovelnose sturgeon is much smaller and usually weighs no more than . Pallid sturgeon are much paler in coloration with grayish white backs and sides, while shovelnose sturgeon are brown. Pallid sturgeon turn whiter as they age and younger specimens are easily confused with adult shovelnose sturgeon since they are similar in color. Like the shovelnose sturgeon, their tails are heterocercal, with the top tail fin being longer than the bottom fin, though this is more pronounced in pallid sturgeon.