The question of whether a sawfish is a shark is common, driven by their imposing, shark-like bodies and famous snout. Sawfish are definitively not sharks; they are a unique type of ray. They are among the largest fish, characterized by their long, flattened, tooth-studded rostrum, which causes confusion regarding their classification. This marine animal belongs to a different biological superorder than true sharks, despite sharing a common ancestor in cartilaginous fishes.
Classification: Sawfish Are Rays
Sawfish belong to the superorder Batoidea, the group that includes skates and stingrays. They exhibit key anatomical features that separate them from true sharks, which belong to the superorder Selachii. The most distinguishing trait is the location of their gill slits.
Sawfish, like their ray relatives, possess five pairs of gill slits situated on the ventral surface, or the underside of their head. This placement is a defining characteristic of rays, allowing them to rest on the seafloor while still drawing water over their gills. True sharks have their gill openings positioned laterally, on the sides of their bodies.
While many rays have flattened, disc-shaped bodies, sawfish retain a more elongated, shark-like appearance, contributing to the misidentification. However, the sawfish’s large pectoral fins are fused to the sides of its head, similar to other rays, rather than being distinct appendages as seen in sharks. These anatomical differences confirm the sawfish’s identity as a specialized member of the ray family Pristidae.
The Source of Confusion: The Rostrum
The most recognizable feature of the sawfish is the long, flat, paddle-like structure known as the rostrum. This extension, which can constitute up to a quarter of the animal’s total body length, is a cartilaginous outgrowth of the skull. It is lined on both edges with a series of modified dermal denticles, often referred to as rostral teeth.
This formidable saw is not just for defense; it is a sophisticated sensory and hunting tool. The rostrum is riddled with thousands of minute pores connected to electroreceptors called Ampullae of Lorenzini. This sensory system allows the sawfish to detect the weak electrical fields generated by prey, even when they are hidden beneath the seabed sediment.
Once prey is detected, the sawfish uses the rostrum to rapidly slash through schools of fish or to dislodge invertebrates from the substrate. This side-to-side motion stuns or injures the prey, making it easier to consume. The development of this saw in both sawfish and sawsharks is an example of convergent evolution, where two unrelated groups evolve similar structures to fill a comparable ecological niche.
Distinguishing Sawfish from Sawsharks
The confusion between sawfish and sharks is compounded by the existence of sawsharks, a separate group of animals that are true sharks and possess a similar-looking saw. To avoid misclassification, observers must focus on three primary anatomical distinctions. The most reliable difference remains the placement of the gill openings: sawfish have ventral gills, while sawsharks have lateral gill slits, just like other sharks.
The second distinction is related to overall size and body shape. Sawfish are giants, with some species growing to lengths of over 20 feet, and they have a noticeably flattened body profile. Sawsharks are comparatively small, rarely exceeding five feet in length, and they maintain a more slender, cylindrical body shape typical of sharks.
A third clear marker is found directly on the saw itself. Sawsharks possess a pair of prominent, whisker-like sensory barbels located on the underside of their rostrum. Sawfish completely lack these barbels. Furthermore, the sawshark’s rostral teeth are typically uneven in size, alternating between large and small, whereas the sawfish’s rostral denticles are generally uniform.