Cartilaginous bones, five to seven-gill slits on the sides of the head, and pectoral fins that are not connected to the head characterize sharks. Modern sharks belong to the cladeSelachimorpha (or Selachii) and are a sister group of rays. The term “shark” has also been used for prophets of doom. So how many times have you heard that sharks are blind? Well, they’re not.
Sharks do not have eyelids, so the eyes must be closed when they are resting. However, under each eye is a small hole called a “nictitating membrane”. This transparent membrane simply closes over the eye for protection when hunting or feeding and it also helps to remove sand particles after swimming near the shore.
Sharks cannot see in murky water since organic materials absorb light instead of being reflected back as clear waters. Another reason why sharks can’t see is because their lenses are made of cartilage which doesn’t transmit light well.
Sharks’ sense of sight comes from photoreceptor cells called “rods” and “cones”. These specialized cells in the retina of their eyes are sensitive to different frequencies of light. Rods are more sensitive to lower levels of light, but cannot detect color at all. On the other hand, red on a black-and-white chart is seen by many sharks because it has longer wavelengths that fall within cones’ visual spectrum.
Evolution Of Sharks
Sharks are usually classified into two types: the elasmobranchs (sharks, rays and skates) or the Holocephali (chimaeras), which only have cartilaginous skeletons. A group of sharks known as squaliforms are characterized by their short gill slits even when they are developed. These sharks also have small spiracles behind their eyes to improve water circulation in the gills while resting on the sea bottom.
Squaliforms include an extinct shark order known as Xenacanthida , whose members were characterized by huge dorsal spines on their backs, presumably for sexual purposes. This evolutionary feature may have been lost during later lineages’ evolutions.
Some of the most primitive sharks, the Paleozoic Cladoselachidae – which lived in marine habitats during Carboniferous and Devonian periods, are believed to be the ancestors of even modern day sharks. These ancient sharks have numerous teeth on their upper and lower jaws that are serrated for efficient hunting.
One thing is clear though about sharks. They have come a long way since they first appeared around 450 million years ago!
So, Are Sharks Color Blind?
Well, they can see a little. Sharks have two types of cells in their retina that are sensitive to light: rods and cones. Rods detect levels of light and dark while cones detect colors. Humans have three types of cones so we can see color in images – red, green, and blue.
Sharks likely have different numbers of cone types from humans, but their ratios may be similar. Since sharks cannot see red or green very well but can see blue fairly well, their color vision is roughly similar to a human with red-green color blindness! This condition does not mean these individuals cannot see any colors at all, it only means that they will struggle in distinguishing between close shades of red and green.
The visual systems of many different species of elasmobranch (sharks and rays) were investigated in a study published in Biology Letters by a team at the University of Western Australia. They discovered that the eye design varies according to taxonomic diversity (a population of organisms). There was some speculation that sharks had extremely poor eyesight based on their nocturnal habitat usage for early studies.
The researchers examined the retinal cells of 17 species of shark caught off Queensland and Western Australia using micro-spectrophotometry, a method that looks at how much light is absorbed by the rods in the retina. The most frequent type of light receptors was found to be “rod” cells, which are highly sensitive to light but cannot distinguish colors. According to this research, which is the first to look at genetic basis and spectral tuning in sharks’ visual system, forbearers were seeing the world in black and white.
According to researchers at the University of Western Australia, many sharks are active during the day. This behavior has evolved multiple times independently. Many benthic (ocean-floor) dwelling species are active at night, while open water species are more active during the day.
The reason why elasmobranchs might be active during the daytime is because it helps them locate their main prey items that rise up from the deep at dusk to feed in surface waters.
It also makes it easier for females to find males for mating purposes since male frillfin gobies gather every morning around coral reef structures that have small openings through which females can enter and mate with a male before returning to deeper waters.
There is also another factor among sharks regarding why they are diurnal. It is because sharks use the sun to determine their geographical location by the time of day, which is known as “Positional Astronomy” , similar to how we humans use stars at night. Sharks can do it even during early evening when the moon is out since if they go out far enough into the open sea, they will see sunlight before moonlight or see both at once coming from opposite directions.
Sharks are almost always meat-eaters. Basking sharks, whale sharks, and megamouth sharks have independently evolved distinct ways of filtering plankton. Ram feeding is practiced by basking sharks, while whale sharks use suction to ingest plankton and tiny fish, and megamouth sharksuction feeding is more efficient thanks to the luminescent tissue inside their mouths, which attracts prey in the deep ocean.
The gill rakers on this species’ feeding style are long, slender filaments that function like a very efficient sieve to remove food particles just like the baleen plates of the largest whales. The plankton is trapped in these strands and eaten in huge mouthfuls by the shark. Because they aren’t required for nutrition, teeth in these species are tiny.
Sharks are at the top of most oceanic food chains. This implies that their position in ecosystems is closely linked to the health of those systems, and when these hunters are damaged, all aspects of aquatic life may be affected. The fact that sharks consume a wide range of prey, including fish, mollusks, crustaceans, and other big and small creatures ensures biodiversity balance since they all have important functions in maintaining the ecosystem healthy and functional. If you want to learn more about animals, keep reading our blogs from hedge the book.