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Strange Animals

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Podcast Welcome

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to Strange Animals Podcast.

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I'm your host, Kate Shaw. This

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week we're going to learn about

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an amazing fish suggested by Marillo.

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It's the Sawfish, and while we're at

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it, we're also going to learn about

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a different fish called the Saw Shark.

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There are five species of sawfish

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alive today in two genera, and

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they're all big. The smallest

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species can still grow over 10 feet

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long or 3 meters, while

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the biggest species can grow over 20

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feet long or 6 meters. The

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largest sawfish ever reliably measured was 24

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feet long or 7.3 meters. Since

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all species of sawfish are

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endangered due to overfishing, pollution,

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and habitat loss, really big

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individuals are much rarer these

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days. The sawfish

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lives mostly in warm, shallow

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ocean waters, usually where the

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bottom is muddy or sandy.

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It can also tolerate brackish and

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even freshwater, and will sometimes swim

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into rivers and live there just

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fine. The large-toothed sawfish

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is especially happy in freshwater.

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Let's talk specifically about the large-toothed

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sawfish for a moment, since we

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know the most about it. Like

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other sawfish, the female gives birth to

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live young, up to 13 babies at

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a time, and the babies can be

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up to 3 feet long at birth

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or 90 centimeters. When

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a baby is born, its saw, which

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we'll talk about in a minute, is

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covered with a jelly-like sheath that keeps

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it from hurting its mother. The

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sheath dissolves soon after birth.

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The mother usually gives birth around

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the mouth of a river, and

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instead of swimming into the ocean,

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the babies swim upstream into the

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river. They live there for

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the next several years, and some

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individuals and even some populations may

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live their whole lives in the

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river. It's sometimes called

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the river sawfish or the freshwater

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sawfish for this reason. One

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interesting thing about the largetooth sawfish

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is how agile it is. All

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sawfish are good swimmers, but the

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largetooth sawfish is especially good. It

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can swim backwards, it can jump more

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than twice its own length out of

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the water, and it

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can climb over rocks and other

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obstacles using its fins, even if

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the obstacle isn't completely submerged. It's

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possible that other species of sawfish

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can do the same, but scientists

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just haven't observed this behavior yet.

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We actually don't know that much

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about most species of sawfish because

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of how rare they've become. The

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sawfish is a type of ray, and

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rays are most closely related to sharks.

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Like sharks, rays have an internal

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skeleton made of cartilage instead of

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bone, but they also have

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bony teeth. You can definitely

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see the similarity between sharks and

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sawfish in the body shape, although

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the sawfish is flattened underneath, which

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allows it to lie on the

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ocean floor. There's also another

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detail that helps you tell a sawfish

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from a shark, the rostrum or snout.

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It's surprisingly long and studded with

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teeth on both sides, which makes

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it look like a saw. The

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teeth on the sawfish's saw are actual

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teeth. They're called rostral teeth,

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and the rostrum itself is part of

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the skull, not a beak or a

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mouth. It's covered in skin

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just like the rest of the body. The

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sawfish's mouth is located underneath the

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body quite a bit back from

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the rostrum's base, and the mouth

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contains a lot of ordinary teeth

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that aren't very sharp. So

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you may be asking, if the sawfish

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has plenty of teeth in its mouth,

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how and why does it also have

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those extra teeth on both sides? both

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sides of it saw. It's

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because the rostral teeth evolved

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from dermal denticles. We've

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talked about dermal denticles a few times

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before but a few months ago we

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had a Patreon bonus episode that went

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into more detail. In that

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episode I talked about an article about

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a type of catfish so let me

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just quote the whole section of that

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episode. It's not long and I think

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it's really interesting. Heck I'll

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just drop the audio in directly

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from that Patreon episode. Quote, our

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next article is from October 2017

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and is intriguingly titled When

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teeth grow on the body. It sounds

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horrific but it's actually a study

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of certain catfish that grow bony

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plates with tiny teeth on their

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bodies as defense. Catfish

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don't have scales but some species

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of denticulate catfish that live in

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South America grow bony plates that

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act like armor. Many of these

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plates are covered in thin little teeth.

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Actual teeth including enamel and

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dentin with pulp inside. They're

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called extra oral teeth dermal denticles

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or adontides and the study determined

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that they appeared about 120 million

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years ago in ancient catfish

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that hadn't yet evolved the bony

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plates. The teeth regrow when they're

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lost and in some species males

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grow larger teeth than females and

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use them to fight other males.

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Imagine biting someone without needing

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to open your mouth. Unquote.

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Anyway dermal denticles aren't all that

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rare in fish. Sharks and

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rays are both covered with them. They're

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also called placoid scales but

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they're literally teeth. They're just

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not used for eating. In the

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case of the sawfish the rostral teeth

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grow much larger than an ordinary dermal

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denticle and stick out sideways like the

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teeth of a saw. Different

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species have differently shaped rostral

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teeth. Teeth grow throughout

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the sawfish's life, but unlike the

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teeth in the mouth, if the

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sawfish loses a rostral tooth, it

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doesn't grow back. If it

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chips the top off a rostral tooth,

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though, that part will grow back, which

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is handy. The sawfish uses

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its rostrum to find the

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fish, crustaceans, and mollusks it

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eats. Both the rostrum and

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the head are packed with electroreceptors

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that allow the sawfish to sense

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tiny electrical charges that animals emit

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as they move. This might

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mean a school of fish swimming through

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muddy water, or it might mean a

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crustacean hiding in the sand. The

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sawfish sometimes uses its rostrum to dig

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prey out of the sand, but it

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also uses it to slash at fish

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or other animals. Then the

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sawfish can either grab the injured or

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dead animal with its mouth, or pin

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it to the sea floor with its

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rostrum to maneuver it into its mouth.

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Its mouth is relatively small and

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it prefers to swallow its food

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whole head first, so it can

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only eat fish that are smaller

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than its mouth. This means

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the sawfish leaves humans alone because

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we're way too big to fit

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into its mouth, even a big

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sawfish's mouth. It doesn't want

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anything to do with us. Unfortunately,

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people keep bothering the sawfish,

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either by catching it illegally,

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leaving fishing nets and other

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trash in the ocean that

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sawfish and lots of other

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animals get tangled in, or

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by destroying its habitat with

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destructive dredging or trawling. The

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large-toothed sawfish used to live around

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southern North America, but it relied

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on mangrove swamps to act as

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a nursery for baby sawfish. So

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many of the mangrove swamps have

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been destroyed so that people can

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build fancy hotels and shopping centers,

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that the large-toothed sawfish hasn't been

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seen around North America in over

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50 years, although

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the small-toothed sawfish is still

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hanging on. Sawfish

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do well in captivity but require

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gigantic tanks, and even when given

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the best of care, they

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almost never breed in captivity. They

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live a long time though, sometimes

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for decades. Luckily for

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the sawfish, the female can reproduce without

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a male if she can't find a

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mate. Instead of her

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eggs being fertilized by the male's

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sperm, sometimes a female's eggs will

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just develop into her genetic clones.

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Humanists are working to make sure

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the sawfish and its habitat are

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protected, so the babies can grow

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up safe and healthy. We

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can't talk about the sawfish without

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mentioning the saw shark. It's

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a shark, not a ray, but

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it looks a whole lot like

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a sawfish, so much so that

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in places where both animals live,

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such as around Australia, people have

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a hard time telling them apart.

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The saw shark mostly lives in much

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deeper water than the sawfish and is

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much smaller on average, about 5 feet

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long, or 1.5 meters. It

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has a pair of barbells about halfway down

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its saw that help it find food when

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there's not much light to see by. Another

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major difference is that its gill slits are

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on the sides of its neck instead of

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under its body. It eats

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fish, squid, and crustaceans. The

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saw shark's rostrum also contains electroreceptors,

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although we don't know for sure

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that it uses its saw the

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same way as the sawfish does.

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We actually don't know very much

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about the saw shark, not even

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how many species are alive today.

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A new species was described in

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2013, and two new species were

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described in 2020. There

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are probably more that are completely

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unknown to science, and maybe completely

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unknown to people in general. Finally,

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there's another fish that looks like

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a sawfish or saw shark. The

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saw's skate, but its entire suborder,

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sclero rincueidae, is

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completely extinct. It

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disappears from the fossil record 66 million

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years ago. I feel like I

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need a sound effect to play

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every time I mention that an

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animal went extinct 66 million years

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ago to remind listeners that that's

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the date of the extinction event

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that killed off the non-avian dinosaurs

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and many other animals. Maybe

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something like this. Anyway,

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scientists are pretty sure the

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sawskate wasn't very closely related

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to sawfish or sawsharks, but

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was more closely related to

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modern skates. Skates look

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a lot like rays but belong to

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a different family. Modern skates

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don't have much of a rostrum

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at all, but the sawskate had

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a long tapering rostrum and some

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species had rostral teeth. Most

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species of sawskate were fairly small,

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but at least one grew an

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estimated six feet long or about

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two meters. If you've

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been thinking that a rostrum with

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teeth on both sides sounds like

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the kind of sword that old-timey

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warriors would use, you're actually right.

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Traditionally, people in parts of the

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world where sawfish are common would

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sometimes use a big dried rostrum

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as a weapon. These days,

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of course, sawfish are protected species.

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That means you can't have a

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sawfish rostrum sword. Sorry, let

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the sawfish keep its sword. You

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can find Strange Animals

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Podcast at strangeanimalspodcast.blueberry.net. That's

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