I just saw a Gurnard fish featured on David Attenborough's Life on Earth. Episode Five 'The Conquest of the Waters'

Hey,

I don't know the species name off the top of my head but I am familiar with the fish and can tell you, just for interests sake(!), that the 'legs' are actually modified fin bones that originated from, but are no longer attached to, the pectoral fins.

In the same way that the fish can move its fins, it can move these unattached appendages too. Because they are no longer attached to the fin via skin tissue, they can be moved independantly and act therefore as 'legs'.

(posted in Fishes (Including Sharks))

That's fantastic, I'm very jealous Dean!

(posted in Fishes (Including Sharks))

Well that clears that up. Thanks for replying Emilio, we look forward to hearing from you again

(posted in Fishes (Including Sharks))

To summarise my answer regarding sharks as pets: "No no no no no no no no no no no no nooooooooooooooooooooooo!!!!!"

(posted in Fishes (Including Sharks))

Hey Emilio,

Are you able to post a link to the website you found detailing the hybrid? I'm intrigued.

In the mean time...

Great Whites and Makos are significantly different species and I feel it is extremely unlikely they would ever mate naturally.

Say for a moment that the Great White, starved of affection (!), had 'romantic intentions'... the Mako would likely percieve the GW as a predator and swim away. The GW would
have little hope of catching the Mako as they are one of the fastest
long distance sharks, if not fish. (NB. The Great White is also one of the fastest sharks but can only maintain speed in extremely small bursts.)

And if the Mako had 'other ideas'... the Great White would more likely see the Mako as prey than a potential mate.

However, can we have the link? Maybe some mad scientist has been playing with embryos?

P.S.

I'm not saying it definitely wasn't a parasite, I was just offering my opinion!

Many sharks and rays exhibit prolapse when stressed

Prolapse is a condition where internal organs slip out of place and protrude through the anus (or vagina in females)

It is common and sounds a likely suspect given your description

(posted in Fishes (Including Sharks))

Full grown Great White and full grown Tiger shark- sat in front of each other so no ambush and no advantage to either, and both actually wanting to attack the other for some unfathomable reason- hmmm.... my money's on the Tiger. Great Whites are bigger but Tigers have a dentition that can inflict greater damage and they have a stronger bite force (allegedly). I suspect they may also be slightly more agile in such a scenario.

But really- I'm glad to say it is HIGHLY unlikely to ever actually happen!

(posted in Fishes (Including Sharks))

The easiest way to solve this issue is to tell you that there is a comprehensive list of all named shark species and the depths at which they are found in the following book:

Compagno, L. J. V., Fowler, S. L. and Dando, M. 2005. Sharks of the World: Field Guide. Collins. 368pp

Lots of great illustrations and tonnes of additional data also

(posted in Fishes (Including Sharks))

All modern shark teeth are white, almost translucent when still in the mouth of a living shark. When teeth become fossilised, that is when the colour change occurs. It is not a case of the older the fossil the darker the tooth, it is actually to do with the sediment type in which the tooth was buried. For example, teeth from the Albian of Folkestone in the south of England vary from grey through to black in the same locality, whereas most fossil shark teeth from the Maastrichtian of Morocco are reddish or can even be as white as modern teeth. In the latter case it can be had to tell a fossil from a modern tooth. The clue is in the weight (fossils are heavier) and the appearance of the root... if it is still attached.

(posted in Fishes (Including Sharks))

Oooh this is very cool! My money is on a partial skull of a bony fish. I know someone who could help if so, so I shall forward your question and get back to you. Unless someone else answers you first!

I'm afraid the honest answer is that we don't know the world population of Great White sharks. They are listed on CITES as 'vulnerable to extinction' which may sound odd if we don't know how many there are but the problem is that Great Whites are a migratory species- i.e. they swim across vast expanses of open water. They are impossible to count in the middle of the ocean because we cannot see them and so we look at local populations, (coastal hotspots- Australia, South Africa, etc) to gain an idea. Numbers in coastal regions are still hard to ascertain with a great degree of accuracy but if populations seem depleted in an area where they were once abundant, this is a good indication that the populations worldwide are in trouble. As is current;y the case. Scientists are currently trying ways to track the movements of various large migratory species but it is very difficult.

Sand Tiger sharks are also listed as vulnerable but there is at least one population that is on the brink of local extinction. Sand tigers are not known to make huge migratory journeys so a local extinction is very serious for globabl populations.

I don't know of any species of shark that would habitually prey on swordfish- i.e. swordfish do not form a regular part of any sharks diet. Hypothetically speaking though, if a shark was weakened for some reason and so desperate for food that it tried to go for a swordfish, the swordfish would almost certainly be able to swim much faster and get away with ease.

(posted in Fishes (Including Sharks))

A side note for sharks!

A lot of people believe that if sharks stop swimming they will drown. As with bony fish, the process of respiration occurs as oxygen moves over the gill openings and is exchanged for carbon dioxide (a waste product, just like humans) in a process called the countercurrent principle. The gills need a constant supply of water and so muscles work to draw water into the mouth before squeezing it out through the gills when the mouth is closed. Water is prevented from entering the throat via valves and gills via gill flaps. Swimming forward aids this process by the natural movement of the water.

The common tale of sharks drowning if they stay still comes from the large ocean faring sharks that really rely on the movement of the water induced by swimming and are barely able to use the pumping mechanism. If they are then trapped in a net, for example, they get into severe difficulties and eventually drown. The majority of sharks fall into this category.

However there are other sharks that rely more on the muscles to do the work and there are even a number of species that spend the majority of their time sitting on the sea floor, not moving at all. These species rely solely on being able to pump oxygen using their musculature.

A couple of species have some further wacky adaptations but that is a general summary!

(posted in Fishes (Including Sharks))

Whilst all sharks and rays are carnivorous the group as a whole has a very varied diet. No shark species preys exclusively on seals and any species large enough to take seals, as Alistair says, will also prey on bony fish and even other shark species. Seals take a lot of energy to catch as they are fast and agile. They are therefore only hunted due to their large reserves of blubber that make it worth while in terms of energy expenditure.

Conversel, many species of shark are durophagous i.e. they have teeth that crush shelled invertebrates, such as crabs. Three of the largest shark species- the Megamouth shark, the Whale shark and the Basking shark, feed almost exlcusively on plankton- they also take small fish and other small organisms that get in their way when scooping up plankton.

Great Whites are comparatively fussy eaters whereas the tiger shark has a dentition that is able to cope with eating anything it finds meaning that they are generally not in the least bit fussy. One tiger shark was found with a piece of a suit of armour in its stomach!

(posted in Fishes (Including Sharks))

If all of our Hominid ancestors had been vegetarians, modern society wouldn't exist.

(posted in Mammals)

I'm not a specialist but I have done some work on mammoths and essentially yes I agree!

When looking at elephant ancestry you have to remember that firstly they weren't all mammoths and secondly not all mammoth species were the same size, for example there is the dwarf Sardinian mammoth (Mammuthus lamarmorae).

In terms of the largest elephant that ever lived (that we know of) for a long time the Imperial Mammoth (Mammuthus imperator) was considered the largest at 4.9m total height, but it has been surpassed (albeit only just) by the Songhua River Mammoth (Mammuthus sungari) which reaches 5.3m in total height.

I do not work on dinosaurs but from the point of view of an anatomist I would suggest Triceratops' skull structure is not suited to this life habit. Semi or fully aquatic animals that need to breathe air tend to have nostrils on the top of the head- hippos and crocodilians or whales and dolphins for example. For Triceratops to act in this way it would have to have held its head up at a peculiarly high angle and, given the head shield acting as a restriction in serious vertical tilting, I doubt this would have been the case.

As for other dinosaurs- personally I can't think of any examples, but maybe someone who works on dinosaurs will come up with something.

(posted in Fishes (Including Sharks))

Really sorry- shark moderator has been away for a few months! Back now! An educated guess would be around 10 -15 minutes for nurse sharks but it will vary greatly depending on the environmental conditions at the time, plus how many sharks are involved (males can be both persisted and impatient to wait their turn so try to take over when another male is already mating!)

The other thing to point out is that the VAST majority of shark species are less than 2m in length and are frequently prayed upon by other sharks as well as many species of bony fish. However, more in tune with the point of your question- an interesting shark predator is the giant octopus!

(posted in Fishes (Including Sharks))

Hey! Sorry- i've been in Kuwait chasing sharks around the Persian Gulf.  I agree with Alistair. All fish workers that i have spoken to class fish as the plural for fish in terms of a number of individuals but fishes as the plural for a number of fish species.

(posted in Mammals)

That's so cute! :-D

(posted in Fishes (Including Sharks))

Abundance:

In any ecosystem there is a balance of predators and prey. Sharks are what we call apex predators, they have no natural enemies. This means that their maturation rate is slow, they reproduce slowly, and they live a long time (in general). These are all reasons why they are unable to cope with the modern human induced pressures of fishing and finning.

Anyway, the ecosystem is a triangle of total biomass . This means, for example, that for every 100 antelopes on the African savannah, you have 10 lions. Or 50 antelopes would be enough to only support 5 lions and so on. Now imagine a more complex ecosystem- say a leopard seal, a penguin and a fish. You would need a 100 fish to feed 10 penguins which would feed 1 seal. Or 200 fish would sustain 20 penguins which would provide enough food for 2 seals. (All numbers are approximate!)

So, teleosts and sharks work in the same way. Sharks are predators with no natural enemy and so are at the top of the triangle. Telesosts have numerous predators and so are in the middle of the triangle. They need to be far more numerous than their predators but less numerous than their prey. The creatures at the bottom of the triangle that get eaten by hundreds of different predators have to be the most numerous in order to cope with the predatorial pressures. Think how much grass is needed to sustain a herd of antelope!

Diversity:

Teleosts are found globally. Speciation occurs for a number of reasons including population isolation and adaptation to environmental pressures. So the more numerous and wider spread you are, the greater the number of species will occur. They also speciate based on predatorial pressures, climate, disease, mutation, water depth, salinity, and so on. Also individual populations may appear different even if they are the same species for example Bonnethead sharks that live in the shallow waters of Florida are slightly darker than elsewhere because they get suntanned!

Shout if any of that is not clear!

Research and academic scientists in general have to be very hard working because of the demands of the profession. Teaching commitments, undertaking field work and research, writing academic papers and constantly trying to meet targets, are just a few of the reasons that can and do keep scientists in their offices for more hours in the day (and night) than is probably healthy. To say that palaeontologists are the cleverest scientists would be unfair for the same reason that it would be unfair to say that people who went to Imperial College London are cleverer than people who went to Kings College London. In some cases it may be true, in other cases it may be the other way around- it is all down to the ability of the individual.

The monthly cycle may have evolutionary advantages that we modern female humans do benefit from, but it is difficult to be grateful for the absence of one problem when you are suffering from the presence of another. I can only hope Daves answer has helped a little

:-)

(posted in Mammals)

Elephants can apparently maintain a swimming speed of about 1.5km/h for up to six hours. I believe that is based on an African elephant though i doubt the speed differs too much, if at all, for the smaller Asiatic elephants.

Also, here is a nice anecdote!:

Amazingly, in the late 1970s, two bulls swam from Zimbabwe’s Spurwing Island across Lake Kariba to Kariba town, a distance of at least 25km. These 20-year-olds took turns to rest, one placing his forelegs on the haunches of his companion in front. Apparently their 24-hour-long trip followed an old elephant migration trail that had been covered by the lake for 25 years!

Both facts are from the website: http://www.africaguide.com/features/trvafmag/005.htm if you wanna check out any more information.

Hope that helps!

Hey Dave! All euripteryd questions should be directed at Simon Braddy of Bristol University. If he doesn't know, he will know who to ask :-)

(posted in General Biology)

I don't think there is a known answer to this question. Many scientists have their own opinions about which animals are intelligent and which are not, but generally i think it is fair to say that it is an area full of extreme subjectivity.

Until of course we (presumably) one day find a way to measure intelligence in non-verbally communicative animals. But the 'code' required would be different for every animal group and is way way way beyond us at the moment i would say. Also, being able to define 'intelligence' itself into a quantitative element is a difficult enough task on its own!

(posted in Research and Careers)

As a PhD student i work 67- just for the record! Plus additional hours for demonstrating for classes, working at the Sedgwick Museum in Cambridge and sporadic field trips. It is a demanding profession but one that is well worth it if you love what you do!

As i work on sharks i get hundreds of questions about Great Whites in the UK and the simple honest answer is that the conditions in the UK are perfect for Great Whites (always have been- nothing to do with global warming) and although there are theories, shark experts really don't know for sure why they aren't resident here. We have some of Europes largest seal populations including Grey seals that reach similar sizes to the fur seals in South Africa for example plus other pelagic sharks to feed on (another favourite of the Great White) such as the Thresher, the Mako and the Porbeagle (there are in fact as many as 40 shark species that DO visit our waters). However, whatever their reasons for not coming to visit the UK, they are not resident here and are unlikely to be drawn here by the affects of global warming as the conditions are already right for them.

The reason that some sharks are fossilised whole whereas most are just reduced to teeth is to do with how rapidly the animal was buried. All sharks that have their body preserved have been buried extremely quickly meaning that the carcass was not disarticulated and the soft parts were not decayed. As a result, any shark that is preserved in this way is flattened. Shark vertebrae are commonly fossilised as the cartilage in the spine is made of slightly harder materials than that of the rest of the skeleton. However they are nearly always found disassociated from each other unless they are part of a whole skeleton that has been fossilised in the way just described. Also dermal denticles (small 'scales' on the skin that give sharks that rough texture) are readily preserved but they are so tiny that you have to be very patient to find them, and are subsequently not often recovered. Under a microscope, a lot of them look just like teeth and are frequently misidentified!

(posted in Fishes (Including Sharks))

Another phenomena that adds to this fearsome look is that Great White sharks thrust their jaws out from their natural position when they bite their prey. This adds to the bloody, gorey impression that the teeth and jaws have in so many photographs.

Another thing worth mentioning to do with photography of Great Whites is that the tip of the snout of a Great White is stuffed full of nerves and sensitive receptors. People who go cage diving etc have discovered that by touching the nose of the shark it stimulates the receptors so much that the shark rears its head up out of the water and opens its mouth really wide. This is when the shark is most commonly photographed- or these are the pictures that are most commonly published at least. What the pictures don't show is that the shark then sinks back down into the water without attempting any form of attack on its protagonist. It is not known whether this strange behaviour is a response to pain caused by touching them in this way or whether it is for some other unknown reason. But either way it is now illegal for tour guides to touch the Great Whites noses to provoke this reaction.

But of course- a) that doesn't stop everyone even though it should and b) hundreds of photographs are in existence that were taken before it was banned. If you look at any textbook on sharks or Great Whites in particular, when the jaws are in their normal relaxed position. they do not look nearly as bloody. It is all about photo timing and the portrayal of the sharks sporadic ability to look ferocious.

(posted in Fishes (Including Sharks))

As much as the previous answers were far more entertaining as resident shark expert i feel the need to be pedantic! The actual number of modern shark species is somewhat higher than advertised. There are over 800 species of Elasmobranchii (the Sub-Class that includes both the batoids and sharks) 463 of which are sharks and 337 of which are batoids (the groups that consist of rays and skates). Then there are the fossil sharks and rays that bring the number of species up to way over 1000!

(posted in Fishes (Including Sharks))

Although no study has been done on menstruating women, the finely tuned senses of a pelagic shark such as the great White (used as an example as it is the species most often associated with shark bites) can smell a drop of blood from over a kilometer away. In my eyes it is therefore quite logical to believe that sharks are more likely to be attracted to menstruating women but two points should be raised here. First is that enough of the womens blood would have to be free to reach the outside of the body which is unlikely unless she is in heavy flow and has insufficient 'protection' (too light a tampon for example). Secondly, just because the shark is attracted to the female does NOT mean automatically that it will attempt a bite. It depends entirely upon whether the shark thinks that the women has a high enough nutritional value to be worth eating which in fact- humans do not. It is uncertain as to what provokes a shark to bite a human though there are many theories. 1) They mistake the human for it's normal prey- it is thought that to a shark a man/woman on a surfboard may look like a seal from below. 2) Sharks do not have hands with which to investigate an object. The sea is the sharks home, they are both territorial and curious. If a foreign object, such as a human, is in its home it is very possible that the shark bites to found out what the human is (some of the sharks most sensitive receptors are in the roof of its mouth) or that it is being territorial. Unfortunately for humans- they are not built to cope with even a gentle investigatory bite from a 4-5 m shark. 3) it may just be a case of 'fair game'. Every human ever bitten by a shark in the wild has been in the sharks natural environment. Humans are not aquatic, we are terrestrial. If we invade the sharks home- why shouldn't they think of us as prey?