[thedoc (OP)]

Fossilised remains have revealed that ancient marine-dwelling dinosaurs and turtles used the pigment melanin for camouflage and keeping warm

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[Professor Mega-Mind]

Not actually dinos , but earlier forms such as archosaurs .  They were also warmblooded . As predators , their colorations would have needed to be within certain parameters .  Diving pursuers would have been overall dark , like otters or seals , with some light color underneath  for ambushing prey from above .  Sharks and birds of prey use this camo. scheme also .  Variations include stripes , patches , & rings .  Black , brown , gray , & white are the basic colors .
 Otay , you well done now !   P.M.

[Professor Mega-Mind]

Exception : Spinosaurus
These would have been a solid tan color , the better to blend into their preferred habitat ; sandy dunes .  N. Africa 100mya was a flooded , riverine environment , with modest vegetation , but sand & dunes everywhere .  The Spinosaurus' were not marine lizards , they lived more like otters , or perhaps , fishing cats .  Like those , they hunted primarily in shallow water , using both shore-born ambush tactics , and water-born lie in wait tactics .  The thin-hump cast a very large shadow , which ( as with crocodiles ) attracted fish , seeking to avoid the tropical sun .  Spino.s long neck & head were very good at suddenly snapping up smaller fish .  Larger fish would have been grabbed midsection  ( to avoid severe thrashing forces ) and hoisted onto land for dissection .  Lifting & carrying large , heavy fish is why Spino.s jaw had a crook in it .  It is also why it's legs were large  ( though this also helped it to ambush & chase prey , especially in river-deep water ) .  Spino.s sandy coloration , and sand-dune imitating hump were actually needed .  They helped camouflage it for ambush , and helped hide it from competing predators as well .  These competitors would attack opportunistically , much as sparrows mob crows . 
Okay , old story over .      P.M.

[Professor Mega-Mind]

Note on Spinosaurus .
These had a smooth surface (think penguin ) , hydrodynamic shape (think otter ) , and smooth & thin-lipped face ( think stretch seal ) .  The eyes were also very seal or dog-like .  The bulge of the eyes is why it needed that protuberance between them .  It helped keep flopping fish fins off of Spino.s eyes .
Alright , 'nuff said .      P.M.

[Professor Mega-Mind]

.....The Exceptional Basilosaurus
This marine monster lived in an atypical manner , distinct from that of most giant marine predators .  The primitive whale was a shallow water hunter of fish , birds , and smaller aquatic mammals .  This put special emphasis on coloration and camouflage for the 70 ft. long beast . Drawing upon appearances of many land , and sea-based shallow-water hunters , it becomes apparent that Basilosaurus would have looked APPROXIMATELY like so : An overall grey appearance , much lighter on the underside , much darker on the topside .  The face had a masked appearance , reminiscent of a raccoon's .  The under-skin was covered with hollow rosettes of all sizes , a carpet of tiny ones , with a smaller number of much larger ones easily visible .  When viewed from beneath , the light skin would resemble the sea surface , with a number of jellyfish floating beneath it . The outline of the head was broken up by the "mask" .  When viewed from the front or side , the same applied .  When viewed from above the whale was almost invisible , with no rosettes apparent anywhere on it's top-skin.
The change from dark to light was more gradual than that of a killer whale , it appeared to be caused by a sharply increased density of the tiniest rosettes . 
Apparently , Basilosaurus' camouflaged appearance fit his preferred habitat very well .
P.M.

[Bored chemist]

These would have been a solid tan color , the better to blend into their preferred habitat ; sandy dunes

Is there any evidence that their predators or prey had colour vision?

[Professor Mega-Mind]

Convergent Evolution demands it , their descendants , the birds , have it , and it has been revealed by scientific study , that camouflage works even in a low/no color environment .  In otherwords , it was a tool/advantage they could not afford to lack .
P.M.

[Colin2B]

Convergent Evolution demands it ,
P.M.

That’s illogical. Convergent evolution is not a law and can demand nothing.

[Bored chemist]

....  In otherwords , it was a tool/advantage they could not afford to lack .

By that argument, all animals would have colour vision.
But they don't.
So your argument is invalid.

What you should have said was "I don't know". Why didn't you say that?

[Professor Mega-Mind]

First off , Convergent Evolution is married to Nature .  It can demand all kinds of mess , and get it !
Secondly , Nature invests in color-vision when it is worth it .  Not all species give good ROI .
Thirdly , camouflage is everywhere in nature , even colorblind animals use it .
Note-Many species possess partial  colorvision .  Nature invests in it sparingly .
Hmm , seems I know a lot more than you !
P.M.

[Bored chemist]

Hmm , seems I know a lot more than you !

It may seem that way to you.
The rest of us may disagree.
You seem to have got nearly half way to thinking this through.

Nature invests in color-vision when it is worth it .

Do you understand that the same is true of camouflage?

camouflage is everywhere in nature , even colorblind animals use it .

Yes, and the fact that colour blind animals use it proves that the important question about camouflage is whether or not your predators use colour vision.
Simplistically, zebra have (some) colour vision because it's important for them to tell green grass from brown grass, but they have monochrome camouflage because lions have monochrome vision.

Now, since we don't actually know what ate Spinosaurus, we don't know whether or not it needed coloured camo.
So we don't know if it was sand coloured or not.
So you were still wrong to pretend that you did know and asy

These would have been a solid tan color

Speaking of zebra, they live in a largely dusty brown environment.
By your "logic" they should be a solid tan colour.
LOL

[Professor Mega-Mind]

..............Mr. Ass-umptIon .
By your own nose-up logic , zebras also have colorvision in order to tell lions from green foliage .  The zebras themselves are black and white striped in order to present the appearance of a solid mass of light & dark stripes .  This makes it extremely difficult for predators to single out an individual zebra for am bushing and killing .  Many of Africa's animals ARE brown grass or sand colored , including lions .  Spinosaurus would have also been so colored , to hide from prey , predators , or other Spino.s . 
Whoops !  Seems my logic trumps yours again !
P.M.

[Bored chemist]

Seems my logic trumps yours again !

It may seem that way to you.
The rest of us may disagree.
You seem to have got nearly half way to thinking this through.

What would stop Spinosaurus being black + white striped like zebra?.
Or they may have gone for other variations on the theme.
https://en.wikipedia.org/wiki/Disruptive_coloration


You can only assume they are coloured if you assume their predators had colour vision- and you can't know that.
So you are insisting on a guess built on a guess.

Many of Africa's animals ARE brown grass or sand colored

Many  is not the same as "all".

[Professor Mega-Mind]

I can't quite see a herd of Spino.s being hunted , by anything ! I don't see tiger stripes camouflaging them in sandy Africa either .  Last , colored camo. can be quite effective at deceiving color-blind predators and prey .
Good THEORIES are built on pre-existing patterns , relationships , and empirical evidence .  They are typically confirmed by scientific experiment .
In this particular case , brain morphology is as close as we can get to empirical evidence .
Enough grilling !
P.M.

[Bored chemist]

I don't see tiger stripes camouflaging them

That's the point.

However, it remains the case that, as I pointed out earlier, you simply don't know, and you should say so.

[Professor Mega-Mind]

....Theory !
P.

[Bored chemist]

....Theory !
P.

...is not the same as guess.

[jeffreyH]

If the colour of your fur or skin prevents you from being seen and eaten then it is an aid to survival. Therefore, the polka dot blue and orange animals die out. Since they are easy to hunt. To the unthinking this looks like a grand plan and not simply natural selection.

[Professor Mega-Mind]

.......................Tigers .
Why are they orange , white , and black ?  Because in the middle of a forest , to colorblind eyes , they melt right into the shrubbery and trees .
P.M.

[RD]

... the polka dot blue and orange animals die out  ...

Except the poisonous ones , (or those impersonating something which is poisonous).