Ecology And Spinosaurus

[ashcraft]

What kind of environmental conditions must have existed to support such a huge apex predator in a population density high enough to maintain a species in what I assume is a fairly small area? I can't think of anything analogous in a modern environment, except perhaps saltwater crocs. The fish density (assuming they fed on such), must have been tremendous, implying upwellings? Cold water? Spinosaurus being cold blooded (hate the term) in order for population densities to be high enough for ample population size?

Can anybody educate me on such things? Are my perceptions of the area that spinosaurus occupied way too small?

Brent Ashcraft

[Ludwigia]

http://de.wikipedia.org/wiki/Spinosaurus#Pal.C3.A4o.C3.B6kologie_und_Ern.C3.A4hrung

[painshill]

Not such a small area. This map comes from the University of Chicago website:

[Auspex]

They do seem to have been prodigious producers of teeth, but verifiable skeletal remains are super rare.

Too, the span of time represented in the deposits can skew the apparent population density.

[John K]

This was the subject of a radio story I listened to on the way home last night

"Crocodile Meets Godzilla — A Swimming Dino Bigger Than T. Rex"

http://www.npr.org/2014/09/11/347488364/crocodile-meets-godzilla-a-swimming-dino-bigger-than-t-rex

" "Big predatory dinosaurs, giant fish, crocodile-like predators. In fact, the place was really pretty predator-heavy, so I call it the most dangerous place in the history of our planet," Sereno says."

and this; pretty fascinating:

"In fact, spinosaurus bones were first discovered 100 years ago, by a German scientist in Egypt. The find puzzled researchers. "A lot of the skeleton was missing," explains Thomas Holtz, a paleontologist at the University of Maryland. "It was sort of a mystery dinosaur, and the mystery was furthered when all the specimens were destroyed during World War II.""

Edited September 12, 2014 by John K

[ashcraft]

That area just seems pretty small for such a large predator, especially considered that it was probably a specialist feeder restricted to coastal areas, assuming a warm blooded lifestyle, where predator densities would have to be extremely low in a typical environment to minimize over-feeding.

Most environments only support 3-4 trophic levels due to lack of energy entering at the bottom level. In highly productive environments more trophic levels can be added, like on coral reefs.

You don't find tigers on Komodo Island, not because they can't get there, but because the island can't support a breeding population. Similarly, there is a population of lions that live in a volcanic crater in Africa that can only support one pride due to the size of the crater. The only access is through a very rough trail, so new lions rarely enter. This scenario leads to inbreeding and occasional complete extirpation of the pride, until new lions wander in.

It seems to my uneducated line of thought that for spinosaurus to have existed as such, it may have been cold blooded, similar to Komodo dragon's, where much of their energy is solar, allowing for more individuals in a limited area, or the area was extremely productive, possibly indicating an upwelling, which makes that area of the ocean extremely productive (Gallapogos Islands come to mind).

It could also be that I am completely wrong, maybe the area is much greater then perceived, or they were more generalist feeders, or etc.

The answers could have been in the wiki article, unfortunately I only speak Red-Neck, although I understand English and Mer-can. German is way past my capabilities.

Brent Ashcraft

[non-remanié]

You have to refrain from looking at the issue in terms of a fossil market place where on the surface it sure seems like Spinosaurus teeth are incredibly common. What undoubtedly could be said about the situation is that there is a huge collecting bias due to the market value of dinosaur fossils and impoverished local enonomy that produce the abundancy of fossils for the global fossil market. I am not going to claim to know specifics, but the same discussions have been had about the Moroccan shark teeth deposits, especially considering large Otodus teeth; that Otodus must have been bigger and gotten larger in the ancient seas of Morocco. Those deposits are inherently different than many other fossil shark tooth sites from the same age around the world. Trangressive conditions in a confined geographic setting; in combination with massive die-offs likely caused by cyclical algal blooms seem to have produced dense and widespread marine bonebeds. The local collector economy and phosphate mining operations give us a perfect window into those deposits and past ages. But the density of those fossil bonebeds is in no way unprecedented in the fossil world, look no further than the well known Shark Tooth Hill site, for example, which is similarly quarried systematically for the global market. The main reason prices are so much higher for fossils from there is the cost of the US land and labor involved in the operation. And perhaps the bonebed isnt quite as widespread (not sure). In relation to Spinosaurus we have a very near-shore or estuarine deposit, which is exactly what is needed to preserve this semi-aquatic predator who lived in that environment. I bet if you look at the fossil record you will find that many similar deposits tend to be thicker and therefore more unlikely to find such a densly packed bonebed in them. Its very tempting to make conclusions based on the simple seeming abundancy of Spinosaurus teeth, but that idea needs to be considered in depth before going anywhere further with the discussion. Dinosaur fossils are considered very rare on the Atlantic Coastal Plain. But what I have seen is that, what is actually rare is right type of deposit to preserve these remains IN the few instances where there is an estuarine transgressive deposit that is exposed enough to be collected (transgressive conditions ensure thinner layers and more likely bonebed formation) it seems that without fail, dinosaur fossils are fairly plentiful. Regional depositional patterns from the late Cretaceous in combination with widespread thick Pleistocene layers on the East Coast are the main reasons for that.

Edited September 12, 2014 by non-remanié

[Auspex]

A couple thoughts:

>The animal's mass may have mitigated the need for true energy-intensive endothermic temperature regulation. (Was the fin a solar panel/heat radiator?)

>Being semi-marine, the animal had the benefit of a huge, self-replenishing food source.

[painshill]

That area just seems pretty small for such a large predator...

The distribution on the map I posted covers an appromimately oval area that's almost 2,000 miles by 1,000 miles... around a third the size of the entire United States! It's also likely that the fossil finds don't reflect the full extent of the territory which, at the time, had an undulating coastline enclosing a vast swampland and shallow estuarine environment.

[ashcraft]

That seems like a large area, 2,000,000 square miles. However, a grizzly bear has a home range of 1500 square miles, which would account for only1300 individuals alive at any one time. That seems a little small to me for a healthy continuing population? That is assuming that the spinosaurus was extremely territorial, and all of the habitat was ideal.

I am only speculating, I would love to hear why I am incorrect.

Brent Ashcraft

[non-remanié]

The "abundance" of fossil teeth in the deposits could be an accumulation on the scale of 10k to 100k years. I dont know if there is only bed that produces these teeth, but that amount of time would just cover that one layer. Using your polar bear numbers, that is 13,000,000 apex predators in just that area. As Painshill notes, most of their range of territory probably has no fossil record, of if there is one, its buried in the ocean or under 100s or 1000s of meters of sediment in nearby countries. My friend was just in SD on a private ranch dig. One conclusion he told me is that Trex teeth are not really that rare. Its all about exposure and time and effort. They have to dig very slowly or else something like a Trex tooth would be absolutely destroyed. They had one small gulley of exposure to dig in. If the 1000s of square miles of Hell Creek exposures were exposed better and quarried more extensively and quickly....

As for your comments on the possible upwelling and productivity.... that is probably true. The Phosphate areas fossil richness in that entire region show that the seas were quite rich and an active area of upwellling. I just am not sure if that extends back further in time to the Kem Kem beds.

That seems like a large area, 2,000,000 square miles. However, a grizzly bear has a home range of 1500 square miles, which would account for only1300 individuals alive at any one time. That seems a little small to me for a healthy continuing population? That is assuming that the spinosaurus was extremely territorial, and all of the habitat was ideal.

I am only speculating, I would love to hear why I am incorrect.

Brent Ashcraft

[squali]

well if we want our theoretical population to perpetuate there needs to be 26,000,000 mature animals plus juveniles

[Auspex]

Again, a large coastal area can supply an amount of food all out of proportion to the same land-locked acreage; prey base might not have been the most limiting factor.

[Opisthotriton]

To put the map Painshill posted (http://www.thefossilforum.com/uploads/monthly_09_2014/post-6208-0-07555400-1410522281.jpg) into perspective:

http://blogs.worldwatch.org/nourishingtheplanet/wp-content/uploads/2011/03/Africa_map_National_Public_Radio_NPR_Krulwich_Wonders.bmp

The entire north coast of Africa is a huge area. Not at all comparable to the Komodo Islands or a single crater. If Africa's not big enough for a coastal animal, where would be?

[ashcraft]

So maybe they existed similar to ocean going predator mammals such as seals and killer whales, maybe in pods? Large concentrations of individuals in small areas where easy access to prey allows for such conditions? Not a way I normally would think of dinosaurs, but should.

[Stocksdale]

Area would also have a lot of shallow coastal islands, channels and peninsulas.

Image of mid-cretaceous Europe and Africa.

Edited September 12, 2014 by Stocksdale

[Auspex]

Until very recently, one of the things I knew to be "true" about dinosaurs it that they never took to the sky, and they never took to the oceans. Well, this one was, it seems, at least partly aquatic. It's almost a relief to see the near-shore environment exploited by this clade (and a puzzlement that more of them didn't)!

[Stocksdale]

It is a mystery why there are so many teeth being found but skeletons are so extremely rare.

Edited September 12, 2014 by Stocksdale

[painshill]

James Farlow et al. at Purdue University explored the numbers and the logic behind the calculation of population densities in: “On the rareness of big fierce animals: speculations about the body sizes, population densities and geographic ranges of predatory mammals and large carnivorous dinosaurs”, linked below.

http://earth.geology.yale.edu/~ajs/1993/11.1993.06Farlow.pdf

Drawing on the work of Owen-Smith (1988) for example – albeit for a terrestrial environment – he calculated a maximum likely herbivore density of 10 animals (of average 2,000 Kg body mass, suitably sized as dinosaur prey) per square kilometre and a dinosaur carnivore predator density of 0.2 animals per square kilometre. For larger prey (average body mass of 5,000 Kg), the predator density drops to 0.08 animals per square kilometre.

As Colinvaux said: “It’s lonely at the top of the food chain”, but for a large territory that could still represent a substantial number of animals.

I didn’t actually say that the territory was 2 million square miles since I approximated it as an oval... so more like 1.5 million square miles (3.9 million square kilometers) but nevertheless a large territory. It also only broadly represents the mapped area for Spinosaurus fossils – not the likely potential habitat in total. Nevertheless (accepting all the approximations, limitations, arguments against direct comparability and speculation) that could still mean an area that size could have supported something in the region of say 300,000 – 700,000 “big fierce animals” as Farlow puts it (at any moment in time).

You then need to factor in the amount of that area which was actually habitable, offset that against the fact the deeper water areas uninhabitable by Spinosaurus were nevertheless inhabitable to its (mobile) prey. We’ll never know the answer, but I don’t see any reason to suppose that Spinosaurus numbers were small.

[Stocksdale]

So, are spinosaurus teeth really that more common than other dinosaur teeth or are they just being pulled from the ground at a faster pace than T-rex and others.

[Stocksdale]

Related to the ecology..... I'd heard that the sail may have been like a camels hump instead of the sail that most picture. Some have dismissed this since fat and water storage would not be necessary in a swampy area. However I wonder, if it was living in salt water, would a hump be helpful since the water would be undrinkable to the fresh-water creature.

[Ludwigia]

The answers could have been in the wiki article, unfortunately I only speak Red-Neck, although I understand English and Mer-can. German is way past my capabilities.

Brent Ashcraft

Oooooooops! Sorry bout dat! I guess it was getting late as I posted that. Actually I meant to link it to Canajun, eh?

[ashcraft]

James Farlow et al. at Purdue University explored the numbers and the logic behind the calculation of population densities in: On the rareness of big fierce animals: speculations about the body sizes, population densities and geographic ranges of predatory mammals and large carnivorous dinosaurs, linked below.

http://earth.geology.yale.edu/~ajs/1993/11.1993.06Farlow.pdf

Drawing on the work of Owen-Smith (1988) for example albeit for a terrestrial environment he calculated a maximum likely herbivore density of 10 animals (of average 2,000 Kg body mass, suitably sized as dinosaur prey) per square kilometre and a dinosaur carnivore predator density of 0.2 animals per square kilometre. For larger prey (average body mass of 5,000 Kg), the predator density drops to 0.08 animals per square kilometre.

Thanks for the article, very interesting read. Wish I had time to read and follow all of these journal articles that interest me, but alas, high school is not set up to deal with true scientific research.

Juvenile dinos eating different prey then parents was a connection I hadn't made, which certainly expands the energy base of their trophic level. I was familiar with the concept in animals that morph, like insects and amphibians, which removes competition between the parents and their offspring. Tough to think "outside the box".

Good discussion, thanks for the input. Reminds me that education isn't always about technique, something lost in my school at the moment.

Brent Ashcraft

Edited September 13, 2014 by ashcraft

[Koss1959]

A new spinosaurus fossil has been unearthed. The article gives very little information about the new fossil. It would be nice if it gave us an approximation of completeness.

http://www.bbc.co.uk/news/science-environment-29143096

According to other articles, it is now believed it walked on all four legs. Making it the only known carnivorous dinosaur to do so. I always thought it looked awkward in an upright pose.

Edited September 14, 2014 by Koss1959

[ashcraft]

A new spinosaurus fossil has been unearthed. The article gives very little information about the new fossil. It would be nice if it gave us an approximation of completeness. http://www.bbc.co.uk/news/science-environment-29143096

According to other articles, it is now believed it walked on all four legs. Making it the only known carnivorous dinosaur to do so. I always thought it looked awkward in an upright pose.

Interesting, maybe the "sail" was an anchor point for muscles, similar to a "breastbone" on a bird, allowing for powerful swimming strokes? Doesn't really look structurally robust enough to my untrained eye. Easy enough to see if you have a complete skeleton. Just trying to get "outside the box".

Brent Ashcraft