Spinosaurs as macropredators

[dinosauria101]

So as some of us may know, river dolphins are able to seriously kill and injure sizable opponents with jaws that look like this (very small teeth, long, thin, and seemingly weak)

en.wikipedia.org/wiki/Amazon_river_dolphin

Later, it was shown that males were larger than females and are documented wielding an aggressive sexual behavior in the wild and in captivity. Males often have a significant degree of damage in the dorsal, caudal, and pectoral fins as well as the blowhole due to bites and abrasions, in addition to the numerous secondary teeth-raking scars. This suggests fierce competition for access to females, with a polygynous mating system, though polyandry and promiscuity cannot be excluded.

editors.eol.org/eoearth/wiki/Amazon_River_dolphin

Botos do not appear to establish a social hierarchy through aggression in captivity, but violent acts are not uncommon and have even resulted in the death of some individuals.
However, males are now known to be larger than females, and very aggressive sexual behavior in males has been observed. Some authors have observed hostility between pink botos in the wild, while others have noted extremely aggressive activity during copulation in captivity. Males also have a higher degree of damaged fins, flukes, and blowholes due to biting and abrasion, in addition to more abundant scarring due to tooth-raking. This evidence suggests that there may be intense competition for access to females.

www.nationalgeographic.com/magazine/2009/06/dolphins/

The males beat the hell out of each other," says Martin. "They are brutal. They can snap each other's jaws, tails, flippers, lacerate blowholes. The large males are literally covered with scar tissue

Spinosaurs have larger teeth in comparison, more robust snouts, and some of the earlier members even had serrations still. On top of that, they had immensely powerful arms and MASSIVE claws. What does everyone think about them preying on sizable animals?
I think they would have been OK at it if they had to

[Infinity Blade]

"sizable animals". You mean like, animals as big as themselves or just any animal big in absolute terms? I don't think anyone denies they could have done the latter. I'm sure spinosaurids could and did hunt animals large in absolute terms but still substantially smaller than them.

As for animals as big as themselves: note that just because they theoretically could seriously harm something that large wouldn't necessarily mean they regularly targeted such animals as prey. I don't know a whole lot about Amazon river dolphins, but, at least from what I can gather, they don't seem to actually target similarly large animals as prey. When they do seriously injure, possibly kill, animals as big as themselves (namely each other), it's for non-predatory reasons.

[dinosauria101]

Yeah, I agree with you on that. If they were going to hunt very big, mean, powerful animals on a regular basis it would make more sense for tyrannosaur or carnosaur like jaws, not spinosaur jaws.
However, I don't necessarily think they would be BAD at killing or at least injuring similar sized or larger animals, just that they would not frequently do so.

[elosha11]

In general, I think your analogy to river dolphins relatively routine mating/territorial disputes is a bridge too far in proving Spinosaurs, a vastly different species, was a macropredator.

[creature386]

Even humans can kill each other bare-fisted in intraspecific conflict, that doesn't mean we are good hunters without our toys.
Not saying spinosaurids couldn't have killed similarly sized animals when it really came down to it, but your dolphin analogy doesn't prove as much as you think it does.

[dinosauria101]

Elosha and creature, you both do have good points; this may not be on the same level as, say, big carnosaurs.
I just posted it because spinosaurs are probably not as poorly armed as many think.