What is the basis for all the large length estimates for Spinosaurus?

[andrewsaurus rex]

The recent discoveries of Spinosaurus made in the last several years all have length estimates in the mid 30 foot range.  Yet length estimates for Spinosaurus are still in the 45 to 49 foot range.  Is that just because of the one skull, destroyed during WWII that no longer exists?

To my knowledge no Spinosaurus remains have been found that are anywhere near the 45+ foot size and since that one skull no longer exists for examination, i think the maximum size for Spinosaurus needs to be rethought.

[MLMjp]

The MSNM v4047 snout, currently assigned to Spinosaurus, and we still have it.



There is also a lower jaw fragment, NHMUK VP 16421, which is also quite big.

These two pieces are the basis for the larger estimates of Spinosaurus.

[andrewsaurus rex]

thanks for that.

I still have a very hard time believing that Spinosaurus was just a wader.  I know all the arguments but the comparisons to a Heron or bear don't hold water (pun intended).  Herons have LONG legs, which of course is what an animal that wades would greatly benefit from as it allows access to more prey.  Spino has stubby legs, which are illogical to evolve for a wading animal. 

And the analogy to bears...well, bears eat everything, not just fish,  So fish are not a main diet item for them but just one of several diet items.  Spino's main source of food would be fish.  For such a large animal to be limited to wading along the shore, where most of the fish would be small makes no sense.  Scavenging along the shore would not be enough to supplement, again, especially for such a large animal.

My feeling still is that it paddled around on the surface of the water, where its buoyancy would be useful and its sail could keep it warm from the sunlight shining on it and then it would do sudden dives when prey was spotted.  It may have also waded but to live exclusively on wading, just does not add up for big Spinosaurus.

[Ajax88]

Spinosaurus makes almost no biomechanical sense as an aquatic pursuit predator. It was likely primarily terrestrial.

[Torvosaurus]

Spinosaurus makes almost no biomechanical sense as an aquatic pursuit predator. It was likely primarily terrestrial.

Doesn't Ibrahim also agree that it was likely a terrestrial predator that fished from the shore, like a heron? I know he now agrees that walking on all fours was facultative rather than obligate, but I can't find anything that supports how he feels about feeding methods. Regardless, plenty of paleontologists agree that it didn't swim after its prey and was a wader.

Torvo

[Ajax88]

Spinosaurus makes almost no biomechanical sense as an aquatic pursuit predator. It was likely primarily terrestrial.

Doesn't Ibrahim also agree that it was likely a terrestrial predator that fished from the shore, like a heron? I know he now agrees that walking on all fours was facultative rather than obligate, but I can't find anything that supports how he feels about feeding methods. Regardless, plenty of paleontologists agree that it didn't swim after its prey and was a wader.

Torvo

Not sure what hos current interpretation is, but terrestrial wader is still IMO the only feasible niche for Spinosaurus. Nothing aquatic would be slower or less agile than a swimming Spinosaurus, which would make active aquatic pursuit pretty useless.

[Cretaceous Crab]

We really don't know for certain. Look at pandas. Their jaws and teeth aren't dissimilar to that of true bears, yet they predominantly subsist on bamboo. Go figure.

Also, while we do have significant fossil evidence of the fauna that lived with Spino, but it is still only a glimpse. We don't have the full picture.

All that said, we do know Spino wasn't a pursuit swimmer, and with those shortened hind legs and extra weight (sail), it wasn't a runner either. Living at and around the water's edge gave it the best ecological advantage to feed in both realms. I tend to think that despite all its specialized features, Spino was ironically an opportunist that would snap up anything it could: fish, small plesiosaurs & other aquatic reptiles, smaller dinos, pterasaurs...they were all on the menu.

[andrewsaurus rex]

but would small plesiosaurs, decent sized fish etc come within reach of a wading Spinosaurus?  Remember, its legs are really short.  It could only wade out to about 5 or 6 feet of water before it would start to float and then lose a lot of agility, according to the research.  Even before it started to float it would have it's quickness and agility hampered by the deep water.  Anyone who has ever waded into thigh high water knows it slow going to move....not easy to catch a fish for sure.

And Spinos were huge......up to 45 feet or more according to calculations and evidence.  A big animal like that needs to be more than an opportunistic feeder.  It needs to be able to actively hunt decent sized prey.

The shape of its mouth and teeth certainly look best suited for aquatic animals.  Taking down large terrestrial animals would be a strain on those slender jawbones.  It's a puzzle for sure...at least for me.  I am far from convinced it  was a shoreline wader, despite that seemingly being the only niche it could succeed in.

[Torvosaurus]

Onchopristis may have been seasonal, depending on its breeding cycle to bring it upriver. But there were other species: Mawsonia, Neoceratodus, various four to six foot lungfish, maybe Paranogmius. It may have only been able to wade out 5 or 6 feet, but its body extended out of the water maybe 15 to 20 feet, greatly extending it's reach. I'm sure it also ate young and small crocodylomorphs. I'd have to research the exact climate, but digging up lungfish during the dry season if there was one, once the pools with fish dried up. It was likely an ambush predator for terrestrial species and likely hunted small to medium dinosaurs. I'm guessing there was quite a bit of food for Spinosaurus out there without it being a swimming aquatic predator.

Torvo

[Protopatch]

Spinosaurus makes almost no biomechanical sense as an aquatic pursuit predator. It was likely primarily terrestrial.

Doesn't Ibrahim also agree that it was likely a terrestrial predator that fished from the shore, like a heron? I know he now agrees that walking on all fours was facultative rather than obligate, but I can't find anything that supports how he feels about feeding methods. Regardless, plenty of paleontologists agree that it didn't swim after its prey and was a wader.

Torvo

Talking of Nizar Ibrahim, I've noticed that he has lately become more talkative on social networks where he wasn't initially so much active. I mean, Instagram and LinkedIn among other things.
He should probably prepare himself either for the expected groundbreaking "revelations of the year" on Spino or for the WWD2's promotion or for both ?

[Cretaceous Crab]

but would small plesiosaurs, decent sized fish etc come within reach of a wading Spinosaurus?  Remember, its legs are really short.  It could only wade out to about 5 or 6 feet of water before it would start to float and then lose a lot of agility, according to the research.  Even before it started to float it would have it's quickness and agility hampered by the deep water.  Anyone who has ever waded into thigh high water knows it slow going to move....not easy to catch a fish for sure.

And Spinos were huge......up to 45 feet or more according to calculations and evidence.  A big animal like that needs to be more than an opportunistic feeder.  It needs to be able to actively hunt decent sized prey.

The shape of its mouth and teeth certainly look best suited for aquatic animals.  Taking down large terrestrial animals would be a strain on those slender jawbones.  It's a puzzle for sure...at least for me.  I am far from convinced it was a shoreline wader, despite that seemingly being the only niche it could succeed in.

There are theories that its size was perhaps an advantage in this regard. The animal is so massive that if it remained motionless long enough, the surrounding aquatic fauna would fail to distinguish it from the environment...until it was too late. Its body would cast a huge shadow, creating a shaded spot to draw fish in.

Remember that most of the action may only include the neck and jaws suddenly darting forward to strike, not the entire body lunging. Another thing to keep in mind with the "heron" approach is that many shore birds, like bitterns and small heron species, do not all have immensely long legs. Some of them practically hug their bodies to the ground, which move very little when they strike.

There is also the subject of tool use. We have evidence that both crocodilians and birds (the closest groups to dinos) employ tools. I don't think it is outside the realm of possibility. Along a similar vein is the possibility of lures, like an alligator snapping turtle using its pink tongue as a decoy to draw prey in.

We also do not have a lot of information on the forelimbs, mostly inferring what we know from related genera.

Given the studies done on the biomechanics of its skull and jaws, as well as its overall physiology, evidence indicates that Spinosaurus:

• was not built for chasing prey on land; too heavy for those short legs.
• was not built for chasing prey in the water; i.e. too much drag and not flexible enough.
• jaws were not built for "crushing" bites on large prey, but rather quick, snapping up of smaller prey.

So my conclusions are that Spinosaurus could not rely on pursuing prey; it had to draw prey in. And likewise, it only had to get prey within reach of those jaws so it could lunge suddenly and snap it up. We know that herons and crocs are fairly patient, so I can believe an adult Spino could stay in one spot and remain nearly motionless for a while waiting for something to come close enough to strike.

As far as being sustained enough, many large predators fill their figurative plates with small prey, with larger victims being less frequent. There's also scavenging, or even downright bullying smaller carnivores to steal their kills. I would imagine that all but the largest Carcharodontids and Bahariasaurus would not push the issue with an adult Spino.

Size doesn't always matter; sometimes, a fierce attitude can go a long way. Even the diminutive weasel or stoat is aggressive and tenacious enough to keep larger animals at a distance. Honey badgers and wolverines are fierce enough to hold their own against leopards, hyenas, lions, wolf packs and bears, respectively.

Spino could also have added other fauna, such as invertebrates to the menu; crustaceans, cephalopods, etc. things that are harder to find in the fossil record, but no doubt existed in this environment.

This is what I absolutely love about Spinosaurus. Every new thing we learn about it leads to more mysteries. But the fact of the matter is that it still somehow existed and managed to maintain a huge size along other predators in the same ecosystem.

[Protopatch]

This is an interesting theory @Cretaceous Crab
However, I'm wondering : if Spinosaurus was more an "ambush predator" rather than a "pursuit predator", it probably had to draw a phenomenal amount of preys in, to keep up with its daily needs of calories inherent in its outstanding size.

[Ajax88]

This is an interesting theory @Cretaceous Crab
However, I'm wondering : if Spinosaurus was more an "ambush predator" rather than a "pursuit predator", it probably had to draw a phenomenal amount of preys in, to keep up with its daily needs of calories inherent in its outstanding size.

Big herons eat dozens of prey items a day that are minnow to frog sized. I see nothing wrong with Spino taking dozens of 50 to 100lb prey animals per day in the same way.

[andrewsaurus rex]

but again, would their be dozens of 50 to 100 pound fish come within reach of Spinosaurus every day given it's inability to wade out very far because of its short legs?  I think it would have a better chance going out deeper, floating on the surface, motionless, picking off fish that swam within reach.  Perhaps, as suggested above, using some kind of lure.  This would give it access to more and larger prey.

The cooling effect of long hours in the water being offset by the warming sun on its sail.

[stargatedalek]

Spinosaurus makes almost no biomechanical sense as an aquatic pursuit predator. It was likely primarily terrestrial.

No sense based on what? It has webbed hind limbs, a tail with a vertical paddle surface, a long jaw with conical teeth, and higher density bones than it's relatives which would make diving easier. To say nothing of the isotope studies which, if I am recalling correctly (I believe this was pre-2014 remains), estimated the head was primarily above water and the body below.

The idea that it was an aquatic ambush predator hunting terrestrial dinosaurs like a crocodile is very silly if you ask me, as it simply does not display the adaptations we would expect for an ambush predator hunting large prey like that (crushing jaws, bulky frame, strong limbs for short bursts of speed exiting water, etc.).

Same for being a wading predator. Why would a wading predator have the body plan of a cormorant? Sure maybe it sat in shallow water until fish gathered, but is that even a "wading" predator anymore? And that still doesn't account for the tail or webbed feet that clearly indicate aquatic movement? If it moved aquatically outside of hunting... why not just hunt floating at the surface instead of sitting in the shallows? What possible benefit would that offer?

All of this is also ignoring something very important. We have (last I knew) less than 10 specimens attributable to Spinosaurus, even if we count "Sigilmassasaurus" and "Oxalaia", only 2 of which (as mentioned above) seem to be adults. For a species from such a small number of remains to be known almost entirely from juveniles and even a baby, well it paints a rather clear picture that this was a nursery environment. Which makes sense given these were not inland wetlands at the time but rather coastal mangrove forests.

Thus to me it seems a rather bold assumption to even presume Spinosaurus was a freshwater animal as opposed to a marine or coastal one, and so many of the theories about its behaviour hinge on that, which I believe to be a huge misconception about its habitat.

I believe the most obvious anatomical analogues are cormorants, loons, and auks, having similar adaptations and being primarily calm surface swimmers but capable of diving in short bursts to hunt. Spinosaurus could have hunted in a similar way, or more akin to pelicans, herding prey and scooping it directly from the surface, diving only as needed. Heck perhaps we should branch our thinking out even further from reptilian archetypes? What if it hunted like whale sharks sometimes do? A slow swimmer herding large shoals of fish together, that rested and travelled at the waters surface for most of the time.

As out-there as those may sounds, they don't conflict with the animals known anatomy like arguing it was terrestrial, crocodile styled ambushing, or wading most certainly do.

[andrewsaurus rex]

yes i tend to agree. An ambush predator with a big goofy sail on its back would starve; it would be seen from a mile away.  And a wading predator with stubby legs would struggle to find food....evolution would have favoured selection for long legs.

I know the tail was supposedly used for display rather than swimming, but why not both?  Regardless of why it originally evolved.

I still can't buy into the wading theory and agree that its body plan is best suited for paddling around on the surface, in deep water, picking off or luring fish all day long.

if it walks like a duck and quacks like a duck, its probably a duck.

[Shane]

I'm not an expert on the issue, but wouldn't the fact that the limbs are reduced in size, especially the hind limbs, make wading an extremely unlikely option? Waders typically have long thin legs in extant animals. And given that the back feet are webbed, wouldn't it being SOME kind of swimmer be the most likely option? Especially with a tail like that.

[PumperKrickel]

Ambush predator?
Swimmer?
Wader?

Nah, my boy was a flier.

[Shane]

Can't argue with that.

[andrewsaurus rex]

lucid thinking at last.