(02-07-2022, 04:09 AM)JurassicDD Wrote: The fall of the bipedal Spinosaurus

*This image is copyright of its original author

*This image is copyright of its original author
Some current information regarding the issues with Spinosaurus being a functional biped in a detailed journal 
https://www.deviantart.com/battlechampio...-906201392

(06-23-2021, 05:18 AM)DinoFan83 Wrote: Delving a little deeper into things, I've relatively recently come to notice something that's made me raise my eyebrows in regards to the FSAC-KK 11888 volumetric model of 3864.7 litres from Ibrahim et al. (2020), that has a marked effect on the mass estimates for both that specimen and the giant possible adult Spinosaurus.

More specifically, as can be seen here, the new volumetric estimate does not account for an appropriate amount of flesh on the spines. At all.
Making the correction for this would have quite a crucial effect on the mass of the animal - fortunately, there are 2 pre-existing parameters that can help us get the correction right: modern crested chameleons, and SpinoInWonderland's earlier GDI of Spinosaurus with segment masses.

In addition, I have word from SpinoInWonderland about this. He makes a suggestion that Spinosaurus would have proportionally more flesh than the oft-cited crested chameleon because its spines are much thicker and less spaced. That I could not agree more with - it's blatant in the hyperlinked images how well the spines match with his statements.

With these in mind, let's take a look at the flesh in the earlier GDI and the crested chameleon.

One thing is immediately clear - the GDI has far less spine flesh proportionally than the actual crested chameleon does, well under half as much. Considering how the spacing and robusticity of the spines compare, it's clear that using the segment mass of the GDI as-is would produce a major underestimate for the volume of a FSAC-KK 11888 with adequately fleshed spines.

However, no direct parameter exists for how much more fleshed Spinosaurus' spines would be, so bearing in mind that it's almost certainly still an underestimate, I'll simply assume a doubled thickness from the GDI segments to add to the new model. 

For example, the volume of FSAC-KK 11888 in that GDI is 4443.13 litres, with a ridge of 459.98 litres. Doubling the ridge, we get a total volume of 4903.11 litres with a ridge volume of 919.96 litres, meaning that doubling the ridge would make it account for about 18.8% the mass of the animal.

Applying this to FSAC-KK 11888 gives us 4591.26 litres, which gives us a mass of 4820 kg with a density 5% greater than that of water as proposed for spinosaurids by Greg Paul and Asier Larramendi (2020).

The really big specimens get an update in size as well. As of now, the only one of these that can be estimated from overlap with others is NHMUK R-16421, which SpinoInWonderland restores at 38.7% larger than FSAC-KK 11888.
That allows us to estimate it at 12250 litres in volume (4591.26x1.387^3), which gives a mass of 12860 kg with the recommended density - and it shouldn't be forgotten that the fleshing is still almost certainly too minimal, meaning the live animal has a very high chance of being larger than that.
This could change somewhat when more specimens are found that overlap with others and allow an estimate to be made, but for now, NHMUK R-16421 is the average, maximum, and minimum for possible adults that I am aware of.

Unsurprisingly, this size is quite consistent with what Nizar Ibrahim estimated in the 2020 'Ask Me Anything' on Reddit.

@GuateGojira 

Since you follow the information on Spinosaurus quite closely (as I do) and since we have had a number of discussions on it size, you may find this post to be worth a read. There's really no shortage of vindication for what Ibrahim said.

(02-07-2022, 09:23 PM)GuateGojira Wrote: The personal estimation of Dr Ibrahim is just that, his personal estimation and until is published and reviewed we can't take it seriously.

(02-16-2022, 01:13 AM)LoveAnimals Wrote: To add that Nizar Ibrahim's 2020 model, which is the one Dinofan continously used as reference, has a good amount of inaccuracies.
First of all, there is no evidence that spinosaurus aegyptiacus had such massive crocodilyan-like neck.
Lastly, its torso is way too deep, it's literally deeper than the pubis and it should be noted that no theropod that has ever existed had its torso deeper than the pubis, spinosaurids included. Therefore that 2020 model is long outdated and even when it was up to date it presented a good amount of inaccuracies, the too deep chest is the most evident one

Quote:The aquatic hypothesis

Recent discovery of the tall-spined tail bones of the neotypic skeleton reinvigorated the interpretation of S. aegyptiacus as the first fully aquatic dinosaur (Ibrahim et al., 2020b), here dubbed the ‘aquatic hypothesis,’ which makes three basic propositions. Unlike any other theropod, according to the hypothesis, S. aegyptiacus:

1. reverted to a quadrupedal stance on land, as shown by a trunk-positioned center of mass (Ibrahim et al., 2014; Ibrahim et al., 2020b), ostensibly knuckle-walking with long-fingered, long-clawed forelimbs;
2. functioned in water as a capable, diving pursuit predator using an expanded tail as a ‘novel propulsor organ’ (Ibrahim et al., 2020b) or as a ‘subaqueous forager’ (Fabbri et al., 2022); and
3. fossils would be found exclusively in coastal or deep-water marine habitats, like all large-bodied secondarily aquatic vertebrates, and would not be expected to be found in freshwater inland environments.
   We test these three central propositions.
   

Critique of the aquatic hypothesis thus far has focused on an alternative functional explanation for the high-spined tail as a display structure and largely qualitative functional interpretations of its skeletal anatomy (Hone and Holtz, 2021). Biomechanical evaluation of the aquatic functionality of S. aegyptiacus remains rudimentary. The propulsive capacity of the tail in water was judged to be better than terrestrial counterparts by oscillating miniature plastic tail cutouts in water (Ibrahim et al., 2020b), a limited approximation of the biomechanical properties of an anguilliform tail (Lighthill, 1969; van Rees et al., 2013; Gutarra and Rahman, 2022) that failed to take account of the bizarre anterior half of the animal. The center of body mass, a critical functional parameter, has been estimated for S. aegyptiacus three times, each estimate pointing to a different location ranging from the middle of the trunk (Ibrahim et al., 2014; Ibrahim et al., 2020b) to a position over the hind limbs (Henderson, 2018). Quantitative comparisons have not been made regarding the size or surface area of the limbs, hind feet, and tail of S. aegyptiacus to counterparts in extant primary or secondary swimmers.

Thus, adequate evaluation of the aquatic hypothesis requires more realistic biomechanical tests, quantitative body, axial and limb comparisons between S. aegyptiacus and extant primary and secondary swimmers, and a survey of bone structure beyond the femur and shaft of a dorsal rib. Such tests and comparisons require an accurate 3D digital flesh model of S. aegyptiacus, which, in turn, requires an accurate skeletal model. Hence, we began this study by assembling a complete set of CT scans of the fossil bones for S. aegyptiacus and its African forerunner, Suchomimus tenerensis (Sereno et al., 1998).

Quote:Thirteen principal conclusions can be drawn from this study, all of which may be tested:

1. Adult S. aegyptiacus had a body length of under 14 m with the axial column in neutral pose.
2. The reduced hind limb long bones in neotypic skeleton of S. aegyptiacus are infilled likely as an adaptation to weight support on land rather than functioning as ballast to increase density in water.
3. The segment-crossing caudal neural spines in S. aegyptiacus suggest that its tail functioned more as a pliant billboard than flexible fluke.
4. S. aegyptiacus, like S. tenerensis and other spinosaurids, was bipedal on land with its CM positioned over its hind feet. The long-clawed forelimbs of S. aegyptiacus were not used in weight support on land.
5. S. aegyptiacus could wade into shallow water for feeding with flotation occurring at water depth greater than ~2.6 m.
6. An adult flesh model of S. aegyptiacus has a body mass of ~7400 kg and average density of ~830 kg/m3, which is considerably less than the density of saltwater (1026 kg/m3).
7. S. aegyptiacus was incapable of diving, given its buoyancy and incompressible trunk. Full submergence would require 15–25 times the maximum force output of its tail, depending on estimated lung volume.
8. S. aegyptiacus was unstable in deeper water with little ability to right itself, swim, or maneuver underwater. Maximum power from its tail, assuming it could undulate as in Alligator, is less than 700 N, which would generate a top speed of ~1 m/s, an order of magnitude slower than extant large-bodied pursuit predators.
9. All extant and extinct large-bodied (>2 m long) secondarily aquatic vertebrates are strictly marine, whereas fossils pertaining to Spinosaurus have been found in inland basins distant from a marine coast.
10. Transition to a semiaquatic lifestyle, as occurred in the evolution of spinosaurid theropods, can occur at any body size. Transition to an aquatic lifestyle among tetrapods, in contrast, has only occurred at relatively small body size (<3 m) with subsequent radiation once in the marine realm into larger body sizes.
11. S. aegyptiacus is interpreted as a semiaquatic shoreline ambush predator more closely tied to waterways than baryonychine spinosaurids.
12. Spinosaurids flourished over a relatively brief Cretaceous interval (~35 My) in circum-Tethyan habitats with minimal impact on aquatic habitats globally.
13. Two phases are apparent in evolution of aquatic adaptations among spinosaurids, the second distinguishing spinosaurines as the most semiaquatic of non-avian dinosaurs.