Spinosaurus: Hone and Holtz 2021 minimize the unique traits

Summary for those in a hurry:
A unique morphology + a unique niche + a unique prey assemblage = a unique hunting technique.

From the Hone and Holtz 2021 abstract:
“We conclude that …the pursuit predation hypothesis for Spinosaurus as a “highly specialized aquatic predator” is not supported. In contrast, a ‘wading’ model for an animal that predominantly fished from shorelines or within shallow waters is not contradicted by any line of evidence and is well supported. Spinosaurus almost certainly fed primarily from the water and may have swum, but there is no evidence that it was a specialised aquatic pursuit predator.”

Hone and Holtz pay little attention to the fact that Spinosaurus was the only large theropod that had such short hind limbs and had a dorsal fin much deeper than its ribcage. The authors cherry-picked less obvious traits to support their hypothesis, giving only passing notice to what makes Spinosaurus unique.

From the Hone and Holtz introduction:
“In short, these animals [spinosaurs] acted like large herons or storks, taking fish and other aquatic prey from the edges of water or in shallow water, but also foraging for terrestrial prey and scavenging on occasion.”

In paleontology, if Spinosaurus is going to be compared to large herons or storks, it should look overall like a giant heron or stork. It does not.

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish.

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish.

Hone and Holtz keep hammering away at a single point:
“The hind limbs of Spinosaurus do potentially provide evidence for aquatic locomotion and even striking at prey underwater, but specifically not in the sense of pursuit predation.” 

“Surface swimming is considerably less efficient than submerged swimming and incurs considerable extra wave drag for animals moving at, or just below, the surface.”

The problem is, Hone and Holtz want Spinosaurus to be built for speed, like a sailfish, if they are to grant it a submerged aquatic existence. Unfortunately, the authors are caught in a logic rut based on some sort of straw man. They end up cherry-picking traits less important traits while trying to weave their story away from the larger, unique traits.

Spinosaurus was not built for speed.
It didn’t need to be built for speed. Look at the prey taxa available (Fig. 1). Lungfish, giant bichirs and coelacanths are big, fat and slow-moving fish. Sawfish are lethargic bottom-dwellers. Drag is not a factor when moving slowly, like Spinosaurus.

As the only aquatic dinosaur,
Spinosaurus may have developed a sail to help regulate body temperature while staying submerged (except to lay eggs). It may have never needed to stand bipedally, like its theropod sisters. Hence the small legs and quadrupedal center-of-balance.

The tiny backset naris of Spinosaurus
was on its way to complete closure. That’s not a problem as many extant birds without nares demonstrate. They can all breathe throughout their mouth and throat.

Figure 2. Diagram from Dal Sasso et al. 2005, colors and overlay added to show dorsal expansion of the maxilla to cover an elongate naris.

Figure 2. Diagram from Dal Sasso et al. 2005, colors and overlay added to show dorsal expansion of the maxilla to cover an elongate naris.

Hone and Holtz summarize their study:
“If swimming to engage prey, based on the drag, performance and body shape it would be limited to lunging attack in shallow waters, not pursuit predation at speed in open water.”

No.  Spinosaurus was a slow swimmer, unaffected by drag. It would not be limited to lunging attacks in shallow water, contra Hone and Holtz. Rather, slow, steady underwater predation with its sail exposed to maintain a 99º body temperature in an 80º river is still the best explanation for this unique theropod.

“The information provided through recent discoveries may suggest an increase in aquatic affinities for Spinosaurus, and it may have been able to swim with its tail, and even swim well compared to other theropods, but nothing presented to date contradicts the fundamentals of the ‘wading model’ and does not support active pursuit predation.”

Hone and Holtz failed to consider a semi-active, semi-submerged method of predation. “Nothing presented to date” = failure to consider all options. Spinosaurus is indeed a “highly specialized aquatic predator”, just not a fast one.

Earlier we looked at Spinosaurus in its environment here, its ability to swim deep here and its tiny naris here.

Unfortunately, papers from co-author David Hone are infamous for taxon exclusion, inaccurate observation, and illogical interpretation. Not sure why referees and editors are letting him get away with negating good solid science with bad flimsy science.


References
Hone DWE and Holtz TR Jr 2021. Evaluating the ecology of Spinosaurus: Shoreline generalist or aquatic pursuit specialist. Palaeontologica Electronica 24(1):a03 Online Here.  

https://doi.org/10.26879/1110

The near closure of the naris in Spinosaurus

Short note on a long rostrum today:

Figure 1. The rostrum of Spinosaurus. Note the maxilla rising to close off the elongate naris into a reduced anterior and posterior opening.

Figure 1. The rostrum of Spinosaurus MSNM V4047. Note the maxilla rising to close off the elongate naris into a reduced anterior and posterior opening. SF = sub-narial foramen. 

I just found this fascinating.
The naris of Spinosaurus (Stromer 1915; Cretaceous; MSNM V4047) was overlaid by the maxilla sealing off most of what had been the elongate opening (Fig. 1).  I suppose that supports a semi-aquatic niche and reduced olfactory input. As others have noted, the rostrum has sensory pits, perhaps, as in crocodilians, for underwater vibration sensing.

Figure 2. Diagram from Dal Sasso et al. 2005, colors and overlay added to show  dorsal expansion of the maxilla to cover an elongate naris.

Figure 2. Diagram from Dal Sasso et al. 2005, colors and overlay added to show dorsal expansion of the maxilla to cover an elongate naris.

Dal Sasso et al. 2005 wrote:
“The external naris is retracted farther caudally on the snout than in other spinosaurids and is bordered exclusively by the maxilla and nasal.” The authors identified the anterior naris as a ‘sub-narial foramen’. The naris continues to contact the premaxilla in all related taxa (Fig. 1). Here, just thinking about things differently, and more parsimoniously, the naris continues to contact the premaxilla.

According to Wikipedia
MSNM V4047 (in the Museo di Storia Naturale di Milano), described by Dal Sasso and colleagues in 2005, consists of a snout (premaxillae, partial maxillae, and partial nasals) 98.8 centimetres (38.9 in) long from the Kem Kem Beds. Like UCPC-2, it is thought to have come from the early Cenomanian. Arden and colleagues in 2018 tentatively assinged this specimen to Sigilmassasaurus brevicollis given its size. In the absence of associated material, however, it is difficult to be certain which material belongs to which taxon.”


References
dal Sasso C, Maganuco S, Buffetaut E, Mendez MA 2005. New information on the skull of the enigmatic theropod Spinosaurus, with remarks on its sizes and affinities. Journal of Vertebrate Paleontology. 25 (4): 888–896.
Ibrahim N et al. 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science 345 (6204): 1613–1616.
Stromer E 1915. Ergebnisse der Forschungsreisen Prof. E. Stromers in den Wüsten Ägyptens. II. Wirbeltier-Reste der Baharije-Stufe (unterstes Cenoman). 3. Das Original des Theropoden Spinosaurus aegyptiacus nov. gen., nov. spec. Abhandlungen der Königlich Bayerischen Akademie der Wissenschaften, Mathematisch-physikalische Klasse (in German). 28 (3): 1–32.

wiki/Spinosaurus

New thoughts on a swimming Spinosaurus

Earlier we looked at an illustration of Spinosaurus (Fig. 1) showing how the sail could have emerged from cooler waters into hotter atmospheres to regulate internal temperature through blood flow.

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish.

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish.

That illustration 
(Fig.1) showed Spinosaurus in waters shallow enough to barely touch the bottom with toes and fingers. Pretty conservative. Today, let’s go deeper (Fig. 2).

Figure 1. Spinosaurus in deeper waters. Graphic is from Henderson 2018 with water line as he indicates.

Figure 1. Spinosaurus in deeper waters. Graphic is from Henderson 2018 with water line as he indicates. Five images change every five seconds. More stability occurs when the skull and/or tail drops and by even partially allowing the sail to be filled with air. Maybe that’s why Spinosaurus has a sail!

Henderson 2018
brings his own doubt to the floating Spinosaurus hypothesis using computer models (Fig. 2) despite all other evidence, including stomach contents (fish) pointing to an aquatic niche. Henderson’s data indicated a lack of stability in water for his spinosaur models. Henderson’s computer models of pterosaurs have been infamous for their inaccuracy.(Several pterosaur workers also opined on this.)

This time morphological accuracy doesn’t seem to be the problem.
Instead his models appear to float a little too high out of the water, the model appears to be a little ‘stiff’ (flexibility and dynamism are present in all tetrapods), AND he assumes the spaces between the dorsal spines were solid, even if thin.

Here
(Fig. 2) alongside the underwater lounging croc, spinosaurs could have floated with greater stability by simply dropping the solid tail or by dropping the skull to search for fish… while floating. When diving, Spinosaurus could have filled the spaces between the tall dorsal ribs with air, or emptied them, precisely as necessary. Theropods are famous for being pneumatic.

So, perhaps the most important part
of the Spinosaurus sail is the space between the bones. And if soo, is that why Spinosaurus had a sail to begin with? Sometimes you just have to look at a problem from another point-of-view. Toss that idea around. See if it generates any further discussion…

Don’t hold your breath waiting for consensus on this one.
It takes about a hundred years for paleontologists to agree to anything.

References
Henderson D 2018. A buoyancy, balance and stability challenge to the hypothesis of a semi-aquatic Spinosaurus Stromer, 1915 (Dinosauria: Theropoda). PeerJ 6:e5409; DOI 10.7717/peerj.5409

Hone and Holtz review spinosaurids

It’s always good to have a clade reviewed now and then.
Reviews form ready references for those just diving into a subject for the first time, or need to get ‘brushed up’ on all the latest literature. However…

You know you’re in a wee bit of trouble
when authors Dr. David Hone and Dr. Thom Holtz open their abstract with “The spinosaurids represent an enigmatic and highly unusual form of large tetanuren theropods.” In this day and age, after two decades of phylogenetic analysis, there is no longer ANY excuse for labeling ANY taxon or clade enigmatic” or “highly unusual.” Every taxon should be phylogenetically ‘buttoned down’ by now. And this one is, more or less…

Everyone agrees
that spinosaurs nest with megalosaurs… but which ones? This is where avoiding suprageneric taxa pays off. And spinosaurs are not all that weird, especially the early ones. Most of their parts (bones) have readily recognizable counterparts in more typical (non-spinosaurid) theropods.

ALL phylogenetic analyses nest EVERY included taxon.
So, there is always a closest known sister taxon, but you have to do the work and not just repeat old adages or promote old papers…and by all means, avoid suprageneric taxa!

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish.

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish.

The authors recover only one suprageneric outgroup taxon
in their tiny six taxon cladogram. Unfortunately, this provides no clue as to the origins of the Spinosauridae other than somewhere within the suprageneric “Megalosauridae”. Hone and Holtz report, “The origins of the Spinosauridae remain somewhat obscure. There is a seemingly undocumented phase of the spinosaurid lineage from 170 until 130 mya.”

Unfortunately,
we’ve seen Dr. Hone punt and sidestep on clade origins before. This habit not only leads to disappointing reading, but feeds into traditional “enigmatic and highly unusual” paradigms that were answered a year ago here (Fig. 1) and should have been answered seven and five years ago by Benson (2010) and by Carrano, Benson & Sampson (2012). Sinocalliopteryx entered the literature in 2007, but was mislabeled a ‘compsognathid.’ There is no longer any value in keeping the sacred vaults of paleontology full of mysteries. To do so runs the risk of permitting amateurs and bloggers to make discoveries that should clearly be in the province of the PhDs. Unless they don’t want to do the work.

Figure 1. The LRT nests spinosaurids with Sinocalliopteryx and other taxa not mentioned in Hone and Holtz 2017.

Figure 1. The LRT nests spinosaurids with Sinocalliopteryx and other taxa not mentioned in Hone and Holtz 2017. All clade members are long-snouted theropods.

Here
at the large reptile tree (LRT, 1033 taxa, subset Fig.1) the following taxa nest with Spinosaurus and Suchomimus.

  1. Sinocalliopteryx – 125 mya
  2. Xiongguanlong – 112 mya
  3. Deinocheirus – 70 mya
  4. Proceratosaurus – 165 mya

Obviously all these taxa
had earlier origins and radiations, based on their late appearances in the fossil record and nesting in the cladogram.

Here’s an OPTION for all paleontologists struggling with a phylogenetic enigma:
Just take a look at the LRT, where every taxon is comfortably nested…(even spinosaurs!), request the .nex file, add your taxon to it, review for errors, then report your results. Or keep the results a secret and perform your own analysis while including all pertinent taxa, and then reporting your own results. The days of enigmatic taxa should be over, though I’m sure we’ll keep seeing moderately unusual taxa. The highly unusual ones are getting to be more commonplace and easier to handle given the large gamut already in our vaults. And the biggest benefit: you won’t have bloggers chiding you for taxon exclusion.

References
Benson RBJ 2010. A description of Megalosaurus bucklandii (Dinosauria: Theropoda) from the Bathonian of the UK and the relationships of Middle Jurassic theropods. Zoological Journal of the Linnean Society 158:882–935.
Carrano MT, Benson RBJ and Sampson SD 2012: The phylogeny of Tetanurae (Dinosauria: Theropoda), Journal of Systematic Palaeontology, 10:2, 211-300.
Hone DWE and Holtz TR Jr. 2017. A century of spinosaurs — a review and revision of the Spinosauridae with comments on their ecology. Acta Geologica Sinica (English edition) 91(3):1120–1132.