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Pachyornis — Theropod necks: horse-neck vs. conventional
Published: 2019-10-11 15:14:02 +0000 UTC; Views: 9924; Favourites: 271; Downloads: 0
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A figure in Bakker 1998 (Brontosaur killers paper) includes a reconstruction of the neck muscles of Ceratosaurus based on alligator muscles. The reconstruction itself looks plausible, and the interesting detail is that the muscles attach rather straight at the scapula and would not show the usual S-curve in live as we use to reconstruct theropods and other dinosaurs. Adding the M. latissimus dorsi plus the M. trapezius there would be even more bulk added to the neck base region.I could not resist to reconstruct a number of theropods this way, f.e. see my most recent Allosaurus based on S. Hartman's skeletal. I also took a number of older drawings and changed the neck after Bakker 1998 in the picture above. The left drawings show the conventional necks, the right drawings the "horse neck" versions. I think that this "horse neck", although it did not find its way into mainstream, might be way more plausible from the anatomical perspective (why should the muscles curve down that much and why should the trapezius and latissimus be that flat and thin as usually reconstructed?) and the functional perspective too (a way more stronger neck, especially for tearing down prey or ripping off chunks of flesh). The theropods look way more stronger this way (just compare how much stronger the Giganotosaurus appears), and more like other sauropsids. Honestly, I am that much fond of these "horse neck" that I keep on illustrating my dinosaurs this way until there are arguments against it. The difference shows the most on short, thick necks, not so much in long and thin necks such as in Spinosaurids.
From left to right, top down:
Ceratosaurus nasicornis
Giganotosaurus carolinii
Baryonyx walkeri
Allosaurus sp. MOR 693
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Comments: 15
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I'm not sure exactly where I stand on this, but I do have some thoughts:
Mammals with a horse-like cervical musculoskeletal arrangement have pretty limited neck mobility and are adapted for sustaining high moments. While the ability to elevate the neck is considerable, the cervical vertebrae remain quite straightly alligned and un-flexed.
The arrangement and shape of theropod cervical vertebrae is very different, and they seem to be more able to exhibit a greater range of plausible neck postures. Bakker's 1998 Ceratosaurus illustration only looks so straight and superficially horse-like in outline because the cervical vertebrae are depicted at close to maximum extension - the illustrated relative positions of the muscle outlines and cervical vertebrae are pretty different to the habitual postures of horses.
Given that the spinalis, longissimus and iliocostalis group of muscles have multiple insertion points on almost every single cervical verterbrae or cervical rib (the fibres aren't just clustered around a single tendon running between the skull and base of the neck), flexation and elevation of the cervical vertebrae towards to the curved or sigmoid allignment likely to be habitual in theropods would probably also lead to at least the dorsal muscle outline bending to reflect this.
All of this said, I think you could still probably make a case for something a little more habitually horse-like in dinosaurs with somewhat less flexible necks than most theropods.
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Those are good points, especially the movability of the neck. (I have to point out though, I never used mammals as an analogue for this, only other sauropsideans and crocodilians in particular, I just called it "horse neck" because of the superficial optic similarity).
Cocnerning Bakker's illustration, yes, I am aware that the neck in that figure is extended maximally, and I considered that in my drawings. As you see, the muscles in my drawing aren't as crescent-shaped as in Bakkers illustration but somewhere between Bakker 1998 and an S-shaped neck; especially in the Allosaurus you see that. Because I do not think that the muscles as illustrated in Bakker 1998 would form the S-curve as usually depicted in paleoart; you see that many of them actually insert at the scapula and I doubt that an all too sigmoid curve would be that functional. But those are only my personal guesses.
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Of the neck traversing muscles illustrated by Bakker, only levator scapulae attaches to the scapula, with sternomastoideus and stenohyodeous attaching to either the coracoid or wishbone.
It's not particuarly clear the way he's illustrated it, but spinalis, longissimus and iliocostalis pass beneath the scapula, they do not attach to it.
In theropods, spinalis and longissimus (or a division of them) attach to the spinous processes and transverse processes of every single vertebrae all the way down to the tail. Iliocostalis should attach to almost every single rib (including the cervical ribs) and finally the ilium. However, I don't think Bakker illustrated iliocostalis as attaching upon the cervical ribs, which from a contemporary lens would be considered incorrect.
Because of these attachments, the lines of action of each these muscles should more-or-less reflect the contours of the vertebral collumn depending on posture (hence the commonly illustrated sigmoidal dorsal outline when the cervical vertebrae are flexed as such), even if the muscle itself is extremely bulky.
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Many thanks for the info - I have a question though; where do we know form that in theropods the spinalis capiti and the semispinalis would attach to the processus of each vertebra, or, is there a difference in the way they are attached in crocodilians? I am looking the muscle figure for the crocodile in Bakker 1998, the muscles quite clearly surpass the row of the spinous processes of the vertebrae. Looking back at theropods, when adding the trapezius and lat. dorsi we might get something similar to my drawings. I doubt that both muscles were that flat and thin as usually reconstructed. What do you think?
Do you maybe have an idea what made Bakker reconstruct the muscles in the Ceratosaurus in that very convexly curved manner?
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These muscles in crocs still attach to processes of each vertebrae, there's just a lot of vertically/dorsally projecting bulk, or at least that's the best way I can word it. Spinalis captitis thus fills in a lot of that dorsal concavity of the neck, straigtening out the outline of the neck in life relative to the actual orientation of the vertebrae.
However, what is important to remember is that spinalis is a muscle complex with multiple divisions. Spinalis capitis/Transversospinalis captitis, which is the primary division of this muscle complex in the cervical region, terminates at either the last few cervical vertebrae or first few dorsal vertebrae in crocodylians and lepidosaurs. What this means is that assuming a crocodylian muscle model, the aforementioned dorsal concavity infill should be mostly restricted to the cervical zone. Snively and Russell, 2007, "Functional Variation of Neck Muscles and Their Relation to Feeding Style in Tyrannosauridae and Other Large Theropod Dinosaurs" demonstrates pretty nicely how this would look and vary in tyrannosaurids, Allosaurus and Ceratosaurus, as well as overviewing pretty rigorously where the muscles actually attach.
With that in mind, your thick-necked version of the Allosaurus in this image looks pretty great to me. However the thick-necked versions of your Giganotosaurus, Ceratosaurus and your more recent Tyrannosaurus look less agreeable, as they give the impression that Spinalis capitis is attaching further along the dorsal vertebrae series than it probably should be. Your "traditional" variants of those latter three actually reflect the thick crocodylian muscle model really well.
I would also tentatively suggest that overall, the apparent outline straightening in theropods caused by this concavity infill would neutrally look somewhat lesser than that of crocodiles, simply because the neck is more habitually flexed, thus adding greater curvature to the lines of action of those epaxial muscles.
To be honest, I feel as if I may be have been too harshly nitpicky here, because the idea you're demonstrating is along the right lines, and is definitely preferable to the super-skinny, more avian-like cervical reconstructions of large theropods popularised by people like Greg Paul.
As for the trapezius/cucullaris and latissimus dorsi, that's a tricky one. They are pretty flat and sheet like in crocodylians, but a large component of their origin is from fascia, not from bone directly, and it's never clear how thick these fascia should be in dinosaurs. There's also the case to be made for the absence of trapezius/cucullaris in derived theropods, as while present in crocs, it's absent in birds. This may only apply to super-specialised coelurosaurs though.
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Ok, many thanks for the information! I think you are right, the neck in my Giganotosaurus and Tyrannosaurus look indeed a bit exaggerated to me now. I did a sketch of the muscles now, trying not to exaggerate it. What do you think of it?
The subadult Ceratosaurus by the way is based directly on Bakker 1998, I simply took the figure and put the neck in a flexed position with GIMP and then made a drawing of it.
It's mostly the trapezius that makes the neck base more bulky in my theropods (I think it would be likely that the trapezius and lat were less sheet like than in crocodylians for functional reasons, but probably we can only guess).
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Nice! They look like a good demonstration of the somewhat bulkier end of a crocodylian-based muscle model applied these taxa. You could maaaaybe even add a little more bulk to the Giganotosaurus if you wanted to, but I personally think it looks about right. There's not really been enough work done on sensitivity analysis of overall "best estimate" neck muscle mass/volume in theropods. Outside of Snively et al's 2015 Allosaurus paper, nothing mathematically deep enough that focuses on just neck muscle mass has gone to publication - at least not yet anyway. But the lines of action/muscle pathways, which can be somewhat more confidently inferred, look right here given the posture.
I think that the way you've restored the trapezius/cucullaris is also a very reasonable estimate, if this muscle is indeed present in these taxa. There's enough room for the other scapular muscles and the dorsal fascia without things being too tight or too slack.
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I like the horse neck versions. They do look more functional. Then again my anatomical knowledge is close to zero
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I'VE BEEN WAITING FOR SOMEONE TO REALIZE THIS!!! when I looked at horse and cow skeletons I said "if people didn't know what a horse or cow looked like, they'd assume they had necks like dinosaurs." if you assume the body shape is exactly shaped like the skeleton, you get a totally different animal and nobody would ever figure out what they actually looked like. I like how the snake/dragon-necked dinosaurs look in art but to be honest, a lot of their skeletons look suspiciously similar to horse and cow skeletons to me ( and I've seen people drawing them with big cow shoulders with the neck dropped down low and I'm like why? this is what a cow looks like and a cow doesn't have a snake neck ), and people can blah blah about birds all they want but a big heavy animal like a dinosaur has a lot more in common with a big heavy animal like a horse or cow than it does with a stork.
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I actually really like this concept. It seems very likely, and looks more natural.
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Pretty cool to see this. You can really see how practical these affect design choices. Really useful for paleoartists. I'll try to remind me myself of this.
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