The Sauropod's Trunk - Updated Commentary  (Part Two of Four Articles)
Once I posted my original commentary on my website, Loren Coleman referenced the commentary with one of his own on the Cryptomundo website. Loren also invited a second opinion from a paleontologist, Darren Naish, who brought to our attention several scientific papers which studied and discussed the theory. I had an opportunity to correspond directly with Darren, and he was kind enough to provide me with direct page links to the two scientific papers and this allowed me to read these documents myself.
This new information should definitely be factored into the discussion and I wanted to offer my appraisal of these two papers and how they impact on the theory in general, and how they seem to compare with my prior notes and ideas. But I also think it's time to split the discussion, covering the diplodocus-type dinosaurs in one discussion, and the brachiosaurus-type in a separate discussion. This specific commentary will be a generalized discussion based on my review of the new scientific papers brought to my attention. Two additional commentaries will address each dinosaur type specifically.
So these comments about the scientific papers are initially generalized. Reference to these Papers is at the bottom of THIS PAGE
The paper by Lawrence M. Witmer, titled "Nostril Position in Dinosaurs and other Vertebrates and its significance for Nasal Function" appears to say, in my simple English understanding, that when there are large nostril openings in the skull, and the presumed nostril openings of the skin are smaller, then those nostril openings in the skin will tend to be positioned more forward and downward on the face. Mr. Witmer addresses the generalization across all dinosaurs where the nostril opening on the skull appears far larger than an expected nostril opening in the skin would be, and he illustrates the concept on a Brachiosaurus, a T Rex, and a Triceratops.
His generalized conclusion, that nostril openings in the skin should be in the lower and more forward position of any set of position options tends to agree with my notes which stated: "As such, it (the nostril openings of the skin) should be situated close to the mouth. It should be situated at the front of the face so the head can point the nose at a source of odor, and ideally, the eyes should be able to see what the nose is smelling so that the brain can get a visual/olfactory correlation." So it seems that Mr. Witmer's paper and my original notes (actually written in 1995) do concur on that matter.
Moving on to the second paper, "Paleoneurological evidence against a proboscis in the sauropod dinosaur Diplodocus" by Fabien Knoll, Peter M Galton, and Raquel Lopez-Antonanzas, this paper looks at casts of brain chambers in known Diplodocus skulls, which allows the scientist to actually map the brain shape and size, and reference lobes of the brain generally considered to have identified functions. It's summary conclusion is that, in essence, the nerves from an elephant's brain which are known to operate the trunk have a substantial size, and no comparable sized nerves can be determined or anticipated from the brain casts of Diplodocus, leading these researchers to state " the absolute as well as relatively small size of the facial nerve in Diplodocus (deduced from an endocranial cast) indicates there is no paleoneuroanatomical evidence for the presence of an elephant-like proboscis in this genus (the Dilpodocids, my addition for reference)."
The Paper ends with "We conclude that the anatomy of the head and the endocranial cavity unambiguously indicates that a proboscis (at least a large muscular one) was not present in Dilpodocus. This also holds true for Camarasaurus, which had necessarily a small facial nerve, but not for Brachiosaurus (although the presence of a proboscis in the latter genus has not been convincingly argued, this hypothesis remains)".So this paper itself splits the discussion and offers separate conclusions for the Diplodocus as compared to the Brachiosaurus, supporting my inclination to separate the two discussions.
Second Issue Still to be Resolved
Now, the second issue which I feel is still not necessarily resolved is in the phrase "an elephant-like proboscis" This phrase can be used with several levels of exactitude, so perhaps some of the disagreement in conclusions (trunk or no trunk) may indeed stem from two different perceptions of what exactly is meant by "an elephant-like proboscis".
We should consider the prospect of what defines "an elephant-like proboscis". My first concern is level of complexity or biomechanical sophistication. The elephant's trunk is reported to have about 40,000 muscles in it. It also has an astonishing array of sensory nerves for tactile perception. And it is an amazing organ, truly one of nature's miracles of engineering. But does a trunk need to be that complex? Could it be a lot simpler and still serve a sauropod well enough to justify its evolution? And if we greatly simplified this appendage, would we still call it an "elephant-like proboscis"?
The elephant's trunk is an appendage generally categorized as a "hydrostatic organ", one which has no internal skeletal structure to support muscles, yet it has tremendous power and precise manipulation capabilities because of the large number of interwoven muscles. Another example of a hydrostatic organ is the octopus tentacle. So the hydrostatic organ is not exclusive to elephants (and tapirs), but rather occurs in other forms in nature, thus allowing us to hypothesize that maybe a hydrostatic organ on the nose of a sauropod is non-mammalian in it's architecture, but still a highly prehensile organ.
The elephant's trunk does many things. It gathers food and puts it into the mouth. It sucks up water and then squirts it into the mouth. The trunk can be used as an appendage for aggressive physical action against another creature. The trunk, in more peaceful social circumstances, is used by the elephant for socialized physical contact, expecially putting their trunk into the mouth of another elephant as a gesture of social bonding. The paper by Knoll, Galton, and Lopez-Antonanzas explains this nicely as well (with more technical vocabulary than my plain English)
But a hypothesized sauropod trunk, by comparison, may not need to do as much. My assumption is the first function, assisting in food gathering, is needed, but a short and simple trunk could conceivably do that, in essence just a tongue outside the mouth instead of inside the mouth.. The second function, sucking up water, the sauropod doesn't need, because the Diplodocus-types can lower the head to the ground (or water level at the edge of a lake), and the Brachiosaurus-types hold their head so high, a trunk dangling down to the ground would be far beyond my expectation of physical probability. The third function, using the trunk as an appendage for self defense against other creatures, does not seem likely, because on the Diplodocus-types, any trunk on the end of that long neck would need to be small so it didn't add much weight to the head, the way the neck is held, and on the Brachiosaurus-types, again, the head is so high above other creatures, a trunk doesn't seem likely to help in any self defense action. A kick or a tail whip seems more likely as a self defense gesture. Finally, the socializing contact, if done, could presumably be satisfied by a small and mechanically simple type of trunk, or by a multitude of gestures not specifically involving the food gathering trunk.
So this brings me to wonder, can a sauropod trunk (a prehensile appendage on it's face) exist, but be relatively small and mechanically far simpler than an elephant's trunk, and not necessarily have a mammalian-type complex architecture? I think it could, and if so, the facial nerve could thus be far smaller, as the scientists have noted, to serve a less complex hydrostatic organ or prehensile appendage.
Biomechanical Designs
For example, when I think of a biomechanical design for a tubular structure which can bend in all directions, I imagine segments where there are eight muscles around the ring of the segment (two on top, two on the bottom, two on each side, a sort of octagon configuration. And I can see this segment being capable of a ten degree bending in any direction. So to bend the extended tubular mass a full 360 degrees, 36 segments would be needed, which is 36 x 8 for 288 muscles. Now if we allow for a portion of the trunk (like the outer third of it) to do the full 360 degree curl, we might increase the number of segments to 100 or so, which makes 800 muscles. Then we might add some muscles running the full length of the trunk, and estimate about 1000 muscles in total.
But the elephant had about 40,000 muscles, which means the facial nerve needs to be about 40 times as large, in area cross-section, as a facial nerve driving a trunk-like appendage with only 1000 muscles. That's about 6.4 times smaller in diameter than the elephant's facial nerve. If we simplify the nerves needed for tactile sensation, we further shrink the size of any necessary facial nerve.
So while the author's of this paper discounted the prospect of a trunk with elephant-like structural complexity, which would require a large facial nerve, I must wonder if they considered a less complex trunk-like appendage with less muscles, less tactile nerve sensation, and thus a smaller facial nerve feeding those muscles? Reducing the muscle inventory by a factor of 40 would certainly result in a much simpler appendage, but one which I believe could still substantially function as a food gathering appendage. Reducing the sensory nerve inventory as well might reduce the facial nerve cross-section area by a factor of 50, 60, or even more. The resulting substantially smaller facial nerve may be within the size estimates determined by the endocranial casts of the study.
In this regard, I personally would think the issue of the trunk has not been conclusively discounted, while I will concur that a elephant-like trunk as extensively muscled as an elephant's, with the extensive array of tactile nerves as well as muscle-control nerves, is not supported by the Diplodocus brain study. But I do think there are options of a more simplified prehensile appendage (which we'd probably call a trunk) and a non-mammalian design architecture of unique configuration, because the Diplodocus has already demonstrated it's evolution into a shape like nothing existent today (the horizontal long neck), and the facial shape and any potential trunk should be considered part of that unique evolutionary adaptation. A study of how much anatomical complexity might need to exist to satisfy a food gathering functional appendage (while excluding the other functions elephant trunk's perform), may indeed result in a simpler appendage with less muscle inventory and thus a structure fed by a much smaller facial nerve.
And nothing in either paper offers a solution to the simple question, why is the nostril opening in the skull in the "wrong place" (atop the skull)?  Witmer's intriguing study seems to reinforce the preferred practicality and demonstrated commonality of nostril openings in the skin to be low toward the mouth and as far to the front of the face as possible. My assumption is nature does not design things "wrong", so there is a reason for the nostril openings in the skull at the top of the head, deviating from almost all other known skulls of terrestrial creatures. Neither paper has offered a statement  to say "the nostril openings in the skull are atop the skull because. . . . .(plus some answer to complete the statement)". As long as that question lingers, and the above statement is incomplete, the prospect of a trunk has not been fully discounted.
Two additional commentaries will now discuss the two types of dinosaurs specifically relative to their unique anatomy, and with references to the papers described above.
Diplodocus Discussion          Brachiosaurus Discussion       Original Notes     Images of the Proposed Trunk
The Essential Mystery
In my mind, the single most profound mystery of this discussion is the simple question, why (in sauropods) has the nostril opening of the skull been moved away from the more common and functional position, as Witmer describes, and I concur, at the front of the face, low and close to the mouth. The charts below show both a Diplodocus skull and a Brachiosaurus skull as they actually are, and as they should be following traditional skull design putting nostrils forward and close to the mouth. And the essential mystery, which as far as I know is still unanswered, is what biological justification resulted in these openings being moved away from where they should be?