Depictions of dinosaurs today may not be entirely accurate. The skeletal framework does indeed suggest a basic shape to the animal and does provide with enough rational for certain scientific conclusions. However, examples from animals living today such as the Sperm Whale demonstrate that the animal shape doesn't always conform to the skeletal structure such as a Blue Whale.
Is it possible that some dinosaurs may have had a spermaceti-type organ designed for a specific water or land-use during the period? The remains are not found because they decay similar to cartilages and flesh. Modern animal fibrous models may provide a general understanding of how an ancient animal might have appeared but do not guarantee by any means an entirely accurate reproduction. Another key understanding is that animals with extended sensory organs like an elephant's trunk decay away as well. In cases like an elephant trunk, our only clues to their existence in ancient animals comes from the understanding of modern living animals and how they relate.
This means animals discovered from dinosaur periods may actually look quite different from their commonly accepted renditions. Given the time-line between today's animal relatives and their great ancestors, it is not unreasonable to believe that those ancestors might have had additional appendages or limbs which we may never know by scientific fact to have ever existed at all. Another great example of this is the T-Rex. The closest animal from modern times that resembles a short upper arm configuration is, the kangaroo. It's difficult to imagine a T-Rex posturing as kangaroos do, so perhaps there was another significant purpose. Suppose the small arms Tyrannosaurus is classically depicted with were actually skeletal bone structure for a type of wing system or lower neck frill - Something which would not preserve in fossil record, yet the supporting bones are there!
Pressure on the scientific community from the general public to produce visual reference of unearthed bone sets could have rushed the process. Artistic interpretations have shaped common beliefs to become the accepted norm. It would be very difficult and require a lot of time to determine if certain species of Dinosaurs really did have an extra apparatus, especially considering the biological decay difference between fleshy materials and bone.
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