Making Lip of It

I’m more than a little interested in the “how you know” of paleontological reconstruction. As it may be apparent by now, I’m an artist, and as such tend to see things on an aesthetic level more than a technical one. Although I still see things technically, I look at them through aesthetic eyes. Because I’m a relativist, I try to put perspective on this by occasionally taking those glasses off, and look at something ONLY in a technical light, but this is hard: There are times when, regardless of the technical expertise of the work, I like its aesthetic, and this causes me to have issues on writing, where my tone and thoughts jumble together. It feels right, now you’re making me read it through like an editor?!

But art sometimes must take precedence, because in technical illustration, we have to be able to easily understand what we are seeing. A highly technical illustration is easy:

Skull of Velociraptor mongoliensis Osborn, 1925.

The above image was produced from multiple source skulls, primarily based on GIN 100/25 (the “Fighting Dinosaurs” specimen, which is somewhat crushed and eroded). It is presented here at top left lateral view, below that with the same perspective through sagittal section anterior to the lachrymal, in coronal section at the fourth maxillary tooth/fifth dentary position, in dorsal view, and in ventral view of the snout (upper rostrum and lower mandible). This is technical because having your proportions, measurements, and superficial details accurate is the point. It is generalized, and does not represent an actual specimen, but its close to virtually all of them. This is technical, but it’s still art, because I chose to stipple the skull, rather than pencil shade it, I chose a stylized method of depiction rather than just a photograph, I “faked” the lighting, etc. There are flaws, such as where the jaw is illustrated separately, so that shadows from the upper teeth do not fall on the lower jaw, and I decided not to add them in after the fact. I also had to “guess” at the medial view, based on description and what meager evidence there is from other, related taxa (I had to use the maxilla of Velociraptor osmolskae [IMM 99NM–BYM–3/3; Godefroit et al., 2008] and the snout and jaws of Dromaeosaurus albertensis [AMNH 5356, following Currie, 1995] and Deinonychus antirrhopus [YPM 5210 and YPM 5232, following Ostrom, 1969] as sources), and as such it becomes an approximation.

But the depiction of soft tissues is more difficult. It requires a substantial knowledge of technical details, photographic or on-hand material in the form of living or cadaverous specimens. Despite this, reconstructing this tissue for presentation is almost all art, and it goes doubly so for dinosaurs as they are extinct, and triply so because of the problem of the phylogenetic bracket:

When comparing dinosaurs as living creatures to their extant survivors (birds) and living remnants of their sister group crurotarsans, Crocodilia, dinosaurs exist in a grey area. On the one hand, they contain birds, which have scales only on their legs, and go otherwise feathered or naked skinned on the face, and always have a keratinous beak. Crocs, on the other hand (or face), have a squamous (scaly) integument all over the face, teeth, and absolutely no feathers. I won’t even try to draw that, artistic license or no.

However, recent dinosaur “documentaries” (Discovery Channel’s Dinosaur Revolution and BBC’s Planet Dinosaur) have pushed further on the dinosaur reconstruction angle, and I became prompted to remark on one peculiarity that struck me going all the way back to 1993, with the release of Universal’s Jurassic Park. As a kid barely into dinosaurs, I was massively stoked by this movie, but unlike many then and current budging artists, I had been inundated under the “real” dinosaur revolution of the 80s, wherein I learned about fluffy dinosaurs from Bob Bakker, reading frequently-signed out copies of Greg Paul’s Predatory Dinosaurs of the World, and the earlier controversy with John Ruben and Alan Feduccia among others countering the argument that not only were dinosaurs likely scaly beasts, they had nothing to do with bird evolution.

Because I happen to be a relativist and a cynic, my thoughts on these were “how do they know?” Then I started reading work by a guy named Larry Witmer, whose college and professional career has been to precisely answer that question. Having formulated the argument of the phylogenetic bracket, Witmer proceeded to them apply it to soft-tissue reconstruction, and has been steadily dismantling various hypotheses and building new ones from the remnants. This, I thought, is why I don’t stick to a single type of dinosaur reconstruction. It essentially led to me placing disclaimers, either in the description or in my own head, that everything I drew was based on the preconception of what I knew, and the best way to draw better was to know more.

Most certainly, the thing that strikes out most when it comes to dinosaur reconstruction is integument, because it is the first visually-striking thing next to posture. Below that, though, there are fleshy tissues, such as skin itself, fat, ligaments and muscle, and so forth.

Komodo dragon (Varanus komodoensis), borrowed from Zooillogix.

Consider above, the position of the nostrils. These are placed roughly at the lateral margins of the underlying bone, and extend somewhat to the limits of the rostral and lateral bony jaw. Everything beyond that is essentially soft tissue: ligament, muscle, skin, scale.

Now look at a dinosaur:

“Velociraptors.” Left, Velociraptor mongoliensis, from Greg Paul (1987, 1988). Middle, Mark McCreery’s “velociraptor” from Jurassic Park III (you can tell because the head has “feathers”). Last, Deinonychus from Dinosaur Revolution, rendered from Dave Krentz and by far the best digital reconstruction to date.

There are various things going on here that are complicated to explain simply, but notice that all of these reconstructions are nice and fluffy (well, the first and third are). Greg Paul’s reconstruction, favoring at times an upper lip, upper dentition that fit over the lower lips, and a rostral beak, is the most svelte: the animal represented was the size of a small dog, or turkey, but long-legged and tailed. Mark “Crash” McCreery’s designs for Jurassic Park have been largely preserved for the “velociraptors” in all three films, with the addition of “feathers” on the head in the third installment, but the head is very fleshy and reminds me of naught but a monitor lizard, with a broad U-shaped jaw that belies the slender, narrow tooth row you can see in this image (and why I chose it). Paleoartist Dave Krentz designed much of the dinosaur-y look for Dinosaur Revolution, and the extensive feathery covering shows. The facial reconstruction, however, borrows much from the look of McCreery’s “velociraptors,” down to the broad lips that covered the upper dentition, unlike as in Paul’s reconstruction.

The question, then, has been whether dinosaurs had lips. The tissues involved differ from group to group, as in mammals these are formed from large bundles of muscles that are anchored to the bone and skin around the oral cavity, and incorporate muscles linking the jugal (zygomatic arch) and mandible to form “cheeks,” while in reptiles they are lightly muscled and largely incorporate a large ligamentous band that wraps around the rostrum and connects to the skull at the jugal arch on either side of the upper jaw, and towards the coronoid in the lower jaw. In lizards and snakes, this band is large and distinct, and the muscles in snakes can be very numerous and the band very elastic. In crocs, however, this band is very thin, or may even be absent, but the fleshy tissues are still fairly broad:

Not much room for a lip here, is there?

The teeth here cross one another, passing one another to lie on the external margins of the jaw of both upper and lower jaws. In alligatorids, the lower dentition lie inside the upper, and connect to pits between upper teeth, so the lower dentition is generally not visible, but this is generally not the case in crocodilids, where the lowers pass the lateral margin of the upper jaw. A crocodilid is shown above.

If birds lack lips, and crocodilians have little or no lip, but the ancestors of both likely had them (an inference from lizards such as the monitor above), then how do we arrive at lips in dinosaurs?

The first clue, of course, is studying the analogues of “lips” in reptiles and mammals, and determining if they exist in dinosaurs. There is a line of foramina along the margins of the skull, known as nutrient foramina.

Foramina of the Velociraptor skull.

Typically, these are round and sit within small depressions that form channels along the bone surface toward the jaw rim, where exiting nerves, veins and arteries extend toward the gums that the teeth sit within. The mandible might have a deep channel linking several of these foramina in the posterior portion of the jaw, often connecting to the anterior surangular foramen at the dentary-surangular contact, while the upper jaw might have a shallow channel connecting to the jugal foramen, which is almost certainly pneumatic as it connects inside the bone to a large hollow diverticular “camara.”

These, as in reptiles, are linked also to the nerves and blood vessels that “feed” the labial soft-tissues (ligaments, muscles, skin) and are thus connected to the implications for “lips.” However, the constraint here with mammals ends. Mammals typically only have a few foramina connected to these tissues, maxillary, mental, and anterior and posterior mandibular foramina. As noted, mammalian facial muscles make the bulk of their lips, while reptiles are less muscly in the face. The extensive nutrient foramina then are linked to a different set of tissues, larger branchings of the facial nerves, and external nutriation of the teeth than in mammals (which are primarily fed from branches of the nerves and blood vessels within the jaw). More extensive gum tissue, surrounding the teeth, also characterize reptiles. This fact of gum tissue, a feature that McCreery and Krentz also adopt, ends up resulting in “small” teeth as apparent from outside the jaw:

These animals seem like they have a whole set of toothy jaws inside a set of lippy jaws!

(Despite the amount of flesh wrapped around these jaws, the rims of the antorbital fenestra and orbit are still plain to see, and this should certainly NOT be the case.)

McCreery manages to follow lizards in another aspect, that of characterizing large labial scales. Crocs have very small labial scales, and they are thin and broad but closely associated to the jaw margin, just as any ligamental tissue is reduced. Lizards and crocs, just as in some birds, have some additional facial features that mammals lack, such as the presence of electrosensory organs like dermal pressure organs or Herbst corpuscles. These require additional innervation. Were these likely present in dinosaurs? The answer to this is unknown, but the jaw anatomy at least points to dinosaurs like Velociraptor mongoliensis as having lizard-like facial tissues, in nature if not in exact form. Phylogenetically, however, they are close to birds, and this has caused some artists (notably, Greg Paul) to “thin down” the integument and bring the skin close to the bone surface. Lips are a passing fad in this case, except when needed. This can have comical effects on the appearance of the animal, as McCreery’s “velociraptors” may attest (and yes, I find them humorous to look at).

The reason I doubt the extensive tissues of film “raptors” is that the soft tissue of lizards generally follow the bony jaw margin, so that the rounder the bony rostrum in monitors, the rounder the fleshy rostrum; narrower, narrower. And Velociraptor mongoliensis has a very narrow rostrum:

Snout of Velociraptor, showing the upper rostrum and mandible in ventral views, and then combined, and finally below with the “fitted” ligamental bands of the “lips.” The broad black bar indicates the room between upper and lower jaws.

Relative to the breadth across the orbits, the snout of Velociraptor is almost 1/3 as broad. This is ridiculously narrow in comparison to, say, Dromaeosaurus albertensis, a related taxon, in which the snout is more than half as broad and the mandibular halves broadly approach one another in a tight V. Moreso the mandibular halves, as they are essentially parallel for over half their length. Velociraptor mongoliensis lacks a broad rostrum, has a very narrow palate, and the palate is highly vaulted in the midsection of the snout, leaving little room for a narrower jaw to have extensive soft tissues. When one places the skin of an animal with a jaw twice as wide around this, to produce McCreery’s “monitor” look, it is rather comical, and there is no analogue for this.

Like slapping lipstick on a rather predatory pig.

Pretending here that I have any sort of credibility, I present the extremes of the discussion for lip tissues in the “monitor” style of McCreery at top, and at bottom in the “fleshless” style of Paul; between these is a moderate compromise of limited tissues and ligamental bands. Not clear in the image above is that in the bottom depiction, the mandibular ligament band is between the jaw and the teeth of the upper jaw, and this is almost certainly wrong as it compares to no living animal. It is my conclusion that if there is a fleshy lip from the lower jaw, it covered the upper dentition, concealing them. The alternative is that the lips of both jaws are short and retracted, exposing the margins of uppers and lowers equally.

As there is (as yet) no evidence of a fleshy-lipped bird (rather than a beak, and no, I’m not talking about toothy birds like Archaeopteryx or Xiaotingia — these birds should have “lizard-like” jaws even so) the conclusions on lip-ness must derived from anatomical analysis, and so far, this data has yet to be produced (yes, I’m hinting at work down the road, especially that of Witmer and Holliday and the like).

Snout cross-sections and tissue analogues and arrangement.

Above is my crack at conceptualizing the constraints on what we can infer from the tissues alone: The types of tissues and their arrangements in a lizard, croc and bird, as well as the (current) covered-lipped ‘raptor from Greg Paul, and the older version (termed “Dinosaur”). The cross-section is modeled from Velociraptor mongoliensis above, but is more stylistic. The ridge extending upward within the chamber marked “nasal passage” represents the vomer, which would support additional structures such as thin bone dividing the chamber in two vertically, and turbinate bones curling to the sides, and are not shown for simplicity. In all depictions, the jaw structure is shown identically, and where is seems interdental plates are present, know that the space dividing the bone represents lingual nutrient foramina innervating the base of the dental alveoli. In “Paulian ‘Raptor,” note that a bit of the orange (rhamphotheca) exists atop the snout, an allusion to Paul’s continuing hypothesis that dromaeosaurs (and Archaeopteryx) have rostral beaks.

Also note that this is art. While I may be somewhat scientifically informed, I am covering my inadequacy by being very limited and stylistic in depictions: a pure sciency presentation would show actual tissue sections alongside representations, and I lack the means of producing the former. Thus I am making my arty stuff very colorful. Forgive me. But because I am trying to be all sciency — and I’ve been doing this over the course of only two days — it is not the best art I can do, and if I wished to try hardest, I would likely produce vector versions for absolutely clean lines and the ability to retain sharp margins at any scale, but alas, not yet (also, I lack the software).

Back to the image. In a typical reptile (“Lizard”), the lips (tan) contact one another outside the dentition, and they are further concealed by labial scales (yellow). Ligaments (blue) are large and pull the facial tissues outwards. This increases in some flexible-snouted lizards, such as monitors, where the tissues are even broader. In a crocodilian, the ligaments are smaller, and the labial scales are thinner and curve along the tissues, supplanting and covering the gum tissue (red) alongside the teeth (black, along with bone). In a bird, gum tissue and facial skin are supplanted by rhamphotheca (orange, here not depicting the separate plates that are distinct in many taxa), and I’ve modified the jaw to coincide with modern birds lacking teeth.

The two “dinosaur” depictions consider the two most heavily used depictions for theropod lip structure. The first,”Dinosaur,” is the most common version, and this generally follows a desire to show the upper teeth. Generally, theropods are shown either having fleshy lips à la lizards, or with almost none (as in Rudolph Zallinger’s mural, The Age of Reptiles, at Yale’s Peabody Museum). I’ve shrunk the mandibular ligament to correspond to the tight fit (as seen in my Velociraptor snout above), and the lips are also fit in but had to be extremely slimmed to do so. Because depictions of the squamation of dinosaurs varies relative to how close to birds they might get, I’ve shown this form of ‘raptor without squamation, and thus omit the labial scales. I’ve left labial scales off of the second depiction of a dinosaur as well, the “Paulian ‘Raptor.” Here, however, the lips are passed outside of the teeth and are thicker.

The real question, then, is which one of these is closest to the true dinosaur? It may and very likely is relative to the group. It is my impression that there is absolutely no evidence for lower lips fitted between the jawbone and the upper teeth. This doesn’t mean that the lower lip was lateral to the upper teeth, as a condition present in long-toothed mammals likely precludes this in some theropods or ornithischians in which upper dentition extends below the jaw margin. This is due to an additional anatomical constraint, and is the second clue.

Remember Dilophosaurus wetherilli?

Skulls of Dilophosaurus wetherilli Welles, 1970 (Welles, 1954).

When closing the mandible, the upper teeth extend well below the mid-height of the jaw, meaning that any soft-tissues wrapping up and around the teeth to close the lips would have to extend deeply and below the jaw, a feature unknown in extant reptiles aside from various crocodilians, and in none that have lips that conceal the teeth. Is there something different going on? I also wondered about how sabre-toothed mammals deal with this issue. Canines (Canis lupus) and all cats have long canines: the lower canines slide into slots called diastemata between the upper incisors and the upper canines, and these diastemata are fairly large in cats but less so in dogs. The upper canines, however, extend well below the mid-high up the upper jaw in most felids, and in sabre-toothed cats, can be as long as the lower jaw itself. This is accommodated in these carnivorans by the lower lip being protruded below the teeth, but not covering them.

Cats both domestic and sabre-toothed. Thin lines depict the margin of the fleshy lower lip. Light grey on the right depists the exposed soft-tissue of the inner lower lip and gum.

Is it possible then, that dinosaurs could have had similar lips for elongated teeth, but shorter, “normal” lips for shorter teeth? Certainly, although I will not claim to assert these to be true. It may simply be that long-toothed dinosaurs had fleshier jaws in the style of monitors and McCreery’s “velociraptors,” just fleshier and deeper. And with something like Velociraptor, it may not be so easy to distinguish the two:

Velociraptor mongoliensis jaw “fitting.”

So back to Velociraptor mongoliensis. Depending on how closely one wishes to “fit” the jaws, one gets different levels of soft-tissue “room.” First, lizard-style, the teeth do not necessarily pass further than the bony margins of the opposing jaw, and this depends on how tightly left and right halves were. Very tight, and we might get the “lightly closed” perspective, with virtually no room to go further. But I suspect the jaws were capable of further closure, and can close the jaws at least as far as the upper dentition coming to the nutrient foramina of the lower jaw (middle). Here, the teeth come close to palatal surface of the maxilla and premaxilla, but barely. And lastly, if the jaws are broad enough, the teeth press all the way to the palate, and the jaw is positioned as it has been preserved in several specimens. I wonder if that is rather based on distortion, but if not, it implies the “croc” style jaws shown above (and inset in the image). This would leave little room otherwise to the sides of the lower jaw (shown in coronal section at right) for lips, and we might get a broader, yet less fleshy head. The upper teeth would protrude almost past the gular (ventral) margin of the jaw, and this might imply a “cat-like” lower lip.

Which one, which one?

In the end, I am not satisfied with any of these ideas. This is because I do not think we have all the details at hand in order to correctly depict these lips. Until then, i tend to favor the model of existing reptiles and place lips around the dentition, as I described a few posts earlier:

Velociraptor, lipped and beaked according to Paul.

As an aside, but no less important, it should be noted that I absolutely disagree with the mere hypothesis that any sort of remnant of a beak exists in toothed “velociraptors,” sensu Greg Paul. There is quite literally no reason aside from speculation that even early birds like Archaeopteryx had beaks, and no reason to think, even if Paul’s “neoflightlessness” hypothesis is correct, to presume that larger-bodied, larger- and many-toothed theropod dinosaurs would have had them. This is especially significant given the similarity in snout anatomy to fleshy-jawed reptiles, the rounded margins of the bone, and the absence of any argument for an analogue to a rhamphotheca aside from “numerous foramina” or “rough texture” (both of which exist in squamous, non-beaked reptile jaws). I will actually return to this concept where, showing data outlined here, I demonstrate the artistic inconsistency in which even Greg Paul has attempted to demonstrate this idea.

Currie, P. J. 1995. New information on the anatomy and relationships of Dromaeosaurus albertensis (Dinosauria: Theropoda). Journal of Vertebrate Paleontology 15(3):576-591.
Godefroit, P., Currie, P. J., Hong L., Yong S.-c. & Dong Z.-m. 2008. A new species of Velociraptor (Dinosauria: Dromaeosauridae) from the Upper Cretaceous of northern China. Journal of Vertebrate Paleontology 28(2):432–438.
Osborn, H. F. 1924. Three new Theropoda, Protoceratops Zone, central Mongolia. American Museum Novitates 144:1–12.
Ostrom, J. H. 1969. Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana. Bulletin of the Peabody Museum of Natural History 30:1-165.