Giants & Other Early Reptiles Online

When your average modern dino fan hears the name "David Peters", they probably think of lepidosaurian pterosaurs, archosaurian mammals, invisible babies and the most extreme examples of paleontological pareidolia since Chonosuke Okamura. But to the surprise of some commenters , Peters was, for a while, a somewhat prolific and outstanding paleoartist. I have long credited his two early 'gallery' style books with being one of my main early influences. These books more than anything except maybe Phil Tippet's Prehistoric Beast fostered my interest in paleontology as a kid and kept it going, giving me ample figures to copy... I mean... giving me plenty of references to use in my first attempts at palaeontography. Looking back through them I reckon those influences are still very much with me. Each page even functions as a scale chart, which must not have made too much of an impression on my developing mind.

For those also looking to be inspired by some 'old school' but still fairly accurate (especially in Gallery which features a Deinonychus so bird-like it blew my 12 year old mind) or at least interesting renditions of prehistoric animals, I recently discovered both of these gallery-style books are available as free PDFs from Peters' art site (often overlooked in favor of his more, um, eccentric science and phylogeny site).

Tyrannosaur Tooth Count

Making the rounds right now in the media is a story about a newly described, well-preserved baby Tarbosaurus bataar that helps shed some light on the way tyrannosaurs grow, as well as touches on lingering controversies. Plenty of other blogs have already covered this, so here's a link to the backstory from Brian Switek at Dinosaur Tracking.

Interestingly, the baby Tarb has 15 teeth in the lower jaw, the same number as adult T. bataar. There has been controversy over whether or not tyrannosaurs reduced their number of teeth as they grew, particularly when it comes to the controversial taxon Nanotyrannus lancensis. Nano is known from two specimens (one is nicknamed "Jane") that, depending who you talk to, might really be simply juvenile specimens of the contemporary Tyrannosaurus rex. The differences cited to separate the two boil down to differences in the braincase (certain braincase changes were demonstrated in the new juvenile Tarbosaurus as well), and the number of teeth. Adult T. rex are usually said to have only about 12 teeth in the dentary, while specimens of N. lancensis have a whopping 17. The new juvenile Tarb suggests that in at least some tyrannosaurs, the tooth count is not drastically reduced during growth from juvenile to adult. However, as the authors caution, this same pattern may not necessarily hold true for other tyrannosaurs, even very close relatives.

And, the same pattern does not hold true for the very closely related T. rex. Also making the blog rounds these last few days has been this video of Jack Horner's talk at TEDx in Vancouver (thanks to David Orr at Love in the Time of Chasmosaurs for posting the video link!).



Here Horner gives the basics of his theory that dinosaurs are oversplit, not in the subjective taxonomic sense, but in the more objective biological sense that specimens that could be shown to belong to one species actually represent juveniles of other species. You've all heard the details before, but towards the end he shows a slide (reproduced above) that is pretty damning to the crowd who support the validity of N. lancensis. In fact, adult specimens of T. rex show a very wide ranging tooth count, and it even appears to correspond with relative size (and presumably growth stage. If anything, the number of teeth seen in N. lancensis specimens are only one or two teeth outside the range of variation for T. rex proper, a minor variant that can almost certainly be attributed to ontogeny, and not some cryptic species of giant tyrannosaur lurking in the Lancian faunas that has so far only been identified by two juvenile specimens, while the very common T. rex is known from no juveniles at all.

Anybody know the tooth count for the "Tinker" specimen, currently held in a private collection?

Confuciusornis: Bird-o-Dactyl

There's been a lot of debate about Confuciusornis lately. Could it fly? If so, how? And how well? It probably wasn't doing anything like a modern bird does. Studies of its feather strength suggest it couldn't do more than glide (or could it?). But studies of its forelimb and shoulder girdle show it couldn't lift its arm much above the horizontal plane, making flapping pretty much impossible. Unless that huge, fenestrated deltopectoral crest gave it a rather unique flight stroke that only minimally involved the humerus.

Or, maybe this was a small theropod with enormous, high-aspect ratio wings larger than those of any other early bird, with asymmetrical feathers, puny feet and short legs ill suited for running and a small, barely reversed hallux ill suited for climbing, which couldn't flap and could barely glide with its thin feather shafts, yet is consistently found preserved as enormous flocks at the bottom of deep lake deposits. In which case the giant wings would be for display, obviously, to hopefully impress a predator so much that they decline to eat the poor bird which has no means of escape or defense other than to flee into the depths of the water like a 1960s brontosaur, only to remember that it also can't swim. No wonder they're extinct! Anyway... I hope much, much more study (and some wind tunnel tests) will eventually help untangle this mystery. For now, I was struck by something a little more frivolous. Working on a lateral view of Confuciusornis sanctus, checking and re-checking papers to make sure proportions are right, it started to look unmistakably like the profile of a... rhamphorhynchid pterosaur? Between this, and basal paravians with expanded, diamond-shaped vanes on the tips of their tails, in terms of general body plan there are some curious similarities (convergences?) between the first gliding/flying birds and primitive, long-tailed, high-aspect ratio-winged pterosaurs. My PhyloPic style silhouette version above.

Restoring _Hesperornis_

Wow, lots of great responses to Monday's challenge! Some of you came very close to the particular aspect of the anatomy I was thinking of, though nobody got the specifics. However, many of you brought up additional issues with the reconstruction so I'll address some of those observations below before I get to the real answer.

1. Trish brought up the Coot-like lobed feet. While not the major fix I had in mind, this is also something I had already changed in the new version. The toes of Hesperornis are extremely similar to Grebes in terms of their anatomy, so while no soft tissue impressions of the toes exist for this group, it is almost certain that the toes were lobed rather than webbed (as in Loons and many other diving birds). I had initially based my illustration on this model, which restores the toe lobes divided into somewhat Coot-like segments. However, given the similarity to Grebes, it's probably a safer bet to go with a Grebe-like foot, with non-segmented, asymmetrical lobes (that is, like the flight feathers of birds, the 'vane' of each lobe would be small on the outside edge of the toe but broad on the inside edge). As this was still a work in progress when I began the revisions, I didn't yet add to the podotheca (foot skin covering) with its distinct scutes, but skin impressions from Parahesperornis show that they were present and, again, fairly Grebe-like in appearance.

Above: The feet of Hesperornis probably looked very similar to those of this Grebe.

2. Nobu Tamura pointed out that I bungled my interpretation of the leg integument. Good catch! In my own defense the text of Williston 1896 (which described skin and feather impressions in a specimen now referred to Parahesperornis) isn't exactly clear on the issue and the figure doesn't help much. Williston wrote: "I count twenty-six [metatarsal scutes] on the slab, and to the back part of the bone, while impressions of the feathers will be seen on the opposite side. These feathers were evidently long, reaching nearly to the phalangeal articulation". I remembered this as saying that the feathers essentially cover the tarsometatarsus and that the scutes were present close to the phalanges, but re-reading it sounds more like the MTs were only partially covered in long feathers (on the proximal part of the bone?) while the scutes were present across the distal part. The feathers were long enough to reach the toes, forming some very odd 'bellbottoms' around the scaly part of the metatarsus. I've tried to make this more clear in the new version.

3. Several people suggested that the wings are too prominent/visible, and honestly I'm not sure about this one. I don't know of any research on forelimb musculature that could suggest whether they were external or internal to the body wall, or whether or not they'd be useful in steering or something. I suppose we artists have license to go either way on this one right now, but as you can see I've de-emphasized them in the new version. The old one began to strike me as too Penguin-like, suggesting (even subconsciously) a role in propulsion that was probably not there in life.

4. Marco Tedesco wondered if the orange feathers on the head were incorrect. I have previously blogged about the likelihood of certain feather colors based on diet and structure. However, I don't think Hesperornis would have had much trouble sinking its teeth into some carotenoids to deepen the chestnut hue possible through melanin alone into a richer orange. We know that many cephalopods (including, apparently, some ammonites with preserved pigment) contain deep red carotenoid pigmentation, as do many fish, both of which may have been parts of hesperornithine diet. And in fact, these are colors found in modern Penguins. While on the subject of color, I chose to give Hesperornis a distinct, Penguin-like counter-shaded pattern. It seems to me that counter-shading gets apparently stronger in several independent lineages of diving birds, with more specialized diving forms (Penguins, Loons, Auks) wearing similar black/white colors (at least among breeding males) while less specialized forms (ducks, etc.) are counter-shaded with more subtle earth tones. Hesperornithines are probably the most specialized diving birds of all time (Zinoviev 2010) so it made sense to me to give them generally Penguin or Auk-like coloration.

Ok, now on to the "real" answer. Several people got this pretty close. It does indeed involve the hindlimb anatomy, including the position of the femur, the degree of sprawl in the legs and, ultimately, the life posture and ability to move around on land.

Several online sources have stated that Hesperornis was unable to walk, and must have instead slid around on its belly when on land. As I hinted in the last post, the Web site for the BBC show Sea Monsters (and possibly the show itself which I haven't seen) flat out states that they couldn't walk. But as we all know, TV documentaries are not exactly reliable sources. I tried and (initially) failed to find any support for this in the literature, aside from Marsh's own speculation in his famous Odontornithes monograph: "It may be fairly questioned whether it could even be said to walk on land, although some movement on shore was of course a necessity."

Two pieces of information can be combined to give the answer, the second of which also strongly impacts any life restoration, on land or swimming/diving. First, while the feet of hesperornithines are extremely Grebe-like, the rest of the hind limb anatomy is very similar to that of Loons (Reynaud 2005). Like Loons, hesperornithines had very long tibiotarsi, very short femora, and a high-angle hip socket with a very limited range of motion. Essentially, this means that the upper legs of Hesperornis were locked into a sprawl, which would have made standing upright very awkward. Loons rarely walk upright, and in fact I can't find any images online of such behavior. Loons also will push themselves along on their bellies, "flopping and dragging" as one site describes it (image above from birdinginformation.com)

Now, while the femur was basically immobile, it still had a role in contributing propulsive forces, as demonstrated by the arrangement of muscle attachments, which allowed it to conduct strong backward force through the leg. This is quite a feat because, (finally the answer to the challenge!) as in Loons, the entire, laterally projecting femur, the knee joint, and most, if not all of the tibiotarsus, was likely encased inside the body wall! Yes, according to some recent research (Zinoviev 2010), "the tibiotarsus...was held close to the body and was probably enclosed in the thickly feathered skin of the body wall". So images like mine, and the one below by Nobu Tamura (from Wikimedia Commons, CC licensed) showing free legs are wrong.

Like Loons (image of Common Loon above by Matthew Studebaker, from his photo blog), the feet stick out laterally from the very rear end of the animal near the tail, and it is the feet, rather than the leg as a whole, that provide most of the thrust and control (though, again, even the internalized leg musculature contributes to this).

So, congrats you those who noticed something wonky with the hind limbs! In all, hesperornithines were essentially super-Loons with Grebe feet, though their unique specializations for diving exceeded nearly all modern divers, making them possibly the most truly aquatic dinosaurs that have ever lived.

One last thing: quilong suspected something off with the posture of the neck. As he points out, highly specialized diving birds tend to have advanced ligament systems to keep the neck positioned during dives, and it tends to be streamlined into the body, often in a tight s-curve. This is correct, and my image is a bit misleading as it's meant to depict a hesperorn swimming at the surface with its neck at full extension to reach above the water, like an Anhinga (or indeed, a swimming Loon, which tend to swim almost completely submerged except the top of the back, the head, and the neck). While diving, the long neck would almost certainly be held in a position closer to the body so as not to be subject to forces that would bend it every which way. Whether or not hesperorns did have advanced ligament systems in the neck to help with this, I don't know, but given their extremely derived morphology it wouldn't surprise me.


References:
* Johnsgard, P. (1987). "Diving Birds of North America: 2 Comparative Distributions and Structural Adaptation. " Papers in the Biological Sciences.

* Reynaud, F.N. (2005). "Functional morphology of the hindlimbs of Hesperornis regalis: A comparison with modern diving birds." Geological Society of America, 37(7): 133A.

* Zinoviev, A. (2010). "Notes on the hindlimb myology and syndesmology of the Mesozoic toothed bird Hesperornis regalis (Aves: Hesperornithiformes)." Journal of Systematic Paleontology, 9(1): 65-84.

I'm Doing It Wrong: More on _Hesperornis_

Following the last post on beak anatomy in toothed birds like Hesperornis regalis, I have been coming across some confusion online about another aspect of this ancient diving bird's anatomy. This factoid shows up in a lot of sources (including the official web site for a certain CGI-based TV show) but never, it seems, with a solid reference. I have been trying to dig into this issue myself and am finding out some interesting new info on the anatomy of this bird, to the point that one of my in-progress drawings had to be halted and revised. More on this in an upcoming post, but for now, see if you can figure out what's wrong with this picture:

You're Doing It Wrong: Birds With Teeth

Above: If only Charlie from Always Sunny could visit the Mesozoic.

My previous post on beaked theropods left one thing a little too ambiguous for my taste. We know that many non-avian theropods had beaks, but we also know that, famously, many of these also possessed teeth. An issue I've often come across in palaeontography is how exactly to restore this. Should the teeth erupt directly from the beak? Were they segregated to different portions of the jaw? Did the beak edge overlap an inset tooth row? This is an issue which I've rarely seen discussed online, let alone in the literature, so hopefully this post can be a starting point to suss things out. Because it's one of the most famous examples and one that's been frequently discussed in the lit, I'll focus specifically on Hesperonris regais here.

Look at almost any life restoration of Hesperornis, and it will show a keratinous beak covering the entire extent of the upper and lower jaws. I say "almost" only hypothetically, because I've literally never seen a hersperornithine drawn any other way (please link me one if you can). Here's a link to a google Image search for Hesperornis, and every reconstruction is the same. Some, like the beautiful painting above (by artist Larry Felder), clearly show teeth erupting directly from the tomia (edge) of a continuous keratin beak. As discussed last time, the continuous appearance of this beak is likely incorrect in itself, since non-avian birds probably all had 'compound rhamphotheca' made up of several distinct plates that are often visible in life.

Above is bit of anatomy lingo to make this discussion easier. The rhamphotheca ("beak") is usually divided (and literally divided, in the case of compound beaks) into several segments or regions. The figure is figure 5 from Heironymus & Witmer, 2010.

Now, for comparison, here are two views of the skull of Hesperornis regalis. On top is a ventral view of the skull showing the premaxilla and maxilla, from Elzanowski 1991. The bottom is a right lateral view of the skull taken from Heilman, 1926.

A few things to note here. The dentary teeth continue almost all the way to the tip of the jaw, though the very tip (and small predentary that was probably present) were toothless. In the ventral view of the upper jaw, you can see indentations where the lower teeth would have locked into the premaxilla. If there was a hard beak present, it would have been pitted to accommodate the dentary teeth (these are labelled dp, dental pits, in the top figure above). However, you can also see that the indentations are inset to the jaw a bit. The edges of the upper jaw slightly overhung the lower jaw, which would have allowed for the tomia, if it was there, to not come into contact with the lower teeth, causing wear any time the mouth closed.

The back of the jaws are a different story. As you can see in the lateral view, upper teeth are present only in the maxilla, not the premaxilla, and therefore restricted to the very back of the mouth. This can also be seen in the 'dental grooves' (dg) in the ventral view of the skull.

According to Heironymus & Witmer 2010, in both Ichthyornis and Hesperornis, the premaxillary nail and mandibular nail were the most heavily keratinized part of the beak. This is where the beak would have been most solid, like a normal bird bill. The same authors note that the simple presence of teeth in the maxilla and dentary of these species probably means that they lacked the latericorn and ramicorn parts of the beak entirely, and that the presence of cornfield rhamphotheca on the edges of the jaws may be unique to modern birds. However, as I noted above, the premaxilla in Hesperornis is also toothless and provides area for a tomia of some kind to be present. This would have been somewhat softer tissue, like the more pliable bills of ducks and geese. Further support for the presence of a beak on the premaxilla comes from the presence of a rhamphothecal groove on the dorsal part in front of the naris (visible but unlabeled in the figure above).

So how far did the beak extend? Heironymus & Witmer found that the latericorn almost always extends to the back of the subnarial bar in birds. This is a process of the premaxilla that extends back to separate the naris from the maxilla. Basically, this means that the beak will very rarely, if ever, extend onto the maxilla itself. As you can see in the lateral figure above, the maxilla in Hesperornis even compensates for this limitation by extending a bit forward underneath the subnarial bar to extend the tooth row anteriorly a bit past the possible full extent of the beak.

So, based on the evidence above, Hesperornis probably had a beak like the recon I whipped up below. The toothless, pointed tips would have been solid, normal beak, while the rest would have been more like stiffened skin grading into normal skin and feathers toward the back of the skull. At no point would the teeth have occupied the same physical space as the rhamphotheca. Basically, the rhamphotheca never seems to have housed tooth sockets. The beak and the teeth were segregated to different parts of the jaws. In short, no Mesozoic birds had "teeth in their beaks" as is often stated and depicted in art, but rather had both beaks and teeth, in different parts of the skull, and presumably serving different roles in food capture and processing.

References:

-Elzanowski, A. (1991). "New observations on the skull of Hesperornis with reconstructions of the bony palate and otic region." Postilla, 207: 1-20.

-Heironymus, T.L. and Witmer, L.M. (2010). "Homology and evolution of avian compound rhamphothecae." The Auk, 127(3): 590-604.

April fools! A bit late but who's counting?

UPDATE!

This is a late-arriving April Fools joke. Got me!

Archaeocursor. The bahariasaurid (yes, new family) with feathers. Commence head explosions.

Paul C. Sereno, Oliver Rauhut, Xing Xu, Wang, Y., Zhu, T., Gao, X. & Gong, D. (2011). "Basalmost theropod with filamentous integumentary structures and new clade of basal 'carnivorous' dinosaurs". Kirtlandia 37: 82-113.

I haven't seen any discussion of this, save that it's been added to Wikipedia. Apparently from the Tiaojishan formation, the same beds that have yielded Anchiornis and Tianyulong. Also, note the scare quotes around "carnivorous." Could their proximity to Limusaurus mean bahariasaurids are partially or wholly herbivorous? Just idle speculation for now. More if/when I get my hands on this paper.