Troodontids and All That Jazz

This post originally appeared on a mailing list discussion by yours truly back in 2000, here. I am posting it here in order to reintroduce the topic and begin elaborating on it, as I have a few/many comments on the topic of troodontids, deinonychosaur phylogeny, bullatosaurian phylogeny, their teeth, the nature of carnivore "guilds," and the general topic of teeth and tooth-based taxa and what to do about them (which pretty much sums up my research work).

The post begins below.

A few taxa were based on teeth, and these are generally referred to as nomina dubia, but as Currie, Rigby, and Sloan (1990) showed, are diagnostic individually, and different genera can show differences based solely on dentition. Koparion douglassi from the (LJ) Morrison Formation is one such example, based largely on the bulbous base of the tooth and low height/length aspect ratio. Pectinodon bakkeri was synonymized with Troodon formosus based on extreme similarities in that they fell within the same expected range of morphology for the same jaw, by Currie et al. (1990). Ciski and Grigorescu (1999) suggest that Pectinodon may be a distinct species of Troodon, T. bakkeri, based on another set of teeth from Romania, including another suggestion that Euronychodon is a troodont. I have no diagnostic opinion of Saurornithoides/Troodon asiamericanus and S./T. isfarensis.

Other troodont taxa are based on pedal elements only, such as Borogovia gracilicrus and Tochisaurus nemegtensis, but then again, these pes differ markedly from those of Troodon, Saurornithoides, and even Sinornithoides (pers. ob.). Short pedal toe 2 in Borogovia with the relatively strait claw is strange and unexpected, but also found in the deinonychosaur (sensu recens) Adasaurus. It's a troodont, though. But unlike other known troodont pes, Tochisaurus had a very short mtII which, given the average relative length of digit II to the metatarsal, would have prevented the toe from touching the substrate, and making it functionally didactyl, as in ostriches, hence the name (toch' in Mongolian refers to ostriches).

The taxa represented by more complete material including parts of several regions of the body, include Saurornithoides, Troodon, Sinornithoides, Byronosaurus, and another troodont from Ukhaa Tolgod. These taxa differ from each other in more significant ways, based largely on the more complete material, and are the main diagnostic tools for the group. A complete skeleton is known only for Sinornithoides youngi, and proportions are similar to ornithomimosaurs in many respects, especially the skull with Pelecanimimus.

The skulls of Byronosaurus, Troodon, and Saurornithoides are less complete, but are still complete enough to compare, and all are relatively more derived and closer to each other than to Sinornithoides, and this suggests that Sinornithoides is more basal. The skull is longer snouted with a deeper snout and less triangular profile in the last group, and the form of the pes is not indicative of any derived form. The pelvis is propubic with a derived, oviraptorosaurian-like anterior pubic process with the ilium, so that the pubis is slightly offset under the acetabulum then curves forward. Very short ischium with no elongate post obturator process in Sinornithoides and Saurornithoides, as far as I can see. Long tail lacks stiffening structures except for possible craniocaudally long chevrons in the distal half. Manus of the dromie/caenagnathid form, with a shorter third finger than second, and semilunate does not contact the third metacarpal [could be wrong on a few cases]. Long, long necks, very slender. Coracoids are intermediate between the ovate ornithomimosaur form and the everted rectangular form of oviraptorosaurs, closer to the latter than the former. Sinornithoides preserved furcular splints, or true clavicles, whereas the condition appears to be unknown in all other troodonts.

Taxonomy suggests that Koparion, Sinornithosaurus, and Byronosaurus are successive outgroups of the group formed by Saurornithoides and Troodon. Borogovia and Tochisaurus could lie anywhere along the line. Ornithodesmus has been hypothesized as a troodont, and it too, may lie anywhere, as a comparison of sacra has not been done so far on troodonts, and I am unaware of the full condition in Sinornithoides.

Hope this helps, and I would enjoy corrections on any errors or any additions that could be made to this.

Data comes from Russell and Dong, 1994; Currie, 1987, 1990; Barsbold, 1976; Makovicky et al., 1999; Chure, 1994; Currie et al., 1990; Russell, 1970; Osmólska, 1988; Osmólska and Kurzanov, 1992; and Glut, 1997.

——

Current research (as of 2006, in order to show this comment is current):

A new troodontid, Mei long, has refocused the evolution of troodontids towards the base of the avian divergence within dinosaurs, near dromaeosaurids. Remarkably tiny, Mei contains a skull much like Byronosaurus but with many other peculiarities of the jaw bone and braincase that make it rememble an Archaeopteryx-mimic. Even more recently, skulls of some alvarezsaurids (such as Shuvuuia and some more peculiar skulls from Liaoning in China and Ukhaa Tolgod in Mongolia) show a similar morphology that may have conceptualized the ur-bird and close relatives, from alvarezsaurids, troodontids, and dromaeosaurs like Microraptor. This new animal and another, described as a bird (Jinfengopteryx) show that the origin of troodontids was complex and peculiar, and that their evolution was to increase in size and diversify. The largest troodontid was also one of the latest surviving, "Troodon" or Stenonychosaurus.

More work to come.

Teeth and Why They Matter to Me

I first started this blog to post my long and sometimes convoluted ideas about the relationship of teeth to evolution, biology, and ecology. Since then, I have been posting commentaries and one single discussion that might have anything to do with teeth (on the despots). This should be changing shortly, as I delve into the past to bring up some old Mailing List posts of mine on the subject as I write concepts out that have only been ML posts to begin with. So at first, expect to see a few posts about some critters both toothed and non and my arguments about them. Links to discussions already posted will be made available in addition.

A Parable On Two Doors

Prof. P.Z. Myers has a post over at Pharyngula from last March (over a week ago!), discussing a parable on the choice of two doors. There are some obvious symbolic inferences, but I was not satisfied by the given scenarios, which only seem to attest to a particular bias on the part of the author on how to choose between two apparent positive options (though the description quickly diverged into one being more positive than another, obviating the given choices we are being asked to make) . I chose to muddy the waters a little by recasting the parable.

The parable begins:

A man named George comes into a chamber with two doors before him. Before each door is a man dressed in a white robe. Each man is identical save for an ornament around their neck. The first man wears a gold key with ornate designs in the handle, while the second man wears a silver key without any ornamentation. The doors they stand before are also distinct, though identical in size; the first is made of a golden brown wood giving off a soothiung scent, covered in fine brass filligree. The second door is made of a fine paper mesh covered in scroll work and small lines that, upon closer inspection, would reveal intricate writing, and the door's frame is a light cork and balsa.

George, curious, steps forward, choosing at random the first filligreed door and the man before it. "What are these doors?" he asks.

The man with the golden key about his neck steps forward, and, bowing his head, answers: "Truth."

George, never one to accept things too simply, walks over to the second door and asks the same question. It's guardian steps forward and responds, "Truth."

George ponders this for a moment. "Surely both doors cannot have the same thing behind them?"

The first man answers, "Light derives from the candleflame, so that in the presence of light, one knows there is a candleflame. Look, and you will see."

George turns to the second man, who answers "Blindfold a man, and he can feel the flame. Is this faith? Take the blindfold off, and you will know."

"What must I do to go through those doors?" George asks.

The first man answers, "I will escort you. There are pitfalls in the path, and I am knowledgeable of them. Without my aid, you will stumble."

George asks him, "What is at the end of the path?"

"Truth. There is peace and light, joy and no suffering."

George turns to the second man, who answers, "You must go alone. I do not know the path, therefore my guidance would be as youthfully unknowing as yours. What lies beyond this door, you must find for yourself."

"Have you been through his door?" George asks the first man, guesturing toward the second door.

"I have no need, for I am at peace with where I am," he answers.

George turns to the second man, who answers, "I have looked through there, I did not find the path so challenging, but I found myself curious, and there was nothing to see."

George looked at the first man. "It is true," he said. "There is nothing beyond the door to see. It is a place where there is both everything and nothing. Yet, as I said, there is joy and peace. There is no suffering beyond this door, if you are but guided to its end. But consider, beyond his door, there is nothing as well."

The second man responds, "There is nothing only because we stand here. Neither of us has been through the door to investigate. Would you listen to a man who says each leaf that falls from the oak is the same? Would you listen to a man who says that each leaf he has seen fall even from a single oak is different? One must consider for himself."

The first man responds, "It is through revelation and guidance that danger and pitfalls are avoided. How else to live in a words of flames and tigers?"

The second man responds, "Should I trust the flame that does not burn? How should I consider the flame but through all of it? Do you know the flame burns or the tiger bites without someone being burnt or bitten? Were you guided to this, or felt it yourself? It is through experience and living that one learns."

The first man responds, "Yet through such living there is pain, strife, suffering, death. Why live through such horrors and instead seach unity and peace? Converge, collect, and reconcile. The world is danger, thus guidance is required to gain peace. Absolution cannot be sought and learned, it must be given, revealed to the consolate man, that he may be at peace."

The second man responds, "The world has pain and suffering, yes, but there is joy and life. Consider my hands, they are calloused, and this comes from much toil. But for me, my works are my own, and I was not given these callouses without effort. Would you be lazy and slothful to be given something without question?"

The first man responds, "What would you do when all effort finds you nothing? Where is the goal of life? My path has but one goal, and I have been there and there is peace and joy. Would you strive and never gain?"

The second man responds, "My goal is life. A goal need not be concrete and placed so as to touch. It is no game for sport. A goal can be anything, the measure of effort, the product of toil. But what of this door? Why would I know what lies beyond, for I have never been? Would that you joined me to discover?"

Palaeontological Apologists?

Well, apologists as far as creationism, anyway. A group called Creation Expeditions (link) seek to recover fossils to "prove" creation and disprove evolution. However, the group is peppered with some of the more egregious and most easily falsifiable (as well as down-right ridiculous) statements that show how little some of these investigators are really willing to go to study the fossils they encounter, other than to shoehorn them into some preconceived notions.

But really, first, this post takes the cake. This one starts off with a humdinger:

Fossilized skin imprints from “Ezekiel” the Edmontosaurus point to recent catastrophic death of this duck-billed giant. Find counters the myth that the Edmontosaurus was a transitional dinosaur with feathers.

Now, having "followed" the literature to some extent, I am at a loss to figure out how Edmontosaurus, a hadrosaurid ornithischian dinosaur from the Maastrichtian Late Cretaceous of southern Canada and north-central USA, is in any way related to the dinosaur-bird debate. And I've certainly never seen anyone propose it had feathers! There have been some folks, due to a particular ornithischian, Psittacosaurus, who have suggested that quill-like integument (see Mayr et al 2002), scales, and feathers, are all the same thing.

An excellent rending of a Psittacosaurus with the quills in place as discovered is here. Meanwhile, a more elaborate, yet less likely, rendition is here. Note that only the tail has been found with the quills, and they are more apparently similar to mammalian fur than they are to feathers.

In fact, based on observing the development of feathers and scales and even fur, several biologists, including a molecular chemist and an ornithologist, disagree. Chuong, on his part, has studied the genetic development of feathers, and Prum (followed by Prum & Brush in a review) has modelled the origin of feathers into developmental stages that should, they theorize, correspond to finds in the fossil record. Indeed, they propose each stage can concfer a utility on the bearer, and thus allow that animal to use these structures. No where in the origin of feathers debate has anyone considered Edmontosaurus to have had feathers. Indeed, fossil finds of hadrosaur skin have been known for a CENTURY, and because of this, one once has the topic came up.

An Edmontosaurus ... without feathers.

But perhaps these apologetics on the part of the post authors is an attempt to steer the readers into assuming such a theory was formulated? To argue that they, in finding a fossil of which several like it are also known, means something more? By framing it as part of the dinosaur-bird debate, the authors have stepped outside of the entirety of the scientific literature in order to make their proposal "mean something." Does it?

But wait, there's more:

“Our find dispels the myth that the Edmontosaurus was a pre-bird,” said Pete DeRosa, president of Creation Expeditions and team leader on the South Dakota dig. “The rich ash and sulfur content in the soil beautifully preserved the animal’s skin down to the very pigment. It is clear that this was a reptilian-like animal with skin closer to that of a crocodile than a bird. Our discovery demonstrates that there is no reasonable possibility of feathers on this animal.”

More of that false myth used to create a dichotomy, this time a "pre-bird". No theory, however small, has ever argued that Edmontosaurus was a pre-bird. There have been some ideas, back in the 1800's, that argued the ornithischian hip design, because the pubis projected rearward along with the ischium, that they were allied to birds somehow, and that birds may be related. However, with newer study, over a century ago, has thouroughly trashed this idea and theropods have been, by benefit of the work of Thomas Huxley in the 1890's--1920's and John Ostrom in the 1960's--1970's. So there is more "debate" without debate. Just an invention of a desire to create one for excitement. Anmd don't get me started about the comment on pigment....

DeRosa continued, “Buried in the same strata with Ezekiel were evidences of animals which, by evolutionary standards, should not be there, including garfish and turtles. The deposition of the animal, the fossilization and preservation of the skin, the full articulation of the animal, and the fact that it appears to be part of a fossil graveyard[."]

First we have the oldest saw in the anti-evolution book, the "if there are these advanced forms, why are there still primtive ones" argument. This is so bogus it doesn't take a genius to unravel. There is simply no sane reason to expect that "garfish and turtles" would NOT be there, unless they were never found. Nonetheless, the "garfish" in question, likely the garpike Lepisosteus, is a recent, Cretaceous innovation. They are a far younger (and completely extinct group) that did not appear until well after the origin of turtles and dinosaurs, which were very nearly at the same time in the Late Triassic. The oldest known turtle, Proganochelys, is from the Late Triassic of Germany, is in fact coincident with some of the very earliest dinosaurs, including Plateosaurus and the possible dinosaur Procompsognathus (which could even be a sphenosuchian croc). Triassic fossils from Argentina, including Herrerasaurus and the tiny Eoraptor, show that these animals appeared at the same time, and there is no reason not to expect them at the same time and place just as we find crocs, turtles, birds, and mammals and fish all in the same place (say, a Nile shorebank) today. There is, in fact, no scientific reason, only an apologetic one, to argue the opposite. My last statement is borne out by the following:

["]We believe he died thousands, not millions, of years ago. His death is best explained by the catastrophic events surrounding the flood of Noah’s day, as described in the Bible.”

And here, ladies and gentlemen, is the crux of the issue. The apologetics, the attempt to reconcile the natural world with Biblican text. Moreover, a LITERAL reading of that text and an outlanding interpretation of inferred dates based on the long-dead Ussher, whose own ideas have been disproven almost TWO centuries ago. Talk about clinging to the past. The Bible is treated as first, and all fossils come after it, despite the Bible teaching that all things created by God cannot be destroyed. To fix this, fellows like Ken Ham and the great "Dr." Kent Hovind (certainly not a doctor of any science, I can assure you) have simply decided that the Flood killed everything. Yet the Bible states Noah collected ALL animals of the earth, including the "unclean" ones, so there seems little room to leave out the dinosaurs.

But it was worth a laugh, right?

--

Chuong, C.-m. Literature.

Mayr, G., D. S. Peters, G. Plodowski & O. Vogel. 2002. Bristle-like integumentary structures at the tail of the horned dinosaur Psittacosaurus. Naturwissenschaften 89(8):361-365.

Prum, R. 1999. Development and evolutionary origin of feathers. Journal of Experimental Zoology 285:291-306.

Prum, R. & A. H. Brush. 2002. The evolutionary origin and diversification of feathers. The Quarterly Review of Biology 77:261-295.

Tyrants, Despots, and Peons (Update)

I prepared an illustration of the skulls of these "despots" for the sake of comparison, which can be viewed here. The caption is in the figure itself, and the description below is the same as the post I originally mentioned these animals in.

Witmer and Horner on Tyrannosaurus rex

From Michael Ryan's (CMN) blog, Palaeoblog, Larry Witmer (University of Ohio's Associate Professor of Anatomy) and Jack Horner (Montana State University's Museum of the Rockies' Curator of Vertebrate Paleontology) have a series of presentations at this year's American Association for the Advancement of Science meeting in St. Louis, Missouri (always in the USA):

Larry Witmer's talk:

T. rex appears to have had sensory systems that were "even more heightened than we thought," said Ohio University paleontologist Lawrence Witmer. That's based on CT scans of fossilized dinosaur skulls that can indicate the size of areas devoted to particular tasks. Such an analysis indicates that T. rex had "an inner ear structure consistent with a dynamic lifestyle involving rapid tracking movements of the eyes and head," Witmer said. Based on brain size, the senses of smell, sight, hearing and balance were also relatively well-developed.

Indeed, because you see, Tyrannosaurus needed those tracking and jerky head capability to keep an eye on all the other tyrannosaurs that wanted to steal the animal that keeled over for no explicit reason, but makes a good scavenging target.

Witmer joined with Jack Horner to discussion general motion:

T. rex was not particularly agile — even though it's portrayed that way in "Jurassic Park" and other dinosaur movies. based on the biomechanical evidence, Witmer and Horner agreed that T. rex couldn't jump or run in the sense of having both feet off the ground at once. "We have an animal that looks like it should be agile, but isn't. ... I don't think T. rex could dance," Horner said.

It's actually nice to see some neurological data to add to this discussion on tyrannosaur speed, but this doesn't conclude anything that Hutchinson and Hutchinson & Garcia haven't said already: that Tyrannosaurus did not have the muscle mass in its legs required to move it faster than, say a quick walk for maybe a slow jog, and certainly seems to show it couldn't acheive a suspension phase in its stride. But I gather Horner's introduction into this is that predators need to run, so it was a scavenger. Perhaps, maybe, but then, no one is assessing speed in the prey to date, either. Thus arguments about the utility of speed in prey capture are meaningless as long as Tyrannosaurus is in a vacuum.

References --

Carrano, M. T. & J. R. Hutchinson. 2002. Pelvic and hindlimb musculature of Tyrannosaurus rex (Dinosauria: Theropoda). Journal of Morphology 253:207-228. (free pdf available from J. Morph.)
Hutchinson, J. R. & M. Garcia. 2002. Tyrannosaurus was not a fast runner. Nature 415:1018–1021. (subscription based fulltext and pdf of paper)

On Tyrants, Despots, and Peons

We all know and love our tyrannosaurs, and anyone who's seen Jurassic Pork -- I mean, Park -- knows these things. Indeed, Tyrannosaurus rex is the #1 ranking most favorite dinosaur in the world, and in history. Save before the 1900's, there was no other truly popular dinosaur, and before it, only scientists really cared about dinosaurs. It wasn't until the popularization in the early 1900's that children, and laypeople, and scientists of other fields, and indeed most everyone in Europe and North America, half of Asia, northern Africa, and even portions of South America, and finally Australia, fell in love with the newest and possibly one of the first tourist attractions: The gorgeous free-standing Tyrannosaurus rex mount designed by C. R. Knight and H. F. Osborn. Even after, the next most astounding skeleton mount would be another Tyrannosaurus rex, that of the infamous "Sue", largest and oldest of its species.

But these are classic tyrannosaurids. Some have been recovered in Mexico, one was found as far flung as Alberta and New Jersey from the American West from whence they first came, and they are known throughout the Plains Provinces of Canada, also in the West. Then they found them in Asia, where they are known in Mongolia and northern China and fragments from Russia. But they were all large, massive animals, over 25 feet in length and bulky. Some smaller ones have been found -- Nanotyrannus lancensis, Shanshanosaurus houyanshanensis, and Alioramus remotus -- but they may end up just as babies, teenagers on the dinosaur timeline.

Then they found one in Europe ... and the finds haven't stopped. They've gotten smaller, hairier, fluffier, and they've been found with a third finger, not the classic two-fingered "wiggler" Ray Harryhausen showed off in his movies Creation and Caveman. The arms are longer, and the head did not look the way they used to. ...

Perhaps more shocking is that these animals are also OLD, known over 80 million years before there ever was a Tyrannosaurus rex. And one was sporting headgear....

Guanlong wucaii (Xu et al. 2006) offers an interesting specimen in regards not just to considering the development of ornamentation of the skull and its extent in tyrannosauroids proper, but the origin and placement of tyrannosauroids in context with the rest of Coelurosauria. Sereno (1998, 1999) found a placement at odds with that of Holtz (1998), and offered the name Tyrannoraptora for the group comprising Tyrannosaurus and Neornithes. Holtz (2004) modified this definition, "The least inclusive clade containing Tyrannosaurus rex Osborn 1905 and *Passer domesticus* (Linnaeus 1758)." (as given from Sereno, 2005, TaxonSearch ).

Details of the postcrania also appear to offer a substantial consideration for the anatomy of early tyrannosauroids, but they may also elucidate the origin of tyrannoraptorans, and this issue has been of more and more recent concern now that we are finding smaller, odder, and far less "tyrannosaur-like" tyrants. Last July, I had the opportunity to go over the paper reporting a new Jurassic theropod taxon Tanycolagreus topwilsoni (Carpenter, Miles & Cloward, 2005) that came with some peculiar observations of the cranial anatomy and some features of the postcrania. This included (but is not limited to) the presence of a posterior "boss" on the lachrymal projecting into the orbit, a coincident process on the postorbital also projecting into the orbit, a very short, high premaxilla, and a lachrymal with a ventral extension of the caudal margin that formed part of the orbital rim, whereas the ventral margin is V-shaped to accomodate the jugal. As was pointed out then and in private, some of these features are not exclusively known to tyrannosauroids, as abelisaurs also possess the medially inclined and deep premaxillary body. Nothing else is particularly useful, however, save the lachrymal and a referred premaxilla originally referred to Stokesosaurus clevelandi by Madsen (1976), which has the added benefits of having a tooth attached showing a lingually-rotated mesial carina and a lingual-rotated distal carina, as well as fused interdental plates. This brought me to consider these features may be tyrannosauroid in nature, and that Tanycolagreus may be a basal tyrannosauroid. But this is speculative, and there is another side to this coin.

The situation could very well be that it IS tyrannoraptoran, not tyrannosauroid, and that the features listed above were present in basal tyrannosauroids but lost in the maniraptoriform branch and retained (and exapted) by the tyrannosauroid branch. This would argue that the complex of basal coelurosaurs could all have been tyrannosauroid-like, but only the Tyrannosauroidea are Tyrannosauroidea, and those silly little dinos are just playing with their skulls.

However, there are some other considerations. Stokesosaurus from the Upper Jurassic Morrison Formation possesses a distinctive ilium with a vertical supracetabular ridge at the midlength of the iliac blade, and an anterior notch on the cranial margin of the preacetabular blade. This anatomy has been used to refer the Lower Cretaceous Wealden English theropod Iliosuchus incognitus (Galton, 1976) to a position similar to Stokesosaurus, and the referral of an ilium from Portugal's Upper Jurassic Guiamarota Formation to Stokesosaurus as a possible new species, and then to a new taxon, Aviatyrannis jurassica by Rauhut (2003). The early "tyrannosauroids" becoming expanded, the first cranial evidence to support this came from England's Early Cretaceous sediments on the Isle of Wight, Sussex, producing Eotyrannus lengi (Hutt et al., 2001). While further work on Eotyrannus elicidates it's cranial and postcranial anatomy, the strength of the morphology of the premaxillary teeth, premaxillary bone, nasal, and lachrymal is only further supported by Dilong paradoxus (Xu et al. 2003) from China's Lower Cretaceous Yixian Formation, as well as all that and the ilium in addition of the newest member of this "mini-tyrant" grade, Guanlong wucaii (Xu et al. 2006), from China's Upper Jurassic Shishugou Formation.

I've taken to calling these critters despots. Tyrants they may or may not be, they were hardly the rulers of their domains, but their relationships may speak of tyrants-to-be.

But this leads me to some curious considerations: Do all these features really add up to Tyrannosauroidea? Or are they basal to the clade as a whole? Upon further investigation, I have found cranial and pelvic features in compsognathids that closely parallel that of the tyrannosauroids, though this is hardly new and compsognaths have always been very similar, perhaps plesiomorphically so, to their huger cousins. These animals were not tyrants, or despots, but peons, whose's right is to rule over nothing but be ruled.

Compsognathus longipes (Wagner, 1859), from Germany's Upper Jurassic Solnhofen Limestone [Formation], unfortuntely, is poorly preserved. The holotype is missing large portions of the pelvis, and manus is scattered, and the skull is lacking the premaxilla in much detail, aside from being crushed and partially disarticulated. Furthermore, the referred specimen from France's Upper Jurassic, C. "corallestris" ( Bidar, Demay and Thomel, 1972), has an even worse preservation of the pelvis, the manus is almost entirely missing, and the skull split down the middle of the bones, making details difficult to assess. Though Karen Peyer in her thesis and has upcoming publication on these critters, our use of these forms is ... problematic.

Sinosauropteryx prima (Ji & Ji, 1998), also from China's Lower Cretaceous Yixian Formation, is known from three specimens, one which has been alleged as distinct from the holotype and was not part of Currie and Chen's 2001 revision of the taxon. Nonetheless, the specimens are complete in all details we might consider save the skull has been split so that surface bone is hardly preserved, and only shapes are apparent. Nonetheless, distinctive features such as the arched lachrymal and short premaxilla with elongated caudal ramus overlying the maxilla can be compared to tyrannosauroids exclusively.

Compsognathids also bear pelvises with a large ischiadic obturator process, a little ischiadic boot, and a long pubic boot. Nearly all tyrannosauroids also have these features, but oddly, the earliest ones appear to have lacked some of them. Dilong, for example, possesses a long pubic boot, lacks an anterior projection of the boot, and even the ischiadic boot and obturator, though Guanlong, amazingly, does not. Rather, the ischiadic obturator is enclosed in a plate forming an ischiadic fenestra, there is a slight ischiadic boot, smaller than in Dilong, and the pubic boot has a small anterior projection, unlike in Dilong. Most interesting, however, is Mirischia asymmetrica (Naish, Martill & Frey, 2004) from the Brazilian Lower Cretaceous Santana Formation, a place also known for its fish and pterosaur fossils. This specimen exposes a particularly odd pelvis, which on one side shows an open pubic fenestra and a close ischiadic fenestra, and on the other a closed pubic fenestra and an open ischiadic one, forming an ischiadic obturator process. It seems that this "compsognathid" may in fact be a tyrannosauroid, albeit a small one, and likely the most tyrannosauroid-like "peon".

There are other animals to consider, however.

There is the Wealden Aristosuchus pusillus (Owen, 1876; Seeley, 1887), based on a pubis and sacrum, similar to both Dilong and Compsognathus, currently treated as a compsognathid (Naish, 2002).

And there is the Yixian Huaxiagnathus orientalis (Hwang et al., 2004), a very large (1m, 3ft.+) specimen with a peculiar skull and generalized postcranium, including a long process of the maxilla as in Guanlong with the premaxilla extending a process caudally atop it.

And Proceratosaurus bradleyi (Woodward, 1910; von Huene, 1917) from England's Great Oolite, Upper Jurassic of Gloustershire, which is known from a skull lacking the braincase and roofing bones, save for one tiny, enigmatic, and scintillating fragment of a nasal, which has been used, as in Paul, 1988a and 1988b, to give it a nasal crest (which he also reconstructed for Ornitholestes, though Carpenter et al. 2005 have rejected this hypothesis).

Carpenter et al. referred Tanycolagreus to the "Coeluridae", a group of possibly paraphyletic taxa that has been used to lump many disparate (and primitive) coelurosaurs. I do not think their plesiomorphic nature warrants recognition of this grouping, but then, I am loathe to prevent it based on the possibility of these "plesiomorphies" being consistent and apomorphic for a group named "Coeluridae". Other coelurids, however, include the eponymous Coelurus fragilis (Marsh, 1886) and Ornitholestes hermanni (Osborn, 1906), both from the Upper Jurassic Morrison Formation, and both substantially well known from vertebral, limb, and at least in Ornitholestes, a complete skull. Even so, Ornitholestes bears several "tyrannosauroid" apomorphies: Both lachrymal and postorbital bear these "suborbital" projections noted for Tanycolagreus, as present in Dilong but absent in Guanlong; the premaxilla is short and deep, though relatively large compared to the skull, which is relatively short for the skeleton, but this shortness of skull seems to be present in a referred specimen of Guanlong with a skull length shorter than the ilium, whereas the holotype adult skull is 250% longer, and the ilium only 20%; the short skull and the bound, but distinct neurocentral sutures in dorsal vertebrae in Ornitholestes suggest that it may not have been fully mature. The pelvis is well-preserved, and the ischium bears a nearly complete, Mirischia-like obturator process, such that it is likely to have been closed by cartilage in life. However, the pubis lacks a long boot, and a break in the anterior margin of the ilium, which lacks a vertical crest, does not help us resolve whether the pelvis is "tyrannosauroid," and it's like the animal wasn't.

This might then lead us to speculate that the so-called Tyrannosauroidea features of Tanycolagreus may not, in fact, be such, though it doesn't remove the considerations involved in the premaxilla and ventral lachrymal morphology, which optimize in cladistic analyses as tyrannosauroid autapomorphies, as well as the tooth morphology, which is shared by Dilong and Guanlong to the exclusion of all "coelurids" save Tanycolagreus.

So in the end, this leads us to the original speculation:

Are these coelurids tyrannosauroids? Or are some basal tyrannosauroids ... not tyrannosauroids? It seems that Tyrannosauroidea may be almost indistinguishable from within these animals, and Guanlong supports the origins of Tyrannosauroidea within the Jurassic Period. We may find the remainder of coelurosaur origins a large "mess," but it gives us plenty of work ahead to consider all the differences involved and also the similarities, and their implications for phylogeny, biogeography, and paleoecology.