Berthasaura (Cretaceous noasaurid, Brazil) dentary shows tooth loss during growth

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

A new paper:

Felipe Ferreira Pierossi, Rafael Delcourt, Daniel de Melo Casali, João Alberto Leme, Neurides de Oliveira Martins, Paulo Manzig & Max Cardoso Langer (2025)
Convergent evolution among non-carnivorous, desert-dwelling theropods as revealed by the dentary of the noasaurid Berthasaura leopoldinae (Cretaceous of Brazil)
Palaeontology 68(4): e70014
doi: https://doi.org/10.1111/pala.70014
https://onlinelibrary.wiley.com/doi/10.1111/pala.70014


The Cretaceous witnessed the establishment of many desertic landscapes across the globe, including the Early Cretaceous Caiuá palaeodesert, in south-central Brazil, and those of several Late Cretaceous deposits of the Gobi Desert. Although separated in time and space, their faunas share the presence of medium-sized, edentulous theropods (e.g. oviraptorids and Berthasaura leopoldinae) which depart from the typically carnivorous diet of the group. Here, we report a new dentary of the latter taxon, which bears alveolar vestiges, suggesting that its teeth were lost during ontogeny, as previously reported for another noasaurid, Limusaurus inextricabilis, from the Late Jurassic of China. In addition, we used geometric morphometrics to quantitatively analyse the shape of theropod jaw bones, revealing a significant morphological convergence signal for the dentary of Be. leopoldinae and oviraptorids, which are dorsoventrally deep, and bear a large mandibular fenestra. This probably resulted from adaptations to feed on the tough parts of xerophytic plants, which are important food sources in desertic environments.

[Dawid Mazurek]

A propos recent debate here:

" suggesting that its teeth were lost during ontogeny "

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[Jura]

True, but this is also from another noasaurid, which already show precedence for this happening and may be a unique quirk of this group in particular.

[Franco Sancarlo]

I think you mean the debate about Paul (2025) literally is a noasaurid like its cousin Limusaurus and therefore cannot be used as an argument. This is something stated both in the supplementary material and in the main text and in the discussion on the paper in the group.furthermore they also showed that this reduction of teeth is an analogy with Limusaurus 

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[Jaime Headden]

You can't use two taxa as evidence that it can occur in more than one taxon? Are you assuming Limusaurus (LK of Laurasia, China) and Berthasaura (LK of Gondwana, Brazil) are so close that ontogenetic tooth loss becomes a broader taxonomic trait, yet somehow not applicable to another taxonomic group?

Cheers,

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[Franco Sancarlo]

In humans we are born prematurely because if we grew more in the womb we could not come out, so since it happens in humans can it be applied to other mammals without providing proof?In Tyrannosaurus a proof has been brought, but it is only in one specimen (as already said previously, it remains to be seen whether the other specimens show this decrease or whether it is an exception.) and Paul 2025 also answered him in the supplementary materials

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[Tyler Holmes]

Limusaurus and Berthasaura may not be the best proxies, but I would hesitate before saying "it absolutely cannot be used". Tooth loss is a key point in the debate about tyrannosauroid ontogeny, with statements like "tooth count does not change at all, ever, during ontogeny". Noasaurids are obviously not great analogs for tyrannosaurs, but it does show that a group of theropods did evolve tooth loss. 

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[Franco Sancarlo]

I didn't say it couldn't happen, but using such distant examples isn't appropriate. In Limusaurus, it happens because the teeth are replaced by the beak, and as Paul already answered, only reptiles with a beak usually lose their teeth.

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[Gregory Paul]

Have you seen this? 

https://purehost.bath.ac.uk/ws/portalfiles/portal/345019394/290609155_Redacted.pdf

It supports Huxleysaurus and Sellacoxa, not Darwinsaurus. 

Note that the Dollodon holotype plots well away for Mantellisaurus. I think the later is going to be validated when it is described by the Belgian team. 

[Franco Sancarlo]

yes I read it, I disagree only on Darwinsaurus (on which I wrote a paper not yet published in its favor), also the thesis makes hypselospinus invalid

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[Jaime Headden]

This is a peculiar line of reasoning. We have studied both short term gestation (marsupials) and long term (whales, elephants, taking years) and can make generalized assumptions for both depending on various osteological factors and eruption of teeth, among other things. The general assumption isn't that a trait is wholly unique to a taxon, but that its expression in a lineage might be unique (autapomorphic). The appearance of ontogenetic tooth loss makes the assumption that its appearance in Limusaurus is not actually autapomorphic, and it might be more homoplastic---that is, that it can periodically appear without a definite phylogenetic signal involved. And if it's not autapomorphic, then it's likely to be expressible further out.

As I attempted to explain in the other thread, we expect tooth loss in dinosaurs (which is homoplastic) to occur in a step-wise fashion, and there would, by necessity, be cases where it would appear intermittently in specimens. Some would have more teeth, others less, and tooth counts might vary left to right, mostly from either end, sometimes in the middle, and with clear cases of resorption and alveolar bone remodelling. This would happen before the traits settle and ecological constraints enforce a fitness regime in tooth count through ontogeny in a given population, which we'd pretend is the "species" whereas all the others are ... I suppose we'd call them "transitional taxa" or some sort, and pretend they're not the same bloody thing. 

Whether these are found depends on luck and sampling size, which would have to be extensive and replete: whole skulls, both sides included, or lucky finds such as a "deformed" jaw or possibly ascribing jaw "injuries" to resorption events. Which means we'd have to look at pathologies and possibly reframe a few of them. (I should note that Dr. Holtz commented about Tyrannosaurus in an aside because it's difficult to use such a case for or against as the specimens are very hard to verify, being in private hands; Rest assured, it is one of Dr. Carr's most favorite bugbears that many specimens that should be studied cannot be because of this very situation, or his database would be much, much larger.)

The evolution of tooth loss is a particular interest to me, as I have been intrigued by the process of developing it in various tetrapods, including synapsids (Gorgonopsids, biarmosuchians, anomodonts, monotremes, placentals, etc.), much less sauropsids, especially reptiles. Perhaps one of the least studied patterns of tooth loss occur on the palate and vomer, in which teeth become more sporadic and less regular before reduction leads to complete loss in cynodonts leading up to mammals. Irregular positions and consistency in shape in therapsid postcanines, for instance, can be indicative of potential tooth loss, as there is a reduced constraint on dental expression, size, and function. But we're digressing at this point.

We're too used to thinking that the dentigerous bones are highly constrained---they're not. Rhetorically, we keep assuming that the presence of teeth is enforced by their function in feeding, and thus that their loss must be peculiar; when, in fact, it happens frequently and likely sporadically within near-lineages. Tooth loss appears at least two separate times in pterosaurs (pteranodont ornithocheiroids and azhdarchoids), and might have occurred in two different patterns, if not three: from the back forward in istiodactylids, and from forward to the back in azhdarchoids, but that's only implicated when dsungaripterids are basal. It happens so often in dinosaurs not including birds (from both directions) that at this point I can't see a singular pattern whatsoever, merely that ornithischians have evolved rostral tooth loss in all three major lineages separately (in marginocephalians twice! and that only in Ceratopsia after the evolution of the rostral bone, lacking in all other ornithischians). Pygostylian avialaeans evolved tooth loss in Confuciusornithids (total loss), posterior loss (bohaironithid enantiornithines, aves convergently), and rostral loss (hesperornithines, ichthyornithines, again convergently!) and all of this while occurring separately on the upper or lower jaws, with edentulous mandible tips in some taxa but not in others.

Constraining a singular model as "the pattern" is, effectively, a form of madness. The truth is, tooth loss is varied and inexplicable; the process by which it occurs moreso; and we shouldn't expect that animals conform to a model of loss without some damn good evidence and excellent sampling. Ganzhousaurus is a basal oviraptorosaur that has of late found itself nested among toothed oviraptorosaurs despite lacking any teeth whatsoever (Similicaudipteryx, Caudipteridae, Incisivosaurus, Protarchaeopteryx, which show variable expressions of dentary teeth several to few to none, maxillary teeth several to few to none, and premaxillary teeth four to three to none; and in the reverse of basal carinate birds, the tips of the mandibles are edentulous, but not the tips of the upper jaws---how strange if it should all happen just one way). It should be further notes that several of these basal oviraptorosaurus show variable shape, number and expression of tooth counts and have variously been assumed to be juveniles or adults of one another---again, with different tooth counts among them.

Thus, I would argue that Berthasaura showing a similar pattern of ontogenetic tooth loss as Limusaurus not to be a peculiarity of certain derived noasaurids but a reflection of homoplasticity in the development of tooth loss ... and leave it at that.

Cheers,

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[Franco Sancarlo]

All the points you bring up have already been discussed about synapsids and animals that have beaks or a subspecies of beak (they have already been explained as being unusable). Berthasaura, as we read, lost its teeth not for the same reasons but similar in this case  the need to eat xerophytic plants (probably cacti) without damaging its palate, thus losing its teeth and replacing them with its beak . This provides previously undiscussed evidence of tooth loss in Tyrannosaurus.

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[Tim Williams]

Franco Sancarlo <franco.sa...@gmail.com> wrote:

> I didn't say it couldn't happen, but using such distant examples isn't appropriate. In Limusaurus, it happens because the teeth are replaced by the beak, and as Paul already
> answered, only reptiles with a beak usually lose their teeth.

As mentioned previously, also in _Opisthodontosaurus_ (a captorhinid reptile) and some ichthyosaurs.  The argument appears to run (as with noasaurids and avialans) that because ontogenetic tooth reductions in these lineages occur due to unique circumstances, they can be dismissed as being relevant to tyrannosaurids.  I don't find this argument compelling.

[Franco Sancarlo]

Hi Tim, regarding the captorhinids, I missed this information. I'll look into it further and then I'll give you my opinion. As for the ichthyosaurs, I think Paul has already answered them. In any case, it's a process similar to beak replacement. So, it can't be used as an argument.

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[Jaime Headden]

> I didn't say it couldn't happen, but using such distant examples isn't appropriate. In Limusaurus, it happens because the teeth are replaced by the beak, and as Paul already
> answered, only reptiles with a beak usually lose their teeth.

> Berthasaura, as we read, lost its teeth not for the same reasons but similar in this case  the need to eat xerophytic plants (probably cacti) without damaging its palate, thus losing its teeth and replacing them with its beak .

As I stated in the previous thread, we don't actually "know" this. Loss of teeth in a region does NOT necessarily lead to beaks, and thus they can be divorced from one another. In birds, beak development coincides with closure of cranial sutures of the formerly-dentigerous bones, up to and including coossification of the entire mandible. This is merely coincidental with tooth loss. Ichthyornis and Hesperornis, as exemplars, have edentulous premaxilla with other osteological indicators for a beak, but otherwise lack fusion of the adjacent bones (although the premaxillae themselves are fused). This is actual evidence for a lack of a mandibular beak in these taxa. Ornithischians solve this problem by developing novel bones (predentary, rostral) and then developing regional tooth loss.

But I'm getting ahead of myself. There are a good number of tetrapods that evolved edentulism and didn't evolve beaks, including, but not limited to, ichthyosaurs, frogs, a half dozen distinct mammals (they actually have a "horny palate" in many cases, and coincidental cranial fusion! but they're not "beaks") and so forth. Some animals developed beak-like tooth structures that coossify with the dentigerous bones, such as acrodont lizards like chameleons, tuatara, or perhaps rhynchocephalians. But none of these other than lepidosauromorphans develop coossified dentigerous bones (other than mostly premaxilae, but that's a plesiomorphy in most cases).

It is massively presumptive to assume that tooth loss and beak development are one for one when each are uncoupled from the other and each has its own constraints and developmental markers that one can predict from based on osteological correlates (alveolar bone without teeth, for example), and a remodeled exterior bone structure with low-relief spiculate texture and oblique nutrient foramina. Moreover, we make assumptions in the noasaurids that, because some of them lack teeth, those taxa must be beaked. And this is, frankly, begging the question.

I mean, it looks like a beak, but is it? Is there bilateral coossification? Do the premaxilla fuse? The dentaries? A rhamphotheca is there to reduce strain to the bone, which is what teeth also do (Lauthenschlager et al, 2013), but also reduce weight in place of teeth, but an effective strain reduction occurs also in coossification, distributing it across the suture. In its absence, ornithischian increase the size of the edentulous portions of their jaws, but still exhibit bilateral coossification. I mean, there might be a beak, but we won't know based on the published data (I'd put the probability above 50% and that's it).

Lautenschlager, S., Witmer, L. M., Altangerel, P., Rayfield, E. J. (2013): Edentulism, beaks, and biomechanical innovations in the evolution of theropod dinosaurs. PNAS, 110, 20657–20662.

http://www.pnas.org/content/110/51/20657.full.pdf (free)

Anyways, lest I begin repeating myself, or there's NEW DATA and not repeating the same talking points, or someone wants a legitimate dialogue, I'm out.

Cheers,

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[Franco Sancarlo]

Paul had already answered Ichthysaurs: mammals and amphibians are not reptiles; they are not close cousins ​​and cannot be used for tooth loss. Now let's get to the point: do you have any new evidence that this happened in tyrannosaurids? If the answer is no, then please do not reply anymore.

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[Stephen Poropat]

With the greatest respect, Franco: Jaime has been a contributor to this group for a long time, so neither you nor anyone else has the right to try and silence him, especially when the points that he is raising are valid.

I think this argument needs some perspective, which Jaime and Tom Holtz and others have tried to provide: 1) evolutionary novelty exists, meaning that 2) phylogenetic brackets (extant or extinct) are imperfect guidelines only, not rigid rules. 

As far as I know (and I will happily be corrected if I am wrong), Tyrannosaurus went through a much more marked ontogenetic change than any of its relatives for which we have ontogenetic sequence knowledge (with Tarbosaurus presumably next most pronounced). If it became adapted for bone-crushing as an adult to a greater degree than other tyrannosaurids, then perhaps there was evolutionary pressure towards having fewer, larger, and more robust teeth as adults. The mechanism by which this occurs remains to be demonstrated, but at least one viable pathway has already been alluded to (by Tom Holtz). Just because no other tyrannosaurid seems to set a precedent for ontogenetic tooth loss does not mean that Tyrannosaurus could or did not; given that it was chronostratigraphically more recent than the rest, maybe it blazed a novel ontogenetic trail owing to the unique ecological pressures emplaced upon it. 

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[Franco Sancarlo]

I apologize if I seemed rude, that wasn't my goal, the problem is that as shown in Paul (2025) we have baby Tyrannosaurus with a similar number of teeth and all the points mentioned have already been addressed before in another discussion on Paul (2025). If tooth loss is to be applied to Tyrannosaurus, evidence must be provided that takes into account baby Tyrannosaurus with the same number of teeth. Holtz however mentioned the loss of only 1 tooth for which we need more data at the moment. This discussion arose from the fact that Paul claims that Nanotyrannus cannot be Tyrannosaurus for a number of reasons including the teeth. If we assume this loss of 1 tooth then Nanotyrannus should still lose many more.

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[Henry Thomas]

For the record, there is at least one predatory beakless amniote that has large, functional, isodont, thecodont, and non-diphyodont teeth throughout its life that decrease in number (but are not completely lost) ontogenetically (paralleling a larger evolutionary trend in the clade that it belongs to): the melon-headed whale.

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[Franco Sancarlo]

we are talking about reptiles, not mammals

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[Dawid Mazurek]

Well, that specific line of reasoning is invalid, IMHO. Why? Change whale to allosaurid. Then, one could say: we are talking about coelurosaurs, not carnosaurs.

[Thomas Richard Holtz]

We're talking about amniotes. Don't assume one arbitrary human term holds more weight than another one in this context. Typological thinking is counterproductive. 

Evolutionarily, teeth and tooth-genesis well predates Tetrapoda. And the particular details of the formation of synapsid and sauropsid jaw formation are ancestrally the same.

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[Gregory Paul]

Interesting. But for the record this is not of import to the ETRH debate, which is focused on Reptilia. 

GSPaul

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[Franco Sancarlo]

Actually, no, Limusaurus was not usable because the teeth decreased as they were replaced by the beak and, to my knowledge, the number of teeth did not decrease in Allosaurus. Furthermore, the best example would be a cousin that is a tyrannosaurid or at most a tyrannosauroid.

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[Dawid Mazurek]

I was not referring to Limusaurus, but a hypothetical allosaurid. If such an example were to be found in a tyrannosaurid, say Gorgosaurus, one could still say: we are talking about tyrannosaurines, not albertosaurines. That was my point.

[Gregory Paul]

The below statement is incorrect. 

Tyrannosaurus DID NOT undergo an exceptional ontogenetic change. Such a radical and recent fantasy is obsolete and should not be repeated, much the same as claiming that no dinosaurs were feathered (I used to get severely criticized for feathering my dinosaur illustrations, imagine that). 

The modern fantasy that growing Tyrannosaurus had wild and weird growth started in 1999 JVP in which Carr mistakenly believed that Gorgo lost teeth with growth. Despite that being immediately refuted, the myth that Nano, Stygi, Jane, Petey, Bloody Mary were baby Tyrannos even though at least some of them are not tyrannosaurids for no good reason has grown into the establishment norm (kind of like dinos are not birds becoming the paleostandard). Despite Larson and others showing otherwise, including the big big hands of some lithe specimens. 

We know Tyranno grew up in the tyrannosaurid norm. we know that because as Longrich and Saitta pointed out last year, and me this year (and Burnham et al. 2018 concerning the KUVP specimen), there are about seven actual, real, bonafide juvenile Tyrannosaurus! They have the same tooth counts as the grownups, the teeth are more like the adults, and they lack the prominent dentary groove,etc (Fig. 8A-D). This is now in the peer reviewed literature. These juveniles are in full accord with the growth of other tyrannosaurids such a Gorgo and Tarbo. Some who continue say that Tyrannosaurus grew in an odd manner have it would seem to not have bothered to read these open access papers (this includes Carr who in an online post said "Although I haven't read the article or supp info in detail, my impression is that hasn't meaningfully engaged with the critique of Carr & Napoli et al. (2022) and so his new article is just a repetition of Paul et al. (2022)," which is as off base of C et al. 22 claiming that Paul et al. 22 used only 2 characters, and that we used different sides of dentaries to produce incisor ratios which is silly, and much of the Supplementary is a discussion of the many flaws of C et al. 22). Read the papers before commenting on them. If you then can in some manner refute the now published data do so. Otherwise if you autorepeat the false belief that Tyranno growth was atypical you are being inaccurate, the fossils show it was not. Thanks for that knocking that off as I have no doubt all will do. 

But seriously now, with no decrease in tooth count in growing Tyrannosaurus, why are people going on and on and on about how some marine ichthyosaurs lost teeth, or a basal reptile with hollow teeth set atop its jaw rims, and a small set of basal theropods who had beaks as grownups? (I do not object to such being noted, but how some then appear to claim this is a major item in the TT-zone tyrannosaur taxa debate). Or whales losing teeth with maturity. Or that some big Tyrannos have evidence of shifts in teeth when their young had the same tooth low tooth counts, what is the issue here? (And did albertos and tarbos not have similar tooth position alterations? Have you folks looked?). These come across like Feduccia's and friend's attempts to wave away feathered dinosaurs.  

The variation in the anatomy of small TT-zone tyrannosaurs is astonishing. In tooth counts and form, dentary grooves, other skull details and overall shape, apparently limb proportions. This is not true in Gorgo. This is not true in Tarbo (the small skulls that are different from juv Tarbo are Alio). It is not true as far as I know in any dinosaur, or reptile, or animal. So somehow Tyranno is so special that all these skull types as they grew up whether or not they started out with the adult tooth count and skull form or not, ended up with the same low tooth count and skull form? Where else does that happen? 

Among creatures, the juveniles are similar in form. In many species the adults are too. But in many species as growth occurs the girls and the boys diverge in via via dimorphism. I don't think there are examples of growing animals that start out diverse in osteology, and then converge to being much more similar in the adults. Are they any examples that show the same is likely to have occurred in Tyrannosaurus? 

And how are Jane and Petey young Tyranno when their bone rings show that were subadults slowing growth in their teens, at the same time actual growing Tyranno were standing on the growth pedals fast accelerating their wonder years growth? 

Gilmore set the solid, comparative anatomy and ontogeny parsimony and null hypothesis science standard in 42 when he made Nano into a new taxon rather than a juv Tyranno. The Tyranno grew like a fish model is a new and radical notion of the new century that was never in accord with known beakless nonmarine diapsids, and has been further disproven with the identification of actual growing Tyrannos, and the big hands of the basal eutyrannosaurs of the TT-zone. 

Because of the Carr and company errors, the study of TT-zone tyrannosaurus has been tied up in a simplistic dogmatic manner for a quarter century. So much so that the rigidity continues. We now know that adult Tyrannosaurus exhibit remarkable diversity in postorbital display boss form which is a classic species identification feature than is seen in any other tyrannosaurid taxa, or even all other tyrannosaurids combined. (An online comment claimed this is fossil distortion, but such is not seen in other tyrannosaurids, the bosses on similar on both sides of a given skull, and they chart out stratigraphically). There is more Tyrannosaurus diversity in dental and cranial proportions than all other tyrannosaurids combined. There is the extreme diversity of the small specimens in which some are exactly what one expects in actual juv Tyranno but most do not even fit into Tyrannosauridae. And Appalachia where they came from had jut been re-attached to Laramidia. It is obvious what was going down in the latest Maastrichtian, and it is not the ETRH. 

What should be happening is everyone saying like wow cool man there are all these Tyrannosaurus species and let's be looking into how many there were and when and how they evolved. And like wow cool man there were all these big handed, many toothed lithe taxa running around in the Tyrannosaurus habitat competing with the actual Tyranno juveniles and how did that work out. And how many taxa were there and when, and where did they come from?  

So far there has been none of that forward, innovative thinking on this list, or in the dinocommunity in general. None. That is an embarrassment. Instead it is the same old, dreary dour nonsense about somehow the incredible diversity of TT-zone tyrannosaurs great and small can all be somehow if biological norms are waved away squeezed into just one beloved species in gross violation of biology and parsimony. Without positive evidence to the contrary offered up. And those of us having to blow time pointing out how absurd that is -- just as we rolled our eyes at non feathered, ectothermic dinosaurs back in the 70s-90s.  

Why are people repeating the mistake of Tarsitano, Martin, Feduccia, Ruben, Czerkas, Lingham-Solair in going on and on and on about no dinosaurs were feathered for decades? The everything was T. rex hypothesis is as dead as non-avian dinosaurs. The ETRH is about to take another torpedo when Bloody Mary is published. The Zanno team has the funding and will get the report out in the not distant future. They have signaled the results by not referring the fossil to Tyranno in the same sentence they label the other Triceratops. The ETRH is like the Titanic an hour and a half after it hit the berg, going down fast and not enough boats to get off. Why are people so enamored of going down with the ETRH ship? As did those who denied birds are dinos? 

The question is not whether there were multiple taxa, but how many and why. Franco is right in that the defense of the ETRH is passe, and it is time to move on with discussion about the far more fascinating discussion of what was really going down in the TT-zone. 

Item. T. rex specimens make up around a third of the adult Tyrannosaurus that can be assigned to species, with it being about equal in numbers to the contemporary T. regina. By my extremely rough and I'm presumably missing some, there are somewhere in the area of 70 TT-zone tyrannosaur specimens, of which approaching 20 are not Tyrannosaurus. In that case T. rex makes up just a sixth or less of the TT-zone eutyrannosuaur population. Now why would that be. 

I have no doubt that even as earlier T. imperator is accepted there are those who will consider T. regina to be a sexual morph of T. rex. That is a possiblity, although as explained at length that is the inferior hypothesis. What do folks think about that? 

And where did the baso-eutyrannosaurs come from? Appalachia which was the land of long handed dryptosaurs? Or at least some of them from elsewhere? 

See, those are the interesting, real evolutionary paleo items folks could be discussing. Instead of on and on and on about the damn teeth of marine reptiles and mammals never mind that known juvenile Tyrannosaurus is the same tooth count as their parents. 

Now is that too much to ask? 

GSPaul

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