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Updated 1/17/20 I've taken a pretty firm position on the validity of Nanotyrannus ever since I spent some time looking at the Dueling Dinosaurs shortly after they were discovered. Subsequent to that, new information that I've become aware of just cemented my position. I'm interested in understanding the "truth" and have no problem looking at all available specimens that are in private hands or museums. The optics are very clear to me and I have difficulty understanding the debate. Collectors need to form their own opinion on this but I would like to share with you why I believe its a valid species. A recent paper that CLAIMS that Jane and Petey are still growing that they have to be T Rex is ridiculous. WHY? Just because they are growing.... We have no idea what stage in their life cycle they were and obviously they are not adults. Nano's grow, we have no idea how large, and have similar life cycles has do T rex's. If it was not for all the other supporting evidence to validate Nanotyrannus it might make sense but the claim is nonsensical. I present here several examples supporting my case, many others exist but will leave it at this. You always hear we need see sub-adult/baby specimens of Trex so a comparison can be make against Nanotyrannus claimed specimens. Shocking but some specimens do exist in institutions and private hands. Included in this discussion are a couple of examples of these specimens other are out there some in private hands and hopefully will be published. Jaws Case in point here is a jaw of a Baby T rex in private hands. Its only 35 cm wide. Paleontologists involved in this debate are very well aware of its existence. This cast is in my collection Top jaw: T rex (BHI6439), White jaw: Nanotyrannus (BMPR2002.4.2) Note that the length of the tooth row is nearly identical, Top jaw contains 12 circular alveloi typical of adult T rex's while the white jaw contains 17 rectangular alveloi typical of what is described as Nanotyrannus. Morphology of the teeth is classic for Trex: fat, oval and robust. Morphology of white jaws teeth is classic for Nanotyrannus: rectangular, lean and more gracile. There are a number of other morphological differences that Pete Larsen has identified with the jaws but the eye test should be enough for this discussion Compare the widths for both of these species, there is no comparison its pretty obvious how robust one is over the other. ARMS If the Jaws were not enough here are the arms and claws. Here is a sub-adult Trex arm (UCRC-PV1) housed at the University of Chicago (Paul Sereno). Paleontologists involved in this debate are very well aware of its existence. This is the only complete Trex arm and hand that has been found to date and articulated including the scapula and coracoid and partial skeleton including vertebrae. The bones including the claws compare well with those of known adult T rex and the vertebrae are about twice the size of Jane (Nanotyrannus) Added (1/7/20) Pete Larsen : "Adult and sub adult hands of T.rex (A, B and D) compared to the hand of Nanotyrannus (C), BHI 6437, which has a skull length of 610mm, the same as Jane BMRP2002.4.1." How can the rational paleontologists support the papers claim B is a Sub-Adult T rex (UCRC PV1) who's bones look just like D from an adult T rex.(MOR 555) C bones a Nanotyrannus is larger with very different bone morphology Every known bone from the hand of a Nanotyrannus is larger than and morphologically different from every known hand bone of adult or sub-adult T rex. I'm not aware of any other Tyrannosaurid where juvie and adult arms become smaller as the animal ages. Here is an sketch comparing the two to see how different the bones are. Pete Larsen also points out that "Animals do not change the orientation of semicircular canals, imbedded within solid bone, as they grow" Compare the long bone of Nanotyrannus with arrow to the one below on T rex Sue Sue - Carpal is much shorter and with a different morohology... Here is a comparison of a carpal digit I Wyrex (Top), Nanotyrannus (Middle), Sue (Bottom) Both Trex's have a larger bulge at the end of the bone. Very different morphology. You can argue ontogenetic changes but the robustness is present in the arm from above. Added 1/17/20 From left to right : Gorgosaurus TVM 2001.89.1, Nanotyrannus BHI-6437, adult T.rex MOR-980, and sub adult T.rex TCM 2001.90.1. Your can see on similarities with the two on the right both of Trex of different ages. Interesting thought the paleontologists said the younger one should be longer CLAWS Lets move on to the claws - Top T rex Digit I - Sue (Left), Digit II - Victoria (Right) Bottom Nanotyrannus - Digit I (Left), Digit II (Right) (BMRP 2006.4.4) (Petey's) Morphology is very different and Digt II of Victoria is very similar to that of the sub adult claw see below. Sub Adult Trex claw Digit II, 5 cm .. compares quite well to adult Victoria not Nanotyrannus Lots of the photos provided by Peter Larsen Added 1/7/20 Pete recently posted "But wait, you say. wasn’t Jane still growing? She certainly was, comparing Jane size BHI-6437’s manus claws ( Brown) to Petey’s (BMRP 2006.1.1) (White). The question I have is: when do the hands stop growing so they can shrink (a lot) and then begin growing again?" Braincase One last item to present is the Witmer Labs study on Tyrannosaurid braincases...it clearly demonstrates that there is a difference between T-rex and Nanotyrannus. Conclusion on the Cleveland "Nano" skull "Given the obvious closeness of CMNH 7541 and BMR P2002.4.1 "Jane", it would likely have been taxonomically decisive. Our data on CMNH 7541 may be taken as evidence for the validity of N. lancensis on the grounds that it is ‘‘too different’’ from T. rex. However, we are hesitant to argue that the debate over its status is settled for the simple reason of sample size. CMNH 7541 presents one specimen—one highly divergent specimen. Although we see no clear signs of distortion or pathology in the braincase, its divergent nature concerns us, and we maintain that the possibility remains that future discoveries will show CMNH 7541 to be aberrant. For that reason, we urge caution and continue to regard the specimen’s status as open" https://onlinelibrary.wiley.com/doi/full/10.1002/ar.20983 New Insights Into the Brain, Braincase, and Ear Region of Tyrannosaurs (Dinosauria, Theropoda), with Implications for Sensory Organization and Behavior Lawrence M. Witmer Ryan C. Ridgely First published: 26 August 2009 https://doi.org/10.1002/ar.20983 It's unfortunate that the skeleton Jane does not have the two skeletal areas discussed in this topic: Arms and Braincase. More reason for the Dueling Dinosaur Nanotyrannus to be studied it's almost a complete skeleton. The End...