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Hello Everyone, I bought this tooth nearly ten years ago as a Albertosaurus tooth from the Two Medicine formation, Montana, U.S.A. Whilst updating my labels I have learnt that Albertosaurus is not found in the Two Medicine Formation. As a result, i am asking if anyone can ID this tooth (i know it is very difficult or more likely impossible). I believe it is either a Distal Maxillary or a Distal Dentary tooth. The MC is 18 whilst the DC is 16 which gives it a DSDI of 1.125. The tooth is 2.90cm tall and the base of it is 1.22cm by 0.86cm. the link to some fairly high quality photos is: Tooth Id - Imgur thanks in advance, Josh

Tyrannosaurus rex (Osborn, 1905) Late Cretaceous, c. 67 Ma Hell Creek Formation, Isabel, Dewey Co., South Dakota, USA. It has been a dream since childhood to own a Tyrannosaurus rex tooth and my dream came true with this recent acquisition of a gorgeous T. rex 1.5” dentary tooth.

Triceratops horridus (or prorsus) (Marsh, 1889 /1890) Late Cretaceous, c. 67 Ma Hell Creek Formation, Powder River Co., Montana After acquiring a gorgeous T. rex tooth, I could not resist the opportunity of acquiring a tooth of its likely prey - Triceratops. I’m aware of the difficulty in identifying ceratopsian teeth and the impossibility of distinguishing between T. horridus and T. prorus. As Triceratops is the most commonly encountered genus within the HCF, this is labelled as being Triceratops horridus or prorus in my collection. I understand that the locality is known for T. prorus so it may well be that this is T. prorus. I love this specimen for it still having the root - so unlikely to be a shed tooth.

Found these vertebra in same area as some turtle scutes but also dino bones. The large one was on a separate butte than the small ones. The small ones were from an area where I found maybe 6 more, various degrees of breakage. They are all acoelus. The largest doesn't have signs of broken neural processes. All have that hourglass shaped groove down the back between series of ridges. I can't find similar configurations anywhere. Turtle?

Updated Nov 25, 2022 Collectors, online sellers and some dealers periodically ask me to help them in the identification of tyrannosaur type teeth. So I thought I would put together a guide from Western North America (US/Canada) to help in identification. The following is the current understanding of those Tyrannosaurids described/known with the stratigraphic unit where they are found. If I missed any let me know. Albertosaurus sarcophagus : Horseshoe Canyon Formation cf Albertosaurus indet: Wapiti Formation Gorgosaurus libratus : Dinosaur Park Formation Gorgosaurus sp. or cf Gorgosaurus: Two Medicine Formation, Oldman Formation, Foremost Formation, Daspletosaurus horneri : Two Medicine Formation Daspletosaurus wilsoni: Judith River Formation Daspletosaurus torosus : Oldman Formation Daspletosaurus sp. or cf Daspletosaurus: Dinosaur Park Formation Dynamoterror dynastes: Menefee Formation Tyrannosaurus rex : Hell Creek Formation, Lance Formation, Frenchman Formation, Scollard Formation, Denver Formation, (Trex fossils are also known from: Livingstone Fm, Laramie Fm, McRae Fm, Willow Creek Fm) Tyrannosaurus sp.: Javelina Formation, Ojo Formation Nanotyrannus lancensis : Hell Creek Formation, Lance Formation cf Nanotyrannus : Frenchman Formation, Scollard Formation, Denver Formation Thanatotheristes degrootorum : Foremost Formation Tyrannosaurid indet. (spp): Judith River Formation, Mesaverde Formation (Group), Fruitland Formation, Aguja Formation Teratophoneus curriei: Kaiparowits Formation Lythronax argestes: Wahweap Formation Nanuqsaurus hoglundi: Prince Creek Formation Tooth Identification Aublysodon mirandus Premaxillary teeth, those without serrations. This dinosaur is considered nomen dubium and teeth ascribed to it belong to other Tyrannosaurs. Albertosaurus sarcophagus Probably the easiest to identify since its the only Tyrannosaurid described from the Horseshoe Canyon Formation. The most important item in acquiring one of these teeth is the provenance of where it was found. Alberta is not adequate to identify it. You need a specific locality like Drumheller or Tolman Bridge. BTW this is true for all the Tyrannosaurid's discussed in this topic. A disposition is also needed for all dinosaur teeth removed from Alberta. These teeth can get quite large from collection of SMM Gorgosaurus libratus (cf, sp.) The first step in identification is Provenance: you need to know State/Province along with the County (USA) or Locality (Canada) where the tooth was found. Differentiating isolated teeth between Gorgosaurus and Daspletosaurus is very difficult and in most cases its indeterminate. A paper that came out in 2005 which was authored by Phil Currie et al. studied isolated teeth from this period looking at tooth and serration morphology. Their conclusion was that "it is difficult to quantifiably distinguish these teeth reliably by taxon". Therefore identifying them as Tyrannosaurid indet. is the easiest approach in those faunas that Gorgosaurus may be present? There is a quantitative process described in a new paper that may help which will be discussed later. Please note that lots of collectors would like to use size to differentiate these teeth from Daspletosaurus. However Gorgosaurus teeth can get quite large as seen in this photo of a Maxilla with one tooth which is over 3 inches and located in the back of this jaw. Daspletosaurus horneri, D. wilsoni, D. torosus (cf, sp.) The first step in identification is Provenance: you need to know State/Province along with the County (USA) or Locality (Canada) where the tooth was found. A paper that came out in 2005 which was authored by Phil Currie et al. studied isolated teeth from this period looking at tooth and serration morphology. Their conclusion was that "it is difficult to quantifiably distinguish these teeth reliably by taxon". Therefore identifying them as Tyrannosaurid indet. is the easiest approach in those faunas that Daspletosaurus may be present? However, its reasonable to say that teeth over 4" are PROBABLY from a Daspletosaurus. There is a quantitative process described in a new paper that may help which will be discussed later. *****Since the Judith River and Two Medicine Formations fall within the range of all three of these species its going to be difficult to assign teeth to a specific species unless you know the age of the deposit it. Denver Fowler: "Hill County exposures are more easy to date because there we have the boundary between the upper Oldman Fm and the lower part of the Dinosaur Park Fm. Havre exposures were called Judith River Fm historically, but we should probably use Oldman & Dino Park now." And maybe ditto for those teeth found in the Belly River Group of Alberta. Denver Fowler "I expect that D. wilsoni is stratigraphically equivalent to the lower part of the Dinosaur Park Formation. At the moment this is based on the fact that the Judith in eastern Montana was deposited at the time when the WI seaway was receded at its maximum (in the Campanian)" Denver's response to my question on this subject. "There isn't currently any evidence for stratigraphic (time) overlap between the species. However, the 2Med and Judith River likely represent enough time such that it would be possible to find D. torosus in the Judith and both D. torosus and D. wilsoni in the 2Med." (Posted by Denver Fowler) Tyrannosaurus rex/ Nanotyrannus lancensis (cf, sp.) Whether you agree or disagree that Nanotyrannus is a valid taxon what is very clear to me is that we have two distinct morphologies of tyrannosaurid teeth at the very end,of the cretaceous. I can say that because I have handled over 1000 teeth over the years ranging from 3 mm to 5 inches two morphs are present in all ranges up to around 2 inches. Serration density through sampling I've done with teeth in my collection do not appear by itself to be a differentiator between these two morphologies. Density will change with size becoming less on larger teeth and can be the same with equivalent size teeth with both morphologies. DSDI (Denticle Size Difference Index) is also not a differentiator and through my sampling and Carr (2004) and indicates that DSDIs decrease in progressively larger specimens, that is, there are fewer mesial denticles per given unit length than distal denticles in large specimens and there are as many or more mesial than distal denticles in small specimens. Also, the DSDI among dentary teeth is higher than that in the maxilla, indicating that mesial denticles are smaller in the dentary than in the maxillary dentition. So how do you tell the difference between these two morphologies. Well, if a tooth is larger than 2 1/2" and has bulk its clearly T rex, regardless of what the serrations say. It cannot be anything else. With small teeth since serrations density is not a differentiator the other characteristic of the tooth plays a key role. I've found that maxillary teeth can be the most difficult to differentiate and a few teeth are just indeterminate, at least with me. The best way to distinguish between the two morphology the shape at the base, compression of the crown and tip and if there is a pinch at the base. Shape at the base T rex dentary teeth and the very anterior maxillary teeth are oval at the base while Nano teeth are unique as tyrannosaurids and rectangular. However, T rex maxillary teeth can be rectangular so you will have to determine if there is a pinch at the base a characteristic found on Nanotyrannus teeth Here are examples of the cross sections of couple small Rex teeth under 1 1/2 inch and Adult Nano's Tyrannosaurus rex Dentary teeth are oval Maxillary Teeth are rectangular Nanotyrannus Bases are rectangular and show a pinch on both sides. Profile of the teeth is another characteristic Nanotyrannus teeth are compressed, with a pointed tip T rex teeth are fat, with a rounded tip, often the serrations wrap around from the mesial to distal carina to form a continuous carina Crown Height Ratios In the study I did, since nothing is published, with 30 Nanotyrannus teeth the average was 2.2 For Trex teeth the mean for Maxillary teeth is 1.75 and for Dentary its around 2 but all these can change depending on position Heterodonty in Tyrannosaurus rex: implications for the taxonomic and systematic utility of theropod dentitions Joshua B. Smith (2005) T rex Premaxillary Teeth can easily be confused with dentary D1 position. Here is a photo of how to determine what you have. Identifying Gorgosaurus and Daspeletosaurus Teeth using Dental Features A recent paper by Hendrickx et al. (Oct 2019) has provided us a way to try to identify certain teeth using dental features. Positional Daspletosaurus & Gorgosaurus teeth have distinct denticle features that can hopefully can be used to differentiate the species which currently does not exist. Together with @Omnomosaurus we are looking at studying this technique to determine if its a practical method for collectors to use for identification, obtain data on campanian tyrannosaurid teeth and try to understand if the results we are getting is any good? We will be using teeth from my collection and members for the study. @dinosaur man has a topic where a lot of member data will be collected. Step 1 The most critical part in using this process is knowing where the tooth sits in the jaw - Premaxillary, Mesial or Lateral Here is a photo of to help in determining its location Paper https://www.researchgate.net/publication/261630184_Morphometry_of_the_teeth_of_western_North_American_tyrannosaurids_and_its_applicability_to_quantitative_classification Step 2 DSDI (Denticle Size Difference Index) needs to be determined DSDI = MC / DC MC = Number of denticles per 5 mm on the mesial carina at mid-carina DC = Number of denticles per 5 mm on the distal carina at mid-crown Mesial Carina is on the outer curvature Distal Carina is on the inside curvature Step 3 1) If your tooth is from a lateral position in the jaw and your DSDI is <0.8 your tooth may be considered a Gorgosaurus or cf Gorgosaurus depending on the locality of where it was found. 2) If your tooth is from a Mesial position in the jaw and your DSDI is >1.2 your tooth may be considered a Daspletosaurus sp. or cf Daspletosaurus depending on the locality of where it was found. Premaxillary Teeth 1) In my opinion all these teeth should be identified as "Tyrannosaurid indet" 2) The paper does make the following statement "In the young specimens of Daspletosaurus, the carinae of the premaxillary teeth are unserrated (TMP 1994.143.1; Currie, 2003) and show the beaded condition. My concern is that it does not specify what size young teeth are and its looking at TMP 1994.143.1 which is a Daspletosaurus sp in Dinosaur Park Fm. Do all Daspletosaurus premax teeth in other faunas have contain similar features? Gorgosaurus premax teeth are not mentioned. Study Currently 33 teeth from the collection of Troodon, Omnomosaurus, dinosaur man Localities included : Judith River Formation (18 teeth), Two Medicine Formation (13 Teeth), Dinosaur Park Formation (1 Tooth), One unknown Results: 1) None of the lateral teeth have had DSDI < 0.8 and could be described as Gorgosaurus 2) Three of the Mesial teeth had DSDI > 1.2 and could be described as Daspletosaurus 3) One of the Premaxillary teeth was not serrated but could not verify if it was a young tooth 4) So 9% of the population can be tentatively assigned Hendrickx et al paper https://palaeo-electronica.org/content/2019/2806-dental-features-in-theropods