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Hi everyone, Recently, while researching the morphology of machimosaurid crocodile teeth, I bumped into the below specimen, identified as Machimosaurus hugii (presumably based on its size). And although I can't confirm the specific name, I'm confident the referral to Machimosaurus is correct. When taking a closer look at the tooth's striations, however, I noticed not all of them actually run the whole apicobasal length of the tooth as I expected. And although some striations have undoubtedly been terminated and/or interrupted by wear, I was more genetically wondering if striations not running the full apicobasal length of the tooth is a know characteristic of crocodile teeth. For I'm only familiar with teeth that are either entirely smooth, or that have fine striations on one or both sides of the tooth, where only those striations that run into one of the tooth's carinae may be truncated before reaching the full apicobasal length of the tooth. That having been said, though, I can imagine crocodilian dental ornamentation being more varied, with different patterns of organisation in their striations, as Madzia (2016, A reappraisal of Polyptychodon (Plesiosauria) from the Cretaceous of England), in an annotation with his figure 8 illustrating pliosaurid tooth crown morphologies following Tarlo (1960) (reproduced below), observes that the teeth with the most striae, previously referred to Simolestes nowackianus, are now considered Machimosaurus nowackianus. And with the great variation of expression in striations on pliosaurian teeth, I don't think it would be such a leap to assume the same for this species of teleosaur... So, my question is: are striations on crocodilian teeth as variable as they are amongst pliosaurs? Can individual striae end prior to stretching the full apicobasal length of the tooth, and, if so, in which clades or under what conditions? Do crocodilian teeth exhibit patterns of striations of interchanging lengths (e.g., short-long-short)? Thanks for your help!

Hey everyone! Continuing from the other ID thread, I’d like to hear your opinions on another recent acquisition from the Oxford Clay: a group of associated metriorhynchid teeth. Now, there are several metriorhynchid taxa described from the Oxford Clay Formation: Gracilineustes leedsi, Ieldraan melkshamensis, Suchodus brachyrhynchus, Suchodus ?durobrivensis, Thalattosuchus superciliosus, and Tyrannoneustes lythrodectikos. Pretty much all of them have decent descriptions of their dentition available, so comparing these teeth to the literature facilitates the ID process quite a bit. First off: We’re examining 3 teeth, none of which are complete (all lacking the apex), but are seemingly unworn and thus have some distinctive diagnostic features preserved. They display weak to moderate mediolateral compression and some lingual curvature as well as free, smooth, and opposed carinae. The basic texture of the enamel is slightly rough or pitted on both lingual and labial surfaces. Tooth A is the larger of the more complete teeth. It preserves about half of the crown as well as part of the root. No constriction is apparent at the transition between root and crown. The tooth displays slight lingual and distal curvature. Slight ridges overlay the basic enamel texture. Labially, these striae are long, continuous, and become less numerous apically. Lingually they are shorter, more numerous, and show no apical reduction in the part preserved. On both surfaces the striae are similar in strength and separate (non-fusing and non-anastomosing). Tooth B is the smaller of the more complete teeth. It preserves a more apical portion of the crown than tooth A and no root. Again, the tooth displays slight lingual and distal curvature. There are no apparent striations on the labial surface. On the lingual surface, striae are distinctly apparent without magnification. Among these, some are continuous while the majority is singular or discontinuous. The striae are longest medially, some spanning the entire preserved length of the crown, and become shorter and less dense towards the carinae. Again, all striae are separate. Tooth C only preserves one anteroposterior half of the crown, the exact position of which is indeterminable through curvature. Similar to tooth A, parts of the root are preserved and show no constriction at the transition towards the crown. There are no conspicuous striations present on either surface. Since the teeth are relatively small, excluding taxa based on size alone isn’t possible. Therefore, we can best approach this ID by looking at the characteristic morphologies of each taxon: Gracilineustes leedsi ANDREWS 1913 The teeth of G. leedsi are conical, unfaceted, and display moderate to strong mediolateral compression and lingual curvature. Ornamentation occurs in the form of short, low apicobasal ridges that are barely visible with the naked eye. These are more abundant and strongly developed lingually, most numerous basally and become reduced apically, but do not interact with the carinae (YOUNG et al. 2013, 2015). Overall, G. leedsi appears to be a poor fit, as the striae in one tooth are not only very strongly developed, but also continuous along the length of the crown. Ieldraan melkshamensis FOFFA et al. 2017 The teeth of I. melkshamensis exhibit a unique morphology among metriorhynchids, in which the labial surface is divided into three distinct apicobasal planes. The central plane is distinctly fluted by five strongly developed troughs, a feature that is found in all known teeth of the species. Additionally, the teeth are ornamented by overlaying apicobasal striae. These are short, discontinuous, and occur on both lingual and labial surfaces, giving the enamel a rough appearance. Again, the ornamentation does not interact with the carinae (FOFFA et al. 2017). Like Gracilineustes, I. melkshamensis has to be considered a poor fit: The typical dental morphology of this species is not present, and the ornamentation differs quite a bit from what we see in these teeth. Suchodus brachyrhynchus EUDES-DESLONGCHAMPS 1867 The teeth of S. brachyrhnychus show a varying degree of mediolateral compression, weak in some teeth and strong in others (unspecified whether this is positional). Enamel ornamentation consists of weakly developed apicobasal ridges of unspecified extend on the lingual side, while the labial side is described to lack conspicuous ornamentation entirely (FOFFA et al. 2017, YOUNG et al. 2013). Again, as enamel striations in S. brachyrhynchus differ substantially from the ones seen in these teeth, this species seems to be an unlikely fit. Suchodus ?durobrivensis LYDEKKER 1890 The validity of this species has been disputed in the past, certain authors regard it as synonymous with S. brachyrhynchus, and I couldn’t find many references to it in more recent papers. ANDREWS 1913 calls this species ‘Metriorhynchus durobrivense’ – his description of the teeth as possessing a nearly smooth enamel with only slight ornamentation in the form of ‘extremely’ fine apicobasal ridges of unspecified extend certainly sounds similar to the general attributes of S. brachyrhynchus teeth. Varying descriptions of the teeth as mediolaterally compressed (sometimes this compression is specified to be ‘weak’) align with this as well (ANDREWS 1913, FOFFA et al. 2017). Regardless of whether S. brachyrhynchus and S. durobrivensis represent the same species, neither of their teeth show the morphology we are looking for and are a poor fit for this ID. Tyrannoneustes lythrodectikos YOUNG et al. 2013 The teeth of T. lythrodectikos are moderately to strongly mediolaterally compressed. The enamel lacks distinct ornamentation on both labial and lingual sides, except for the very base of the crown, where low, well-spaced, and short apicobasal ridges are present (FOFFA et al. 2017, YOUNG et al. 2013). T. lythrodectikos exhibits strongly reduced ornamentation, a condition not found in these teeth, and can therefore be disregarded as a possible ID. Thalattosuchus superciliosus YOUNG et al. 2020 Lastly, we must examine Thalattosuchus superciliosus. The YOUNG et al. 2020 paper on the description of the genus is unfortunately not openly accessible, yet detailed descriptions of the dentition exist in prior literature from when it was still assigned to ‘Metriorhynchus’ superciliosus. The teeth of this species are conical and curve lingually, sometimes with a certain degree of mediolateral compression (this condition is reportedly more apparent in newly erupted teeth). The ornamentation is strong, with short to moderately long apicobasal ridges that are distinctly visible on the lingual side, but less developed labially (newly erupted teeth feature strong ornamentation on both surfaces, suggesting that differences in ornamentation might be caused by wear). Ornamentation does not interact with the carinae. (ANDREWS 1913, VIGNAUD 1997, YOUNG et al. 2013). Overall, T. superciliosus appears to be a good ID for these teeth: The most extreme example of ornamentation observed in tooth B excludes all other taxa, but fits well with the typical dentition of this species. The variation between the teeth is easily explained by the natural variation that can be observed in individual metriorhynchids due to tooth position and wear. T. superciliosus has a relative abundance of specimens assigned to it, especially when compared to some of the other taxa, and thus our understanding of its dental characteristics is fortunately rather extensive. Considering everything, I'm rather confident in this ID. Still, I’d very much like to hear your thoughts! Especially if anyone has a PDF of the YOUNG et al. 2020 paper on Thalattosuchus, I’d really appreciate it! Thank you for your help! ADAMS-TRESMAN, S.M. (1978): The Callovian (Middle Jurassic) Marine Crocodile Metriorhynchus From Central England ANDREWS, C.W. (1913): A Descriptive Catalogue Of The Marine Reptiles Of The Oxford Clay - Part II FOFFA, D., YOUNG, M.T., BRUSATTE, S.L., GRAHAM, M.R. (2017): A New Metriorhynchid Crocodylomorph From The Oxford Clay Formation (Middle Jurassic) Of England, With Implications For The Origin And Diversification Of Geosaurini VIGNAUD, P. (1997): La Morphologie Dentaire Des Thalattosuchia (Crocodylia, Mesosuchia) YOUNG, M.T., DE ANDRADE, M.B., BRUSATTE, S.L., SAKAMOTO, M. (2013): The Oldest Known Metriorhynchid Super-Predator: A New Genus And Species From The Middle Jurassic Of England, With Implications For Serration And Mandibular Evolution In Predatious CLades YOUNG, M.T., BEATTY, B., STEEL, L. (2015): First Evidence Of Denticulated Dentition In Teleosaurid Crocodylomorphs