T. rex Ontogeny

So today I finally got around to finishing this after several weeks of working on it: a chart to show the roughly complete ontogenetic sequence of Tyrannosaurus rex. All of the ontogomorphs depicted in this are based on specific specimens for which we know at least approximate ages. They are as follows:

2 year old- What I would refer to as a chick, this is based on MOR 6625, or "Chomper", the youngest T. rex specimen we have (or at least the youngest that is not in private hands; not much more to say regarding Chomper given the fragmentary nature of the specimen making it difficult to discern much of its anatomy, hence this reconstruction is mainly based on MPC-D 107/7, a very young T. bataar specimen (though given the extreme differences in ontogeny between the two species, that might not necessarily reflect reality). Full piece here: sta.sh/025or5rksp6a

3 year old- Based on LACM 28741, also known as “Jordan”, this specimen shows that juvenile 'rexlets' had elongate snouts and extremely long legs, in addition to being very slender overall. Based mainly on GetAwayTrike's skeletal of the specimen. Full piece here: sta.sh/01ewuzm6sbmx

11 year old- As far as we can tell, not much really changed in these nine years, other than a slight increase in size a robusticity. This is primarily based on ScottHartman's skeletal BMRP 2002.4.1, or "Jane" (before you ask, no "Nanotyrannus" is almost certainly not a valid genus, and even if by the very distant possibility it was, it would mean that there was another roughly T. rex sized tyrannosaurid in the ecosystem, which is in and of itself, very unlikely). These adolescent specimens show that individuals of this age were still very gangly and quite awkward looking, with long, lanky legs. They still possessed relatively blade like teeth compared to the adults. Full piece here: fav.me/dbcna19

13-14 year old- A growth stage that I find is very often overlooked, but also clearly shows the transition between younger, lanky individuals, and the massive and robust adults. These subadult animals are known from very few specimens, such as LACM 23845 (which this depiction is based on, in particular GetAwayTrike's skeletal of it) and the slightly older MOR 1125, or B-rex. It is around this age that the, still skeletally immature, individuals reached sexual maturity, following the typical non-avian dinosaur pattern of beginning to reproduce years before being full size. Full piece here: sta.sh/01rrg7efmhbq

18 year old- Young adult, based on ScottHartman's skeletal of BHI 3033, "Stan", which is also the basis for Saurian's adult rex. These adult specimens are already massive and extremely robust, with the crushing dentition and huge skull that Tyrannosaurus is infamous for, after a very short growth spurt in only around four years. The keratin on their skulls begins to become very rugose, and some specimens show a series of strange leaf shaped maxillary indentations noticed by WitmerLab, which may also be associated with some form of soft tissue, perhaps for display reasons. Full piece here: sta.sh/01gghsxao59h

29+ year old- These are the massive and extremely old specimens dubbed by the Saurian development team as "superadults". These specimens include the largest (note: in mass, tyrannosaurs seem to stop growing in length in their early twenties or so, and just get girthier/more rotund as they age) and most robust specimens of T. rex, including arguably the most famous: FMNH PR 2081. This reconstruction is based on ScottHartman's skeletal reconstruction of the specimen. Animals of this age were likely breeding very little, and may even have been completely sterile as occurs in crocodylians 'superadults' today. The oldest specimens may even have eventually started becoming toothless. These specimens have extremely rugose skulls, much more so than the younger adult specimens do. Sue may actually be the youngest of these specimens, at 29 years of age, as the specimens "Trix", "Tristan", and "Scotty" all appear to be in their early to mid thirties. Full piece here: fav.me/dbc015h

T. rex goes through extreme changes not only physicially, but also ecologically as it ages, with the younger individuals occupying very different niches to the larger and more massively built adults. The niche differentiation between ontogomorphs of this species is extreme even for Tyrannosauridae (with the exception of Albertosaurus sarcophagus). What appears to be happening, as presented at the 2016 SVP meeting, is that tyrannosaurs that are coexisting with other tyrannosaur species (such as A. libratus and Daspletosaurus sp. in the Dinosaur Park Formation) go through much less drastic ontogenetic change, and greater niche differentiation between the species as a whole, whereas tyrannosaurs that are the only giant theropods in their ecosystem, like T. rex, go through much greater change and occupy more of the predatory niches in their ecosystems. This study is still unpublished, however it is mentioned here: fav.me/dan49zu