A brand new evaluation of Tyrannosaurus skeletal stays reveals bodily variations within the femur, different bones, and dental constructions throughout specimens that might recommend Tyrannosaurus rex specimens have to be re-categorized into three distinct teams or species, studies a examine printed in Evolutionary Biology.
Tyrannosaurus rex is the one acknowledged species of the group of dinosaurs, or genus, Tyrannosaurus so far. Earlier analysis has acknowledged variation throughout Tyrannosaurus skeletal stays within the femur (thighbone) and specimens with both one or two slender incisor tooth on all sides of entrance ends of the jaw.
Gregory Paul and colleagues analyzed the bones and dental stays of 37 Tyrannosaurus specimens. The authors in contrast the robustness of the femur in 24 of the specimens, a measure calculated from the size and circumference that provides a sign of the power of the bone. In addition they measured the diameter of the bottom of tooth or area within the gums to evaluate if specimens had one or two slender incisiform tooth.
The authors noticed that the femur various throughout specimens, some with extra strong femurs and others with extra gracile femurs. The authors discovered there have been two instances extra strong femurs than gracile ones throughout specimens, which means that this isn’t a distinction attributable to intercourse, which might doubtless end in a extra even break up. The authors additionally recommend that the variation in femurs is just not associated to progress of the specimen as strong femurs have been present in some juvenile specimens two thirds the scale of an grownup and gracile femurs have been present in some specimens that have been full grownup dimension.
Dental construction additionally various throughout specimens, though these with each femur measurements and dental stays was low (12 specimens). Specimens with one incisor tooth have been correlated with typically having increased femur gracility.
Of the Tyrannosaurus specimens, 28 may very well be recognized in distinct layers of sediment (stratigraphy) on the Lancian higher Masstrichtian formations in North America (estimated to be from between 67.5 to 66 million years in the past). The authors in contrast Tyrannosaurus specimens with different theropod species present in decrease layers of sediment.
Solely strong Tyrannosaurus femurs have been discovered within the decrease layer of sediment (six femurs). The variation of femur robustness within the decrease layer was not completely different to that of different theropod species, which signifies that doubtless just one species of Tyrannosaurus existed at this level. Just one gracile Tyrannosaurus femur was recognized within the center layer with 5 different gracile femurs within the higher layer, alongside different strong femurs. The variation in Tyrannosaurus femur robustness within the high layer of the sediments was increased than what was noticed in some earlier theropod specimens. This means that the Tyrannosaurus specimens discovered at increased layers of sediment bodily developed into extra distinct types in comparison with specimens from decrease layers, and different dinosaur species.
Gregory Paul, lead writer, mentioned: “We discovered that the adjustments in Tyrannosaurus femurs are doubtless not associated to the intercourse or age of the specimen. We suggest that the adjustments within the femur could have developed over time from a typical ancestor who displayed extra strong femurs to grow to be extra gracile in later species. The variations in femur robustness throughout layers of sediment could also be thought-about distinct sufficient that the specimens may doubtlessly be thought-about separate species.”
The authors nominate two potential new species of Tyrannosaurus based mostly on their evaluation. The primary, Tyrannosaurus imperator (tyrant lizard emperor), pertains to specimens discovered on the decrease and center layers of sediment, characterised with extra strong femurs and normally two incisor tooth. The authors argue these options have been retained from earlier ancestors (tyrannosaurids). The second, Tyrannosaurus regina (tyrant lizard queen), is linked to specimens from the higher and probably center layers of sediment, characterised with slenderer femurs and one incisor tooth. The acknowledged species Tyrannosaurus rex (tyrant lizard king) was recognized within the higher and probably center layer of sediment with specimens classed as retaining extra strong femurs whereas having just one incisor tooth. Some specimens couldn’t be recognized based mostly on their stays so weren’t assigned to a species.
The authors acknowledge that they can’t rule out that the noticed variation is because of excessive particular person variations, or atypical sexual dimorphism, moderately than separate teams, and so they additionally warning that the placement inside sediment layers is just not recognized for some specimens. The authors focus on the difficulties of assigning fossil vertebrates to a possible new species.
The authors conclude that the bodily variation present in Tyrannosaurus specimens mixed with their stratigraphy are indicative of three potential teams that may very well be nominated as two new species, T. imperator and T. regina, alongside the one acknowledged species so far, T. rex.
Reference: “The Tyrant Lizard King, Queen and Emperor: A number of Traces of Morphological and Stratigraphic Proof Help Refined Evolution and Possible Speciation Inside the North American Genus Tyrannosaurus” by Gregory S. Paul, W. Scott Individuals IV and Jay Van Raalte, 1 March 2022, Evolutionary Biology.
DOI: 10.1007/s11692-022-09561-5
