Earlier the large reptile tree (Fig. 4) nested Tianyuraptor, Zhenyuanlong, Ornitholestes and Microraptor in the same clade as Tyrannosaurus. At the same time the LRT nested former long rostrum tyrannosauroids, like Dilong, Guanlong, Proceratosaurus, and Xiongguanlong with spinosaurs. That differs from prior published studies.
In correspondence with the author
of a recent tyrannosauroid paper, the author made these statements with regard to the cladogram (Fig. 4) that I sent along, “Your tree is so iconoclastic* that, if correct (or even remotely correct), it means that everyone else working in theropod systematics over the past two decades has been blatantly wrong. Having spent many years working on tyrannosauroids and dromaeosauroids I can’t fathom why you’re not finding a monophyletic Tyrannosauroidea, or why you’re placing some tyrannosauroids with abelisaurids (Yutyrannus + Majungasaurus), or how Tyrannosaurus could possibly be linked with Zhenyuanlong/Tianyuraptor. The last one in particular is, let me put it frankly, impossible.”
iconoclastic = characterized by attack on cherished beliefs or institutions.
Well, I’m not trying to promote the impossible.
This is just what you get when you plug the numbers in to the LRT, where all sister taxa look similar to one another (see below). I know why the LRT recovers the sisters that it does (see below). I don’t know why prior studies recover the sisters that they do.
At the heart of science
is an essential balance between two seemingly contradictory attitudes –
an openness to new ideas, no matter how bizarre or counterintuitive,
and the most ruthlessly skeptical scrutiny of all ideas, old and new.
This is how deep truths are winnowed from deep nonsense.
— Carl Sagan —
I have attempted to be ruthless,
trying to see what it would take to shift taxa back to their traditional order. I have to say, I have failed to do so in the Theropoda. This topology appears to make more sense here and the scores reflect that.
Something I should have done earlier
is provide side-by-side comparisons (Figs. 1-4). Of course, the LRT dataset is available to anyone on request.
Tyrannosauroids are most readily united by
their relatively deeper rostra, short necks and short torsos. This also gives them the impression of having longer hind limbs. The pubis is not oriented posteriorly, as in dromaeosaurids like Velociraptor (Fig. 1).
Figure 2. Tianyuraptor and Zhenyuanlong compared to Tyrannosaurus and to Velociraptor. The two taxa in question traditionally nest with the latter. Tyrannosauroids are united
The sisterhood of
Ornitholestes, Tianyuraptor and Microraptor are readily visible here (Fig. 2). I hope the sisterhood of Tyrannosaurus, Zhenyuanlong and Tianyuraptor is also obvious (Fig. 1) as opposed to the dromaeosaurs shown above.
The long-rostrum taxa here removed from
the tyrannosauroids all nest more parsimoniously with spinosaurs and their kin, including Deinocheirus (Fig. 3). Compare them all to Albertosaurus and decide for yourself which one is the oddball here.
Figure 1. Murusraptor compared with related taxa to scale.
In the Allosaurus clade
the former tyrannosauroid, Yutyrannus now nests with the abelisaurid, Majungasaurus, among tested taxa. They both share a median nasal crest absent in Allosaurus, but retained by Ceratosaurus, Proceratosaurus and Guanlong. (But that’s not all, of course). Here it is a little more difficult to lump and split due to the many convergent characters shared by unrelated giant theropods. In Yutyrannus the skull is larger relative to the shorter neck, for instance. Even so, the large forearm, and long torso stand out as starting points for uniting Yutyrannus with allosaurs. Note that Yutyrannus lacks the pinched proximal metatarsal 3 characteristic of tyrannosaur clade members. And that is not even a character in the LRT matrix.
Figure 4. Yutyrannus compared to Tyrannosaurus and Allosaurus. There is quite a bit of convergence here. Surprisingly, Yutyrannus is actually closer to the tiny-handed abelisaur, Majungasaurus.
It takes 30 more steps
at present to shift Yutyrannus to Tyrannosaurus (Fig. 4). That’s substantial.
Figure 4. The Dinosauria subset of the large reptile tree as of February 5, 2016. Here several former long-snouted tyrannosaurs now closer to spinosaurs and allosaurs.
If a cladogram is valid,
it should recover taxa that are similar to one another both overall and in detail. One should be able to trace the evolution of character traits in a gradual fashion without having to resort the to the term ‘aberrant’ at any time, now that we have dozens of taxa to compare one to. Moreover, if a matrix is scored correctly, no matter which characters are chosen (so long as 150+ are used) all tree topologies should match. That’s the ideal. That’s not happening quite yet.
If I have made mistakes,
I will correct them when valid data becomes available that changes the tree topology. At present, however, with every added taxon, and there have been quite a few lately, the tree topology has not changed and autapomorphies are relatively rare.
The Pterosaur Heresies 