Rise of the Tyrannosaurs by Stephen Brusatte

Revised May 15, 2016 with a longer neck for Tianyuanlong, more like that of its outgroup sister, Ornitholestes. Grateful to M. Mortimer for suggesting I take another look at it, but the objections raised were not valid for this taxon. 

Scientific American has published several articles devoted to dinosaurs. “Rise of the Tyrannosaurs – New fossils put T.rex in its place” (Brusatte 2015) is one of the latest (Fig 1).

Figure 1. Rise of the Tyrannosaurs by Stephen Brusatte, Scientific American

Figure 1. Rise of the Tyrannosaurs by Stephen Brusatte, Scientific American. Cover art by James Gurney of Dinotopia fame.

From the online access page:

  • Paleontologists have known about T. rex and other giant tyrannosaurs for decades. But they were unable to piece together when the tyrannosaurs originated and what they evolved from because they lacked the fossils to do so.
  • Recent fossil finds have gone a long way toward filling those gaps in scientists’ understanding of this iconic group.
  • Together these discoveries reveal that tyrannosaurs have surprisingly deep—and humble—evolutionary roots.
  • Furthermore, the group encompasses a far greater diversity of forms than experts had anticipated—including some with truly bizarre anatomical features (Fig. 2).
Figure 2. Tyrannosaur ancestors according to Brusatte, artwork by Todd Marshall. Those on the left are actually closer to allosaurs and spinosaurs. Drag to desktop to enlarge.

Figure 2. Tyrannosaur ancestors according to Brusatte, artwork by Todd Marshall. Those on the left are actually closer to allosaurs and spinosaurs. Click to enlarge.

Despite the fantastic artwork,
the taxa in ‘the rise’ are actually basal to allosaurs and spinosaurs, not tyrannosaurs (Fig. 1), according to the large reptile tree (Fig. 4). Some of the ancestors recovered in the large reptile tree, like Zhenyuanlong, had extensive wing feathers (Fig. 3), which actually makes the ancestry of T-rex more interesting. And it makes the little hands of T-rex, vestigial wings.

Figure 3. Tyrannosaur ancestors to scale according to the large reptile tree. Drag to desktop to enlarge.

Figure 3. Tyrannosaur ancestors to scale according to the large reptile tree. Click to enlarge.

Here’s the subset of the large reptile tree
focusing on basal theropods (Fig. 4). Note how Proceratosaurus, Guanlong and Dilong could be considered basal to tyrannosaurs, but really they are closer to allosaurs in this cladogram. I think the mistake may lie, once again, in taxon exclusion, but also to misinterpretation.

Figure 4. Subset of the large retile tree focusing on theropods. Note the green taxa. While technically basal to tyrannosaurs, this clade is actually closer to allosaurs and spinosaurs. And the Brusatte text does not consider Zhenyuanlong, Tianyuraptor, Fukuiraptor and Ornitholestes.

Figure 4. Subset of the large retile tree focusing on theropods. Note the green taxa. While somewhat basal to tyrannosaurs, this clade is actually closer to allosaurs and spinosaurs. And the Brusatte text does not consider Zhenyuanlong, Tianyuraptor, Fukuiraptor and Ornitholestes.

We first learned about T-rex ancestors
(according to the large reptile tree) here, here, here and here. Here are Zhenyuanlong and kin again (Fig. 5), the more parsimonious ancestors of T-rex.

Figure 5. Ornitholestes, Tianyuraptor and Zhenyuanlong are close relatives of Tyrannosaurus rex in the large reptile tree. See how those little arms are actually vestigial wings?  The short back, long legs, large head are all tyrannosaur traits.

Figure 5. Ornitholestes, Tianyuraptor and Zhenyuanlong are close relatives of Tyrannosaurus rex in the large reptile tree. See how those little arms are actually vestigial wings?  The short back, long legs, large head are all tyrannosaur traits.

References
Brusatte S 2015. Rise of the Tyrannosaurs. Scientific American 312:34-41. doi:10.1038/scientificamerican0515-34

See a video on the production of the cover art and a peek inside the James Gurney studio here.

Learn more about artist Todd Marshall here.

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5 thoughts on “Rise of the Tyrannosaurs by Stephen Brusatte

  1. Your interpretation of theropod phylogeny, including these basal tyrannosauroids, is primarily due to your reconstructions being inaccurate. For instance, Tianyuraptor doesn’t have an anterior pubic boot, you presumably traced the pedal phalanges in that position as part of the boot. There’s an oblique photo of the specimen online that shows this, even if you distrust the authors’ drawing. You also gave it seventeen dorsal vertebrae, when no theropod with five or more sacrals has more than thirteen or fourteen. Or for Zhenyuanlong, you reconstruct a tyrannosaur-like dorsally expanded quadratojugal, but it actually has a dromaeosaurid-like quadratojugal with a narrow dorsal process and long posterior process as seen and labeled in the paper’s figure 2. Their figure 3 clearly shows the scapula lacks a distal expansion, like dromaeosaurids but unlike tyrannosaurs. Etc.. For theropods, you can’t argue taxon exclusion is the reason other analyses get different results than you, as these analyses (like those in the descriptions of Tianyuraptor, Zhenyuanlong and Fukuivenator, and Brusatte’s latest from his thesis) contain way more tyrannosauroids and dromaeosaurids than yours does, and use about four times as many characters to boot.

    • Grateful for your note, Mickey. I can only comment on Tianyuraptor at present. Earlier I trusted the original tracing to make my reconstruction and was probably biased to a short neck by previous work with Zhenyuanlong. In a few days I will show a DGS tracing in which more cervicals were found in Tianyuanraptor, approaching the number found in Ornitholestes. You are correct, 17 dorsals is too many for Tianyuraptor, but your comment about the maximum number of dorsals in theropods is not correct. Ornitholestes, Tianyuanlong, Sinornithosaurus and Compsognathus all have more than 25 presacrals and these all have 15 dorsals. Two scores changed, but now Tianyuraptor shares two more traits with its predecessor rather than its successor. So, at present the tree topology has not changed and trust/laziness, rather than DGS, is to blame for the earlier error. Thanks for shining a flashlight on those roaches. More to come later.

  2. I will try to post new figures and overlays today or tomorrow.
    re: inaccurate reconstructions

    You are correct.
    Tianyuraptor has no anterior pubic boot. That has been repaired but there is no score for ‘anterior pubic boot’ so no score changes were made.

    You are correct.
    I gave Tianyuraptor 17 dorsal vertebrae. I trusted the drawings and did not perform a DGS color examination of the bones. That has been repaired. See upcoming blogpost.

    You may be correct
    when you say no theropod with five or more sacrals has more than 13 or 14 (why don’t you just say 14?) After making the color tracings I do note that Tianyuraptor does have 15 dorsals and so does Compsognathus and Ornitholestes. Have not counted the sacrals on those taxa.

    On Zhenyuanlong skull
    The back of the skull is such a mess that Lü and Brusatte opted to avoid identifying any bones there. What Lü and Brusatte identify as a right anlgle quadratojugal I identified as two bones, the horizontal rim of the surangular and a vertical slender bone with an expanded base that appears to be the broken jugal ramus of the quadratojugal, which currently lacks a jugal ramus if all identifications are correct. I can see how that bone could be identified as a quadratojugal as it was by Lü and Brusatte. They also identified the top of the quadratojugal as the quadrate, but that would be a very short quadrate with an expanded dorsal rim. They did not identify the bone inside the surangular, which I identified as the quadrate. It fits the skull reconstruction better and looks like a tyrannosaur quadrate. They key to this argument may be higher resolution images and a disassembly of the Zhenyuanlong skull, either by hand or digitally, to identify all the bones properly. The rest of the skeleton (except the stiffened tail) more parsimoniously nests with tyrannosaurs, so, being human, I lean that way on skull IDs. And they seem to be working on reconstructions. Too bad Lü and Brusatte did not test their IDs with a reconstruction.

    On Zhenyuanlong scapula

    The left one is hidden behind the cervicals, but dorsal expansions of the anterior/distal end DO appear to be peeking out from behind the neural spines. And the left scapula likewaise appears to sweep up, so thank you for alerting me to those missed tyrannosaur traits, which are not listed in the current character list.

    • I don’t ‘just say’ 14 dorsals because the taxa in question (including Allosaurus) have vertebrae which could count as cervical or dorsal depending on how you define the terms (presacral 11 has the parapophysis contact the neural arch, presacral 11 has the first hypapophysis, presacral 10 has the first long and horizontal transverse processes, etc.).

      Only ten dorsals were preserved in Ornitholestes, which you should know since the gray skull you use is figure 3.2D of Carpenter et al. (2005), who state this fact. I assume you were using skeletal mount photos to code from, which was an issue with your basal dinosaur data too. Ostrom (1978, pg. 88) argued Compsognathus’ holotype has thirteen dorsal vertebrae due to changes between the tenth and eleventh presacrals and the fact the twenty-second and twenty-third have missing centra so were not fused to the sacrum. Peyer (2006) showed that the referred specimen has twenty-three presacrals, though the eleventh is too poorly preserved to classify and the twelfth only differs in being shorter and having a possibly associated dorsal rib, which would leave it with 11-13 dorsals. For Tianyuraptor, there are three below the left ilium, two sets of two in the middle, the first three if we arbitrarily start above the coracoid, another an extra vertebra’s length behind them, and nothing else that’s clearly a dorsal though there are a couple masses that might be. So that’s at least eleven.

      On Zhenyuanlong’s skull-
      Basal paravians do have short quadrates, though I’m not sure what you mean about an expanded dorsal rim (the flange over the paraquadrate foramen?). I’m not even sure what you identify as the quadrate is one bone. Part could be the articular, it might be braincase fragments, I can even see a cervical neural arch there if I try (with your expanded dorsal quadratojugal process being the postzygapophyses). By the way, your articular is the right half of a complete cervical neural arch in dorsal view (anterior is upper left), your anterodorsal jugal process is the posteroventral rim of the lacrimal, the posterior lacrimal processes are not fused prefrontals (note Sinornithosaurus has both these long processes and free prefrontals), and you got the palate all wrong (the palatine is in lateral view taking up most of the ventral half of the antorbital fenestra, with attached vomer and pterygoid pieces).

      On Zhenyuanlong’s scapula-
      I’m confused what you did. Your colored tracing correctly has the far scapula’s barely expanded distal end rising posterodorsally over the dorsals in light blue. But then your reconstruction has a longer distally expanding orange bone as the scapula. By the distal end I meant the end away from the coracoid, generally pointing posterodorsally.

      References- Carpenter, Miles, Ostrom and Cloward, 2005. Redescription of the small maniraptoran theropods Ornitholestes and Coelurus from the Upper Jurassic Morrison Formation of Wyoming. In Carpenter (ed.). The Carnivorous Dinosaurs. Indiana University Press. 49-71.

      Ostrom, 1978. The osteology of Compsognathus longipes. Zitteliana Abbandlungen Bayerischen Staatssammlung Paldontol. historische Geol. (Munchen). 4, 73-118.

      Peyer, 2006. A reconsideration of Compsognathus from the Upper Tithonian of Canjuers, Southeastern France. Journal of Vertebrate Paleontology. 26(4), 879-896.

  3. Thanks for clearing up the distal question. I don’t have the Carpenter or Ostrom references, but will seek them. The other issues will have to await review following the process.

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