Fukuivenator: not a mystery, the basalmost tyrannosaur!

Updated February 28, 2016 with new restorations of Fukuivenator and Tianyuraptor and shifting Fukuivenator one node more primitive. 

Fukuivenator paradoxus 
(Azuma et al. 2016, FPDM-V8461, Fig. 1), was originally described as, “a bizarre theropod.” With a specific name like “F. paradoxus,” it’s easy to see there was mystery surrounding this theropod.

Unfortunately, this may just be a case
of taxon exclusion and a sour matrix. No reconstructions were published and several scale bars do not appear to be valid. I had no trouble nesting this theropod. Rather than bizarre, it shares a long list of traits with its new sisters (Figs. 2, 3).

Figure 1. Fukvenator parts to scale lifted from Azuma et al. 2016. Note, the larger skull, hind limb and foot match Zhenyuanlong in size and general morphology. Only the manus is relatively larger. I suspect the smaller skull scale bar.

Figure 1. Fukvenator parts to scale lifted from Azuma et al. 2016. Note, the larger skull, hind limb and foot match Zhenyuanlong in size and general morphology. Only the manus is relatively larger. I suspect the smaller skull scale bar.

From the abstract:
“While Fukuivenator possesses a large number of morphological features unknown in any other theropod, it has a combination of primitive and derived features seen in different theropod subgroups, notably dromaeosaurid dinosaurs.” 

From the Diagnosis
A relatively small theropod with the following unique features (comments follow):

  1. unusually large external naris (slightly smaller than antorbital fenestra in dorsoventral height) – also in Ornitholestes and Tianyuraptor (O&T)
  2. large premaxillary fenestra subequal in size to maxillary fenestra – also in Zhenyuanlong (Z)
  3. large oval lacrimal pneumatic recess posterodorsal to the maxillary fenestra on antorbital fossa medial wall – also in the tyrannosaur clade
  4. lacrimal with a distinct groove on lateral surface of anterior process and a ridge on lateral surface of descending process – detail too small to see
  5. postorbital frontal process with T-shaped-cross section and laterally-flanged squamosal process – also in the tyrannosaur clade
  6. an elongate tubercle on posterior surface of basal tuber of the basicranial region – detail too small to see
  7. highly heterodont dentition featuring robust unserrated teeth including small spatulate anterior teeth, large and posteriorly curved middle teeth, and small and nearly symmetrical posterior teeth  – also in the tyrannosaur clade
  8. cervical vertebrae with a complex lamina system surrounding the neural canal resulting in deep and wide grooves for interspinous ligaments and additional deep sockets  – also in the tyrannosaur clade
  9. anterior cervical vertebrae with interprezygapophyseal, postzygadiapophyseal, prezygadiapohyseal, and interpostzygapophyseal laminae connecting to each other to form an extensive platform  – also in the tyrannosaur clade
  10. anterior and middle cervical vertebrae with transversely bifid neural spines  – also in the tyrannosaur clade
  11. dorsal, sacral, and anterior caudal vertebrae with strongly laterally curved hyposphene and centropostzygapophyseal laminae that, together with the postzygapophyseal facet, form a socket-like structure for receiving the prezygapophysis – unfamiliar with this
  12. dorsoventrally bifurcated sacral ribs – also in Zhenyuanlong (Z)
  13. caudal zygapophyseal facets expanded to be substantially wider than the zygapophyseal processes;– unfamiliar with this and
  14. middle caudal vertebrae with transversely and distally bifid prezygapophyses.– unfamiliar with this
Figure 2. Ornitholestes, Tianyuraptor and Zhenyuanlong are close relatives of Fukuivenator at the base of the tyrannosaur clade. Gray zone on Ornitholestes skull marks off the boundary of the external naris.

Figure 2. Ornitholestes, Tianyuraptor and Zhenyuanlong are close relatives of Fukuivenator at the base of the tyrannosaur clade. Gray zone on Ornitholestes skull marks off the boundary of the external naris.

Nowhere in the text
do the authors list Zhenyuanlong, but Tianyuraptor is listed.The large reptile tree (subset fig. 3) nests Fukuivenator at the base of the tyrannosaurs between Tianyuraptor and Ornitholestes. One tree published by Azuma et al. also nests Fukuivenator with Ornitholestes, but it has many other problems and lacks resolution at several nodes. So here we have a tentative agreement with the published work.

Like Ornitholestes and Tianyuraptor
Fukuivenator has an enormous round naris (“all the better to smell you with, my dear~”)

Like Zhenyuanlong and T-rex
Fukuivenator has a taller than wide orbit and deeply rooted teeth. Premaxillary teeth are incisor (‘D’) -shaped.

Like Ornitholestes
The skull is shorter than the cervical series and shorter than half the presacral length.

Figure 2. Fukuiraptor nests with basal tyrannosaurs in the theropod subset of the large reptile tree.

Figure 2. Fukuivenator nests with basal tyrannosaurs in the theropod subset of the large reptile tree.

The authors note several dromaeosaurid traits
but Fukuivenator does not have a large killer claw. Fukuivenator actually provides more evidence that basal tyrannosaurs were dromaeosaur mimics, with large wing feathers and stiff tails, just like Microraptor, the bird mimic. Instead of being sharp-eyed predators, as we presume the deinonychosaurs, troodontids and birds were/are, some basal tyrannosaur clade members may have used their nose. So this is where T-rex became “a stellar smeller” back in the Late Jurassic/Early Cretaceous.

Not sure why professional paleontologists
are not seeing these relationships, but I think I smell a sour matrix over there that, like an old sock, has been used to many times without running it through the washer every so often.

As in pterosaurs and turtles and Vancleavea and caseids and mesosaurs…
if you can’t find a good sister taxon among the traditional sister taxa, then maybe you need to look elsewhere. In this case, Fukuivenator does not nest with dromaeosaurs, but very nicely with basalmost tyrannosaurs without paradox or bizarre qualities. I note this, as usual, without seeing the fossil firsthand, for which I am often vilified. This study shows that contributions can be done in paleontology without seeing the fossils firsthand.

References
Azuma Y, Xu X, Shibata1 M, Kawabe S, Miyata K and Imai T 2016. A bizarre theropod from the Early Cretaceous of Japan highlighting mosaic evolution among coelurosaurians. Nature Scientific Reports | 6:20478 | DOI: 10.1038/srep20478

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