Liaoningosaurus: perhaps not an ankylosaur

This one goes back several years… with several updates!
Xu, Wang and You 2001 described what they thought was a juvenile ankylosaur, Liaoningosaurus paradoxes (Early Cretaceous, Yixian Formation) featuring “a large bony plate (somewhat shell-like) shielding the abdomen.” They tested it against only 13 other taxa and nested it outside the nodosaurs and outside the ankylosaurs…with no taxa between it and Stegosaurus.

Figure 1. Several specimens of Liaoningosaurus crushed flat plus a lateral view based on original holotype tracings.

Figure 1. Several specimens of Liaoningosaurus crushed flat plus a lateral view based on original holotype tracings.Note the lizard-like sprawling limbs in situ, a product of taphonomic crushing. Like all dinos, this one also had vertical limbs. Only a few small osteoderms are identified.

Xu et al. report:
“Diagnosis. An ankylosaurian that differs in having: shell-like ventral armour, trapezoidal sternum with slender and distally pointed posterolateral process and short medial articular margin, and pes more than twice as long as manus.”

Perhaps Xu et al. focused on ankylosaurs and nodosaurs
because all the specimens of Liaoningosaurus I have seen in publications or online (Fig. 1) have been crushed flat, with ribs spread out like ankylosaur ribs. Moreover, the pelvis was very wide, with limbs beneath the ilia, like those in ankylosaurs.

A closer look
(Fig. 1) reveals the ribs would have enclosed a deeper chest, not a wider one, though not as relatively deep as in Stegosaurus. Other more primitive stegosaurs likewise had a shorter, rounder torso cross-section.

the limbs are preserved sprawling, like those of the horned lizard, Phrynosoma. No dinosaur had sprawling limbs, so it’s okay to bring in both the limbs and the ribs (Fig. 1).

basal stegosaurs also have a very broad pelvis with limbs rotating beneath the ilium. Considering how closely ankylosaurs and stegosaurs match each other in so many traits, it is a tribute to the LRT that it recovers them in separate clades, separated by bipedal agile taxa like Lesothosaurus and Heterodontosaurus. It is unlikely that ankylosaurs ever reared up on their hind limbs, but stegosaurs appear to be able to do this.

Osteoderms are rare in Liaoningosaurus,
which is odd for an armored ankylosaur.

Ankylosaur teeth and stegosaur teeth greatly resemble one another and also resemble Liaoningosaurus teeth (Fig. 1), despite the great difference in size.

There are five digits on the manus
in Liaoningosaurus (Fig. 1) and metacarpal #5 is as long as #4. Unfortunately, ankylosaurs and kin in the LRT lack a preserved manus, but a look through the Princeton Field Guide to Dinosaurs (Paul 2010) finds no similar ankylosaur manus.

Arbour et al. 2014 report, “Examination of the holotype of Liaoningosaurus paradoxus, IVPP V12566, indicates that the ventral “plastron” is better interpreted as epidermal scales, because the broken edges do not reveal any bony histology.” Readers will note that the odd ventral plate (closeup in Fig. 2) does not appear in other Liaoningosaurus specimens (Fig. 1), but they are exposed dorsally.

Figure 2. Liaoningosaurus ventral patch. Note the scales.

Figure 2. Liaoningosaurus ventral patch. Note the scales.

The large reptile tree (LRT, 1005 taxa) includes several more ornithischian taxa, though fewer taxa with armor. In the LRT Liaoningosaurus nests between Scutellosaurus and Stegosaurus, several nodes away from the other armored ornithischians, Minmi and Scelidosaurus. No skull traits were tested in Liaoningosaurus due to the low resolution of the available images.

The armored ornithischians (stegosaurs and ankyosaurs) are so similar
to one another they are traditionally nested in one clade: Thyreophora. By contrast, the LRT separates ankylosaurs from stegosaurs. Here the few hind limb traits that separate Liaoningosaurus from Scelidosaurus and/or Minmi and ally it with Scutellosaurus and/or Stegosaurus include the following:

  1. Tibia/femur ratio not less than 1:1
  2. Fibula not appressed to tibia
  3. Fibula diameter not > half tibia diameter
  4. Metatarsus not compact
  5. Metatarsal 1 < half metatarsal 3
  6. Metatarsal 1 not > half metatarsal 4
  7. Metatarsals 2 and 3 align beyond p1.1
  8. Pedal 4 length <  metatarsal 4

Perhaps better imagery
of the skull and other parts will add to or modify this list and nesting.

The addition of a basal ankylosaur
with these traits would nudge Liaoningosaurus toward the ankylosaurs. In the LRT ankylosaurs were derived from large, armored, lumbering Scelidosaurus. By contrast, the stegosaurs were derived from small, agile Lesothosaurus and Scutellosaurus. So finding a small armored dinosaur with the above list of traits, even if it is a juvenile, should suggest taking a close look at its stegosaur affinities, despite the initial appearance of a wide round horned-lizard-like torso.

Ji et al. 2016 found fish within the torso (but not restricted to the gut) of a Liaoningosaurus suggesting a fish diet, rather than an herbivorous one.

Xu et al. 2001 reported, “Liaoningosaurus has an unusual combination of characters and it might (for example) represent a third ankylosaur lineage.” Perhaps one closer to stegosaurs. Xu et al. 2001 also report, “all manual and pedal unguals claw-shaped.” At present the manual unguals do not appear to be claw-shaped, with the the exception of #3, as in stegosaurs… AND as in ankylosaurs.

Xu X, Wang XL and You HL 2001. A juvenile ankylosaur from China. Naturwissenschaften 88:297. doi:10.1007/s001140100233
Ji Q, Wu X, Cheng Y, Ten F, Wang X and Ji Y 2016. Fish-hunting ankylosaurs (Dinosauria, Ornithischia) from the Cretaceous of China. Journal of Geology, 40(2).
Thompson RS, Parish JC, Maidment SCR and Barrett PM 2011. Phylogeny of the ankylosaurian dinosaurs (Ornithischia: Thyreophora). Journal of Systematic Palaeontology. 10 (2): 301–312. doi:10.1080/14772019.2011.569091
Arbour VM, Burns ME, Bell PR and Currie PJ 2014. Epidermal and dermal integumentary structures of ankylosaurian dinosaurs. Journal of Morphology, 275(1): 39-50. doi:10.1002/jmor.20194


Will the real Minmi please stand up?

Earlier the ankylosaurs, represented by Minmi, (Figs 1, 2) were phylogenetically and heretically separated from their putative Thyreophoran sisters, like Stegosaurus. A phylogenetic analysis nested the former with the basal orinithischian, Scelidosaurus, while nesting the latter with the more derived and much smaller ornithischian, Scutellosaurus. All prior studies presumed Scelidosaurus and Scutellosaurus were sisters in armor. In the large reptile tree the two armored clades of ornithischians developed their defenses by convergence.

Minmi paravertebrai (min-my, Molnar 1960, early Cretaceous, 3m, Fig. 2) ) is one of the most popular dinosaurs and very likely THE most popular ankylosaur. It’s small and Australian. It’s been an illustration, a sculpture, a toy, and a stamp––all in addition to its original role as a fossil (Fig. 1).

When I went searching for Minmi data
I found little consistency in Minmi reconstructions (Fig. 1). Many seem to be based on something other than the original fossil (Fig. 2). Some have a nodosaur-like skull. Some have legs that are too long. Others make up their own armor.

Figure 1. The many ways the Australian ankylosaur, Minmi, has been portrayed. Each one is different.

Figure 1. The many ways the Australian ankylosaur, Minmi, has been portrayed. Each one is different. The illustration in the lower right hand corner appears to most closely resemble the original fossil material.

That’s why
Minmi is shown here (Fig. 2) as a reconstruction, along with its original fossil and tracings. There should be a one-to-one correspondence of elements here. At least that was the intention. The distal tail is unknown and restored here.

Figbure 2. Minmi paravertebra as found, tracings in both dorsal and ventral aspect and reconstruction based on the tracings.

Figbure 2. Minmi paravertebra as found, tracings in both dorsal and ventral aspect and reconstruction based on the tracings. The skull is not heavily armored, so provides skull sutures, colorized here from hints provided by Molnar. 

Minmi paravertebra was recovered as the most basal anklylosaur by Thompson et al. 2011. Overall smaller than most ankylosaurs, the skull was larger, the torso shorter and the legs relatively longer than larger, later forms like Ankylosaurus and Euoplocephalus.

Distinct from the more basal Scelidosaurusthe torso of Minmi was wider than tall. The pubis was a vestige. The limbs were all subequal in length. The ilia rotated laterally so their medial surfaces became dorsal, acting like armor plates. Individual osteoderms were larger. No temporal fenestra appear on the skull as bone infilled all those cavities.

Interesting gut contents
consist of fragments of fibrous or vascular plant tissue, fruiting bodies, spherical seeds, and vesicular tissue (possibly from fern sporangia). The fragments are uniform in size and cut cleanly, indicating oral processing supported by inset teeth probably within cheeks.

Haubold H 1990. Ein neuer Dinosaurier (Ornithischia, Thyreophora) aus dem Unteren Jura des nördlichen Mitteleuropa. Revue de Paleobiologie 9(1):149-177. [In German]
Molnar RE 1980. An ankylosaur (Ornithischia: Reptilia) from the Lower Cretaceous of southern Queensland. Memoirs of the Queensland Museum 20:65-75
Thompson RS, Parish JC, Maidment SCR and Barret PM 2011. Phylogeny of the ankylosaurian dinosaurs (Ornithischia: Thyreophora). Journal of Systematic Palaeontology 301-312.

Minmi YouTube video here.