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I'll break into non-theropods for a while, as I've
been concentrating on them lately. I must warn you all that my
ornithischian knowledge and references are much less extensive, so I rely more
on the original description and less on my own interpretations. Thanks to
Jaime Headden for his suggestions.
Liaoningosaurus Xu, Wang and You 2001
L. paradoxus Xu, Wang and You 2001
Etymology- "paradoxical lizard from
Liaoning"
Barremian, Early Cretaceous
Yixian Formation, Liaoning, China
Holotype- (IVPP V12560) (330 mm, juvenile)
premaxilla, maxilla, mandibles, quadrate, pterygoid?, basioccipital?,
basisphenoid?, paroccipital process?, teeth, several cervical vertebrae, three
dorsal vertebrae, twenty-three dorsal ribs (to 54 mm), four sacral vertebrae (6
mm), two sacral ribs, about twenty caudal vertebrae, chevrons, scapulae (32 mm),
coracoids, sternal plate, humeri (27 mm), radii (19 mm), ulnae (21 mm),
metacarpus (5 mm), manual phalanges, manual unguals, ilium (51 mm), proximal
pubis, ischia (30 mm), femora (28 mm), tibiae (28 mm), fibulae (25 mm),
metatarsus (13 mm), pedal phalanges, pedal unguals, cervical scutes?, five
cervicopectoral spines (5-8 mm), three cervicopectoral plates (7-11 mm),
posteroventral plate (67 mm)
Diagnosis- sternum trapezoidal with slender, curved
and tapered posterolateral process; enlarged armor plate covering pelvic
area ventrally.
Description- The holotype is a juvenile as shown by
the unfused cranial and neurocentral sutures. It is 330 mm as preserved,
although few vertebrae are present, so this is probably not completely
accurate.
Several cranial elements are preserved, but the
small figure, lack of labels, crushing in ventral view and my poor knowledge of
ankylosaur anatomy make them difficult to identify. The skull is longer
than wide. It has a toothed premaxilla, and a maxilla with an
antorbital fossa and ten teeth. Portions of the posterior skull are
present, probably including pterygoid, quadrate, basisphenoid, basioccipital and
paroccipital process. The premaxillary teeth lack cingula and have five
cusps. The maxillary and dentary teeth have cingula and low rounded crowns
with eight cusps, with fluting extending to the cingula. The
mandible probably possesses an external mandibular fenestra.
Several cervical vertebrae seem to be preserved,
but they are mixed with the pectoral armor and details can not be seen.
Similarily, three dorsals and four sacrals are preserved. Eleven almost
complete dorsal ribs are present on the left side, while twelve ribs (some
partial) are seen on the right side. At least two long sacral ribs contact
the preacetabular process. About twenty caudal vertebrae are preserved
including fragments of the proximal section of the tail and articulated
sequences from the mid and distal sections. The proximal caudals have
transverse processes over twice as long as their neural spines and centra equal
in width and length. The latter character is apparently otherwise only
known in Gargoyleosaurus. Distal caudals have elongate zygopophyses and
chevrons that contact each other. However, there are no ossified
hypaxial tendons and no distal club.
The scapulae are bowed anteriorly are exapanded
slightly distally. There is a pseudoacromial process, but as the scapulae
are visible in medial view, its shape and orientation cannot be
determined. Xu et al. suggest that it may be obliquely directed, but
Shamosaurus' non-obliquely directed process looks identical in medial
view. The acromion itself is poorly developed and the scapular blade
narrow, reminiscent of Texasetes. The coracoid is a tall parallelagram and
the coracoid glenoid is about half the size of the scapular glenoid. The
sternal plates differ from Silvisaurus, Sauropelta and Euoplocephalus at least
in having a short tapered posterolateral process. They are more like
nodosaurids than ankylosaurids in not having greatly expanded trangular medial
ends.
The humerus is plesiomorphically slender with a
short deltopectoral crest. The radius and ulna are more slender than most
ankylosaurs, the latter having a small olecranon process. The manus has a
phalangeal formula of 2-3-3-2-0, metacarpals I and V are subequal to III in
width. The unguals are claw-like, being longer than wide and laterally
grooved.
The ilium is preserved in ventral view and has an
extremely elongate preacetabular process oriented horizontally, like
ankylosaurs. The preacetabular process is not as laterally deflected as
stegosaurs, nodosaurids or ankylosaurids, being closer to Mymoorapelta or Minmi
(~25 degrees). The acetabulum is closed, and the postacetabular process is
greatly reduced and faces laterally. The latter is a plesiomorphy retained
in Scelidosaurus and Mymoorapelta among ankylosaurs. The pubis is larger
than most ankylosaurs, being comparable to Scelidosaurus and Minmi, though
probably somewhat larger than the latter. The postpubic process extends at
least halfway down the ischial shaft. The ischium is typically
ankylosaurian- slightly bowed, tapering distally and having a convex acetabular
edge.
The femur is fairly robust and has a crest-like
(non-pendent) fourth trochantor located proximally. Proximally, the
anterior and greater trochantors are unfused, as in Minmi, Cryptosaurus and
Hoplitosaurus. The tibia is notable for having subequal proximal and
distal expansions (anterior view) and being subequal to the femur in
length. The fibula has a more gradual proximal expansion and greater
distal expansion than Sauropelta. Both astragalus and calcaneum are
preserved, the latter is said to be larger than most ornithischians, though it
seems smaller than Scelidosaurus. The metatarsi are more elongate than
ankylosaurs other than Scelidosaurus, being almost 50% of tibial length.
This contrasts with other ankylosaurs, which have metatarsotibial ratios of 20%
or so. The pedal phalangeal formula is 0-3-4-5-0. Metatarsals I and
V are reduced and splint-like and the unguals are elongate and claw-like.
Metatarsals II and IV are shorter than III and the proximal phalanges are
longest in digits II and III.
Armor is amazingly sparse. No osteoderms are
reported to be present on the skull or dentary. Armor is only preserved in
the cervical and pectoral area. At least three pairs of flattened,
slightly recurved spines are present in the cervical area. Also, two pairs
of oval scutes were present, the more posterior larger and positioned over the
pectoral girdle. Small ossicles and scutes may be present in the cervical
area as well. Strangely, the back, hips and tail are devoid of
armor. Half of a large plate is preserved ventral to the pelvis. It
is thickest medially and covered with hexagonal and rhombic tubercles about .5
mm wide. In life, it would have started midway down the dorsal column,
ended at the posterior ilial edge and extended transversely across the whole
belly. Impressions indicate another plate was present anteriorly that
extended to the pectoral girdle.
Relationships-
We must keep in mind that the holotype is a
juvenile, so ontogeny may have affected various characters used in ankylosaurian
phylogenetic analyses. Comparison to juvenile Pinacosaurus suggests that
the elongate tibia and metatarsus are not juvenile characters in
ankylosaurs.
The authors conducted a phylogenetic analysis taken
directly from Sereno's (1999) thyreophoran analysis excluding the stegosaur
characters. They added Liaoningosaurus and condensed the stegosaurs into a
single OTU. The final analysis includes 14 taxa and 95
characters. The result is 24 MPT's of 123 steps with a large polytomy
within Ankylosauria due to Liaoningosaurus jumping around from nodosaurid to
derived ankylosaurid.
Examination shows many problems with the matrix
however. For instance, stegosaurs are coded as having a sinuous dentary
tooth row, when it is actually curved in one direction. They are also
coded as having only five premaxillary teeth, but Huayangosaurus has
seven. The character "scapular blade parallel-sided" really needs work, as
it is coded as present in all eurypods, but Stegosaurus,
Liaoningosaurus and especially Polacanthoides have distally expanded
blades. The character "preacetabular blade laterally deflected 45 degrees"
is incorrectly coded as present in Liaoningosaurus and Minmi.
Scelidosaurus has an unexpanded distal ischium similar to Liaoningosaurus and
Minmi, so is coded incorrectly. I don't think that stegosaurs or
ankylosaurs have especially spreading metatarsi compared to Liaoningosaurus or
Scelidosaurus. Stegosaurs have an occiput that's wider than tall, cingula
on their cheek teeth and oval premaxillary palates, so are coded
incorrectly. The character "Snout low: maximum preorbital depth less (0),
or more (1), than twice maximum preorbital length." makes no sense, as no
thyreophore has that short of snout. The dentary has a sinuous ventral
edge in stegosaurs, just as in ankylosaurs (and Scutellosaurus slightly), so
this character is coded incorrectly. Stegosaurs have a proximal scapular
blade much less than 75% the acromial width, contra Xu et al.. I don't see
any lateral component to stegosaur glenoids, so I don't understand why they're
coded as having glenoids oriented "posteroventrally and laterally".
Liaoningosaurus is coded as lacking a fused skull, but it's a juvenile, so this
is expected in ankylosaurs. It should be coded as unknown.
Pinacosaurus is coded as having state 2 for "accessory dermal ossifications on
posterior skull roof" when only states 0 and 1 are defined. It should be 1
of course, but I don't know how the other ankylosaurs were coded, as they are
only known from adult material lacking the sutures to show the presence of
"tabulars", "postfrontals" and such. Two characters are repeats of
each other. "Distal chevrons T-shaped and contact each other" is just like
"distal chevrons contact each other". What's even odder is that Mimmi,
Hylaeosaurus and "other nodosaurines" are coded as having the first, but lacking
the second. This is impossible and makes me trust the matrix even less
than before. Indeed, I found all the above errors while trying to validate
the codings of stegosaurs, which are very well studied and illustrated.
I'm sure going through the codings of the other taxa would show similar
problems. I lack the references and expertise to check many codings, so
even if I went through the whole thing as best I could, I would not trust it to
be accurate. Because of this, I have not attempted to correct and rerun
the matrix. I recommend the papers phylogenetic results not be trusted and
must look to other sources to evaluate Liaoningosaurus'
relationships.
Other studies of ankylosaur phylogeny have focused
on the skull, which is largely undescribed and poorly illustrated in
Liaoningosaurus. However, Kirland (1998) published an analysis with 17
taxa and 46 characters, including fifteen from the postcranium. This
matrix looks more accurate than Xu et al.'s (though I see a few problems, ex.
Gastonia is the only taxon coded as having an obliquely directed pseudacromial
process) and adding Liaoningosaurus results in 3 MPT's of 80 steps. These
trees have the following topology-
--+--Scelidosaurus
`--+--Liaoningosaurus |--Minmi `-----+--+--Pawpawsaurus | `--+--Sauropelta | `--+--Edmontonia | `--Panoplosaurus `--+--Shamosaurus `+-+--Mymoorapelta | `--+--Gastonia | `--Polacanthus `--+--Tsagantegia `--+--Pinacosaurus `--+--+--Saichania | `--Tarchia +-----Ankylosaurus `-----Euoplocephalus I like this phylogeny more than Sereno's because it
matches the most extensive phylogenetic analysis yet (Carpenter, in press) in
many details and does not assume monophyly of certain clades ("other
nodosaurines", "other ankylosaurines") a priori. In addition, I see many
characters suggesting Liaoningosaurus is more basal than nodosaurids,
polacanthids and akylosaurids. These include- antorbital fossa present;
external mandibular fenestra probably present; claw-like manual and pedal
unguals; preacetabular process laterally deflected only 25 degrees;
postacetabular process faces laterally; pubis not extremely reduced; unfused
anterior and greater trochantors; tibia subequal to femur in length; tibial
distal width subequal to proximal width in anterior view; metatarsi almost 50%
of tibial length. Minmi also has claw-like manual unguals, a slightly
deflected preacetabular process, slightly reduced pubis and unfused femoral
trochantors. It is more derived in lacking an antorbital fossa
and having a ventrally facing postacetabular process. The presence of
ventral armor is the only character I can find that would unite the two, so
placing Minmi as more derived than Liaoningosaurus is most parsimonious.
Ankylosaurid-like characters include- extremely elongate distal caudal
prezygopophyses; indistinct femoral head. Others suggested by Xu et al.
are plesiomorphic (non-enlarged radial condyle of humerus), also seen in Minmi
(ischial acetabular margin convex) or erronous (chevrons interlock;
straight medial sternal margin; deltopectoral crest and transverse axis through
distal condyles in same plane). The nodosaurid-like characters cited are
plesiomorphic (maxillary and dentary teeth with cingulum; slender humerus;
deltopectoral crest extends less than of half shaft length; proximally located
fourth trochantor), unknown in polacanthids and more basal taxa (sub-trapezoidal
sternum), also present in polacanthids and ankylosaurids (preacetabular process
faces ventrally) or undefendable (obliquely directed pseudacromial
process). The two ankylosaurid-like characters are best seen as
convergences when the many primitive characters are taken into account.
Still, despite its basal placement, Liaoningosaurus is more derived than
Scelidosaurus based on- strong maxillary/dentary cingula; elongate proximal
caudal transverse processes; elongate distal caudal zygopophyses; distal
chevrons contact each other; pseudacromial process on scapula; horizontallly
oriented preacetabular process; non-pendent fourth trochantor. Only the
probable presence of an external mandibular fenestra would suggest
otherwise. In conclusion, I suggest placing Liaoningosaurus as a basal
ankylosaur, more derived than Scelidosaurus, but probably less than
Minmi.
Anyone who wants the pdf, contact me offlist.
Before I venture back into the Theropoda, I'll take a swing at
Jeholosaurus.
Mickey
Mortimer |