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Erliansaurus bellamanus discussion



Erliansaurus Xu, Zhang, Sereno, Zhao, Kuang, Han and Tan 2002
E. bellamanus Xu, Zhang, Sereno, Zhao, Kuang, Han and Tan 2002
Turonian-Campanian?, Late Cretaceous
Iren Dabasu Formation, Nei Mongol Autonomous Region, China
Holotype- (LH V 0002) (~2.8 m, ~150 kg, subadult) mid cervical vertebra (61
mm), posterior cervical vertebra (50 mm), anterior dorsal vertebra (45 mm),
two proximal caudal vertebrae (50, 47 mm), incomplete scapula (227 mm),
humerus (276 mm), radius (220 mm), ulna (237 mm), metacarpal I (57 mm),
phalanx I-1 (58 mm), manual ungual I (91 mm), metacarpal II (116 mm),
phalanx II-1 (40 mm), phalanx II-2 (45 mm), manual ungual II (~76 mm),
metacarpal III (79 mm), phalanx III-1 (17 mm), phalanx III-2 (14 mm),
phalanx III-3 (43 mm), manual ungual III, partial ilium, pubic fragments,
ischial fragments, femur (412 mm), tibia (373 mm), fibula (~350 mm), partial
metatarsals
Diagnosis- large nutrient foramina in proximal caudal centra; crest-like
posterior humeral trochanter; trochanteric crest on femur; posterior edge of
proximal fibula reaches much further proximally; enlarged m. iliofibularis
tubercle on fibula.
Description- The holotype is a subadult specimen as shown by the weak suture
between the centra and neural arches of the caudal vertebrae.  It was
approximately 2.8 meters long and 150 kilograms in mass, using Alxasaurus as
a reference.
The cervical vertebrae have a single pair of pleurocoels and unfused ribs.
A hypapophysis is also developed on the posterior cervical, projecting 8 mm
ventrally.  The anterior dorsal is amphicoelous, with a lateral fossa, but
no pleurocoel.  The authors say it may be a proximal caudal.  The proximal
caudals are amphicoelous, with a nutrient foramen on each side (but no
pleurocoels), and a weak ventral groove posteriorly.
The scapula is very slender and curved, with a reduced acromion.  The
glenoid is not preserved.
The humerus is generally similar to Erlikosaurus, but has a well developed
posterior trochanter (posteromedial crest at midlength) and a less
well-developed entepicondyle.  Also, the ventral process is smaller and the
radial and ulnar condyles are more widely spaced.  The ulna is not bowed.
The manus is very well preserved.  Metacarpal III is not bowed, manual
ungual I is the largest by far.  There are no proximodorsal lips (Xu et al.
claim one is present on ungual I, but it is not apparent).  There is a fossa
on the proximolateral side of metacarpal III.  The metacarpals and phalanx
I-1 have shallow ligament pits, but other phalanges lack them.  Phalanx II-1
can extend 45 degrees above the horizontal from metacarpal II.  The unguals
are all strongly curved and very deep proximally.
Only the posterior portion of the ilium is preserved.  It has a very short
tapered postacetabular process, postacetabular tubercle (as in other
therizinosauroids), a prominent antitrochanter and a supracetabular crest.
The femur has a trochanteric crest, no fourth trochanter and an elevated
head.  The tibia is markedly expanded distally, with a distally placed
fibular crest.  The astragalus has a tall and broad ascending process, and
the condyles are reduced.  The ascending process does not hook laterally as
seen in other segnosaurs, including Beipiaosaurus and Therizinosaurus.
There is no proximomedial fibular fossa, and the m. iliofibularis tubercle
is directed laterally.
Relationships-
The authors do a good job summarizing characters that may be
phylogenetically informative for Erliansaurus and Neimongosaurus.  They even
seem to prefer Enigmosauria over arctometatarsalian segnosaurs.  Here are
the characters they discuss and my thoughts on them-
1. dorsal pleurocoels absent.
Beipiaosaurus lacks posterior pleurocoels, Erliansaurus lacks anterior
dorsal pleurocoels, Neimongosaurus has pleurocoels at least to dorsal eight
and probably through the whole series considering the sacral pleurocoels,
Nothronychus has anterior dorsal pleurocoels and Nanshiungosaurus lacks any
dorsal pleurocoels.  Though the condition in Alxasaurus is undescribed, the
possible presence of a sacral pleurocoel may suggest all dorsals were
pneumatic too.  I coded this character as "anterior pleurocoels absent", as
they are present in outgroups (eg. Caudipteryx), unlike posterior dorsal
pleurocoels.
2. proximal caudal nutrient foramina
Only known in Neimongosaurus and Erliansaurus, but not in Nothronychus.
Better descriptions are needed for Alxasaurus and Segnosaurus.  Jaime makes
a good argument why these "nutrient foramina" may be pleurocoels instead.
3. caudal pleurocoels
Present in Nothronychus, but not Erliansaurus, Neimongosaurus or "most other
therizinosauroids".  If only I knew which other segnosaurs lacked them.
Again, the state could probably be determined in Alxasaurus and Segnosaurus.
The authors cite the absence of caudal pleurocoels as a potential
therizinosauroid synapomorphy, assuming Enigmosauria is correct.  However,
the basal oviraptorosaurs Caudipteryx and Microvenator lack caudal
pleurocoels.
4. dorsal flange on scapular blade
Present in Therizinosaurus and Neimongosaurus, but not Beipiaosaurus,
Alxasaurus, Erliansaurus, Nothronychus or Segnosaurus.
5. distally narrowed scapula
They argue this is a segnosaurian synapomorphy, but though it is present in
Nothronychus and Erliansaurus, Segnosaurus', Beipiaosaurus' and Alxasaurus'
expand distally.  The condition in Therizinosaurus and Neimongosaurus is
uncertain.
6. enlarged ventral process of humerus
Well developed in Neimongosaurus and Erlikosaurus, but not Alxasaurus,
Nothronychus, Erliansaurus, Therizinosaurus and probably Segnosaurus.
7. anterior tuberosity on distal humerus proximal to ectepicondyle.
Cited as a segnosaurian synapomorphy.
8. posterior trochanter on humerus
Found in Erliansaurus, Therizinosaurus, Erlikosaurus and Segnosaurus, but
not Beipiaosaurus, Neimongosaurus or Nothronychus.
9. enlarged entepicondyle
Absent in Alxasaurus, Nothronychus and Erliansaurus, but present in
Neimongosaurus, Erlikosaurus and Therizinosaurus.
10. distal condyles of humerus located anteriorly
A segnosaurian synapomorphy, though found in birds and perhaps a few other
maniraptorans as well.
11. humeral distal condyles closely appressed
Found in Erlikosaurus, Therizinosaurus and Neimongosaurus, but not
Alxasaurus, Nothronychus(?) or Erliansaurus.
12. proximodorsal lip on manul unguals
Absent in Beipiaosaurus and Erliansaurus.  Ungual I of Alxasaurus lacks it,
but ungual II has it.  Present in two of three unguals in Therizinosaurus.
Two manual unguals (unknown if from same or different digit number, they are
very close in size) lack them in Nothronychus.  Caudipteryx lacks these, but
Microvenator, caenagnathids and some oviraptorids have them.
13. proximal end of manual unguals >45% of ungual length
Found in Alxasaurus, Erliansaurus, Nothronychus and Segnosaurus, but not
Beipiaosaurus or Therizinosaurus.
14. reduced postacetabular process
Found in Erliansaurus, Segnosaurus, Nanshiungosaurus and Enigmosaurus, but
not Alxasaurus, Neimongosaurus and Beipiaosaurus.
15. dorsal margin of postacetabular process straight.
This can only be proved to be present in Segnosaurus, so is not useful
phylogenetically.
16. thickened posterior end of ilium
Absent in Beipiaosaurus, but present in Alxasaurus, Erliansaurus,
Neimongosaurus, Segnosaurus and Enigmosaurus.  Though Xu et al. argue this
is only poorly developed in Erliansaurus, based on a small crest, their
supposedly apomorphous "rugose swelling" resembles the structure in
Segnosaurus.  I feel it may be homologous.
17. This is where they note the boss above the antitrochanter (considered
apomorphic), whereas they homologize a smaller slight expansion further
posteriorly with the structure in Segnosaurus.
18. supracetabular crest pronounced
Present in Erliansaurus and Neimongosaurus, but not in Beipiaosaurus,
Alxasaurus, Segnosaurus or most other maniraptorans.  Must be a secondary
development.
19. posterior edge of proximal fibula reaches much further proximally
An apomorphy of Erliansaurus.
20. m. iliofibularis tubercle positioned distally
Present in Erliansaurus, Segnosaurus and Nothronychus.  But not
Beipiaosaurus or supposedly other theropods.  Haven't checked this yet.
21. m. iliofibularis tubercle laterally directed
Absent in Segnosaurus, but present in Beipiaosaurus, Erliansaurus and
Nothronychus.  Also present in mononykines, troodontids and most birds I
believe.
22. tibia shorter than femur
Present in Neimongosaurus, Erliansaurus and Segnosaurus, but not
Beipiaosaurus.
23.  elongate fibular crest of tibia
Present in Erliansaurus and Neimongosaurus, but not in "other segnosaurs".
That of Nothronychus is too broken to be useful, they must be referring to
Beipiaosaurus and/or Segnosaurus.
24. reduced astragalar condyles
A segnosaurian synapomorphy.
25. fibula tapering posteriorly in proximal view
Present in at least Erliansaurus and Alxasaurus.  Supposedly a segnosaurian
synapomorphy.
So, there's a good starting database for analyzing the relationships of
segnosaurs.
Running these characters in PAUP (ordered, DELTRAN), using Beipiaosaurus,
Alxasaurus, Nothronychus, Neimongosaurus, Erliansaurus, Therizinosaurus,
Erlikosaurus and Segnosaurus resulted in two most parsimonious trees (32
steps, CI .81, HI .19), with the consensus as-
|-outgroup
`-+-Beipiaosaurus
  `-+-Nothronychus
    `-+-Erliansaurus
      |-Segnosaurus
      `-+-Alxasaurus
        `-+-Therizinosaurus
          `-+-Erlikosaurus
            `-Neimongosaurus
Note this was my analysis, Xu et al. did not run their characters in a
phylogenetic analysis, nor do they support the above topology (I don't
either).  Pretty strange, eh?  Incidentally, the ex-Beipiaosaurus clade has
an 84% bootstrap, while the Therizino+Erliko+Neimongo clade has an 80%
bootstrap.  My big coelurosaur analysis uses all of these taxa (as well as
Nanshiungosaurus and Enigmosaurus, in case they don't cause big polytomies)
and plenty more characters, so should give a better result.  Though Xu et
al. don't come to any firm phylogenetic conclusions, they do make a few
suggestions- Beipiaosaurus is most basal; Neimongosaurus, Nothronychus,
Alxasaurus and Erliansaurus are more primitive than Segnosaurus,
Erlikosaurus, Nanshiungosaurus and Therizinosaurus; Erliansaurus may be more
derived than Alxasaurus, Nothronychus and Neimongosaurus based on- no dorsal
or caudal pleurocoels (unknown in Alxasaurus, Neimongosaurus lacks caudal
pleurocoels), posterior humeral trochanter (unknown in Alxasaurus) and short
postacetabular process (unknown in Nothronychus); Erliansaurus may be the
sister taxon of Neimongosaurus based on- oval depression on humeral
midshaft; supracetabular crest; elongate fibular crest of tibia.
Finally, Xu et al. redefine two clades-
Therizinosauroidea is defined as "all coelurosaurs closer to Therizinosaurus
than either Ornithomimus, Oviraptor, Velociraptor or Neornithes".  I would
rather this be a less inclusive node-based clade, to preserve Segnosauria,
but at least it's rooted on Therizinosaurus.
Therizinosauridae is defined as the "common ancestor of Segnosaurus,
Erlikosaurus, Nanshiungosaurus and Therizinosaurus and all descendants".
With no good phylogenetic analysis of segnosaurs avaiable, such fragmentary
material known/described for most, and topologies like the above appearing
when some characters are analyzed, I don't think a multi-taxon internal
specifier is wise at the moment.

Mickey Mortimer