[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Iren Dabasu Humeri Return: Erliansaurus



Okie, boys,

  With *Erliansaurus*, we have the second taxon from the Iren Dabasu
Formation to be described, and yet another consideration of referral of
the AMNH specimen, #6368. To refresh, I found that the humerus of the AMNH
specimen was more than half as long again as *Neimongosaurus*, and much
more slender, indicating a lack of ontogenetic transformation. Well, not
only does *Erliansaurus* come from the same formation, the describers are
the same (with the addition of Han Jun), the paper is the same, and the
specimen numbers are next to each other on the rack: LH V0001 for
*Neimongosaurus yangi* and LH V0002 for *Erliansaurus bellamanus* (also,
LH V0008, a referred specimen to *Neimongosaurus*). Note, *Erliansaurus
bellamanus* means ?beautiful-handed Erlian lizard?, in reference to the
complete right manus and its gorgeous state of preservation, and the
region of Nei Monggol Zizhiqiu (Autonomous Region), China, where the
formation exposes; this is also where *Neimongosaurus* comes from, and
both from the same Sunitezuoqi locality, Sanhangobi.

  Well, I will leave this post to a description of the only bone all three
taxa have in common, the humerus, which was the focus of the last post on
Iren Dabasu posts I wrote. This will also be a more complete comparison of
the AMNH 6368 to segnosaurs. First, comparison of four different
measurements:

Specimen:     ||  length  |  prox. width  |  mid. width  |  dist. width
AMNH 6368     ||  390mm   |     112mm     |     38mm     |      89mm
N. yangi      ||  222mm   |      93mm     |     29mm     |      79mm
E. bellamanus ||  276mm   |     110mm     |     30mm     |      80mm

  and ratios between three indices:

Specimen:     ||  length:prox  |  length:dist  |  prox:dist
AMNH 6368     ||     3.48      |     4.38      |    1.26
N. yangi      ||     2.39      |     2.81      |    1.18
E. bellamanus ||     2.51      |     3.45      |    1.38

  As you may note, *Erliansaurus* has a humerus of almost intermediate
form in proportion between *Neimongosaurus* and AMNH 6368. Only in the
proximal/distal end ratio does *Erliansaurus* exceed the pattern set by
the other Iren Dabasu segnosaurs. That of the only other "similar"
segnosaur, *Alxasaurus*, is very slender and has virtually no distal
widening, unique among segnosaurs. The morphology of *Alxasaurus* is also
unique in the proximal end that precludes the assignment of LH V0002 to
*Alxasaurus*. In fact, the proximal end of the humerus of *Erliansaurus*
is unique among segnosaurs in having a deep triangular adductor crest
(posterior process, or medial tubercle, take your pick [note below]), but
shares with *Neimongosaurus* in having no differentiation between the
dorsal edge of the crest and the humeral caput, though in *Erliansaurus*
it is declined from the caput, not as in *Neimongosaurus*. The
deltopectoral crest is low and rounded, with a low apex, occurring in both
*Neimongosaurus* and *Erlikosaurus*. The shaft is not strongly reflexed
cranially in the distally end, nor does it reflex caudally at the caput
much, shallow reflexion/curvature in the shaft occurring also in AMNH
6368, and the proximal *Alxasaurus*, but both ends are not strongly
reflexed in *Segnosaurus*. The distal condyles do not curve far forward,
but are set close together without a deep intercondylar channel; the
nearness and small size of the condyles (viz., condyli) is known in
*Nothronychus* and AMNH 6368, where they are about half the width of the
distal end at the epiphyses. The lateral, radial condyle is lower than the
medial, ulnar condyle, as in *Therizinosaurus* and *Erlikosaurus*, but not
as in *Nothronychus* or AMNH 6368, where it is the ulnar condyle that is
lowest; *Neimongosaurus*, *Alxasaurus*, and *Beipiaosaurus* have condyli
that are even in depression. The medial, entepicondylar crest is wider
than the lateral, ectepicondylar crest, as in *Nothronychus*,
*Erlikosaurus*, AMNH 6368, *Alxasaurus*, but are even in *Therizinosaurus*
and *Neimongosaurus*. There is a posteromedial crest on the shaft below
the level of the deltopectoral crest apex, as in, AMNH 6368,
*Therizinosaurus*, and *Erlikosaurus*, but not in *Nothronychus*,
*Beipiaosaurus*, or *Neimongosaurus*, and it is unknown whether the
condition is present in *Alxasaurus* due to extreme crushing of the
elements of the arm (a photo of some elements as preserved shows that a
heavy amount of reconstruction and gluing was required to estimate their
length and structure; length estimates are weak, and should be about 5%
accurate, whereas other dimensions, e.g. width, are more or less likely to
be true, and some morphological features are very tentative). There is no
cranial (flexor) fossa on the distal humerus, and the proximal cranial
fossa does not form a channel on the cranial shaft distally, as it does in
*Erlikosaurus*, *Therizinosaurus*, *Neimongosaurus*, and in
*Nothronychus*; there is no channel in AMNH 6368, but a distal cranial
fossa is present, as in all other segnosaur humeri (unknown in
*Beipiaosaurus*). Finally, the extensor crest (greater trochanter) is
somewhat declined from the humerus, giving the proximal humerus in cranial
view an arched aspect, also in AMNH 6368, *Nothronychus*,
*Therizinosaurus*, *Erlikosaurus*, but not as in *Neimongosaurus* and
apparently not in *Alxasaurus*.

  ** The term favored by Baumel and Witmer is ventral process, a term that
is exclusively effective only for birds where humerus is oriented so that
the caudal edge is lying against the back (or sides) of the animal. This
is why in birds it's called a ventral tubercle. But this is known only for
birds, and calling it a ventral tubercle and applying it to something that
does not have the shoulder to perform this action is a really, really bad
idea; "adductor crest" is irrelative of position and orientation, and is
favored here as elsewhere (Headden, in prep.).

  In conclusion, the humerus of *Erliansaurus* is similar to both
*Erlikosaurus* in proximal morphology, and *Nothronychus* in distal
morphology. This suggests, using humeral trends, that *Erliansaurus* is a
therizinosaurid.

  Collaboration with other postcrania includes a short, robust manus with
strong curvature of the claws (unlike AMNH 6368), a broader first
metacarpal than second, bowed radius (unlike *Neimongosaurus* or
*Nothronychus*) and ulna, the latter which is very narrow, and a
preacetabular ala that is more medially non-divergent than in
*Neimongosaurus* or what is suggested for *Beipiaosaurus* (based on a
pers. comm. from Xu, 1999); the postacetabular ala is much shorter and
appears to show robust antitrochanters, so this appears to show a closer
allegiance to therizinosaurids, and possibly close to *Therizinosaurus*
than is *Nothronychus*. The scapula is much deeper relative to length than
in *Alxasaurus* or *Nothronychus*, and expands distally (unlike
*Nothronychus* and *Alxasaurus*), but incomplete in *Therizinosaurus* or
*Segnosaurus* and therefore with little comparison; in *Beipiaosaurus* the
scapula appears to consistently increase in depth distally, but there is
no distinct expansion, though this mat be present in the distal end of
*Nothronychus*, despite becoming shallower distally (it is broken
distally). Caudals bear a small pneumatophore (nutrient foramen of Xu et
al., 2002) as in *Neimongosaurus* and *Nothronychus*, but not in
*Beipiaosaurus* or *Alxasaurus* (apparently, crushing may obscure
details); the centrum of caudals are quadrangular in lateral aspect, as in
*Alxasaurus* and *Neimongosaurus*, but are rhomboid in *Nothronychus*. It
is unlikely that any of the segnosaur material currently identified from
Iren Dabasu beds refers to a single phylogenetic grade.

  Tentatively, I offer the following topology to provide relationships of
the Iren Dabasu forms, having humeral material:

--+---Beipiaosaurus inexpectatus Xu, Tang and Wang, 1999
  `--+-?-Neimongosaurus yangi Zhang, Xu, Zhao, Sereno, Kuang and Tan, 2001
     |-?-AMNH 6368 (cf. Gilmore, 1933 & Mader and Bradley, 1996)
     |---Alxasaurus elesitaiensis Russell and Dong, 1994 (1993)11
     `--+---Nothronychus mckinleyi Kirkland and Wolfe, 2000
        `--+---Erliansaurus bellamanus Xu, Zhang, Sereno, Zhao, Kuang, Han
           |                           & Tan, 2002
           `--+---Erlikosaurus andrewsi Perle, 1981
              |---Segnosaurus galbinensis Perle, 1979
              `---Therizinosaurus cheloniformis Maleyev, 1954 (sensu
                                                Barsbold, 1974)

  Cheers,


=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

__________________________________________________
Do You Yahoo!?
Yahoo! Health - Feel better, live better
http://health.yahoo.com