New Segnosaurs, a Reveiw and a Criticism

["Jaime A. Headden" <qilongia@yahoo.com>]

  Well, I finally got my hands on these two papers, thanks to Mickey Mortimer:

  Kirkland, J.I. & Wolfe, D.G. 2001. First definitive therizinosaurid 
(Dinosauria: Theropoda) from
  North America. _Journal of Vertebrate Paleontology_ 21 (3): 410-414.

  Xu X.; Zhao X.-J.; & Clark, J.M. 2001. A new therizinosaur from the Lower 
Jurassic Lower Lufeng
  Formation of Yunnan, China. _Journal of Vertebrate Paleontology_ 21 (3): 
477-483.

  In the first case, we have *Nothronychus mckinleyi*, and I must say i am glad 
to see this fellow
in print, after getting to play with the arm and see some of the dorsals in 
Denver, in 1999. The
animal is quite spectacular, with a unique ischium and teeth having extensive 
serrations. It's
from the Haystack Butte Locality of the southern Zuni Basin, Catron County, New 
mexico, USA, a
bonebed that also includes several *Zuniceratops* individuals (so it's no 
wonder the ischium was
confused with *Zuniceratops*'s frill) in the Moreno Hill Formation mid 
Turnonian of the Upper
Cretaceous, and the *Collingnoniceras woollgari* Zone is suggested as the 
bio-layer from whence it
is identified. This makes the layer roughly contemporaneous with the Bissekty 
of Uzbekistan. The
beds of Bayn Shireh, Mongolia, where *Segnosaurus*, *Erlikosaurus*, and 
*Enigmosaurus* (as well as
*Harpymimus*) are found is relatively undated, but generally placed between the 
Cenomanian and
Turonian (Maryanska and Barsbold, 1990). As such, *Nothronychus* is younger 
than most other
segnosaurs, and all but *Therizinosaurus* and *Nanshiungosaurus*.

  "Nothronychus" is derived from _nothros_ (Grk., slothful) + _-onyx_ > 
_onychos_ (Grk.) claw; the
species is named after Bobby McKinley who supported Wolfe's excavations and 
Kilkand's researches =
"[Bobby] McKinley's sloth-claw."

  The holotype is MSM P-2117, compirsed of a partially disarticulated skeleton 
(estimated, 5
meters) having several isolated teeth that are definitively therizinosaur in 
form, some fragmented
cranial material that is difficult to interpret (the authors state that it will 
be discussed
elsewhere); several cervical vertebrae (there are five, either crushed or 
distorted otherwise
preventing accurate measurements of length and width (and boy are they 
squished, the verts are
averagely crushed or diagenetically compressed mediolaterally), having short 
but definite
rectangular neural spines; a single anterior dorsal centrum, suggested as 
belonging to the first
dorsal, having a short but well-defined hypoaphysis; an anterior caudal 
vertebra with a neural
spine only as high as the neural pedicel; several flattened, sauropod-like ribs 
[as in
*Therizinosaurus* and *Alxasaurus*], and gastralia pairs that are fused (there 
are multiple sets
of these, and any previous suggestions of furculae are discarded); a left 
scapula without coracoid
fusion, long and slender, and the blade is shallow without a distinct acromial 
expanse, contra the
form of *Alxasaurus* or *Therizinosaurus*; a right humerus with a distinct 
internal tuberosity;
both ulnae, the right one complete and the left one partial; several 
metacarpals and manal
phalanges, and two manal claws; both ischia, having a deep and long, 
sub-circular obturator
process; both flattened tibiae; a right fibula; partial metatarsals, several 
pedal phalanges, and
two large pedal unguals.

  *Nothronychus* is significant and derived from other therizinosaurs 
(segnosaurs) by the presence
of posterior serrations (ant:post serration ratio is 10:13 per 5mm) that 
progress proximally on
the crown to the limit of the "neck" constriction. The dorsal pneumatic fossa 
is enclosed withing
a depression bearing numerus foramina; there is no posteromedial crest on the 
humerus, referred to
as a "spur" by the authors; the claws do not have distinct flexor tubercles or 
flexor lips, unlike
more advanced therizinosauroids or *Beipiaosaurus*; the obturator process of 
the ischium is large
and sub-circular/-rectangular, very thin, with virtually no acetabular margin; 
the anterior
process for the M. iliofibularis is located near the midshaft of the fibula. 
Also, the mid- to
post-cervicals are extensively invaginated by several foramina ventral to the 
parapophysis, and
the pedal unguals have a lateral twist to the claw, making the ventral surface 
face laterally.

  Kirkland and Wolfe cite the deep anterior dorsal neural pedicels as 
autapomorphic, but these are
present in other taxa for which anterior dorsals are known and are likely 
prevalent within
therizinosauroids. They also refer to the laterally facing glenoid of the 
scapula, lacking in
*Alxasaurus* and *Therzinosaurus*, so this may be a plesiomorphic condition for 
therizinosauroids,
present in *Beipiaosaurus* as well, and in outgroups (oviraptorosaurus, 
avialans, dromaeosaurs,
and possibly troodontids). The authors also cite Barsbold, 1974 for 
Therizinosauridae, but this
was Maleyev, 1954.

  The teeth are curved medially, and have a strong caudal curvature, unlike all 
other segnosaurs,
including *Beipiaosaurus*. Cervicals are platycoelous to amphicoelous, like 
other
therizinosauroids but not either species of *Nanshiungosaurus*, and the neural 
spine shape is
distinctively rectangular and thin, rather than broad and distally tapering, as 
in
*Nanshiungosaurus* and *Alxasaurus*; the cervicals of *Segnosaurus* remain 
unfigured and
un-comparable. The anterior cervical has a hyposphene, so it is presumable that
hyposphene--hypantra progress through the anterior dorsals, they are lacking in 
cervicals. The
authors suggest that *Chilantaisaurus zhejiangensis* may be referrable to 
*Nanshiungosaurus*.
Kirkland and Wolfe discuss slightly the jaw of *Eshanosaurus*, remarking on the 
presence of a
medial ridge on the crowns as in prosauropods. They suggest a phylogenetic 
analysis is in
preparation by the authors, but so far the animal is referred to as a 
therizinosaurid, more
advanced than *Alxasaurus*, but as the most basal therizinosaurid.

  Personal comments: The vertebral column is similar to that of 
*Nanshiungosaurus*, and it is
possible that that Asian taxon is derived more directly from *Nothronychus* 
than other
therizinosaurids are. The claws are well-recurved, but with shallow flexor 
tubercles, and shallow
articular facets, suggesting reduction is curling capability, whereas the 
humeral adduction
capability suggests the arms were well adapted and mobile. Pedal claws are 
well-recurved, and it
is apparent that they were held slightly laterally, so may have approximated 
the xenarthran
twisted ankle, allowing locomotion and sharp claws. The ischium and pubis were 
not parallel to
each other, as shown by the angle of the pubic facet on the obturator process, 
and this suggests
that therizinosaurid parallelism occured after the obturator came in contact 
with the pubis.
Otherwise, *Nothronychus* appears to be a rather convenient intermediate 
between all the other
therizinosaurids and *Alxasaurus*, by definition it is a therizinosaurid 
(Russell and Dong, 1994,
*Therizinosaurus*, *Nanshiungosaurus*, *Segnosaurus*, *Erlikosaurus*, 
*Enigmosaurus* <=
*Alxasaurus*).

-------------

  Okay, now for the tricky one:

  Previously described by Zhao and Xu, 1997, as a coelurosaurian similar to 
therizinosauroids,
*Eshanosaurus* is identified from a left dentary with incomplete posterior and 
posteroventral
margin (IVPP V11579), bearing 34 alveoli and only eight of these are preserved, 
including five in
the front, two in the middle, and one in the back. The crowns are higher 
mesially than distally,
and are distinctly phyllodont in form. The type locality is in the marlite 
portion of the lower
part of the Lower Lufeng Formation, Lower Jurassic. It was found in Eshan 
County, Yunnan Province,
China, in the Dianzhong Basin. 200m above the site of collection, a bed 
containing
*Lufengosaurus*-like prosauropods was located.

  The name is derived from Eshan County, Yunnan, China, and the species is to 
honor Deguchi
Hikaru, misspelled "Deguchiianus", who supported and encouraged Xu Xing into 
studying dinosaurs
(and boy are we grateful!) = "Eshan lizard belonging to Deguchi [Hikaru]."

  There are several autapomorphies for the jaw, indicating it is a new species, 
and probably not
referrable to anything else specifically and probably not generically in the 
Lufeng: there is a
small fenestra bound under the dorsal portion of the posterior extent of the 
dentary (this is
questionably referred to as a external mandibular fenestra, unique in it's 
position, and forming a
distinct fossa on the lateral surface , so it is not an artifact of 
preservation); the anglation
of the denticles are perpendicular to the margins of the crowns, mesial and 
distal. An
autapomoprhy is offered that works only if the animal is a segnosaur: denticles 
relatively small
compared to the crown size; the denticles are somewhat larger in basal 
ornithischians and in
prosauropods, as in segnosaurs.

  *Eshanosaurus* is referred to the Therizinosauroidea, outside of 
*Beipiaosaurus* and
Therizinosauroidea, but Therizinosauroidea is defined as (Russell and Dong, 
1994, *Alxasaurus* +
*Therizinosaurus*, *Nanshiungosaurus*, *Segnosaurus*, *Erlikosaurus*, 
*Enigmosaurus*), and thus
*Beipiaosaurus* is effectively removed from the Therizinosauroidea, contra Xu 
et al., 1999 (Xu,
Wang, & Tang, 1999. A new therizinosauroid dinosaur with integumentary 
structures from China.
_Nature_ 399: 450-454) -- see below, *. The following features are used to 
indicate a
therizinosauroid relationship:

  1. anterior teeth larger than posterior teeth [nearly in prosauropods], 
generally true due to
     the regular distal reduction in tooth crown height, where the posterior 
and anterior crowns
     are effectively similar in ratio between prosauropods and segnosaurs -- 
whereas the middle
     crowns are much shorter in hight than in anterior process and there is an 
abrupt shortening
     in the segnosaurs, but not in *Eshanosaurus*, where the fifth and twelfth 
crowns are
     relatively even in height;
  2. teeth generally small and large in number [also in some prosauropods], 
most prosauropods have
     about 24 or so dentary teeth, but *Lufengosaurus* and *Plateosaurus* have 
greater counts, up
     to 28--30, whereas the count in *Beipiaosaurus* and *Alxasaurus* is close 
to *Eshanosaurus*
     by only 4--5 more;
  3. dentary crowns recurved [also in some basal prosauropods, primitive 
ornithischians];
  4. denticles nearly perpendicular to margins of crowns [not in prosauropods 
or therizinosaurs],
     related to a tearing function, with action directed more or less backwards 
on the plane of
     the level of the jaw margin, at least on posterior margins -- this was 
cited as an
     autapomorphy and not effectively a synapomorphy;
  5. crowns curve lingually [not in prosauropods, or basal ornithischians, or 
segnosaurians];
  6. basal crown constricted [also in prosauropods and ornithischians];
  7. root mediolaterally wider than crown [not in prosauropods or 
ornithischians];
  8. root subcircular in section [also in prosauropods and ornithischians];
  9. interdental plates [also in prosauropods];
  10. broad flat buccal shelf lateral to tooth row on dentary [also in 
prosauropods and
      ornithischians];
  11. mesial end of dentary curved ventrally [also in prosauropods].

  Personal comments: As noted before, 4 is effectively autapomorphic of 
*Eshanosaurus*, and all
but one feature (7) do not diagnose a relationship with segnosaurs. Character 1 
is not true at all
and should be discarded. Contra Xu et al., nearly all these features are found 
in some
prosauropods, and I effectively examined illustrations of the skulls of 
*Plateosaurus*,
*Lufengosaurus*, *Massospondylus*, and  *Thecodontosaurus*. Xu et al. compared 
to
*Azhendohsaurus*, and upon looking at that prosauropod, I also concur that 
there are enough
similarities to the jaw that *Eshanosaurus* cannot be a therizinosaur but is 
probably a
prosauropod. Despite pervious suggestion by myself and a friend, it is not 
likely to be
*Lufengosaurus*, but a related animal. As noted by Kirkland and Wolfe, 2001, a 
concern, raised by
Lamanna (pers. comm. to those authors), is the median keel on the crowns, not 
discussed by Xu et
al.. There is work in progress to demonstrate this in the literature, so please 
be patient. 

  *-- The name Segnosauria is available (Perle and Barsbold, 1981) to encompass 
all taxa closer to
*Segnosaurus* or *Therizinosaurus* than to *Oviraptor*, *Troodon*, 
*Ornithomimus*, *Velociraptor*,
*Mononykus*, or birds, rather than the use of Therizinosauria. Segnosauria is 
effectively used to
include *Beipiaosaurus*, as well as *Alxasaurus* and *Nothronychus*, plus all 
other
therizinosaurids.


=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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