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New Segnosaurs, a Reveiw and a Criticism
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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