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Re: Psittacosaurus queries



Steve Brusatte wrote-

> Also, in his 2001 paper Sereno only recognizes six species (he discounts
_P. sattayaraki_ and _P. mazongshanensis_ due to the paucity of both
material and any diagnostic characters).  However, I had once read (maybe
onlist) that seven species were recognized.  Sereno sees these as valid: _P.
mongoliensis_, _P. sinensis_, _P. neimongoliensis_, _P. ordosensis_, _P.
xinjiangensis_, and _P. meileyingensis_.  Am I missing any valid species?
Of coures, some of the others (_P. osborni_, _P. tingi_, and _P.
guyangensis_ ) might be valid, but likely not.

You forgot P. sibiricus (
http://www.cmnh.org/dinoarch/2002Feb/msg00838.html ) and the nomen nudum P.
"chaoyoungi" (which may be Chaoyangsaurus).  Have I ever mentioned I dislike
the habit of making taxa nomina dubia without extensive comparison? ;-)

> And, if scans are impossible or difficult to send, if someone would list
any diagnostic characters or other interesting osteological features
(especially those regarding the premaxilla-maxilla-lacrimal-jugal joint,
maxillary secondary depression, lacrimal foramen, and dentary) it would also
be appreciated.

Psittacosaurus mazongshanensis is diagnosed in Xu (1997) by- elongate snout
(ventral surface of mandible formed mostly be dentary); deep buccal recess
on maxilla; posterior maxillary process projects ventrally; sharp right
angle between ventral and medial margins of jugal; lateral process on dorsal
rim of predentary; more than fourteen denticles on maxillary crowns; fossa
ventral to exoccipital-opisthotic contact.  Additional characters supposedly
distinct from other Psittacosaurus species are- large size; mandibles
Y-shaped ventrally; lateral ridge of postorbital weaker; deeply cupped
articular surface for quadrate on mandible.  I think Xu makes a good case
for this species being valid.  It has characters 2, 4, 6, 9 and 11 that
diagnose Psittacosaurus, in the order listed by Steve.  It lacks the
upturned lateral margin of the prefrontal of P. mongoliensis; has an
external mandibular fenestra unlike P. sinensis (and P. youngi, if it's
valid); the snout is more elongate than other species, opposite of P.
meileyingensis; lacks the anteriorly flat jugal horn of P. xinjiangensis;
the external mandibular fenestra and antorbital fossa distinguish it from P.
neimongoliensis; it lacks P. ordosensis' maxillary fontanel.  In conclusion,
I see no reason to support making this taxopn a nomen dubium as Sereno
(2001) suggests.

Russell and Zhao (1996) include 13 characters in their Psittacosaurus
phylogenetic analysis-
1. skull rectangular with long antorbital region (0); intermediate (1);
rounded with short antorbital region (2).
2. antorbital fossa very shallow or absent.
3. ten or less maxillary and dentary teeth.
4. lateral margin of prefrontal strongly upturned.
5. postorbital region broad.
6. horizontal ridge strongly developed on postorbital.
7. anterior squamosal process extends to anterior margin of supratemporal
fenestra.
8. laterally projecting jugal horn.
9. posterior quadrate margin deeply sulcate.
10. external mandibular fenestra absent.
11. ventrolateral dentary ridge.
12. posteroventrally angled primary ridge of maxillary teeth.
13. metatarsal I >65% of metatarsal III.
I think 5 is useless, as it's just an apomorphy of P. mongoliensis.  Also, I
would recommend quantifying several characters, but I have coelurosaur
characters to worry about, someone else can refine psittacosaur phylogeny.
:-)
P. mazongshanensis codes the following way-
                  111
        1234567890123
outgroup0000000000000
P.mongo 0101001000111
P.sinen 1010111111000
P.meile 211001101011?
P.xinji ?11??0110??1?
P.neimo 1010110001011
P.ordos 101?1??100101
P.mazon 00?010?00011?
Running this through PAUP yields 3 most parsimonious trees, with the
following topology-
|-mazongshanensis
`-+-mongoliensis
  `-+-meileyingensis
    |-xinjiangensis
    `-+-neimongoliensis
      |-ordosensis
      `-sinensis
So if you have some urge to split up Psittacosaurus, I recommend making P.
mazongshanensis a new genus, though I don't think it would be very useful.

Mickey Mortimer