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Protopteryx Zhang and Zhou 2000
P. fengningensis Zhang and Zhou 2000
Etymology- "primitive feather from Fengning
County", after the locality the holotype was discovered in.
Barremian, Early Cretaceous
Yixian Formation, Liaoning, China
Holotype- (IVPP V 11665) skull (28.3 mm), lower
jaw, seven or eight cervical vertebrae (18.5), twelve dorsal vertebrae (33.9
mm), dorsal ribs, sacrum, seven free caudal vertebrae (9.4 mm), pygostyle
(11.3 mm), scapulae (21.7 mm), coracoids, furcula (14.7 mm), sternum, forelimbs,
ilium (14.8 mm), pubis (22.3 mm), ischium (12.9 mm), hindlimbs (86.3 mm),
feather impressions
Paratype- (IVPP V 11844) skull, lower jaw, seven or
eight cervical vertebrae (19.1), twelve dorsal vertebrae (34 mm), dorsal ribs,
sacrum, seven free caudal vertebrae, pygostyle, scapulae, coracoids (12.7
mm), furcula (14 mm), sternum (15.9 mm), forelimbs, ilium (15.3 mm), pubis,
ischium, hindlimbs, feather impressions
Diagnosis- one tooth per premaxilla; procoracoid
process.
Description-
The skull is complete and resembles other basal
avians in basic shape, being triangular with large circular orbits. The
fused premaxillae possess long nasal processes that extend to the lacrimal and
one tooth each. The external naris appears enlarged and retracted
somewhat. A maxillary fenestra is still present. The postorbital is
Y-shaped and has a rodlike jugal process that probably contacted the
jugal. The quadrate lacks an orbital process, is not pneumatic and is
not sutured to the quadratojugal. The lower jaw is slender and
straight, with possible hyoids preserved. Two teeth are preserved in the
dentary. The teeth are conical, unserrated and one possesses a
reabsorbtion pit.
Seven or eight cervical vertebrae are present, the
last of which is very elongate. The twelve dorsal vertebrae have
craniocaudally short rectangular neural spines. Their centra are strongly
grooved laterally and have centrally placed parapophyses. There are twelve
pairs of dorsal ribs, the first very short. Uncinate processes are
absent. Seven vertebrae make up the sacrum. The last three have long
transverse processes and the last two have fused neural spines. The six or
seven free caudals also have transverse processes and are slightly shorter than
the pygostyle.
The scapula is curved and tapers distally.
The coracoid is articulated with the scapula through a flat mobile joint and at
an acute angle to it. It is elongate and strut-like, with a concave
lateral edge. There is a procoracoid process and a prominent lateral
process distally. Dorsally, the coracoid is concave. The sternum is
roughly diamond-shaped, with a much shorter anterior end. There is a keel
posteriorly and a single pair of lateral processes. These processes
project posterolaterally from slightly behind the lateral corners. They
are proximally forked, the lateral processending abruptly, the posterior process
extending almost past the posterior sternal edge and expanding slightly
distally. The furcula has an interclavicular angle of 65 degrees (the
paper says 50, but the figure and photo show 65) and a very long
hypocleidium, more than half as long as an arm. It is laterally
excavated.
The humerus is subequal to the ulna in
length. It has a well developed capital groove and cranioventrally
projected bicipital crest, but lacks a well developed transverse ligamental
groove. The proximal and distal ends are expanded in different planes and
the distal condyles are located mainly cranially. It lacks the expanded
deltopectoral crest of confuciusornithids. The ulna is bowed with the
dorsal condyle developed as a semilunar ridge. The radius is 55% of ulnar
width. Two carpals are preserved, the semilunate and a smaller carpal
contacting metacarpal III. The metacarpus is unfused and lacks an extensor
process. Metacarpal I is 23% as long as metacarpal II. It has an
elongate phalanx that reaches slightly past metacarpal II and a reduced
ungual. There are three phalanges on digit II. The first is shortest
and slightly expanded distally, while the ungual is the largest on the
manus. The third metacarpal is slender, bowed and longer than metacarpal
II. It has two phalanges, the last a tiny ungual.
The pelvic elements are unfused. The ilium
has an elongate rounded preacetabular process and a short slender postacetabular
process. The acetabulum is more than 11% of ilial length. There is
no fossa for the m. cuppedicus. The pubis has an oval section, distal foot
and short symphysis. The plate-like ischia taper distally and lack a
symphysis. They are 58% of pubic length.
The femur has a trochanteric crest, a posterior
trochantor and a distally bound popliteal fossa, but lacks a deep patellar
groove and a distinct neck. The tibia is about 120% of femoral length and
lacks a cranial cnemial crest and an extensor canal. The fibula is
elongate, but it is uncertain whether it contacted the calcaneum. The
astragalus and calcaneum are unfused to each other or the tibia. There is
a shallow notch between them. A single unfused distal tarsal is
present. The metatarsus is fused proximally. Metatarsal I is
slightly curved, about 25% as long as metatarsal II and lies on its mediodistal
end. Metatarsal II has a wider trochlea than metatarsal III, and
metatarsal IV is slightly more slender than the others and bowed a bit
laterally. Metatarsal V is present. There is no intercondylar
eminence or distal vascular foreman. Digit II is most robust, digit IV is
least.
The body is covered with down feathers, which range
from 10 to 20 mm long. An isolated down feather shows barbs converged
proximally and an afterfeather. There is no evidence for barbulae or
hooklets. Flight feathers reach 94 mm long and are asymmetric. An
alula is present. Two long central tail feathers lack barbs or rami
proximally, but possess both distally.
Relationships-
The authors performed a cladistic analysis with 86
characters and 11 taxa. This resulted in a single most parsimonious tree,
with Confuciusornus basal to an enantiornithine group and an euornithine
group. The topology of the enantiornithine group was (Protopteryx
(Cathayornis (Concornis + Enantiornis))), while the topology of the euornithine
group was (Chaoyangia (Hesperornithiformes (Ichthyornithiformes +
Neornithes))). It was grouped in the Enantiornithines based on thirteen
characters: scapula with taped distal end (ornithothoracine character); V-shaped
furcula with long hypocleidium (Jibeinia + ornithothoracine character); ulna
subequal or longer than humerus (Jibeinia + ornithothoracine character, also in
some basal oviraptorosaurs); ventral tubercle of humerus separated from head by
deep capital incision (ornithothoracine character); prominent cranioventrally
projecting bicipital crest on humerus; strong lateral grooves on dorsal centra
(pygostylian character); parapophyses located on center of dorsal centra;
metatarsal IV significantly smaller than metatarsals II and III (the authors
state it is only "slightly more slender", a condition also present in
Confuciusornis); trochlea of metatarsal II broader than those of metatarsals III
and IV; round articular surface in the proximal tibiotarsus; furcula laterally
excavated; metacarpal III extends past metacarpal II. As is apparent, the
list drops to six characters once they are examined more closely. Are
these enough to keep Protopteryx in the Enantiornithines? I compiled a
list of twenty-five phylogenetically informative characters (some multiple
state) known in Protopteryx and performed an
analysis on Protopteryx and its relatives to determine its phylogenetic
position. I only included these twenty-five characters and the
enantiornithine synapomorphies Protopteryx exhibits because nearly all analyses
(Chiappe 1997, in press; Sereno 2000; Zhang and Zhou 2000; my own) agree on the
topology (Archaeopteryx (Confuciusornithidae (Enantiornithines + Ornithurae))),
so this need not be tested. Any characters which are unknown in
Protopteryx are not going to help determine its placement within a known
topology. Also, I am not testing enantiornithine monophyly or
interrelationships. Where known, all enantiornithines would score
identically in my matrix in any case (even the possibly basal genus
Eoenantiornis). The same statements apply to various euornithine taxa I
could have included, so they were all condensed into Ornithurae. I also
added Jibeinia, as my previous study indicated it had a position between
confuciusornithids and ornithothoracines, which is a potential position for
Protopteryx as well. My analysis of 31 characters and 6 taxa resulted in a
single most parsimonious teee (CI .81, HI .19, RI .78). This tree shows
Protopteryx is more derived than confuciusornithids based on: mobile
scapulocoracoid joint; interclavicular angle of furcula 70 degrees or less; ulna
subequal or longer than humerus; less than four phalanges on manual digit III;
reduced manual unguals; scapula tapered distally; long hypocleidium; ventral
tubercle of humerus separated from head by deep capital incision; ulnar dorsal
condyle developed as a semilunar ridge; alula present. It is more
primitive than Jibeinia based on: manual digit I longer than metacarpal II;
manual phalanx II-2 longer than phalanx II-1. It is more primitive
than ornithothoracines based on: less than eight sacral vertebrae;
interclavicular angle of furcula more than 50 degrees; more than one phalanx on
manual digit III; maxillary fenestra present; postorbital contacts jugal;
metacarpal I not fused to metacarpal II; extensor process absent on metacarpus;
pelvic elements unfused; metatarsal V present. The six enantiornithine
characters are most parsimoniously seen as convergences. Therefore, I
would suggest Protopteryx is a pygostylian more derived than confuciusornithids,
but less so than Jibeinia and ornithothoracines. Interestingly,
confuciusornithids, Protopteryx, Jibeinia and some enantiornithines all have
elongate caudal feathers with the characteristic morphology described
above. This seems to have been a symplesiomorphy for pygostylians,
although I believe it is derived within Theropoda, not indicative of feathers'
prototypic state.
Those who want figures of Protopteryx, just
ask. That was relatively painless compared to Microraptor, with a stable
phylogeny and everything. Next comes Eoenantiornis.
Mickey Mortimer
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