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Chatterjee and Templin 2004, review, part I (long



Posture, locomotion, and paleoecology of pterosaurs
Geological Society of America
Special Paper 376, 2004   64pp.
Chatterjee, S. and Templin, R.J.

In the words of Chatterjee and Templin (C&T) â??In this paper we investigate  
the posture, locomotion, and paleoecology of pterosaurs based on anatomy and 
biomechanics: how they walked, how they flew, and how they lived. We want to 
understand how evolution has adjusted their skeletal structures and movements 
to maximize performance.â?? 

Itâ??s a large and comprehensive work. 64 pages. Lots of figures and photos. 
Much needed. 

Much of the first half on terrestrial locomotion recapitulates, reviews and 
dissects the literature and so most of this will pass without comment. Where 
the literature should be questioned and wasnâ??t Iâ??ll make comment. Where 
novel ideas are expressed that do not make sense Iâ??ll also make comment. 

The second half is about aerodynamics, but also covers takeoffs and landings 
and a myriad of other subjects inlcuding sexual dimorphism, thermoregulation, 
aerial turns (wasnâ??t lumped in with aerodynamics), ecology, evolution and 
extinction, all which will be reviewed later.

Bottom line for the impatient: 

internal inconsistencies, lack of a holistic approach, inaccurate models, 
reliance on out-dated literature, ignoring critical work, and using highly 
derived taxa to generalize basal and pterosaur-wide characters mar this paper. 
And once again, if you donâ??t get the wing shape right, all the math you throw 
at the aerodynamics will be off the mark.

>>>>>>>>>>>>

Comments are numbered for ease of reply.

Part I : introduction, hindquarters and terrestrial posture

1. In the abstract C&T describe pterosaurs as â??knuckle-walkers with laterally 
directed digitigrade manus,â?? which is an a hard concept to imagine until you 
realize itâ??s just one knuckle thatâ??s being walked on, No. 4, but itâ??s 
kept elevated by I-III, which are not flexed at the knuckle, but 
hyper-extended, as in all tetrapods except apes and anteaters, I think.

2. In the introduction C&T refer to pterosaurs as archosaurs that maintain 
their primitive manual proportions. Unfortunately, you have to go back to 
Prolacerta to find a manus in which digit IV is longer than three and maintains 
5 phalanges (ungual included) as in pterosaurs. Thatâ??s rather primitive.  A 
more parsimonious match, according to PAUP, is sister taxon, Protorsaurus. From 
this taxon _all_ of its descendants maintain a longer digit IV than III with 5 
phalanges. Conveniently, but rather rudely, C&T ignore the protorosaur 
(prolacertiform) hypothesis which preceded this paper by four years and has not 
been disputed in print since, but is mentioned briefly later in the text.

3. C&T report: â??The .... external nares are  set far back from the tip of the 
beak.â?? Only in one branch of the Pterosauria, not other one, the 
Dimorphodontoidea.

4. C&T report: In pterodactyloids â??The fifth toe becomes relatively short due 
to the loss of digits.â?? They probably meant phalanges, but even this is 
incorrect as the phalanx count remains the same, only shorter, except in one 
derived clade.

5. C&T report: The reduction of the tail reduces the stalling speed of large 
pterodactyloids.  As a private pilot, I donâ??t see how this can take place. 
Airplanes towing huge banners have the same stalling speed as when they are 
not. The stall depends chiefly on the angle of attack of the wing and airspeed.

Terrestrial Locomotion - Stance and Gait
6. C&T report that pterosaurs were both quadrupedal and bipedal. Finally!! 

7. CM  11431 skeleton used in their study, is a  Rhamphorhynchus gemmingi, not 
muensteri. Manual 4.1 when folded extends past the elbow.

8. C&T used a cast of Anhanguera to understand pterosaur gait and stance. While 
admirable to use three-dimensional material, this is a derived taxon leaving no 
descendants. Anhanguera is very unusual. It had the smallest pes/tibia ratio of 
any pterosaur (feet are largely unknown though among higher ornithocheirds) and 
the pubes recontacted ventrally as in few to no other pterosaur taxa. You might 
ask, where are the prepubes in this taxon? They are absurdly tiny in sister 
taxa. Perhaps missing here. Iâ??ve never seen or heard of them.

9. C&T report: â??The spine was inclined  45º or more...â?? yet figure 7 shows 
their model of a wireframe Anhanguera with a spine lower than 45º. 

To that point: the wireframe stick diagram in Figure 7 is supposed to be based 
on Anhanguera, but the proportions donâ??t match. The skull is too small or the 
torso is way too big. The skull should equal the cervicals + torso. The feet 
are twice their natural size and the wing is too short, almost by a phalanx.

Forelimb Joints
10. C&T report: â??During normal walking, the elbow would be directed 
backward...â?? yet figure 7 shows the elbow oriented ventrolaterally. 

11. C&T report, quoting Lockley et al. (1995): The manus tracks are oriented 
laterally indicating lateral torsion of the hand. I know itâ??s hard to work 
with a complete pterosaur skeleton, but when you do you discover that when the 
elbows are back, as they in cowboys preparing to draw guns from holsters, the 
palms are medial. Drop the hands  to the substrate, whether a tree trunk or a 
sandy beach and the fingers are laterally oriented. No lateral torsion is 
necessary. Raise the elbows and youâ??re flying. Itâ??s that simple.

12. C&T report: (when grounded) â??The flight digit was folded subparallel to 
metacarpal four and tucked up behind the pelvis,â?? yet figure 7 shows the 
flight digit folded subparallel to the antebrachium and not tucked up but 
exposed, crossing the knee. Other awkward figures throughout shows an apparent 
inability for the flight digit to flex closer than 60 degrees to the 
metacarpus, ignoring  insitu finds, studies, and manipulations that have shown 
that in pterosaurs the wing folded completely against the metacarpus.

13. Figure 7, the wireframe Anhanguera, shows the animal in a pose used prior 
to resting (my opinion, not theirs). The wings are far forward, the legs far 
back, just prior to bending the elbow and knee for the final collapse to the 
belly. The knees are hyper-extended and less wide apart than the shoulder 
glenoids.  A better illustration might have been showing the four steps in a 
step cycle. Or perhaps a pose which permitted a bipedal posture simply by 
lifting the wings off the substrate, which C&T advocate.

Hip Joint
13. C&T report: â??All pterosaurs have a uniform pelvic morphology...â?? 
Nothing could be further from the truth, as I have discovered reconstructing 
the pelves of 125 different pterosaurs (see pterosaurinfo.com). The variety in 
shapes in not widely discussed in the literature, but all are diagnostic to 
small clades. In some the prepubis is much larger thanthe pubis. In others just 
the opposite. Most do not fuse ventrally. Some are quite gracile. 

14. C&T report: â??The acetabulum is  imperforate.â?? Often,  but sometimes 
not, as in Sordes.

15. C&T report: â??The pubo-ischiadic plate is short and broad.â?? Sometimes, 
but this time typically not.

16. C&T report: â??The two halves of the pelvis are fused along the ischial 
symphysis in all pterosaurs...â?? which is incorrect for a majority of them in 
which the pubis and ischium are widely separated by a recess that extends 
nearly to the acetabulum.

17. C&T report: â??The femoral component is a well-defined spherical head, 
which is distinctly separated from the shaft by a narrow, non-articular neck at 
an obtuse angle of 160º.â?? Once again C&T have chosen a highly derived 
specimen to characterize all pterosaurs. Primitive pterosaurs did not have  a 
distinct femoral head and neck, and the femoral head was often set off from the 
shaft at a more acute angle than 160º, very much like that of the typical 
theropod femur (is there one?) to which C&T make comparison.

18. C&T report: â??The hip joint is fully congruent and stable throughout an 
enormous range...â?? yet a few sentences later show their bias when they pick a 
favorite without any other landmarks or guidelines : â??the most stable 
position of the femur is in the horizontal direction of the wing plane...â??

19. C&T report and illustrate the amount of adduction possible at the hip joint 
ranges to 25º away from ventral using an illustration of the pelvis and femur 
alone. That is well within the range of the rhea and ostrich, by the way, but 
C&T call this a near-erect stance. How much more erect can you get? What C&T 
fail to do is note that at that angle, the typical tibial articulation would 
end up crossing the ankles. Hopefully future work will be more holistic in 
their approach and show the whole leg, or the whole animal from many angles.

20. C&T report that â??The unusual elongated fore limb defines the gait and 
restricts the forward and backward swing of the femur during locomotion.â?? But 
not if the forelimbs swing wider than the hindlimbs, as tracks indicate. 

21. C&T report: â??The retraction of the femur was somewhat limited in 
pterodactyloids because of the loss of the tail.â?? If one were to compare as 
far back as Prolacerta/Protorosaurus one would see the dramatic reduction of 
the chevrons in Protorosaurus and all of its ancestors, including pterosaurs, 
and their elongation in  Prolacerta and all of its ancestors, except birds, 
etc. This is where the caudal retractors of the tail began diminish, in a 
lumbering quadruped. Furthermore the caudal transverse processes , the lateral 
caudofemoral anchors, are greatly reduced in Sharovipteryx and basal 
pterosaurs. This occurs at the same time that the prepubis and anterior process 
of the ilium get really big. That means, thereâ??s a shift going on from 
femoral retractors to femoral rotators. The complete elimination of the last 
three tiny (in birds theyâ??re d even larger) transverse processes in 
pterodactyloid-grade pterosaurs and anurognathids simply erased the vestiges. 
The same thing
 happened in mammals. Sure they have a tail, but it doesnâ??t â??wag the dogâ?? 
as it does in lizards, crocs and dinos.

To that point, C&T report: â??In the long-tailed â??rhamphorhynchoidsâ?? the M. 
caudofemoralis was large and important, allowing a wide range of femoral 
retraction.â?? Not true, as described above. The femur rotated. It didnâ??t 
retract. A subtle difference mostly involving muscle selection (hip and 
prepubis anchors as opposed to tail anchors) in early pterosaurs with more 
erect femora. Increasingly obvious in later pterosaurs with more widely splayed 
femora in which the femur is practically turning on its long axis, staying in 
the plane of the wing all the time.

Knee Joint
No comments here.

Ankle Joint
22. C&T describe: â??the loss of the calcaneal tuber.â?? Pterosaurs and 
nonvolant protorosaurs never had one.

23. C&T report: â??The â??crocodile-reverseâ?? joint... supports its inclusion 
in the ornithosuchian lineage.â?? Except that this arrangement is convergent 
with certain protorosaurs. Fusion of the tibia and tarsus is also a convergent 
character, and certainly unlike the situation in dinosaurs which have an 
ascending astragulus that is not duplicated in pterosaurs.

24. C&T report: â??[unlike theropods]...the inner four metatarsals of 
pterosaurs are subequal in length...â?? Not true. In basal pterosaurs, the 
digits increase in length laterally. In scaphognathids up to basal 
ornithocheirids the digits increase in length medially. This misstatement 
over-generalizes the wide variety in pterosaur pedes that is largely unreported 
in the literature (but no for long!)

And following that, C&T continue: â??...and do not show any tridactyl trend 
[compared to theropods].â?? This never stopped pigs, cattle and goats from 
becoming digitigrade. Why did pterosaurs need just three toes?

25. C&T support Clark et al., (1998) and their pronouncement that the pes of 
Dimorphodon weintraubi was plantigrade. While this specimen demonstrated that 
the metatarsophalangeal joint was stiff, which rocked an earlier Padian 
hypothesis, sufficient extension of the interphalangeal joints permitted a low 
digitigrade configuration, as demonstrated by Peters (2000), and as 
demonstrated by digitigrade protorosaur tracks matched by Peters (2000) and  
Avanzini,  & Renesto (2002). This was yet another bad Nature pterosaur report. 
By the way, a good extant analog for the pterosaur pes is the pes of most 
facultatively bipedal lizards, movies of which can be seen at: 
http://www.biology.uc.edu/faculty/jayne/bruce.htm Watch them go digitigrade and 
narrow gauge at high speed with sprawling femora!

Peters, D. 2000a. Description and Interpretation of Interphalangeal Lines in 
Tetrapods. - Ichnos 7(1): 11-41.

Avanzini,  M. & Renesto, S. 2002. A review of Rhynchosauroides tyrolicus Abel, 
1926 ichnospecies (Middle Triassic: Anisian-Ladinian) and some inferences on 
Rhynchosauroides trackmaker. Rivista Italiana di Paleontologia e Stratigrafia 
108 (1): 51-66.

Trackways
26. C&T repeat the manus torsion problem. See above.

27. Figure legend number 9 notes: â??manus tracks are typically deeper than the 
pes tracks, suggesting that the majority of weight was supported by the front 
limbs.â?? Nobody seems to notice that the manus prints are much smaller in area 
than the pes prints and if equal weight is distributed on all of them (the 
entire weight of the pterosaur on each extremity in a typical walk cycle > for 
an animation matched to tracks see pterosaurinfo.com/behavior.html) then sure 
the manus is going to press deeper. 
 
Later the figure continues: â??note manus digits were directed laterally...â?? 
Digit I in figure 9 is directed laterally, but digits II and especially III are 
directed posteriorly. That canâ??t happen in a standard lineage of quadrupedal 
tetrapods unless something intervenes â?? like a strictly bipedal phase! 
Remember, not only do you have to look at the individual pterosaur 
holistically, making sure all the parts work together, you also have to make 
sure the entire lineage works logically and efficiently without any strange 
unexplainable gaps.

Quadrupedal Walking
28. C&T report: â??The limbs in pterosaurs were held in a near-parasagittal 
position.â?? Again, look at extant lizards capable of bipedal progression. 
These make good models. Also make sure the axis of the femoral neck is aligned 
witht the axis of the actebulum. That gives your pterosaur femur a  sprawl -- 
bit a good sprawl.

29. C&T report: â??Elongation of McIV probably signaled a dramatic change in 
terrestrial locomotion from â??rhamphorhynchoidsâ?? to pterodactyloids, a 
posture associated with a more upright vertebral column.â?? This is a bad guess 
based on bad old illustrations. When you see accurate reconstructions, as in 
pterosaurinfo.com, you can see that in almost all cases the posture is the 
same, bipedal or quadrupedal. The difference is moot.

30. C&T report (based on a digitized walking model by Henderson and Unwin 
(1999) that: â??In pterosaurs, the center of mass lay between the two girdles 
when on the ground.â?? A correct configuration shows that the center of mass 
stayed close to the center of balance, between the shoulder girdles, a point 
directly above the pedes in a bipedal pose with all elements in balance. From 
there a slight pitch forward got a walk started. Again, this is clear in the 
animation referenced earlier.

Furthermore, addition or subtraction of the tail had little to no effect on the 
ability to walk bipedally. Early and late pterosaurs were equally competent.

31. C&T report: â??In bipedal running, bent knees would confer speed.â?? Not 
sure what is meant by this. Donâ??t all tetrapods have bent knees?

32. C&T report: â??Although the bipedal position is unstable, the caudally 
directed folded wings could balance the body.â?? The balancing abilities of 
pterosaurs or any tetrapod should never be questioned or assisted with circus 
props. Even tetrapods with vestigial arms have enough leg-brain feedback that 
instability is rarely a problem. Even geese without feet can walk well.

33. C&T report: â??...the drastic change of gait from quadurpedal to bipedal 
mode [from rhamphs to pterodacs].â?? Not true. Simply lift the hands off the 
substrate and youâ??re bipedal (see any taxon in pterosaurinfo.com) when the 
configuration is correct. Itâ??s the same throughout the lineage.

34. C&T report: â??Moreover, during the transition from walking to running, the 
stance changes from plantigrade to digitigrade mode, making less contact with 
the surface...â?? Hey, theyâ??re trying to have it both ways!! The footprints 
are never digitigrade, even during rapid locomotion. Clark, et al. (1998) 
demonstrated it, right? Where does this digitigrade stuff come from? Thereâ??s 
no evidence for it in pterosaurs, that is... in the clades of wading pterosaurs 
that were plantigrade that left all the tracks (...a little tongue-in-cheek, 
but not for lack of logic.) 

More later starting with â??Wing Designâ??

David Peters
St. Louis