Pivot Joint

[tmaromine]

The more I think about it...

Any animal that can turn it's paw/foot inward would have to have a pivot joint. Yes/no?

 

-squirrels

-raccoons

-bears

-etc...

 

I'd say yes. Do they ? I shall have to (unharmingly) see if my cat's paw can turn inward...

[CraigD]

The hand/paw/hoof turning trick is requires, as best I can tell, separate bones in the lower arm – an ulna and a radius.

 

A quick glance at several skeletons can show which animals have them:

horse skeleton = no;

cat skeleton = yes;

human skeleton = yes;

etc.

 

So, as I think everyone has already surmised, a pivoting elbow joint isn’t unique to primates, nor common to mammals.

 

I shall have to (unharmingly) see if my cat's paw can turn inward...

I just happened to have a docile cat (a healthy 10 month old neutered male) on me when I discovered this thread, and made a quick check of his “hand”. It’s pretty pivot-y, about 90° or so, but nowhere near as much as my own 180° or so (I’m a healthy 47 year old unneutered male ).

 

As I recall, animals like horses lost their separate radius and ulna by the bones becoming fused as they adapted to bear a lot of weight on fairly thin bones. Oddly enough, even though it supports a lot of weight, an retains its separate ulna and radius.

[Dracontes]

Good info (quoted text). Unfortunately it only discusses one type of dinosaur. It's also important to note that MANY anatomical changes occurred between dinosaurs and modern day birds.

 

It does say that the range of movement resembles that of less derived dinosaurs namely, Herrerasaurus and Dilophosaurus, the former being somewhat iffy as a theropod.

 

Take a look at this link I posted before:

Wing Anatomy

Take note that the word "elbow" is in quotes.

 

Hmm... Looks more like nomenclatural niggling on the part of the person who labeled the schematic to me: the shoulder is in quotes also. IMHO it's unnecessary to do that.

 

Here are a few quotes from papers that I found pertinent while searching my scientific article collection:

 

Kenneth Carpenter. (2002) "Forelimb Biomechanics Of Nonavian Theropod Dinosaurs In Predation". Concepts Of Functional, Engineering And Constructional Morphology - Senckenbergiana Lethaea 82 (1) 59 – 76 Senckenberg Museum, Frankfurt Am Main.

The elbow complex is formed by the humerus, radius and ulna.

As with the shoulder complex, the degree of movement is restricted by ligaments and muscles, but also by the trochlear notch of the ulna. The joint at the elbow is a simple hinge, with movement in a single plane. In humans, a trochlear notch is developed along the anterior face of the olecranon, but in the crocodilians, most theropods and birds, the trochlear notch is poorly developed and is a sloped surface descending anteroventrally from the olecranon. In most theropods, the olecranon is less than 20% ulna length, but is 55% in Mononykus. No theropod has the mechanical interlocking mechanism at the elbow seen in humans and other mammals. In mammals, the trochlear notch is constricted from below by a slight dorsal projecting of the coronoid process of the ulna and above by the overhanging olecranon process. This structure of the trochlear notch embraces the distal end of the humerus making the elbow difficult to disarticulate.

 

Image pertinent to the text above and below: http://www.maj.com/gallery/Dracontes/Scans-and-screens/dinoelbow.png

 

The elbow in humans is also where rotation of the forearm occurs. Rotation is possible because the proximal end of the radius is almost circular in proximal view and can roll in the concentric radial notch. The distal end of the ulna is arcuate and can accommodate the roll of the concentric facet of the radius. Crocodiles, birds and theropods lack the capability of forearm rotation because the rolling surfaces are not developed. As a result, the palmar surface of the manus remains basically in the same plane as the ulna and radius. Human like pronation and supination cannot occur in most theropods. Instead, pronation (palm facing ventrally) occurs by abduction of the entire forelimb, which in birds, occurs during flight. A modified form of pronation at the wrist occurs in Deinonychus. Birds also have a peculiar gliding mechanism at the elbow that is intimately associated with the folding of the wing, and which theropods do not have. Wing extension and flexion occurs with the wing partially abducted.

Extension occurs when the triceps pull on the ulna the dorsal collateral ligament pulls the radial head along the elongated, shallow trough-like radial notch of the ulna. This action in turn pulls the ligaments attached to the radial carpal and to the carpometacarpus, thus extending outwards the distal portion of the wing. When the biceps and brachialis flex the forearm, the radial condyle of the humerus pushes the radius. The radius pushes against the radial carpal, which in turn pushes against the carpometacarpus.

Ligaments, especially on the ventral side, restrict the movement of the carpometacarpus to a rotation, thus folding the wing. Movement of the radius in the radial notch is variable and is about 5 mm in Anser and 7.5 mm in Meleagris.

The wing folding does not occur in a single plane because of the oblique angle of the radial condyle of the humerus. As the elbow is flexed, the radial head glides medially on the radial condyle. The distal end is rotated a few degrees but is kept from separating from the ulna by the interosseus ligament. Despite the small rotation of the radius (~2-3°), it is enough to supinate the wrist and distal wing out of the plane formed by the forearm and humerus. When folding of the wing is completed against the side of the body, the distal part of the wing (carpometacarpus + phalanges) angles slightly away from the sagittal plane of the body.

This complex wing folding mechanism of the birds is absent in theropods and it is clear that they are unable to fold the forelimb in avian fashion. The radial notch lacks the gliding surface seen in the bird ulna, and the radial head has a broad contact with the ulna. Furthermore, as the radial head glides on the laterally oblique radial condyle during flexion, the radius and ulna are adducted slightly.

 

Phil Senter. (2005) "Function in the stunted forelimbs of Mononykus olecranus (Theropoda), a dinosaurian anteater". Paleobiology, 31(3), pp. 373–381 The Paleontological Society.

 

Radioulnar Joint

An articular surface on the distal end of the ulnar coronoid process fits precisely into an articular surface on the radial head. Here the two bones contact each other directly with no intervening space for articular cartilage. Attachment was therefore sutural, causing the antebrachium to operate as a single functional unit, with no pronation or supination possible.

There is no distal radioulnar joint, as the two bones are distally separated by a small space.

 

Matthew; Phil Senter (2007). "Were the basal sauropodomorph dinosaurs Plateosaurus and Massospondylus habitual quadrupeds?", in Paul M. Barrett & D. J. Batten (eds.): Evolution and Palaeobiology of Early Sauropodomorph Dinosaurs, Special Papers in Palaeontology 77. London: The Palaeontological Association, 139–155.

 

Abstract

The basal sauropodomorph dinosaurs Plateosaurus and Massospondylus are often portrayed as habitual quadrupeds that were facultatively bipedal. Surprisingly, the functional morphology of their forelimbs has rarely been considered when reconstructing their locomotor habits. If Plateosaurus and Massospondylus were efficient, habitual quadrupeds we predict that the manus would have been pronated such that it produced a caudally directed force in parallel with the pes. We articulated and manipulated the forelimbs of Plateosaurus, Massospondylus and several extant outgroup taxa (Varanus, Alligator, Anser and Struthio) using a standardized protocol. Moreover, we compared our results with previously published estimates of forelimb movement in saurischian outgroup taxa from Theropoda and Sauropoda and with the basal sauropodomorph/sauropod Melanorosaurus. Our results indicate that the range of motion in the forelimbs of Plateosaurus and Massospondylus did not allow efficient, habitual quadrupedal locomotion. The range of humeral flexion and abduction is limited and the articular surfaces of the radius and ulna orient the palmar surfaces of the manus medially in semi-supination. Active or passive pronation of the manus was not possible and the manus could not function in a dynamically similar way to the pes for efficient quadrupedal locomotion. Our results also rule out specialized forms of quadrupedal locomotion, such as the knuckle-walking gait of some mammals.

 

Joanna L. Wright. (1999). "Ichnological Evidence For The Use Of The Forelimb In Iguanodontid Locomotion". Special Papers In Palaeontology No. 60, Pp. 209-219. The Palaeontological Association.

 

The form of this trackway also shows that, when walking quadrupedally, iguanodontids, at least occasionally, placed their hands on the ground outside the line of tracks made by their feet, with the dorsal surface of the manus facing outwards parallel to the trackway midline. This is in contrast to the way in which iguanodontids are often reconstructed, with their forelimbs placed slightly cioser to the midline than the hindlimbs, and with the dorsal surface of the manus facing forwards. This latter posture is problematical because it would necessitate rotation of the radius around the ulna leading to distortion and dislocation of the joint at the wrist or elbow. The posture indicated by the trackways obviates the need for unnatural twisting of the bones of the lower forelimbs, and is thus more compatible with what is known regarding the skeletal anatomy of these animals. This does not mean, however, that iguanodontids had a sprawling forelimb posture. The placing of the feet almost directly upon a single line is related to the location of the centre of gravity near the pelvic girdle, since, in a bipedal animal, the feet would need to be placed directly beneath the body midline to maintain balance, because these were the weight-bearing limbs. The forelimbs of this track-maker were not necessary for weight-bearing and balance in locomotion and thus did not have to operate under such constraints. The width of the angulation pattern of the manus tracks is c. 0.5 m (average 484 mm) which is about the width of the shoulder girdle of Iguanodon atherfieldensis. These relative proportions suggest that the arms would have been held in a vertical position when the forefeet were in contact with the ground.

 

Image pertinent to the text above: http://www.maj.com/gallery/Dracontes/Scans-and-screens/dinoelbow0.png

 

P. Senter (2007) "Analysis of forelimb function in basal ceratopsians" Journal of Zoology 273 (3), 305–314.

 

Abstract

Here, I present the first study of forelimb function in basal ceratopsians Dinosauria: Orthischia. I examined forelimb bones and casts of Psittacosaurus neimongoliensis, Psittacosaurus mongoliensis, Leptoceratops gracilis and Protoceratops andrewsi. For Ps. neimongoliensis and L. gracilis, I used manual manipulations of bones and casts to determine the range of motion at available forelimb joints. I then used range of motion and morphology to test the predictions of several hypotheses of forelimb function. Forelimb morphology and range of motion indicate that Psittacosaurus was an obligate biped and that Leptoceratops and Protoceratops were capable of quadrupedal locomotion. Forelimb mobility was too limited in Psittacosaurus for the hands to reach the mouth. Leptoceratops and Protoceratops are members of an evolutionary radiation in which an extension of the glenoid enabled the forelimbs to sprawl laterally for transverse pivoting, perhaps for display, but quadrupedal locomotion was accomplished with the elbows tucked in. In Protoceratops, the radius crosses over the ulna, causing the palms to face caudally. In Leptoceratops, the radius does not cross over the ulna; the palms face largely medially and the fingers have been reoriented so that flexion produces a caudal, propulsive force, even without caudally facing palms.

 

One has also to bear in mind the inference method used here: phylogenetic bracketing.

 

Then there is this paper on new remains for the chalicothere Tylocephalonyx skinneri, a relative of the horse:

 

Robert M. Hunt, Jr. (2005) "An Early Miocene Dome-Skulled Chalicothere From The ‘‘Arikaree’’ Conglomerates Of Darton: Calibrating The Ages Of High Plains Paleovalleys Against Rocky Mountain Tectonism". American Museum Novitates. Number 3486, 45 Pp., American Museum Of Natural History

 

Ulna: A proximal ulna (UNSM 44810) preserves the olecranon process, semilunar notch, and coronoid process, demonstrating the nature of the articulation with the radius.

The proximal ulna was similar in size and form to the ulna of Moropus elatus. Features of M. elatus mentioned by Coombs (1978) are present: a prominent anconeal process, deep semilunar notch with strong medial expansion, radius facet distal and at an acute angle to the semilunar notch and forming a deep articular fossa. Ulnar width at the level of the coronoid process is ~11 cm. The shape of the semilunar notch for articulation with the humerus and the reduced coronoid process demonstrate that the radial head, which fits tightly against the radial notch, was immobile and did not rotate. Only extension and flexion occurred at the elbow; there was no rotation of the radius around the ulna, an aspect of the anatomy of M. elatus previously noted by Coombs (1978: 25). The ulnar fragment exhibits considerable preburial flaking and cracking of the cortical bone—it must have been scavenged and exposed to weathering for some time prior to burial.

Coombs (1979: 23) regarded the radius/ulna of Tylocephalonyx skinneri as little different from that of M. elatus. She did note that the lateral extent of the proximal facet on the ulna for the radial head is slightly smaller in T. skinneri; despite the damaged state of UNSM 44810, it seems to show this more restricted condition of the proximal facet. In both species the radius and ulna were incapable of independent movement— locked by fusion of the distal shafts, the form of the proximal articulation, and by strong interosseous ligaments.

 

Okay, I admit that was long and haphazard but in the end I hope it was informative. I'll reserve my own notions for another post.

[freeztar]

Good stuff Drac! That certainly helps clear up a lot of hanging questions. :eek2: