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A Free-Standing Mount of an Indian Rhynchosaur

PRANAB KUMAR MAJUMDAR

GEOLOGICAL STUDIES UNIT

INDIAN STATISTICAL INSTITUTE, CALCUTTA

Rhynchosaurs were a widely distributed group of reptilian vertebrates during the Triassic Period, and they are recorded in the nonmarine rocks of all continents except Australia and Antarctica. The animals constitute the family Rhynchosauridae, which includes seven genera. The creatures probably lived in floodplains or marshy environments, where they fed only on mussels. The Indian genus Paradapedon was a clumsy, heavily built animal. When fully grown, it supposedly at- tained the size of a cow.

Until recently, only two mounts of rhynchosaur skeletons were known, at the University Museum of Tubingen, West Germany, where the animals are shown in the normal standing position. The skeleton of one of the mounts is Scaphonyx (Fig. la), a South American genus. The other mount shows two animals, both of the East African genus Stenaulorhynchus (Fig. lb). In the second mount one can see how these animals searched for their food by using their hind limbs to dig up the earth.

From the red beds of the Upper Triassic Maleri formation in the Pranhita-Godavari Valley, Deccan, India, six associated skeletons of Paradapedon, an Indian rhynchosaur, were recently collected by S. Chatterjee of the Geological Studies Unit, Indian Statistical Institute, Calcutta. One of the skeletons was found to be nearly complete and was in an excellent state of preservation. This article describes the mounting of this skeleton, now exhibited in the museum of the Geological Studies Unit in Calcutta. The size of the mounted Para-

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dapedon skeleton is about 1.4 meters from the nose to the tail tip and its height is about thirty-seven centimeters.

Normally, mounting a skeleton involves preparation of an armature made up of iron rods, plates, and wires, which are held together by means of welding. In the Paradapedon mount, a slightly modified method was used.

In the very beginning, a temporary mount of the skeleton of Paradapedon was erected with the help of iron rods and clamps to show the normal dimensions and posture of the animal. The general curvature of the vertebral column, which could be obtained if the vertebrae were placed in association, was taken into proper account. I t could be seen that the dorsal vertebrae formed an arch between the two girdles, and there was a formation of a slight upward arch in the neck region anterior to the shoulder girdle. Also, the caudals, posterior to the pelvis, gradually slanted downward.

With the estimation of the type of curvature of the vertebral column, the girdles were taken into account. The sacrum fixed the attitude of the pelvis. Fixation of the attitude of the shoulder girdle lacked any landmark. The scapula was placed on the anterior dorsal region of the vertebra, in the normal reptilian posture. The limbs were held somewhat close to the body instead of the primitive sprawling posture. The manus and pes were kept in the plantigarde fashion. The skull of the animal, which was heavier, was placed somewhat downward, rather than in the horizontal fashion.

When the temporary mount was complete, a clay model was prepared depicting the exact dimensions and the natural posture of Paradapedon. The clay was kept wet throughout the preparati6b work and was gradually wholly removed, inch by inch, during the process.

For the erection of the mount, it was found very suitable to use a thin, flat, T-shaped, iron plate with a projection ridge. The width of the plate was about six millimeters. The plate was placed on top of the backbone of the life-size clay model, with the ridge kept dowfi- ward in order to follow the curvature of the vertebral column. This natural curvature was approximately obtained by curving the iron plate on heating. The armature of the vertebral column was con- nected with the help of two temporary vertical supports, giving rise to a cantilever structure.

It was found convenient to use the common steel spring of a table clock for the purpose of clamping each vertebra with the above-men- tioned curved iron plate. The spring was cut into several small pieces; each piece was about one and a half inches in length. Each piece was

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a

b

1 Rhynchosaur mounts at the University Museum, Tiibingen, West Germany. a Scaphonyx. b Stenaulorhynchus.

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turned into a U-shaped form, and the base of the U was welded with the armature of the vertebral column. The U-shaped clamps sur- rounded the centrum of each of the vertebrae. One by one, the clamps were fixed. The space between any two adjacent clamps was constantly checked, placing the vertebra of that particular position.

The armatures for the pectoral and the pelvic girdles were prepared with the aid of a thick wire two millimeters in diameter. It ex- tended laterally from the armature of the vertebral column. From the girdles, the attaching armatures for the front and hind limbs were prepared by using thick circular rods three millimeters in diameter.

Once the armature was complete, a rectangular iron structure was prepared. Two supporting rods for the front and the hind limbs were connected with the rectangular frame after some careful manipula- tion. The supporting iron plate for the caudal vertebrae was welded with the rectangular structure. The temporary vertical supports were then removed. At this moment, the whole weight of the body was nicely distributed through the armatures for the limbs and the caudal vertebrae to the rectangular basal frame, thereby permitting an upright standing mount.

Several moderately thick wires one millimeter in diameter were then cut, and the pieces were placed on the surface of the clay model in order to get an approximate measurement of the inside curvature of the rib cage. These wires were then connected with the armature for the vertebral column. The manus and pes were held in place with the help of fine wires and clamps.

A new technique was employed to connect the skull with the main body (Fig. 2). The skull with the jaw in place was mounted separately by means of the iron rods. The two supporting rods, on either side of the skull, were brought together along the median support behind the skull. A semicircular iron plate three and a half centimeters in diameter with two holes was welded terminally. Two nuts were welded with the two holes at the back of the iron plate. An identical semicircular plate, with two holes in similar positions, was welded in front of the armature of the vertebral column. Putting the bolts through the last two holes, the skull was then quite easily connected with the armature of the rest of the body. This method permitted dismantling of the skull with less effort from the rest of the body. The bones were then placed in their respective positions on the com- plete armature. For holding the limb bones in their respective places, the wire clamps were used, and any of the bones can be removed easily from the armature for study without any disturbance to the

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a

5 o mic trc u la r

armotuve for

vovto brof column

I5 C I C 1

2 Procedure for mounting the Rhynchosaur skull. a Ventral view. Thick black lines: armature of the skull; thick dotted lines: annature of the lower jaw. b Posterior view. Thick black lines: armature of the skull and lower p w . The semi- circular iron plate at the center fit8 with the corresponding armature plate of the vertebral column. c Armature of the vertebral column.

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3 Rhynchosaur as completed at the Geological Studies Unit in Calcutta.

mount. The rectangular base of the armature was then placed on the corresponding grooves on a wooden platform.

Today the Indian rhynchosaur Paradapedon stands completed, and the iron armature remains almost hidden from the visitors looking at the mount (Fig. 3). Incidentally, this is the first complete restora- tion of a fossil reptile from the Indian Gondwanas.

ACKNOWLEDGMENTS

During the course of the work, I received valuable and constant encouragement from S. Chattejee. Dr. Chattejee and D. K. Rudra critically reviewed the manuscript and offered important suggestions. Shyama Das also cooperated with me during the preparation work. I am indebted to Edwin H. Colbert of the Museum of Northern Arizona in Flagstaff for critically appraising the final draft.

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