Henry C. Raven

PART I: PAIRED FINS AND GIRDLES IN OSTRACODERMS, PLACODERMS, AND OTHER PRIMITIVE FISHES

How did the paired fins and girdles of the earlier vertebrates arise? This classic and perennial question is gradually being answered by converging investigations in the fields of palaeontology, comparative anatomy and embryology. To cite only some of the later contributions to the subject, we may mention : (1) the numerous discoveries of Dr. Lauge Koch and his staff (especially Stensio and SaveSoderbergh) among the Devonian fishes of East Greenland; (2) the valuable papers by Watson, Westoll, Moy-Thomas, and others on the Devonian fishes of Great Britain and eastern Canada; (3) the careful descriptions of ontogenetic stages in the limbs of recent amphibians by Schmalhausen, Steiner, and Holmgren; (4) the intensive and extensive analyses of the interrelations of nerves, muscles, and skeletal parts in the pectoral girdle and limbs of vertebrates by Brazier Howell; (5) the description of the pectoral girdle and limb of the lower Carboniferous fish Suuripterus by one of us; (6) the synthesis of palaeontological and morphological data by Romer and Byrne. All this has brought the general problem to a critical phase which will be discussed below. The problem of the origin and evolution of the paired appendages and girdles has usually been considered as if it could be settled by itself, but inasmuch as these structures are merely parts of an organic whole the question of their derivation is obviously connected with other problems relating to the several ways in which the known fossil and recent amphibians may have derived the complex patterns of their skulls, vertebral columns, brains, circulatory systems, and the like. This in turn is but part of a still larger picture of the origins and subsequent histories of all the lqwer classes of vertebrates. In the latter field the cumulative result of more than a century of investigation is now quite rapidly revealing the broad outlines, although there is still great need for more precisc knowledge of details. The oldest forerunners of the fishes and higher vertebrates known to palaeontologists are the Palaeozoic ostracoderms. These formsare barely indicated in the Ordovician and are chiefly represented near the close of their range in theupper Silurian and Devonian. It used to be customary to dismiss them as aberrantly specialized early side branches of the vertebrate stock, but through many explorations and discoveries of the past few decades it has been established that the ostracoderms belong to a

Notes on the Anatomy and Relationships of the Ocean Sunfish (Mola mola)

The fish was caught off Sandy Hook in the lower bay of New York on September 15, 1932. It weighed 175 pounds, which is only about one-tenth the maximum weight recorded by Jordan and Evermann.2 Nevertheless it was a male with fully developed testes. Hence it seems that Mola probably goes on increasing in weight long after the testes attain maturity. The total height from the tip of the dorsal fin to the tip of the anal fin is about 64 inches, the total length 47 inches. Thus the total height is about 1.36 times the length. In the front view the body is deep and keel-like below with a knife-like lower edge in front of the vent. The thickness increases dorsally and there are prominent swellings above the eyes. The ordinary axial musculature is absent and the body is enveloped in a very thick rubber-like skin from two to two and a half inches in thickness. Hence flexure of the body must be slight and movement must be largely confined to side-to-side waving of the high median fins and gentle undulations of the scalloped border of the abbreviated deep tail, which serves also as a rudder. Lateral stability is aided by the wide, more or less truncate pectorals, which have a long range of abduction and adduction. The entire surface of the skin is covered with close-set denticle-like

PART IV: A NEW THEORY OF THE ORIGIN OF THE PELVIS OF TETRAPODS

In the pelvic limb (FIGURE 28) the trarisforrnation is less complicated than in the pectoral limb. The fin of necessity becomes narrow a t the base so that it may swing forward. There is no twisting as in the pectoral limb but merely a bendirig to form 3 knee and ankle joint. Romer’s figure 5 (FIGUHE 29) admirably illustrates what took place if we m3ko allowances for the lirnh’s being attached much too high on the side of the body. The pelvic lirnbs to begin with are beneath the body arid

Discussion and Summary

In order to encourage further morphologic research on this problem we propose the following trial hypotheses: (1) That, by analogy with the better known history of the pectoral girdle, the first part to bcconie enianripated WM the ilium, which may have arisen possibly as an apophyseal knob above the acetabulum, pan’ passu with the increase of the m. extensor femoris. By subsequent growth this iliac “apophysis” extended its sutural boundary downward into the dorsal tliird of the acetabulum. Thus we would have a division into one dorsal branch, the ilium, and a single ventral base, the puboischiadic plate, corresponding to the undivided coracoid of the primitive tetrapods. Again by analogy, the apparently sudden division of the ventral plate into two subcqual park was no major morphological achievement since it evidently did occur when the single coraeoid of the primitive cotylosaurs became subdivided into the anterior and posterior coracoids of the pelycosaurs and therapsids. This hypothesis supposes a gradual upgrowth of the ilium and a rather sudden subdivision of thr ventral plate into pubis and ischium. (2) Our second and preferrrd trial hypothesis (FIGURE 32) siipposcs that near the caudal end of the pubo-ischiadic plate of the ancestral rhipidist two rapidly growing and a t first subequal processes devcloprd : the first grew medially from the acetabulum, forming the ischiuni; the second grcw dorsolrrterally from the acetabulum, forming the ilium. Both these processes were analogous with such apophysrs as the great trochanter of the femur, or the greater tuberosity of the humerus, and their sutural contacts, together with that of the remaining “shaft” of the bone (= pubis) all met in the acetabular depression. As the acetabuluin travelled onto the lateral surface of the pubo-ischiadic plate, it carried with i t all three of its primary contacts (with the pubis in front, the iliac epiphysis above, and the ischial epiphysis posteriorly). In other words, the sutures stayed in the acetabulum and as the ilium and ischium (which were, so to speak, offsets from the parent pelvic rod) grcw larger, the areas bounding the iliac and ischial portions of the acetabulum grew larger at the expense of their parent; the sutural contacts merely emphasized the triradiate character which had been pokntially present as soon as the iliac and ischial apophyses developed.

PART II: A NEW RESTORATION OF THE SKELETON OF EUSTHENOPTERON (PISCES CROSSOPTERYGII, DEVONIAN, QUEBEC) WITH REMARKS ON THE ORIGIN OF THE TETRAPOD STEM

In continuation of our former studies on the evolution of the pectoral and pelvic paddles of rhipidistian fish type into the paired appendages of land-living vertebrates we undertook about two years ago to revise, and if possible to correct, previous restorations of the skeleton of Eusthenopteron foordi Whiteaves, which is from the upper Devonian, Escuminac formation, near Maguasha West, Quebec (Russell 1939). The prime basis for our studies was o, collection of this fossil fkh made for the American Museum of Natural History by Dr. Louis Hussakof in 1906 but this collection was eventually supplemented by several others from the same locality, namely, those of Dr. and Mrs. Horace Elmer Wood, 2nd) Dr. Thomas Barbour of the Museum of Comparative Zoology, Harvard University, Dr. Glenn L. Jepsen of Princeton University. The collections made for the Buffalo Society of Natural Sciences and described by William L. Bryant (1919) were represented by a fine series of photographs, which were kindly sent us by Dr. Bryant. The New York State Museum collection of Eusthenopteron at Albany, New York was studied there by the senior author through the courtesy of Director C. C. Adams. This collection includes the largest known and one of the most complete specimens of this fish, which was described by Hussakof in 1912. To all these persons and institutions we desire to express our most cordial thanks and appreciation, and especially to Mrs. Helen Ziska of the American Museum of Natural History, who, with infinite patience, has made and remade the drawings and successive restorations for the preseht paper.