Myology and Serology of the Avian Family Fringillidae.
by William B. Stallcup.
INTRODUCTION
The relationships of many groups of birds within the Order Pa.s.seriformes are poorly understood. Most ornithologists agree that some of the pa.s.serine families of current cla.s.sifications are artificial groups. These artificial groupings are the result of early work which gave chief attention to readily adaptive external structures. The size and shape of the bill, for example, have been over-emphasized in the past as taxonomic characters. It is now recognized that the bill is a highly adaptive structure and that it frequently shows convergence and parallelism.
Since studies of external morphology have failed in some cases to provide a clear understanding of the relationships of pa.s.serine birds, it seems appropriate that attention be given to other morphological features, to physiological features, and to life history studies in an attempt to find other clues to relationships at the family and subfamily levels.
This paper reports the results of a study of the relationships of some birds of the Family Fringillidae and is based on the comparative myology of the pelvic appendage and on the comparative serology of saline-soluble proteins. Where necessary for comparative purposes, birds from other families have been included in these investigations.
It has long been recognized that the Fringillidae include dissimilar groups. Recent work by Beecher (1951b, 1953) on the musculature of the jaw and by Tordoff (1954) primarily on the structure of the bony palate has emphasized the artificial nature of the a.s.semblage although these authors disagree regarding major divisions within it (see below).
The Fringillidae have been distinguished from other families of nine-primaried oscines by only one character--a heavy and conical bill (for crushing seeds). Bills of this form have been developed independently in several other, unrelated, groups; as Tordoff (1954:7) has pointed out, _Molothrus_ of the Family Icteridae, _Psittorostra_ of the Family Drepaniidae, and most members of the Family Ploceidae have bills as heavy and conical as those of the fringillids. The ploceids are distinguished from the fringillids by a single external character: a fairly well-developed tenth primary whereas in fringillids the tenth primary is absent or vestigial. Tordoff (1954:20) points out, however, that this distinction is of limited value since in other pa.s.serine families the tenth primary may be present in some species of a genus and absent in others. The Genus _Vireo_ is an example. Furthermore, at least one ploceid (_Philetairus_) has a small, vestigial tenth primary, whereas some fringillids (_Emberizoides_, for example) possess a tenth primary which is rather large and ventrally placed (Chapin, 1917:253-254).
Thus, it is obvious that studies based on other features are necessary in order to attain a better understanding of the relationships of the birds involved.
Sushkin"s studies (1924, 1925) of the structure of the bony and h.o.r.n.y palates have served as a basis for the division of the Fringillidae into as many as five subfamilies (h.e.l.lmayr, 1938:v): Richmondeninae, Geospizinae, Fringillinae, Carduelinae, and Emberizinae.
Beecher (1951b:280) points out that "the richmondenine finches arise so uninterruptedly out of the tanagers that ornithologists have had to draw the dividing line between the two groups arbitrarily." His study of pattern of jaw-musculature substantiates this. He states further that the cardueline finches arise without disjunction from the tanagers. He suggests, therefore, that the two groups of "tanager-finches" be made subfamilies of the Thraupidae and that a third subfamily be maintained for the more typical tanagers. He states that the emberizine finches are of different origin, arising from the wood warblers (1953:307). Beecher (1951a:431; 1953:309) includes the d.i.c.kcissel, _Spiza americana_, in the Family Icteridae, chiefly on the basis of jaw muscle-pattern and the h.o.r.n.y palate.
Tordoff (1954:10-11) presents evidence that the occurrence of palato-maxillary bones in nine-primaried birds indicates relationship among the forms possessing them. He points out that all fringillids except the Carduelinae possess palato-maxillaries that are either free or more or less fused to the prepalatine bar. He points out also that in all carduelines, the prepalatine bar is flared at its juncture with the premaxilla, and that the mediopalatine processes are fused across the midline; noncardueline fringillids lack these characteristics. In addition to the above he cites differences between the carduelines and the "other" fringillids in the appendicular skeletons, in geographic distribution, in patterns of migration, and in habits. Tordoff concludes, therefore, that the carduelines are not fringillids but ploceids, their closest affinities being with the ploceid Subfamily Estrildinae. On the basis of palatal structure, the Fringillinae and Geospizinae are combined with the Emberizinae, the name Fringillinae being maintained for the subfamily. The tanagers merge with the Richmondeninae on the one hand and with the Fringillinae on the other.
On this basis, Tordoff (1954:32) suggests that the Family Fringillidae be divided into subfamilies as follows: Richmondeninae, Thraupinae, and Fringillinae. The carduelines are placed as the Subfamily Carduelinae in the Family Ploceidae.
From the foregoing, it is apparent that the two most recent lines of research have given rise to conflicting theories regarding relationships within the Family Fringillidae. The purpose of my investigation, therefore, has been to gather information, from other fields, which might clarify the relationships of these birds.
Since the muscle pattern of the leg in the Order Pa.s.seriformes is thought to be one of long standing and slow change, any variation which consistently distinguishes one group of species from another could be significant. With the hope that such variation might be found, a study of the comparative myology of the legs was undertaken.
The usefulness of comparative serology as a means of determining relationship has been demonstrated in many investigations. Its use in this instance was undertaken for several reasons: comparative serology has its basis in biochemical systems which seem to evolve slowly; its methods are objective; and its use has, heretofore, resulted in the acc.u.mulation of data which seem compatible, in most instances, with data obtained from other sources.
I acknowledge with pleasure the guidance received in this study from Prof. Harrison B. Tordoff of the University of Kansas. I am indebted also to Prof. Charles A. Leone without whose direction and a.s.sistance the serological investigations would not have been possible; to Professors E. Raymond Hall and A. Byron Leonard whose suggestions and criticisms have been most helpful in the preparation of this paper; and to T. D. Burleigh of the U. S. Fish and Wildlife Service for gifts of several specimens used in this work. a.s.sistance with certain parts of the study were received from a contract (NR163014) between the Office of Naval Research of the United States Navy and the University of Kansas.
MYOLOGY OF THE PELVIC APPENDAGE
General Statement
In an excellent paper in which the muscles of the pelvic appendage of birds are carefully and accurately described, Hudson (1937) reviewed briefly the more important literature pertaining to the musculature of the leg which had been published to that date. A review of such information here, therefore, seems unnecessary.
Myological formulae suggested by Garrod (1873, 1874) have been extensively used by taxonomists as aids in characterizing the orders of birds. Relatively few investigations, however, involving the comparative myology of the leg have been undertaken at family and subfamily levels. The works of Fisher (1946), Hudson (1948), and Berger (1952) are notable exceptions.
The terminology for the muscles used in this paper follows that of Hudson (1937), except that I have followed Berger (1952) in Latinizing all names. h.o.m.ologies are not given since these are reviewed by Hudson. Osteological terms are from Howard (1929).
Materials and Methods
Specimens were preserved in a solution of one part formalin to eight parts of water. Thorough injection of all tissues was necessary for satisfactory preservation. Most of the down and contour feathers were removed to allow the preservative to reach the skin.
In preparing specimens for study, the legs and pelvic girdle were removed and washed in running water for several hours to remove much of the formalin. They were then transferred to a mixture of 50 per cent alcohol and a small amount of glycerine.
All specimens were dissected with the aid of a low power binocular microscope. Where possible, several specimens of each species were examined for individual differences. Such differences were found to be slight, involving mainly size and shape of the muscles. The size is dependent partly on the age of the bird, muscles from older birds being larger and better developed. The shape of a muscle (whether long and slender or short and thick) is due in part to the position in which the leg was preserved; that is to say, a muscle may be extended in one bird and contracted in another. For these reasons, descriptions and comparisons are based mainly on the origin and insertion of a muscle and on its position in relation to adjoining muscles.
Birds dissected in this study are listed below (in the order of the A.
O. U. Check-List):
SPECIES
_Vireo olivaceus_ (Linnaeus) _Leucosticte tephrocotis_ _Seiurus motacilla_ (Vieillot) (Swainson) _Pa.s.ser domesticus_ (Linnaeus) _Spinus tristis_ (Linnaeus) _Estrilda amandava_ (Linnaeus) _Loxia curvirostra_ Linnaeus _Poephila guttata_ (Reichenbach) _Chlorura chlorura_ (Audubon) _Icterus galbula_ (Linnaeus) _Pipilo erythrophthalmus_ _Molothrus ater_ (Boddaert) (Linnaeus) _Piranga rubra_ (Linnaeus) _Calamospiza melanocorys_ _Richmondena cardinalis_ (Linnaeus) Stejneger _Guiraca caerulea_ (Linnaeus) _Chondestes grammacus_ (Say) _Pa.s.serina cyanea_ (Linnaeus) _Junco hyemalis_ (Linnaeus) _Spiza americana_ (Gmelin) _Spizella arborea_ (Wilson) _Hesperiphona vespertina_ (Cooper) _Zonotrichia querula_ (Nuttall) _Carpodacus purpureus_ (Gmelin) _Pa.s.serella iliaca_ (Merrem) _Pinicola enucleator_ (Linnaeus) _Calcarius lapponicus_ (Linnaeus)
Description of Muscles
The descriptions which follow are those of the muscles in the leg of the Red-eyed Towhee, _Pipilo erythrophthalmus_. Differences between species, where present, are noted for each muscle. The term thigh is used to refer to the proximal segment of the leg; the term crus is used for that segment of the leg immediately distal to the thigh.
_+Musculus iliotrochantericus posticus+_ (Fig. 2).--The origin of this muscle is fleshy from the entire concave lateral surface of the ilium anterior to the acetabulum. The fibers converge posteriorly, and the muscle inserts by a short, broad tendon on the lateral surface of the femur immediately distal to the trochanter. It is the largest muscle which pa.s.ses from the ilium to the femur.
Action.--Moves femur forward and rotates it anteriorly.
Comparison.--No significant differences noted among the species studied.
_+Musculus iliotrochantericus anticus+_ (Fig. 3).--Covered laterally by the _m. iliotrochantericus posticus_, this slender muscle has a fleshy origin from the anteroventral edge of the ilium between the origins of the _m. sartorius_ anteriorly and the _m.
iliotrochantericus medius_ posteriorly. The _m. iliotrochantericus anticus_ is directed caudoventrally and inserts by a broad, flat tendon on the anterolateral surface of the femur between the heads of the _m. femorotibialis externus_ and _m. femorotibialis medius_ and just distal to the insertion of the _m. iliotrochantericus medius_.
Action.--Moves femur forward and rotates it anteriorly.
Comparison.--No significant differences noted among the species studied.
_+Musculus iliotrochantericus medius+_ (Fig. 3).--Smallest of the three _iliotrochantericus_ muscles, this bandlike muscle has a fleshy origin from the ventral edge of the ilium just posterior to the origin of the _m. iliotrochantericus anticus_. The fibers are directed caudoventrally, and the insertion is tendinous on the anterolateral surface of the femur between the insertion of the other two _iliotrochantericus_ muscles.
Action.--Moves femur forward and rotates it anteriorly.
Comparison.--No significant differences noted among the species studied.
_+Musculus iliacus+_ (Figs. 4, 5).--Arising from a fleshy origin on the ventral edge of the ilium just posterior to the origin of the _m.
iliotrochantericus medius_, this small slender muscle pa.s.ses posteroventrally to its fleshy insertion on the posteromedial surface of the femur just proximal to the origin of the _m. femorotibialis internus_.
Action.--Moves femur forward and rotates it posteriorly.
Comparison.--No significant differences among the species studied.