serological relationship. Their nearest relatives, serologically, seem
to be the carduelines. The classification (Wetmore, 1951) that places
_Passer_ in the same family with the estrildines is not upheld by the
serological data available. _Passer_ is not, serologically, closely
related to any of the birds tested. It is of interest that Beecher
(1953:303-305), on the basis of jaw musculature, places _Passer_ and
the estrildines in separate families (Ploceidae and Estrildidae,
respectively).
_Molothrus_ shows greater serological correspondence to the
richmondenine-emberizine-thraupid assemblage than to any of the other
birds tested. It is definitely set apart from this group, however, and
its position, serologically, is compatible with that based on evidence
from other sources.
There seems to be but little argument among ornithologists that
icterids, fringillids, and ploceids constitute families which are
distinct from one another. If, then, the serological differences
between _Molothrus_ (Icteridae) and _Richmondena_ (Fringillidae),
between _Molothrus_ and _Zonotrichia_ (Fringillidae), and between
_Richmondena_ and _Poephila_ (Ploceidae) are indicative of family
differences, there are four families represented by the birds
involved. _Molothrus_ represents one family; _Piranga_, _Richmondena_,
_Spiza_, _Junco_, and _Zonotrichia_, a second; _Estrilda_, _Poephila_,
_Carpodacus_, and _Spinus_, a third; and _Passer_, a fourth.
CONCLUSIONS
The heterogeneity of the Family Fringillidae has been emphasized by
many authors. The relationships of the species now included in this
Family have been the subject of much discussion and constitute an
important problem in avian systematics.
Sushkin's studies (1924, 1925) of features of the horny and bony
palates have served as a basis for the present division of the Family
into subfamilies. Recently, Beecher (1951a, 1951b, 1953) and Tordoff
(1954) have used these features and others which they thought to be of
value in an attempt to clarify the relationships of the species
involved.
Beecher's work (1951a, 1951b, 1953) on jaw-musculature is a valuable
contribution to our knowledge of the anatomy of passerine birds. His
myological studies were so thorough and his presentation so detailed
that students who disagree with his interpretations can draw their own
conclusions. Beecher (1951b:276) points out that there are two basic
types of skeletal muscle--those with parallel fibers and those with
pinnately arranged fibers. The muscles with pinnate fibers seem to be
more efficient, each muscle having a greater functional cross section
for its bulk than does one with parallel fibers. He assumes that
muscles with parallel fibers are more primitive, phylogenetically,
than are those with fibers arranged pinnately. Since his study of the
jaw muscles of the Icteridae (1951a) revealed that patterns of
jaw-musculature within this Family remain constant regardless of the
methods used in procuring food, he assumes that such patterns may be
used as indicators of relationship throughout the entire oscinine
group. These two assumptions, then, serve as the basis for his
hypothesis concerning relationship and phylogeny within this
assemblage. Beecher (1951b:278-280; 1953:310-312) maintains that
within the Family Thraupidae there are two main lines which lead with
almost no disjunction to the Carduelinae and Richmondeninae. The
thraupid-richmondenine line involves a shift in the nature of the _m.
adductor mandibulae externus superficialis_, which becomes more
pinnate in the richmondenines. This results in greater crushing power.
The thraupid-cardueline line involves a shift in emphasis from the the
_m. adductor mandibulae externus medialis_ to the _m. pseudotemporalis
superficialis_ and the forward advance of the insertion of the latter.
This, also, promotes greater crushing ability. He states that features
of the horny palate and of the plumage provide further evidence of
close relationship of these groups. He includes, therefore, the
Thraupinae, the Carduelinae, and the Pyrrhuloxiinae (=Richmondeninae)
in the Family Thraupidae. Beecher (1953:307) indicates that the
patterns of jaw-musculature of the Parulinae (wood warblers) and
Emberizinae (buntings) are similar and suggests that the buntings had
their origin from the wood warblers. He includes these subfamilies,
therefore, in the Family Parulidae.
Beecher's reasoning may be criticized on several points. It may be, as
he suggests, that muscles with parallel fibers evolved earlier,
phylogenetically, than did muscles with pinnate fibers, but he does
not give adequate consideration, it seems to me, to the possibility
that parallel fibers may also have evolved secondarily from pinnate
fibers. Since Beecher (1951a) found that patterns of jaw-musculature
within the Family Icteridae were conservative, he is reluctant to
admit the possibility of convergence among any of the other families.
Differences in patterns of jaw-musculature are, however, functional
adaptations and like the bill, which is also associated with
food-getting may be subject to rapid evolutionary change. Finally, in
attempting to classify the oscines, he has relied almost entirely on a
single character--the pattern of jaw-musculature.
Tordoff's attempts (1954) to clarify the relationships of the
fringillids and related species are based chiefly on features of the
bony palate. He assumes that since palato-maxillaries seem to be
absent in the majority of passerine birds, their occurrence in certain
nine-primaried oscine groups indicates relationship among these
groups. He points out that these bones, when present, are important
areas of origin of the _m. pterygoideus_ which functions in depression
of the upper jaw and in elevation of the lower jaw. He assumes,
therefore, that palato-maxillaries were evolved to provide for a more
effective action of the _m. pterygoideus_. The need for such action
could be associated with a seed-eating habit. All richmondenines and
emberizines possess palato-maxillary bones either free or fused to the
prepalatine bar, but there is no trace of these bones in the
carduelines. Carduelines, furthermore, possess prepalatine bars that
are characteristically flared anteriorly. This condition does not
exist in the richmondenines or in the emberizines.
Tordoff points out, also, that the irregular, erratic migrations of
the New World Carduelinae are unlike the more regular migrations of
the richmondenines and emberizines. The carduelines, furthermore, are
more arboreal in their habits than are these other groups and exhibit
a decided lack of nest sanitation during the later stages of nesting,
a situation which contrasts with that found in the Richmondeninae and
Emberizinae. He suggests, therefore, that the carduelines are not so
closely related to the richmondenines and the emberizines as
previously has been thought.
Since there are only two cardueline genera, _Loximitris_ and
_Hesperiphona_, endemic to the New World and at least 10 genera with
many species endemic to the Old World, Tordoff (1954:15) suggests an
Old World origin for the carduelines. He strengthens his argument for
this hypothesis by pointing out that in features of the bony palate
and in habits the carduelines resemble the estrildines of the Family
Ploceidae.
Tordoff (1954:29-30) states that the tanagers not only merge with the
richmondenines but also grade imperceptibly into the emberizines. He
includes, therefore, the Richmondeninae, Emberizinae, and Thraupinae
in the Family Fringillidae. He suggests that the carduelines are
ploceids, closely related to the Subfamily Estrildinae, on the basis
of structure of the bony palate, geographic distribution, social
behavior, and habits such as nest-fouling and nest-building.
Tordoff, like Beecher, has based his interpretations chiefly on one
feature--structure of the bony palate. Since this feature also is
associated with food-getting, the possibilities of convergence of
distantly related species with similar habits and divergence of
closely related species with different habits may not be excluded.
The hazard of unrecognized adaptive convergence cannot, of course, be
excluded from most fields of taxonomic research, but some features of
morphology and biochemistry are notably more conservative than others
and undergo slower evolutionary change. Such features are often of
utmost importance in distinguishing the higher taxonomic categories.
Most ornithologists are aware that, within the Order Passeriformes,
patterns of musculature in the leg have evolved at a slow rate and
exhibit little variation within the Order. Differences which do occur,
therefore, probably are significant, especially those that are
consistent between groups of species. As I have pointed out earlier
(p. 184), there are no significant differences in leg-musculature
between the Richmondeninae, Emberizinae, and Thraupidae. Indeed, it is
difficult to define these groups on the basis of leg-musculature. If
these groups are of common origin, the lack of distinct boundaries
between them is not surprising. A muscular band which extends from the
_pars interna_ of the _m. gastrocnemius_ around the front of the knee
is present in every emberizine species that I studied and in the Genus
_Piranga_. With the exception of _Spiza_ none of the richmondenines
possesses this band.
The significant differences in leg-musculature which have been
discussed above (pp. 183-184) distinguish the carduelines from the New
World finches and tanagers. Even the cardueline _Leucosticte_ and the
emberizine _Calcarius_, which resemble one another in general
adaptations and in several myological features of the leg (p. 183),
agree in significant features of the musculature with the respective
groups to which they belong. The carduelines agree in the major
features of leg-musculature with the ploceids which I studied.
The use of serological techniques in taxonomic work has two main
advantages. The biochemical systems involved in such investigations
seem to be relatively slow to change in response to external
environmental influences, and the quantitative nature of the results
obtained makes possible objective measurement of resemblances among
species.
I have pointed out (p. 200) that the carduelines are excluded,
serologically, from the distinct assemblage formed by the
richmondenines, emberizines, and tanagers. Actually, the carduelines
show less serological resemblance to this assemblage than do the
estrildines, and most ornithologists agree that the Estrildinae are
not at all closely related to the Richmondeninae, Emberizinae, and
Thraupidae. _Molothrus_, representing a family (Icteridae) recognized
as distinct from the Family Fringillidae, also more closely resembles
the fringillid assemblage, serologically, than do the carduelines.
Although the Carduelinae constitute a distinct group serologically,
they show greater serological resemblance to the estrildines of the
Family Ploceidae than to any of the other species tested. At least the
carduelines and the estrildines form a group as compact as the
subfamilies of the Fringillidae. Thus, the serological data correlate
well with those obtained from the study of the leg-musculature.
Present systems of classification include the subfamilies Passerinae
and Estrildinae in the Family Ploceidae. _Passer_, however, is less
closely related to the estrildines serologically than are the
carduelines, and is less closely related to the estrildines than
_Molothrus_, an icterid, is to the fringillids. This raises a question
as to the homogeneity of the Family Ploceidae as presently recognized
by most ornithologists. If the Passerinae and the Estrildinae are
placed in a single family, the serological divergence among members of
this group is certainly greater than it is in the Family Fringillidae.
Additionally, Beecher (1953:303-304) found that the estrildines
possess a pattern of jaw-musculature different from those in other
ploceids.
The combined evidence from jaw-musculature and serology has caused me
to conclude that the estrildines should be excluded from the Family
Ploceidae (see below).
In an attempt to clarify the relationships of the Fringillidae and
allied groups, I here review briefly the evidence which has been
presented. From his studies of jaw-musculature (1951a, 1951b,
1953) Beecher concludes that the Pyrrhuloxinae (=Richmondeninae),
the Carduelinae, and the Thraupinae are closely related.
He places these groups in the Family Thraupidae. He excludes the
Emberizinae from this group and places them with the wood warblers
in the Family Parulidae. He suggests that the estrildines constitute
a family (Estrildidae) separate from the Family Ploceidae.
From his studies of certain features of the bony palate Tordoff
(1954:25-26, 32) concludes that the richmondenines, the emberizines,
and the tanagers have a common origin and places these groups in the
Family Fringillidae. He excludes the carduelines from this assemblage,
suggests that they are closely related to the estrildines, and
includes them as the Subfamily Carduelinae in the Family Ploceidae.
In this paper I have presented data obtained from the study of certain
features of morphology and biochemistry which I think are less subject
to the influence of environmental factors than those features studied
by recent workers. It is significant that the data obtained by use of
serological techniques and those obtained from the study of
leg-musculature point to the same conclusions. On the basis of these
data I have drawn several conclusions concerning the relationships of
the groups which I studied.
The richmondenines, emberizines, and tanagers are closely related and
should be included in a single family, Fringillidae. The Carduelinae
and the Estrildinae are closely related subfamilies. Although most
recent classifications place the Estrildinae and Passerinae in the
Family Ploceidae, the serological evidence indicates that these groups
are not closely related. Beecher (1953:303-304) drew the same
conclusion from his study of jaw-musculature (see above). I suggest,
therefore, that the Carduelinae and the Estrildinae be placed in a
family separate from the Ploceidae and that the name Carduelidae
(rather than Estrildidae) be used for this group. At present, neither
is an accepted family name. Because _Carduelis_ Brisson 1760 is an
older name than _Estrilda_ Swainson 1827 and because _Carduelis_ seems
to be a centrally located genus in the family, I have chosen the
former (although the International Rules of Zoological Nomenclature do
not specify that priority must apply in forming family names).
I have been unable to study any of the species included in the
subfamilies Fringillinae (not Fringillinae of Tordoff, see 1954:23-24,
and below) and Geospizinae of recent classifications; thus these
groups have not been discussed above. Beecher (1953:307-308) includes
_Fringilla_ in the Subfamily Carduelinae; he includes the geospizines
in a separate family, Geospizidae, and states that they are derived
from the emberizines. Tordoff (1954:23-24) found that in features of
the bony palate _Fringilla_ and the geospizines resemble the
emberizines and, on this basis, includes them in the Subfamily
Fringillinae.
The Dickcissel, _Spiza americana_, possesses certain features which
merit special discussion. Beecher (1951a:431; 1953:309), on the basis
of jaw-musculature, considers it an icterid. To be sure _Spiza_ is in
many ways an aberrant member of the group to which it is now assigned
(Subfamily Richmondeninae). _Spiza_, serologically, is closely related
to all species of the richmondenine-emberizine-thraupid assemblage.
Within this assemblage its nearest relatives are the richmondenines.
_Spiza_ differs from the other richmondenines studied and resembles
the emberizines and tanagers in the possession of the muscular band
which extends from the _pars interna_ of the _m. gastrocnemius_ around
the front of the knee. This band, in _Spiza_, is smaller, however,
than in any of the other species. No icterid dissected possesses such
a structure. Tordoff (1954:29) states that _Spiza_ is typically
richmondenine in palatal structure and makes the suggestion, with
which I agree, that _Spiza_ is a richmondenine and may be closely
related to the ancestral stock which gave rise to the fringillid
assemblage. The serological position of _Spiza_, approximately
equidistant from the other fringillids (Figs. 22, 23), and the
presence of the small muscular band around the front of the knee
constitute evidence supporting the central position of _Spiza_.
After consideration of evidence from the studies of external
morphology, ethology, myology, osteology, and serology, I propose here
an arrangement of the groups which I have studied and submit for
comparison the arrangements (of these groups) proposed by Beecher and
Tordoff. The names of subfamilies that I have been unable to study are
included in my classification and are placed in brackets.
------------------------+----------------------+-----------------------
| Proposed by Tordoff | Proposed by Beecher
Here proposed: | (1954) on the basis | (1953) on the basis
| of the bony palate: | of jaw-musculature:
========================+======================+=======================
FAMILY PLOCEIDAE | FAMILY PLOCEIDAE | FAMILY PLOCEIDAE
| |
[Subf. Bubalornithinae] |Subf. Bubalornithinae |
| |
Subfamily Passerinae: |Subfamily Passerinae | Subfamily Passerinae
distinguished from the | |
Estrildinae by patterns | |
of jaw-musculature | |
(Beecher, 1953:303-304) | |
and on the basis of | |
comparative serology of | |
saline-soluble proteins.| |
| |
[Subfamily Ploceinae] |Subfamily Ploceinae | Subfamily Ploceinae
| |
[Subfamily Viduinae] |Subfamily Viduinae | Subfamily Viduinae
| |
FAMILY CARDUELIDAE | |
| |
Subfamily Estrildinae: |Subfamily Estrildinae | FAMILY ESTRILDIDAE
similar to the | |
Carduelinae in features | |
of the bony palate and | |
habits (Tordoff, 1954: | |
18-22) and in patterns | |
of leg-musculature and | |
comparative serology | |
of saline-soluble | |
proteins. | |
| |
Subfamily Carduelinae: |Subfamily Carduelinae | [In Thraupidae below]
distinguished from the | |
Fringillidae by features| |
of the palate, | |
geographic distribution,| |
migration patterns, and | |
habits (Tordoff, 1954: | |
14-18) and by patterns | |
of leg-musculature and | |
comparative serology | |
of saline-soluble | |
proteins. | |
| |
FAMILY FRINGILLIDAE: all| FAMILY FRINGILLIDAE | FAMILY PARULIDAE
members of this family | | Subfamily Parulinae
show similarities in | | Subfamily Emberizinae
features of the bony | |
palate (Tordoff, 1954: | |
22-23), patterns of | |
leg-musculature, and | |
in comparative serology | |
of saline-soluble | |
proteins. | | FAMILY THRAUPIDAE
| |
Subf. Richmondeninae |Subf. Richmondeninae | Subfamily
| | Pyrrhuloxiinae
| |
Subfamily Thraupinae |Subfamily Thraupinae | Subfamily Thraupinae
| |
Subfamily Emberizinae |Subfamily Fringillinae| [In Parulidae above]
|(including Emberizinae|
[Subfamily Fringillinae]| and Geospizinae) | Subfamily Carduelinae
| |
[Subfamily Geospizinae] | |
------------------------+----------------------+-----------------------
SUMMARY
It has long been recognized that the Family Fringillidae includes some
dissimilar groups. Specifically, the relationships of the subfamilies
Richmondeninae, Emberizinae, and Carduelinae of the Family
Fringillidae are poorly understood. Data from two recent studies, one
on patterns of jaw-musculature and the other on features of the bony
palate, emphasize the dissimilarity of these subfamilies but have
given rise to conflicting concepts of the relationships of subfamilies
within the Family.
This paper reports the results of studies involving morphological and
biochemical features that I consider less sensitive to external
environmental factors than are features which have been studied
previously. Patterns of leg-musculature were chosen for study because
earlier work showed that muscle patterns in the legs of passerine
birds are highly stable and vary but little. Variations, therefore,
which are consistent in separating groups of species should be
significant. Serological techniques were used because the biochemical
systems involved seem to be relatively slow to change in response to
environmental influences and because the data obtained may be used in
a highly objective manner to measure resemblance among species.
Individual differences in the patterns of leg-musculature were found
to be slight and involved mainly the sizes and shapes of muscles. For
this reason variations involving origin, insertion, or relative
position of a muscle, were judged significant. In leg-musculature the
Richmondeninae, the Emberizinae, and the Thraupidae resemble one
another closely. Several differences in muscle pattern were found,
however, which distinguish these groups from the Carduelinae. The
leg-musculature of the carduelines closely resembles that of the
Ploceidae.
Serological techniques involved the extraction of saline-soluble
proteins from the tissues of the species to be studied. These extracts
were carefully processed and were used as antigens. Formolization of
the antigens was necessary as a means of preventing denaturation of
the proteins by enzymatic activity. Antisera were produced in rabbits.
The method of testing involved turbidimetric analysis of the
precipitin reaction. Utilizing the values for the precipitin tests a
model was constructed which showed the relationships of the eleven
species used in these tests. From a study of the model and the data
used in its construction, it was determined that the Richmondeninae,
Emberizinae, and Thraupidae constitute an assemblage distinct from the
other species studied. The Carduelinae are excluded from the
assemblage and serologically are most closely related to the
Estrildinae. The estrildines, serologically, do not closely resemble
_Passer_, Subfamily Passerinae, although recent classifications place
these two subfamilies in the Family Ploceidae.
Upon consideration of all evidence now available--from external
morphology, ethology, myology, osteology, and serology--several
hypotheses regarding the relationships of the groups studied are set
forth. The richmondenines, emberizines, and tanagers are closely
related subfamilies and are here included in the Family Fringillidae.
The Estrildinae and Carduelinae are closely related subfamilies, but
neither group is closely related to the Passerinae. The estrildines
and carduelines, therefore, are placed in a separate family, the
Carduelidae. In some ways, _Spiza_ is an aberrant member of the
Subfamily Richmondeninae but should be retained in that subfamily. It
is suggested that _Spiza_ is a primitive richmondenine closely related
to the ancestral fringillid stock.
LITERATURE CITED
AMERICAN ORNITHOLOGISTS' UNION
1931. Check-list of North American birds. Fourth edition.
Lancaster, Pa., xix + 526 pp.
BEECHER, W. J.
1951a. Adaptations for food-getting in the American blackbirds.
Auk, 68:411-440, 11 figs.
1951b. Convergence in the Coerebidae. Wilson Bull., 63:274-287,
5 figs.
1953. A phylogeny of the oscines. Auk, 70:270-333, 18 figs.
BERGER, A. J.
1952. The comparative functional morphology of the pelvic
appendage in three genera of Cuculidae.
Amer. Mid. Nat., 47:513-605, 29 pls.
BOYDEN, A.
1942. Systematic serology: a critical appreciation.
Physiol. Zool., 15:109-145, 12 figs.
CHAPIN, J. P.
1917. The classification of the weaver-birds. Bull. Amer. Mus.
Nat. Hist., 37:243-280, 10 pls., 9 figs.
CUMLEY, R. W., and IRWIN, M. R.
1941. Pictorial representation of the antigenic differences
between two dove species. Jour. Hered., 32:178-182,
frontispiece, 2 figs.