A Taxonomic Revision of the Leptodactylid Frog Genus Syrrhophus Cope Part 1

A Taxonomic Revision of the Leptodactylid Frog Genus Syrrhophus Cope.

by John D. Lynch.

INTRODUCTION

Cope (1878) proposed the genus _Syrrhophus_ for a medium-sized leptodactylid frog from central Texas; in the ensuing 75 years the genus was expanded to include a heterogeneous group of frogs ranging from Texas to Peru. Taylor (1952) and Firschein (1954) limited the genus to several species of frogs occurring in Guatemala, Mexico, and Texas.

Lynch (1968) provided a definition of the previously loosely-defined genus.

With the exception of Taylor (1952), who treated the Costa Rican species, none of these authors dealt with the present status of the nineteen species erroneously a.s.signed to _Syrrhophus_. These species are listed in Tables 1 and 2 with the name currently applied. Some of them are new combinations and their justifications will be published elsewhere. Gorham (1966) is the most recent author to include South American species in the genus _Syrrhophus_.

Smith and Taylor (1948) recognized two species groups of the genus in Mexico, an eastern and a western group (here termed complexes for purposes of discussion), separated on the basis of the number of palmar (metacarpal) tubercles (three palmar tubercles in the members of the eastern complex and two in those of the western complex). Duellman (1958) reviewed the species of the genus occurring in western Mexico and concluded that there were five species (two polytypic). Dixon and Webb (1966) described an additional species from Jalisco, Mexico. The distributions of some species have been extended, but otherwise the western complex of species remains unchanged since Duellman's review.

Smith and Taylor (1948) recognized seven species of the genus in eastern Mexico. Firschein revised the eastern complex (as then understood), and in so doing added one new species and treated _Syrrhophus verruculatus_ as a _nomen dubium_. Dixon (1957) redefined the related genus _Tomodactylus_ and transferred _T. macrotympanum_ Taylor to the genus _Syrrhophus_. Neill (1965) described a new subspecies of _S. leprus_ from British Honduras. Two species (_S. gaigeae_ and _S. marnockii_) were recognized in Texas until Milstead, Mecham, and McClintock (1950) synonymized _S. gaigeae_ with _S. marnockii_. Thus, at present, nine species (one polytypic) are recognized on the eastern slopes and lowlands from central Texas to British Honduras. These are currently placed on one species group equivalent to the western complex reviewed by Duellman (1958).

In the course of preparing an account of the species of _Eleutherodactylus_ occurring in Mexico and northern Central America, it became necessary to reexamine the status of the genus _Syrrhophus_ and its nominal species. It soon became evident that there were more names than species, that some previously regarded species were geographic variants, and that the eastern and western groups (complexes here) were artificial divisions of the genus. I conclude that there are seven species (one polytypic) of _Syrrhophus_ in eastern Mexico, Texas, and El Peten of Guatemala, and seven species (one polytypic) in western Mexico.

The current status of each of the 23 names correctly a.s.signed to the genus is presented in Table 3.

The fourteen species recognized by me are placed in five species groups.

Two of these groups are presently placed in the western complex (_modestus_ and _pipilans_ groups) and three in the eastern complex (_leprus_, _longipes_ and _marnockii_ groups). The two complexes do not correspond exactly with the eastern and western groups of Smith and Taylor (1948), Firschein (1954), and Duellman (1958) since _S. rubrimaculatus_ is now a.s.sociated with the eastern _leprus_ group.

The definitions and contents of the five species groups are as follows:

_leprus_ group: digital pads not or only slightly expanded, rounded in outline; first finger longer or shorter than second; snout ac.u.minate or subac.u.minate, not rounded; outer metatarsal tubercle conical; digits lacking distinct lateral fringes.

content: _cystignathoides_, _leprus_ and _rubrimaculatus_.

_longipes_ group: digital pads widely expanded, triangular in outline; first finger shorter than second; snout ac.u.minate; outer metatarsal tubercle not conical; digits bearing lateral fringes.

content: _dennisi_ and _longipes_.

_marnockii_ group: digital pads expanded, rounded to truncate in outline; first finger equal in length to second or slightly shorter; snout rounded; outer metatarsal tubercle not conical; digits lacking lateral fringes; generally stout-bodied frogs.

content: _guttilatus_, _marnockii_, and _verrucipes_.

_modestus_ group: digital pads expanded, truncate in outline; first and second fingers subequal in length, first usually slightly shorter than second; snout subac.u.minate; inner metatarsal tubercle twice as large (or larger) as outer metatarsal tubercle; digits bearing poorly-defined lateral fringes.

content: _interorbitalis_, _modestus_, _nivocolimae_, _pallidus_, and _teretistes_.

_pipilans_ group: digital pads not or only slightly expanded, truncate in outline; first finger equal in length to second; snout subac.u.minate; metatarsal tubercles subequal in size; digits lacking lateral fringes.

content: _pipilans_.

_Acknowledgments._--For loan of specimens, I am indebted to Richard J.

Baldauf, Texas A & M University (TCWC); W. Frank Blair, University of Texas (TNHC); Charles M. Bogert and Richard G. Zweifel, American Museum of Natural History (AMNH); James E. Bohlke and Edmond V. Malnate, Academy of Natural Sciences of Philadelphia (ANSP); Robert F. Inger and Hymen Marx, Field Museum of Natural History (FMNH); Ernest A. Liner (EAL); Michael Ovchynnyk, Michigan State University collection (MSU); James A. Peters, United States National Museum (USNM); Douglas A.

Rossman, Louisiana State University Museum of Zoology (LSUMZ); Hobart M.

Smith, University of Illinois Museum of Natural History (UIMNH); Charles F. Walker, University of Michigan Museum of Zoology (UMMZ); and John W.

Wright, Los Angeles County Museum (LACM). Specimens in the collection at the University of Kansas Museum of Natural History are identified as KU.

The abbreviations EHT-HMS refer to the Edward H. Taylor-Hobart M. Smith collection and FAS to the Frederick A. Shannon collection. The type-specimens from these collections are now in the Field Museum of Natural History and the University of Illinois Museum of Natural History.

I have profited from discussions concerning this problem with several persons, most notably William E. Duellman, Hobart M. Smith, Edward H.

Taylor and Charles F. Walker. Nevertheless, the ideas and conclusions presented here should not be construed as necessarily reflecting their opinions.

David M. Dennis executed all of the figures, and my wife, Marsha, typed the ma.n.u.script.

_Materials and Methods._--In the course of this study, 1003 specimens of the genus were examined. The holotypes of 21 of the 23 nominal species are extant; I have examined 19 of these. Nine measurements were taken, and five ratios computed for each of 338 specimens. Females are available for all species but one; thus, measurements were taken on individuals of both s.e.xes.

a.n.a.lYSIS OF CHARACTERS

_Size and proportions._--Frogs of this genus range in size from 16 to 40 mm. in snout-vent length. Five species are relatively small: _S. cystignathoides_, _modestus_, _nivocolimae_, _pallidus_ and _rubrimaculatus_; one, _S. longipes_, is relatively large, and the remaining eight species are intermediate in size (22-30 mm.).

Males are generally smaller than females and have proportionately longer heads and usually larger tympani. No significant differences were found among proportions, except that _S. longipes_ has a larger tympanum/eye ratio than any other species. Frogs in the _Syrrhophus marnockii_ group tend to have shorter shanks and feet, thereby giving those species a more stocky appearance. However, the differences are not significant.

A summary of the data on size and proportions for the frogs of the genus _Syrrhophus_ is given in Tables 4, 5, and 6.

_Hands and Feet._--Taylor and Smith (1945), Smith and Taylor (1948), Firschein (1954) and Duellman (1958) discussed the value of the palmar tubercles in identifying frogs of this genus. The eastern complex in general has a well-developed outer palmar tubercle (Fig. 1) in distinction to the western complex in which the outer palmar tubercle is reduced or absent (Fig. 2). Dixon and Webb (1966) imply that the outer palmar tubercle is rarely absent but is usually smaller than the first supernumerary tubercle of the fourth finger. My study of the western species demonstrates that the outer palmar tubercle is indeed usually present and smaller than the first supernumerary tubercle.

Differences in interpretation of the terms "unexpanded" and "narrow," as well as differences in techniques of preservation, have led to confusion of the reported digital shapes in various species. Constant specific differences are evident in the hands (Fig. 1). Except in the cases of excessive uptake of fluids, all species have a terminal transverse groove at the tip of each digit. Taylor (1940b) stated that _S. smithi_ lacked grooves, but examination of the holotype reveals faint grooves at the tops of the digits. _Syrrhophus guttilatus_, _leprus_, _pipilans_, and _verrucipes_ lack lateral fringes on the fingers. Lateral fringes are well developed in the _longipes_ and _modestus_ groups but poorly defined or absent in the other members of the genus. The digital pads of the frogs of the _longipes_ group are much broader than those of the other species and are narrowest in the frogs of the _leprus_ group.

Supernumerary tubercles are present on the palmar surfaces of all species of the genus.

In _S. cystignathoides_ and _leprus_, the first finger is longer than the second, and the first two fingers are equal in length in _guttilatus_ and _marnockii_. In the other species the first finger is shorter than the second.

Supernumerary tubercles are well developed on the plantar surfaces in all species, except _S. guttilatus_, in which they are poorly defined (Fig. 3). The relative sizes of the metatarsal tubercles has been used in the cla.s.sification of the species and species groups of _Syrrhophus_.

The metatarsal tubercles are similar in all species of the eastern complex (including _rubrimaculatus_); the outer tubercle is always about one-half the size of the ovoid inner metatarsal tubercle. In the _leprus_ group the outer tubercle is conical and compressed. The metatarsal tubercles of _pipilans_ are about the same size, or the outer is slightly smaller than the inner. In the _modestus_ group the outer metatarsal tubercle is about one-third the size of the inner.

All species, except _guttilatus_, have well-defined to poorly defined lateral fringes on the toes. All species have expanded toe pads. The fifth toe is usually shorter than the third, but the second is equal in length to the fifth in some specimens of _S. cystignathoides_ and _S. marnockii_. _Syrrhophus nivocolimae_ is the only species with tubercles along the outer edge of the tarsus; this is merely a reflection of the highly tuberculate nature of the skin in this species.

_Skin texture._--The skin of the dorsum is smooth or very weakly pustular in all species of the genus except _nivocolimae_ and _verrucipes_. The dorsal surfaces of _nivocolimae_ are warty; in _verrucipes_ the skin is pustular. The skin of the venter is areolate in _cystignathoides cystignathoides_, _dennisi_ and _verrucipes_ but is smooth in all other species of the genus.

[Ill.u.s.tration: FIG. 3: Plantar views of feet of four species of the eastern complex of _Syrrhophus_. (A) _guttilatus_ (UIMNH 55519, 6), (B) _leprus_ (UIMNH 42726, 6), (C) _verrucipes_ (UIMNH 15995, 6), and (D) _longipes_ (TCWC 12179, 4.6).]

_Color pattern._--As is evident in the diagnoses, the color patterns of given populations have been regarded as useful in separating the species and subspecies. Duellman (1958) suggested that the coloration, with the exception of _modestus_, was a dark ground color with pale markings. It is a moot point whether the frogs have light spots on a dark background or have a light background with an extensive reticulate dark pattern. The venters are gray or white, and the vocal sac is nearly black in some species. Interorbital dark bars or triangles are absent in only two species of the eastern complex, _cystignathoides campi_ and _marnockii_; the latter lacks a supratympanic stripe, which is present in the other members of the eastern complex. _Syrrhophus interorbitalis_ and _nivocolimae_ have light interorbital bars; these bars occur in only one other population of the genus (_S. c. cystignathoides_). Bars on the thighs are ill defined or absent in the members of the _marnockii_ and part of the _modestus_ groups. The color in life is noted in the species accounts.

_Voice._--The voices of all _Syrrhophus_ can be described as a single short chirp or peep; without audiospectrographic a.n.a.lyses the significance of the differences between a chirp, peep, or short whistle cannot be appreciated. Martin (1958) and Wright and Wright (1949) reported multi-noted calls, and one collector of _S. verrucipes_ noted the frog "trilled."