were paromomyids gliders? maybe, maybe not

David W. Krause Department of Anatomical Sciences, State University of .New York, Stony Brook, New York 11794-8081, U.S.A

Received 4 December 1990 Revision received 1 February 1991 and accepted 18 February 1991

E;eymords;Paromomyidae, Plesiadapiformes, Dermoptera, Eocene, functional morphology, gliding adaptations.

Were paromomyids gliders? Maybe, maybe not

Beard recently hypothesized that paromomyids were the first mammals to exhibit gliding behavior. He claimed that paromomyids, like the extant dermopteran Cynocephalus (a proficient glider with a well developed patagium that is extended as a web between the digits), have manual intermediate phalanges that are much longer than corresponding proximal phalanges. However, Beard provided no convincing evidence that the isolated phalanges identified as belonging to the manus of the paromomyids Phenacolemur simonsi and Ignaciusgraybullianus are correctly identified and associated. His identifications and postulated associations are but possibilities until directly associated or articulated proximal and intermediate phalanges of the same or similar manual digit are discovered. Indeed, the proximal and intermediate phalanges employed by Beard to argue that P. simonsi had greatly elongated intermediate phalanges on the manus could not possibly have articulated with one another. Although paromomyids may have been gliding mammals, irrefutable or even compelling evidence for this inference has not been presented.

Journal of Human Euolution (1991) 21, 177-188

Introduction

Paromomyids are a group of small mammals from the early Tertiary of both North

America and Europe that have long been regarded by most workers as members of the

Plesiadapiformes. Plesiadapiformes, in turn, have long been regarded by most workers as

primates or a sister taxon of Primates (e.g., Matthew & Granger, 1921; Gidley, 1923;

Simpson, 1945; Gingerich, 1986, 1989; Martin, 1990b and references therein). Evidence for

the affinities ofparomomyids has come entirely from the dentition and cranial skeleton. The

lack of definitely associated postcranial material has precluded not only the possibility of

employing postcranial characters in phylogenetic analyses, but also of inferring the loco-

motor habits of paromomyids. Recent announcements by Beard (19896, 1990) of the dis-

covery of postcranial elements of Phenacolemur simonsi and Ignacius graybullianus, representing

two of the five known genera of Paromomyidae, are therefore of considerable interest and

importance. Beard concluded that paromomyids were not primates but instead were

dermopterans and that paromomyids, like the only living dermopteran, Cynocephalus (the

“flying lemur”), were gliders. These conclusions appear to have gained rapid acceptance

(Martin, 1990a; Shipman, 1990; Pettigrew, 199 1) and have been touted as among the 50

most significant scientific discoveries of 1990 (Zimmer, 199 1) , but the evidence employed to

infer gliding behavior in paromomyids is unconvincing.

Beard’s (1990) conclusion that paromomyids possessed a patagium with significant inter-

digital webbing and that they represent the earliest known mammalian gliders rests solely on

one character, the relative length of proximal and intermediate phalanges of the manus (not

the manus and pes, as stated by Martin, 1990a). Beard (1990, p. 340) argued that since the manual intermediate phalanges ofparomomyids “are much longer than their corresponding

proximal phalanges,” and since this condition is seen among Recent mammals only in the

“mitten-gliding” Cynocephalus (and in edentates, which, for good reasons, are dismissed from

further consideration), then paromomyids must also have been gliders. Much of the under-

lying indirect evidence and reasoning employed by Beard (1989b, 1990) in identifying and

0047F2484/91/09Oi 77 + 12 $03.00/O 0 1991 Academic Press Limited

178 D. W. KRAUSE

associating isolated proximal and intermediate phalanges OfPhenacolemur simonsi and Ignacius

graybullianus can be found in his doctoral dissertation (1989a). However, the evidence

and arguments presented there, as well as in his shorter publications (19896, 1990), are

insufficient to demonstrate that the isolated phalanges have been correctly identified and

associated. Indeed, first-hand examination of the phalanges assigned by Beard to P. simonsi

and I. graybullianus confirms that some of his identifications and associations are suspect and,

in at least one important instance, erroneous.

Abbreviations

UM University of Michigan, Ann Arbor, Michigan

USGS United States Geological Survey, Denver, Colorado

USNM United States National Museum, Washington, D.C.

Materials

All of the isolated phalanges assigned to Phenacolemur simonsi and Ignacius graybullianus by

Beard (1989a,b, 1990) were extracted from a single calcareous nodule (designated 8ABC and

originally about two cubic meters in volume) recovered from an early Eocene (Wasatchian

Land-Mammal Age) site in or near UM fossil vertebrate locality SC-4 in the northern

Bighorn Basin of northwestern Wyoming. None of these phalanges was found in association with dental remains (Beard, 1989a, p. 10). B eard identified several of the phalanges as

coming from the manus and, implicitly, from the same or similar digital ray. His identifi-

cations are based on comparisons with incomplete phalanges preserved in partial skeletons

(including dental remains), also from Wasatchian horizons in the Bighorn Basin, of two other

species: Phenacolemur praecox (UM 66440 and UM 86352, which, although found 9 years

apart, are apparently from one individual) from UM locality SC-46, and Phenacolemur sp., cf.

P. jepseni (USGS 17847) from USGS locality D- 165 1. None of the phalanges in these two

skeletons was found in direct articulation with another (Beard, 1989a). The following is a list

of all phalangeal specimens assigned by Beard to members of the Paromomyidae (dorsal and

side views of the most complete specimens of proximal and intermediate phalanges are

illustrated at the same scale in Figure 1 to facilitate comparisons) :

Phenacolemurpraecox

UM 6644&a nearly complete proximal phalanx missing a small portion of the distal end

(Figure 1H) and the proximal end of an intermediate phalanx.

UM 86352-the proximal end of a proximal phalanx, the distal ends of two proximal

phalanges [one of which is complete to approximately mid-shaft (Figure lI)], and the proximal end of an intermediate phalanx.

Phenacolemur sp., cf. P.jepseni

USGS 17847-a nearly complete proximal phalanx missing the distal end (Figure 1 J), the

proximal ends of two proximal phalanges, mid-shaft segments of two proximal phalanges,

the distal end of a proximal phalanx, the proximal end of an intermediate phalanx

(Figure 1 A), and an approximately two-thirds complete distal phalanx (missing the distal

terminus) tentatively identified by Beard (1989a, p. 187) as belonging to the manus.

WERE PAROMOMYIDS GLIDERS? 179

Phenacolemur simonsi

USNM 442247-a nearly complete proximal phalanx missing the distal end (Figure 1 L) . USNM 442248-a complete proximal phalanx (Figure 1 M) tentatively identified by Beard

(1989a, p. 181; 1990, p. 340) as belonging to the manus.

USNM 442249-a complete proximal phalanx (Figure 1N) tentatively identified by Beard

(1989a, p. 181) as belonging to the manus.

USNM 442250-a complete intermediate phalanx (Figure 1E) tentatively identified by

Beard (1989a, p. 183) as belonging to the pes.

USNM 442251-a complete intermediate phalanx (Figure 1F) tentatively identified by


USNM 442252-a complete intermediate phalanx (Figure IG) tentatively identified by


USNM 442254-a complete intermediate phalanx (Figure ID) tentatively identified by

Beard ( 1989a, p. 183; 1990, p. 340) as belonging to the manus.

Ignacius graybullianus

USNM 442253-a complete intermediate phalanx (Figure 1B) tentatively identified by

Beard (1989a, p. 257) as belonging to the manus.

USNM 442255-a complete intermediate phalanx (Figure 1C) tentatively identified by

Beard ( 1989a, p. 270) as belonging to the pes.

USNM 442256-a complete proximal phalanx (Figure 1K) tentatively identified by Beard

(1989a, p. 255) as belonging to the manus.

Discussion

Despite the absence of articulated material and despite numerous caveats, Beard (1989a,b,

1990) believed that there is sufficient evidence to identify, however tentatively, the isolated

phalanges of various paromomyid species as coming from either the manus or pes and as

coming from digital rays that were similar enough to warrant comparisons of proportions

between proximal and intermediate phalanges. In this context, it is important to note that

in many mammals that have not undergone digital reduction or loss it is difficult, if not

impossible, to distinguish either proximal or intermediate phalanges from different manual

digits (especially digits II to V). Furthermore, it is extremely difficult to distinguish isolated

phalanges of the manus from those of the pes. In discussing the phalanges of Phenacolemur

simonsi, for instance, Beard (1989, p. 178) admits that “there is no direct evidence that any of

the proximal phalanges known for Phenacolemur represent the manus as opposed to the pess,”

and (p. 183) that “there is no direct evidence that any of the intermediate phalanges known

for Phenacolemur represent the manus as opposed to the pes.” Therefore, in the absence of any

“direct” evidence to the contrary, the elements identified by him as manual proximal

phalanges could be from a relatively short digit on the manus or pes, and the elements

identified by him as manual intermediate phalanges from a relatively long digit on the

manus or pes. It is thus crucial to examine the indirect evidence presented by Beard in his

identification of proximal and intermediate manual phalanges of paromomyids.

In part because there are not two clear size morphs of proximal phalanges among those

that he allocated to individual species of Phenacolemur, Beard concluded that the proximal

phalanges of the manus are similar in length to those of the pes. When discussing the

phalanges of P. simonsi, Beard ( 1989a, pp. 178, 18 1) argued:

80 D. W. KRAUSE

Phenaco- lemur sp., ct.

P. iepseni

3

Phenacolemur praecox

6&l UM

86352

H I

lgnacius

grc

i :

P

1 USNM

442253

B

f- ! USNM

442255

C

Phenecolemur slmonsl

r

i! USNM

442254

D

E USNM

442250

E

r-l

! USNM

442251

F

Pheneco- bmur sp.,ct P. lepsenl

9 USGS 17547

J

& 3 a

USNM 442252

G

Ignaolus ;yra ybull-

c

l!l USNM

442256

K

PhWfUCOlenW SimOnSi

D USNM

442247

L

c

!I USNM

442246

M

c

F USNM

442249

N


“There are no apparent morphologic differences between the manual and pedal proximal phalanges of extant Qnocephalus, although the manual proximal phalanges of this genus do differ

from those of the pes in being longer proximodistally. Given the relatively large number of proximal phalanges known for [all species ofl Phenacolemur (8 relatively complete specimens), it seems unlikely that they all represent either the manus or the pes. Therefore, it seems probable that the difference in length found in the manual and pedal proximal phalanges of Cynocephalus was not characteristic of (or at least was less emphasized in) Phenacolemur.”

Beard’s postulate that some of the proximal phalanges ofPhenacolemur (the six most complete

of which are illustrated in Figure 1) must be from the manus and others from the pes is

unfounded. First, it assumes that the large proximal phalanx (USNM 442256, Figure 1K)

discovered in nodule 8ABC along with three smaller proximal phalanges (USNM 442247,

442248,442249, Figure lL-N) assigned to P. simonsi has been correctly attributed to Ignacius

graybullianus. Second, proximodistal length can be measured in only two of the eight speci-

mens (USNM 442248, USNM 442249). Third and most importantly, ofthe eight specimens,

two have been allocated to P. praecox, three to P. sp., cf. P. jepseni, and three to P. simonsi.

The existence of eight “relatively complete” proximal phalanges of Phenacolemur is largely

irrelevant since the three species of Phenacolemur to which they have been assigned are of

different sizes (as inferred from dentitions). Indeed, because manual phalanges have a

greater likelihood of being preserved with other manual phalanges than with pedal

phalanges (and vice versa), one could make the assumption, which runs counter to Beard’s,

that each of the very small species samples listed above probably contains either only manual

or only pedal phalanges. In fact, however, a choice between these two alternatives cannot be

made. With such small samples there is no compelling evidence to indicate whether the

manual proximal phalanges of individual paromomyid species were shorter than, longer

than, or the same length as those of the pes. Thus, there is no evidence, direct or indirect,

enabling one to identify proximal phalanges as manual or pedal for any of the species samples

of Phenacolemur (or Ignacius) While Beard argued, largely on the basis of frequency data, that the manual and pedal

proximal phalanges ofP. simonsi differ from those of Cynocephalus in being of the same length,

he argued that the manual and pedal intermediate phalanges ofP. simonsi resembled those of

Cjnocephalus in being of different lengths. His argument concerning the latter elements is as

follows (1989a, p. 183):

“The intermediate phalanges ofPhenacolemur show a very close morphologic resemblance to those of extant Cynocephalus. As noted previously, the intermediate manual phalanges ofthe latter genus differ from those ofthe pes in being more elongated. Among the intermediate phalanges attributed here to Phenacolemur simonsi, one specimen (USNM 442254; maximum proximodistal length, L= 8.60 mm)

Figure 1. Phalanges as identified and attributed to species of the Paromomyidae by Beard (1989a,b, 1990). First row, intermediate phalanges in dorsal view (distal end at the top). Second row, the same intermediate phalanges in side view (palmar aspect to the left). Third row, proximal phalanges in dorsal view (distal end at the top). Fourth row, the same proximal phalanges in side view (palmar aspect to the left). (A) Phenacolemur sp., cf. P. jepseni, USGS 17847; (B) Ignacius graybullianus, manus, USNM 442253; (C) I. graybullianus, pes, USNM 442255; (D) P. simomi, manus, USNM 442254; (E) P. simonsi, pes, USNM 442250; (F) P. simonsi, pes, USNM 442251; (G) P. simonsi, pes, USNM 442252; (H) P.praecox, UM 66440; (I) P.praecon, UM 86352; 0) P. sp., cf. P. jepseni, USGS 17847; (K) Z.graybullianus, manus, USNM 442256; (L) P. simonsi, USNM 442247; (M) P. simonri, manus, USNM 442248; (N) P. simonsi, manus, USNM 442249.

182 D. W. KRAUSE

is considerably longer than are the other three (USMN 442250, L = 6.15 mm; USNM 44225 1, L=6.00 mm; USNM 442252, L=6.05 mm). On the basis of the greater elongation of USNM 442254, it is tentatively concluded, by analogy with extant Cynocephalus, that USNM 442254 is a manual intermediate phalanx of Phenacolemur simonsi, whereas the three shorter specimens listed above are believed to represent the pes of this species.”

It is pertinent to point out that, although Beard (1989a, p. 184) asserts that “theintermediate

manual phalanx of Phenacolemur simonsi is closely similar to that of extant Cynocephalus”, the

only similarity listed is the “marked degree ofelongation of the phalangeal shaft” whereas the

differences include the presence in Cynocephalus of “a more proximally projecting dorsal

tubercle on the dorsal side of the proximal articular surface, relatively less marked tuberosi-

ties for insertion of M. flexor digitorum superficialis on the palmar side of the proximal part of

the phalangeal shaft, and a more strongly trochleiform distal articular surface” (p. 187).

Therefore, Beard’s identification of USNM 442254 (F’g 1 ure 1D) as a manual intermediate

phalanx of P. simonsi appears to be based on size alone and contains a strong element of

circular reasoning since the conclusion that P. simonsi was a gliding mammal is, in fact, based

on the presence of relatively long intermediate manual phalanges, as in Cynocephalus. In other

words, Beard has reasoned that the manual intermediate phalanges of P. simonsi are longer

than those of the pes because they resemble the condition in Cynocephalus, and that they

resemble the condition in Cynocephalus because they are longer than those of the pes. Without

the analogy to Cynocephalus and in the absence of any other evidence, it is equally likely,

assuming that these four phalanges are attributable to P. simonsi, that the three short ones

(USNM 442250, 442251, 442252, F’g I ure lE-G) are from the manus and the long one

(USNM 442254, Figure 1 D) from the pes. However, even this assumption is unfounded since

there is purported to be another, larger taxon, I. graybullianus, represented in the same lime-

stone nodule. Thus, it is also possible that the three short intermediate phalanges could be

from either the manus or the pes of P. simonsi, and the long phalanx from either the manus or

the pes of I. graybullianus (see also below).

Beard’s identifications of the proximal and intermediate manual phalanges of Zgnacius are

based, in large part, on the validity ofhis identifications of those ofPhenacolemur. For instance,

Beard (1989a, pp. 255, 257) identifies a proximal phalanx (USNM 442256, Figure 1K) as

coming from the manus of Ignacius graybullianus rather than from the pes “because its distal

articular surface conforms closely with the proximal articular surface of USNM 442253

[Figure IB], an intermediate phalanx that is believed to represent the manus of the species on

the basis of its relatively great elongation and its greater’robusticity compared to USNM

442254 [Figure lD], a manual intermediate phalanx of P. simonsi from the same calcareous

nodule.” However, if there is reason to doubt the identifications of the phalanges of

Phenacolemur as coming from either the manus or the pes, then there is also reason to doubt the

identifications of the phalanges of Ignacius as being either manual or pedal.

Concerning attribution of the phalanges to either Phenacolemur simonsi or Ignacius

graybullianus, Beard (1989a, pp. 247-248) states that:

“Because Phenacolemur simonsi and Ignacius graybullianus are closely related, it is possible that some of the postcranials allocated to 1. graybullianus . . . in fact represent P. simonsi (and vice versa). Until directly associated craniodental and postcranial remains of one of these species are discovered, this possibility cannot be fully discounted. However, judging from their dentitions, Ignacius graybullianus was a significantly larger animal than Phqzacolemur simonsi (Bown and Rose, 1976; Conroy, 1987; Fleagle, 1988). Thus, I have assigned the smaller paromomyid postcranial specimens from the 8ABC


calcareous nodule to Phenacolemur simonsi, while the larger paromomyid postcranial elements from this faunule are here attributed to Ignaciusgraybullianus.”

However, Beard ( 1989a, p. 257) points out that, although it is slightly more robust, the single

intermediate phalanx (USNM 442253, length=8.8 mm: Figure 1B) assigned by him to 1.

gruybullianus is only 0.2 mm longer than the only complete, purportedly manual intermediate

phalanx (USNM 442254, length = 8.6 mm: Figure 1D) assigned to P. simonsi and that “it is

possible that the two specimens are actually conspecific.” I fully concur with this latter

assessment. It seems as likely, or even more likely, that the slight difference in robusticity and

the 0.2 mm difference in length between USNM 442253 and USNM 442254 is owing to ( 1)

intraindividual variation between intermediate phalanges of different digital rays (of the

manus or pes) or (2) intraspecific variation between intermediate phalanges of the same (or

similar) digital ray, as it is to (3) interspecific variation between intermediate phalanges of the

same (or similar) digital ray.

If Beard’s allocation of intermediate phalanges of the same or similar manual digit to

Ignaciusgraybullianus and Phenacolemur simonsi are correct, then that of I. graybullianus (USNM

442253, Figure 1B) is only 2.3% longer than that of P. simonsi (USNM 442254, Figure 1 D).

By contrast, the proximal phalanx (USNM 442256, Figure 1K) identified by Beard as

coming from the manus of I. graybullianus is 30-33% longer than those assigned by him to

P. simonsi (USNM 442248 and 442249, Figure lM, N). Although sample sizes ofwasatchian

P. simonsi and I. graybullianus dentitions are small, examination of average linear molar

dimensions indicates that Wasatchian I. graybullianus is, on average, approximately 34.3%

larger (range = 17.1-53.8Oj,) than P. simonsi (Bown & Rose, 1976). Clarkforkian specimens of

I. graybullianus are, on average, even slightly larger than are Wasatchian specimens of that

species (Rose, 1981). Therefore, if molar tooth size reflects body size in these species, indi-

viduals of I. graybullianus were clearly much larger than those of P. simonsi. Rather than

assigning USNM 442253 (Figure 1B) to 1. graybullianus and USNM 442254 (Figure lD),

which is only slightly smaller, to P. simonsi, it seems that an equally or more parsimonious

argument could be made that both specimens pertain to 1: graybullianus and that neither are

attributable to P. simonsi.

Furthermore, it should be noted that even ifBeard’s (1990, p. 340) assignments ofproximal

and intermediate manual phalanges to Phenacolemur simonsi and Ignacius graybullianus are

correct, his conclusion that paromomyids, as a group, have “intermediate phalanges that are

much longer than their corresponding proximal phalanges” (italics added) is hardly credible

since the intermediate (USNM 442253, Figure 1B) and proximal (USNM 442256, Figure

1Kj phalanges attributed by him to the manus of I. graybullianus are nearly equivalent in

length. This observation also runs counter to his (1989b, p. 13A) statement that “the

manual phalanges of Zgnacius possess all of the (otherwise unique) traits also found in extant

Qmocephalus.” According to Beard’s own measurements (1989a, table 8), the ratio of inter-

mediate to proximal phalangeal length for 1. gruybullianus is 1.05, which is considerably less

than the 1.31 to 1.33 that he lists for P. simonsi.

Another reason to doubt Beard’s identifications is provided by observation of his illustration of the phalanges of Phenacolemur simonsi (1989a, figure 73; 1990, figure 3)) reproduced

here as Figure 2. Despite his statement (1990, p. 340) that “phalangeal morphology is

extremely similar in paromomyids and extant Cynocephalus,” there appear to be some

striking differences. The opposing articular surfaces between the proximal and intermediate

phalanges of Cynocephalus are approximately equal whereas the articular surface on the distal

184 D. W. KRAUSE

Figure 2. Lateral views of the manual phalanges of the edentate Choloepus, the dermopteran Cynocephalus, and the paromomyid Phenacolemur (not to scale). Reprinted by permission from ~Vuture, vol. 345, p. 341. Copyright @ 1990 Macmillan Magazines Ltd.

end of the intermediate phalanx is much smaller than that on the proximal end of the distal

phalanx. By contrast, in Beard’s illustration ofPhenacolemur simonsi, the articular surface on

the proximal end of the intermediate phalanx is markedly larger than that on the distal end of

the proximal phalanx, while the articular surfaces on the distal end of the intermediate

phalanx and on the proximal end of the distal phalanx are approximately equivalent in size

[the provenance of the distal phalanx is not revealed in his 1990 paper, but in his dissertation

Beard (1989a, p. 187) states that it comes from the specimen ofP/zenacolemur sp., cf. P.jepseni, USGS 17847, and therefore not from P. simonsi as labelled-see Figure 21. In other words,

based upon the relative sizes of the joint surfaces as illustrated by Beard (1990), it appears

that the intermediate phalanx (USNM 442254, Figure 1D) is much too large to be associated

with the proximal phalanx (USNM 442248, Figure 1 M).

That the elements identified by Beard ( 1989a, 1990) as manual proximal and intermediate

phalanges of P. simonsi have been incorrectly associated is confirmed by manually approxi-

mating these elements. Whereas the articular fit between the elements identified by Beard as

proximal and intermediate phalanges ofI. gruybullianus (USNM 442256 and 442253, Figure

lK, B) is reasonably congruent, the proximal end of the element identified as a manual

intermediate phalanx (USNM 442254, Figure LD) of P. simonsi has a much greater radius of

curvature than do the distal ends of the elements identified as manual proximal phalanges

(USNM 442248 and 442249, Figure 1 M, N) of P. simonsi. Viewed from its dorsal aspect, the

articular surface on the proximal end of USNM 442254 is much too wide to accommodate

the articular surface on the distal ends ofeither USNM 442248 or 442249, and the reciprocal

ridge and groove morphology between these elements does not match. Indeed, the fit

between these elements is so poor that it is impossible for them to have been in articulation.

By contrast, when the purportedly manual proximal phalanges USNM 442248 and

442249 (Figure 1 M, N) are articulated with the three bones identified by Beard (1989a) as

pedal intermediate phalanges of P. simonsi (USNM 442250-442252, Figure 1 E-G), rather

than with USNM 442254 (Figure iD), the articular fit is reasonably good in terms of the

radii of curvature, the widths of articular surfaces, and the reciprocal ridge and groove

WERE PAROMOMYIDS GLIDERS?

Lemur mongoz (4,4) A l-l

Ratufa macroura (4,4) I

H I

Nycticebus coucang (8.8) H {

Tupaia glis (14.14) n : I

Solenodon paradoxurus ( 11,111 H ’

Erinaceus europaeus (8,8) CI:

Sciurus carollnensls (8,6) H:

Cynocephalus variegatus (1% 15) CI

Plesiadapis tricuspidens (3,2) / H I

Nannodecter gidieyi (2,2) H :

Nannodectes intermedius (2,3) w;

Ignacius graybulfianus ( 1,l) I* I

Phenacolemur simonsi (1.2) ’ R I I

(....,..,‘,....,....I 0 50 100 150 200

lnterphalangeal Proportions Wlthin Digit8 (Beard)

185

I 1

50 100 150 200

Interphalangeal Proportions Among Digita (This paper)

Figure 3. Ranges ofvalues for relative elongation ofmanual intermediate and proximal phalanges in eight extant eutherian species (seven non-gliding species + Cynocephalus uatiegatus), three plesiadapid species, and two paromomyid species. Ranges of values represent length of intermediate phalanx/length of proximal phalanx x 100. Dashed vertical lines represent intermediate and proximal phalanges ofequal length (i.e., ratio = 100). Sample sizes for length of intermediate phalanx (x) and length of proximal phalanx (y) are presented in parentheses as (x, y) after each species name. (A) Comparison of ranges of values when calculated as coming from within individual digital rays (II, III, IV, or V) for the extant species and using Beard’s stated values for the paromomyids Zgnaciusgraybullianus and Phenacolemur simonsi. (B) Comparison of ranges ofvalues when calculated as coming from among all digital rays (II through V) for the extant species and using the possible alternative values for I. gmybullianus and P. simonsi presented in this paper. Note that the values for I. graybullianus and P. simon.si, although still slightly higher than those for plesiadapids, do not fall outside of the distribution for the extant non-gliding species in B. Data extracted from or calculated from Beard (1989ra, tables 7,8).

morphology. It is therefore much more likely that USNM 442248 and 442249 (and USNM

442247, which is incomplete-Figure 1L) are associated with USNM 442250,442251, and

442252, rather than with USNM 442254. Furthermore, if one were to appeal to frequency

data, it would seem more likely that the three small proximal phalanges (USNM 442247,

incomplete; USNM 442248, length = 6.45 mm; USNM 442249, length = 6.55 mm; measure-

ments from Beard, 1989a, table 8) would be associated with the three small intermediate

phalanges (USNM 442250, length = 6.15 mm; USNM 44225 1, length = 6.00 mm; and

USNM 442252, length = 6.05mm) than to associate them with the second longest (USNM

442254, length = 8.6 mm) of the six paromomyid intermediate phalanges preserved in

nodule 8ABC. If this is the case, the preserved intermediate phalanges are 0.92-0.95 of the

length of the preserved proximal phalanges of P. simonsi and they are thus actually shorter

than the intermediate phalanges. This ratio (0.92-0.95) is much less than the 1.3 l-l.33 ratio

calculated by Beard (1989a, table 8) for the manus of P. simonsi and is closer to the ratios

calculated by him for I. gruybullianus (1.05; actually possibly 1.02-1.05 ifboth USNM 442253

and 442254 are intermediate phalanges of that species, see above) and the plesiadapids

Xannodectes intermedius (O-77-0.92), N. gidleyi (0.77-0.84), and Plesiadapis tricuspidens (0.63-O. 7 1) (compare Figure 3A to Figure 3B).

186 D. W. KRAUSE

Beard used the interphalangeal length ratios calculated for plesiadapids and paromomyids

(1989a, table 8) to make comparisons to seven non-gliding extant eutherian mammals and

Cynocephalus variegatus, although he did acknowledge that the proximal and intermediate

phalanges of the fossil taxa “probably do not come from the same digit of the same indi-

vidual” and that “the ratios of proximodistal lengths of these two elements for the fossil taxa

are not strictly comparable to the data provided in Table 7 for the extant taxa” (Beard,

1989a, p. 432). Despite these caveats, Beard (1989a, p. 428) employed the ratios in these

tables to support a claim that:

“Plesiadapid manual intermediate phalanges are shorter than the manual proximal phalanges, as is the case in almost all extant eutherians (see Tables 7-8). In contrast, paromomyid manual intermediate phalanges are greatly elongated proximodistally . ., so that they are actually longer than the proximal phalanges with which they articulate (Table 8). A similar type of elongation of the manual intermediate phalanges is found only in Cynocephalus (Table 7) .”

However, in addition to noting that the intermediate phalanges ofat least Phenacolemur simonsi

may indeed be shorter than the proximal phalanges (see above), of more critical importance

is the observation that there is no basis for the a priori assumption that the small samples of

paromomyid proximal and intermediate phalanges come from even similar digital rays

(assuming also, for the sake of argument, that they have been correctly identified as manual

phalanges).

Beard’s (1989~~) table 7 lists lengths of individual proximal and intermediate phalanges

in digits II through V that were measured in samples of between four and 15 individuals

of eight species of placental mammals (Cynocephalus variegatus and seven non-gliding forms;

values for Cynocephalus volans were not provided). Beard was able to show that Cynocephalus

variegutus, with intermediate phalanges that are 131-159% longer than the proximal phalanges, has relatively much longer intermediate phalanges than in the other, non-

gliding species ( Tupaia glis = 55-7 7 %, Solenodon paradoxurus = 6 l-7 7%) Erinaceus europaeus =

58-82%, Nycticebus coucang= 37-73%, Lemur mongoz = 62-68%, Gurus carolinensis=

75-87%, Ratufa macroura = 56-72%) (Figure 3A). However, his comparisons involve

ratios within each digitial ray (II through V; the pollex was excluded) but, since all of the

phalanges of paromomyids were not found in articulation or direct association and cannot

be assigned to digital ray, comparisons between digital rays would be more relevant. Such

comparisons for the extant taxa yield the following indices: Tupaia glis =45-98%, Solenodon paradoxurus = 48- 10 1%) Erinaceus europaeus = 45- 103 %, Nycticebus coucang = 22-122%,

Lemur mongoz = 53-86%) Sciurus carolinensis = 60- 1 1 1 %, Ratufa macroura = 45-88%) and

Cynocephalus variegates = 95-l 94%. Th ese values confirm that Cynocephalus variegatus does

have, on average, relatively long manual intermediate phalanges, but the shortest inter-

mediate phalanx in the sample of Cynocephalus variegatus is actually shorter than the longest

proximal phalanx and, in four of the seven other species samples, the longest inter-

mediate phalanx is actually longer than the shortest proximal phalanx (Figure 3B). Five

of the seven non-gliding forms have values that overlap those of Cynocephalus variegatus. Therefore, in the absence of independent evidence by which to identify the individual

digital rays from which the known isolated phalanges of Phenacolemur simonsi and Ignacius graybullianus were derived, it is inappropriate to assume that the digital ray from which the

phalanges derive were similar until it is demonstrated that interdigital variation is

minimal.


Summary and conclusions

Beard ( 1989a,b, 1990) has provided no compelling evidence that the manual intermediate

phalanges of paromomyids are much longer than the corresponding proximal phalanges,

the sole criterion employed to support his hypothesis that paromomyids exhibit a gliding

adaptation. His association of proximal phalanges with relatively long intermediate

phalanges in two species of paromomyids are suspect and are but possibilities until directly

associated or articulated proximal and intermediate phalanges ofthe same or similar manual

digit are discovered. Indeed, it is anatomically impossible that the two elements used by

Beard (1990) to support his hypothesis that the intermediate phalanges ofPhenacolemursimonsi

were greatly elongated relative to the proximal phalanges could have articulated with one

another; it is quite possible that the intermediate phalanx comes from Ignacius graybullianus,

a much larger species.

As noted in the introduction to this paper, Beard (1989a, 1990) also employed relative

phalangeal length as a phylogenetic character to support his contention that paromomyids

were, in fact, dermopterans. However, until directly associated or articulated proximal and

intermediate manual phalanges are discovered, there is no convincing evidence from these

elements that paromomyids were either gliders or dermopterans. Even if the hypothesis is

confirmed that paromomyids are cladistic dermopterans, recently put forward on the basis

of other postcranial (Beard, 1990) and cranial evidence (Kay et al., 1990), it does not

ineluctably follow that paromomyids were gliders. Irrefutable or even compelling evidence

for gliding behavior in paromomyids has yet to be discovered.

Acknowledgements

I am indebted to numerous colleagues and students at SUNY-Stony Brook, including

Brigitte Demes, Elizabeth Dumont, John Fleagle, Fred Grine, William Jungers, Susan

Larson, Lawrence Martin, Jack Stern, Suzanne Strait, Randall Susman and Christine Wall,

for discussions concerning this topic and/or for helpful comments on rough drafts of this

manuscript. They, of course, cannot be held accountable for the views expressed in this

critique. I also thank Ken Rose and two anonymous reviewers for their constructive

comments on the manuscript, Chris Beard for providing access to the phalanges, and Luci

Betti-Nash for rendering Figures 1 and 3. The research presented here was supported by NSF

grant BSR 87-22539.

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188 D. W. KRAUSE

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were paromomyids gliders? maybe, maybe not

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