AMERICAN MUSEUM Novitates

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY

NUMBER 2694 FEBRUARY 25, 1980

LEONARD RADINSKY 7 Endocasts of Amphicyonid Carnivorans

AMERICAN MUSEUM Novtitates

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024

Number 2694, pp. 1-11, figs. 1-6, table 1 February 25, 1980

Endocasts of Amphicyonid Carnivorans

LEONARD RADINSKY’?

ABSTRACT

Endocranial casts of 10 genera of amphicyo- nids, ranging in age from about 35 my to 10 my, reveal evolutionary trends of increase in relative brain size and expansion and increased folding of the neocortex. Amphicyonids had a distinctive pattern of cerebral convolutions, characterized by the presence of a long ectolateral sulcus, a short

sulcus between the caudal ends of the ectolateral and suprasylvian sulci, and a complete, unoper- cularized ectosylvian sulcus. The ectolateral sul- cus is a derived character amphicyonids share with canids, in contrast to a derived feature of basicranial circulation that links amphicyonids to ursids.

INTRODUCTION

The Amphicyonidae are an extinct family of carnivorans that lived during middle Ter- tiary time, from about 40 to 10 million years ago. Most amphicyonids were medium-sized to very large, and ranged in appearance from wolflike to bearlike. Some workers believed they were most closely related to the Cani- dae (e.g., Romer, 1966; Bonis, 1969), but the most recent studies have stressed affinities with the Ursidae (e.g., Hunt, 1977; Gins- burg, 1977). During the course of a survey of carnivoran brain evolution, I prepared sev- eral new endocasts of amphicyonids that ex- tend our knowledge of the neuroanatomy of this group. The purpose of the present paper is to review what is known about the external neuroanatomy of amphicyonids, to describe

evolutionary trends, and to call attention to features that may help to assess the phylo- genetic relationships of the family.

ACKNOWLEDGMENTS

I thank Drs. R. Hunt, University of Ne- braska, and R. Tedford, the American Mu- seum of Natural History, for information and advice on amphicyonids, and Dr. G. de Beaumont, Museum d’Histoire Naturelle, Geneva, Switzerland, for a copy of the Pseu- docyonopsis ambiguus endocast. I am grate- ful to the curators of fossil mammal collec- tions at the following institutions for permission to study specimens in their charge: American Museum of Natural His-

1 Research Associate, Department of Vertebrate Paleontology, American Museum of Natural History; Professor

of Anatomy, University of Chicago.

ISSN 0003-0082 / Price $1.00

2 AMERICAN MUSEUM NOVITATES NO. 2694 i __ 5 lO __ 10 amphicyonine I5 _. Amphicyon Pliocyon 15 Amphicyon 20 __ — 20 Daphoenodon 2532 Temnocyon Cynelos (Ysengrinia) = 25 59 — Daphoenus Brachycyon —~ 50 35__ Daphoenus (Daphoenict’s) Pseudocyonopsis ) 35 40 __ __ 40 Fic. 1. Temporal distribution of amphicyonid genera for which endocasts are known. Numbers at

sides indicate millions of years ago. North American occurrences are at left; European at right. Paren- theses indicate genera for which only a little of the endocast is preserved. See text for more detailed

taxonomy and stratigraphic information.

tory; Carnegie Museum, Pittsburgh; Field Museum of Natural History, Chicago; Uni- versité Claude Bernard, Lyon; Museum of Comparative Zoology, Harvard University; Museum National d’Histoire Naturelle, Par- is; Princeton University; and South Dakota School of Mines, Rapid City. This work was supported by N.S.F. grant DEB76-17746.

The following institutional abbreviations are used:

AM, American Museum of Natural History

CM, Carnegie Museum

F:AM, Frick American Mammals, Department of Vertebrate Paleontology, American Museum of Natural History

FMNH, Field Museum of Natural History

GEN, Museum d’Histoire Naturelle

LY, Université Claude Bernard

MCZ, Museum of Comparative Zoology MNHN, Museum National d’Histoire Naturelle PU, Princeton University

SDSM, South Dakota School of Mines

THE EVIDENCE

EARLY AMPHICYONIDS: Amphicyonids appeared about 35 to 40 my in North Amer- ica and Europe, and the oldest known am- phicyonid endocasts are from early to middle Oligocene deposits (about 30 to 35 my) from the European amphicyonines Pseudocyop- sis and Brachycyon, and the North Amer- ican daphoenines Daphoenus and Daphoe- nictis. Daphoenus is the best known of these

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RADINSKY: AMPHICYONID CARNIVORANS 3

2cm.

Fic. 2.

Daphoenus hartshornianus. SDSM 51121, x1. Abbreviations: cl, coronolateral sulcus; ec,

ectolateral sulcus; en, entolateral sulcus; fp, fissura prima; rh, rhinal fissure; ss, suprasylvian sulcus.

genera, and is represented by several endo- casts, one of which was briefly described by Scott and Jepsen (1936). The specimen fig- ured by Edinger (1956, fig. 5) under the name Daphoenus (AM 6946) is an endocast of the canid Mesocyon.

The brain of Daphoenus (fig. 2) had three main neocortical sulci, a relatively straight coronolateral sulcus that paralleled the dor- sal midline, a gently arched suprasylvian sul- cus that approximately paralleled the rhinal fissure, and an ectolateral sulcus that in three of the six specimens I examined extended rostrally to contact the suprasylvian sulcus. In addition, there was a short, variably de- veloped entolateral or postlateral sulcus that is sometimes confluent with the caudal end of the coronolateral sulcus, a short sulcal notch in the caudal border of the temporal lobe between the ends of the ectolateral and suprasylvian sulci, and finally, in some spec-

imens, variably developed dimples under the suprasylvian sulcus that mark the beginnings of an ectosylvian sulcus. In one of the Da- phoenus endocasts (PU 12588), the ectosyl- vian sulcus is expressed as a complete arch, the suprasylvian sulcus is longer and more arched than in the other specimens, and the rostral end of the coronolateral sulcus is bowed out laterally. There is not enough evi- dence to indicate whether the more ad- vanced condition of neocortical folding in this specimen represents a species-specific difference, or merely one extreme of individ- ual or intraspecific variation. The cerebellum was widely exposed, and the configurations of the vermis, with a sharply marked fissura prima, the ansiform lobules and the parafloc- culus are discernible on Daphoenus endo- casts.

A partly exposed natural endocast of Da- phoenictis, from the early Oligocene, was

4 AMERICAN MUSEUM NOVITATES

a 2cm. Fic. 3. Daphoenodon superbus. CM 1589A, x34. Abbreviations: co, coronal sulcus; ec, ec- tolateral sulcus; es, ectosylvian sulcus; la, lateral sulcus; pr, presylvian sulcus; sg, sigmoid gyrus; $s, suprasylvian sulcus; sy, sylvian sulcus.

briefly described by Hunt (1974, p. 1037), who noted that it had an ectolateral sulcus developed as in Daphoenus, with its rostral end confluent with the suprasylvian sulcus.

The brain of Pseudocyonopsis is known from an endocast from the French Quercy Phosphorites, described by Beaumont (1964) under the name Amphicyon ambiguus. (The species A. ambiguus was placed in Pseudo- cyonopsis by Ginsburg, 1966.) Pseudocyo- nopsis ambiguus had a neocortical sulcal pattern similar to that of Daphoenus, with well-developed coronolateral, ectolateral, and suprasylvian sulci. The ectolateral sul- cus contacted the suprasylvian sulcus ros- trally. It is not clear whether there was a notch between the caudal ends of the ecto- lateral and suprasylvian sulci. The brain of Pseudocyonopsis was a bit more advanced than that of Daphoenus in having a longer entolateral sulcus, a more arched suprasyl- vian sulcus, a better developed ectosylvian sulcus, and a notch at the junction of anterior

NO. 2694

and posterior limbs of the rhinal fissure that suggests incipient development of a sylvian sulcus. In addition, there was a presylvian sulcus delimiting a portion of the frontal lobe, the coronal sulci were bowed out lat- erally, and there is a small depression in the dorsal midline that suggests incipient devel- opment of a cruciate sulcus.

An incomplete endocast of Brachycyon, from middle Oligocene (Stampian) deposits near Marseilles, was described by Ginsburg (1966). It suggests a brain similar to that of Pseudocyonopsis, with a depression mark- ing the beginnings of a sylvian sulcus, and with a complete ectosylvian sulcus. There was a short sulcal notch between the caudal ends of the suprasylvian and ectolateral sulci (called the postlateral sulcus by Ginsburg), and a well-developed ectolateral sulcus which did not contact the suprasylvian sul- cus. Ginsburg’s figure indicates a small sul- cus medial to the coronal sulcus, which may indicate incipient development of a cruciate sulcus.

LATER AMPHICYONIDS: A new wave of amphicyonids appeared in the early Miocene of North America (Arikareean, about 20 to 25 my), replacing the Oligocene daphoe- nines, and endocasts are now available for two genera, Daphoenodon and Temnocyon. The brain of Daphoenodon superbus (fig. 3) is known from two endocasts, AM 27568 and CM 1589A. It appears to have been at a sim- ilar stage as that of Pseudocyonopsis and Brachycyon, with incipient sylvian and well- developed ectosylvian sulci, a relatively long and arched suprasylvian sulcus (compared to Daphoenus), a presylvian sulcus, and begin- nings of expansion of the sigmoid gyri (= cortex between the coronal sulci). A trans- versely oriented depression within the sig- moid gyrus may represent incipient devel- opment of a cruciate sulcus. The ectolateral sulcus did not contact the suprasylvian sul- cus, there was a sulcal notch between the caudal ends of the ectolateral and suprasyl- vian sulci, and the entolateral sulcus was not well developed. Details of cerebellar mor- phology are blurred on the endocasts of Da- phoenodon and the other post-Oligocene am- phicyonids, presumably owing to their

1980

RADINSKY: AMPHICYONID CARNIVORANS 5

2 cm.

Fic. 4. Cynelos rugosidens, from the Gervais skull (MNHN), x34. Abbreviations: og, orbital gyrus;

sg, sigmoid gyrus.

relatively large size. The endocast from AM 27568 is larger than that of CM 1589A, and shows more neocortex between the supra- sylvian sulcus and rhinal fissure.

The one endocast known for Temnocyon (F:AM 54134) suggests a brain similar to that of Daphoenodon. The frontal region is shat- tered in F:AM 54134, but one portion pre- serves the imprint of a short sulcus that ex- tended rostrolaterally from the dorsal midline in the middle of the sigmoid gyrus, and prob- ably represents the cruciate sulcus.

Endocasts of European amphicyonids that were approximate contemporaries of Da- phoenodon and Temnocyon are known for species of Cynelos and Ysengrinia, from the French St. Gerand-le-Puy Aquitanian depos- its (about 25 my). An excellent Cynelos en- docast was first described by Gervais (1872),

under the name Cephalogale rugosidens, then figured by Edinger (1929, fig. 127) as Amphicyon (Cephalogale) rugosidens, by Piveteau (1961, p. 814 ) as Amphicyon am- biguus, and by Beaumont (1962) as ‘‘Am- phicyon’’ cf. rugosidens. A second Cynelos endocast, from a skull referred to as the Ju- lien skull by Hunt (1977), is also now avail- able.

The brain of Cynelos (fig. 4) was slightly more advanced than that of Daphoenodon in having a more expanded sigmoid gyrus (cor- tex medial to coronal sulcus), with variably developed dimples suggesting incipient sub- divisions, and a more expanded orbital gyrus (rostral to the presylvian sulcus). The sylvian sulcus is represented by a short notch, and the ectosylvian and suprasylvian sulci were about as tightly arched as in the more ad-

6 AMERICAN MUSEUM NOVITATES NO. 2694

Fic. 5.

2cm.

Pliocyon cf. P. medius. F:AM 54334, x34. Abbreviations: an, ansate sulcus; cr, cruciate

sulcus; fp, fissura prima; pc, postcruciate dimple; pr, presylvian sulcus.

vanced of the two Daphvenodon endocasts (AM 27568). The ectolateral sulcus contact- ed the suprasylvian sulcus in one but not the other of the two Cynelos endocasts, and the entolateral sulcus was moderately well de- veloped in one but absent in the other.

The endocast of Ysengrinia preserves only a portion of the frontal lobe and olfactory bulb, and appears similar to corresponding portions of the Cynelos endocasts. The sig- moid gyrus was equally expanded, and sub- divided by secondary dimples.

The next record of amphicyonid brains is a partial endocast of Amphicyon, from the

Thomas Farm middle Miocene (about 18 my). It shows relatively longer and more tightly arched ectosylvian and suprasylvian sulci, and a more sunken-in insular region (within the arch of the ectosylvian sulcus), than in the older amphicyonid endocasts, suggesting a higher and more rostrocaudally compressed brain. The lateral gyrus was rel- atively narrow and there is no trace of an entolateral sulcus. The frontal region is not preserved on this endocast, but a short sec- tion of the coronal sulcus is present, and its curvature suggests that the sigmoid gyri were expanded at least as much as in Cynelos.

1980

Still more recent amphicyonid endocasts are known from the Barstovian late Miocene (around 12 to 16 my), from Pliocyon cf. P. medius and Amphicyon frendens. The Plio- cyon endocast (F:AM 54334) is an excellent specimen, with slight damage only in the frontal region (see fig. 5). It indicates that the brain of Pliocyon was advanced over that of Cynelos and the older amphicyonids in hav- ing a more expanded frontal lobe. Expansion of the sigmoid gyri is reflected in the bowed- out coronal sulci, the appearance of an an- sate sulcus, a laterally extending cruciate sulcus, and a dimple representing the post- cruciate sulcus. A long presylvian sulcus de- limited an expanded orbital gyrus. The ec- tosylvian and suprasylvian sulci were relatively long and tightly arched, as in the older Thomas Farm Amphicyon endocast described above, and there was a short sy]l- vian sulcus. The lateral gyrus was relatively broad, and was subdivided by an entolateral sulcus. The occipital lobe overlapped the cerebellum more than in the older amphi- cyonids, extending to about the level of the fissura prima of the vermis.

The endocast of Amphicyon frendens (F:AM 54415) is dorsoventrally crushed and also shattered in the frontal region. From what is preserved, it appears that the sigmoid gyri were not expanded around a transverse- ly oriented cruciate sulcus as in Pliocyon, but rather were dimpled, as in Cynelos. The lateral gyrus is relatively narrow, with no trace of an entolateral sulcus, and the occip- ital lobe did not cover as much of the cere- bellum as in Pliocyon.

The youngest amphicyonid endocast avail- able is from an undescribed braincase (am- phicyonine, sp. indet., AM 2792), probably from Clarendonian deposits (10-12 my). It is damaged in the occipital region and lacks the cerebellum. In preserved portions it resem- bles the Pliocyon endocast, and shows nice- ly the sigmoid gyri expanded around a ros- tralaterally oriented cruciate sulcus.

DISCUSSION

EVOLUTIONARY TRENDS: The main evo- lutionary trends seen in the fossil record of

RADINSKY: AMPHICYONID CARNIVORANS 7

amphicyonid brains are expansion and in- creased folding of the neocortex, and in- crease in relative brain size. Expansion and increased folding of the neocortex are nicely illustrated by a morphological series of en- docasts of Daphoenus-Cynelos-Pliocyon (fig. 6). Note the appearance and expansion of the orbital gyrus; the expansion of the sig- moid gyrus, reflected in the bowing out of the coronal sulcus and the eventual devel- opment of a cruciate sulcus; the lengthening and increasingly tight folding of the supra- sylvian and ectolateral sulci, and the appear- ance of ectosylvian and sylvian sulci as the temporal lobe (and frontal lobe) expanded; and the increasing overlap of cerebellum by cerebrum. Similar trends in neocortical ex- pansion patterns can be seen in other fami- lies of carnivorans (see, e.g., Radinsky, 1973, 1975a), and the cruciate sulcus evolved in- dependently at least five times (Radinsky, 1971).

The expansion and increased folding of neocortex appears to indicate an increase in relative amount of neocortex (compared to rest of brain). However, that might not be the case. The apparent increase in relative amount of neocortex may be accounted for, at least in part, by allometry—in particular, the scaling relationships of surface area to volume. Brains of later amphicyonids were larger than those of early amphicyonids, in part owing to the larger body size of the later species, and in part to the trend towards in- creasing relative brain size (see table 1). As noted by Le Gros Clark (1947, and refer- ences cited therein), the neocortex is orga- nized as a thin sheet, and can increase only by areal expansion, while the underlying subcortical matter expands as a volume. With increasing brain size there is relatively less surface area (since surface area is pro- portional to a radius squared while volume is proportional to a radius cubed), and for the neocortex sheet to keep pace, in volume, with the increasing volume of subcortical tis- sue, it must expand disproportionately areal- ly. This is reflected in increased folding and apparent relative expansion of the neocortex over the rest of the brain with increasing brain size. Whether there was an actual in-

8 AMERICAN MUSEUM NOVITATES

NO. 2694 TABLE 1 Relative Brain Size in Amphicyonids Skull Estimated Encephali- Length Body zation Endocast (SL, Body Length Weight Quotient Volume (cm') cm) (cm) (gm)* (EQ) Daphoenus hartshorni- 56 16.5 5.6 SL? = 92.4 18,594 0.64 anus (AM 9757; SDSM 51121) Daphoenus vetus® 65° 18.5 5.6 SL¢ = 103.6 25,411 0.61 (PU 12588) Pseudocyonopsis ambiguus 68° 17.5° 5.6 SL’ = 98 21,834 0.70 (GEN) Cynelos rugosidens¢ 115 24 5.0 SL’ = 120 37,954 0.82 (LY) Daphoenodon superbus 133° 22.8 5.2 SL’ = 118.6 36,723 0.97 (CM 1589) Pliocyon cf. P. medius 240 29,3" 4.5-5.0 SL’ = 49,080- 1.19-1.44 (F:AM 54334) 131.9-146.5 65,438

“From the relationship between body length (L) and body weight (P) in 54 species of modern carnivores: P = 0.080

L?-73 (Radinsky, 1978, p. 820).

>The Encephalization Quotient (EQ) of a species is its brain size (E, gm or cm’) divided by the brain size expected in the average living mammal of that species’ body weight (P, gm). In the average living animal, E = 0.12 P®®. Thus EQ, = E,/0.12 P,°-*7. In a large suite of modern carnivores, EQ ranges from 0.53 to 1.60 (Radinsky, 1978, p.

823).

‘EQ estimates for these species differ slightly from those given in Radinsky, 1978, because additional data on skeletal dimensions allow improved estimates of body weights.

4Proportions from Scott and Jepsen, 1936, p. 74. €Body proportions modeled after Daphoenus. ‘Proportions from Ginsburg, 1977, p. 42. 9Proportions from Romer, 1966, p. 237.

"Modeled after Cynelos (Ginsburg, 1977) and Amphicyon major (Bergounioux and Crouzel, 1973).

" = restored.

crease in relative volume of neocortex com- pared to the rest of the brain in amphicyonid brain evolution cannot be determined from the available data.

The parallel evolution of the same general pattern of neocortical convolutions with in- creasing brain size in various carnivoran lines—in particular, the pattern of arcuate folds arranged concentrically around the syl- vian sulcus—may reflect constraints on fold- ing patterns imposed by inheritance of a common pattern of thalamocortical connec- tions from the Eocene common ancestor of modern carnivorans.

Disproportionate expansion of a particular area of the neocortex may reflect specializa-

tion of function (see, e.g., Welker and Cam- pos, 1963). In amphicyonid brain evolution, such relative enlargement of a cortical area is evident primarily in the region of the cru- ciate sulcus. The cortex around the cruciate sulcus (sigmoid gyrus) contains fore and hind limb representation in primary somatic sen- sory (tactile) and motor areas, and the mul- tiple independent development of the cru- ciate sulcus in carnivoran brain evolution may reflect expansion of motor cortex for improved locomotor control (see discussion in Radinsky, 1971). Early stages of expan- sion of the sigmoid gyrus in amphicyonids were marked by dimpling of the gyrus (see figs. 3 and 4), while in canids and felids the

1980 RADINSKY: AMPHICYONID CARNIVORANS 9

Daphoenus

Pliocyon

an Ae | 2 cm.

Fic. 6. Endocasts of Daphoenus, Cynelos, and Pliocyon to illustrate the evolutionary trend of expansion of neocortex through time. Abbreviations: co, coronal sulcus; cr, cruciate sulcus; es, ecto- sylvian sulcus; la, lateral sulcus; og, orbital gyrus; ss, suprasylvian sulcus; sy, sylvian sulcus. All to

scale, approximately x<0.8.

only infolding was the cruciate sulcus itself (see figures in Radinsky, 1973, 1975a). The reason for that difference is not apparent. It may reflect the larger size of the amphicyo- nid brain (compared to canid and felid

brains) when sigmoid gyrus expansion be- gan.

The trend toward increase in relative brain size is apparent in even the small sample of amphicyonid endocasts now available to us

10 AMERICAN MUSEUM NOVITATES

(table 1). The earliest amphicyonids had En- cephalization Quotients (EQs) of around 0.60 to 0.70, apparently advanced over that of their Eocene miacid ancestors (0.44—-0.52 for late Eocene Procynodictis; Radinsky, 1978). Five to 10 million years later, Cynelos and Daphoenodon had EQs of 0.82 and 0.97, re- spectively, which is within the EQ range of living carnivorans (Radinsky, 1978). Finally, one of the latest amphicyonids, Pliocyon, apparently had an EQ between 1.19 and 1.44, which is high even for modern carnivorans. Increase in relative brain size is a common evolutionary trend in mammals, and its sig- nificance remains a fascinating, open ques- tion.

PHYLOGENETIC SIGNIFICANCE: It has long been recognized that differences in cortical folding patterns distinguish various families of modern carnivorans (Mivart, 1855, and references cited therein). Canids, felids, vi- verrids, and the arctoid group have distinc- tive patterns (Radinsky, 1973, 1975a and 1975b). The brains of amphicyonids also had a distinctive pattern of cerebral convolu- tions, characterized by the presence of a long ectolateral sulcus that usually extended to contact the suprasylvian sulcus, a short sul- cus between the caudal ends of the ectola- teral and suprasylvian sulci, and, in all but the earliest species, an ectosylvian sulcus that was an unbroken arch and remained ex- posed (unopercularized) on the lateral sur- face of the brain.

An ectosylvian sulcus expressed as a com- plete arch evolved independently in many groups of carnivorans in addition to amphi- cyonids (paleofelids, canids, ursids, ota- riids), and in the ursids and otariids it be- came opercularized, buried by expansion of surrounding gyri (=a derived condition). The short sulcus between ectolateral and supra- sylvian sulci occurred only in amphicyonids and, as a variable feature, in a few genera of early canids (e.g., Mesocyon). The ectolat- eral sulcus is rare among carnivorans. Be- sides amphicyonids, it occurs only in canids and a few species of modern mustelids (Eira barbara, Galictis vittatus, and Martes fla- vigula: Theide, 1966, and personal observa- tions). In the early canids the ectolateral sul-

NO. 2694

cus was short, and it was only around 15 my, that it appeared as extensive in canids as in amphicyonids (see figures in Radinsky, 1973). Since the ectolateral sulcus is present in only a few mustelids, it obviously evolved independently in those forms. However, the presence of an ectolateral sulcus in the ear- liest canids and amphicyonids is a shared derived character that may reflect inheri- tance from a common ancestor.

In modern canids the ectolateral sulcus appears to form the rostral border of a sec- ondary visual field (Radinsky, 1973, fig. 11). The appearance of the ectolateral sulcus in early canids and amphicyonids may there- fore reflect early expansion of visual cortex in those families. Such expansion could have occurred independently, or may have been inherited from a common ancestor shared after divergence from the other carnivorans.

Two recent experts on amphicyonids have concluded that amphicyonids are closer phy- logenetically to ursids than to any other car- nivorans. Hunt (1977) stressed their common possession of an enlarged inferior petrosal venous sinus that contains (or contained) a loop of the internal carotid, a specialization for cooling blood to the brain, and a unique shared derived character in ursids and am- phicyonids. Ginsburg (1977) noted that fea- ture plus other aspects of cranial circulation and limb morphology shared by ursids and amphicyonids. To me the most impressive similarity between amphicyonids and ursids is the cranial circulation modification (ca- rotid loop in inferior petrosal sinus). If that shared derived character was inherited from a common ancestor of amphicyonids and ur- sids, then the ectolateral sulcus evolved in- dependently in canids and amphicyonids (as it has done in a few recent mustelids). On the other hand, if the shared derived char- acter of the ectolateral sulcus in canids and amphicyonids was inherited from a common ancestor, then the cranial circulatory modi- fications evolved independently in ursids and amphicyonids. In the absence of information on how easy it is (morphogenetically) to modify either the cortical pattern or the cra- nial circulation, I see no compelling argu- ment for choosing one or the other of those

1980

alternatives. Of course, another possibility is that both derived features evolved inde- pendently in amphicyonids.

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1962. Observations sur l’ostéologie cranienne et la position systématique des petits ‘*Amphicyon’’ de loligocene européen. Bull. Soc. Vaud. Sci. Nat., vol. 68, no. 307, pp. 81-92.

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1966. Les amphicyons des Phosphorites du Quercy. Ann. Paléont. (vert.), vol. 52, pp. 23-64. Cynelos lemanensis (Pomel), carnivore ursidé de |’Aquitanien d’Europe. [bid., vol. 63, pp. 57-104. Hunt, R. M., Jr.

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