FUNCTIONAL-ADAPTIVE ANALYSIS OF THE POSTCRANIAL SKELETON OF A LAVENTAN BORHYAENOID, LYCOPSIS LONGIROSTRIS (MARSUPIALIA, MAMMALIA) Author(s): CHRISTINE ARGOT Source: Journal of Vertebrate Paleontology, 24(3):689-708. 2004. Published By: The Society of Vertebrate Paleontology DOI: http://dx.doi.org/10.1671/0272-4634(2004)024[0689:FAOTPS]2.0.CO;2 URL: http://www.bioone.org/doi/full/10.1671/0272-4634%282004%29024%5B0689%3AFAOTPS %5D2.0.CO%3B2

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FUNCTIONAL-ADAPTIVE ANALYSIS OF THE POSTCRANIAL SKELETON OF A LAVENTAN BORHYAENOID, LYCOPSIS LONGIROSTRIS (MARSUPIALIA, MAMMALIA)

CHRISTINE ARGOT Laboratoire de Pale´ontologie, UMR 5143 du CNRS, Muse´um national d’Histoire naturelle, Paris, France

ABSTRACT—Lycopsis longirostris, a middle Miocene Colombian borhyaenoid, is compared functionally with early Miocene borhyaenoids from Patagonia and the Tasmanian thylacine Thylacinus cynocephalus, the largest Recent mar- supial carnivore. The postcranium of Lycopsis shows a mosaic of features. Although several features characterizing the long bones are consistent with a primarily terrestrial mode of life (e.g., a straight ulna and tibia, a semi-digitigrade forefoot), other features like the development of mm. spinati, pectoralis and biceps and the pseudo-opposable pollex indicate that the forelimb had manipulative and grasping abilities. On the hindlimb, the poorly stabilized lower ankle joint, the short metatarsals, and the well-developed hallux also preclude fast running. When compared to three early Miocene borhyaenoids, Prothylacinus patagonicus, Cladosictis patagonica, and Borhyaena tuberata, which form a mor- phological gradient from the most arboreally-adapted taxon to an incipient cursorial one, Lycopsis is placed between Cladosictis and Borhyaena. Lycopsis was more likely an ambush hunter than a pounce-pursuit predator, stalking small- to medium-sized prey.

INTRODUCTION sis longirostris, comparisons are made with Thylacinus cyno- cephalus, the largest marsupial carnivore in historic times (Jones Only a few highly carnivorous borhyaenoids, ranging from the and Stoddart, 1998), and similar in size to Lycopsis. The skeletal early Paleocene to the late Miocene of South America, are comparisons between both species will take advantage of eco- known by postcranial remains that are complete enough to infer logical and behavioral data that have been compiled about T. potential locomotor activities. Therefore, the analysis of the lo- cynocephalus (Smith, 1982; Johnson and Wroe, 2003). comotor features characterizing the middle Miocene Lycopsis longirostris from Colombia is expected to represent a significant MATERIALS AND METHODS part of the comprehensive review of the evolution of the loco- motion within Borhyaenoidea. The specimen UCMP 38061 is represented by the right half of The fossils described from the Honda Group section in the the skull, the right mandibular ramus, and most of the articulated upper Magdalena River valley (Villavieja Formation, Depart- postcranial skeleton. Originally, the animal was found lying on ment of Huila, Colombia) constitute the La Venta Fauna. This its right side in a partially flexed position (Marshall, 1977). The fauna is of particular interest as it represents the most complete postcranial elements of Lycopsis longirostris are partially record of Tertiary mammals from tropical South America, as crushed, and the articular facets and muscular attachments are well as the youngest endemic fauna known from the northern relatively poorly preserved. However, most of the long bones part of the continent before the arrival of North American im- have been removed from matrix for examination, which allows a migrants (Patterson and Pascual, 1968). Madden et al. (1997) functional comparative analysis. Following the methodology proposed a correspondence between the Laventan Stage, a chro- found relevant for the study of Mayulestes ferox, the oldest nostratigraphic unit well known for the abundance of fossil mam- borhyaenoid known (early Paleocene, Bolivia), it is assumed in mals occuring in the Honda Group, and a geochronologic sub- the description of the postcranial morphology of Lycopsis that division called the Laventan Age, representing the time interval the major muscle scars observed on the skeleton, and therefore between 13.5 and 11.8 Ma. The La Venta Fauna contains a di- the corresponding muscles, are homologous in borhyaenoids and verse assemblage of endemic ungulates and xenarthrans, and the living marsupials (Argot, 2001, 2002, 2003a). The myological in- earliest representatives of several modern South American sub- ferences concerning Lycopsis will occasionally refer to data I families of armadillos, anteaters, bats, opossums, and New World obtained from dissections performed on various genera of living monkeys (Flynn and Wyss, 1998). Paleoenvironmental data sug- Guyanese didelphids. The scarce myological data used in the gest a mosaic of biotopes typical of modern lowland meandering discussion about Thylacinus cynocephalus refer to data from the stream systems (Kay and Madden, 1997). nineteenth century compiled by Smith (1982). The postcranial skeleton of the species Lycopsis longirostris is Thylacinus cynocephalus is the largest carnivorous marsupial known by a single specimen (the holotype UCMP 38061) that for which any firsthand accounts of biology are available. Three has never been described in detail, especially from a functional thylacinid species existed in the Australian late Oligocene, and point of view. The only comments that exist are from Marshall ten species are known from Miocene sites, whereas a single one (1977), who found no major differences between the skeleton of is recognized in Plio-Pleistocene deposits (Wroe and Musser, L. longirostris and those of Prothylacinus patagonicus, Borhy- 2001; Wroe, 2003). The dental remains suggest a considerable aena tuberata, and Cladosictis patagonica. However, it is clear variation in size and diet between these species (the largest ones that the three early Miocene (Santacrucian) borhyaenoids, Pro- being also the most carnivorous: Wroe, 2001; Wroe and Musser, thylacinus, Borhyaena, and Cladosictis, exhibit distinct adaptive 2001). Most of these species are known only from dentitions, features (Argot, 2003b, c), and it is of interest to compare the rarely by cranial elements, and therefore, the potential diversi- younger Lycopsis with these taxa. fication of the locomotion within the family is unknown. Little is In order to assess the functional implications of the morpho- known about the ecology and behavior of the Recent taxon, data logical features characterizing the postcranial skeleton of Lycop- consisting mainly of nineteenth century observations from farm-

689 690 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 24, NO. 3, 2004 ers and other bush workers, and observations made on captive gentina; MNHN, Muse´um national d’Histoire naturelle, Paris, animals (Smith, 1982). However, Jones and Stoddart (1998) have France; PU, Peabody Museum of Yale University, New Haven, recently reconstructed the likely hunting and killing methods of USA; UCMP, University of California, Museum of Paleontol- the thylacine based on canine tooth strength and femur/ ogy, Berkeley, USA. metatarsal length ratio, and conclude that this marsupial was a pounce-pursuit predator of fairly open habitats, which killed me- DESCRIPTION dium-sized prey (1–5 kg), quite small relative to its body size (mean weight: 25 kg). However, a selection of small prey species Axial Skeleton may have resulted from human disturbance as the two largest potential Tasmanian prey species of the thylacine, the emu and Cervical Vertebrae—The dorsal arch of the atlas of Lycopsis eastern grey kangaroo, were being decimated or eliminating by is robust and anteroposteriorly wide. The anterior edge is less the nineteenth century, while the thylacine was restricted to mar- convex than in Borhyaena (Fig. 1A). Moreover, in contrast to ginal habitats (Johnson and Wroe, 2003). The thylacine was char- Borhyaena, the atlas of Lycopsis does not have deep grooves on acterized by a dog-like external aspect: large size, deep chest, the lateral extremities of the anterior edge for the passage of the enlarged brain, long snout, and especially a digitigrade stance first cervical nerve and the vertebral artery. In Lycopsis, the and straight forelimb with non-retractile claws suggesting a simi- anterior sulcus is closed in an intervertebral (or atlantal) fora- lar adaptation for running (Smith, 1982; Jones and Soddart, men as in the Santacrucian Prothylacinus, Sipalocyon, and Cla- 1998). Suggested dietary niche overlap between thylacines and dosictis. The transverse processes of the atlas are partially bro- dingoes, Canis lupus dingo, may have been overstated because of ken, and therefore their anteroposterior length cannot be esti- differences in dentition. Thylacinus was a hypercarnivore lacking mated. However they are not very prominent laterally compared features related to bone consumption, whereas the dingo has a with the transverse width of the dorsal arch, and they are more less specialized dentition and diet (Johnson and Wroe, 2003). constricted at their bases than in Borhyaena and Prothylacinus. Except for Thylacinus cynocephalus, no other living carnivo- The neural process of the axis is well-developed anteroposte- rous marsupials are in the size range of Lycopsis. Therefore, riorly as in all borhyaenoids, although it seems to be relatively postcranial metrical comparisons will also use various eutherian less developed posteriorly than in Borhyaena (compare Fig. 1B carnivorans (Lycopsis has carnivorous dental adaptations like all and 1C). Posteriorly, the neural process of the axis overhangs the borhyaenoids). These taxa, which exhibit distinct locomotor and neural process of the third cervical vertebra, which exhibits a hunting activities, will help to interpret the adaptive features broken apex. The axis of Lycopsis appears to be more massive characterizing Lycopsis. than in the other borhyaenoid taxa, with pedicles much longer Institutional Abbreviations—MACN, Museo Argentino de anteroposteriorly than in the Paleocene Mayulestes, and with a Ciencias Naturales “Bernardino Rivadavia”, Buenos Aires, Ar- dorsoventrally broad posterior part of the neural process.

FIGURE 1. Cervical area. A, atlas of Lycopsis longirostris UCMP 38061 and Borhyaena tuberata PU 015701 in dorsal view. B, cervical vertebrae of Lycopsis longirostris UCMP 38061 in lateral view. C, atlas and axis of Borhyaena tuberata PU 015701in lateral view. D, third cervical of Prothylacinus patagonicus PU 015700 and Thylacinus cynocephalus MNHN 1891-61 in lateral view. The arrows indicate the presence of a ventral sagittal process in anterior cervicals, better developed in borhyaenoids than in Thylacinus. Scale bars equal 10 mm. ARGOT—POSTCRANIAL ANALYSIS OF LYCOPSIS 691

Like the Santacrucian borhyaenoids, the vertebral bodies of along all their length. The articulation with the thoracic verte- the axis and third cervical of Lycopsis exhibit a triangular pro- brae is bicondylar until T10. According to the shape of the ribs cess, which protrudes ventrally at the posterior extremity of the articulating with the middle part of the thoracic area, the trans- sagittal crest (Fig. 1B). This process is not preserved on C4. The verse width of the rib cage was approximately 10–12 cm; a well- inferior lamellae developed along the ventral margin of the trans- preserved rib in Borhyaena (specimen PU 015701) allows to es- verse processes of the posterior cervical vertebrae are particu- timate this width to 19–20 cm. larly well developed and prominent posteriorly on C6 (Fig. 1B). In Lycopsis, the transverse processes of the lumbar vertebrae Thoracolumbar Vertebrae—Lycopsis has 19 dorsal verte- protrude downward but are not particularly prominent anteri- brae, 13 thoracics and 6 lumbars. According to the orientation of orly (Fig. 3A–C, E). They are relatively larger anteroposteriorly the neural processes and zygapophyses of the last thoracic ver- than in Prothylacinus (compare Fig. 3C and D), and hook- tebrae (T10–T13), it can be deduced that the diaphragmatic and shaped in dorsal view. They are not concave ventrally, a condi- anticlinal vertebra was T11, although this vertebra is lacking tion more similar to that of Cladosictis than to that of Mayulestes (Fig. 2). This anterior location is similar to that observed in or Prothylacinus. Comparatively, the transverse processes of Prothylacinus and Cladosictis. The point of maximal dorsal con- Prothylacinus are more protruding forward, more slender an- vexity of the trunk is located at the level of T11–T13. The neural teroposteriorly, and more concave ventrally. process of the first thoracic vertebra (T1) stands upright, ap- Caudal Vertebrae—The sacrum of Lycopsis is made of two proximately perpendicular to the longitudinal axis of the verte- vertebrae as in Cladosictis and Prothylacinus. The first six caudal bral column like the neural processes of the posterior cervical vertebrae are known and articulated, but only the first four are vertebrae (C4–C7), whereas those of the following thoracic ver- relatively well-preserved (Fig. 4A, B). They do not exhibit neural tebrae are inclined posteriorly (Fig. 2). The height and posterior processes. The postzygapophyses are still developed on the fifth inclination of the neural processes is very similar between T3 and caudal. These vertebrae are morphologically quite similar to the T10; they are approximately 35 mm long and form a posterior caudals of Cladosictis, and less robust than in Prothylacinus. The angle of 50–55° with the vertebral column (Fig. 2). The neural transverse processes protrude laterally and suggest a well- process of T2 is relatively more robust than the following ones. developed basal musculature. They exhibit a constant anteropos- Posteriorly to T11, the neural processes are inclined anteriorly terior length between Ca1 and Ca4, and protrude slightly back- (Fig. 2). They are not very high but are large anteroposteriorly. ward. Two caudals belonging to the posterior part of the tail are The anapophyses are well-developed between T12 and L3, wrap- known but are poorly preserved (Fig. 4C). The vertebral body of ping tightly the following vertebra. They are present but reduced these vertebrae represents approximately twice the length of the on L4 and L5. anterior caudals, and the postzygapophyses are reduced. The Most of the ribs are preserved, but are imbedded in matrix. transverse processes are represented by two pairs of small pro- They are elliptical in cross-section, compressed anteroposteriorly cesses. The foramen vertebrale is still present on these vertebrae,

FIGURE 2. Thoracic area of Lycopsis longirostris UCMP 38061, with associated ribs. The supposedly diaphragmatic and anticlinal vertebra (T11) is not preserved. Thirteen left ribs were present; the left ribs of the two anterior pairs have been removed with the long bones of the forelimb, and the two last ribs are not represented. Scale bar equals 10 mm. 692 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 24, NO. 3, 2004

FIGURE 3. Lumbar vertebrae. A, focus on L3–L5 of Lycopsis longirostris UCMP 38061. B, focus on L6–Ca4 and on the right part of the innominate still in matrix of Lycopsis longirostris UCMP 38061. C, lumbar and sacral vertebrae of Lycopsis longirostris UCMP 38061. D, last lumbars of Prothylacinus patagonicus PU 015700 and Thylacinus cynocephalus MNHN 1891-61. E, two lumbars of Lycopsis longirostris UCMP 38061 (lumbars reconstructed from the left part, out of matrix), Prothylacinus patagonicus PU 015700, and Thylacinus cynocephalus MNHN 1891-61. Scale bars equal 10 mm.

suggesting that they are anterior to Ca10. The total number of with a convex medial border and a more flattened lateral border, caudals in Lycopsis is unknown. and less rounded than in Prothylacinus (Fig. 5B). The coracoid process is prominent ventrally (Fig. 5B–D). The proximal ex- Forelimb and Pectoral Girdle tremity of the humerus of Lycopsis is damaged because of post- mortem compression (Figs. 5C, 6). The articular surface of the Scapula and Shoulder Joint—The scapula of Lycopsis is rect- humeral head is convex proximally (Fig. 6C). The greater tu- angular in outline (Fig. 5A). The anterior and posterior borders bercle is as high as the head and prominent anteriorly (Fig. 5C). are almost parallel, and perpendicular to the vertebral border, in On the scapula, the anterior protrusion of the supraglenoid tu- contrast with the condition in the other Miocene borhyaenoids. berosity is consistent with the anteroposterior depth of the proxi- The neck of the scapula is anteroposteriorly large in both Ly- mal extremity of the humerus. The lesser tubercle of the hu- copsis and Prothylacinus. As in the other Miocene borhyaenoids merus, although relatively small, is prominent anteriorly and not (but in contrast with the Paleocene Mayulestes), the anterior appressed against the head in contrast to Prothylacinus (Fig. 5C). border of the scapula of Lycopsis elevates by a steep gradient Laterally, the fossa of insertion of the m. infraspinatus is large back to the neck of the scapula. The scapular spine is inclined (Fig. 6C). posteriorly and is perpendicular to the vertebral border as in the The deltopectoral crest of the humerus is well-developed and other Miocene borhyaenoids but contrary to that of Mayulestes extends slightly farther distally than the proximal tip of the lat- in which both axes form an obtuse angle. The posterior part of eral epicondylar crest (Fig. 6). The proximal part of the delto- the acromion is preserved; it is slender and does not overhang pectoral crest is prominent anteriorly but not the distal part, in the glenoid cavity (Fig. 5A). contrast to Prothylacinus. The diaphysis of the humerus is not The glenoid cavity of the scapula is oval-shaped in distal view, twisted. ARGOT—POSTCRANIAL ANALYSIS OF LYCOPSIS 693

FIGURE 4. Caudal vertebrae. A–C, Lycopsis longirostris UCMP FIGURE 5. Scapula and shoulder joint. A, left scapula of Lycopsis 38061. A, Ca1–Ca5 in dorsolateral view; B, Ca1–Ca4 in dorsal view; and longirostris UCMP 38061 in lateral view; scale bar equals 10 mm. In B, C, C, an isolated posterior caudal vertebra (rank unknown) in dorsal view. and D (not to scale), specimens are Lycopsis longirostris UCMP 38061 D, Ca1–Ca9 of Thylacinus cynocephalus MNHN 1891-61 in dorsal view. and Prothylacinus patagonicus PU 015700. B, glenoid cavity of the left Scale bar equals 10 mm. scapula in distal view; C, left humeral head in proximal view, slightly distorted and damaged in Lycopsis; and D, proximal extremity of the left scapula in posterior view.

Elbow Joint—The distal extremity of the left humerus of Ly- copsis is poorly preserved, especially the anterior side of the (25%) and Cladosictis, Mayulestes, and Prothylacinus (approxi- trochlea (Fig. 6B). In distal view, the anterior and posterior mately 33% in these three taxa). Moreover, there is no anterior grooves of the humeral trochlea are not very concave (Fig. 7A). groove between the medial epicondyle and the trochlea, contrary On the ulna, the anconeal process (beak of the olecranon) is not to Mayulestes, Cladosictis, and Prothylacinus. very prominent anteriorly, and its lateral lip is much better de- The medial epicondylar crest is broken, but the preserved veloped than the medial one (Fig. 7). The distal part of the proximal root indicates that it was more slender than in Clad- humerus is more symmetrical than in Cladosictis, Mayulestes, osictis or Prothylacinus. This also indicates that there was an and Prothylacinus, in relation to a less prominent medial epicon- entepicondylar foramen in Lycopsis, in contrast to Borhyaena dyle (Fig. 7A); the distance between the medial lip of the troch- (Argot, 2003b). The lateral epicondylar crest is relatively well lea and the apex of the medial epicondyle represents approxi- developed along the distal third of the diaphysis (Fig. 6A, B) as mately 28% of the transverse width of the distal extremity of the in the other borhyaenoids. Proximally, it is slightly concave an- humerus in Lycopsis, which lies between values for Borhyaena teriorly along the lateral border, but the proximal apex is not so 694 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 24, NO. 3, 2004

prominent as it is in Prothylacinus. The olecranon fossa is deep, centrally located, slightly wider transversely than the articular facet of the humeral trochlea. The perforation observed on the left humerus is post-mortem damage. On the ulna, the coronoid process is longer anteroposteriorly than wide transversely, and it is slightly depressed medially, which suggests a relatively well- developed medial lip of the trochlea (broken on the specimen). The area of the coronoid process is approximately equivalent to that of the radial head, as in Prothylacinus but contrary to Borhy- aena. The capitulum exhibits a thick lateral lip, better developed than in Prothylacinus, but less than in Cladosictis. Above the articular facet, the radial fossa cannot be observed because of the perforation of the diaphysis. The proximal extremity of the ra- dius is oval-shaped, with a compression ratio of 66%, which is slightly higher than in Borhyaena (63%) but lower than in Pro- thylacinus (76%). The articular surface cannot be detailed as the proximal epiphysis is not preserved. On the ulna, the radial notch is a small rounded facet which forms an obtuse angle with the lateral side of the coronoid process in anterodistal view (Fig. 7B). Ulna and Radius—The ulna is transversely compressed, and its anteroposterior width is almost constant along all its length. The diaphysis is straight (Fig. 8B) and does not exhibit the con- vex posterior border observed in Mayulestes, Cladosictis, and Prothylacinus (Fig. 8A). Distally, the dorsal border is slightly concave posteriorly, but not so much as in Borhyaena (Fig. 8C). The olecranon is relatively long, 20% of the ulnar length as in Cladosictis and Mayulestes, which is between values for Prothyl- acinus (18%) and Borhyaena (23%). It is less inclined posteriorly in Lycopsis than in Thylacinus. On the medial side of the ulna of Lycopsis, the fossa where the ulnar head of the m. flexor digitorum profundus originates is short and shallow. By contrast, the lateral fossa, where the m. abductor pollicis longus originates, is deep and extends along two-thirds of the diaphysis. The insertion for the mm. biceps and brachialis, located mediodistally to the coronoid process, is long and well-defined. The anterior border of the ulna and the pos- terior border of the radius form a sharp crest below the proximal articulation, suggesting the insertion of a strong interosseous membrane. The radius (Fig. 8B) is approximately circular in cross-section at mid-shaft diameter. It is more compressed transversely proxi- mally, whereas it is compressed anteroposteriorly at the distal extremity. The distal extremity is relatively massive, as wide transversely as the distal extremity of the ulna, like that of Borhyaena, but unlike Prothylacinus, where the distal radial epiphysis is almost twice as wide as that of the ulna (Argot, 2003b). The radius of Lycopsis is not extended toward the ulnar diaphysis, and resembles more closely the radius of Cladosictis or Borhyaena in this respect than that of Prothylacinus. The lateral and medial sides of the diaphysis of the radius are flat, and do not exhibit fossae for the mm. flexor digitorum profundus or abduc- tor pollicis longus. Carpus and Manus—The distal facet of the radius articulating with the scaphoid is convex, especially near the styloid process. Consistently, the scaphoid bears a transversely extended proxi- mal groove. This morphology is more similar to that observed in Borhyaena than in Prothylacinus (Argot, 2003b. The proximal articular facet of the unciform is not helical, unlike the unciform of Prothylacinus (Argot, 2003b). The articular facet of the unci- form with Mc V is flat, narrow transversely, and the palmar process of the unciform is not very prominent. The trapezoid and trapezium are equivalent in size, which is consistent with a non- reduced pollex. The trapezium exhibits distomedially a small and FIGURE 6. Left humerus of Lycopsis longirostris UCMP 38061. A, flat facet that articulates with Mc I, different from the well- posterior view; B, anterior view; and C, lateral view. Scale bar equals developed and concave articular facet observed on the trapezium 10 mm. of Borhyaena. The Mc I is more robust than the other metacarpals and the ARGOT—POSTCRANIAL ANALYSIS OF LYCOPSIS 695

FIGURE 7. Elbow joint. Specimens are: Prothylacinus patagonicus PU 015700, Lycopsis longirostris UCMP 38061, Borhyaena tuberata MACN 2074-2078 (humerus) and PU 015701 (ulna), and Thylacinus cynocephalus MNHN 1891-61. A, right humerus in distal view, the arrow indicating the medial development of the entepicondyle. B, proximal extremity of the right ulna in anterior view (top) and anterodistal view (bottom). Not to scale.

proximal part is poorly preserved. The diaphysis is slightly (Argot, 2003c). The distal articular facet is trochlear-shaped. The twisted with the dorsal side facing dorsolaterally near the distal internal (ulnar) part is wider transversely than the medial one epiphysis. The distal epiphysis exhibits a very asymmetrical and prominent distally; the medial (radial) part is transversely shape (Fig. 9A, B), similar to what can be observed in Cladosictis narrower and more prominent ventromedially. Consistently, the

FIGURE 8. Right ulnae and radii in lateral view. A, Prothylacinus patagonicus PU 015700. B, Lycopsis longirostris UCMP 38061 (reconstructed from both ulnae and radii). C, Borhyaena tuberata PU 015701. Scale bar equals 10 mm. 696 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 24, NO. 3, 2004

FIGURE 9. Manus of Lycopsis longirostris UCMP 38061. A, right pollex articulated. B, focus on the elements of the right pollex: bottom, Mc I in distal, dorsal, ventral, and lateral views; middle, first phalanx in proximal, dorsal, ventral, and lateral views; and top, ungual phalanx in proximal, dorsal, ventral, and lateral views. C, Mc II and III in dorsal and lateral views, and Mc V in dorsal view. D, conjectural association of the metacarpals and phalanges of the right manus. E, proximal phalanx in dorsal, ventral, and lateral views. F, intermediate phalanx in dorsal and ventral views. G, ungual phalanx in lateral and dorsal views. Scale bars equal 10 mm.

proximal articular facet of the proximal phalanx of the pollex is cyon, and shorter than in Prothylacinus. However, in Lycopsis asymmetrical, with a medial part narrower transversely but with these phalanges exhibit, as in Prothylacinus, a small palmar fossa a great arc of curvature, and a lateral part that is wider trans- suggesting a greater range of flexion of the claws than in Borhy- versely, but relatively less extended dorsoventrally. This articu- aena, where this fossa is absent (Argot, 2003b). The ungual pha- lation emphasizes the divergence of the pollex from a strict para- langes are transversely wide in dorsal view and they do not ex- sagittal plane during flexion-extension, since it implies a slight hibit a sharp dorsal crest, contrary to Prothylacinus and Sipalo- convergence of the pollex towards the other digits during flexion cyon. The dorsal border is straight proximally, and the ventral vs. a slight divergence during extension. The interphalangeal border of the ungual phalanx is not very concave. The flexor joint is also slightly asymmetrical, although less than the meta- tubercule is relatively well-developed. The ungual phalanges are carpophalangeal one, which increases the obliquity of the orien- slightly shorter than the proximal phalanges, contrary to Proth- tation of the digit during flexion-extension. The pollex of Lycop- ylacinus and Sipalocyon. sis is therefore considered to be pseudo-opposable. The ungual phalanx of the pollex is better developed than the ungual pha- Hindlimb and Innominate langes of the other digits. The Mc III has a rough muscular scar located dorsally in the Innominate and Hip Joint—The left part of the pelvis is re- middle of the shaft, the probable insertion of the m. extensor moved from the matrix but is poorly preserved (Fig. 10A). As in carpi radialis brevis. The distal external articular condyle of Mc the Santacrucian borhyaenoid taxa, but contrary to Mayulestes, V is more developed than the internal one (Fig. 9C, D), and this the ilium is aligned with the ischium. Moreover, the length of the condition suggests that flexion-extension of the fifth digit also iliac neck (between the anterior edge of the acetabulum and the did not take place in a parasagittal plane. posterior edge of the sacral articulation), relative to the total The proximal phalanges of the four lateral digits represent length of the innominate, is approximately 11% in Lycopsis,asin approximately 40% of the Mc III (see Appendix), i.e., they are Cladosictis (12.5–13%), and between Mayulestes (16.5%) and relatively as long as in Cladosictis and Sipalocyon, but shorter Prothylacinus (4.5%). There is no distinct fossa for the m. iliacus, than in Prothylacinus (Argot, 2003b, c). Their palmar side is not except a small ventral thickening of the iliac blade anteriorly to grooved but flat to slightly convex, which increases the robust- the acetabulum. The lesser femoral trochanter, where the m. ness of the phalanges. The intermediate phalanges represent iliacus inserts, is poorly preserved (Fig. 10C). The iliac blade of two-thirds of the proximal phalanges, i.e., they are relatively Lycopsis is quadrangular in shape, high dorsoventrally, and it longer than in Borhyaena, approximately as long as in Sipalo- protrudes dorsally above the sacral articulation as in Cladosictis ARGOT—POSTCRANIAL ANALYSIS OF LYCOPSIS 697

FIGURE 10. Innominates and femora. Specimens are: Lycopsis longirostris UCMP 38061, Prothylacinus patagonicus PU 015700, and Thylacinus cynocephalus MNHN 1891-61. A, innominates in lateral view. B, innominates in dorsal view. C, left femur of Lycopsis longirostris UCMP 38061 in anterior, posterior, and medial views. D, proximal extremity of the femur in two comparative specimens in anterior (top), posterior (middle), and medial (bottom) views. Scale bar equals 10 mm in C.

and Prothylacinus. The anteroventral extremity of the ilium, as relatively longer and more slender than in Prothylacinus and well as the ischiac tuberosity, are deflected outward in dorsal Thylacinus (Fig. 10D). The transverse axes of both epiphyses of view as in Prothylacinus (Fig. 10B). The gluteal fossa is oriented the femur are not parallel in Lycopsis, but form an angle of laterally and the greater trochanter, where the m. glutei insert, is approximately 40° (the transverse axis of the proximal epiphysis as high as the femoral head (Fig. 10C). The right part of the being oriented anteromedially-posterolaterally) as in Sarcophi- innominate, still in the matrix (Fig. 3), indicates that the ventral lus, Thylacinus, and the Paleocene Mayulestes, but contrary to ramus of the pubis is slender, which suggests poorly developed the Santacrucian borhyaenoid taxa where no torsion is observed. adductors. However, the insertion of the adductors is relatively Knee Joint—The distal epiphysis of the femur of Lycopsis is prominent on the posterior side of the femur (Fig. 10C, right), poorly preserved, wider than deep in distal view (Fig. 11A). The although less than in Prothylacinus. No epipubic bones have trochlea is shallow and the lateral ridge is low (the medial ridge been discovered. is not preserved). In anterior view (Fig. 10C, left), the longitu- The acetabulum is poorly preserved (Fig. 10A). The posterior dinal axis of the femoral trochlea seems to be slightly oblique part of the articular facet does not extend so far ventrally as in laterally, although this must be considered with caution because Prothylacinus. In dorsal view, the dorsal border of the acetabu- of the poor preservation of the distal epiphysis. Contrary to Cla- lum of Lycopsis is less concave than in Prothylacinus, partly in dosictis, but as in Prothylacinus, there is no fossa on the femoral relation to a weaker anterior inferior iliac spine, and partly be- diaphysis above the trochlear groove. Contrary to Prothylacinus, cause the articular facet faces slightly more ventrally and less however, no ossified patella has been discovered for Lycopsis. laterally in Lycopsis than in Prothylacinus. The head of the left The femoral condyles are not preserved in their natural shape, femur, removed from matrix for examination, is poorly pre- but they seem to be of similar width. The lateral condyle does not served. The dorsal and posterior sides of the neck of the femur suggest an articulation with the fibula. The proximal epiphyses of are damaged and the extension of the articular surface on the both tibias are poorly preserved. They exhibit a prominent and neck cannot be observed. On the femoral head, the fossa where robust anterior tuberosity, with an apex located more distally the ligamentum teres inserts is very shallow. The femoral neck is than the level of the proximal facets (Fig. 11B, C). This tuber- 698 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 24, NO. 3, 2004

FIGURE 11. Knee joint and crus. A, distal epiphysis of the right femur in distal view: left, Lycopsis longirostris UCMP 38061; and right, Prothylacinus patagonicus PU 015700. B, proximal epiphysis of the right tibia in proximal view: left, Lycopsis longirostris UCMP 38061 (lateral condyle broken); and right, Prothylacinus patagonicus PU 015700. C, right tibia of Lycopsis longirostris UCMP 38061 in anterior and medial views. D, right fibula of Lycopsis longirostris UCMP 38061 in lateral and medial views. Scale bars equal 10 mm.

osity extends distally in a robust anterior crest, well-developed Santacrucian borhyaenoids, which suggests a good stabilization but not sharp. of the astragalonavicular contact during dorsiflexion. The lateral Tibia and Fibula—The diaphysis of the tibia is straight in part of the astragalus articulating with the fibula is small, but too anterior and lateral views and is elliptical in cross-section, trans- damaged to be discussed. versely compressed (Fig. 11C). The anterior crest is slightly con- On the left calcaneum, the calcaneoastragalar and sustentacu- cave medially in the middle of the shaft. Laterally and below the lar facets do not exhibit the same shape as observed in Sipalo- anterior tibial tuberosity, a small fossa indicates the origin of the cyon or Borhyaena.InLycopsis, both facets extend anteropos- m. tibialis anterior. On the medial side, the insertion of the m. teriorly, and are narrow transversely (Fig. 12B). The longitudinal semimembranosus is located proximally and near the posterior axes of these two facets are almost parallel, and parallel to the edge. The insertions of the mm. semitendinosus caput ventrale longitudinal axis of the tuber calcanei, which is slightly inclined and gracilis are not well-defined along the anterior crest. medially. The tuber calcanei is as long in Lycopsis as it is in The fibula of Lycopsis is straight. It is slightly elliptical in Sipalocyon relative to the total length of the calcaneum. The cross-section, but there is no well-developed crest extended to- calcaneoastragalar facet faces dorsomedially in Lycopsis (Fig. ward the tibia as observed in Cladosictis or Prothylacinus. The 12B), whereas it faces dorsally in Borhyaena. The sustentacular fibular head is triangular in shape in lateral view (Fig. 11D). It is facet is slightly concave and faces dorsally. It does not reach the not well-preserved and the lateral part of the proximal epiphyses calcaneocuboid facet distally. The sustentacular and calcaneoas- of both tibiae are damaged, which prevents study of the proximal tragalar facets are separated by a deep fossa suggesting a strong articulation between the two bones of the crus. The posterior ligamentous attachment between the astragalus and the calca- part of the head is prominent proximally as in Sipalocyon, but neum. No peroneal process or calcaneofibular facet is preserved, the presence of an articular facet with a parafibula or with the but the dorsolateral part of the calcaneum is damaged. When femur cannot be ascertained in Lycopsis. Distally, the groove for articulated with the calcaneum, the astragalar head is located the tendons of the m. peronei is shallow. On the distal epiphysis more medially than dorsally to the calcaneocuboid facet. The of the tibia, an articular facet extends anteroposteriorly, suggest- calcaneum of Lycopsis has a deep fossa medioventral to the ing the possibility of anteroposterior gliding movements of the calcaneocuboid facet. A groove found in the same location is distal extremity of the fibula. also present in some fossil eutherians from the Late Cretaceous Ankle Joint—Both astragali and calcanea of Lycopsis are and miacoid Carnivora (Szalay and Decker, 1974), and these poorly preserved, especially the right bones (Fig. 12A). The left authors suggest that it might be related to the attachment of the astragalus exhibits a morphology common to borhyaenoids (see plantar calcaneocuboid ligament. Such a fossa is not observed in Szalay, 1994:204–210 for a description and interpretation of the the other borhyaenoid taxa in which the calcaneum is known. tarsus of a Santacrucian borhyaenoid, Sipalocyon gracilis; see Pes—The entocuneiform is long proximodistally and very also Argot 2002, 2003b, c). The astragalotibial medial (ATim) compressed transversely, which does not suggest a potentially facet is perpendicular to the astragalotibial lateral (ATil) facet divergent Mt I (Fig. 12C). The metatarsal bones are quite poorly and forms a long groove for the guidance of the tibial malleolus. preserved, especially the proximal epiphyses. The longest meta- The malleolus of the tibia protrudes distally and its anteropos- tarsal (Mt ?III) is subequal to Mc III. The first metatarsal is not terior axis is parallel to that of the proximal epiphysis, in contrast vestigial contrary to what is observed in Prothylacinus (compare to Mayulestes. The neck of the astragalus is robust, deep dorso- Fig. 12D, E). The proximal part is broken and therefore does not ventrally. The astragalonavicular facet is deep dorsoventrally allow description of the proximal articular facet. The distal ex- and narrow transversely. The proximal part of this facet is ori- tremity of Mt V is twisted in relation to the proximal epiphysis, ented dorsally and exhibits a transverse groove, unknown in the the dorsal side facing laterodorsally (i.e., externally). The angle ARGOT—POSTCRANIAL ANALYSIS OF LYCOPSIS 699

FIGURE 12. Tarsal bones and pes. A, left astragalus in dorsal (a) and anterior (b) views. B, left calcaneum in dorsal (a) and anterior (b) views. Specimens are Lycopsis longirostris UCMP 38061, Prothylacinus patagonicus PU 015700, and Borhyaena tuberata MACN 2074-2078. C, entocunei- form of Lycopsis longirostris UCMP 38061 in lateral and posterior views. D, associated metatarsals and phalanges of the pes of Lycopsis longirostris UCMP 38061 (the association of the phalanges is conjectural). E, left pes of Prothylacinus patagonicus PU 015700. Scale bars equal 10 mm.

between the transverse axes of both epiphyses is approximately terior part of the neural process of the axis and the ventrolateral 45°, which suggests a convergence of the fifth digit towards the flange of C6 are more slender anteroposteriorly. These features other digits of the foot during flexion, as in the manus. suggest a less powerful nuchal musculature in Thylacinus than in The proximal phalanges exhibit the same shape as those of the Lycopsis, although the former is considered to have had hyper- hand; they are robust dorsoventrally, and the plantar side is carnivorous habits (Johnson and Wroe, 2003). slightly convex. The dorsal edge of the proximal articular facet is The neural processes of the thoracic vertebrae of Lycopsis less prominent proximally than the ventral one, which may in- exhibit a constant shape and posterior orientation between T2 crease the range of dorsiflexion. The longest phalanx of the hind- and T9, in contrast to the robustness and orientation of this foot represents approximately 40% of the length of the longest process in T1. This condition is more similar to that of arbos- metatarsal (same ratio as in the manus). As in the manus, the cansorial model species (Neofelis nebulosa, Eira barbara, Arct- intermediate phalanges have a fossa on the plantar side suggest- ictis binturong) than to that of terrestrial, predatory extant forms ing a great potential range of flexion of the ungual phalanges. like canids, hyaenids, or in the thylacine, where the first three of The ungual phalanges are very similar to those of the manus, and four thoracic neural processes are higher and more robust than not longer in absolute size (however, the tip is broken in several the following ones. The morphology observed in Lycopsis, there- of them). fore, indicates: (1) that the neural process of T1 had to withstand forces from the nuchal musculature, whereas the forces exerted DISCUSSION on the neural process of T2 and posterior thoracic vertebrae Axial Skeleton were from the deep muscles of the back, mm. semi-spinalis and multifidus dorsi; (2) that the anteroposterior tractions exerted on The cervicals of Lycopsis exhibit various features characteris- the anterior part of the thoracic area might have been smaller tic of other Miocene borhyaenoids (Argot 2003b, c). The neural than in living predators. process of the axis is extended anteroposteriorly, and the axis The neural process of T6 in Lycopsis exhibits approximately and the third cervical are strongly keeled. This indicates a pow- the same posterior inclination as the neural process of a pre- erful nuchal musculature, especially the parts involved in the diaphragmatic vertebra (T?7) preserved in Borhyaena (Sinclair, flexion and rotation of the head (Mm. obliquus capitis caudalis, 1906:pl. XLV, fig. 6; Argot, 2003b). However, the neural process longus colli, longus capitis). According to the curvature of the of Lycopsis is less robust and much shorter than in Borhyaena (it neck preserved after death, C6 represents the point of maximal represents only 55% of the length of the neural process in Borhy- curvature (ventral convexity), and its extended ventrolateral aena). This also emphasizes relatively smaller anteroposterior flange represents a powerful leverage for the m. longus colli. forces exerted on the neural processes compared to those ex- Comparatively, the anterior cervical vertebrae of Thylacinus ex- erted in Borhyaena, a condition that could be partly related to a hibit incipient sagittal ventral processes (Fig. 1D), and the pos- less massive skull in Lycopsis. The considerable height of the 700 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 24, NO. 3, 2004 neural spine of the vertebra preserved in Borhyaena provides Thylacinus exhibits a posterior part of the body that differs from greater leverage for the epaxial muscles and allows the develop- placental carnivorans; the tail of this marsupial is not well dif- ment of interspinous ligaments providing resistance towards sag- ferentiated from the body as in canids, but seems to be an ex- ittal stresses. Head support must have been considerable in tension of the hindquarters, and this might have had conse- Borhyaena, a borhyaenoid characterized by a particularly mas- quences on the pelvis and lower back movements. The size and sive skull, in contrast to Lycopsis characterized by a compar- shape of the caudals suggest that in Lycopsis the tail was prob- atively lighter skull and shorter neck. The neural process of T6 in ably externally quite similar to that of Thylacinus (although Thylacinus is equivalent in size to that of Lycopsis, but is rela- heavier), playing a non-negligible role in locomotion, although tively more slender. this is difficult to test since the extinction of the Australian taxon. The anticlinal vertebra is T11 in Lycopsis, like probably in The length of the tail of Lycopsis cannot be estimated. Cladosictis and Prothylacinus (T?11 in these latter taxa where the total number of thoracolumbar vertebrae is unknown: Argot Forelimb and Pectoral Girdle 2003b c), although the anticlinal is a lumbar in the Paleocene Mayulestes (Argot, 2003a). The anticlinal vertebra is T10 in Thyl- acinus, T11 in Canis, T12 in Neofelis and Eira. There are eight The quadrangular scapula of Lycopsis is distinct from that of post-anticlinal presacral vertebrae in Lycopsis and Eira, and nine the Santacrucian borhyaenoids, Prothylacinus and Cladosictis, in Thylacinus, Canis, and Neofelis, because of a variability in the and especially from the triangular scapula of Mayulestes. This total number of thoracolumbar vertebrae. Only some members condition does not suggest frequent climbing habits in Lycopsis, a quadrangular scapula being usually related to walking and trot- of the living Carnivora (e.g., ursids) do not exhibit an anticlinal ting species whereas the triangular scapula of climbing species is vertebra, and within a given family, the species characterized by characterized by a relatively large infraspinous fossa with a cau- speed and flexibility have an anticlinal vertebra located more dal angle extended posteriorly, and by an obtuse angle between anteriorly, and more strongly inclined neural spines than slower the vertebral border and the scapular spine (Maynard Smith and Gulo Mellivora forms (e.g., compared with among mustelids, Savage, 1956; Oxnard, 1968; Roberts, 1974; Taylor, 1974; Argot, pers. obs.). The same has been observed in South American and 2001). In Lycopsis, the glenoid cavity is oriented ventrally Australian marsupials (Argot, 2003a), and the absence of an whereas it is oriented ventroposteriorly in Thylacinus. This con- anticlinal vertebra has also been noticed in some primates and dition, together with the proximal convexity of the articular facet edentates (Jenkins, 1970), this absence being related to lateral of the humeral head, indicates a shoulder joint that is more (instead of sagittal) attachments of the tendons of the m. longis- suitable for abductive movements in Lycopsis than in Thylaci- simus dorsi (Slijper, 1946). The anterior position of the anticlinal nus. The width of the scapular neck and the development of the vertebra in Lycopsis therefore suggests sagittal attachments of greater tubercle of the humerus in Lycopsis indicate well- the extensors of the back, a feature that seems related in extant developed mm. spinati, which mainly help to stabilize the shoul- species to an increased sagittal flexibility. However, the neural der joint (Davis, 1949; Jenkins and Weijs, 1979). processes of the post-anticlinal vertebrae of Lycopsis are not so No clavicle has been located for Lycopsis.InThylacinus the strongly inclined anteriorly than in Cladosictis and they are an- clavicle is vestigial. It is a 5-cm-long curved rod, a condition teroposteriorly wider, which decreases the space for the inter- related to slight modifications in the trapezodeltoidian muscula- spinous ligaments (Gambaryan, 1974). This condition suggests ture (Smith, 1982). The deltopectoral crest is very long in Ly- that the sagittal bending and stretching of the vertebral column copsis, but it is much less prominent and sharp distally than in of Lycopsis was probably not so extensive as in Cladosictis and Prothylacinus. This length suggests a long insertion for the pec- some living taxa like felids (e.g., Neofelis). However, this restric- toralis, but (1) this development is a feature common to all the tion is difficult to evaluate given that the morphology of the borhyaenoids in which it is preserved, and (2) Thylacinus, a fully neural processes of Lycopsis is quite similar to that observed in terrestrial form, also exhibits a very long insertion of the pecto- Eira barbara, a mustelid which climbs with agility and springs ralis (a muscle more developed in the thylacine than in the swiftly through the trees (Brosset, 1968). smaller dasyurids: Smith, 1982). The development of the pecto- The well-developed anapophyses between T12 and L3 also ralis in Lycopsis, combined with the facts that the scapula does contributed to the stability of the vertebral column. Their reduc- not indicate specialized climbing habits whereas the shoulder tion on L4 and L5 suggests that minimal bending movements joint indicates a greater mobility than in a fully terrestrial spe- were exerted on the lower back. The orientation of the trans- cies, suggests an important role of the forelimb in Lycopsis in verse processes of the lumbar vertebrae of Lycopsis, which are manipulative behavior, for foraging or feeding. large anteroposteriorly but not as prominent anteriorly and con- At the elbow joint, the asymmetrical anconeal process of the cave ventrally as in Mayulestes, Prothylacinus,orThylacinus ulna (or beak of the olecranon), together with the slight medial (Fig. 3D, E), does not provide for a great mechanical advantage deflection of the coronoid process, which suggests a well- of the quadratus lumborum: the attachments of this muscle are developed medial lip of the trochlea, are features indicating that not located as far from the center of rotation of each vertebra as flexion-extension did not take place in a strict parasagittal plane. in Mayulestes, Prothylacinus, and Thylacinus (Argot 2003a, b). The entepicondyle of the humerus, less prominent medially than Thylacinus is also characterized by the development of a sagittal in Mayulestes, Cladosictis, and Prothylacinus, together with the crest on the ventral side of the vertebral bodies of L1–L3 (lum- short and shallow fossa on the medial side of the ulna, the ab- bars unknown in Prothylacinus), emphasizing a robust attach- sence of palmar groove on the proximal phalanges of the hand, ment of the quadratus lumborum. The condition observed in and the poorly prominent palmar process of the unciform, im- Lycopsis is consistent with a restricted sagittal flexibility com- plies a relatively weakly developed m. flexor digitorum profun- pared to the potential range in Mayulestes and Prothylacinus. dus. Similar features are found in the terrestrial Thylacinus and The morphology of the anterior caudal vertebrae preserved in indicate that Lycopsis was not an obligate arboreal form. The Lycopsis, quite similar to that of Cladosictis and Thylacinus (Fig. well-developed lateral epicondylar crest of Lycopsis, compared 4D), suggests that the tail was muscular at its base. However, the with Thylacinus, suggests that the m. brachioradialis, a flexor- anapophyses do not exhibit a prominent lateral crest contrary to supinator of the forearm, was much better developed in the what is observed in Prothylacinus, Cladosictis, and Mayulestes, borhyaenoid than in the thylacinid in which this muscle is poorly the presence of this crest being usually associated with a well- developed (Smith, 1982). The bicipital tuberosity is prominent developed m. longissimus caudae (Muizon, 1998; Argot, 2003a). and located proximally on the radius of Lycopsis, a feature that, ARGOT—POSTCRANIAL ANALYSIS OF LYCOPSIS 701 associated with the robustness of the supraglenoid tuberosity of tion of thylacinids and borhyaenoids although they are difficult the scapula, implies a well-developed m. biceps brachii, a condi- to interpret. The broad area of the gluteal fossa and the height of tion consistent with a manipulative role of the forelimb. the greater trochanter (as high as the femoral head in Lycopsis, The straightness of the ulna of Lycopsis, compared with that Cladosictis, and Prothylacinus), suggest well-developed glutei in Prothylacinus, Cladosictis, and Mayulestes in which the posterior thylacinids and borhyaenoids, more than in living South Ameri- border is convex proximally, does not suggest combined trac- can didelphids or Sarcophilus (Argot, 2002, 2003c). The antero- tions of the biceps/brachialis and triceps caput longum as occurs ventral deflection of the ilium and the large area developed an- in arboreal forms (Argot, 2001). However, the posterior border teriorly to the sacral articulation suggests a well-developed lum- of the ulna of Thylacinus is even more concave posteriorly than bar epaxial musculature in Lycopsis. Comparing with in Lycopsis, i.e., it is more similar to the ulna of placental cur- Mayulestes, the iliac neck is shorter in Lycopsis, and the ilium is sorial forms. In Thylacinus, the triceps is extremely well- aligned with the dorsal ramus of the ischium, both features sug- developed (Smith, 1982), as an adaptation to running. Although gesting more important shearing forces exerted on the pelvic the radius of Lycopsis does not exhibit the same anterior curva- girdle of Lycopsis. ture and the same extension towards the ulna than in Prothyl- The length of the ischium relative to the total length of the acinus, which probably reduced the mechanical advantage of the innominate falls between 41% in Cladosictis and Mayulestes, and pronator-supinator muscles, some rotational capabilities are pro- 46% in Lycopsis and Prothylacinus, and an increased postace- posed, given the relative flat angle between the radial notch and tabular length of the pelvis is usually associated with increased the coronoid process of the ulna, a condition that is more fre- leverage for hamstring muscles (Maynard Smith and Savage, quent in species with supinative capabilities (Argot, 2001). 1956; Finch and Freedman, 1988). In Lycopsis, this condition is The scaphoradial joint of Lycopsis suggests limited dorsiflex- consistent with the anteroposterior depth of the posterior ramus ion and a potentially semi-digitigrade or digitigrade posture, con- of the ischium and with ischiac tuberosities slightly deflected sistent with the robustness of the proximal phalanges. The meta- outwards, both features suggesting well-developed hamstring carpals of Lycopsis are slightly longer than in Cladosictis and muscles. As in the other borhyaenoids, no ossified epipubic Prothylacinus relative to the forelimb length, which might rep- resent partly an allometric growth because the forelimb of Ly- bones have been discovered for Lycopsis, and the innominate is copsis is longer than in Prothylacinus and Cladosictis relative to too poorly preserved to check the presence of facets. Thylacinus thoracolumbar length. The relative shortness of the metacarpals had only vestigial epipubic bones that are small and flattened of Lycopsis compared with extant species probably did not pre- fibro-cartilages. They appear as a thickened part of the tendon of clude it from being semi-digitigrade or digitigrade if we refer to the oblique abdominal muscle (Smith, 1982), and their potential Thylacinus which has also short toes on the manus (Smith, 1982). relation with the locomotion performed is yet unknown. Although the distal articular facet of Mc I is asymmetrical in the The hip joint is poorly preserved in Lycopsis. However, a few thylacinid, with an internal condyle more prominent distally than differences can be emphasized in comparison to Prothylacinus: the external one, it does not parallel the trochlear-shaped meta- (1) the posterior part of the acetabulum is less extended ventrally carpophalangeal joint of the pollex of Lycopsis.InThylacinus, in Lycopsis, which suggests a relatively restricted excursion of the pollex is especially short, Mc I represents 46% of the length the femur (especially in protraction); (2) the anterior edge of the of Mc III vs. 55% in Lycopsis. The pseudo-opposable pollex of acetabulum is less extended laterally in Lycopsis because of a Lycopsis certainly provided for grasping ability of the hand, di- weaker anterior inferior iliac spine, which may suggest a rela- verging when extended and converging when flexed. This con- tively reduced thrust exerted by the hindlimb of Lycopsis. Fur- dition certainly allowed this taxon to use its hand for a manipu- thermore, the slender and relatively long neck of the femur of lative behavior, to holding prey or grasping branches. As em- Lycopsis may be partly related to reduced forces exerted at the phasized by Wells and Nichol (1977), such hand patterns are hip joint. The orientation of the acetabulum, which faces more considered suitable for scrambling over rough ground and if ventrally in Lycopsis and Thylacinus than in Prothylacinus, sug- clawed, to climbing. The ungual phalanges of Lycopsis are more gests less abductive capabilities of the femur in the two former robust but quite similar to those of Thylacinus. Their shape taxa, and possibly a relatively more erected hindlimb in Lycopsis (short, wide transversely, and with a dorsal border not sharp and than in Prothylacinus in relation to more terrestrial habits. In not very convex) indicates a mainly terrestrial mode of life com- Lycopsis, the absence of a rugose muscular scar on the dorsal pared with living species (Argot, 2001, 2003b). ramus of the ischium, where the m. gemelli originate, in contrast with Prothylacinus, suggests less rotational constraints exerted on the hip joint of Lycopsis, which is also consistent with more Hindlimb and Innominate parasagittal movements. The knee joint of Lycopsis is very poorly preserved. However, The resemblance of the innominate of borhyaenoids (Lycop- the wide distal femoral epiphysis (in distal view), the shallow sis, Cladosictis, and Prothylacinus) to that of Thylacinus is note- femoral trochlea, and the lack of an ossified patella, compared worthy, especially when comparing with the dasyurid Sarcophi- with the deeply grooved femoral trochlea of Thylacinus, suggest lus. The innominate of Sarcophilus exhibits a very generalized that Lycopsis had a poorly stabilized knee joint, and therefore shape within marsupials. The iliac blades are elongated antero- that it was not a specialized runner. Within Borhyaenoidea, the posteriorly, narrow dorsoventrally, and thick transversely. They femoral condyles of Lycopsis are more similar to those of Clad- represent 66% of the total pelvic length, a value similar to what osictis than to those of Borhyaena, and suggest movements less is obtained for living didelphids (Argot, 2002). The area where restricted in a parasagittal plane than in Borhyaena. the glutei originates is relatively small and oriented dorsally. The diaphysis of the tibia is straight in Lycopsis,asinClad- According to MacAlister (1870), the m. gluteus medius is small. osictis and Prothylacinus, in contrast with the Paleocene Mayule- The acetabular border is well-defined and sharp, and the iliacus stes characterized by a sigmoidal tibia (Argot, 2002). The tibia of fossa is much broader than in borhyaenoids or Thylacinus. Also, Lycopsis is as long as that of Thylacinus relative to thoracolum- contrary to borhyaenoids and Thylacinus, the sacro-iliac articu- bar length, and longer than that of Prothylacinus. This shorten- lation is located far anteriorly to the acetabulum, which suggests ing of the distal part of the hindlimb of Prothylacinus probably less shearing forces applied on the pelvic girdle of Sarcophilus. resulted in more powerful but slower movements of the hind foot The resemblance of the innominate of Thylacinus and borhyae- in relation to arboreal habits (Argot, 2003b) whereas the tibia of noids therefore suggests similar constraints required by locomo- Lycopsis suggests a primary terrestrial mode of life. 702 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 24, NO. 3, 2004

Although the astragalus is not well-preserved, it is clear from PROPORTIONS OF THE LIMBS the astragalotibial articular facets that the upper ankle joint was restricted to flexion-extension occurring in a parasagittal plane. Various elements of the skeleton can be expressed as frac- Moreover, the lateral tibial facet is horizontal in lateral view and tions of one part adopted as a standard, like the thoracolumbar the anteroposterior axis of the tibial malleolus is not oblique length (Fig. 13), and this provides for a quantitative analysis of relative to that of the proximal epiphysis, both features preclud- body form in the species concerned. Because correlations be- ing the foot from abduction-adduction movements during flex- tween indices and habits may be direct, indirect, or accidental ion-extension. It seems that Lycopsis has lost the calcaneofibular (Hildebrand, 1952), this methodology is only used as a comple- articulation, although the size of the fibula suggests that this ment of the previous detailed analysis of the morphology of the bone is still important as a load bearer in the crus. The relatively bones. flat calcaneocuboid facet (much less concave than in Sipalo- The metrical analysis of forelimb length relative to thoraco- cyon), and the poorly convex astragalonavicular facet that is lumbar length reveals that Lycopsis is relatively similar to Eira better developed dorsoventrally than transversely, indicate a re- barbara, Felis yagouaroundi, Neofelis nebulosa, Arctogalidia tri- stricted mobility at the transverse tarsal joint apart from para- virgata, and Ailurus fulgens, i.e, placental Carnivora which are sagittal movements. As a general trend, the tarsal joints of Ly- arboscansorial and relatively agile and fast forms (Brosset, 1968; copsis seem to maximize parasagittal flexion-extension and Nowak and Paradiso, 1983; Sunquist, 1992), except maybe Ailu- transverse stability, which is more suited for terrestrial locomo- rus although detailed ethological data are lacking about it. Fig- tion than arboreal one. However, it is noteworthy that the plane ure 14 confirms that the proportions of the forelimb of Lycopsis of the lower ankle joint forms an angle of 60° with the horizontal match those of placental arboscansorial taxa (Ailurus, Neofelis, plane (Fig. 12B), whereas this angle is only 20° in Borhyaena. Felis, and Eira), although the metacarpals of Lycopsis are This obliquity indicates that the lower ankle joint was not stabi- shorter than in the three latter genera. The ratio proximal pha- lized in Lycopsis when the foot lay on a horizontal ground. lanx/Mc III in Lycopsis is in between Sipalocyon and Cladosictis The hindfoot of Lycopsis is characterized by short metatarsals, on one hand, and Thylacinus on the other hand, all ratios being which precludes fast running. Moreover, the twisted Mt V im- included between 40 and 50% (Table 1). In Prothylacinus, this plies the ability of the animal to grasp curved supports or objects. ratio is over 50%, which is the highest value found within Borhy- It is noteworthy that contrary to Prothylacinus which exhibits aenoidea and increased the grasping ability in this taxon. various features specialized towards arboreal habits combined The proportions of the forelimb of Lycopsis are quite similar with a vestigial hallux, Lycopsis exhibits various features indi- to those of Thylacinus cynocephalus that nevertheless has a rela- cating a more terrestrial mode of life, but does not have a re- tively longer forearm (Fig. 13). This is reflected in the brachial duced Mt I. However, the proximodistally elongated entocunei- index, which is 0.8 in Lycopsis (Table 1), Neofelis, Felis, Ailurus, form leaves little doubt that the hallux was not divergent. The Arctictis, and Ursus, but equals 1 in Thylacinus and Canis lupus. metatarsals of Thylacinus are longer than in Lycopsis compared The relatively longer distal limb elements of Thylacinus is con- with the metacarpals (Table 1) and the thylacine has lost its hallux sistent with the hypothesis of pursuit-predator (Jones and Stod- (as almost all the other dasyurids), whereas the well-developed dart, 1998) in comparison with arboscansorial taxa. However, hallux of Lycopsis is consistent with poor running ability. Thylacinus had a short forelimb comparatively to a placental

TABLE 1. Limb proportions of boryaenoid marsupials and placental carnivorans. Abbreviations: e, estimated proportion; F, femur length; H, humerus length; McIII, third metacarpal length; MtIII, third metatarsal length; PP, proximal phalanx length (phalanx of digit III if associated, maximum phalanx length if not); R, radius length; T, tibia length.

Brachial Crural Tibio-radial Intermembral index Specimens index (R/H) index (T/F) index (R/T) (H+R+McIII/F+T+MtIII) Lycopsis longirostris UCMP 38061 0.81e 0.975 0.70e 0.79 Cladosictis patagonica PU 015070 0.70e 0.93e 0.68e 0.78e Prothylacinus patagonicus PU 015700 0.84 0.87 0.75 0.785 Thylacinus cynocephalus MNHN 1891-61 1.01 1.00 0.85 0.815 Neofelis nebulosa MNHN 1961-101 0.82 0.95 0.77 0.82 Arctictis binturong MNHN 1975-78 0.79 0.91 0.845 0.91 Ursus malayanus MNHN 1913-505 0.845 0.755 1.06 1.00 Canis lupus MNHN 1984-08 1.00 1.05 0.88 0.90 Felis yagouaroundi MNHN 1900-216 0.79 0.94 0.715 0.755 Ailurus fulgens MNHN 1960-85 0.795 0.95 0.82 0.885 Arctogalidia trivirgata MNHN 2001-495 0.69 0.95 0.69 0.795 Eira barbara MNHN 1973-148 0.765 0.95 0.75 0.845

McIII/ MtIII/ Specimens (H+R+McIII) (F+T+MtIII) McIII/MtIII PP/McIII MtIII/F Lycopsis longirostris UCMP 38061 0.125 0.11 0.915 0.445 0.235 Cladosictis patagonica PU 015070 0.11e 0.13e 0.68e 0.41e 0.28e Prothylacinus patagonicus PU 015700 0.11 0.09 0.94 0.515 0.19 Thylacinus cynocephalus MNHN 1891-61 0.115 0.14 0.67 0.47 0.33 Neofelis nebulosa MNHN 1961-101 0.14 0.15 0.765 0.665 0.34 Arctictis binturong MNHN 1975-78 0.105 0.105 0.915 0.655 0.225 Ursus malayanus MNHN 1913-505 0.10 0.095 1.04 0.625 0.19 Canis lupus MNHN 1984-08 0.17 0.17 0.90 0.395 0.43 Felis yagouaroundi MNHN 1900-216 0.15 0.18 0.615 0.68 0.43 Ailurus fulgens MNHN 1960-85 0.13 0.145 0.775 0.57 0.335 Arctogalidia trivirgata MNHN 2001-495 0.115 0.14 0.64 0.725 0.32 Eira barbara MNHN 1973-148 0.15 0.14 0.89 0.56 0.32 ARGOT—POSTCRANIAL ANALYSIS OF LYCOPSIS 703

FIGURE 13. Body proportions of three borhyaenoid taxa and various extant carnivoran model species (same specimens as in Table 1). The neck and individual limb lengths (of humerus, radius, and third metacarpal for the forelimb on left side; femur, tibia, and third metatarsal for the hindlimb on right side) are expressed as a percentage of the thoracolumbar length (used as a standard, equated to 100). A warning has to be put on the graphs obtained for Prothylacinus and Cladosictis, as their axial skeleton is not as well-known as in Lycopsis.

pursuit carnivore like Canis lupus where the length of the limbs in Dasyurus), and an elongated skull which mimics that of the favors a cursorial adaptation (Maynard Smith and Savage, 1946; placental wolf and contrasts strikingly with the foreshortened Hildebrand, 1952; Janis and Wilhelm, 1993). As noticed by Keast and massive skull of the scavenger and bone-crushing dasyurid (1982), the forelimb of Thylacinus is modestly longer than in Sarcophilus (Keast, 1982). Although the Tasmanian tiger pro- smaller and more generalized dasyurids. The forelimb of the vides one of the most striking examples of convergent evolution thylacine represents 74% of the thoracolumbar length, vs. 71% in external aspect with the placental wolf, the similarities were in Antechinus and 69% in Dasyurus, whereas the hindlimb rep- only superficial (Keast, 1982; Smith, 1982; Jones and Stoddart, resents 91% of the thoracolumbar length in Thylacinus and 1998; Johnson and Wroe, 2003). Dasyurus, and 93% in Antechinus (for more details, see Keast, The analysis of the hindlimb reveals that the hindlimb of Ly- 1982:table 1). Keast (1982) concluded that Thylacinus has gen- copsis is as long as in Arctogalidia, Arctictis, Neofelis, and Felis eralized dasyurid proportions, and that it is not much more than relative to thoracolumbar length. The tibia and femur of Lycop- an ‘overgrown’ dasyurid, with little if any advances over that of sis are also as long as in Thylacinus, but the metatarsals of the the smaller members of the dasyurid series: the brachial index, thylacine are longer than in Lycopsis. Also, Lycopsis exhibits crural index, and relative length of Mc III and Mt III compared shorter metatarsals than almost all model species sampled, ex- with their respective limb length is quite similar in Thylacinus, cept the plantigrade and relatively slow-moving Arctictis bintu- Dasyurus, and Antechinus. However, the thylacine exhibits a rong and Ursus malayanus. However, the femur of Lycopsis is slightly higher intermembral index (81% vs. 76% in Antechinus shorter than in Ursus malayanus, and the tibia is longer, a trend or Dasyurus), a longer neck (which represents 32% of the tho- usually observed in fast forms like canids (Hildebrand, 1952). racolumbar length in Thylacinus vs. 20% in Antechinus and 26% Therefore, the combination of a relative long and straight tibia 704 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 24, NO. 3, 2004

FIGURE 14. Limb segments expressed as percentages of total limb length in three borhyaenoid taxa and various extant carnivoran model species (same specimens as in Table 1). Abbreviations: F, femur; H, humerus; Mc III, third metacarpal; Mt III, third metatarsal; R, radius; T, tibia. Forelimb length (H+R+McIII) and hindlimb length (F+T+MtIII) are equated to 100.

with short metatarsals is particularly original in Lycopsis com- cies examined. Although the functional analysis reveals that the pared with living model species. forelimb of Lycopsis (and particularly the scapula and ulna) is It is of interest to compare the proportions of the limbs of not particularly adapted for an arboreal mode of life, the devel- Lycopsis with the estimates of two Santacrucian borhyaenoid opment of mm. pectoralis, biceps, and abductor pollicis longus in taxa, Prothylacinus and Cladosictis (Table 1; Figs. 13, 14). The particular are consistent with the use of the forelimb in foraging first point is that the limbs of both Santacrucian genera are and catching prey. shorter relative to the thoracolumbar length than in Lycopsis, The ratio Mt III/F has long been used as an index of cursori- especially in Cladosictis (Fig. 13). These short limbs, considering ality (Maynard Smith and Savage, 1956; Gambaryan, 1974; Sav- the clear arboreal capabilities of these Santacrucian taxa (Argot, age, 1977; Van Valkenburgh, 1987). Although there are certain 2003b, c), suggest need for strength for climbing as opposed to problems with the use of this ratio, especially because it exhibits speed on the ground. According to the study performed by significant negative allometric scaling (i.e., small carnivores ap- Hildebrand (1952) on canids, the gray fox Urocyon also exhibits pear to be disproportionately long-legged), this ratio remains a short legs relative to vertebral column length. This might be useful general estimate of the primary locomotor strategy, espe- related with less cursorial habits than described for the long- cially if the size range of the animals examined is not too great legged canids, Urocyon is reported to be adept at tree climbing (Janis and Wilhelm, 1993). This ratio is approximately 0.2 in (Terres, 1939; Trapp and Hallberg, 1975). However, it is note- Prothylacinus, 0.23 in Lycopsis, and 0.3 in Cladosictis, which is worthy that other canids that do not climb have similar limb lower than in living active predatory forms (Table 1). Consider- proportions, especially Cuon, which is a fast runner. ing North American fossil predators, the ratio of seven species of With its short legs and arboreal capabilities, Cladosictis would nimravids (most of them of Oligocene age) and five species of achieve stability by bringing the center of gravity of its body amphicyonids (most of them of Miocene age) also falls between closer to the support. To the contrary, the relatively long limbs of 0.2 and 0.3 (Janis and Wilhelm, 1993). Such limb proportions are Lycopsis suggests a more terrestrial mode of life although the typical of present-day ambush predators and far from the pres- relative shortness of the metapodials and grasping ability of ex- ent-day pursuit predators. It seems that as a general trend, the tremities would have precluded this taxon from fast running. fossil taxa are more heavily proportioned and exhibit shorter legs This suggests that another solution than distal elements elonga- than present-day predators. tion might have evolved within borhyaenoids to ensure at least The intermembral index does not vary significantly either short rushes, fast enough for catching prey. The co-existence of among Cladosictis, Prothylacinus, and Lycopsis (between 75 and distinct evolutionary solutions to the problem of running speed 78%), or Thylacinus and other dasyurids (Keast, 1982). This among the quadrupedal terrestrial mammals has already been index suggests a similar basic adaptive pattern for borhyaenoids, suggested by Jones and Stoddart (1998) in their study of Thyl- characterized by use of the forelimb during foraging activities. acinus. An allometric factor cannot be neglected concerning Cla- The intermembral index of borhyaenoids is also more similar to dosictis which has shorter legs but is also much smaller than the that of active taxa examined (Felis, Neofelis,orArctogalidia) two other borhyaenoids considered here. The brachial index of than to that of the slow-moving binturong (91.5%) and sun bear Lycopsis (0.8) is between those of Cladosictis (0.72) and Proth- (100%). The intermembral index of Borhyaena, a taxon that ylacinus (0.84), these values falling within the arboscansorial spe- exhibits incipient cursorial adaptations according to its forelimb ARGOT—POSTCRANIAL ANALYSIS OF LYCOPSIS 705 morphology (Argot, in press a), cannot be estimated because extant carnivorans including Felidae, Canidae, Ursidae, and Hy- most of its hindlimb is unknown. An intermembral index of ap- aenidae (Table 2). When using these equations, the mean esti- proximately 78% is also found in viverrids (regardless of primary mated weight obtained for Lycopsis is 17 kg. Using the same locomotor category, arboreal or terrestrial: Taylor, 1976), mus- equations, the mean estimated weight for Prothylacinus is 32 kg, telids (Heinrich and Biknevicius, 1998) or felid forest dwellers and for Borhyaena, 24 kg (Table 2). The specimen UCMP 38061 like Neofelis nebulosa and Felis yagouaroundi. Borhyaenoids of Lycopsis, therefore, represents approximately half the weight were also mainly forest dwellers, considering that early Miocene of Prothylacinus (specimen PU 015700). The lesser difference of Santa Cruz beds were deposited under warm, humid conditions, weight between Lycopsis and Borhyaena (specimen PU 015701) reflecting a temperate to subtropical coastal plain and a forested is relatively unexpected as Lycopsis was clearly smaller; the milieu (Patterson and Pascual, 1968; Bown and Fleagle, 1993), shoulder height of Lycopsis is estimated to 35 cm vs. 50 cm in and that La Venta area was situated in a tropical region with Borhyaena, and the rib cage is almost twice narrower in Lycop- extensive moist evergreen forests (Kay and Madden, 1997). sis. The long bones of the Santacrucian genera (especially Pro- Among living carnivorans, canids are characterized by a par- thylacinus) were clearly more robust than in Lycopsis, which is ticularly long neck, which represents 36 to 49% of the thoraco- emphasized when comparing the weights obtained when using lumbar length (Hildebrand, 1952). This would be an advantage the femoral length vs. the femoral circumference: the difference in predatory taxa, which do not use their forelimb for grappling of weight between Lycopsis and Borhyaena varies between 2.5 prey, because a longer neck places the biting jaws further in kg (when using the equation based on femoral length) and 12 kg advance of the body (Keast, 1982). Comparatively, the neck of (when using the equation based on femoral circumference), and Prothylacinus and Cladosictis represents 36–37% of the thora- a similar gap exists when comparing with Prothylacinus.Asem- columbar length (Fig. 13). This is in the lower range of canids, phasized by Anyonge (1993), the length of the femur seems to be but is higher than in any arboscansorial species examined, and a less reliable indicator of the weight of the animal than the this is consistent with the predatory habits of the borhyaenoids. femoral circumference, which is more representative of the stat- A powerful nuchal musculature is likely to have characterized ure of the animal and of the loads that the skeleton has to bear. Cladosictis and Prothylacinus (Argot, 2003b, c), as required in Body-weight estimates for a dozen of Tertiary thylacinid spe- carnivorous mammals feeding on living species in order to resist cies span a range from 1 kg to 60 kg (the average body weight for the struggles of active prey. Comparatively, the neck of Lycopsis T. cynocephalus being 29 kg), which suggests a considerable tro- represents only 28% of the thoracolumbar length, which is quite phic diversity among the family (Wroe, 2001). However, most of similar to the value found for Neofelis, but also for Ailurus, these species are known only by dentition, two by near-complete Arctictis, and Sarcophilus, all forms which are less active preda- cranial material, and therefore body masses are estimated on the tors. The difference between the three borhyaenoid taxa is basis of molar dimensions, not on femoral measurements. The clearly not a function of body size, and Hildebrand (1952) also only thylacinid described in the size range of Lycopsis is Max- concludes that in canids, the relative neck length is not correlated imucinus muirheadae (from Riversleigh, Queensland), whose with body size, massiveness of neck, or long-leggedness. The body mass is estimated around 18 kg (Wroe, 2001). short neck of Lycopsis, as well as an upper canine that is pro- Like all the borhyaenoids, Lycopsis is characterized by a rela- portionately smaller than in Prothylacinus and Borhyaena and tively long skull compared with modern taxa, a feature high- jaws that are relatively narrower and more gracile than in the lighted when the weight of the animal (BW) is estimated from latter taxa (Marshall, 1977), might indicate that it was a less the greatest skull length (SKL). This estimation uses the equa- specialized meat-eater than the two larger Santacrucian borhy- tion derived from regressions of body weight against skull length aenoids. It has been observed that primates that use their hands of 70 species of extant fissiped carnivores established by Van Log SKL + Log 0.003 × 3.13 ס to carry food to their mouth are characterized by a relative short Valkenburgh (1987): Log BW -Using this equation, the es .(0.895 ס neck with a reduced mobility, a condition which is compensated (correlation coefficient r by the prehensility of the hands (Lessertisseur and Saban, 1967). timated weight obtained for Lycopsis is 52 kg, which is under- However, such a relation does not exist in borhyaenoids if we estimated as the tip of the snout is broken anterior to the upper compare the relative length of the neck of Cladosictis and Ly- canine. Compared with the weight obtained from femoral mea- copsis, remembering that both of them have a pseudo-opposable surements, this clearly emphasizes a great difference of propor- pollex and therefore shared manipulative abilities. tion between the skull and the rest of the skeleton comparing with extant carnivorans. ESTIMATED WEIGHT CONCLUSIONS In order to complement the evaluation of the size of the ani- mal, an estimation of the body weight was calculated, using two Lycopsis longirostris is one of the smallest and certainly the regression equations based on femoral measurements estab- most omnivorous borhyaenoid of the La Venta fauna, living in a lished by Anyonge (1993) based on a sample of 28 species of forested environment (Marshall, 1977, 1978; Goin, 1997; Kay and

TABLE 2. Estimated body weight of Lycopsis longirostris. Two femoral measurements are used: the proximodistal length of the femur (F) and the circumference of the femur at midshaft (f). The regression equations used here and obtained by Anyonge (1993) are: Log (F) − 5.27; r (the correlation coefficient) is 0.95, and PE (the percentage prediction error, indicative of the × 2.92 ס Log Body Weight (1 difference between the actual weight and that predicted by the regression)is25% Log (f) − 3.40; r is 0.98 and PE is 22% × 2.88 ס Log Body Weight (2 For comparison, the weight of one specimen of Prothylacinus patagonicus, Borhyaena tuberata, and Thylacinus cynocephalus is estimated using the same method.

Estimate using Estimate using Mean weight Specimens F (mm) f (mm) equation 1 (kg) equation 2 (kg) (kg) Lycopsis longirostris UCMP 38061 167 41 16.6 17.6 17.1 Prothylacinus patagonicus PU 015700 198 53 27.3 36.8 32.0 Borhyaena tuberata PU 015701 174.5 49 18.9 29.3 24.1 Thylacinus cynocephalus MNHN 1891-61 173 39 18.4 15.2 16.8 706 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 24, NO. 3, 2004

Madden, 1997). Because of the preservation of the specimen LITERATURE CITED UCMP 38061, some critical postcranial features are lacking, which limits functional interpretations. However, the structural Alexander, R. McNeill. 1993. Legs and locomotion of Carnivora. Sym- analysis of the long bones and vertebrae indicates that, when posia of the Zoological Society of London 65:1–13. Anyonge, W. 1993. Body mass in large extant and extinct carnivores. compared to three early Miocene borhyaenoids, Prothylacinus Journal of Zoology, London 231:339–350. patagonicus, Cladosictis patagonica, and Borhyaena tuberata, Argot, C. 2001. Functional-adaptive anatomy of the forelimb in the Di- which form a morphological gradient from the most arboreally- delphidae and the paleobiology of the Paleocene marsupials adapted taxon to an incipient cursorial one, Lycopsis may be Mayulestes ferox and Pucadelphys andinus. Journal of Morphology placed between Cladosictis and Borhyaena. When these four 247:51–79. genera are compared, it appears that the range of adaptive types Argot, C. 2002. Functional-adaptive analysis of the hindlimb anatomy of that have evolved within the borhyaenoid superfamily during the extant marsupials and the paleobiology of the Paleocene marsupials Miocene is rather subtle. Mayulestes ferox and Pucadelphys andinus. Journal of Morphology At the forelimb level, the quadrangular scapula and straight 253:76–108. ulna, the probable semi-digitigrade posture of the fore foot, and Argot, C. 2003a. Functional-adaptive anatomy of the axial skeleton of some extant marsupials and the paleobiology of the Paleocene mar- the relatively short ungual phalanges indicate that Lycopsis had supials Mayulestes ferox and Pucadelphys andinus. Journal of Mor- clearly less specialized arboreal habits than Cladosictis or Pro- phology 255:279–300. thylacinus. The development of the musculature (especially mm. Argot, C. 2003b. Functional adaptations of the postcranial skeleton of spinati, pectoralis and biceps), as well as a pseudo-opposable two Miocene borhyaenoids (Mammalia, Metatheria), Borhyaena pollex and an asymmetrical distal Mc V suggesting a conver- and Prothylacinus, from South America. Palaeontology 46:1213– gence of the fifth digit towards the other digits during flexion 1267. nevertheless suggest that Lycopsis used its forelimb for manipu- Argot, C. 2003c. Postcranial functional adaptations in the South Ameri- lating prey or holding supports. As a comparison, Borhyaena can Miocene borhyaenoids (Mammalia, Metatheria): Cladosictis, exhibits a more cursorial trend, with an elbow joint providing Pseudonotictis, and Sipalocyon. Alcheringa 27:303–356. Bown, T. M., and J. G. Fleagle. 1993. Systematics, biostratigraphy, and parasagittal flexion-extension, a ulna posteriorly concave like in dental evolution of the Palaeothentidae, later Oligocene to early- cursorial models, metacarpals longer than in Prothylacinus,a middle Miocene (Deseadan-Santacrucian) caenolestoid marsupials digitigrade fore foot, and short phalanges (Argot, 2003b). A digi- of South America. Journal of Paleontology, Memoir 29:1–76. tigrade posture and parasagittal excursion of the limb contribute Brosset, A. 1968. Observations sur l’e´thologie du tayra, Eira barbara to increase the efficiency of terrestrial locomotion in all gaits (Carnivore). Revue d’Ecologie (La Terre et la Vie) 22:29–50. (Janis and Wilhelm, 1993). As emphasized by Alexander (1993), Davis, D. D. 1949. The shoulder architecture of bears and other carni- there are striking differences among Carnivora between the spe- vores. Fieldiana: Zoology 31:285–305. cialized runners (cheetahs and canids) that have remarkably long Finch, M. E., and L. Freedman. 1988. Functional morphology of the limbs for their body mass, and the carnivores with more mobile limbs of Thylacoleo carnifex Owen (Thylacoleonidae: Marsupialia). paws that have retained some climbing ability (most of felids, Australian Journal of Zoology 36:251–272. Flynn, J. J., and A. R. Wyss. 1998. Recent advances in South American ursids, procyonids). All Miocene borhyaenoids examined except mammalian palaeontology. Trends in Ecology and Evolution 13: Borhyaena are characterized by a relatively powerful forelimb 449–454. and a grasping manus which is indicative of a forelimb adapted to Gambaryan, P. P. 1974. How Mammals Run. John Wiley & Sons, Hal- a manipulative behavior, useful for climbing and killing prey. sted Press, New York, 367 pp. Behavioral interpretations based on the hindlimb of Lycopsis Goin, F. J. 1997. New clues for understanding Neogene marsupial radia- are not completely congruous, as it exhibits a hip joint suggesting tions; pp. 187–206 in R. F. Kay, R. H. Madden, R. L. Cifelli, and J. J. less rotative ability than in Prothylacinus, a relatively long and Flynn (eds.), Vertebrate Paleontology in the Neotropics. The Mio- straight tibia, and an upper ankle joint indicating that flexion- cene Fauna of La Venta, Colombia. Smithsonian Institution Press, extension of the pes occurred in a parasagittal plane. However, Washington and London. the knee and the lower ankle joints are poorly stabilized, and the Heinrich, R. E., and A. R. Biknevicius. 1998. Skeletal allometry and in- terlimb scaling patterns in mustelid carnivorans. Journal of Mor- short metatarsals, which contribute poorly to the length of the phology 235:121–134. limb, together with the well-developed hallux and digit V con- Hildebrand, M. 1952. An analysis of body proportions in the Canidae. vergent towards the other digits during flexion as in the manus, American Journal of Anatomy 90:217–256. are more suggestive of a plantigrade posture, grasping ability, Janis, J. M., and P. B. Wilhelm. 1993. Were there mammalian pursuit and reduced running ability. Therefore, Lycopsis was probably predators in the Tertiary? Dances with wolf avatars. Journal of primarily terrestrial but with grasping and climbing features Mammalian Evolution 1:103–125. probably useful in a densely forested environment infested with Jenkins, F. A., Jr. 1970. Anatomy and function of expanded ribs in cer- crocodiles. tain edentates and primates. Journal of Mammalogy 51:288–301. Jenkins, F. A., Jr., and W. A. Weijs. 1979. The functional anatomy of the shoulder in the Virginia opossum (Didelphis virginiana). Journal of ACKNOWLEDGMENTS Zoology, London 188:379–410. Johnson, C. N., and S. Wroe. 2003. Causes of extinction of vertebrates I thank Christian de Muizon, Jean-Pierre Gasc, Frederick Sza- during the Holocene of mainland Australia: arrival of the dingo, or lay, and two anonymous reviewers for many helpful comments human impact? Holocene 13:1009–1016. they made on this manuscript. I also thank Patricia Holroyd Jones, M. E., and D. M. Stoddart. 1998. Reconstruction of the predatory (UCMP, Berkeley) for allowing me to study the specimens of behaviour of the extinct marsupial thylacine (Thylacinus cynocepha- borhyaenoids under her care, and for providing casts of some lus). Journal of Zoology, London 246:239–246. tarsal and carpal bones. I am also grateful to the following people Kay, R. F., and R. H. Madden. 1997. Paleogeography and paleoecology; and institutions for providing comparative specimens of other pp. 520–550 in R. F. Kay, R. H. Madden, R. L. Cifelli, and J. J. Flynn borhyaenoids or of extant carnivorans: Mary Ann Turner, Pea- (eds.), Vertebrate Paleontology in the Neotropics. The Miocene body Museum of Yale University (New Haven, USA); Robert Fauna of La Venta, Colombia. Smithsonian Institution Press, Wash- ington and London. Randall, Department of Mammalogy of the AMNH (New York, Keast, A. 1982. The thylacine (Thylacinidae, Marsupialia): how good a USA); and Francis Renoult, Laboratoire d’Anatomie Compare´e pursuit carnivore?; pp. 675–684 in M. Archer (ed.), Carnivorous (MNHN, Paris, France). The financial support of the visit to the Marsupials. The Royal Zoological Society of New South Wales, UCMP and other foreign museums mentioned was provided by Sydney, Australia. the Muse´um national d’Histoire naturelle (Paris). Lessertisseur, J. and R. Saban. 1967. Squelette appendiculaire; pp. ARGOT—POSTCRANIAL ANALYSIS OF LYCOPSIS 707

584–1123 in P. P.Grasse´ (ed.), Traite´ de Zoologie XVI (1). Masson Marsupialia), from the Miocene of Riversleigh, north-western and Cie, Paris, France. Queensland, with estimates of body weights for fossil thylacinids. MacAlister, A. 1870. On the myology of the wombat (Phascolomys wom- Australian Journal of Zoology 49:603–614. bata) and the Tasmanian devil (Sarcophilus ursinus). Annals and Wroe, S. 2003. Australian marsupial carnivores: recent advances in pal- Magazine of Natural History 5:153–173. aeontology; pp. 102–123 in M. Jones, C. Dickman and M. Archer Madden, R. H., J. Guerrero, R. F. Kay, J. J. Flynn, C. C. Swisher III, and (eds.), Predators with Pouches: the Biology of Marsupial Carni- A. H. Walton. 1997. The Laventan Stage and Age; pp. 499–519 in vores. CSIRO Publishing, Collingwood, Australia. R. F. Kay, R. H. Madden, R. L. Cifelli, and J. J. Flynn (eds.), Ver- Wroe, S., and A. Musser. 2001. The skull of Nimbacinus dicksoni (Thyl- tebrate Paleontology in the Neotropics. The Miocene Fauna of La acinidae:Marsupialia). Australian Journal of Zoology 49:487–514. Venta, Colombia. Smithsonian Institution Press, Washington and London. Received 7 February 2002; accepted 3 November 2003. Marshall, L. G. 1977. A new species of Lycopsis (Borhyaenidae: Marsu- pialia) from the La Venta fauna (Late Miocene) of Colombia, South APPENDIX. Measurements of Lycopsis longirostris. America. Journal of Paleontology 51:633–642. Marshall, L. G. 1978. Evolution of the Borhyaenidae, extinct South All the measurements are taken from the type UCMP 38061. All the American predaceous marsupials. University of California Publica- measurements are in millimeters. Abbreviation: e, estimated tions in Geological Sciences 117:1–89. measurement. Maynard Smith, J., and R. J. G. Savage. 1956. Some locomotory adapta- tions in mammals. Zoological Journal of the Linnean Society 42: Measurements of the left scapula 603–622. Muizon, C. de. 1998. Mayulestes ferox, a borhyaenoid (Metatheria, Mam- Total length, parallel to the spine 113.5 Maximal width of the scapula, perpendicular to the spine 56.3 malia) from the early Palaeocene of Bolivia. Phylogenetic and pal- Maximal length of the supraspinous fossa 82e aeobiologic implications. Geodiversitas 20:19–142. Maximal width of the infraspinous fossa 31.5 Nowak, R. M., and J. L. Paradiso. 1983. Walker’s Mammals of the World, Anteroposterior length of the glenoid cavity 29.1 Fourth Edition. The Johns Hopkins University Press, Baltimore, Dorsoventral height of the glenoid cavity 12.8 Maryland, 1362 pp. Oxnard, C. E. 1968. The architecture of the shoulder in some mammals. Measurements of the left humerus Journal of Morphology 126:249–290. Total length 141.3 Patterson, B., and R. Pascual. 1968. Evolution of mammals on southern Maximum anteroposterior length of the proximal extremity 38.8 continents. V. The fossil mammal fauna of South America. Quar- Maximum transverse width of the proximal extremity 18.3 terly Review of Biology 43:409–451. Anteroposterior length of the humeral head 24.2 Roberts, D. 1974. Structure and function of the primate scapula; pp. Transverse width of the humeral head 17.4 171–200 in F. A. Jenkins, Jr. (ed.), Primate Locomotion. Academic Length of the deltopectoral crest 95e Press, New York. Deltopectoral crest length expressed as a percentage of Savage, R. J. G. 1977. Evolution in carnivorous mammals. Palaeontology the humerus length 67%e 20:237–271. Maximum transverse width of the distal extremity 35.3 Transverse width of the distal articular surface in distal view 17.5e Sinclair, W. J. 1906. Marsupialia of the Santa Cruz beds; pp. 333–460 + Transverse width of the capitulum in anterior view 13.1 plates XL–LXV in W. B. Scott (ed.), Reports of the Princeton Uni- Proximodistal height of the capitulum in anterior view 12.4 versity Expedition to Patagonia, 1896–1899, Vol IV, Part III. Prince- Proximodistal height of the trochlea in posterior view 10.5e ton University and Stuttgart. Length of the lateral epicondylar ridge 45e Slijper, E. J. 1946. Comparative biologic-anatomical investigations on the Lateral epicondylar ridge expressed as a percentage of vertebral column and spinal musculature of mammals. Verma- the humerus length 32%e nuselingen der Koninklijke Nederlandsche Akademie van Weten- Distance between the medial ridge of the trochlea and the schappen 42:1–128. apex of the medial epicondyle (T-E) 10e Smith, M. 1982. Review of the thylacine (Marsupialia, Thylacinidae); pp. T-E expressed as a percentage of the distal extremity width 28.3% 237–253 in M. Archer (ed.), Carnivorous Marsupials. The Royal Mid-shaft anteroposterior diameter 17.1 Zoological Society of New South Wales, Sydney, Australia. Mid-shaft transverse diameter 9.2 Sunquist, F. C. 1992. Les fe´lins actuels; pp. 23–58 in J. Seidensticker and Measurements of the ulna S. Lumpkin (eds.), Les fe´lins. Bordas, Paris, France. Szalay, F. S. 1994. Evolutionary History of the Marsupials and an Analy- Total length 148e sis of Osteological Characters. Cambridge University Press, New Distance between the apex of the olecranon and the centre York, 481 pp. of rotation of the elbow joint (DO) 30.3 DO expressed as a percentage of the ulna length 20.5% Szalay, F. S., and R. L. Decker. 1974. Origins, evolution, and function of Distance between the insertion of the m. biceps/brachialis the tarsus in Late Cretaceous Eutheria and Paleocene Primates; pp. and the centre of rotation of the elbow joint (DFU) 18e 223–259 in F. A. Jenkins, Jr. (ed.), Primate Locomotion. Academic DFU expressed as a percentage of the ulna length 12% Press, New York. Transverse width of the apex of the olecranon 11.3 Taylor, M. E. 1974. The functional anatomy of the forelimb of some Anteroposterior depth of the apex of the olecranon 15.4 African Viverridae (Carnivora). Journal of Morphology 143: Transverse width of the anconeal process 11.8 307–336. Proximodistal length of the trochlear notch in medial view 17.3 Taylor, M. E. 1976. The functional anatomy of the hindlimb of some Transverse width of the coronoid process 9.1 African Viverridae (Carnivora). Journal of Morphology 148: Anteroposterior length of the coronoid process 11.5e 227–254. Anteroposterior depth of the diaphysis at the level of the Terres, J. K. 1939. Tree-climbing technique of a gray fox. Journal of coronoid process 22.2 Mammalogy 20:256. Mid-shaft transverse diameter 7.0 Trapp, G. R., and D. L. Hallberg. 1975. Ecology of the gray fox (Urocyon Mid-shaft anteroposterior diameter 13.0 cinereoargenteus): a review; pp. 164–178 in M. W. Fox (ed.), The Measurements of the radius Wild Canids. Their Systematics, Behavioral Ecology and Evolution. Van Nostrand Reinhold Company, New York. Total length* 114e Anteroposterior length of the head* 7e Van Valkenburgh, B. 1987. Skeletal indicators of locomotor behavior in Transverse width of the head* 10.5e living and extinct carnivores. Journal of Vertebrate Paleontology Distance between the apex and the centre of the bicipital 7:162–182. tuberosity (DFR)* 11e Wells, R. T., and B. Nichol. 1977. On the manus and pes of Thylacoleo DFR expressed as a percentage of the radius length 10%e carnifex Owen (Marsupialia). Transactions of the Royal Society of Anteroposterior depth of the diaphysis at the level of the the South Australia 101:139–146. bicipital tuberosity 9.4 Wroe, S. 2001. Maximucinus muirheadae, gen. et sp. nov. (Thylacinidae: Mid-shaft anteroposterior diameter 7.7 708 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 24, NO. 3, 2004

APPENDIX Measurements of the tibia Continued. Total length 163 Measurements of the radius Maximum transverse width of the proximal epiphysis in proximal view 23e* Mid-shaft transverse diameter 7.7 Maximum anteroposterior length of the proximal Anteroposterior length of the distal extremity 11.8 epiphysis in proximal view 27e Transverse width of the distal extremity 18.1 Transverse width of the medial condyle 8.7 *without the proximal epiphysis Anteroposterior length of the medial condyle 13.9 Mid-shaft anteroposterior diameter 14e Measurements of the manus Mid-shaft transverse diameter 8.8e Metacarpals length Mc I 20e Transverse width of the distal epiphysis in distal view 14e Mc II 35.8 Anteroposterior length of the distal epiphysis in distal Mc III 36.2 view 16.5e Mc IV 36e Anteroposterior length of the malleolus in distal view 9.5e Mc V 28e Proximodistal height of the malleolus 6e Proximal phalanges length 1 (pollex) 14.8 *from the left tibia; all the other measurements are from the right one 14.5 16.1 Measurements of the fibula 16.8 Total length 156e Intermediate phalanges length 10.1 Anteroposterior depth of the head 17.1 10.3 Mid-shaft anteroposterior diameter 6.3 8.7e Mid-shaft transverse diameter 5.5 Unguals length 1 (pollex) 13.6 Transverse width of the distal epiphysis 14.4 2 10e Anteroposterior depth of the distal epiphysis 13.2 3 12.0 Measurements of the left calcaneum 4 10.9 Total length 37.7 Unguals depth 1 (pollex) 8.3 Length of the tuber calcanei (until the ectal facet) 17e 2 6.8 Width of the tuber at mid-length 11 36e Height of the tuber at mid-length 7.5 4 6.8 Transverse width of the ectal facet 5.1 Measurements of the innominate (left part) Proximodistal length of the ectal facet 9.5e Transverse width of the sustentacular facet 4.1 Total length (anterior tip broken) 140e Proximodistal length of the sustentacular facet 6.8 Length of the ilium, between the apex and the centre of Maximal width at the level of facets 15.7 the acetabulum 76e Transverse width of the calcaneocuboid facet 8e Ilium length expressed as a percentage of pelvic length 54.3% Dorsoplantar height of the calcaneocuboid facet 9.5e Length of the iliac neck between the anterior border of the acetabulum and the posterior border of the sacral Measurements of the left astragalus articulation 15e Total length 21.0 Dorsoventral breadth of the iliac blade (dorsal margin Maximum transverse width 15.5e damaged) 34e Astragalotibial lateral facet length 15e Anteroposterior diameter of the acetabulum (anterior Astragalar head width (anterior view) 6e border damaged) 22.5e Astragalar head height (anterior view) 7.5e Measurements of the left femur Measurements of the pes Total length 167 Anteroposterior depth of the head in medial view 17.4 Metatarsals length Mt II 34.7 Proximodistal height of the head in medial view 16.8 Mt ?III 39.5 Distance between the tip of the greater trochanter and Mt V 31.3 the fovea capitis 31.5 Distance between the tip of the greater trochanter and Proximal phalanges length 14e the distal end of the trochanteric fossa 26.8 14e Mid-shaft anteroposterior diameter 14.3 14e Mid-shaft transverse diameter 11.8 14.7 Relative compression ratio of femoral shaft (minimum 15.5 diameter/maximum diameter × 100) 82.5% Intermediate phalanges length 8.5 Width of the lateral condyle, posterior view 9.5e 7.7e Height of the lateral condyle, posterior view 17e Width of the medial condyle, posterior view 10e 7.7e Height of the medial condyle, posterior view 13.5e 9e Height of the trochlea, anterior view 16.3 Ungual phalanx length (the best preserved) 12e Width of the distal epiphysis, distal view 32e Ungual phalanx depth (the best preserved) 5.7 Height of the distal epiphysis, distal view 24e