Animal Skulls Identification

Auditory Bulla Caniformia Feliformia

Fig. 8.9. Auditory structure in carnivores. Elements forming the auditory bulla in (left to right) a bear (arctoid), a dog (cynoid), and a cat (feloid). Top row shows ventral view of adult bulla, middle row shows ventral view of neonatal bulla. Bottom row shows isolated neonatal bulla in medial view, to reveal the rostral entotympanic, which is not exposed ventrally Key: E, caudal entotympanic; R, rostral entotympanic; T, ectotympanic. (From Hunt and Tedford, 1993.)

Fig. 8.9. Auditory structure in carnivores. Elements forming the auditory bulla in (left to right) a bear (arctoid), a dog (cynoid), and a cat (feloid). Top row shows ventral view of adult bulla, middle row shows ventral view of neonatal bulla. Bottom row shows isolated neonatal bulla in medial view, to reveal the rostral entotympanic, which is not exposed ventrally Key: E, caudal entotympanic; R, rostral entotympanic; T, ectotympanic. (From Hunt and Tedford, 1993.)

that supplies the brain. In most feliforms (except nimravids and the extant Nandinia) the bulla is divided into two chambers by a bony septum, the anterior chamber composed of ectotympanic and rostral entotympanic, and the posterior chamber made by the caudal entotympanic (Hunt and Tedford, 1993). The ICA is reduced or absent, the primary en-docranial blood supply instead coming through the external carotid via a pair of arterial networks (or retia; Hunt, 1974b). Caniforms have a bulla with a single chamber and no septum (except in canids, which have a partial septum), and the blood supply to the brain comes through the ICA. Unfortunately the bulla of miacoids is unknown, hence we lack this important criterion for establishing relationship to feliforms or can-iforms. However, indentations in the basicranium of some recently described skulls of Bridgerian and later miacids suggest the presence of a loosely attached compound bulla (either ossified or cartilaginous) consisting of ectotympanic and entotympanic elements (Wesley-Hunt and Flynn, 2005).

Also distinctive of extant carnivorans is a large braincase, with the coronal (frontal-parietal) suture situated well behind the postorbital constriction, owing to cerebral expansion (Wyss and Flynn, 1993). Miacoids differ in having relatively smaller brains, and a more anterior coronal suture. The skeleton of terrestrial carnivorans is usually relatively generalized, but is sometimes overprinted with specializations for climbing, running, or digging. The feet tend to be conservative, typically remaining pentadactyl, and the posture is plantigrade or digitigrade. A fused scapholunate in the carpus is a diagnostic trait of extant carnivorans, but the two elements remain separate in most miacoids. Similarly extant carnivorans lack a third trochanter on the femur, but it is present in miacoids. Marine carnivorans (pinnipeds) show major limb modification or reduction.

Following the work of Lillegraven (1969) there has been general agreement that the teeth of both carnivorans and creodonts can be plausibly derived from those of Cretaceous Cimolestidae, such as Cimolestes (Fig. 8.10). Hunt and Tedford (1993) suggested that Cimolestes is more closely related to Carnivora than to Creodonta and that different lineages of the genus may have given rise to the two families of mi-acoids (Viverravidae and Miacidae). This hypothesis raises the possibility that the order Carnivora is diphyletic and that the classic synapomorphy of the order, P4/Mj carnassials, arose more than once (in fact, it is also present in hedgehogs; see Chapter 9). According to Hunt and Tedford, viverravids such as Torrejonian Simpsonictis might have evolved from a Late Cretaceous species of Cimolestes that had lost its third molars prior to the development of carnassial teeth, whereas miacids could have evolved later from a separate species of Cimolestes (which retained third molars) and evolved carnas-sials independently. Fox and Youzwyshyn (1994) disagreed, however, and postulated a more primitive eutherian ancestry of Carnivora involving neither Creodonta nor Cimolestidae. In view of these uncertainties, the precise timing of the origin of Carnivora is unknown. Unfortunately, the available fossil evidence from the critical interval (Late Cretaceous-early Paleocene) is unable to resolve the matter conclusively

Animal Teeth
5 mm

2 mm

2 mm

Fig. 8.10. Right dentitions of miacoids and Cimolestes: (A) Cimolestes lower teeth; (B, C) lower jaws of two different species of Simpsonictis; (D) Viverravus upper and lower teeth; (E) Ravenictis upper molar; (F) Uintacyon upper and lower teeth. (A from Clemens, 1973; B-D from Gingerich and Winkler, 1985; E from Fox and Youzwyshyn, 1994; F from Gingerich, 1983a.)

Fig. 8.10. Right dentitions of miacoids and Cimolestes: (A) Cimolestes lower teeth; (B, C) lower jaws of two different species of Simpsonictis; (D) Viverravus upper and lower teeth; (E) Ravenictis upper molar; (F) Uintacyon upper and lower teeth. (A from Clemens, 1973; B-D from Gingerich and Winkler, 1985; E from Fox and Youzwyshyn, 1994; F from Gingerich, 1983a.)

Miacoids

Unequivocal Carnivora, as indicated by the presence of the P4/Mj carnassial pair, are first known from the Paleocene of North America. These earliest carnivorans belong to two primitive families, Viverravidae and Miacidae, often grouped as the paraphyletic Miacoidea (but formerly considered subfamilies of a stem family Miacidae). Several members of both families were also present in Europe during the Eocene, whereas only a couple of miacoids are known from the Paleocene-Eocene of Asia. By the end of the Eocene miacoids had disappeared everywhere and were quickly replaced by more modern carnivorans. Most miacoids ranged from weasel-sized to a little larger than a fox, or roughly 100 g to 10 kg.

Miacidae, in the strict sense, are characterized by retention of third molars (a primitive trait) together with reduction or loss of the parastyle on P4 and loss of calcaneo-fibular contact (derived traits). They share these features with caniforms. In Viverravidae the third molars are absent, the parastyle on P4 strong, and the fibula articulates with the calcaneus—features in common with feliforms. Based on these criteria, the two families have been considered to be the earliest representatives of the two major clades of extant Carnivora (Flynn and Galiano 1982; Flynn, 1998), although definitive evidence from the basicranium is lacking.

In addition, most (but not all) miacoids have separate scaphoid and lunate bones in the carpus; fusion of these elements is often considered a diagnostic trait of Carnivora. Consequently, Viverravidae and Miacidae are currently considered to be stem taxa that lie outside the two crown clades of Carnivora (Wyss and Flynn, 1993; Flynn and Wesley-Hunt, 2005; Wesley-Hunt and Flynn, 2005). According to this view, Viverravidae is the sister group of all other Carnivora (making the loss of third molars in this family an autapomorphy), whereas the paraphyletic Miacidae are probably closer to the crown clade.

The oldest securely dated carnivoran, Ravenictis (Fig. 8.10E), comes from the early Paleocene of Saskatchewan, but it is represented only by an isolated upper molar, which is not diagnostic at the family level. Consequently it provides little information beyond extending the geologic range of the order. Ictidopappus (North America) and Pappictidops (China) are nearly as old and also known only from dentitions. They are variously regarded as primitive viverravids or as basal carnivorans of uncertain affinity. By the late early Paleocene (Torrejonian), however, several genera of undoubted viverravids, including Protictis and Simpsonictis, were present in western North America (Gingerich and Winkler, 1985; Flynn, 1998). The earliest record of Miacidae, despite their more primitive dental formula, is not until the latest Paleocene (Clarkforkian) of North American (e.g.,

Coati Formula Dentaria

Uintacyon; Fig. 8.10F). However, if Carnivora is mono-phyletic, they must have existed much earlier (at least as early as the oldest viverravids). This early origin would presumably hold true even if Carnivora is not monophyletic and the two families arose independently from Cimolestes (which is known principally from the Cretaceous and early Paleocene). At present, however, there is little fossil evidence to favor this interpretation over a common origin of miacoids.

Besides their dichotomy in dental formulae, viverravids and miacids also differed in locomotor adaptation, as reflected in their appendicular skeletons (Fig. 8.11). Many features in the limbs of viverravids, such as early Eocene Didymictis, indicate that they were terrestrial and probably incipiently cursorial, although they probably retained the ability to climb, not unlike extant Viverra (Heinrich and Rose, 1997). These features include a prominent greater tuberosity reduced deltopectoral crest, supratrochlear foramen, and wide radial head in the forelimb, and a posteriorly directed lesser trochanter, well-defined patellar trochlea, moderately grooved astragalar trochlea, narrow and more elongate cal-caneus, smaller and more distal peroneal tubercle on the calcaneus, and several other tarsal characteristics in the hind limb. Miacids, however, were adapted for scansorial and arboreal habitats. Vulpavus (Fig. 8.12) and Miacis resemble living palm civets and coatimundis in having a sharp deltopectoral crest, shallow humeral trochlea and olecranon fossa, round proximal radius, medially directed lesser trochanter, shallow patellar groove, and nearly flat astragalar trochlea (Heinrich and Rose, 1995, 1997). Most of these features are associated with increased joint mobility, as would be expected in arboreal animals. Both miacids and viverravids had relatively short, laterally compressed terminal phalanges.

Most authorities agree that miacoids were the source group for more advanced feliforms and caniforms. However, transitional taxa or plausible ancestors for most of the modern families have not been identified. Canidae, which can be derived from Miacis or a closely allied form, is an exception, as discussed below.

Feliformia

Not until the latest Eocene and earliest Oligocene do unequivocal feliforms appear in the fossil record. The early Oligocene Phosphorites of Quercy, France, have produced the most diverse assemblage of primitive feliforms, including skulls of several genera that seem to be close to the base

Fig. 8.11. Comparison of limb elements of miacids (left column: A, E, G, I, Vulpavus; C, Uintacyon) and viverravids (right column: B, D, F, H, J, Didymictis): (A-D) right humerus, proximal and distal ends; (E-F) right radius and ulna (proximal); (G-H) left femur, proximal and distal ends; (I-J) left astragalus and calcaneus. Key: ce, capitular eminence; dp, deltopectoral crest; ecf, ectal facet; gt, greater trochanter; gtb, greater tuberosity; lt, lesser trochanter; ltb, lesser tuberosity; me, medial epicondyle; ol, olecranon process; pt, patellar trochlea; ptb, peroneal tubercle; rn, radial notch; sc, supinator crest; sf, sustentacular facet; sn, semilunar notch; sus, sustentaculum tali; tm, teres major tubercle; tt, third trochanter. (Figure prepared by R. E. Heinrich; modified from Heinrich and Rose, 1997.)

Stenoplesictis

of viverrids and felids, as shown by their possession of a two-chambered auditory bulla (Hunt, 1998c). Although they have been variously referred to these modern families, they differ relatively little from each other in dental or basicranial anatomy which suggests that the Quercy fauna samples the beginning of the modern feliform radiation (Hunt, 1989, 2001). Their sudden appearance in Europe just after the Grande Coupure (Remy et al., 1987) indicates that they are immigrants, perhaps from Asia. The other extant feliform families, Hyaenidae and Herpestidae, did not appear until the Miocene. Nandinia, the extant African palm civet, is the most primitive living feliform. It was long considered to be a viverrid but is now usually placed in its own family

Palaeoprionodon, best known from Quercy, is the oldest feliform with viverrid ear structure (Hunt, 1989, 1998c). Viverrids, an Old World family that includes the extant civets and Asian palm civets, are generally considered to be primitive feliforms. Stenoplesictis (Fig. 8.13A), from Quercy and probable late Eocene deposits of Alag Tsab, Mongolia, has been regarded as the oldest viverrid, based on dental resemblance (e.g., Dashzeveg, 1996). However, its auditory region, although clearly two-chambered and therefore feliform, differs from that of both viverrids and felids; hence Stenoplesictis has been considered a stem feliform (Hunt, 1991, 1998c; Peigné and Bonis, 1999). The oldest viverrid-like skeleton is that of Asiavorator (Fig. 8.13B) from the early Oligocene of Mongolia. It closely resembles that of extant civets and genets and was primarily terrestrial but probably retained the ability to climb trees (Hunt, 1998c).

The earliest felids also come from Quercy Proailurus and Stenogale (Fig. 8.13C,D), known from jaws at Quercy (but no recognized ear regions), can be confidently identified as felids, based on the derived petrosal anatomy of early Miocene representatives (Hunt, 1991, 1998c). Although Proailurus has long been recognized to be a felid, prior to Hunt's study Stenogale was usually identified as a viverrid or a basal feliform. In these basal felids M1 has a well-developed shearing blade formed by the tall paraconid and protoconid and intervening carnassial notch; the metaconid is already reduced or lost. The early radiation of felids took place in the Old World; they did not reach North America until well into the Miocene. The close resemblance among these early feliforms indicates that felids and viverrids are sister taxa.

The remaining feliform family, Nimravidae, was contemporaneous with the oldest feliforms discussed above, appearing in the late Eocene of North America and Eurasia (Martin, 1998). Nimravids were the earliest saber-toothed carnivorans (Fig. 8.14). They were once thought to be felids, which they resemble in having a short face, hypercarnivo-rous dentition, and retractile claws, but analysis of dental characters led Flynn and Galiano (1982) to unite nimravids with caniforms. These catlike late Eocene to Miocene "pa-leofelids," or false saber-tooths, are now placed in a separate family whose relationships remain unsettled (Flynn et al.,

1988; Bryant, 1991). Most recent studies ally them with feloids, based on the reduction of posterior molars and possession of hooded terminal phalanges that bore retractile claws (e.g., Hunt, 1987; Bryant, 1991; Wyss and Flynn, 1993; Martin, 1998; Flynn and Wesley-Hunt, 2005). Nevertheless, nimravids differ from felids and most other feliforms in several cranial details, including having an essentially single-chambered auditory bulla with a uniquely formed anterior septum, a caudal entotympanic that is only partially ossified, and a different conformation of basicranial foramina (Hunt, 1987). Their origin remains obscure.

The earliest nimravids, Dinictis and Hoplophoneus of western North America, were already saber-toothed, with large, serrated, and laterally compressed upper canine teeth and a protective bony flange on the mandible. Some species reached the size of cougars or jaguars (about 100 kg). Hoplophoneus was short-legged and more like an ambush predator, whereas Dinictis had longer limbs and was more cur-sorially adapted, like living pursuit predators (Martin, 1998). It is likely that they were also able to climb trees. These early nimravids (subfamily Nimravinae) became extinct by the beginning of the Miocene, perhaps partly as a result of the spread of grasslands (Bryant, 1996). They were succeeded in the late Miocene by barbourofeline nimravids and saber-toothed felids.

Late Eocene and Oligocene Palaeogale (Fig. 8.15) may also be mentioned here. Long considered a primitive mustelid, this widespread Holarctic taxon is now thought to be a basal feliform (Baskin, 1998) or possibly even a viverravid (Hunt, 1989). Like other feliforms, it has a bladelike trigonid on M1, but it differs from feliforms in having a single-chambered bulla. The third molars are lost and the second molars are very small or absent. Palaeogale could be a pivotal form in the early radiation of modern carnivorans.

Caniformia

Caniforms can be divided into two clades, Cynoidea (canids) and Arctoidea (all other caniforms; see Fig. 8.1). Arctoids are united by two synapomorphies, a suprameatal fossa (a hollow in the dorsolateral wall of the middle-ear cavity) and the loss of M3 (Wolsan, 1993; Wolsan and Lange-Badre, 1996); each subgroup of arctoids has its own distinctive morphology of the suprameatal fossa. Most have a single-chambered auditory bulla composed mainly of the ectotympanic (Hunt, 1974b). Whereas early arctoids were common and diverse in Europe (particularly at Quercy) but sparse in North America, early canids were common in North America but did not reach the Old World until the late Miocene (Hunt, 1998a). Current evidence indicates that canids (dogs) originated in North America, whereas arctoids

Fig. 8.13. Feliform dentitions: (A) Stenoplesictis, right upper and lower teeth; (B) Asiavorator, left P2-M2; (C) Proailurus, right P3-M1; (D) Stenogale, left P3-M1. Proailurus and Stenogale are considered the oldest felids. (A from Peigné and Bonis, 1999; B from Hunt, 1998c; C, D from Bonis et al., 1999.)

Animal Skulls Identification
Fig. 8.14. Late Eocene-early Oligocene nimravid Dinictis. (Skeleton from Matthew, 1901; skull from Scott and Jepsen, 1936.)

evolved in the Old World and dispersed multiple times to North America.

Canidae

Canids comprise dogs, foxes, wolves, coyotes, and jackals, which are cursorial, relatively omnivorous carnivorans. Canids have a primitive placental dental formula except for loss of M3. Although they have well-developed carnassials, their molars also have basins for crushing. The limbs tend to be slender and moderately elongate, and the feet are digitigrade and functionally four-toed. As in many cursorial mammals, the clavicle is lost in extant members. Canids are virtually cosmopolitan today, but they were restricted to

North America for all of their early history, not reaching the Old World until the latest Miocene.

The oldest and most primitive canids are the hesperocy-onines of the late middle Eocene (Duchesnean) to the middle Miocene (Barstovian). They resemble certain species of Miacis or Procynodictis closely enough—especially dentally— to suggest an ancestral or sister-group relationship (Wang and Tedford, 1994; Munthe, 1998; Fig. 8.16), making Canidae the only modern carnivoran family that can be linked to a specific miacid.

The earliest and best-known form is Hesperocyon, a common element of faunas from the White River Group characterized by a trenchant talonid on M1 (primitive for canids). Unlike that of miacids, its auditory bulla is fully ossified and composed mainly of the caudal entotympanic, with contributions from the ectotympanic and rostral entotympanic; the caudal entotympanic forms a partial septum within the middle-ear cavity. The bullar anatomy is thus similar in detail to that in modern canids (Hunt 1974a,b; Wang and Tedford, 1994). In addition, the internal carotid artery, rather than crossing the promontorium as in miacids, is situated medial to the promontorium and outside the bulla on its medial surface, and the stapedial branch is absent. Hespero-cyon was about the size of a small fox, but was proportioned more like extant civets and mongooses. The limb skeleton of Hesperocyon is intermediate between that of its arboreal, plantigrade, miacid progenitors and that of cursorial, fully digitigrade later canids (X. Wang 1993, 1994). A vestigial clavicle was still present. The terminal phalanges were short, deep, and laterally compressed, and may have been retractile. Based on these features, Wang (1993) concluded that Hesperocyon was a plantigrade animal, mainly scansorial in

Fig. 8.16. (A) Skeleton of the primitive canid Hesperocyon. Left P4 and upper molars: (B, C) Miacis; (D) basal canid Prohesperocyon; (E) basal canid Hesperocyon. (A from Matthew, 1901; B-E from Wang and Tedford, 1994.)

habit but incipiently cursorial as well. Hesperocyon appears to be broadly ancestral to most later lineages of canids. These include a diversity of closely related Oligocene hes-perocyonines as well as the borophagines, or "hyaenoid dogs," whose earliest representatives (e.g., early Oligocene Oxetocyon) had bunodont, hypocarnivorous teeth similar to those of procyonids (Munthe, 1998).

Chadronian Prohesperocyon lacks the partial intrabullar septum characteristic of Hesperocyon and all other canids. Its dentition approaches that of the miacid Procynodictis more closely than that of Hesperocyon or any other canid. For these reasons Prohesperocyon is considered the most primitive known canid and the sister taxon of all other canids (X. Wang, 1994).

Ursoidea

The bears (Ursidae) and bear-dogs (Amphicyonidae) are carnivorans that are sometimes united in the Ursoidea, which first appear in the Duchesnean and Chadronian of North America. Both families are usually regarded as arctoids, but the phylogenetic position of amphicyonids remains ambiguous. Parictis (Fig. 8.17A), a rare, primitive arctoid from the Chadronian and Orellan of North America, is usually considered to be the oldest known ursid (Hunt, 1998a). Although bears today are among the largest terrestrial carnivores, Parictis was small ( 2 kg). Like ursids, it had a primitive dental formula except for the loss of M3, robust premolars, and broad, relatively low-crowned molars with large basins. In Europe, the closely related Amphicynodon (Fig. 8.17B) from Quercy (not to be confused with amphicyonids; see below) had similar dental features and also seems to occupy a phylogenetic position near the beginning of ursids. The relationships of these taxa continue to be problematic, how ever. Parictis has been considered to be a canid (Scott and Jepsen, 1936), a member of a new ursoid family Subparic-tidae (Baskin and Tedford, 1996), and even a basal pinniped (Phocoidea; McKenna and Bell, 1997). Cirot and Bonis (1992) regarded Amphicynodon as a stem arctoid, possibly near the origin of both ursids and musteloids.

Identification of Parictis as a primitive pinniped is not as surprising as it may seem, because the basicranial and car-nassial morphologies suggest that pinnipeds evolved from an ursid (Hunt and Barnes, 1994). Pinnipeds are otherwise unknown until the Miocene, however, and their precise origin is uncertain. A recent molecular analysis placed pinnipeds as the sister group of musteloids (Flynn et al., 2005).

Aside from amphicynodonts, the ursid radiation took place primarily later in the Cenozoic (Miocene and thereafter). The only exception is Cephalogale, the oldest member of the hemicyonine ursids, which first appeared in the late Eocene of Asia and the early Oligocene of Europe (McKenna and Bell, 1997). Unlike other bears, which modified their dentition for omnivory, hemicyonines retained well-developed carnassials and did not elongate their molars (Hunt, 1998a).

Amphicyonids, or bear-dogs, first appear in the late middle Eocene (Duchesnean) of North America and slightly later in Europe. The oldest North American form is Daphoe-nus (Figs. 8.17D, 8.18), best known from the White River Group of the mid-continent; Cynodictis from the latest Eocene of Quercy is the oldest European form. Amphicy-onids rapidly became widely distributed. Several lineages, representing three subfamilies, evolved from these two genera by the end of the Eocene (Hunt, 1998b). These early representatives were small (< 5 kg, no bigger than a small fox), but some later amphicyonids reached 200 kg.

Amphicyonids exhibit a mixture of bearlike and doglike features, which has caused confusion about their affinities. In some features they appear to be closely related to canids, whereas others suggest they are close to the base of the arctoid radiation (Wolsan, 1993; Wang and Tedford, 1994). A recent phylogenetic analysis found amphicyonids to be the sister taxon of all other caniforms (Wesley-Hunt and Flynn, 2005), making the name bear-dog truly appropriate. They had a short snout and a single-chambered bulla like that of ursids, in which the ectotympanic is the main element. In early amphicyonids the bulla was incompletely ossified and consisted of a crescent-shaped ectotympanic (Hunt, 1974b). In addition, the basioccipital bone of amphicyonids is excavated to house an enlarged inferior petrosal sinus, which in analogy with bears probably contained a loop of the internal carotid artery for cooling blood en route to the brain (Hunt, 1977). The dental formula was primitively 3.1.4.3/ 3.1.4.3, although M3 was lost and the premolars reduced in some lines. Like canids (but unlike most ursids), they retained shearing carnassials and had a triangular (not quadrate) M1 with three main cusps—primitive features that misled early workers to ally them with canids. Daphoenictis converged on felids in having a large, bladelike lower carnassial. Most am-phicyonids had relatively generalized skeletons. Daphoenus was a subdigitigrade to digitigrade cursor whose feet retained

Fig. 8.17. Left dentitions of primitive arctoids: (A) basal ursid Parictis; (B) Amphicynodon; (C) basal musteloid Mustelictis; (D) amphicyonid Daphoenus. (A from Clark and Guensburg, 1972; B from Cirot and Bonis, 1992; C from Bonis, 1997; D from Scott and Jepsen, 1936.)

the flexibility expected in a climber (Hunt, 1996). It is believed that this skeletal form gave rise to both more cursorial types and more robust, bearlike forms (Hunt, 1998b).

Musteloidea (=Mustelida)

Under this heading are included mustelids (the most diverse extant carnivorans, including weasels, skunks, and otters) and procyonids (raccoons and coatis). The beginnings of the musteloid radiation are found in the late Eocene and early Oligocene of western North America and Europe, but details remain to be resolved. The oldest musteloids are Mustelavus (late Chadronian-Orellan, North America) and Mustelictis (early Oligocene, Europe; Fig. 8.17C). Basal members at this stage are very similar, and it is uncertain whether these genera should be allocated to either family or are better considered stem taxa. Their musteloid status is affirmed by a low trigonid on Mp absence of both upper and lower third molars, and presence of a suprameatal fossa (Bonis, 1997). Additional dental characters (single-rooted first premolars, reduced second molars, and reduced metaconule and postprotocrista on M1) suggest that they are primitive mustelids (Wolsan, 1993; Bonis, 1997; Baskin, 1998). McKenna and Bell (1997), how

ever, consider Mustelavus and Mustelictis to be synonyms of Pseudobassaris, the oldest known procyonid (Wolsan, 1993; Wolsan and Lange-Badre, 1996). Skulls of the latter from Quercy, however, have an inflated, single-chambered audi tory bulla and a deep suprameatal fossa like that of procy-onids, whereas the suprameatal fossa of Mustelictis is shallow. Consequently, Mustelictis, at least, appears to be distinct from Pseudobassaris.

Insectivora

ALTHOUGH THE TERM INSECTIVORA and the vernacular forms insectivoran and "insectivore" are widespread in both popular and scientific literature, they have been used to refer to very different associations of euthe-rians. To mammalogists, Insectivora has usually been considered to include the living hedgehogs, moles, shrews, solenodons, tenrecs, golden moles, and their immediate fossil relatives, which are alternatively (and preferably) united as Lipotyphla (Fig. 9.1A). Anatomy provides weak support (a small number of characters) for a monophyletic Lipotyphla (e.g., Asher et al., 2003; Mussell, 2005). Molecular evidence, however, conflicts with the traditional concept of Lipotyphla and suggests that Lipotyphla is poly-phyletic (Fig. 9.1B), as further discussed below. Lipotyphlans are typically viewed as very primitive eutherians because they retain many plesiomorphic features, often including a basic tribosphenic molar pattern, but this pattern has been modified, sometimes substantially, in some families. Until fairly recently, tree shrews (Tupaiidae) and elephant shrews (Macroscelididae)—once grouped as Menotyphla—were also often included in the Insectivora (e.g., Romer, 1966; Vaughan, 1978), but they are now assigned to separate ordinal-level groups, Scandentia and Macroscelidea, respectively following Butler (1972).

Many paleontological accounts have employed a broader concept of Insectivora that includes not just lipotyphlans but also some or all of the following so-called "archaic insectivores" (many of which Romer, 1966, included in his Proteutheria): leptictids, palaeoryctids, apatemyids, pantolestids, pentacodontids, mixodectids, and a few other families. Most of these families have proven difficult to place phylo-genetically, and they have little in common except relatively unmodified dentitions. Indeed, with the possible exception of the first two families, there is no good evidence

Afrotheria Tree

Fig. 9.1. Lipotyphlan relationships: (A) based on morphology; (B) based on gene sequences. (Positions of taxa within Afrotheria vary in different molecular studies.) Conventional lipotyphlan families are shown in bold. Solenodontidae were not included in the analyses on which these trees are based; they appear to be sorico-morphs closest to Soricidae among extant families. (A simplified after Asher et al., 2003; B modified after Douady et al., 2002, and Asher et al., 2003.)

Fig. 9.1. Lipotyphlan relationships: (A) based on morphology; (B) based on gene sequences. (Positions of taxa within Afrotheria vary in different molecular studies.) Conventional lipotyphlan families are shown in bold. Solenodontidae were not included in the analyses on which these trees are based; they appear to be sorico-morphs closest to Soricidae among extant families. (A simplified after Asher et al., 2003; B modified after Douady et al., 2002, and Asher et al., 2003.)

that they compose a monophyletic group with Lipotyphla. Consequently, an Insectivora of such broad composition is a true taxonomic wastebasket that cannot be defined or characterized except by retention of primitive eutherian features. Fortunately, most of these families are now assigned to other higher taxa, as they are in this book (see Chapters 7 and 10).

Based on a comprehensive analysis of cranial anatomy across the major groups of eutherians, Novacek (1986a) concluded that Leptictida is the sister group of Lipotyphla and proposed that the superorder Insectivora be used to encompass these two orders. This morphologically based arrangement is adopted here (Table 9.1), although the relationship remains to be compellingly demonstrated. It has also been argued that palaeoryctids are closely related to lipotyphlans, specifically soricomorphs or tenrecoids (e.g., Lillegraven et al., 1981; McKenna et al., 1984; Thewissen and Gingerich, 1989; MacPhee and Novacek, 1993), but this hypothesis is also weakly based. Butler (1988) rejected soricomorph, and presumably lipotyphlan, affinities for palaeoryctids. Here

Table 9.1. Classification ofInsectivora

Superorder INSECTIVORA

Order fLEPTICTIDA

fGypsonictops fLeptictidae fPseudorhyncocyonidae1

Order LIPOTYPHLA

fAdapisoriculidae Suborder ERINACEOMORPHA

Erinaceidae fSespedectidae fScenopagidae2 fAmphilemuridae3 fAdapisoricidae fCreotarsidae fChambilestidae4 Suborder SORICOMORPHA fGeolabididae Superfamily Soricoidea fNyctitheriidae5 Soricidae fPlesiosoricidae fNesophontidae Solenodontidae fMicropternodontidae fApternodontidae Superfamily Tenrecoidea6

Tenrecidae Superfamily Talpoidea5 fProscalopidae Talpidae fDimylidae Suborder SORICOMORPHA?

fOtlestes,7 fBatodon,8 fParanyctoides Suborder CHRYSOCHLOROMORPHA Chrysochloridae

Notes: Modified mostly after Novacek, 1986a; MacPhee and Novacek, 1993. The dagger (f) denotes extinct taxa. Families in boldface in this table are known from the Paleocene or Eocene.

1Named as a subfamily of Leptictidae.

2Sometimes considered a subfamily of Sespedectidae.

3Probably includes Dormaaliidae.

4May belong in Soricomorpha.

5Sometimes assigned to Erinaceomorpha.

6 This taxon has also been used to unite Tenrecidae and Chrysochloridae.

7Probable synonym of Bobolestes; better considered a basal eutherian or possibly a zalambdalestoid (Archibald and Averianov, 2001; Averianov and Archibald, 2005).

8Assigned to Geolabididae by McKenna and Bell (1997).

palaeoryctids are included under Cimolesta, following McKenna and Bell (1997).

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