Cynodictis lacustris Gervais, 1852

Fournier, Morgane, Ladevèze, Sandrine, Verger, Kévin Le, Fischer, Valentin, Speijer, Robert P. & Solé, Floréal, 2020, On the morphology of the astragalus and calcaneus of the amphicyonids (Carnivora, Mammalia) from the Paleogene of Europe: implications for the ecology of the European bear-dogs, Geodiversitas 42 (18), pp. 305-325 : 310-313

Cynodictis lacustris Gervais, 1852

( Fig. 2 )

HOLOTYPE. — Fragmentary mandible bearing P4 and M1; MNHN. F.Qu unnumbered ( Gervais 1852).

NEWLY REFERRED SPECIMENS. — Astragali. MNHN.F.Au1076, MNHN.F.Au3169, MNHN.F.Au847, MNHN.F.Au3186I, MNHN.F.Au984, MNHN.F.Au994, unnumbered specimen (astragalus + navicular).

Calcanei. MNHN.F.Au2188, MNHN.F.Au2699, MNHN.F.Au1059*, MNHN.F.Au848, MNHN.F.Au2398, MNHN.F.Au2020, MNHN.F.Au991, MNHN.F.Au2044, MNHN.F.Au2118*, MNHN.F.Au618, MNHN.F.Au822, MNHN.F.Au2209*(10), MNHN.F.Au2705, MNHN.F.Au2703, MNHN.F.Au992, MNHN.F.Au976, MNHN.F.Au2471, MNHN.F.Au845, MNHN.F.Au2391, MNHN.F.Au2018, MNHN.F.Qu9699, MNHN.F.Qu9757.

STRATIGRAPHIC DISTRIBUTION. — MP18-MP21 Priabonian – early Rupelian. It should be noted that some authors suggest that the genus is present up to MP23 (e.g., Kotsakis 1980: 268, 269).

TYPE LOCALITY. — La Débruge (Vaucluse, France).

LOCALITY. — Aubrelong (Lot, France).

AGE LOCALITY. — MP21, early Rupelian.

REMARKS ON NEWLY REFERRED SPECIMENS

These specimens are here identified as Amphicyonidae because of their morphological similarities with European and North American amphicyonids: astragalus with a medial projection of the head and the asymmetry of the trochlea; calcaneus with a rounded shape of the sustentacular facet and a slight tilt in a medioproximal-laterodistal orientation of the cuboid facet. Futhermore, the differences observed with other carnivoran clades found in the Quercy deposits ( Table 1 ) allow us to differentiate the studied bones from these taxa, and to support the assignment to amphicyonids. The specimens are assigned to the species C. lacustris because of their geographic localization, small size, and high relative abundance (see Comparison for determination).

ASTRAGALUS (TALUS) DESCRIPTION ( FIG. 2 A-E)

Dorsal view

The trochlea (trochlea tali proximalis) is deeply excavated. Its proximodistal length is greater than its mediolateral length. The axis of elongation of the trochlea is inclined relative to that of the neck. Its medial and lateral lips are of approximately the same proximodistal length and are more or less parallel. The proximal plantar tuberosity is very small or absent. The neck (collum tali) is mediolaterally thinner than the head (caput tali) and is relatively short. The head is strongly distally convex. It is broad (wider than the mediolateral length of the trochlea) and projected on the medial side. It rises on the neck on the medial side of the astragalus and almost reaches the distal edge of the trochlea.

Ventral view

The ectal facet (facies articularis calcaneae lateralis) is proximodistally elongated and more distally distinct than proximally. It is strongly concave and its medial edge curves slightly. The sinus of the tarsus (sinus tarsi) is deep. It clearly separates the two facets for the articulation with the calcaneus (facies articulares calcaneae). The sustentacular facet (facies articularis calcaneae medialis) is quite large and occupies a large portion of the width of the neck. Its medial and distal edges are well marked. It is elongated and extends proximomedially towards the trochlea. The distolateral part of this facet extends to almost reach the head of the astragalus (caput tali). It is slightly convex except on its proximomedial extension, where it becomes concave. The foramen in the proximal portion of this sinus is present. The head has a small ventral extension that goes partly back to the sustentacular facet.

Lateral view

A slight depression is formed proximal to the fibular facet (facies malleolaris lateralis). The proximomedial edge of the fibular facet forms a nearly right angle with the distal edge. The distal edge is relatively distally convex in the extension of the lateral edge of the trochlea. The ectal facet is well curved.

Distal view

The trochlea is slightly asymmetrical. The head is dorsoventrally flattened, thinner on the medial side, and wider on its lateral side. The axis of elongation of the head is inclined relative to the mediolateral axis of the astragalus. The lateral process is limited in breadth, forming only a slight medially directed tip.

Proximal view

The trochlear foramen is present on some specimens and absent in others. The proximoventral edge of the medial lip of the trochlea forms a slight ventral tip. The plantar tendon groove (for the flexor digitorum fibularis) is very weak. It seems to be fused with the proximal prolongation of the trochlea. The trochlea is mediolaterally thinner on its proximal part than on its dorsal part.

CALCANEUS DESCRIPTION ( FIG. 2 F-J)

Dorsal view

The medial process of the tuber calcanei is slightly proximally broader than the lateral process. The sagittal groove is rather marked. The tuber calcanei is not very mediolaterally broad but rather proximodistally elongated. The ectal facet (facies articularis talaris proximalis) is proximodistally elongated. It is strongly convex in the middle and very slightly proximally and distally concave. Its medial and lateral edges are slightly curved. The edges of this facet are rather well marked, except the distal edge, which merges with the body of the calcaneus and therefore is difficult to delimit. The sustentacular facet (facies articularis talaris distalis) is slightly elongated in the proximolateral-distomedial direction and extends slightly on the proximal edge of the sustentaculum tali. This gives a rather oval shape to this articular surface. The peroneal process is quite broad. The cuboid facet (facies articularis cuboidea) is inclined with respect to the mediolateral axis and its lateral edge rises above the body of the calcaneus.

Lateral view

The dorsal and ventral edges of the tuber are very slightly curved; the tuber is dorsoventrally wide. A well marked ridge is formed at the continuity of the peroneal process and join more distally the tuber calcanei.

Medial view

The groove for the plantar tendon (sulcus tendinis musculus flexor digiti lateralis) is pronounced. The plantar tubercle is distally large, forming a distally oriented tip.

Distal view

The cuboid facet is very slightly concave, quite dorsoventrally thin and mediolaterally elongated. The plantar tubercle is ventrally broad. The edge separating these two structures is not very broad.

Proximal view

The distal part of the tuber calcanei has a rather oval surface that is slightly dorsoventrally elongated. A slightly curved groove is ventrally clearly visible.

COMPARISON

These tarsal elements are all from Aubrelong ( France, MP21; except two specimens whose exact locality is unknown).

Cynodictis lacustris differs from Hyaenodonta (e.g., Hyaenodon Laizer & Parieu, 1838 from the Eocene of Europe [ Bastl 2012] and Galecyon chronius Zack, 2011 from the Eocene of North America [ Zack & Rose 2015]) in its astragalus morphology which displays an astragalar neck that is less distomedially oriented and mediolaterally thinner; a head that extends less on the medial part of the neck, and a medial edge of the head that is more pronounced ( Table 1 ). Moreover, the plantar tendon groove is less pronounced than the proximal plantar tuberosity and the lateral process is slenderer than in Hyaenodonta . For the calcaneus, the cuboid facet of C. lacustris is less inclined than in Indohyaenodon raoi Bajpai, Kapur & Thewissen, 2009 (Ypresian, India; Rana et al. 2015) and Galecyon chronius (Eocene, North America; Zack & Rose 2015).

Compared to Nimravidae , such as Hoplophoneus primaevus (Leidy & Owen, 1851) and Nimravus brachyops ( Cope, 1878) (Oligocene, North America; Barrett 2016), the astragalus of C. lacustris has a longer neck and the head extends less on the medial side of the neck. Its calcaneus has a thinner sustentaculum tali and a shallower plantar tendon groove than in Nimravidae .

Compared to Miacidae such as Vulpavus Marsh, 1871 (Eocene, North America; Heinrich & Rose 1997), the tarsal bones of C. lacustris are smaller, the neck of the astragalus is shorter and less medially projected, and the plantar tendon groove is less pronounced and less dorsally extended. Moreover, the sustentaculum tali is not as medially broad and proximally located, and the cuboid facet is less inclined.

Cynodictis lacustris differs from Ursoidea (only modern forms because of the lack of ursid tarsal bones from the Paleogene or Miocene in the literature) ( Gagnaison et al. 2017), such as Ursus spelaeus Rosenmüller, 1794 (early Pleistocene of Europe; Santi et al. 2005) and Ursus arctos Linnaeus, 1758 (Pleistocene of Europe; Baryshnikov 2015): the astragalus of C. lacustris is thinner, the neck is much longer, and the trochlea is mediolaterally narrower and is not flattened proximodistally. The tuber calcanei is less stockier and mediolaterally thinner. The sustentaculum tali is less distally positioned and its sustentacular facet is shorter, more rounded, and not as inclined in the medioproximal-laterodistal direction.

In comparison with Ailuridae , such as Simocyon batalleri ( Viret, 1929) (Miocene, Spain; Salesa et al. 2008), the astragalus of C.lacustris has a shallower trochlea, a shorter and mediolaterally broader neck, and a less flattened head. The sustentaculum tali of the calcaneus is proximodistally thinner, the cuboid facet is more inclined and the plantar tendon groove is less marked than in S. batalleri.

Compared with mustelids such as Martes sansaniensis Lartet, 1851, Ischyrictis zibethoides Blainville, 1841, and Taxodon sansaniensis Lartet, 1851 (Miocene, Europe; Peigné 2012), the astragalar neck of C. lacustris is shorter and less medially projected and the sustentacular facet is mediolaterally broader. The calcaneus of C. lacustris has a more inclined cuboid facet and a shorter plantar tubercle than in M. sansaniensis. The sustentaculum tali is proximodistally and mediolaterally narrower, the tuber calcanei is mediolaterally thinner and the peroneal process is proximodistally broader than in T. sansaniensis. Cynodictis lacustris also exhibits a smaller calcaneus as compared with I. zibethoides, with a sustentaculum tali that is proximodistally narrower and a thinner medial process of tuber.

All the features discussed above allow us to discriminate the Aubrelong amphicyonids from the other carnivorous groups recorded in Aubrelong and the Phosphorites du Quercy analysed in the framework of this study. The studied bones particularly resemble those of the Amphicyonidae , such as the European Amphicyon major Blainville, 1841 (Miocene) ( Argot 2010) and the North American Amphicyon galushai Hunt, 2003 and Daphoenodon superbus Peterson, 1907 (Miocene) ( Hunt 2009; 2011). In these four species, the head is mediolaterally broad and medially projected, while the trochlea is asymmetrical. Futhermore, the deep and relatively broad thochlea observed in C. lacustris is a characteristic of large amphicyonids according Gagnaison et al. (2017) as Amphicyon giganteus Schinz, 1825. Moreover, some differences are noticeable: for instance, the average length of the C. lacustris astragali (14.91 mm) is much less than the length of those of A. major, D. superbus and A. galushai (around 50 mm) and the neck in C. lacustris is more elongated than in the other two species. The morphology of the calcaneus of Cynodictis lacustris is close to that of Amphicyon major. In these two species, the medial process of the tuber calcanei is proximally longer than the lateral process, the sustentacular facet is prolonged on its proximal edge, the tuber calcanei is quite thick dorsoventrally, and the cuboid facet is inclined with respect to the mediolateral axis. However, the cuboid facet is more inclined and more concave, the peroneal process is less broad and the sustentaculum tali is more distally prolonged in Amphicyon major than in Cynodictis lacustris .

The ratio of tarsal bone length/skull length of C. lacustris described here is similar to that of other amphicyonids. For instance, the ratio for Daphoenodon robustum Peterson, 1910 ranges between 0.14 to 0.16 for the astragalus and 0.24 to 0.26 for the calcaneus ( Hunt 2009). In C. lacustris , the ratio for the astragalus ranges from 0.13 to 0.15 and for the calcaneus 0.18 to 0.26. This ratio is also close to that of modern ursids: 0.11 to 0.14 for the astragalus and 0.18 to 0.22 for the calcanueus ( Baryshnikov & Boeskorov 2004; Baryshnikov 2015). Moreover, it is different from Hyaenodonta : astragalar ratio 0.09 to 0.11, and calcaneal ratio of 0.13 ( Bastl 2012). In S. batalleri ( Ailuridae ), the astragalar ratio is 0.17 and the calcaneal ratio is 0.25. It is close to C. lacustris regarding the ı ( Salesa et al. 2008). The lack of data in the literature prevents us from calculating ratios for other fossil carnivoran clades.

Furthermore, the use of other criteria, such as relative abundance and size, allow us to be more specific and to attribute these tarsal bones to Cynodictis lacustris (Priabonian-Rupelian) , primarily because this species is the only amphicyonid recognized based on dental and cranial elements in the Aubrelong locality (K. Le Verger pers. obs.).

AMPHICYONIDAE Gen. indet.

NEWLY REFERRED SPECIMENS. — Astragali. Morphotype 1: MNHN.F.Qu9986, MNHN.F.Qu10038, KUL.PLV1542.1, KUL. PLV1542_2, KUL.PLV1542_3, KUL.PLV1542_4. — Morphotype 2: MNHN.F.Qu10231, KUL.PLV1542_5, KUL.PLV1542_6, KUL.PLV1542_7, KUL.PLV1542_8. — Morphotype 3: MNHN.F.Qu9570, MNHN.F.Qu9758, MNHN.F.Qu10369, MNHN.F.Qu10368, MNHN.F.Qu10372, MNHN.F.Qu10371, MNHN.F.Qu10042, MNHN.F.Qu10367, ULgPA.17.175_1, ULgPA.17.175_2, ULgPA.17.175_3. — Morphotype 4: MNHN.F.Qu10039.

Calcanei. Morphotype A: MNHN.F.Qu9845, MNHN.F.Qu10095, MNHN.F.Qu10230, MNHN.F.Qu10237, MNHN.F.Qu10284, MNHN.F.Qu10282, MNHN.F.Qu10344, MNHN.F.Qu10350, MNHN.F.Qu10349, MNHN.F.Qu10347, MNHN.F.Qu10351, ULgPA.17.170_1, ULgPA.17.170_2, ULgPA.17.170_3, ULgPA.17.170_4, ULgPA.17.170_5, ULgPA.17.170_6, ULgPA.1 7.1 70_7, UL gPA. 17. 170_ 8, U LgPA. 17. 170_9, ULgPA.17.170_10, ULgPA.17.170_11, ULgPA.17.170_12, ULgPA.17.170_13, ULgPA.17.170_14, ULgPA.17.170_15, ULgPA.17.170_16, ULgPA.17.170_17, ULgPA.17.170_18, ULgPA.17.170_19, KUL.PLV1542_9, KUL.PLV1542_10, KUL.PLV1542_11, KUL.PLV1542_12, KUL.PLV1542_13, KUL.PLV1542_14, KUL.PLV1542_15, KUL.PLV1542_16, KUL.PLV1542_17, KUL.PLV1542_18, KUL.PLV1542_19, KUL.PLV1542_20, KUL.PLV1542_21, KUL.PLV1542_22, KUL.PLV1542_23. — Morphotype B: MNHN.F.Qu10399, MNHN.F.Qu10005, MNHN.F.Qu10003, MNHN.F.Qu9775, MNHN.F.Qu10002, MNHN.F.Qu10381, MNHN.F.Qu10239, MNHN.F.Qu10346, MNHN.F.Qu9987, ULgPA.17.170_20, ULgPA.17.170_21, ULgPA.17.170_22, ULgPA.17.170_23, ULgPA.17.170_24, ULgPA.17.170_25, KUL.PLV1542_24, KUL. PLV1542_25, KUL.PLV1542_26, KUL.PLV1542_27, KUL. PLV1542_28. — Morphotype C: KUL.PLV1542_29.

STRATIGRAPHIC DISTRIBUTION. — MP18-MP30; Priabonian-Chattian.

LOCALITY. — Quercy ( France), exact locality not indicated.

REMARKS ON NEWLY REFERRED SPECIMENS

These fossils are identified as Amphicyonidae because of their relative abundances, size, morphological similarities with European and North American amphicyonids and with C. lacustris described above, together with morphological differences from other carnivoran clades ( Table 1 ). Moreover, relative abundance and body mass criteria support our identifications (see below). Although these bones are similar enough to those of amphicyonids to all be assigned to this family, morphological differences are noticeable between all these different specimens. These differences are perhaps representative of several amphicyonid genera or species, but so far more precise attribution is not possible, for lack of reliable arguments. For these reasons, they remain grouped into several morphotypes in this study, based on morphology and size (see Comparison for more details).

ASTRAGALUS DESCRIPTIONS

This set of astragalus morphotypes has the following characteristics. The trochlea is asymmetrical. Its mediolateral length is shorter than its proximodistal length. The axis of elongation of the trochlea is inclined relative to that of the neck. A depression is formed proximal to the fibular facet. The ectal facet is concave, proximodistally elongated and more distally thin. The sinus of the tarsus (sinus tarsi – sensu Schaller 2007) is deeply excavated. The sustentacular facet rises proximomedially towards the plantar tendon groove (for the flexor digitorum fibularis), as well as distolaterally to the head. This head is strongly distally convex and has a ventral extension that reaches back to the sustentacular facet.The head is dorsoventrally flattened, thinner on the medial side and wider on its lateral side. Four morphotypes are recognized among this sample of astragali due to differences in size and morphology.

Figures

FIG. 2. — Tarsal bones of Cynodictis lacustris from Aubrelong (France; Rupelian, MP21): A-E, MNHN.F.Au994, left astragalus (reversed views); A, dorsal view; B, ventral view; C, lateral view; D, distal view; E, proximal view; F-J, MNHN.F.Au2044, right calcaneus; F, dorsal view; G, lateral view; H, medial view; I, distal view; J, proximal view. Abbreviations: cf, cuboid facet; ef, ectal facet; f, foramen; ff, fibular facet; h, head; ll, lateral lip; lp, lateral process; lpt, lateral process of tuber; ml, medial lip; mpt, medial process of tuber; n, neck; ppt, proximal plantar tuberosity; plt, plantar tubercle; pp, peroneal process; ptg, plantar tendon groove; sf, sustentacular facet; sg, sagittal groove; sit, sinus of the tarsus; st, sustentaculum tali; tc, tuber calcanei; tr, trochlea. Scale bar: 1 cm.