A new species of the amphicyonid carnivore Cynelos Jourdan, 1862 from the early Miocene of North America

2020  42  5 geodiversitas M e m o r i a l S t é p h a n e P e i g n é – C a r n i v o r e s o f t h e C e n o z o i c – Geodiversitas est une revue en flux continu publiée par les Publications scientifiques du Muséum, Paris Geodiversitas is a fast track journal published by the Museum Science Press, Paris Les Publications scientifiques du Muséum publient aussi / The Museum Science Press also publish: Adansonia, Zoosystema, Anthropozoologica, European Journal of Taxonomy, Naturae, Cryptogamie sous-sections Algologie, Bryologie, Mycologie. 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Geodiversitas est indexé dans / Geodiversitas is indexed in: – Science Citation Index Expanded (SciSearch®) – ISI Alerting Services® – Current Contents® / Physical, Chemical, and Earth Sciences® – Scopus® Geodiversitas est distribué en version électronique par / Geodiversitas is distributed electronically by: – BioOne® (http://www.bioone.org) Les articles ainsi que les nouveautés nomenclaturales publiés dans Geodiversitas sont référencés par / Articles and nomenclatural novelties published in Geodiversitas are referenced by: – ZooBank® (http://zoobank.org) 57 GEODIVERSITAS • 2020 • 42 (5) © Publications scientifiques du Muséum national d’Histoire naturelle, Paris. www.geodiversitas.com urn:lsid:zoobank.org:pub:6530B0E7-8731-43B9-B0A0-5599462F7C5F Hunt R. M. Jr & Yatkola† D. A. 2020. — A new species of the amphicyonid carnivore Cynelos Jourdan, 1862 from the early Miocene of North America, in Bonis L. de & Werdelin L. (eds), Memorial to Stéphane Peigné: Carnivores (Hyaenodonta and Carnivora) of the Cenozoic. Geodiversitas 42 (5): 57-67. https://doi.org/10.5252/geodiversitas2020v42a5. http://geodiversitas.com/42/5 ABSTRACT The Neogene sediments of the North American midcontinent, undisturbed by tectonism, have long been the source of abundant well-preserved mammalian faunas critical to the definition of the North American Land Mammal ages (NALMA). In western Nebraska the early Miocene interval (c.23 to 16 Ma) is exceptional for its succession of Arikareean and Hemingfordian mammals that establish a biostratigraphic standard for the region. Fluvial sands, silts, and gravels of the paleovalleys and floodplains of the Runningwater Formation (c.18 Ma) have yielded a rich carnivore assemblage of more than 24 species, many of these representing Old World lineages that migrated into North America via the Bering corridor. Amphicyonid carnivores, among the largest of the Runningwater predators, often surpass their Old World equivalents in completeness and condition, and include species of the immigrant genus Cynelos Jourdan, 1862. Here is described the only intact skull and jaws of Cynelos known from the New World. It is assigned to a new species, Cynelos stenos n.sp., that in its size, the association of a cranium with articulated mandibles, and in its dentition (occlusal detail of P4-M3, m1-3) differs from all others of this genus previously reported from both North America and Europe. Robert M. HUNT Jr Department of Earth and Atmospheric Sciences, University of Nebraska, Lincoln, NE 68588 (United States) [email protected] Daniel A. YATKOLA† Division of Vertebrate Paleontology, University of Nebraska, Lincoln, NE 68588 (United States) Submitted on 30 January 2019 | accepted on 2 August 2019 | published on 5 March 2020 A new species of the amphicyonid carnivore Cynelos Jourdan, 1862 from the early Miocene of North America KEY WORDS Nebraska, Miocene, Carnivora, Amphicyonidae, new species. 58 GEODIVERSITAS • 2020 • 42 (5) Hunt R. M. Jr& Yatkola† D. A. RÉSUMÉ Une espèce nouvelle du carnivore amphicyonidé Cynelos du Miocène inférieur d’Amérique du Nord. Les sédiments néogènes situés au centre de l’Amérique du Nord, n’ont pas été perturbés par des phénomènes tectoniques et, depuis longtemps, ils ont fourni d’abondants fossiles de mammifères bien préservés, essentiels pour la définition des âges des mammifères terrestres d’Amérique du Nord (NALMA). Dans l’ouest du Nebraska, le Miocène inférieur (environ 23 à 16 Ma) est exceptionnel pour sa succession de mammifères arikaréens et hémingfordiens, qui établissent un standard biostratigraphique pour la région. Les sables fluviatiles, les limons et les graviers des paléovallées et des plaines inondables de la formation Runningwater (c.18Ma) ont donné un riche assemblage de carnivores avec plus de 24espèces, dont beaucoup représentent des lignées de l’Ancien Monde ayant migré en Amérique du Nord par le corridor de Bering. Les carnivores amphicyonidés, parmi les plus grands des prédateurs de Runningwater, dépassent souvent leurs équivalents du Vieux Monde en termes de complétude et de préservation; ils incluent des espèces du genre immigrant Cynelos Jourdan, 1862. Ici sont décrits le seul crâne intact et les mâchoires d’un Cynelos du Nouveau Monde. Ilest attribué à une nouvelle espèce, Cynelos stenos n.sp. Connue par l’association d’un crâne et d’une mandibule articulée, cette espèce diffère par sa taille et sa dention (détail occlusal de P4-M3, m1-3) de toutes les autres espèces de ce genre précédemment décrites d’Amérique et d’Europe. MOTS CLÉS Nebraska, Miocène, Carnivora, Amphicyonidae, espèce nouvelle. INTRODUCTION At the advent of the Miocene, amphicyonine beardogs (Car - nivora, Amphicyonidae) began to arrive in the North American midcontinent, representing lineages previously known only in the Old World. During the early Miocene (c.23 to 16 Ma) these species successfully occupied the niche for large predatory carnivores, reaching a climax in the earlier mid-Miocene and then are not seen after c.14 Ma. Cynelos Jourdan, 1862 and Ysengrinia Ginsburg, 1965 first recognized during the c.22-23 Ma interval in the late and latest Arikareean (Ar3Ar4) are followed by Amphicyon, Lartet, 1836 appearing at c.18 Ma in the early Hemingfordian (He1). In Europe, these genera are represented primarily by dental material due to the prevalence at sites of isolated teeth, partial dentitions in jaws, and unassociated postcranials. Intact crania are exceptional. However, Miocene sediments of the Great Plains on occasion yield well-preserved skulls of these beardogs: here we report the first associated cranium and mandibles of Cynelos from North America. It was found with an early Hemingfordian (He1) mammalian fauna in fluvial channel sands of the early Miocene Runningwater Formation in northwest Nebraska. This paper is dedicated to Stéphane Peigné, Muséum national d’Histoire naturelle, Département Histoire de la Terre, Paris, an exceptional colleague and friend long familiar with study of amphicyonid carnivores. MATERIAL AND METHODS A detailed description of the unique cranium and associated mandibles of this Hemingfordian Cynelos is given here. Its excellent preservation and articulation of jaws with the skull when it was discovered has not been reported previously for Cynelos either in the North American Miocene or in the Old World. Species of the genus are primarily based on European dental material defined by size, shape, and occlusal detail of the teeth: here definition of the new species relied on dental comparison with the most similar previously-described western European material of the genus: Cynelos helbingi (Dehm, 1950) and C.lemanensis (Pomel, 1846). The comparative sample included casts of Cynelos assembled in the collections of the University of Nebraska State Museum and the American Museum of Natural History, New York. Estimation of dental variation was obtained from measurements of teeth compiled from the rare Cynelos populations from Wintershof-West (Bavaria) and Ulm-Westtangente (BadenWürttemberg), southern Germany, and from the Bridgeport Quarries, Nebraska, U.S.A. Additional analysis of the paleogeographic distribution and dentitions of species of Cynelos can be found in Hunt& Stepleton (2015). Measurements were made with digital calipers to the nearest 0.1mm; location of dental measurements are shown in Figure 1 and 2. Comparative craniodental data are provided in Tables 1 to 3. The measurements for Table 2 were obtained by enlargement of figures 46 and 47 from Dehm (1950) with the data points then projected to the ordinate and abscissa of each of his graphs and the resulting measurement recorded in Table 2. AbbreviAtions AMNH American Museum of Natural History, New York; BSP Bayerische Staatssammlung für Paläontologie und historische Geologie, Munich; F:AM Frick Collection, American Museum of Natural History, New York; MNHN Muséum national d’Histoire naturelle, Paris; MHNL Muséum d’Histoire naturelle de Lyon, Lyon; OCPC Orange County Paleontological Collection, The Cooper Center, Dept. of Geological Sciences, California State University, Fullerton; SMNS Staatliches Museum für Naturkunde, Stuttgart; UNSM Vertebrate Paleontology, University of Nebraska State Museum, Lincoln. 59 A new Cynelos Jourdan, 1862 from the early Miocene of North America GEODIVERSITAS • 2020 • 42 (5) SYSTEMATICS Order CARNIVORA Bowdich, 1821 Infraorder ARCTOIDEA Flower, 1869 Family AmphicyonidAe Haeckel, 1866 Subfamily AmphicyoninAe Trouessart, 1885 Genus Cynelos Jourdan, 1862 Cynelos stenos n.sp. (Figs3-6; Table 1) urn:lsid:zoobank.org:act:82B04120-7E1C-4CB2-ACD3-5C773281F85C “Cynelos n.sp. II” – Hunt 1998: 211. Cynelos sp. B – Hunt 2002: 35. holotype. — UNSM 44723, a cranium and associated mandibles, with both left and right upper and lower dentition (P1-M3: p1-m3); the left P1-p1 each represented by a single alveolus; the left upper and right lower canines; left I2 and left i3. A partial femur and fragments are attributed to the cranial material. Collected by D. A. Yatkola and William Rovnak, University of Nebraska State Museum. Daniel Yatkola discovered UNSM 44723 during his doctoral study of the Miocene stratigraphy and mammalian fauna of northwest Nebraska (Yatkola 1978). etymology. — From the Greek “stenos” (στενός) (= narrow). The species nomen emphasizes the narrowness of the skull in dorsal view relative to the broader-skulled large contemporary early Miocene amphicyonids Amphicyon galushai Hunt, 2003 and Daphoenodon (Borocyon) robustum (Peterson, 1910). type locAlity. — UNSM 44723 was found in a basal arkosic sand and gravel channel at the stratotype locality of the Runningwater Formation (Cook, 1965), Box Butte Co., northwest Nebraska. The site was designated Runningwater Quarry by its discoverer M. F. Skinner of the American Museum’s Frick Laboratory, and was later reopened by UNSM under the direction of Daniel Yatkola. The fauna is conserved in the F:AM and UNSM collections. geologicAl Age. — Early Miocene c.18 Ma. description Cynelos stenos n.sp. (UNSM 44723) represents the first occurrence in the North American Miocene of a complete skull of the genus with mandibles in articulation. Only two other skulls of Cynelos are known in the early Miocene of North America: the skull of Cynelos idoneus (AMNH 20495) from the late Hemingfordian (He2) of western Nebraska and the skull of Cynelos malasi (OCPC 21791) from the latest Arikareean (Ar4) of southern California. No skulls were found with the Cynelos population sampled from the early Hemingfordian Bridgeport Quarries, western Nebraska, where the genus was represented by over 60 isolated cheek teeth, two maxillae, three mandibles, and numerous postcranials. The skulls attributed to the genus in North America from the early middle Miocene (c.14.8 to 16 Ma) are those of the large early Barstovian C.sinapius from the Olcott Formation, Sioux County, Nebraska, includ - ing one (AMNH 18257: Matthew 1924: figs22-23) very similar in form to the skull of C.stenos n.sp. except for its much larger size. Such narrow skulls probably characterize the Miocene species of Cynelos in North America, including the terminal species, C.sinapius. Cranium (Figs3; 4) The skull is essentially uncrushed preserving its cranial proportions and a nearly intact dentition except for damaged canines and the loss of incisors. It is exceptional in retaining the basicranial region. The sutures of the cranium remain open in the rostral area but due to age have closed elsewhere or are obscured by breakage. Viewed from above, the cranium is quite narrow compared to the larger contemporary amphicyonid species (Amphicyon galushai, Daphoenodon [B.] robustum) that possess much broader skulls. Relative to skull length, the rostrum is short and rather constricted at the level of the P2. Behind this constriction the palate broadens to include the crushing dentition comprising the prominent molars and carnassials. At the posterior palatal border, the nasal cavity opens at the nasal choanal aperture into a ventrally open narrow nasopharyngeal fossa (9cm in length, 2cm in width) that continues to the basicranial region. The considerable breadth of both the basicranium and palate contrast with the intervening narrow interorbital area. Within the broad basicranium the auditory regions have been preserved with minimal damage. Despite loss of the ventral floor, the auditory bulla retains a capsular flask-like form with short bony external auditory meatus that differs from the more plesiomorphic condition of the bulla in the skull of Cynelos lemanensis from St.- Gérand, France (Hunt& Stepleton 2015: fig.8). The C.stenos n.sp. bulla was not large, 2cm in width, and only slightly inflated. a e b c d f M2 M 1 p4 fig. 1 . — Dental measurements for species of the amphicyonid Cynelos Jourdan, 1862. Abbreviations: a, greatest length of P4 from mesial base of paracone to distal limit of metastylar blade; b, greatest width of P4 from lingual border of protocone to labial base of paracone; c, greatest labial length of M2; d, greatest M2 width from paracone to lingual cingulum; e, greatest labial length of M1; f, greatest M1 width from paracone to lingual cingulum. 60 GEODIVERSITAS • 2020 • 42 (5) Hunt R. M. Jr& Yatkola† D. A. In profile the skull has a short, deep rostrum expanded at the canines that slopes gradually upward to the forehead to form a broad frontal region housing inflated frontal sinuses at the level of the postorbital processes. From the frontals the skull roof narrows posteriorly, forming a tall thin sagittal crest 12cm in length and 5mm in width that reaches its maximum height (4cm) above the braincase. The crest then tapers to its termination at the inion. The braincase table 1. — Measurements (in mm) of length and width of the lower teeth of Cynelos stenos n. sp. (UNSM 44723, holotype): upper row, right dentition; lower row, left dentition. Distal width is measured for premolars; trigonid width for m1-3. p1 p2 p3 p4 m1 m2 m3 p1-4 m1-3 p2-m2 6.3 × 3.7 10.3 × 4.8 11.9 × 5.5 16.4 × 9.1 25.3 × 12.4 16.5 × 12.1 12.8 × 9.7 60.4 53.8 90.0 – 10.3 × 4.9 12.1 × 5.5 16.0 × 8.9 25.2 × 12.4 16.4 × 12.2 12.8 × 9.7 – 54.6 92.3 Measurements of length and width of the left upper teeth (in mm) of Cynelos stenos n. sp. (UNSM 44723, holotype). P1 P2 P3 P4 M1 M2 M3 P1-M3 P2-M3 P2-M2 7.3 × 5.5 11.1 × 4.5 12.8 × 6.2 22.4 × 14.2 19.2 × 24.6 15.0 × 22.2 9.2 × 14.9 109.6 96.5 91.6 Measurements of the cranium (in mm) of Cynelos stenos n. sp. (UNSM 44723, holotype). Skull length 324 mm (premaxillary border to tip of inion) Postorbital length 18 cm (postorbital process to tip of inion) Basilar length of skull 29 cm Palatal width at P4-M1 embrasure c. 54 mm (c. 59 mm, 5 mm added due to crushing) Rostral constriction at P2 c. 38 mm (c. 43 mm, 5 mm added due to crushing) Rostral expansion at canines c. 50 mm (c. 55 mm, 5 mm added due to crushing) Palatal length 14 cm (premaxillary border to posterior limit of palatine) Palatal width c. 72 mm (transverse width including M1s) Basioccipital, greatest width 37 mm Occipital condylar width 50 mm Frontal width 70 mm (measured between the postorbital processes) Sagittal crest 33 mm (height above braincase) Nasal length 80 mm Maxilla height above P4 c. 73 mm Preorbital skull length 120 mm (orbital margin to tip of premaxilla Postorbital skull length 208 mm (orbital margin to inion) Orbital margin to occipital condyle 181 mm (measured from lacrimal border) b P4-M1 P 4 -M 1 c f e d a P4 M1 fig. 2. — Dental measurements for species of the amphicyonid Cynelos Jourdan, 1862. Abbreviations: a, greatest length of p4; b, m1 trigonid length from mesial edge of paraconid to central distal base of protoconid; c, greatest length of m1; d, greatest width of the m1 talonid (also for m2); e, greatest width of the m1 trigonid (also for m2); f, distal width of p4 (and for p2-p3). 61 A new Cynelos Jourdan, 1862 from the early Miocene of North America GEODIVERSITAS • 2020 • 42 (5) volume is not large and suggests the less developed brain described by Radinsky (1980). The greater part of the skull (2/3 rds ) lies behind orbits that are set low below the frontal region: here what seems an exceptionally narrow and deep interorbital area intervenes between the orbits and the braincase – much of this interval was occupied by the large temporal and pterygoid musculature essential to the feeding mechanics of this species. Mandibles (Fig. 5) The conjoined mandibles preserve nearly the complete lower dentition; the dentaries are firmly interdigitated at the mandibular symphysis to form an incipient ankylosis in this mature individual. The jaws are elongate (length, c.23cm: articular condyle to canine) in keeping with the length of the skull and are not especially deep below the teeth (4.3cm below m2). Behind the rather shallow masseteric fossae are wide articular condyles, set low at the back of the mandible nearly at the level of the toothrow, indicating nearly simultaneous occlusion of carnassials and molars (P4-M3, p4-m3) at jaw closure. Upper Dentition (Fig. 6; Table 1) The dentition is fully erupted indicating from its moderate wear a mature adult; the canines and slender rostrum suggest a female. The right canine alveolus (L× W, 21.1× 13.9mm) retained the root. The damaged left canine (L× W, 18.2× 12.5mm, measured at the base of the enamel) is broken off at the tip but has mesial and distal thin enamel ridges. All A B fig. 3. — Cynelos stenos n. sp., UNSM 44723, Runningwater Formation, Runningwater Quarry (early Hemingfordian), Box Butte Co., Nebraska. Cranium in right lateral view (A) and in ventral view (B). Scale bars: 5 cm. 62 GEODIVERSITAS • 2020 • 42 (5) Hunt R. M. Jr& Yatkola† D. A. incisors were lost except the left I1 (L× W, 6.3× 4.1mm); however, the I3 alveoli are large relative to those for I1-I2 showing that I3 was much larger than the small I1-I2. The P1-P3 are reduced and separated by diastemata. The left P1 is represented by a small circular alveolus and is separated from P2 by 5mm. The low P2 (L× W, 11.1× 4.5mm) has two roots, a single apical cusp with a mesial and more extended distal slope and short distal shelf; the P2-P3 diastema is 9.2mm. P3has the same form as P2 but is larger (L× W, 12.8× 6.2mm) with a wider distal shelf and a sloping mesial face; the P3-P4 diastema is 3.2mm. The P4 is short relative to the molars; feeding on hard material has blunted the once-sharper paracone and metastylar blade. The small low protocone does not protrude far lingually and is slightly retracted. A thin enamel ridge runs from the P4 paracone to a weak parastyle and there is a weak labial cingulum. The M1-M2 are moderately worn teeth forming a formidable crushing platform together with the small M3. The M1 paracone is larger and although worn was slightly taller than the metacone. A cingulum occupies the labial margin and extends a short distance to the mesial base of the paracone and distal base of the metacone. The cingulum is weak to absent on the mesial and distal sides of the tooth but expands to form a prominent lingual cingulum. The M1 protocone was closer to the mesial border of the tooth and is situated at the lingual apex of the protocone basin. A thin straight mesial enamel ridge extends from the protocone to a weak paraconule at the base of the paracone. A thin slightly curved distal ridge extends from the protocone to the base of the metacone but without a metaconule: the mesial and distal ridges enclose the protocone basin. The M2 is somewhat smaller than M1 – its protocone forms the apex of an arcuate crest but, where the protocone of M1 is nearer the mesial margin of the tooth, the M2 protocone is more centrally situated. The M2metacone is slightly reduced relative to the paracone. On M2 the straight mesial and curved distal ridges are weaker without evident conules. The M2 protocone is worn as in M1 but where in M1 the mesial ridge ended at the base of the paracone, in M2 the mesial ridge reached the mesial border of the tooth to join the cingulum; there is a weak swelling along the ridge. In occlusal view M1 and M2 both extend lingually to form an enamel platform, each tooth surrounded by a prominent lingual cingulum. The small M3 contacted the distal margin of M2; a small low paracone and much reduced metacone are aligned along its labial side. A shallow basin bordered mesially by a weak ridge lies between protocone and paracone; the distal ridge is absent. The small lingual extension of M3 is surrounded by a marked cingulum. table 2 . — Measurements (in mm) of the m1 and m2 from Cynelos helbingi (Dehm, 1950), Wintershof-West, Bavaria (from Dehm 1950). Due to a tapered talonid, Dehm (1950) measured m2 width across the trigonid. m1 L m1W m2L m2W 27.1 13.2 17.7 11.3 25.8 12.5 16.9 10.9 25.8 12.2 16.8 10.6 25.4 12.0 16.7 10.7 25.3 11.9 15.9 10.9 25.3 11.8 15.1 10.2 25.2 11.3 15.0 10.2 25.2 11.2 14.8 9.7 25.0 11.4 14.7 9.9 24.8 11.5 14.7 10.3 24.4 10.9 14.3 9.5 24.3 10.7 13.9 9.3 23.8 11.3 13.8 8.8 23.6 10.3 13.4 8.3 23.5 9.9 13.3 8.3 23.4 9.7 13.2 9.7 23.2 10.1 13.2 8.6 23.2 10.3 13.0 9.2 23.0 10.2 12.9 8.4 22.9 10.8 12.8 8.8 22.7 10.5 12.7 8.2 22.5 10.1 – – 22.2 10.1 – – 21.5 9.9 – – 21.5 9.7 – – 20.8 9.8 – – 19.8 9.2 – – N27 27 21 21 mean 23.75 10.83 14.51 9.61 standard deviation 1.71 0.99 1.53 0.98 CV 7.2 9.2 10.5 10.2 fig. 4. — Cynelos stenos n. sp., UNSM 44723, Runningwater Formation, Runningwater Quarry (early Hemingfordian), Box Butte Co., Nebraska. Cranium in dorsal view. Note the narrow cranium, constricted rostrum, broad frontal region, and tall thin sagittal crest above the small braincase. Scale bar: 5 cm. 63 A new Cynelos Jourdan, 1862 from the early Miocene of North America GEODIVERSITAS • 2020 • 42 (5) Lower Dentition (Fig. 5; Table 1) The incisors in this individual are damaged; however, only i2 and i3 were present in life – the i1s failed to erupt due to marked narrowing of the symphyseal region. The heavily worn left i3 (L× W, 6.8× 5.4mm) is the only surviving incisor; only the broken root of the left i2 remains. The right i2-i3 alveoli are present and show that the root of i3 extended beneath the root of i2 due to crowding of the incisors in the symphysis – Dehm (1950: 24) also observed this in C.helbingi. The well-worn right canine is 16.4mm in length, 11.5mm in width measured at the base of the enamel. Relative to their evident length, the mandibles are rather gracile and not deep even below the molars. The p1-p3 are much reduced compared to p4 and are separated by diastemata: 14.6mm between canine and p1; 3.4mm between p1-p2; 9.2mm between p2-p3; 3.5mm between p3-p4. The p4 is much larger than p3, and wide distally where it abuts the mesial face of m1. The p2-p3 do not show wear and only the fig. 5. — Cynelos stenos n. sp., UNSM 44723, Runningwater Formation, Runningwater Quarry (early Hemingfordian), Box Butte Co., Nebraska. Right and left associated mandibles. Scale bar: 5 cm. fig. 6. — Cynelos stenos n. sp., UNSM 44723, Runningwater Formation, Runningwater Quarry (early Hemingfordian), Box Butte Co., Nebraska. Palatal view of the cranium with right P2-M3 (broken P1) and left P3-M3, partial P2, and P1 alveolus. Plant roots have eroded the enamel on the right M1-M2. Scale bar: 3 cm.