McDonald and Carranza-Castañeda—New Miocene ground sloth from Mexico
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Table 1. Measurements of the mandibles of Zacatzontli tecolotlanensis n. gen. n. sp. (MPG 1312G), Pliometanastes protistus Hirschfeld and Webb, 1968 (UCMP 97371), and Megalonyx curvidens Matthew, 1924 (FAM77800); measurements in mm; *approximate length (posterior margin broken); – data not available.
Measurement
Length from tip of symphysis to posterior margin of angular process Length from tip of symphysis to posterior margin of condyle
Width across buccinator fossae Length of mandibular symphysis Width of spout at midpoint
Height of mandibular symphysis
Mediolateral width of diastema Molariform alveolar length
Dorsoventral depth of horizontal ramus at m1 Dorsoventral depth of horizontal ramus at m3 Length of diastema
Dorsoventral depth of angular process at base Labiolingual width of caniniform Mesiodistal length of caniniform Mesiodistal length of alveolus of m1 Labiolingual width of alveolus of m1 Mesiodistal length of alveolus of m2 Labiolingual width of alveolus of m2 Mesiodistal length of alveolus of m3 Labiolingual width of alveolus of m3 Lower right first molariform (Jal-Teco 8)
Lower left third molariform (Jal-Teco 8)
Table 2. Faunal list of the late Hemphillian deposits of Tecolotlán, Jalisco, Mexico.
Santa María Jalteco 8
Class Reptilia Amphibia Indet.
Order Squamata indet. Suborder Lacertilia indet. Suborder Serpentes indet.
Order Crocodilia Crocodylus sp.
Class Mammalia Order Xenarthra Megalonyx sp.
Order Rodentia Sigmodon sp. Calomys
X X
X X
Zacatzontli tecolotlanensis n. gen. n. sp. Two teeth X X
Order Lagomorpha Notolagus sp.
Spermophilus Order Carnivora Agriotherium schneideri Sellards, 1916
Canis ferox Miller and Carranza- Castañeda, 1998
Borophagus secundus Matthew and Cook, 1909
Machairodus cf.M. coloradensis Cook, 1922
Order Perissodactyla Nannippus aztecus Mooser, 1968 Neohipparion eurystyle (Cope, 1893) Astrohippus stockii Lance, 1950 Dinohippus mexicanus Lance, 1950 Teleoceras fossiger (Cope, 1878)
Order Proboscidea Rhynchotherium cf. R. falconeri Osborn, 1923
Order Artiodactyla Hemiauchenia vera Matthew and Osborn, 1909
Megatylopus matthewi Webb, 1965 Hexobelomeryx frickii Furlong, 1941 Catagonus brachydontus Wright, 1983
X
X X
Jaw X
X X
X
XX X
XX
X X X X X
X ?
X X
XX X
X X
X X X
La Hacienda JalTeco 20
Length fromanteriormargin of alveolus of caniniformto posteriormargin of alveolus ofm3 Length from anterior margin of spout to anterior margin of caniniform alveolus Width across caniniforms
Zacatzontli tecolotlanensis n. gen. n. sp. MPG 1312G
121.6* 120.3 50.0 15.0 34.8 28.0 30.8 15.9 24.7 28.7 25.1 9.1 7.1
Mesiodistal length 7.9 Labiolingual width 9.8
11.1 8.4
Mesiodistal length 8.9 Labiolingual width 11.05
Isotópicos del Centro de Geociencias, UNAM, (LA-ICPMS), basedonU-Pbin zircons andusing laserablationgaveanage of 4.85±0.1Ma. Based on the fauna, the Santa María fauna corre- lates with the Rhino layer of Rancho El Ocote and the lower layer of the Coecillos locality in the state of Guanajuato. Both faunas also include Megalonyx (Table 2).
Systematic paleontology
Order Xenarthra Cope, 1889 Suborder Pilosa Flower, 1883
Family Megalonychidae Gervais, 1855 Genus Zacatzontli new genus
Remarks.—Because Zacatzontli n. gen. is a monospecific genus, all information related to it is given below under the new species.
Zacatzontli tecolotlanensis n. gen. n. sp. Figure 3 Table 1
Holotype.—MPGJ 3126, partial mandible with complete left ramus missing dorsal portion of the coronoid process, posterior margin of the angular process and anterior portion of the right horizontal ramus broken at the midline of the alveolus of the third molariform. Both caniniforms are present, but the molariforms are missing.
Referred specimens.—MPGJ 1381, lower left third molariform and MPGJ 3534, lower right first molariform; both specimens from Jal-Teco 8 Santa María Locality.
30.4 17.8 6.4 6.9 7.5 9.1 6.9 9.6
Pliometanastes protistus
UCMP 97371 226
225
94.3 37.6 58.1 45.7 47.5
49.8 58.7 56.7 25.2 10.0 54.6 36.5 10.8 12.0 14.4 20.8 14.9 21.8 19.1 18.8
Megalonyx curvidens FAM 77800
– –
85.9 18.0
54.1 46.7
52.1 –
21.7 8.8
48.7 –
10.8 19.3
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