Articles

 

Boletín de la Sociedad Geológica Mexicana

Volumen 70, núm. 3, 2018, p. 779 ‒ 784

http://dx.doi.org/10.18268/BSGM2018v70n3a10

Short note

 

 First occurrence of Parksosauridae in Mexico, from the Cerro del Pueblo Formation (Late Cretaceous; late Campanian) at Las Águilas, Coahuila

Héctor E. Rivera-Sylva1, Eberhard Frey2, Wolfgang Stinnesbeck3, Natalia Amezcua4, Diana Flores Huerta4

 

1Departamento de Paleontología, Museo del Desierto, Carlos Abedrop Dávila 3745, 25022, Saltillo, Coah., México.
2Staatliches Museum für Naturkunde Karl­sruhe, Geowissenschaftliche Abteilung, Erb­prinzenstraße 13, D76133 Karlsruhe, Germa­ny.
3Institut für Geowissenschaften, Universität Heidelberg, Im Neunheimer Feld 234-236, 69120 Heidelberg, Germany.
4Servicio Geológico Mexicano, Blvd. Felipe Ángeles km 9.5-4, Pachuca, Hgo., México.

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Abstract

The Las Águilas locality near Porvenir de Jalpa, Coahuila, Mexico, is extremely rich in fossil remains comprising both bones and trackways of several late Campanian dinosaur taxa. Here we present a tooth with an asymmetrically bulged crown and an isolated shallow amphicoelous vertebral centrum. Both are assigned by us to Parksosauridae. The material represents the first occurrence of this enigmatic family in Mexico.

Keywords: Cerro del Pueblo Formation, Parksosauridae, Campanian, Coahuila, Mexico.

Resumen

La localidad de Las Águilas cerca de Porvenir de Jalpa, Coahuila, México, es extremadamente rica en restos de fósiles dinosaurios comprendiendo huesos y huellas de varios taxa Campanianos. Aquí presen­tamos el registro de un diente con una corona bulbosa y asimétrica además de un centrum de una vértebra anficélica. Ambos asigna­dos por nosotros como Parksosauridae. El material representa el primer registro de esta enigmática familia para México.

Palabras clave: Formación Cerro del Pueblo, Parksosauridae, Campaniano, Coahuila, México.

 

1. Introduction

Parksosauridae are a little understood family of small ornithischian dinosaurs, with a controversial phylogenetic relationship within Ornithopoda (Bucholtz, 2002; Boyd, 2015). As its skull and dentition appear to be primitive within Ornithop­oda, much resembling hypsilophodontids (Galton, 1974a; Boyd, 2014), the family it has been grouped either as “hypsilophodontid” (Sereno, 1998), a member of the Thescelosauridae (e.g. Galton, 1973; Butler and Galton, 2008), or equivalent to that family (Boyd, 2015).

Parksosauridae are small-bodied, bipedal, curso­rial, lightly-built dinosaurs, which are known from the Aptian to Maastrichtian of North America and Asia (Norman et al., 2004; Boyd et al., 2009). The skull is proportionally small with respect to the body, it is elongate with flat frontals and has lingually curved and labiolingually compressed leaf-shaped teeth (Galton, 1997). The enamel of the teeth crowns is crenulated and lacks serration.

Parksosauridae is documented from Canada and the United States, while it was hitherto unknown in México. Here we describe the fossil remains to a basal ornithopod remains found during the spring of 2014, 4.2 km east of the Las Águilas locality, east of the hamlet Porvenir de Jalpa, and about 50 km west of Saltillo, Coahuila, north-eastern Méx­ico, in rocks of the Cerro del Pueblo Formation (Figure 1).

Institutional Abbreviations: CPC- Colección Paleontológica de Coahuila, Saltillo, Coahuila, México; CNA- Consejo Nacional de Arqueología, México; IEUH- Institute of Earth Sciences, Hei­delberg University, Germany; INAH- Instituto Nacional de Antropología e Historia; MUDE-Museo del Desierto, Saltillo, Coahuila, México; SMNK- State Museum of Natural History, Karlsruhe, Germany; SGM- Servicio Geológico Mexicano, Pachuca, México.

 

2. Materials and Methods

The geology, stratigraphy, and paleoecology of the Las Águilas section have recently been presented by Vogt et al. (2016) and Rivera-Sylva et al. (2017). The locality with remains of Parksosauridae, with the field number “Las Águilas 14” (LA 14), is a new site located about 1.5 km west of Cerro de Angostura. At LA 14, abundant surface material has weathered out of a fine-grained, green-to buff-colored siltstone.

The fossils documented here at LA14 were col­lected during an extensive surface survey in 2014 by a joint team from MUDE, SMNK, IEUH, and SGM. They are housed and cataloged at the Museo del Desierto (MUDE). Locality informa­tion is on file at that institution. The specimens were photographed using an Olympus E 620 with an Olympus Zuiko standard lens (14 – 42 mm, f/3.5 – 5.6), an Olympus Zuiko macro lens (35 mm, f/3.5); and a Canon EOS Rebel T2i with a Canon lens 18 – 55mm, 1:3.5 – 5.6 IS II.

The specimens reported here were collected with permission of the INAH through its Con­sejo Nacional de Arqueología [CNA; Oficio 401.B(4)19.2013/36/1862].

 

3. Systematic paleontology

Ornithischia Seeley, 1888

Cerapoda Sereno, 1986

Parksosauridae Bucholtz, 2002

Parksosauridae indet.

 

Referred specimens – CPC 1872 (Figure 2, A-B), a right premaxillary tooth; CPC 1866 (Fig­ure 2, C-H), a posterior sacral vertebral centrum.

Locality – LA 14 near Las Águilas, Porvenir de Jalpa, Coahuila, northeast México (Figure 1).

Description – CPC 1872 (Figure 2, A-B) con­sists of a premaxillary tooth crown, slightly labi­olingually compressed and slightly constricted at its base. Apically to this constriction, the crown is asymmetrically bulged. The bulge is twice as pronounced distally compared to mesially, and only misses the labial face of the crown. The tip of the crown is blunt. The tooth crown is slightly curved lingually and bears a small wear facet on its tip, showing a few coarse labial striations, which display a high degree of wear. The absence of the root suggests a shed tooth (Frey and Monninger, 2010). The crown height is 5 mm, with a basal maximum diameter of 3 mm.

 

Figure 1. Geographic location of the Porvernir de Jalpa, Las Águilas fossil site in Coahuila, north-east México.

 

CPC 1866 (Figure 2, C-H) is a posterior sacral vertebral centrum, interpreted as the fifth sacral, which is shallowly amphicoelous and constricted around its middle. The bone is 1.5 times longer and slightly higher than wide. In anterior and pos­terior views, the centrum is rounded triangular in cranial outline and has a concave area separated by a dorso-medial ridge, with a flat dorsal margin and slightly convex lateral margins. The dorsal surface is ornamented with deep transverse striae that accommodate the peduncles of the neural arch. The floor of the neural canal is hourglass shaped in dorsal aspect. It is 48 mm long, 42 mm deep and 31 mm wide.

4. Discussion

The shape of the premaxillary tooth face, includ­ing the blunt tip, the striations on the lingual side, the smooth lingual surface, the constricted base, and the lingually curving blunt crown, are seen in Thescelosaurus and Hypsilophodon (Galton, 1974b; Boyd, 2014). In Parksosaurus, the premaxilla is miss­ing (Parks, 1926; Sternberg, 1940), thus differing from other ornithischians with leaf-shape teeth (i.e., pachycephalosaurids). Serrations are absent on both the anterior and posterior margins, which also is the case in neoornithischians Changchunsau­rusHaya, and Jeholosaurus (Barrett and Han, 2009; Jin et al., 2010; Makovicky et al., 2011).

 

Figure 2 Parksosauridae fossils from the Cerro del Pueblo Formation. A right premaxillary tooth (CPC 1872) in: (A) labial view and, (B) lingual view. Fifth sacral vertebra (CPC 1866) in: (C) left lateral view; (D) right lateral view; (E) ventral view; (F) dorsal view; (G) cranial view; (H) caudal view. Scale in A-B: 5 mm; C-H: 5 cm.

 

The sacral vertebrae of ParksosaurusThescelosaurus, and Dysalotosaurus are very similar to those reported for Hypsilophodon (Galton, 1974b). The constricted centrum across their middle circumferrence and the shallow platycoelous intervertebral joints are features seen only in this group (Gilmore, 1915; Brown et al., 2013). The widened centrum, in cra­nial view, towards the caudal face, and ventrally longitudinally concavity, identifies this vertebra as the posterior-most sacral element of the series (sa. 5) (Galton, 1974b) it much resembles vertebrae illustrated by Carr and Seitz (2015; p. 107) for Thescelosaurus, and Galton (1974b) for Hypsilopho­don. The neural arch is not preserved and may have fallen off during diagenesis. The striae on the centropeduncular articulation indicate that the neurocentral suture must have been open, which is suggestive for an immature individual (Brochu, 1996; Irmis, 2007), contrasting with the vertebrae of adult pachycephalosaurids, which show strong sutural fusion (Gilmore, 1924; Sues and Galton, 1987).

The only well-known basal cerapoda taxon from the late Campanian of North America, Orodromeus, occurs in the Two Medicine Formation (Montana). These osteological remains resemble an unnamed basal ornithopod from the Kaiparowits Formation Utah; Gates et al., 2013.

 

5. Conclusions

The material described here represents the first evidence of Parksosauridae in México. This dis­covery from the northeastern Mexican state of Coahuila extends the geographic range of Parkso­sauridae for about 2000 kilometers to the south of North America.

 

Acknowledgements

We wish to thank the following friends and col­leagues for their participation in fieldwork in the Las Águilas area: Lucía Alfaro (Saltillo), Felix Bayer (Heidelberg), Christiane Birnbaum (Karlsruhe), Kristina Eck (Heidelberg), Aaron Linsler (Heidelberg), Tim Niggemeyer (Karl­sruhe), Melissa Perner (Heidelberg), Ulli Karas (Siegburg), Sarah Stinnesbeck (Karlsruhe), Eva Susanne Stinnesbeck (Troisdorf), Manfred Vogt (Heidelberg), and Sven Wetzel (Heidelberg). The Museo del Desierto in Saltillo provided the infra­structure for the fieldwork of HR, EF, and WS. Rubén Guzmán-Gutierrez (Aguascalientes) is gratefully acknowledged for providing literature. The Servicio Geológico Mexicano supported field research for NA and DFH. Iván Erick San­chez Uribe is thanked for image editing. Kenneth Carpenter and Rodolfo Coria are thanked for their reviews and useful comments. The Deutsche Forschungsgemeinschaft (DFG) covered travel and fieldwork expenses for EF (FR1314/19) and WS (STI128/24 and 44).

 

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Manuscript received: January 30, 2018.
Corrected manuscript received: February 13, 2018.
Manuscript accepted: February 18, 2018.