Hindawi Publishing Corporation Journal of Geological Research Volume 2012, Article ID 808729, 7 pages doi:10.1155/2012/808729

Research Article Lower Cretaceous Dinosaur Tracks from ,

Ruben´ A. Rodrıguez-de´ la Rosa,1 Vıctor´ M. Bravo-Cuevas,2 Enrique Carrillo-Montiel,3 and Arturo Ortiz-Ubilla3

1 Unidad Acad´emica de Ciencias Biologicas,´ Universidad Autonoma´ de Zacatecas, Campus 2, 98060 Zacatecas, Mexico 2 Museo de Paleontolog´ıa, Centro de Investigaciones Biologicas,´ Universidad Autonoma´ del Estado de Hidalgo, Pachuca, C.P. 42184 Hidalgo, Mexico 3 Escuela Nacional de Ciencias Biologicas,´ Instituto Polit´ecnico Nacional, C.P. 11340 M´exico City, DF, Mexico

Correspondence should be addressed to Ruben´ A. Rodr´ıguez-de la Rosa, ruben [email protected]

Received 2 August 2011; Accepted 7 November 2011

Academic Editor: David T. A. Symons

Copyright © 2012 Ruben´ A. Rodr´ıguez-de la Rosa et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Dinosaur tracks have been identified near San Mart´ın Atexcal, southern Puebla, Mexico, within the sedimentary sequence of the San Juan Raya Formation of Lower Cretaceous (Albian) age. The tracksite, located in the bed of the Magdalena River, reveals six different ichnofossiliferous levels identified within a 9 m thick sedimentary sequence. The inferred environment is that of a tidal (marginal marine) mudflat (Level I). Level I preserves three theropods trackways (?Allosauroidea), additionally, isolated tracks belonging to iguanodontids (Ornithopoda). Level II preserves faint iguanodontid tracks. Levels III to V preserve sauropod tracks. Younger level VI preserves, although morphologically different, a track belonging to Ornithopoda. The dinosaur tracks from San Mart´ın Atexcal support the existence of continental facies within the San Juan Raya Formation; they represent the second record of dinosaur tracks from the Lower Cretaceous of Mexico and are part of an important but little documented record of Lower Cretaceous dinosaurs in Mexico.

1. Introduction is to document this dinosaur track site, to comment on the observed ichnofaunal succession, and place the information Since the first report on dinosaur tracks from Mexico, the regarding the tracks in the broader context of the Lower number of reported localities has increased considerably [1– Cretaceous dinosaur paleoichnology. 3]. To date, this record includes three reports of Jurassic dinosaur tracks, plus several dinosaur tracks and trackways of Late Cretaceous dinosaurs; most of these localities are 2. Study Area and Geological Context distributed from the central through northern parts of the This Lower Cretaceous dinosaur tracksite is located in country [3]. southern Puebla, 1 km west of the town of San Mart´ın Atexcal However, the evidence of Mexican dinosaurs of Lower and within the stream channel of the La Magdalena River Cretaceous age is now restricted to the site reported here (Figure 1(b)). (see [3, 4]). This track site is located near the small town The tracks were originally registered on grayish shale; of San Martin Atexcal in southern Puebla, central Mexico however, these are mostly preserved as convex hyporeliefs in (Figure 1), and it represents the first known dinosaur track brownish, fine to medium-grained sandstone layers. These site of this age from Mexico. Two other small outcrops, rocks belong to the upper portion of the stratigraphic recently discovered, reveal more dinosaur tracks within the sequence of the San Juan Raya Formation of Lower Creta- San Juan Raya Formation; however, these remain unstudied. ceous age. The site herein reported reveals dinosaur tracks in at The inferred paleoenvironment for the San Juan Raya least six different stratigraphic levels in the upper part of Formation is that of a shallow lagoonal, tidal-flat setting, bet- the San Juan Raya Formation. The objective of this paper ween reefs and the coast line; this interpretation is confirmed 2 JournalofGeologicalResearch

U.S.A. Puebla IV Mexico´ VI V San Mart´ın Atexcal II III

I (a)

Figure 2: Panoramic view of the San Martin Atexcal track site. N Numbers are placed at the six ichnofossiliferous levels identified; white arrows point to a couple of observable footprints on ichno-

La Magdalena river fossiliferous levels III and VI.

San Mart´ın Atexcal, River). Following the code, a letter was assigned to each of Puebla, Mexico´ the trackways, and to complete the designation a consecutive number for each of the tracks composing a particular trackway. This final number (without a trackway-designating letter) is also used to designate isolated tracks that do not form part of a recognizable trackway sequence. Tracksite Measurements such as pace, stride, and pace angulation Cemetery were taken; in addition to these, the measurements for each track include the maximum length, measured across digit (b) III; maximum width, measured from the lateral margin to the medial margin of the track; total angle of divarication Figure 1: Geographic location of the State of Puebla (a) in central Mexico and the Lower Cretaceous dinosaur track site near San between digits II–IV, as well as each angle between digits II- Martin Atexcal, Puebla (b). The locality is indicated by the asterisk. III and III-IV.

4. Results by the presence of alternating layers of shale, sandstone, and calcareous shale [5, 6]. The known paleofauna is A 9 m thick local stratigraphic section was measured in composed mostly of invertebrates such as corals, gastropods, the site, within this column at least six ichnofossiliferous cephalopods, pelecypods, echinoderms, and crustaceans; levels were identified (Figures 2 and 3). The older one is a Lower Cretaceous age, Aptian, is supported by some herein named Level I and includes three trackways (ATRM- elements of this invertebrate fauna [5, 6]. The San Juan Raya A, ATRM-B, and ATRM-C) plus associated isolated tracks Formation is overlayed by the Cipiapa Formation of Albian- (Figures 4 and 5). The remaining five levels were named II to Cenomanian age and is underlain by the late Barremian VI, in consecutive ascendant order, and they preserve isolated Zapotitlan´ Formation [5, 6]. tracks that are relatively well preserved.

3. Material and Method 4.1. Trackways A map of the distribution of the tracks over the main surface 4.1.1. ATRM-A. Represents a trackway of a theropod dino- (or Level I, see below) was made on a plastic sheet, drawing saur. It starts with a single impression of digit III followed the track outlines with a water-proof ink marker. Track by two tridactyl and mesaxonic tracks. Digits are stout and measurements were taken with a standard metric tape, and narrow and end in subacute tips. Digits II and IV are shorter the angles between digits as well as pace angulations were than digit III, with digit II being the shortest in the track. measured with a standard 360◦ protractor. ATRM-A-1 is well defined, and it represents just the The trackways were identified using the nomenclature impression of digit III; it is elongate, 22 cm long, and proposed by recognized vertebrate paleontologists, such as 8 cm in maximum width. At the most elevated portion, the Leonardi and Carvalho [7, 8, and references therein]. For impression has fusiform ends and it is 4 cm wide. The digital this particular case, the code is composed of the letters impression preserves a well-defined mud rim around it. ATRM, which indicate the Municipio de Atexcal (AT) and ATRM-A-2 represents a left track; it is 32 cm long, the locality name known as R´ıo Magdalena (RM, Magdalena 25.5 cm wide, and has a width/length ratio of 0.79. The JournalofGeologicalResearch 3

VI 8 m V 4 m

IV 7 m 3 m

III

6 m 2 m II I (a)

S 5 m 1 m

San Mart´ın Atexcal, Puebla, Mexico´ Sandstones Allosauroidea Thin shale layers Iguanodontidae Calcareous shales Sauropoda S Ornithopoda

Figure 3: Stratigraphic local column of the San Martin Atexcal (b) (c) track site, with the ichnofossiliferous levels indicated by Roman numerals I to VI; dinosaur silhouettes indicate the particular dino- Figure 4: General view of dinosaur tracks and trackways from ich- saur taxon in each ichnofossiliferous level, being Allosauroidea in nofossiliferous level I (a), compare with Figure 5.(b),trackreferred level I, Iguanodontidae in levels I and II, Sauropoda in levels III to herein to a member of Allosauroidea (ATRM-B-3) and (c), Iguan- V, and Ornithopoda in level VI. odontidae (ATRM-1). Two poorly preserved theropod footprints are not shown in this photograph; however, these are illustrated in Figure 5. interdigital angulations are of 46◦ and 22◦ for digits II-III and III-IV, respectively, thus the total angle of divarication Digitsareinappearancerobustandwide;however,ineach is of 68◦. of the digits, it is recognized as a longitudinal central border ATRM-A-3 represents a right track however shallow that represents the real toe impressions, which are slender impressed; it is 28 cm long and 26 cm wide, the width/length and stout. The plantar area is relatively as wide as the heel ratio is 0.93. The interdigital angulations are of 34◦ and 37◦ area. The interdigital angulation is in both cases for digits II- for digits II-III and III-IV, respectively, so the total angle of ◦ ◦ III and III-IV of 33 , in this way the total angle of divarication divarication is of 71 . ◦ is of 66 . This trackway (ATRM-A) has a mean step of 93.8 cm, a ATRM-B-2 represents a right track; it is 26 cm long and stride of 185 cm, and a pace angulation of 172◦.Thetracks ◦ 25.5 cm wide; its width/length ratio is 0.98. The interdigital show a light inner rotation of 9 with respect to the trackway ◦ ◦ angulation is 46 and 22 for digits II-III and III-IV, midline. respectively; in this way the total angle of divarication is of 68◦. In this track, digits are well defined, and they are robust 4.1.2. ATRM-B (Figure 5). Represents a theropod dinosaur with well-defined, subtriangular claw impressions. trackway; it is composed of three tridactyl and mesaxonic ATRM-B-3 represents a left track (Figure 4(b)), it is tracks. The first of these tracks shows a morphological sim- 28 cm long and 26 cm wide, and its width/length ratio is 0.93. ilarity with the tracks of iguanodontid dinosaurs; however, The interdigital angulation is of 34◦ and 37◦ for digits II-III the next tracks that compose this trackway show clearly and III-IV, respectively; thus, the total angle of divarication the morphological traits of theropod tracks, such as well- is of 71◦. All the digits have well-defined, acute distal ends. defined claw impressions. The extramorphological variation In addition, digit II has a subtriangular claw impressions exhibited is related to substrate conditions. isolated somewhat from the digital impression (Figure 4(b)). ATRM-B-1 corresponds to a left impression; it is 34 cm ATRM-B has a mean pace of 90 cm, a stride of 179 cm, long and 33.5 cm wide; its width/length ratio is thus 0.98. and a pace angulation of 169◦. The tracks show a slight 4 JournalofGeologicalResearch

ATRM-B, 1–3 interdigital angulation between digits II-III is 29◦,between digits III-IV is 31◦, so the total angle of divarication is 60◦.A ATRM-1 ATRM-5 shallow indentation is observed posteromedially, just behind ATRM-4 digit II; digit III is arched toward the track medial side. In ATRM-A, 1–3 addition to these observations, the impression of digit III ATRM-C, 1-2 of this track partially overlaps the track ATRM-C-1; this suggests that the producer of ATRM-3 crossed the area later that produced the ATRM-C trackway. Most of the features ATRM-2 ATRM-3 observed in this track agree with those seen in theropod dinosaurs [9, 10]. ATRM-4 and ATRM-5 are partially preserved; however, they share their general morphology and sizes with ATRM-3 and are equally assigned to Theropoda. Level II preserves poorly preserved ornithopod tracks Figure 5: Map of the distribution of dinosaur tracks and trackways similar to those observed in Level I. However, in the next in level I. Dashed area indicates the place where one of the tracks levels (III–V), a change in the composition of track makers was vandalized. Scale bar equals 1 m. is observed, where the tracks of sauropod dinosaurs are recognized. These sauropod tracks are preserved as convex hypore- inward rotation of 13.3◦ with respect to the trackway mid- liefs (Figure 6); however, Level V preserves tracks as concave line. epireliefs over thin sandstone (Figure 6(c)).Thesetracksare of subcylindrical form; they have a mean diameter of 33 cm and depth of 10–15 cm. One of the sauropod tracks from 4.1.3. ATRM-C (Figures 2 and 4(a)). Represents a short Level IV preserves a prominent, “V”-shaped (as seen in cross trackway composed of a single step of a theropod dinosaur. section), mud rim; a possible manus tracks were recognized ATRM-C-1 corresponds to a left tridactyl and mesaxonic in association with this pes track (Figure 6(b)). track; it is 33 cm long, 25 cm wide, and has a width/length Tracks on Level V are preserved in a brownish sandstone ratio of 0.76. The interdigital angulation is 26◦ between digits ◦ bed 22 cm thick; however, this bed thins to 10 cm thick in II-III and III-IV, so the total angle of divarication is of 52 . some areas. These tracks are observed in cross section. At This is one of the best preserved tracks on the outcrop, the least one of these tracks seems to be made by a member of digits preserve well-defined distal ends, and digit II is slightly Sauropoda; features such as large size and rounded shape separated from digits III and IV by a shallow indentation. support this assignment. ATRM-C-2 represents part of a right track, preserving Level VI corresponds to the youngest ichnofossiliferous only the impressions of digits II and III and part of the medial level (Figure 3); at this level it is possible to recognize tracks area of the heel. The estimated length of this track is 31 cm, ◦ attributable to Ornithopoda and perhaps to Sauropoda. and the angle between digits II and III is 33 . One of the preserved tracks, ATRM-6, preserves features that undoubtedly permit its assignment to Ornithopoda 4.2. Isolated Tracks. The first level (Level I) preserves five (Figures 7 and 8); the general morphology of ATRM-6 isolated tracks; there were initially six tracks, but one was strongly recalls those of iguanodontids reported from the vandalized. These tracks were labeled ATRM-1 to 5. Dakota group of western USA [11]. ATRM-1 (Figures 4(c) and 5)ischaracterizedbywide ATRM-6 is tridactyl and mesaxonic, 24.7 cm long and digits with rounded distal apices and a wide plantar zone. 21 cm wide, so the width/length ratio is 0.85. This track This track is 25 cm long, 19.5 cm wide, and the width/length preserves a well-defined, rounded plantar pad and teardrop- ratio is 0.78. The angle of divergence among digits II-III shaped digital pads with the acuminate ends pointing is 22◦, while the III-IV is 25.5◦; thus, the total angle of distally. This track bears concave, nearly circular, interdigital divarication among digits II–IV is 47.5◦. The heel is bulbous areas and a rounded heel. Digits are separated from the and bears a shallow concavity in a posterior position with plantar pad by skin folds (Figure 7(b)). respect to one of the digits (II or IV); in addition, it preserves The digits of ATRM-6 have a total angle of divarication a well-defined mud rim approximately 4 cm wide. Most of of 99◦; this is 55◦ between digits II-III and 44◦ for digits the features of this track agree with those of ornithopod III-IV. Another feature of this track is that the distal ends dinosaurs, in particular iguanodontids [9, 10]. of the digits are displaced from their original positions due ATRM-2 has a configuration similar to that of ATRM- to a small fracture that affected this ichnofossiliferous level 1, so it is attributed as well to an iguanodontid ornithopod (Figure 7(a)). (Figure 5). This track is 20.5 cm long, 17.5 cm wide, and has a ◦ width/length ratio of 0.85. The interdigital angulation is 27 5. Discussion and 33◦ between digits II-III and III-IV, respectively, so the total angle of divarication is 60◦. The inferred paleoenvironment of the San Mart´ın Atexcal ATRM-3 (Figure 5) is characterized by narrow digital track site (at least that represented in track-bearing Level I) impressions ending in subacute apices. This track is 27 cm corresponds to that of a tidal (marginal marine) mudflat. In long, 23 cm wide, and the width/length ratio is 0.85. The this way, the tracks and trackways from the San Juan Raya JournalofGeologicalResearch 5 S V P 10 cm

(a)

S (a) 10 cm V P

m p mr

(b) 10 cm

(b)

Figure 7: Ornithopod footprint from level VI. The white arrows in (a) point to a fracture that displaced the digit apexes from their original sites; (b), digital reconstruction of the footprint with the digit apices on their site.

(c)

Figure 6: Sauropod tracks preserved as natural casts (a, b) and as seen in cross section (c). These tracks correspond to levels III, The theropod tracks from this locality (Level I) suggest IV, and V, respectively; m, manus; p, pes; mr, mud rim. Geological medium-sized individuals, with an estimated hip-height of hammeris28cminlength. 1.50 m, using the method of Thulborn [9]. Based solely on size and age of the locality, it is probably that the track maker was a member of the Allosauroidea, a group of dinosaurs that Formation support the evidence of continental facies in such includes carnivorous forms that are widely distributed and a formation. have a time span ranging from the Late Jurassic to the Late The tracks on Level I show differential preservation; Cretaceous [13]. this is due to different conditions of the substrate (e.g., Most of the theropod tracks reported from the Lower variations in humidity, composition, and/or texture), which CretaceousofNorthAmericarepresentsmallformssuch result in shallower or deeper tracks within the same track- as coelurosaurian dinosaurs [14]. There exists evidence bearing layer or even within the same trackway. Thus, these of theropod tracks made by larger forms such as those conditions help to explain the extramorphological variation attributed to the allosauroid Acrocanthosaurus [15]; however, observed in the tracks that compose the trackways ATRM-B these traces differ in size and configuration from those found and ATRM-C; these tracks show a morphological similarity in the San Mart´ın Atexcal track site. to those of iguanodontid dinosaurs; however, among other ATRM-1 and ATRM-2 can be clearly attributed to igua- features, the presence of well-defined claw impressions, nodontid dinosaurs. In particular, ATRM-1 strongly recalls arching of some digits, indentation between digits II and III- the iguanodontid tracks found in some Cleveland-Lloyd IV, and a long step, supports their assignment to Theropoda. outcrops, in eastern Utah; in both cases, the tracks are 6 JournalofGeologicalResearch

(a) (b) (c)

Figure 8: Comparison between track ATRM-6 from level VI (a) with Dinehichnus from the Late Jurassic Morrison Formation (b) and an ornithopod track from the Dakota group of the western USA (c). Note the morphological similarities between ATRM-6 and the track from the late Albian Dakota group. (b) from [12], (c) from [11]. Scale bar equals 30 cm.

characterized by having a rounded heel and a strong concave of years during the Aptian and Albian [14, 27]. However, indentation located posteromedially (cf. [14] Figure 5.2). Berriasian dinosaur footprints are known from the Mist Within this dinosaur ichnofauna, it is possible to recog- Mountain Formation in Canada [28]. Most of these are nize at least another group of ornithopod dinosaurs. One recordsfromafewgeologicalformationssuchastheGatesin of the best preserved tracks from Level VI (ATRM-6) shows Alberta (Canada) and in the United States such as the Cedar similarities with Dinehichnus; however, its general morphol- Mountain (Utah) and the Dakota Group in Colorado, New ogy strongly recalls the ornithopod tracks reported from the Mexico, Oklahoma, Kansas, and Utah [14, 27]. Dakota group of the western USA (Figure 8)[11, 12, 16, 17]. Thus, the dinosaur tracks from San Mart´ın Atex- The dinosaur tracks from San Martin Atexcal permit cal, Puebla, establish the geographical continuity of the an appreciation of an interesting ichnofaunal succession. Dinosauria from Alaska to Central Mexico during Early Levels I and II preserve iguanodontid tracks; however, the Cretaceous times and obviously place this record as the first level preserves theropod tracks as well; levels III to most austral in the North American subcontinent during ff V preserve, among other undi erentiated tracks, those of that time. This record adds importantly to the scarce sauropod dinosaurs; finally, level VI preserves a track from paleoichnological knowledge about dinosaurs during epochs ff an ornithopod dinosaur, morphologically di erent, from the such as the early Cretaceous in Mexico and other areas in iguanodontids present in lower levels. North America. Sauropod body fossils are known to occur in sediments of diverse terrestrial environments; however, the tracks of sauropod dinosaurs are conspicuously present in coastal Acknowledgments marine facies [18, 19]. Thus, the track distribution in the San Martin Atexcal section may reflect facies change, from The authors want to thank the people of the town of San less coastal environments (levels I, II, and VI) to more coastal Mart´ın Atexcal, in particular Mr. Prisciliano Oyarzabal Luna environments (levels III to V). for his great interest in the dinosaur tracks from nearby the The dinosaur ichnofauna from Atexcal represents the town.Theythank(E.C.MontielandR.A.R.delaRosa) second report of dinosaur tracks from the State of Puebla Mr. Manuel Octaviano Mar´ın Osio and his family for their (cf. [20]) and the second record of dinosaur tracks from the friendship and hospitality during thier stance in Atexcal. Lower Cretaceous of Mexico (cf. [21]). Recently, two other Thanks are also due to Jaime Romero Gallardo and Jacobo tracksites have been recognized within the San Juan Raya by their help during fieldwork. They also thank Oscar Polaco Formation; however, these require further study [22]. Ramos (†)andJoaqu´ın Arroyo Cabrales (I.N.A.H.-S.L.A.A.) Lower Cretaceous dinosaur tracks are known from many and archeologist Zaid Laguna Rodr´ıguez (I.N.A.H.-Puebla) deposits in Europe, eastern Asia, and South America [14, 23– for their support of the present Project. Thanks are given to 26]. In most cases, the dominant track morphotypes are Spencer G. Lucas (New Mexico Museum of Natural History attributed to iguanodontid dinosaurs and related taxa. and Science) and Martin G. Lockley (Dinosaur Tracks In North America, most of the record of Lower Creta- Museum, University of Colorado) for their kind review of the ceous dinosaur tracks is restricted to the last 19 millions paper, as well as English and content improvement. JournalofGeologicalResearch 7

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