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To restudy the Los Menucos ichnites, including all the original material described …


Biology Articles » Paleobiology » Paleoichnology » Tetrapod footprints from the Triassic of Patagonia: reappraisal of the evidence » Description of the footprints and trackways

Description of the footprints and trackways
- Tetrapod footprints from the Triassic of Patagonia: reappraisal of the evidence

Morphotype A (" Shimmelia chirotheroides ")

Material. MLP 60-XI-31-1, a slab with a cast of a right pes and a right? manus impression (figure 3.A); MLP 60-XI-31-2, a slab with, apparently, a cast of a left pes impression; three isolated uncatalogued specimens (figure 3.B-C) in the sidewalks of the shoreline of the Nahuel Huapi Lake (Bariloche, Río Negro province).

Locality and horizon. "Cantera Vieja", Cerro Las Lajas, Los Menucos (aprox. 40? 53' S - 63? 11' W), Río Negro province, Argentina; Vera Formation (Los Menucos Group), Late Triassic (Labudía et al ., 2002).
Description. The slab MLP 60-XI-31-1 is a pale yellowish brown fine-grained sandstone which preserved two poorly defined footprints which are probably under prints. They correspond to a pes and a manus and, due to their relative size and position, they do not belong to the same pair. The pes is pentadactyl with digits I-IV anteriorly directed and digit V partially everted. Digit III is longer than II and IV, which are similar in length, and digit I is the shortest of the series; none of them presents claw marks. The manus track is tetradactyl with the digits of similar length and printed relatively spread out from each other.
Discussion. The specimens MLP 60-XI-31-1 (holotype) and MLP 60-XI-31-2 (paratype) were assigned to a new ichnotaxon, " Shimmelia chirotheroides ", by Casamiquela (1964, pl. XV, fig. 2 and pl. XVI, fig. 1) who also suggested that they could belong to a primitive saurischian or derived prosauropod dinosaur. Subsequently, he related them to "pseudosuchian" archosaurs (Casamiquela, 1975). These tracks were also mentioned in the literature by other authors who also related them to "pseudosuchian" archosaurs (Leonardi and Henrique de Oliveira, 1990; Leonardi, 1994). "Chirotheroid" footprints have often been regarded as crurotarsal archosaur prints (Parrish, 1989; Haubold, 1983, 1986; Demathieu and Wright, 1988; Courel and Demathieu, 1995; Haubold and Klein, 2000; Lockley and Meyer, 2000), although there is no evidence preserved in isolated "chirotheroid" tracks that might be used to distinguish among different crurotarsal archosaur taxa (see Sereno, 1991; Parrish, 1993).
As mentioned above, the pes and manus impressions in the holotype specimen do not belong to the same pair. The manus is comparatively large in relation to the pes and, moreover, its position (posteromedially to the pes) is unusual for this type of track in which the manus generally is imprinted in front of the pes (Peabody, 1955; Sarjeant, 1975; Lockley and Hunt, 1995). The isolated track in MLP 60-XI-31-2 and the footprints from Bariloche (see figures 3.B-C) although badly preserved, are considered here to represent the same morphotype.

Morphotype B (" Ingenierichnus sierrai ")

Material. MLP 60-XI-31-3, one slab, which preserves a cast of a trackway of 12 footprints with marks of body and tail drag (figure 4.A); two uncatalogued slabs with a trackway showing marks of body and tail drags (figure 4.B) housed in the Museum of Ingeniero Jacobacci (Río Negro province).

Locality and horizon. "Cantera Vieja", Cerro Las Lajas, Los Menucos (aprox. 40? 53' S - 63? 11' W), Río Negro province, Argentina; Vera Formation (Los Menucos Group), Late Triassic (Labudía et al ., 2002).
Description. The slab MLP 60-XI-31-3 is a pale yellowish brown fine-grained sandstone with a smoothly preserved elongated trackway of a quadruped animal crossing its surface. It consists of twelve relatively small footprint impressions with a body drag throughout its length. Each impression shows a circular to oval outline and probably corresponds to the superposition of a manus and pes print. Thus, the more circular impressions might be interpreted as a total superposition and the elongate ones to a partial superposition (see Leonardi, 1987). In the midline of the trackway there is a broad, "sine-wave-shaped dragmark" (see Farlow and Pianka, 2000) as wide as the intermanus distance. Along the trackway, the body drag partially razes the footprints thus suggesting, together with its wideness, that it might correspond to both the belly and tail drag (see Farlow and Pianka, 2000).
The trackway pattern shows a regular progression of the trackmaker, with short steps, and small footprints relatively close to the midline of trackway. Moreover, the moderately low pace angulation (approximately 106º, table 1), and the shape of the body/tail drag indicate an elongated animal with a sprawling gait and having part of its body in continuous contact with the substrate surface during progression (see Boggs, 1987).

Discussion. The specimen MLP 60-XI-31-3 (holotype) was originally included in the new ichnotaxon " Ingenierichnus sierrai " by Casamiquela (1964, pl. XVII, fig. 4) who allied it to several different groups of tetrapods such as amphibians, "lizard-like" reptiles, crocodiles, "thecodonts", and theropod dinosaurs (Casamiquela, 1964, 1975). In the same publication, Casamiquela figured (1964, pl. XIX, fig. 3) a slab with a trackway of " I . sierrai " from the sidewalks of Bariloche which is at present in the collections of the Museum of Ingeniero Jacobacci. Subsequently, Leonardi recognized the holotype specimen as produced by a "lizard-like" reptile (Leonardi, 1994). The trackway probably corresponds to an undertrackway due to the lack of any detail in the footprints beyond their general outline.
The trackway was made by a quadruped animal with a sprawling gait, according to the low pace angulation. The shape of the body drag and the relatively long stride suggest an animal with short limbs and relatively long body, thus not able to maintain the belly away from the substrate. Trackways with a similar pattern have been described for extant salamanders (Peabody, 1959; Brand, 1996), Paleozoic trackways assigned to amphibian trackmakers (Haubold, 1971; Scarboro and Tucker, 1995; Clack, 1997) and extant lizards (Peabody, 1948; Farlow and Pianka, 2000). Nevertheless, the lack of information about the morphology of the manus and pedes in the specimen from Patagonia prevents discrimination between a putative temnospondyl or a lepidosauriform trackmaker. Temnospondyl amphibians are well-known in the Upper Triassic of Argentina although lepidosauriforms are as yet unknown from the Triassic of Gondwana.

Morphotype C (" Calibarichnus ayestarani ")

Material. MLP 60-XI-31-4, one slab with an isolated manus-pes set preserved as a cast (figure 5.A); MLP 66-XI-15-2, one slab with a cast of manus-pes set (figure 5.B); MLP 93-XII-13-2, one slab with a cast of two superimposed footprint impressions (figure 5.C), one uncatalogued specimen with a manus-pes set (figure 5.E) housed in the Museum of Ingeniero Jacobacci (Río Negro province), a manus-pes set (figure 5.D) in the sidewalks along the shoreline of Nahuel Huapi Lake (Bariloche, Río Negro province).

Locality and horizon. "Cantera Vieja", Cerro Las Lajas, Los Menucos (aprox. 40? 53' S - 63? 11' W), Río Negro province, Argentina; Vera Formation (Los Menucos Group), Late Triassic (Labudía et al ., 2002).
Description. All analyzed material (MLP 60-XI-31-4, MLP 66-XI-15-2, MLP 93-XII-13-2) is preserved on slabs of pale yellowish brown fine-grained sandstones and they are very well impressed. All the tracks correspond to quadrupedal, semi-plantigrade, near-symmetrical, and pentadactyl animals with marked homopody. Each pes and manus impression shows two well defined pads (p1 and p2 in figure 5.A), one located just behind the digit impressions and other, anteroposteriorly elongated, behind the former; this latter pad probably represents a heel impression. The pedes impressions are somewhat longer than wide, whereas the manus prints are slightly wider than long. The manus are imprinted in front of the pedes and pedes digit impressions are anteriorly directed, subequal in size, similar in shape, and with the most external digits (I and V) slightly separated from the others (II, III, IV). All the digits have triangular and broad-based claw marks.
Discussion. The specimen in MLP 60-XI-31-4 is the holotype of " Calibarichnus ayestarani ", Casamiquela, 1964 (pl. XVII, fig. 2) which was attributed to several tetrapod groups such as Chelonia (Casamiquela, 1964) and therapsids (Casamiquela, 1964, 1975; Haubold, 1971; Leonardi, 1994). The tracks in MLP 66-XI-15-2 were formerly assigned to a different ichnotaxon (" Gallegosichnus garridoi ") by Leonardi (1994) which is also present in the Los Menucos assemblage (see below Morphotype F). Nevertheless, the general shape of the prints and the presence of well developed claw marks in MLP 66-XI-15-2 (figure 5.B) are here considered to include it in the Morphotype C group. The undescribed material in MLP 93-XII-13-2 (figure 5.C), in the uncatalogued slab of the collections of the Museum of Ingeniero Jacobacci (figure 5.E) and in the sidewalks of Bariloche (figure 5.D) are here considered indistinguishable from the holotype specimen.
The morphology of the prints (near-symmetrical, marked homopody and pentadactyly) relates the trackmaker to non-mammalian therapsids ( e.g. Haubold, 1971; Olsen and Galton, 1984; Leonardi and Henrique de Oliveira, 1990; Hunt et al ., 1993; Leonardi, 1994; Retallack, 1996; Lockley and Meyer, 2000). Within this clade ( sensu Sidor and Hopson, 1998; Rubidge and Sidor, 2001), the presence of nearly equal sized toes indicates a relatively derived form with an erect gait (Hopson, 1995; Peters, 2000). Moreover, the presence of a well developed heel impression (calcaneal heel sensu Hopson, 1995) and the Late Triassic age of the track-bearing levels suggest that the trackmaker might be allied with the eutheriodontian group (see Jenkins, 1971; Hopson, 1994, 1995).

Morphotype D (" Rogerbaletichnus aguilerai ")

Material. MLP 60-XI-31-5, one slab containing a natural mould of a trackway with four manus-pes sets, two complete and two incomplete impressions with evidence of limb-drags (figure 6) one slab, housed in the Museum of Ingeniero Jacobacci (Río Negro Province), containing a natural mould of a trackway with four manus-pes sets with evidence of limb-drags.

Locality and horizon. "Cantera Nueva", Cerro Las Lajas, Los Menucos (aprox. 40? 53' S - 63? 11' W), Río Negro province, Argentina; Vera Formation (Los Menucos Group), Late Triassic (Labudía et al ., 2002).
Description. The trackway is on the surface of a light brown very-fined sandstone preserved as a natural mould and faint small symmetrical ripple marks are superimposed on the footprints. The material indicates the presence of a quadrupedal plantigrade animal that drags the limbs during progression. The trackway consists of four manus-pes sets where the pedes prints are larger than those of the manus (table 2) and partially overprint the posterior half of the former. The manus impressions are slightly rotated inwards and are, apparently, tetradactyl with the digit impressions anteriorly directed. The digit impressions are similar in shape and size, with the first inner digit shorter than, and somewhat separated from, the others (II, III and IV). The pedes impressions are anteriorly directed and the digit impressions are subequal in size although they are poorly preserved due to partial superposition over the manus prints. Arcshaped limb drags are present along the trackway, produced by the forelimbs (figure 6). The limb drag marks show striations that run parallel to the margins. These may represent toe drag traces.

The trackway starts with an incomplete left manus print followed by three alternating complete manus-pes sets and ends with an incomplete left pes print. The trackway pattern is broad (low pace angulation, see table 2) and shows short steps suggesting a trackmaker with a relatively short body. Also, the pattern of the limb drags, in an open laterally convex arc, indicates an animal that had its elbows-out, at least for the forelimbs, and laterally flexed the vertebral column during progression (see Smith, 1993).
Discussion. The specimen MLP 60-XI-31-5 (holotype) was originally described by Casamiquela (1964, pl. XVII, fig. 3) as a new ichnotaxon, " Rogerbaletichnus aguilerai ", and which he related to Chelonia (Casamiquela, 1964). In the original publication, Casamiquela assigned an uncatalog specimen as paratype (1964, pl. XIV, figs. 5 and 6) which was part of the same trackway of the holotype (Casamiquela, 1964). This specimen is at present housed in the collections of the Museum of Ingeniero Jacobacci. The trackmaker of " R. aguilerai " was interpreted as a possible cynodont (Casamiquela, 1975) or anomodont therapsid (Leonardi and Henrique de Oliveira, 1990; Leonardi, 1994).
The trackway denotes the progression of a quadrupedal animal with a sprawling gait evidenced by the relative breadth of the trackway and the shape of the limb drag traces. Trackways that show a similar degree of drag to the limbs as that analyzed above are, hitherto now, known for South America. In general, the described trackways frequently preserve only isolated toe dragmarks and they were mentioned for extant amphibians (Peabody, 1948, 1959), paleozoic trackways attributed to amphibians and basal amniotes (Haubold, 1971; Demathieu et al ., 1992; Haubold et al ., 1995), and chelonians (Ellenberger, 1974; Bernier et al ., 1982; Wright and Lockley, 2001). According to the Late Triassic age of the material, temnospondyl amphibians and turtles could be proposed as possible trackmakers. However, the reduction of the manus digits in the specimen to four, if it is not a preservational effect (Peabody, 1959; Brand, 1979, 1996; McKeever and Haubold, 1996), cannot be used as a character to distinguish between these tetrapod groups. Even though temnospondyls have a four digit manus, the same condition has been also described for Triassic turtles such as Proterochersis from west-central Argentina (Rougier et al ., 1995). Another possibility is that the trackmaker may correspond to a Late Triassic non-mammalian therapsid as was previously proposed (Casamiquela, 1964; Leonardi and Henrique de Oliveira, 1990; Leonardi, 1994) although, the lack of details in the trackway does not allow us to confirm the attribution of its trackmaker to this group of tetrapods. In any case, the trackway pattern and the apparent sinuous progression strongly suggests a quite primitive progression of its trackmaker.

Morphotype E (" Palaciosichnus zettii ")

Material. MLP 60-XI-31-6 (figure 7.A), a slab with a natural mould of a trackway of six steps (three manus-pes sets), MLP 60-XI-31-2, a slab with a cast of a trackway of five footprints (two manus-pes sets and one isolated print) all preserved as underprints; several uncatalogued slabs with trackways (figure 7.B) housed in the Museum of Ingeniero Jacobacci (Río Negro province) preserved as a natural mould; six trackways in the slabs of the sidewalks along the shoreline of Nahuel Huapi Lake (Bariloche, Río Negro province).

Locality and horizon. "Cantera Vieja", Cerro Las Lajas, Los Menucos (aprox. 40? 53' S - 63? 11' W), Río Negro province, Argentina; Vera Formation (Los Menucos Group), Late Triassic (Labudía et al ., 2002).
Description. The specimens are preserved on slabs of pale yellowish brown fine-grained sandstones. The MLP 60-XI-31-6 consists of a well preserved trackway of three manus-pes sets starting with a right manus-pes pair. It corresponds to a quadrupedal, pentadactyl, semi-plantigrade animal. All the tracks are very similar (homopody), with the manus prints a little larger than those of the pedes. In each set the manus is imprinted in front of the pes, and is slightly rotated outwards, whereas the pedes are anteriorly directed. All the footprints have several small rounded palm/sole pad impressions and five very short subparallel toes. In all the prints, digit III is the longest, II and IV are of similar length and digits I and V are the shortest of the series.
The size of the footprints relative to the stride length and the narrowness of the trackway with the slightly laterally placed position of the manus suggest an animal with a parasagittal gait, holding the elbows beneath the body during progression (table 2).
Discussion. The specimen was originally described as the new ichnotaxon " Palaciosichnus zettii " (Casamiquela, 1964, pl. XVIII) and related to different groups of therapsids (Casamiquela, 1964, 1975; Haubold, 1971, Leonardi, 1994). In the original publication, Casamiquela figures several undescribed slabs from the sidewalks of Bariloche (Casamiquela, 1964 pl. XX, XXI and XXII), apparently still in place, which are here considered to represent the same morphotype. Another undescribed specimen is housed in the Museum of Ingeniero Jacobacci (figure 7.B).
The trackway of MLP 60-XI-31-6 shows a quadrupedal animal with homopody and an upright posture that probably relate it to non-mammalian therapsids (e.g. Haubold, 1971; Olsen and Galton, 1984; Hunt et al ., 1993; Retallack, 1996; Lockley and Meyer, 2000). According to recent phylogenetic hypotheses of therapsid relationships (Sidor and Hopson, 1998; Rubidge and Sidor, 2001), the presence of nearly equal-sized toes and the upright posture of the limbs in the trackmaker suggest the presence of a derived therapsid (Jenkins, 1971; Hopson, 1994, 1995; Pough et al ., 1999; Peters, 2000; Blob, 2001). The trackway pattern also suggests that the trackmaker was running during the imprinting of the trackway and the speed was estimated using Alexander's formula (Alexander, 1976; see table 2). The resulting speed is relatively high (4.35 m/s) and the stride length is 2.7 times the estimated trackmaker hip height (relative stride length) thus indicating a trotting/running gait for the trackmaker (Alexander, 1976; Thulborn, 1989, 1990; McKeever, 1994). This result was based on the assumption that h (hip height) was about four times the pes length (mean estimated for erect reptiles sensu Thulborn, 1989, 1990). If calculation of hip height ( h ) is considered less than four times the pedes length (see McKeever, 1994), judging from reconstructions of Triassic cynodonts (e.g. Jenkins, 1971; Benton, 2000), the calculated values indicate an even faster gait for the trackmaker. Therefore, the trackway suggests the presence of quite a small animal that could have developed a derived, fast gait such as galloping. As no synapomorphies are preserved in Late Triassic eutheriodontian footprints that might discriminate between non-mamalian eutheriodonts and mammals as possible trackmakers, mammalian affinities cannot be rejected for the " Palaciosichnus " trackmaker.
The MLP 60-XI-31-2 slab contains one isolated track (see above, discussion of Morphotype A) and a poorly preserved small trackway of five steps. This small trackway is equivalent to that discussed above, and also shows an animal that developed a fast running gait.

Morphotype F (" Gallegosichnus garridoi ")

Material. MLP 60-XI-31-7, a slab containing a trampled surface, including seven footprints as casts (figure 8.A); MLP 60-XI-31-8, a slab which preserves a cast of a trackway of six steps plus two isolated footprints and a tail drag (figure 8.B); MLP 60-XI-31-9, a slab with a cast of part of a trackway of two (left- right) manus-pes sets and an isolated left set; MLP 66-XI-15-1, a slab with a cast of a left manus-pes set and, apparently, an incomplete right set (figure 8.C); MLP 66-XI-15-3, a slab containing a cast of a complete left manus-pes set? (figure 8.D); MLP 93-XII-13-1, a slab which preserves a cast of a probable isolated right pes footprint (figure 8.E); MLP 93-XII-13-3 ( a and b ), a large slab with a natural mould of two trackways, one ( a ) of thirteen steps and the other ( b ) of twelve steps (figure 9); four uncatalogued specimens housed in the Museum of Ingeniero Jacobacci town (Río Negro province) (figures 8.F-G); several slabs of uncatalogued specimens in the sidewalks of the shoreline of the Nahuel Huapi Lake (Bariloche, Río Negro province) (figure 8.H).

Locality and horizon. "Cantera Vieja", Cerro Las Lajas, Los Menucos (aprox. 40? 53' S - 63? 11' W), Río Negro province, Argentina; Vera Formation (Los Menucos Group), Late Triassic (Labudía et al ., 2002).
Description. All material previously mentioned is preserved on slabs of fine-grained pale yellowish brown sandstones and, in general, they are very well impressed. They correspond to quadrupedal, plantigrade animals with two well defined pads in both the manus and pedes prints (p1 and p2 in figure 8.A). One pad is located just behind the digits and another anteroposteriorly elongated (probably a heel impression) posterior to the former. The manus and pedes tracks are pentadactyl, and quite similar in size (homopody), although the pedes tracks are slightly longer than wide whereas the manus tracks are somewhat wider than long. The manus tracks are imprinted in front of the pedes tracks and are rather rotated inwards; the digits are anteriorly directed, similar in shape, with digit IV slightly longer than the others and the most lateral digits (I and V respectively) slightly separated from the others (II, III, IV). The pedes impressions are anteriorly directed with the digit impressions subequal in size with digit III somewhat longer than the others and digits I and V shorter than all remaining digits. In the manus prints the digit imprints are more spread out than in the pedes prints. None of the studied footprints shows claw marks.
The trackway pattern visible in slabs MLP 60-XI-31-8 (figure 8.B) and a and b in MLP 93-XII-13-3 (figure 9), indicate a regular progression of the trackmakers, with short steps (measurements summarized in table 3), and the manus and pedes prints rather close to the midline of trackway (relatively narrow trackway). Moreover, the pace angulation (between 104? and 124?, table 3) indicates an animal with a sprawling to semi-erect gait. In the specimen MLP 60-XI-31-8, a narrow tail dragmark is preserved along the midline of the trackway (figure 8.B).

Discussion. The ichnites in MLP 60-XI-31-7 (holotype), MLP 60-XI-31-8 (paratype) and in MLP 60-XI-31-9 (paratype) were originally included in " Gallegosichnus garridoi " (Casamiquela, 1964, pl. XV, fig. 1 and pl. XVI, fig. 2) and related to several different groups of synapsids (Casamiquela, 1964; Haubold, 1971; Casamiquela, 1975; Leonardi, 1994). The undescribed slab MLP 93-XII-13-3 preserves three trackways, two of them ( a and b ) are here recognized as the same type as the material described above. The third trackway ( c ) was originally also assigned by Leonardi to " G . garridoi " (Leonardi and Henrique de Oliveira, 1990; Leonardi, 1994), although the manus prints are rotated outwards in contrast to the trackways a and b where the manus prints are rotated inwards. This condition suggests a different position of the fore limbs during progression in the trackmaker of trackway c , with the manus rotated outwards and thus, possibly, the elbows held underneath the body (Jenkins, 1971). The undescribed specimens from Bariloche and Jacobacci were previously partially figured by Casamiquela (Casamiquela, 1964 pl. XIX, figs. 1 and 2) and Leonardi (Leonardi, 1994 pl. XVI, fig. 1).
All the specimens described above denote an animal with a quadrupedal progression, homopody and pentadactyly; this morphology relates them to nonmammalian therapsids (e.g. Haubold, 1971; Olsen and Galton, 1984; Hunt et al ., 1993; Retallack, 1996; Lockley and Meyer, 2000). The presence of a heel pad (calcaneal heel sensu Hopson, 1995) in the prints suggests a relatively derived non-mammalian therapsid trackmaker (Jenkins, 1971; Hopson, 1995), probably a eutheriodont ( sensu Sidor and Hopson, 1998; Rubidge and Sidor, 2001). The inward rotation of the manus suggests an elbows-out gait (Smith, 1993), and the shape of the digits might indicate a basal position of the trackmaker within that clade (see Jenkins, 1971; Hopson, 1994, 1995; Sidor and Hopson, 1998; Peters, 2000). In the three known trackways (MLP 60-XI-31-8 and, a and b in MLP 93-XII-13-3), the speed of the trackmakers was estimated (Alexander, 1976; see above discussion of Morphotype E). In the three cases, the animals were walking, although the relative speeds (table 3) are slightly different. The speed of the trackmaker in MLP 60-XI-31-8 shows that progression was comparatively much slower than in trackways a and b . This trackway is the only one with a tail dragmark preserved and the relatively low pace angulation and the higher manus-pes distance are also consistent with slower progression by its trackmaker (see Peabody, 1959).

Morphotype G (" Stipanicichnus bonetti ")

Material. CICRN 1-X-72-3, one slab containing a natural mould of a trackway of eleven footprints with five complete manus-pes sets and one isolated pes print (figure 10).

Locality and horizon. "Cantera Vieja", Cerro Las Lajas, Los Menucos (aprox. 40? 53' S - 63? 11' W), Río Negro province, Argent ina; Vera Formation (Los Menucos Group), Late Triassic (Labudía et al ., 2002).
Description. The trackway is well impressed on a slab of a fine-grained sandstone and it corresponds to a quadrupedal, plantigrade, pentadactyl animal. All the footprints are similar in size (homopody). As mentioned above, the trackway consists of four manus-pes sets and one isolated print. In each set, the manus is imprinted medially and slightly anterior to the corresponding pes print. The manus tracks are somewhat rotated inwards whereas the pedes tracks are more anteriorly directed and the interpedes distance is greater than that of the manus tracks spacing. The sole pads are posteriorly elongated which probably denotes the presence of a heel impression. In general, all the digits are subequal, similar in shape and have pointed claw-marks medially directed. The manus digits are more spread out than those of the pedes, in particular digits I and V are more separated than the inner ones. The trackway starts with a left manus-pes set followed by four alternating manus-pes sets and ends with an incomplete right pes print. It shows regular progression by the trackmaker with very short steps and footprints particularly widely separated from the midline of the trackway (broad trackway). Moreover, the very low pace angulation (table 4) indicates an animal with a sprawling gait ( sensu Leonardi, 1987).

Discussion. The specimen in CICRN 1-X-72-3 is the holotype material of Stipanicichnus bonetti Casamiquela, 1975 (pl. 6), which was related to Cynodontia (Casamiquela, 1975). Subsequently, the same specimen was allied to "Therapsida or Mammalia" (Leonardi, 1994).
The morphology of the prints (e.g. homopody) relates the trackmaker to non-mammalian therapsids (e.g. Haubold, 1971; Olsen and Galton, 1984; Leonardi and Henrique de Oliveira, 1990; Hunt et al ., 1993; Leonardi, 1994; Retallack, 1996; Lockley and Meyer, 2000). Moreover, within that group the presence of a probable heel impressions (calcaneal heel sensu Hopson, 1995) might be correlated with relatively derived therapsids (Jenkins, 1971; Hopson, 1995). Nevertheless, the marked broadness of the trackway suggests a sprawling posture for both the forelimbs and hindlimbs. Moreover, the pattern observed in the trackway is very peculiar due to the sideways orientation of the footprints. This arrangement of the prints has been related to animals that walked, probably uphill, across a steep surface (McKeever, 1994). The lack of information about the environmental context where the trackway CICRN 1-X-72-3 was imprinted does not allow us to corroborate this hypothesis.


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