Pyramiodontherium bergi ( Moreno & Mercerat, 1891 )

Brandoni, Diego, Carlini, Alfredo A., Pujos, François & Scillato-Yané, Gustavo J., 2004, The pes of Pyramiodontherium bergi (Moreno & Mercerat, 1891) (Mammalia, Xenarthra, Phyllophaga): the most complete pes of a Tertiary Megatheriinae, Geodiversitas 26 (4), pp. 643-659 : 645-655

Pyramiodontherium bergi ( Moreno & Mercerat, 1891)

Megatherium burmeisteri Moreno & Mercerat, 1891: 229 .

Megatherium bergi Moreno & Mercerat, 1891: 231 .

Pyramiodontherium dubium Rovereto, 1914: 89 .

Pyramiodontherium bergi – Cabrera 1928: 344.

MATERIAL EXAMINED. — MLP 2-66 (holotype). In addition to the remains described and illustrated in Roth (1911), De Iuliis (1996), and Carlini et al. (2002), the following well preserved material is here described: left and right astragali, left calcaneum, right navicular, left and right cuboids, left and right ectocuneiforms, left and right mesocuneiforms, left and right entocuneiforms, right metatarsal III, left metatarsal IV, right metatarsal V, phalanx 1+2 of left and right digit III, left and right ungual phalanx, and phalanx 1 and 2 of right digit IV. Comparison specimens listed in Table 1.

COMPARATIVE DESCRIPTION

The foot bones of P. bergi ( Fig. 1 ) are described in anatomical position during locomotion. As in the other megatherines, the pes has undergone torsion, resulting in a deviation of its axis with respect to the horizontal. Consequently, pedal elements are inclined along a dorsolateral-ventromedial major axis.

Astragalus

The astragalus of P. bergi ( Fig. 2 A-D), partially described by Roth (1911), has the typical shape for the subfamily Megatheriinae . It is massive, with a well developed central odontoid process in dorsomedial view, and a navicular facet in anterior view.

As in other megatherines, the fibular facet in P. bergi is divided into two portions, an anteroposteriorly elongate dorsal division that joins the discoid facet, and a ventral portion with a rather circular surface that is slightly extended ventrally. This latter division has well defined margins anteriorly. A similar morphology is also seen in MLP 68- III- 14-1, but in this specimen the ventral portion is oval with the long axis perpendicular to the anteroposterior axis of the fibular facet, and the dorsal portion is reduced. In MACN 4992 the ventral portion of the fibular facet is similar in shape to that of P. bergi , although in some specimens of M. americanum ( MLP 2-29), the ventral portion of the facet is semilunar in shape and in general more depressed. On the basis of his observations on E. laurillardi, De Iuliis (1996) states that the shape of the fibular facet may have intraspecific variation. In addition, he outlines the well defined margins and a bilobate facet in M. americanum (MNHN P1871) .

The troclea tali is composed of two portions: a lateral, wide, discoid portion, and another semicylindrical, positioned in the middle of the for-

Anatomy of the pes of Pyramiodontherium bergi ( Mammalia, Xenarthra )

mer. Both portions correspond to the discoid facet and the odontoid process of De Iuliis (1996). The dorsal part of this process has a semicylindrical facet termed the odontoid facet, and this feature is related to the torsion of the pes, as verified in several large-sized tardigrades.

In P. bergi the odontoid process (middle portion) is peg-shaped as in Megathericulus patagonicus , although in the latter, it is anteriorly inclined in dorsal view. Specimens MACN 4992, MACN 13218, and MLP 99-XI-1-1 are similar to P. bergi in the shape of the odontoid process, the facet, and its inclination. In distal view the odontoid process is somewhat compressed in the contact with the discoid facet. The angle between the odontoid and discoid facets is nearly straight in P. bergi and MLP 68- III- 14-1, whereas it is obtuse in the remaining members of the subfamily. De Iuliis (1996) states that the compression of the odontoid process in P. bergi results from deformation, but there seems to be no deformation as in both astragali the shape of the odontoid process is the same. In addition, this author states that the odontoid process of P. bergi is as extended as in E. laurillardi .

In distal view the width of the discoid and odontoid facets is similar in M. americanum and M. urbinai . In P. bergi and MLP 68- III- 14-1 the odontoid facet is larger than the discoid facet, and in M. tarijense the discoid facet is wider.

In M. americanum and MACN 4941 the odontoid process is dome-shaped, with the largest width at the contact with the discoid facet. In P. bergi , the proximal-distal width of the odontoid facet represents one third of the width of the discoid facet in medial view. In MLP 68- III- 14-1 the middle facet is larger, occupying half the width of the discoid facet.

In P. bergi , a prominent portion of non-articular bone projects anteroventrally from the odontoid process. De Iuliis (1996) termed this portion the odontoid tuberosity. This tuberosity is present, although less developed in MACN 4941, MACN 4992, MLP 68-III-14-1, as well as in M. patagonicus . In M. americanum the odontoid tuberosity is somewhat less prominent than in the aforementioned specimens.

In some species (e.g., M. patagonicus ) a small oval facet for articulation with a sesamoid can be seen between the odontoid tuberosity and the posteromedial portion of the odontoid facet. In P. bergi , this facet is absent.

The facet for the navicular on the anteriormost part of the astragalus is approximately oval, with the main axis oriented dorsolateral-ventromedially. The facet has two surfaces, a concave dorsolateral portion termed the astragalar depression and another ventromedial convex portion. The astragalar depression is deeper in M. americanum than in P. bergi , but similar to P. bergi in MACN 4941, MACN 4992, MACN 13218, MLP 99- XI-1-1, and MLP 68-III-14-1.

In P. bergi , the dorsomedial half of the navicular facet is positioned dorsally with respect to the plane of the discoid facet ( Fig. 3A ). This situation is similar in M. patagonicus (MLP 68-III-14-1, MACN 4992, MACN 13218, MLP 99-XI-1-1, and MACN 4941). By contrast, in M. americanum the dorsomedial part of the navicular facet is at the same level with discoid facet. At the other extreme, in E. laurillardi and M. urbinai the dorsal margin projects by one third over the discoid facet. The navicular facet in M. tarijense displays an intermediate position between M. americanum and M. urbinai .

In dorsomedial view the odontoid facet is semicylindrical in section and the projection of the base exceeds the navicular facet in P. bergi ( Fig. 3B ) as in all other Tertiary astragali. In M. americanum this plane cuts the navicular facet whereas in MLP 68-III-14-1 the plane scarcely cuts the facet.

The cuboid facet appears on the external side of the astragalus where it is slightly differentiated from the convex portion of the navicular facet. The cuboid facet is convex and subtriangular to pyriform in shape.

There are two facets for articulation with the calcaneum; the smaller sustentacular facet and the ectal facet. These two facets are separated by a deep and wide non-articular bony canal, the sulcus tali. A similar arrangement can be verified in most megatherines except one specimen of M. americanum ( Kraglievich 1926) , one specimen of E. laurillardi (ROM 22006 in De Iuliis 1996 and Pujos 2001 pers. obs.), one specimen of M. urbinai (UNA V 2642 in Pujos & Salas 2004) in which these facets are fused, and in M. tarijense (MNHN TAR 269 Pujos 2002 pers. obs.) where they are partially fused. In MLP 68- III-14-1, the bony canal is deep but narrow due to the large size of the ectal facet.

The sustentacular facet is continuous with the cuboid facet but is separated from the ventral portion of the navicular facet. It is almost planar or flat and subtriangular in shape. The ectal facet is oval in shape, with the main axis anterolateral to posteromedial, parallel to the sulcus tali. The ectal facet is concave along the main axis and convex along the other axis. In dorsolateral view the distance between the ectal and the discoid facets is greater than in M. americanum , whereas in MLP 68-III-14-1, MACN 4941, MACN 4992, MACN 13218, MLP 99-XI-1-1, although separated, the distance is shorter.

Calcaneum

The calcaneum of P. bergi ( Fig. 2E, F ) is shaped as in other megatherines, although somewhat more gracile than in M. americanum and E. laurillardi and both more compressed and elongated posteriorly behind the articular end. The calcaneum has three articular facets on its anterior end; two articulate with the astragalus and one with the cuboid. The largest facet articulates with the ectal facet of the astragalus. This facet is also the most dorsal and is oval in shape with the main axis oriented anterolateral to posteromedially, parallel to the sulcus calcanei (placed ventrally to the facet). The facet is convex along the main axis, medially concave along the secondary axis, and flat laterally. A second facet articulates with the sustentacular facet of the astragalus. This facet is relatively quadrangular to pentagonal in outline, planar, and is separated from the former by the sulcus calcanei. The third or cuboid facet is smaller, positioned lateroventrally with respect to the sustentacular facet, and semicircular to oval in shape. In P. bergi , this facet and the sustentacular facet are not in contact. The sulcus calcanei, separating the ectal and sustentacular facets, runs transversally and of uniform width throughout its full extent. Finally, it should be noted that the calcaneum of MLP 68-III-14-1 is more robust and shorter than that of the type of P. bergi .

Navicular

The navicular ( Fig. 4 A-C) is oval to subrectangular in shape (distal view), antero-posteriorly compressed with the main axis oriented dorsolateral to ventromedially. In MLP 2-66 a portion of the dorsolateral half is missing.

The astragalar facet is located on the proximal surface, and may be differentiated into dorsolateral and ventromedial halves. The dorsolateral half is more or less circular and is formed by a condylar projection that fits into the circular depression of the astragalus (facie articular navicularis). This projection is not as well developed as in Megatherium americanum . The ventromedial half is relatively oval, concave along its main axes and articulates with the condylar portion of the astragalus. Both halves are similar in size, as in M. americanum . In M. altiplanicum from the Pliocene of Bolivia, the medial part of the facet is larger than the lateral part (Saint-André & De Iuliis 2001).

On the distal surface the navicular is convex along its main axes. On this aspect there are three articular facets. Ventrally there are two ectocuneiform facets, the smallest is subtriangular and ventromedial with respect to the other which is larger, quadrangular to trapezoidal, and positioned dorsolaterally.

Dorsomedially to the aforementioned facets there is a large facet that articulates with the internal meso- and entocuneiforms. This large facet is oval, elongate along the main axis of the navicular, but broken on its central part. This facet joins dorsally with the square ectocuneiform facet, being a rebound on the border (as in MACN 4983). In M. americanum , the ectocuneiform facets are fused and the internal cuneiform facet is smaller than the facet for the ectocuneiform.

A cuboid facet lies on the ventrolateral portion of the navicular. It is elongate along the dorsolateral-ventromedial axis. This facet has two different portions, one dorsolateral and other ventral. The dorsolateral portion contacts with the dorsal portion (condylar projection) of the navicular facet proximally, and the dorsal (square) ectocuneiform facet distally, in both cases in an approximately right angle. The lower portion of the cuboid facet contacts with the ventral portion of the astragalar facet posteriorly, and anteriorly is separated from the ventral ectocuneiform facet by a non-articulate furrow. In M. americanum the cuboid facet is located in a single plane, as may be seen on the navicular facet of the cuboid.

Cuboid

The cuboid ( Fig. 4 D-H) is irregular in shape, more or less cubic, massive, and supports two complex articular surfaces separated by non-articulating bone. On the posteromedial surface there are facets for the calcaneum, astragalus, navicular, and ectocuneiform. On the anteroventral surface of the bone, there are facets for metatarsals III, IV, and V. The dorsal surface of the cuboid is rugose, relatively flat, and devoid of articular facets. The ventral portion is more irregular, with some plantar projections, and a posterolaterally projecting crest that reaches the dorsal surface. A deep dorsoventral furrow occupies the medial side of the cuboid and separates the articular areas.

The calcaneal facet is posterolateral, square, with the dorsomedial half concave, and the ventrolateral convex. The astragalar facet is posteromedial, and contacts the calcaneal facet forming a straight angle between them. It is approximately oval with the main axis dorsolateral to ventromedial and concave in both main axes.

The navicular facet is placed medially in front of the astragalar facet. The latter is subdivided into two different planes corresponding to those developed for the lateral facet of the navicular. The navicular facet is dorsoventrally elongate and narrow; the posterior margin contacts the astragalar facet and the anterior margin contacts the ectocuneiform facet.

The small and semicircular ectocuneiform facet contacts the navicular facet posteriorly and the medial furrow anteriorly. This facet is absent in M. americanum , occasionally present in E. laurillardi ( Cartelle 1992) and always present in M. tarijense ( Pujos & Salas 2004) .

The facet for metatarsal IV has two portions, each plane almost perpendicular to the other. The posterior portion is elongate along the dorsolateral-ventromedial axis, and the more anterior and dorsal plane is oval in shape, and placed on an anterior laminar projection of the cuboid. In M. americanum the angle between these two portions is wider.

The metatarsal V facet is next to the most elongate portion of the Mt IV facet, in a straight angle. It is almost triangular with a ventral apex, convex in both axis.

On the anteromedial end of the cuboid, support- ed medially by the laminar projection, there is a small oval facet for metatarsal III that is extended dorsoventrally. This facet is present in M. americanum , but M. tarijense has no articulation between the cuboid and metatarsal III.

Mesocuneiform

The mesocuneiform ( Fig. 4I ) is trapezoidal in medial view. It has three articular facets, two lateral facets, one proximal for the navicular, another distal for metatarsal III, and one ventral facet (on a slightly inclined plane) for the entocuneiform. The navicular facet is oval but has a downward projection that is continuous with the ascending lateral proximal entocuneiform facet. Both these facets form a continuous, dorsoventrallyoriented functional surface. The Mt III facet is circular and articulates with the medial proximal facet of metatarsal III. The two lateral mesocuneiform facets, equal in size, are separated by a fragment of non-articulating bone, also similar in size. The entocuneiform facet contacts the navicular facet and is separated from the Mt III facet. It is the largest of the articular facets and is oval to triangular in shape.

Entocuneiform

The entocuneiform ( Fig. 4I ) is rectangular in medial view, larger than the mesocuneiform, and has two articular facets: one lateral and the other dorsal, which articulate with the navicular and the mesocuneiform, respectively, and are in contact proximally. The navicular facet is oval and is continuous upward with the descending portion of the mesocuneiform lateral proximal facet. The mesocuneiform facet is placed located almost horizontally and perpendicular to the lateral facet. It is larger and matches in shape with the mesocuneiform ventral facet. On the internal lateral surface there is a fragment of non-articulating bone that bears a semilunar depression of flat bottom that divides the bone in two parts, one principal and other reminiscent of a plantar tuberosity.

In P. bergi there is no fusion of the meso- and entocuneiform, termed the mesoentocuneiform complex by De Iuliis (1996). In megatherines (e.g., Megatherium sp., Eremotherium sp.) that have this complex, it is triangular (or pentagonal) with the apex anteriorly directed. The proximal surface has an elongate navicular facet, and the distal surface displays a small oval Mt III facet dorsolaterally.

Ectocuneiform

The ectocuneiform ( Fig. 4 J-L) is triangular with its base dorsolateral, apex ventromedial, and elongate in its main axis. It is anteroposteriorly compressed, convex anteriorly, and diminishes in thickness dorsolaterally-ventromedially. It is more gracile, elongate and tapered than in other genera (i.e. Megathericulus and Megatherium ).

The proximal and distal surfaces of the ectocuneiform are almost entirely articular, with two main areas (proximal and distal) that follow the triangular shape of the ectocuneiform, and are separated by non-articular bone. Proximally, two navicular articular facets are developed: one laterodorsal facet that is subtrapezoidal to square, and another ventromedial facet that is subtriangular. Both facets fit in shape and size with their counterparts developed on the distal surface of the navicular. Also like those of the navicular, they are separated by a transverse fringe of nonarticular bone. At the same level, the laterodorsal facet is continuous ventrally with a subrectangular facet and their articular planes meet in a 120° angle. The subrectangular facet articulates with the small semicircular cuboid facet, which is absent in M. americanum and M. urbinai , and present in M. tarijense . Most of the distal surface of the ectocuneiform is occupied by a facet for Mt III that is approximately triangular and convex, although it has a small furrow near the ventromedial apex. In other genera (i.e. Megatherium ), the distal facet is completely convex. In M. urbinai , the ectocuneiform articulates with metatarsals III and IV ( Pujos & Salas 2004). There is no articulation between the ectocuneiform and the internal cuneiforms in P. bergi . In M. urbinai (MUSM 15) and M. tarijense (FMNH P14216), the ectocuneiform articulates with the mesoentocuneiform complex and a similar articulation is also present in some specimens of M. americanum (e.g., MNHN PAN 295).

Metatarsal III

In P. bergi , the metatarsal III ( Fig. 5 A-E) is anteroposteriorly very compressed compared to metatarsals IV and V. The posterior portion is strongly compressed transversally, while in other megatheres (i.e. E. laurillardi ), this portion is shorter ( Paula Couto 1978).

The ectocuneiform facet is posteromedial, almost triangular with ventral apex, and concave along both axes. A small mesocuneiform facet, oval in shape, occupies the proximomedial side of the metatarsal III. This facet contacts posteriorly with the ectocuneiform facet in straight angle.

The facet for metatarsal IV is lateral, oval in shape, and extended dorsoventrally. The surface is undulate, markedly concave anteriorly, and convex posteriorly. The articular surface is nearly parallel to the ectocuneiform facet. A small accessory Mt IV facet appears on the dorsolateral surface of the metatarsal III.

Between the facets for ectocuneiform and Mt IV, there is a posterolateral projection that supports an oval cuboid facet.

On the distal surface a crest articulates with phalanx 1+2 of digit III. It is slightly concave dorsoventrally, it narrows ventrally becoming also more acute, and is inclined along a dorsolateral to ventromedial axis. We conclude that this crest is almost entirely articular because in the middle of its dorsoventral extent (on the deepest part of the concavity) there is a small nonarticulating area that fits with the corresponding phalanx 1+2 of digit III. An elongate internal surface continues beyond the crest to complete the articulation. In M. americanum the crest is interrupted and continues medially as an independent small oval facet. The ventromedial end of the keel has an articular facet probably for a sesamoid. On the most ventrolateral portion of metatarsal III there is a plantar prominence.

Metatarsal IV

Metatarsal IV ( Fig. 5 F-I) is long and not as compressed as metatarsal III. The diaphysis is triangular in section with lateral apex, whereas in M. americanum the section is subtriangular to oval. The proximal portion is laterally compressed and dorsoventrally expanded.

Three articular facets appear on the proximal epiphysis, an anteromedial facet for Mt III, a posteromedial facet for the cuboid, and a lateral facet for Mt V. The facet for Mt III is oval, dorsoventrally extended, anteroposteriorly convex at the anterior part, and concave in both directions posteriorly. This facet is separated posteriorly from the cuboid facet. The cuboid facet is rectangular, dorsoventrally extended, and its anterior two-thirds is dorsoventrally concave and occupies the medial side. The posterior third is proximal in position.

The metatarsal V facet is located on the external side of the proximal epiphysis. This facet is pentagonal, with a central depression and a small extension that is continuous with the posterior portion of the cuboid facet.

The distal epiphysis is triangular with laterodorsal apex and tripod-like base. The facet for the proximal phalanx of digit IV is crested, as that for metatarsal III, but less acute in section, and narrowing ventrally. Ventromesially there is a small, and convex subcircular facet for a sesamoid. This facet was first mentioned by Cabrera (1929) when describing the pes of Megatherium . This same extension is present in E. laurillardi , but no sesamoid bone can be seen ( De Iuliis 1996). Occasionally there occurs ankylosis between Mt IV and Mt III in E. laurillardi ( Paula Couto 1978; Cartelle 1992).

Metatarsal V

Metatarsal V ( Fig. 6 A-C) is slightly longer than metatarsal IV but depressed dorsoplantarly with the lateral margin expanded and dorsoventrally compressed (especially the proximal two thirds). The distal portion is almost isodiametric. The medial side has two contiguous articular facets that are inclined dorsomedially. The anteriormost facet for Mt IV is pentagonal, relatively flat, and continuous posteriorly with the cuboid facet. The cuboid facet is concave and triangular with ventral base and anterior apex. The posterior end of metatarsal V is prominent and point-shaped in P. bergi , while in M. americanum it is blunted. The distal surface has a small oval, convex facet elongated along the dorsolateral-ventromedial axis for a nodular vestigial phalanx.

Digit III

Digit III is the only posterior clawed digit in Megatheriinae . It is composed of a single proximal bone (fused phalanxes 1+2 according to Cartelle 1992) ( Fig. 6D-F), and a strong ungual phalanx that is claw-shaped ( Fig. 6 G-I).

The proximal surface of the phalanx 1+2 bears a wide facet for metatarsal III. This facet is canalshaped and elongated along the dorsolateralventromedial axis. Non-articular bone subdivides it into two parts. Distally it bears a trocleated surface that is transversely elongate and bears an incomplete non-articular bony area. The phalanx is obliquely oriented and consequently the ungual phalanx is deviated ventromedially.

The ungual phalanx articulates with the proximal phalanx (1+2) by a deeply depressed surface divided into two oval parts. This surface is oriented obliquely to the sagittal plane, very well developed, relatively short and robust, and high- er than wide (especially the distal portion). Proximally it bears a crown-like expansion that would have covered the base of a large corneal claw. The central bone is also short and high, triangular in section, and projects beyond the bone that sheathed it on the proximal two-thirds of the phalanx.

Digit IV

Unlike other megatherines that have only two phalanxes, digit IV of P. bergi has three phalanxes. Phalanx 1 ( Fig. 6J, K) is anteroposteriorly compressed and elongate along the dorsoventral axis. The proximal surface for the Mt IV facet is well developed and almost entirely articular. This facet is elongate and strongly concave transversely. The distal surface bears a dorsoventrally convex bilobate facet. The second phalanx articulates on this facet. Phalanx 2 ( Fig. 6L, M) is smaller and more anteroposteriorly compressed than phalanx 1. The proximal facet is bilobate, somewhat circular, and concave on both directions. A small almost circular facet on the distal surface must have articulated with a third, probably vestigial phalanx.

Figures

FIG. 1. — Dorsolateral view of a compose pes of Pyramiodontherium bergi (Moreno & Mercerat, 1891) (MLP 2-66). Abbreviations: DIII P1+2, digit III, phalange 1+2; DIII UP, digit III, ungueal phalange; DIV P1, digit IV, phalange 1; DIV P2, digit IV, phalange 2; Mt III, IV, V, metatarsals III, IV, V. Scale bar: 100 mm.

FIG. 2. — Pyramiodontherium bergi (Moreno & Mercerat, 1891) (MLP 2-66); A-D, left astragalus; A, dorsomedial view; B, anteromedial view; C, fibular view; D, ventral view; E, F, left calcaneum; E, specular lateral view; F, specular distal view. Abbreviations: AEF, astragalar ectal facet; ASF, astragalar sustentacular facet; CEF, calcaneal ectal facet; CSF, calcaneal sustentacular facet; Cub, cuboid; DF, discoid facet; FF, fibular facet; Nav, navicular; OF, odontoid facet; OP, odontoid process; OT, odontoid tuberosity; SC, sulcus calcanei; ST, sulcus tali. Scale bar: 50 mm.

FIG. 3. — Astragalus of Pyramiodontherium bergi (Moreno & Mercerat, 1891) (MLP 2-66); A, anterior view; B, dorsolateral view. a-a’ line, projection of the plane of the discoid facet; b-b’ line, projection of the plane of the base of the odontoid facet. Abbreviations: DF, discoid facet; FF, fibular facet; Nav, navicular; OF, odontoid facet; OP, odontoid process. Scale bar: 50 mm.

FIG. 4. — Pyramiodontherium bergi (Moreno & Mercerat, 1891) (MLP 2-66); A-C, right navicular; A, proximal view; B, distal view; C, lateral view; D-H, right cuboid; D, posteromedial view; E, posterolateral view; F, proximal view; G, proximolateral view; H, dorsolateral view; I, right mesocuneiform and entocuneiform, lateral view; J-L, right ectocuneiform; J, proximal view; K, distal view; L, lateral view. Abbreviations: Ast, astragalus; AF, astragalar facet; Calc, calcaneum; Cub, cuboid; EctC, ectocuneiform; EntC, entocuneiform; MesC, mesocuneiform; Mt III, IV, V, metatarsals III, IV, V; Nav, navicular. Scale bar: 50 mm.

FIG. 5. — Pyramiodontherium bergi (Moreno & Mercerat, 1891) (MLP 2-66); A-E, right metatarsal III; A, posteromedial view; B, lateral view; C, distal view; D, dorsolateral view; E, posterolateral view; F-I, left metatarsal IV; F, ventrolateral view; G, proximal view; H, dorsolateral view; I, distal view. Abbreviations: Cub, cuboid; DIII P1+2, digit III phalanx 1+2; DIV P1, digit IV phalanx 1; EctC, ectocuneiform; MesC, mesocuneiform; Mt III, IV, V, metatarsals III, IV, V; PP, process plantar; S, sesamoid bone. Scale bar: 50 mm.