PalZ

pp 1–17

The dentition of a well-preserved specimen of Camarasaurus sp.: implications for function, tooth replacement, soft part reconstruction, and food intake

Research Paper

DOI: 10.1007/s12542-016-0332-6

Cite this article as:
Wiersma, K. & Sander, P.M. PalZ (2016). doi:10.1007/s12542-016-0332-6

Abstract

The basal macronarian genus Camarasaurus was the most common sauropod in the Upper Jurassic Morrison Formation of North America and is known from several complete and partial skeletons. The specimen used for this study is Camarasaurus sp. SMA 0002 from the Sauriermuseum Aathal, Switzerland. This specimen was found in the Howe-Stephens Quarry, Bighorn Basin, WY, USA. In this study, the dental morphology, characterized by the spatulate, broad-crowned teeth, the tooth replacement pattern, and the function of the dentition and its implications for food intake is described. Features such as the absence of denticles, the wrinkled pattern of the enamel, and the occurrence of large wear facets on older teeth are characteristic for Camarasaurus sp. A slab of sediment with soft tissue impressions ranging up to the middle part of the crown suggests the presence of a gingival soft tissue structure partially covering the teeth. The wrinkled enamel on the crown of the teeth of Camarasaurus sp. and other sauropods is interpreted as indication of this cover of gingival connective tissue. In addition, there possibly was a keratinous beak, which together with the gingiva held the teeth in the jaw and provided stability for teeth in which the root is almost completely resorbed.

Keywords

Camarasaurus sp. Dentition Morphology Function Soft tissue 

Abbreviations

CMNH

Carnegie Museum of Natural History, Pittsburgh, PA, USA

DfmMh/FV

Dinosaurier-Freilichtmuseum Münchehagen/Verein zur Förderung der Niedersächsischen Paläontologie, Münchehagen, Germany

DINO

Dinosaur National Monument, Jensen, UT, USA

GMNH

Gunma Museum of Natural History, Gunma, Japan

MfN

Museum für Naturkunde, Berlin, Germany

SMA

Sauriermuseum Aathal, Aathal, Switzerland

Kurzfassung

Die basale Macronaria-Gattung Camarasaurus war einer der häufigsten Sauropoden der oberjurassischen Morrison-Formation in Nord-Amerika und ist anhand mehrerer vollständig erhaltener Skelettfunde bekannt. Für diese Studie wurde das Exemplar eines Camarasaurus sp. (SMA 0002) des Sauriermuseums Aathal in der Schweiz, untersucht. Dieses Exemplar wurde im Howe-Stephens-Steinbruch im Bighorn Basin, Wyoming, USA, gefunden. In dieser Studie wird die Morphologie der Bezahnung beschrieben, die durch breitkronige, spatelförmige Zähne gekennzeichnet ist. Weiterhin werden der Zahnersatz und die Funktion der Bezahnung sowie die daraus resultierenden Folgen für die Nahrungsaufnahme beschrieben. Diagnostische Merkmale für die Bezahnung von Camarasaurus sp. sind die Abwesenheit von Dentikeln, die Runzelung des Zahnschmelzes und das Auftreten von großen Abrasionsflächen an älteren Zähnen. Eine Struktur mit Hauterhaltung, welche die Zähne bis zur Mitte der Krone bedeckt, deutet auf die Anwesenheit einer zahnfleischähnlichen Struktur hin, welche die Zähne zum Teil bedeckt. Der runzelige Zahnschmelz auf den Zahnkronen von Camarasaurus sp. und anderen Sauropoden wird als ein weiterer Hinweis auf diese zahnfleischartige Struktur interpretiert. Zusätzlich zum Zahnfleisch besaß Camarasaurus wahrscheinlich einen keratinösen Schnabel, der zusammen mit dem Zahnfleisch die Zähne in ihrer Position im Kiefer hielten und Stabilität für Zähne mit fast vollständig resorbierten Wurzeln bot.

Schlüsselwörter

Camarasaurus sp. Bezahnung Morphologie Funktion Weichteilerhaltung 

Introduction

Sauropodomorph dinosaurs were the largest terrestrial vertebrates that ever walked the earth. Various studies have been done covering a wide range of topics concerning their morphology, phylogeny, and biology (e.g., Curry-Rogers and Wilson 2005; Klein et al. 2011; Sander et al. 2011a, b; Sander 2013). Still, many open questions remain, mainly regarding their biology and ecology. The basal macronarian sauropod Camarasaurus is one of the most iconic sauropods and probably the genus best known from the material. Unequivocal finds of Camarasaurus are limited to North America and include at least five almost complete specimens, one of which is specimen SMA 0002 (Ayer 2000; Ikejiri et al. 2005; Tschopp et al. 2014, 2016; Waskow and Sander 2014). Currently, SMA 0002 cannot be assigned to a particular species of Camarasaurus, and work in progress (Tschopp et al. 2014) suggests that it may be closely related to “Cathetosauruslewisi. The aim of this study is to obtain a better understanding of the morphology and function of the dentition of Camarasaurus based on specimen SMA 0002 that preserves the skull with in situ functional and replacement teeth in the premaxilla, maxilla, and dentary (Fig. 1). Because of the completeness, good preservation, and skilled preparation of SMA 0002, it is considered an excellent specimen to use for studying camarasaur morphology, including dental morphology. Unlike in another described Camarasaurus skeleton (McIntosh et al. 1996), in which the skull was disarticulated and nearly all teeth had fallen out of their alveoli, the dentition of SMA 0002 is perfectly preserved in articulation in the jaws. Neither the studies by McIntosh et al. (1996) and Madsen et al. (1995) described the dentition in much detail, but the description of the Camarasaurus dentition is important for reconstructing sauropod food intake and herbivory (Hummel et al. 2008; Sander et al. 2010, 2011a; Gee 2011).
Fig. 1

Mount of the skull and lower jaws of Camarasaurus sp. specimen SMA 0002 in left lateral view. The skull itself is still connected to the matrix, but the lower jaws were moved to their present position during preparation. Scale 10 cm

The evolution of the sauropod dentition

Sauropods show a great diversity in their tooth morphology, even though the sauropods are accepted as exclusively herbivorous (Upchurch and Barrett 2000; Barrett and Upchurch 2005; Stevens 2013). The teeth of basal sauropods maintained mostly the same morphology as that of basal sauropodomorphs with some slight differences (Upchurch and Barrett 2000). The lingual ridge, coarse denticles, mesiodistal symmetry, the lingually curved form, and the “en echelon” tooth arrangement are retained. Different, however, is the slightly concave lingual side of the dentition, and, in some basal sauropods, the broader crown proportions due to a larger mesiodistal expansion (Chure et al. 2010).

Within the more derived sauropods, two tooth type trends can be recognized (von Huene 1926; Janensch 1929; 1935–1936; Upchurch 1995, 1998; Sander 1997; Wilson and Sereno 1998; Upchurch and Barrett 2000; Chatterjee and Zheng 2002; Wilson 2002; Upchurch et al. 2004; Barrett and Upchurch 2005; Sander et al. 2011a), yet intermediate tooth type trends can be observed (e.g. Chure et al. 2010; Díez Díaz et al. 2013, 2014). The first tooth type (broad-crowned), consists of stout, spatulate teeth, and is typical for basal sauropods and basal macronarians (Upchurch 1995, 1998; Sanz et al. 1999; Wilson and Sereno 1998; Upchurch and Barrett 2000; Wilson 2002; Upchurch et al. 2004; Barrett and Upchurch 2005; Chure et al. 2010; Sander et al. 2011a). The second tooth type (narrow-crowned) consists of slender and pencil- or peg-shaped teeth, which evolved at least twice within the Sauropoda, e.g., in Diplodocoidea and in Titanosauria (Calvo and Salgado 1995; Upchurch 1995, 1998; Salgado et al. 1997; Sanz et al. 1999; Wilson and Sereno 1998; Upchurch and Barrett 2000; Curry-Rogers and Forster 2001; Wilson 2002; Upchurch et al. 2004; Barrett and Upchurch 2005; Chure et al. 2010; Sander et al. 2010, 2011a).

A feature that is known from all sauropods, but lacking in basal sauropodomorphs is the presence of a wrinkled pattern on the outer enamel surface. While incipient wrinkling on the enamel is also present in some basal sauropodomorphs, such as Mussaurus patagonicus (Pol and Powell 2007), it has been retrieved as a synapomorphy of Eusauropoda (Wilson and Sereno 1998; Allain and Aquesbi 2008; Carballido and Pol 2010; Holwerda et al. 2015). The function of the wrinkled enamel surface has not received much attention. Common sauropod finds are isolated tooth rows, which are sets of articulated teeth preserved with little or no surrounding bone structures (Britt et al. 2008).

Features such as wrinkled enamel and the presence of “ITRs” (isolated tooth rows) may indicate that some sort of soft tissue was present that held the teeth in place after the death of an individual. This hypothesis is studied in detail on the dentition of Camarasaurus SMA 0002 E.T.

Locality and geological setting of SMA 0002

The Upper Jurassic Morrison Formation of the western interior region of North America is known world-wide for its dinosaur remains, including several major dinosaur quarries such as those on the Howe Ranch in Wyoming (Ayer 2000; Foster 2007), which lies at the eastern margin of the Bighorn Basin in the northern-central Wyoming (USA). The Camarasaurus sp. specimen SMA 0002 was found in the Howe-Stephens Quarry (Fig. 2) located on the Howe Ranch (Ayer 2000; Waskow and Sander 2014). Continental sediments, ranging from coarse sandstones to fine mudstones, make up the rock in the Howe-Stephens Quarry (Ayer 2000). Stratigraphically, the Howe-Stephens Quarry is located within the Brushy Basin Member (middle to upper Kimmeridgian) of the Morrison Formation.
Fig. 2

Quarry map of the Howe-Stephens Quarry, WY, USA, with the 1992–1996 finds. The skeleton of Camarasaurus sp. SMA 0002 is orange in color (courtesy of the Sauriermuseum Aathal, Aathal, Switzerland)

Materials and methods

Material

During excavation, one manual digit was sticking up from the sediment, earning Camarasaurus sp. specimen SMA 0002 the nickname “E.T.”. The skeleton is preserved in the commonly observed opisthotonic body posture with three-dimensional bone preservation (Michelis 2004). The skeleton is articulated and nearly complete; only the vomers, the splenial bones, one terminal phalanx of the right pes, and some caudal vertebrae at the distal end of the tail are missing (Waskow and Sander 2014). The teeth are preserved in three dimensions, and the left dentary is partially covered by soft tissue remains. The dentition of the upper jaw of SMA 0002 has been slightly displaced towards the posterior during burial, whereas that of the lower jaw is not displaced. Therefore, the upper and lower dentition no longer occlude. Table 1 contains the measurements of the premaxillae, maxillae and dentaries of Camarasaurus sp. SMA 0002.
Table 1

Length of the premaxillae, the maxillae, and the dentaries of Camarasaurus sp. SMA 0002

Bone

Measurements (left)

Measurements (right)

Premaxilla

117

78.5

Maxilla

198.5

161

Dentary

266.5

229.5

All measurements are in mm

The three-dimensionally preserved skull and lower jaws of SMA 0002 were prepared by Dr. Ben Papst and is on display at the Sauriermuseum in Aathal, Switzerland. The right side of the skull is still in the original matrix, whereas the right lower jaw only rests on the matrix and can be removed. The left lower jaw rests on a steel frame and can also be removed. Apart from the splenials, which were not found, the bones of both lower jaws remain in articulation, but the lower jaws were found disarticulated from the skull. Although some taphonomic loss of teeth is possible, this is unlikely since no isolated teeth were found near the skull and lower jaws of SMA 0002.

For comparison with other well-preserved basal macronarian dentitions, we studied material of the dwarf basal macronarian Europasaurus (Sander et al. 2006; Marpmann et al. 2015) from the Langenberg Quarry near Goslar in Lower Saxony, Germany, and of the brachiosaurid Giraffatitan (Janensch 1935–1936) from the Tendaguru Beds of Tanzania, Africa. Europasaurus material includes the “ITR” (isolated tooth row) DfmMh/FV 580.1, the premaxillae DfmMh/FV 032, DfmMh/FV 061, DfmMh/FV 652.2, DfmMh/FV 982, DfmMh/FV 291.18, the maxilla DfmMh/FV 291.17, and the dentaries DfmMh/FV 653, DfmMh/FV 654, and DfmMh/FV 291.11. Of Giraffatitan, the skulls MfN t1, MfN S66, and MfN S116, and “ITRs” MfN WJ 4170, MRB 2181.23.4, MRB 2181.23.2, and MRB 2181.23.1 were studied.

Methods

The morphological description of the dentition is at the macroscopic level. The length and width of the crowns of the teeth were measured with a digital caliper with an accuracy of 0.02 mm, but were rounded off to the nearest tenth of a millimeter. The length of the crown is defined as the distance between the apex of the tooth and base of the enamel cover measured on the labial side of the crown. Tooth width was measured at the widest mesiodistal expansion of the tooth. The Slenderness Index (SI) of Barrett and Upchurch (2005), the ratio between length and width of the crown, was calculated from these measurements (Table 2). Among sauropods, broad-crowned teeth have an SI of ≤4.0, whereas narrow-crowned teeth have a higher SI of ≥4.0 (Barrett and Upchurch 2005). The length of the premaxilla, maxilla, and dentary was measured with a tape measure with an accuracy of 0.5 mm from the anterior end of these bones to their posterior end.
Table 2

Measurements and proportions of the functional dentition of Camarasaurus sp. SMA 0002

Tooth position

Crown height

Crown width

SI

Left Premaxilla

 1

45.8

28.9

1.58

 2

48.1

30.9

1.56

 3

39.6

28.9

1.37

 4

41.6

26.4

1.58

Left Maxilla

 1

38.3

26.3

1.46

 2

37.7

26.6

1.42

 3

28.7

26.0

1.1

 4

29.6

24.4

1.21

 5

27.6

24.0

1.15

 6

24.7

20.0

1.24

 7

25.5

20.1

1.27

 8

23.7

18.6

1.27

 9

18.6

14.7

1.27

Left Dentary

 1

nm

23.9

 2

42.5

25.3

1.68

 3

35.0

24.9

1.41

 4

36.3

25.8

1.41

 5

35.5

25.9

1.37

 6

nm

nm

 7

nm

24.2

 8

24.7

20.6

1.2

 9

nm

nm

 10

21.9

16.9

1.3

 11

19.6

14.7

1.33

 12

17.4

12.9

1.35

 13

13.8

11.2

1.23

Right Premaxilla

 1

40.9

26.3

1.56

 2

44.5

30.7

1.45

 3

45.4

25.7

1.77

 4

48.5

nm

Right Maxilla

 1

43.5

23.6

1.84

 2

43.0

25.1

1.71

 3

38.3

nm

 4

35.0

nm

 5

32.6

21.8

1.5

 6

27.9

nm

 7

28.9

nm

 8

nm

nm

 9

15.6

15.1

1.03

Right Dentary

 1

48.2

25.9

1.86

 2

42.5

25.0

1.7

 3

40.3

29.4

1.37

 4

36.2

25.3

1.43

 5

35.2

22.4

1.57

 6

38.4

22.6

1.7

 7

33.4

21.6

1.55

 8

27.7

20.5

1.35

 9

23.3

16.5

1.41

 10

20.8

14.7

1.41

 11

nm

nm

 12

nm

nm

 13

14.6

11.3

1.29

See “Methods” section for explanation of measurements. All measurements in mm

SI slenderness index, nm not measurable

The following notation for the individual tooth positions was used in this study: Premaxillary tooth positions were written as left pm1 to left pm4 and right pm1 to right pm 4 and so on. The notation for the maxillary tooth positions is as follows: left m1–9 and right m1–9, and the dentary tooth positions are left d1–13 and right d1–13.

Photos of individual teeth and parts of the dentition were taken with a Sony α NEX-3 N digital camera with interchangeable lenses under normal lighting conditions. A set of photographs were also taken for a photogrammetric 3D model of the skull of SMA 0002. These photos were acquired from different angles and with sufficient overlap with a Sony α NEX-3 N digital camera and a Canon EOS 400D digital camera. The photos were processed with the commercial software Agisoft PhotoScan (AgiSoft LLC), which calculates the position and orientation of each photo after which a three-dimensional point cloud is created. Agisoft PhotoScan offers several editing tools, including several model surface functions such as the point cloud, solid, and shaded surface. Finally, the program incorporates the texture of the model from the color information from the pictures, creating a 3D model which resembles the original specimen.

The terminology used in the dental professions is also applied to reptiles (Edmund 1969; Smith and Dodson 2003) and has been used by others for describing sauropod dentitions. The terminology used in this study was chosen so that a comparison with other descriptions of dentition is possible. The terms mesial vs. distal are used to describe the location of the teeth relative to the symphysis, and the terms rostral vs. caudal are used to describe the directions for the jaws. The terminology for wear facets follows Janensch (1935–1936) and Chatterjee and Zheng (2005). These authors defined three different kinds of wear facets. An occlusal wear facet is a steeply inclined, flat surface with a round to oval form, which occurs only at the apex of the crown. A mesial wear facet is an elongated, vertically aligned facet along the mesial ridge of the crown. It is more extensive along the ridge than the distal wear facet and is almost always connected to the occlusal wear facet. A distal wear facet is located on the distal ridge of the crown with a similar morphology as the mesial wear facet, but it is not as expanded.

Tooth growth stages, abrasion stages, and tooth replacement pattern were determined, respectively inferred, from the degree of wear and the relative height of the root by Chatterjee and Zheng (2005). Five abrasion stages (Table 3) of functional teeth (F1–F5) and four growth stages (Table 4) of replacement teeth (R0–R3) were recognized based on tooth exposure, tooth size, tooth length and relative position in the alveoli, and wear facets (modified from Chatterjee and Zheng 2005). The abrasion stages of the teeth of Camarasaurus sp. SMA 0002 are listed in Table 5.
Table 3

The five abrasion stages F1–F5 of the functional dentition

Abrasion stage

Description

F1

The tooth is fully developed; the crown lacks wear facets, and the root does not show any sign of resorption

F2

The tip of the crown shows the occlusal wear facet, resorption of the root begins

F3

A second wear facet occurs on either the mesial or distal side, the occlusal wear facet has grown in size. Root resorption removed between 25 and 50% of total root length

F4

All three wear facets are present, the apex of the tooth becomes rounded, and root resorption has consumed 50–75% of total root length

F5

The three wear facets merge to form a single larger wear surface which extends horizontally along the crown of the teeth. Root resorption has reached >75% of the total root length

Table 4

The four growth stages R0–R3 of the replacement dentition

Growth stage

Description

R0

Small incipient tooth, which is not or hardly visible

R1

Small incipient tooth which only shows the tip of the crown

R2

Fully erupted tooth in alveolus

R3

The completely exposed crown has reached the labial margin of the jaw bone

Table 5

Abrasion stages and wear facets in the functional dentition of Camarasaurus sp. SMA 0002

Tooth position

Abrasion stage

OWF

MWF

DWF

Left Premaxilla

 1

F3

y

y

 2

F1

n

n

n

 3

F5

y

y

y

 4

F4

y

y

y

Left Maxilla

 1

F4

y

y

y

 2

F3

y

y

y

 3

F4

y

y

y

 4

F4

y

y

y

 5

F3

y

y

n

 6

F4

y

y

y

 7

F2

y

y

n

 8

F1

n

n

n

 9

F2

y

n

n

Left Dentary

 1

F4

y

y

 2

F4

y

y

y

 3

F5

y

y

y

 4

F4

y

y

y

 5

F3

y

y

y

 6

F5

y

y

y

 7

F4

y

y

y

 8

F3

y

n

y

 9

rt

 10

F3

y

n

y

 11

F2

y

n

n

 12

F1

n

n

n

 13

F2

y

n

n

Right Premaxilla

 1

F5

y

y

 2

F4

y

y

 3

F4

y

y

y

 4

Right Maxilla

 1

F4

y

y

y

 2

F4

y

y

y

 3

F2

y

n

 4

F5

y

y

y

 5

F3

y

y

n

 6

F1

n

n

 7

F4

y

y

 8

rt

n

n

n

 9

F2

n

y

n

Right Dentary

 1

F1

n

n

 2

F4

y

y

y

 3

F3

y

y

y

 4

F5

y

y

y

 5

F4

y

y

y

 6

F3

y

n

y

 7

F5

y

y

y

 8

F4

y

y

y

 9

F2

y

n

n

 10

F2

n

n

 11

 12

rt

 13

F2

y

n

n

See “Methods” section for explanation of measurements

Note that in tooth positions left m2, left d5, and right d3 (which all show abrasion stage F3), all three wear facets could be observed, yet the last wear facet only just started to develop. Therefore, the incipient presence of this wear facet is not yet taken into account when assigning the F stages to these teeth. The same situation applies to the left m7 assigned to F2, where the occlusal wear facet is fully developed but the mesial wear facet is incipient and not taken into account in abrasion stage assignment

OWF occlusal wear facet, MWF mesial wear facet, DWF distal wear facet, y present, n not present, rt replacement tooth

Based on these wear and replacement stages, the Z-spacing after DeMar (1972) was determined for Camarasaurus sp. SMA 0002. Z-spacing is the number of tooth positions located between two teeth of the same growth or abrasion stage.

Description

Tooth formula

The right and left premaxillae show four alveoli each, the maxillae have nine alveoli, and the dentaries have 13 alveoli. The tooth formula of Camarasaurus sp. specimen SMA 0002 thus is pm4 + m9/d13.

Functional dentition

The lengths of the left and right premaxillae (Table 1) differ due to stronger deformation of the right side of the skull during burial. As noted, both bones contain four alveoli. The teeth are symmetrical mesiodistally; crown height varies between 48.5 and 39.7 mm and crown width between 30.9 and 25.7 mm (Fig. 4; Table 2). The variation of crown heights within the premaxillary teeth is mainly irregular, possibly due to stronger deformation. As noted, in Camarasaurus, the tooth crowns are generally spatulate, massive, and expanded mesiodistally but are relatively short (Chatterjee and Zheng 2005); they narrow towards the apex (Fig. 3). The enamel of the crown possesses a well-developed wrinkled surface. At the base of the crown, its cross-section is round to oval, but towards the apex, the cross-section becomes more D-shaped. In SMA 0002, the color of the enamel is black. The upper parts of the roots stick out of the jaw for approximately 20 mm and are of a light brown color. The exposed parts of the roots have a smooth surface (Fig. 3) and a round to oval cross-section. The transition from crown to root is more apical on the tooth in mesiodistal direction and more basal along the mesial and distal faces of the tooth. The bases of the roots of the functional dentition of SMA 0002 are not visible because they are set in alveoli and lingually covered by the interdental plates. The interdental plates, also known as the paradental plates are a well-known feature for theropod dinosaurs and crurotarsans, but can also be observed in sauropods. They are flat bony structures medial to the dental tooth row and are attached to the lateral wall of the dentigerous bone (Hendrickx and Mateus 2014). Perpendicular and mediolaterally oriented lamina separate each individual tooth socket. The interdental plates vary in size and can either be completely fused, or separated by interdental gaps (Hendrickx and Mateus 2014).
Fig. 3

Photographs of the functional dentition of Camarasaurus sp. SMA 0002 in labial view (a, b) and lingual view (c, d). a Left premaxilla, maxilla and dentary with the characteristic spatulate, massive crowns with wrinkled, black enamel, and smooth brown roots. Note that the size of the teeth towards the posterior decreases, and tooth asymmetry increases. b Close-up of the teeth in tooth positions left pm 2–4. c Lingual view of the teeth of the left dentary with the characteristic lingual ridge. Note tooth positions d3 and d6, where the functional teeth are no longer connected to the jaw bones and the replacement teeth are visible. The functional tooth in position 9 has been ejected. d Close-up the teeth from tooth positions left d2-4

In both the upper jaw and the lower jaw, the tooth crowns gradually and continuously decrease in size from anterior to posterior, being larger mesially and smaller distally (Fig. 4; Table 2). In the more mesial region, the apex of the crown is located directly apically to the base of the crown. Going to the more distal region, the apex is shifted more distally, giving the tooth an asymmetric, S-shaped appearance in mesiodistal view (Fig. 3). The teeth are aligned “en echelon”, i.e., the teeth are so closely spaced that the distal edge of one tooth overlaps the mesial edge of the succeeding tooth labially, fitting into a labial groove on the mesial edge of the crown. Another groove occurs on the distal edge of the crown; however, this is not as distinctive as the groove on the mesial edge. In rostral view, the mesial edges of the teeth appear convex labially, whereas the distal edge is straighter. This asymmetric feature makes it possible to assign isolated teeth to the right or left side of the jaw. The labial face of the crown is convex. The lingual face is concave and shows an apicobasal ridge flanked by a groove on both the mesial and distal side (Fig. 3). The crown apices are slightly curved lingually in the upper jaw, whereas those of the mandible are straight. This makes an assignment of isolated teeth to the upper vs. lower jaw possible.
Fig. 4

Graph of crown height vs. tooth position, illustrating the decrease in size of the tooth crowns in the jaws of Camarasaurus sp. SMA 0002 from mesial to distal

Both maxillae contain nine alveoli, which all contain functional teeth, with the exception of the right m8. The teeth become more asymmetrical towards the posterior end of the jaw because of the distal translocation of the apex. The lingual side of the teeth is more concave than that of the premaxillary teeth, and the degree of concavity increases from anterior to posterior. The lingual ridge of the maxillary teeth is more dominant than that of the premaxillary teeth. The crown height varies between 43.6 and 15.7 mm, and the crown width between 26.7 and 14.8 mm (Fig. 4; Table 2). The decrease in crown height in the maxillae is mostly regular from rostral to caudal, with some irregularities due to the different stages of wear. Note that the crown width of the right maxilla cannot be measured at positions 3, 4, and 6 to 8 because the teeth are still partially embedded in the matrix.

With 13 alveoli on both the left and the right side, the dentary contains the highest number of teeth among the dentigerous bones. The right dentary is shorter due to stronger deformation during burial (Table 1). Crown heights of the right dentary vary between 48.2 and 14.6 mm, and crown width between 29.4 and 11.3 mm; the crown heights of the left dentary vary between 42.5 and 13.8 mm, and the width of the crowns between 25.9 and 11.2 mm. Functional teeth can be seen in all positions except the left d9, right d11, and right d12. Replacement teeth can be seen in position left d9 and right d12. However, tooth position right d11 bears a functional tooth that is positioned in the jaw upside-down (Fig. 5). Possible explanations for this peculiarity are likely taphonomic in nature. Tooth position right m8 does not contain a functional tooth and shows an empty alveolus without any sign of a replacement tooth in the alveolus. Therefore, the inverted tooth in position right d11 could be the tooth from position right m8 that had separated from the jaw during burial and “slipped” into the alveolus upside-down. The length of the teeth adjacent to position right m8 coincides with the estimated length of the inverted tooth in position right d11. Therefore, it is likely that the inverted tooth is the dislocated tooth from position right m8. However, only a CT scan will provide more reliable information because the characteristic lower and upper dentition features are located on the tip of the crown, which resides in the alveolus. The inverted tooth was already observed when the jaws were taken out of the plaster jacket and during preparation (Dr. Ben Pabst, pers. comm.). However, the possibility that the tooth was placed incorrectly in the jaws during excavation cannot be excluded.
Fig. 5

Lingual view of tooth position right d11 of Camarasaurus sp. SMA 0002. The tooth in this position is upside down; the root (illustrated with R) is directed apically and the crown (illustrated with C) basally. The labial side of the tooth is directed lingually

The degree of concavity on the lingual side of the dentary teeth does not increase from anterior to posterior, unlike in the maxillary teeth. Tooth position left d3 shows an important feature: the root resorption has progressed heavily, so that the tooth is no longer anchored in the jaw, but it is still in situ with the adjacent teeth.

A dark carbonatious film, which was first observed during preparation of SMA 0002 covers an area of about 100 × 100 mm of the teeth on tooth positions 5–8 of the left dentary (Fig. 6) and was identified as a thin patch of preserved soft tissue remains. Soft part preservation is known from another specimen (Stegosaurus Victoria) from the locality where SMA 0002 E.T. was excavated (Siber and Möckli 2009). This patch covers the exposed parts of the roots, and large parts of the crowns of the teeth in these positions. A similar, but smaller patch can be found covering the teeth of positions 1 and 2 of the left dentary.
Fig. 6

Soft tissue patch on the left dentary of Camarasaurus sp. SMA 0002 in left lateral view. The patch covers tooth positions left d5–8 and presumably represents integumentary remains. A similar, smaller patch can be seen in tooth positions left d1–2

To permit the study of tooth replacement, the disarticulated interdental plates of the rostral part of the right were not reattached to the jaw during preparation (Dr. Ben Pabst, pers. comm.), leaving the roots of positions right d1–5. Thus, at these positions, the entire length of the roots can be observed, however only lingually. The roots are relatively short and massive, and the tips are slightly lingually curved.

Patterns of tooth abrasion

Tooth abrasion is an important character for determining jaw movement, food intake, and tooth replacement pattern. Various wear facets develop from the abrasive action of food on teeth and of teeth on teeth, as reviewed above. In this section, abrasion patterns due to tooth on tooth contact will be reconstructed for Camarasaurus sp. SMA 0002, using the nomenclature set up by Janensch (1935–1936) for Giraffatitan. This nomenclature was adopted since the close phylogenetic relationship between and Giraffatitan. All five abrasion stages are illustrated in Fig. 7.Camarasaurus
Fig. 7

Morphology of different abrasion stages observed in the dentition of Camarasaurus sp. SMA 0002. a Tooth left pm 1, abrasion stage F1: no wear facets can be observed. b Tooth right m3, abrasion stage F2: the occlusal wear facet has developed. c Tooth left m2, abrasion stage F3: the occlusal and the mesial or distal facet (here, mesial facet) have developed. d Tooth left m1, abrasion stage F4: all three wear facets have developed and are connected to each other. e Tooth left pm1, abrasion stage F5: All three wear facets have merged to form a large horizontal wear surface. f Tooth right m5, abrasion stage F3, showing the tear drop occlusal wear facet. The round margin of the tear drop wear facet is located on the apex of the tooth, the point of the tear drop wear facet runs down along the mesial edge of the tooth

Camarasaurus sp. SMA 0002 shows several teeth of wear stage F1 (Table 5). The wrinkled enamel surface (see Sander 1999 and Sander 2000 for a discussion of wrinkling) is still widely preserved on the teeth.

In Camarasaurus sp. SMA 0002, tooth positions left d12 and right m9 did not develop consistently with the F2 abrasion stage. Here, the distal wear facet is the first wear facet to have developed instead of the occlusal wear facet. These teeth were possibly displaced during life and, therefore, occluding slightly differently. As the lower anterior teeth ground against the lingual side of the upper anterior teeth, a steep and flat wear surface is produced, with an inclination towards the lingual side on the upper teeth, and a labial inclined wear surface on the lower teeth. Specimen SMA 0002 shows these features of wear stage F2 on tooth positions left m9, left d11, right m3, right d9, right d10, and right d13. Because the apices of the posterior teeth are displaced more lingually and distally, the areas of contact with the antagonistic teeth are larger. The occlusal wear facet appears tear drop-shaped (Fig. 7f), with the rounded edge of the drop located on the distal edge of the apex. The point of the tear drop faces mesially and represents the transition to the mesial wear facet. The enamel and dentin are both equally worn down. The polishing of the outer enamel surface, resulting in the removal of the wrinkles, has extended to 5–10% of the length of the crown as measured from the apex.

During stage F3, the mesial side of the upper teeth of Camarasaurus sp. SMA 0002, which is directed mesiolingually, grinds against the distal side of the lower teeth, which is directed distolabially, thus producing the mesial wear facet on the upper teeth and the distal wear facet on the lower teeth. An exception is position right m9, however, where the distal wear facet had developed first. In all teeth, the mesial wear facet expanded along the mesial side of the tooth crown as a long and slender surface that is slightly concave due to the more extensive abrasion of the dentine then that of the enamel. The distal wear facet of the lower teeth is more expanded along the edge of the tooth and more concave than the mesial one. The mesial wear facet is normally connected to the occlusal wear facet. The polishing of the enamel surface has increased to 10–25% of the length of the crown.

During wear stage F4, the distal wear facet develops on the upper teeth and the mesial wear facet on the lower teeth. The facets are similar in size but do not expand very far along the tooth edges. The polishing of the enamel surface has increased to 25–40% of the length of the crown.

The final stage, stage F5, is represented by tooth positions left m3, left d3, left d5, right m4, right d4, and right d7 (Table 5). The polishing of the enamel surface is at its highest, covering up to 40–55% of the tooth crown.

Root resorption

As noted, the roots of positions right d1–5 of Camarasaurus sp. SMA 0002 are visible because the disarticulated interdental plates were not reattached during preparation. This region reveals that as a tooth reached the end of its functional life, the replacement tooth pushed the worn-out tooth out of the alveolus from below. At this stage, the replacement tooth consist only of the tooth crown and the upper part of the root, indicating that root formation continued as the tooth entered use. Resorption of the root began on the lingual side of the root because this is where the replacement teeth are formed. The location of the initial resorption pit may vary from the base of the root to several milimeters higher. The initial resorption pit has an oval shape.

Root resorption of the teeth in positions 4 of the right dentary and 3 of the left dentary had progressed so much that the teeth were no longer anchored in the jaw. However, these teeth are still in their proper position within the tooth row. A possible explanation for this could be that gingival connective tissue held the teeth in place (see discussion on soft part preservation).

Replacement dentition

The replacement dentition of SMA 0002 can only be described from a few positions. These include the aforementioned positions 1–5 of the right dentary (Fig. 8), positions 3, 6, and 9 of the left dentary, and position 12 of the right dentary. The latter are also examples of the loss of functional teeth revealing at least the tip of the replacement teeth in the alveoli. Note that only the lingual side of the replacement dentition of SMA 0002 can be described, because the labial side is not exposed.
Fig. 8

Photograph of the replacement dentition of the right dentary of Camarasaurus sp. SMA 0002 in lingual view. The interdental plates on the lingual side of the right dentary were partially removed, which leads to visualization of the replacement dentition in tooth positions right d1–5. Here, only positions right d2–4 can be seen

In positions 1, 3, 4, and 5 of the right dentary, both functional and replacement teeth are preserved, and tooth position 2 only holds a functional tooth. The replacement teeth are all of the stage R0, indicating that they are set too deep in the jaw to protrude beyond the alveolar margin. In positions 1 and 4, the apex of the replacement tooth is located at the same level as the root of the functional tooth. In positions 3 and 5, the apex of the replacement tooth is separated from the root of the functional tooth by approximately 5 mm. A possible explanation for this gap could be that root resorption advanced more rapidly than replacement tooth formation. Alternatively, the gap was caused by post-mortem dislocation of the teeth.

The replacement teeth in positions 3, 6, and 9 of the left dentary can be assigned to growth stage R2, being fully erupted in their alveoli and showing approximately half of the crown. The tooth in position 9 is most advanced, followed by position 3. In positions 3, 6, and 12, the functional teeth are still in place, whereas in position 9, the functional tooth has already been ejected. The functional tooth must have been ejected due to extensive resorption of its root. This thus represents the earliest stage at which a functional tooth is lost due to resorption because in positions left d3 and left d6, the replacement teeth under the functional teeth has not erupted as far as this tooth, i.e., left d9. Due to the fact that the replacement tooth in position 9 has not yet fully erupted, it is not yet a functional tooth. Tooth position 12 of the right dentary contains a replacement tooth of stage R1, in which only the tip of the crown has erupted.

The general features of the replacement dentition coincide mostly with those of the functional dentition. Slight differences include teeth that only consist of the tooth crown, the intensity of the wrinkling on the enamel surface is higher in the replacement teeth than in the functional teeth, the apex of replacement teeth is slightly distally curved, and in growth stage R0 the replacement teeth appear to be more labioligually flattened than the functional teeth. This may be because the pulp cavity may not have been filled with dentin completely, making the tooth more susceptible to crushing and flattening during fossilization.

Z-spacing

Camarasaurus sp. SMA 0002 shows a well-organized tooth replacement. The Z-spacing (Edmund 1969; Whitlock and Richman 2013; Schwarz et al. 2015) varies between 2.0 and 3.0 (Fig. 9), which correlates with the values established for most reptiles by DeMar (1972). Notably, an increase in Z-spacing is observed from the anterior to the posterior teeth (Edmund 1960), which can be related to a higher replacement rate in the anterior dentition due to increased usage, causing these teeth to wear faster. If Z > 2, the replacement wave proceeds from posterior to anterior; if Z < 2, it procedes from anterior to posterior; and if Z = 2, all teeth of the even and odd tooth positions will be replaced at the same time (Osborn 1970). In specimen SMA 0002, the Z-Spacing is >2, so replacement proceeds from posterior to anterior.
Fig. 9

Graphs showing the different abrasion stages (F stages) for all tooth positions of the premaxillae, the maxillae, and the dentaries of Camarasaurus sp. SMA 0002. The Z-Spacing, i.e., the number of tooth positions located between two teeth of the same abrasion stage, was calculated from these graphs

Discussion

Comparison with other individuals of Camarasaurus and with Giraffatitan, Europasaurus, and other basal macronarians

For comparison, apart from other Camarasaurus individuals, the dentition of Giraffatitan and Europasaurus were observed firsthand. These are the two taxa most closely related to Camarasaurus for which dentitions are known, the two sistertaxa from Camarasaurus in the macronarian phylogeny (Yates et al. 2010; Zaher et al. 2011; D`Emic 2012; Carballido and Sander 2013; Sander 2013). However, since Camarasaurus is a basal macronarian, basal neosauropods and derived non-neosauropod eusauropods (such as Shunosaurus and Mamenchisaurus) as well as basal members of the Diplodocoidea seemingly would have to be considered as well. All, apart from the Diplodocoidea, possess broad-crowned spatulate teeth, which is the plesiomorphic condition in sauropodomorph tooth shape (Barrett and Upchurch 2005; Whitlock 2011; D’Emic et al. 2013). Diplodocoidea tooth shape is narrower and more derived (Whitlock 2011).

Comparison with other specimens of Camarasaurus

This comparison primarily relied on the literature (Calvo 1994; Madsen et al. 1995; McIntosh et al. 1996; Chatterjee and Zheng 2005; D’Emic et al. 2013), although isolated shed teeth of Camarasaurus were studied firsthand at the Dana Quarry during the excavations of 2011–2013 organized by the Sauriermuseum Aathal, Switzerland.

McIntosh et al. (1996) describe the dentition of Camarasaurus grandis as homodont, spatulate, larger in size anteriorly, and becoming smaller posteriorly. They state that the teeth from the upper jaws are more robust than those of the lower jaws. McIntosch compared the skull of Camarasaurus grandis GMNH-PV 101 with the skull of a juvenile Camarasaurus sp. (CMNH 11338) and found no significant differences between the two. The dentition of Camarasaurus lentus (DINO 28) was described by Chatterjee and Zheng (2005) as homodont with massive, transversaly expanded spatulate teeth.

The tooth formula of Camarasaurus sp. specimen SMA 0002, pm4 + m9/d13, is consistent with the general tooth formula previously described for Camarasaurus sp. as pm4 + m8-10/d11-14 (Janensch 1935–1936; Madsen et al. 1995; Christiansen 2000; Chatterjee and Zheng 2005). Tooth formulas of other Camarasaurus species are: Camarasaurus grandis (GMNH-PV 101): pm4 + m10/d14, Camarasaurus sp. (CMNH 11338): pm4 + m8-9/d12-13 (both taken from McIntosh et al. 1996), Camarasaurus lentus (DINO 28): pm4 + m10/d12 (taken from Chatterjee and Zheng 2005). Intraspecific and intrageneric variability in tooth formula has been described for other sauropods by Janensch (1935–1936) as well as for Camarasaurus sp. by McIntosh et al. (1996) and Europasaurus by Régent (2011).

The studied isolated shed teeth, which were found by the Sauriermuseum Aathal in the Dana Quarry, Wyoming, and probably belong to different individuals of Camarasaurus, show that, in mesial or distal view, the long axis of the roots of the premaxillary and maxillary teeth runs fairly straight from the middle of the crown nearly to the tip of the root. However the apex of the crown is curved lingually, as is the root tip. Therefore, the labiolingual axis forms a C-shape. This can also be seen in Fig. 2 of D’Emic et al. (2013). The C-shape cannot be seen in the dentary teeth, and their labiolingual axis remains straight, making a distinction of teeth from the upper and lower dentitions possible. This distinction probably applies to Camarasaurus sp. SMA 0002 as well, since both the isolated teeth and the premaxillary teeth of the skull studied by D’Emic et al. (2013) show C-shaped roots. However, a CT scan would be required to test this hypothesis since the roots of the teeth are still in the jaws.

In general, the morphology of the dentition of Camarasaurus grandis (GMNH-PV 101), Camarasaurus lentus (DINO 28), and that of another Camarasaurus species which does not differ from that of Camarasaurus sp. SMA 0002; therefore, Camarasaurus sp. specimen SMA 0002 is presumably representative of the genus Camarasaurus.

Comparison with Giraffatitan and Europasaurus

While the general morphology is roughly the same, some differences can be seen in the tooth formula and in the morphology of the teeth of the three taxa Camarasaurus, Giraffatitan, and Europasaurus. The tooth formula of Giraffatitan and Europasaurus are relatively similar; both have more maxillary teeth than Camarasaurus. The formula of Giraffatitan is pm4 + m11-13/d12-14 (Janensch 1935–1936; Christiansen 2000), and that of Europasaurus is pm4 + m12/d13–14 (Régent 2011). The number of premaxillary and dentary teeth is similar in all three taxa. In the Giraffatitan skull MfN S116, a rare asymmetry can be observed: the number of dentary alveoli (and teeth) of the left lower jaw differs from that of the right lower jaw (14 in the left and 15 in the right). This is not observed in the Europasaurus material nor the Camarasaurus sp. SMA 0002.

As in all basal macronarians, the three taxa possess spatulate teeth, being mesiodistally broad, labiolingually compressed, and possess a slightly lingually curved apex. The main morphological differences in the teeth of the three taxa are the slenderness index, the denticles, and abrasion type. The teeth of both Giraffatitan and Europasaurus appear more slender than the teeth of Camarasaurus. The SI of Giraffatitan (Chure et al. 2010) and Europasaurus (Régent 2011) varies between 2.5 and 3.0, and that of Camarasaurus species varies between 1.0 and 2.0. The lingual ridge is present in both Giraffatitan and Europasaurus, but not as well developed as in Camarasaurus. The lingual grooves on the sides of the ridge are also present in all three taxa. The upper teeth of Giraffatitan and Europasaurus are lingually curved; the lingual side is concave, giving the teeth an asymmetrical appearance and a D-shaped cross section. In Europasaurus, small depressions in the enamel on the labial side of several teeth can be seen on the base of the crown, which are not present in Giraffatitan and Camarasaurus. The labial grooves are more prominent on the distal side of Giraffatitan and Europasaurus teeth, whereas the grooves on the mesial side are hardly recognizable, if at all, in Camarasaurus. Denticles are known from both Giraffatitan and Europasaurus; however, they are better developed in Europasaurus than Giraffatitan, but completely lacking in Camarasaurus. The teeth of all three taxa possess a wrinkled outer enamel surface, Camarasaurus having the most prominent wrinkling.

Because of their “en echelon” alignment, the teeth are very closely spaced in Camarasaurus sp. The spacing of the teeth of Europasaurus is similar to that of Camarasaurus sp. The teeth of Giraffatitan, however, are more widely spaced in the jaw, leaving gaps between the teeth, which can be observed in specimen MfN t1, “ITR” MfN WJ 4170, and several other partial “ITRs” (MRB 2181.23.4, MRB 2181.23.2, and MRB 2181.23.1) that consist of two teeth. “ITRs” are sets of articulated teeth preserved with little or no surrounding dentigerous bone (Britt et al. 2008). Even though the teeth are not contacting each other, the labial grooves making the “en echelon” alignment possible in the two other taxa, are present in Giraffatitan as well. In all three taxa, the teeth are sticking out of the jawbones, leaving the upper part of the roots exposed. In certain teeth of both Camarasaurus sp. SMA 0002 and Europasaurus, root resorption has progressed so heavily that the roots are no longer anchored in the jaw, but the teeth are still in place. This feature suggests the presence of strong connective tissue, holding the rootless teeth in place. Giraffatitan skull MfN t1 does not show this feature. However, several Giraffatitan “ITRs” that were studied, including “ITR” MfN WJ 4170, and the Europasaurus “ITR” (DfmMh/FV 580.1), show teeth which are aligned as if they were still located in the jaw, but no bone has been preserved. These “ITRs,” therefore, also indicate the presence of connective tissue, holding the teeth in place in the ITR after their postmortem separation from the jaw bone, including the rootless teeth.

Two types of abrasion exist in sauropod dentitions: type A and type B (Saegusa and Tomida 2011, Fig. 10). Teeth of Camarasaurus sp. show abrasion of type B, in which the wear facets develop along the mesial and distal edges of the crown. The teeth of Giraffatitan show abrasion of type A, which produces a larger, flat wear surface on the apex of the crown (Saegusa and Tomida 2011). The wear surface does not, or only very late in tooth development, spread to the mesial and distal edge of the teeth. Europasaurus shows signs of both abrasion types.
Fig. 10

Two types of abrasion in the sauropod dentition. Type A has a larger, flat wear surface on the apex of the crown. In type B, the wear facets extend alongside the mesial and distal edge of the crown. Camarasaurus sp. SMA 0002 shows abrasion of type B (modified from Saegusa and Tomida 2011)

Tooth replacement pattern in Camarasaurus sp. SMA 0002

Polyphydonty, the condition of having continuous tooth replacement, is plesiomorphic for tetrapods, and this has been recognized for over 150 years (Owen 1840–1845; D’Emic et al. 2013). As can be seen in CT sections of a Camarasaurus premaxilla (D’Emic et al. 2013), and also in Camarasaurus SMA 0002 E.T., the replacement of a worn-out functional tooth is caused by the growing replacement tooth pressing against the lingual wall of the functional tooth. The slightly conical shape of the replacement teeth of SMA 0002 forces the functional teeth anteriorly and then out of the socket. The replacement teeth move from the lingual base to the labial margin of the jaw bones (D’Emic et al. 2013). In neosauropods, including Camarasaurus, teeth are organized into tooth families, where there is more than one replacement tooth being formed at the same time, each younger tooth forming lingually from the older one (D’Emic et al. 2013). This feature unfortunately cannot be observed in Camarasaurus SMA 0002 E.T., since only the first replacement tooth is visible.

In reptiles, it has long been noted that teeth typically become replaced in an alternating fashion. However, subtle differences in the timing of those replacements between rostral and caudal teeth exist. Edmund (1960) noted that this pattern of replacement happens in “waves” or “Zahnreihen”, such that tooth germination generally propagates from distal to mesial (D’Emic et al. 2013). This is also the case for Camarasaurus.

Reconstruction of soft tissue

Arguably the most peculiar fossils of sauropod dinosaurs are their “ITRs”. “ITRs” are reported across the sauropod phylogeny, from their most basal record in the basal eusauropod Shunosaurus (Chatterjee and Zheng 2002), to diplodocoids such as Apatosaurus (a specimen from Dana Quarry, Wyoming; Gael Summer, pers. comm.) and basal macronarians such as Europasaurus (Régent 2011), Abydosaurus (Chure et al. 2010), and Giraffatitan (Janensch 1935–1936), and even titanosaurs (Phuwiangosaurus, pers. comm. V. Suteethorn). As noted, no “ITRs” are known for Camarasaurus despite the abundance of skull material of this genus. To explain the “ITRs”, Britt et al. (2008) suggested that osseophagous insects consumed the dentigerous bones, leaving the teeth untouched in their life position. However, this hypothesis can be rejected based on a Europasaurus skull, of which the teeth were found in the process of separating from the jaw bones that were fully intact and show no signs of insect damage (Régent 2011).

Another explanation is a process observed in the taphonomy of whales. Schäfer (1962) described that during the mummification of a porpoise, the teeth, together with the gingiva and the periosteum, were pulled out of the alveoli because of shrinkage of the soft tissues caused by strong desiccation. A similar process acting on sauropod dentitions would separate the teeth from the jaw bone while keeping the teeth in the correct position.

A third hypothesis, which does not contradict Schäfer’s hypothesis (1962), is proposed here, which is the presence of a beak-like structure made of gingival connective tissue and keratinous tissue that led to a wholesale postmortem separation of the entire functional dentition. The dentition of SMA 0002 permits the evaluation of this hypothesis, because the functional teeth in positions 3 and 6 of the left dentary and positions 4 and 8 of the right dentary are barely or not at all anchored in the jaw bones, but are still in place. This observation can only be explained by the presence of some type of soft tissue that held the teeth in place and kept them functional in the dentition after they lost contact with the jaw bone. The presence of connective tissue in a beak-like structure would have provided stability for the rootless teeth, because such teeth would have been immediately shed once their roots had been resorbed.

Another piece of evidence is provided by extensive exposure of the roots above the jaw bone in SMA 0002, in other specimens of the genus, protruding beyond the jaw bones 20 mm on average, as well as in Europasaurus and Giraffatitan. Such exposure of the sensitive and soft roots has not been observed in basal sauropodomorpha, theropods, and ornitischians. The exposed roots would, therefore, indicate a thick cover of tough gingiva. The labial side of the gingiva may well have been covered by a keratinous beak or large scales. The pattern of wear of the wrinkled enamel surface of the teeth of Camarasaurus sp. SMA 0002 indicates that at least half of the crown was protected from wear before the tooth was shed, which is consistent with the gingiva and beak extending onto to the crown, with only the tip of the tooth crowns protruding from the soft tissue. The strong wrinkling could have served in mechanically improving the attachment of the soft tissue to the outer enamel surface. Direct evidence for the “beak” is seen in the patches of soft tissue (Siber and Möckli 2009) preserved on the left dentary of SMA 0002 which partially cover the tooth crowns and not only the roots. The function of the “beak” would have been to provide protection from abrasive plant matter during feeding and to provide a continuous cutting surface minimizing the gaps caused by tooth replacement. Evidence for the presence of such a “beak” in many sauropods may also be provided by the extensive vascular foramina and vascular grooves of the labial surface of the jaw bones (e.g., Chatterjee and Zheng 2005; D’Emic et al. 2013 for Camarasaurus, and Zaher et al. 2011 for Tapuiasaurus).

Conclusions

This study provides a detailed characterization of the morphology, wear, and function of the dentition of the genus Camarasaurus based on an exceptionally well preserved individual, SMA 0002, on display in Sauriermuseum Aathal, Switzerland. Camarasaurus possesses spatulate teeth that are slightly lingually curved and transversely expanded. Its teeth decrease in size and increase in asymmetry from anterior to posterior. The mesial edges of the teeth of Camarasaurus are more convex, the distal edge of the teeth is more straight. This feature makes it possible to assign isolated teeth to the right or left side of the jaw. Like in Giraffatitan and Europasaurus, the teeth of the upper jaw are C-shaped due to the lingually curved apex and root. The teeth in the lower jaw are straight, making differentiation between teeth from the upper and lower dentitions possible. Abrasion of the teeth can be observed in five different stages based on three wear facets. The wear facets also allow identification of upper and lower dentition because the wear facets of the upper teeth are directed lingually, those of the lower teeth labially. Features of the dentition of Camarasaurus sp. SMA 0002, as well as preserved soft tissue suggest the possible presence of a beak-like structure of gingival connective and keratinous tissue partially covering the tooth crowns which would have stabilized the dentition. Such a “beak” may have been widespread among sauropods.

Acknowledgements

Our foremost thanks go to Dr. Hans Jakob “Köbi” Siber, director, and Dr. Thomas Bolliger, vice director of the Sauriermuseum Aathal, Switzerland, for collaboration and granting us access to the Camarasaurus sp. SMA 0002. Furthermore, we would like to thank Dr. Ben Papst and Dr. Emanuel Tschopp for providing detailed information about SMA 0002. Many thanks go to Nils Knötschke from the Dinopark Münchehagen, Germany, and Dr. Oliver Wings, formerly at the Museum für Naturkunde, Berlin, Germany, for allowing us to study the Europasaurus and Giraffatitan material under their care. Special thanks go to Dr. Heinrich Mallison for providing the photogrammetric 3D model of the skull of SMA 0002. Members of the DFG Research Unit 533 “Biology of the Sauropod Dinosaurs” are greatly acknowledged for inspiring discussion, especially Katja Waskow and Jessica Mitchell. Special thanks go to Verena Régent for providing access to her unpublished diploma thesis. Funding of this project was provided through DFG grant SA 469/19. This is contribution number 167 of the DFG Research Unit 533 “Biology of the Sauropod Dinosaurs. The Evolution of Gigantism”.

Copyright information

© Paläontologische Gesellschaft 2016

Authors and Affiliations

  1. 1.Steinmann Institute of Geology, Mineralogy and Paleontology, Rheinische Friedrich-Wilhelms-Universität BonnBonnGermany