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© 2010 Dinosauria International Ten Sleep Report Series No. 1 Sauropodomorph incertae sedis. However, if the holotype can be shown to be part of a more complete individual with definable specific diplodocid characters, then the genus name Apatosaurus may have priority over Amphicoelias. But as a fragmentary sacrum the type can only be judged nomen dubium. Fig 29 Illustration of AMNH 223 after Osborn 1900, in this study referred to Amphicoelias altus, exhibits elongated prezygapophyses not seen in A. “brontodiplodocus”. long quadrate from Quarry 10, places this cranial material outside the size range of the holotype sacrum. In comparison with the sacrum belonging to the type of A. lousiae, the quadrate would represent an individual approximately half the size. The size of the quadrate in the “probable skull” belonging to A. lousiae, is 18.5 cm (7.28 inches) . According to Ostrom and McIntosh (1966), Quarry 10 has produced the remains of three sauropod skeletons – Atlantosaurus immanis, Apatosaurus laticollis and A. ajax. So, it does not seem possible that the holotype of A. ajax can ever be sorted reliably. Furthermore, it is not clear if the collection from Quarry 10 belongs to one taxon or a mixture. Apatosaur cervical vertebrae and limbs are often mistaken for bones of Camarasaurus, and vice versa, which may be the case in the type of A. ajax. A point of similarity between Camarasaurus and the type of A. ajax has not been addressed. The illustrations in Marsh 1896 of D. longus (pl xxv111), Morosaurus lentus (pl XXX111), Atlantosaurus montanus (pl XV11), and Ostrom & McIntosh (1966) of A. amplus YPM 1981 type, Brontosaurus excelsus YPM 1980, and Morosaurus grandis YPM 1900, reveal an interesting disparity in the relative proportional lengths of S 2 and S 3 against S 4 in the sacrum. Other differences include the ventral shape of the centra, which are broadly rounded in Camarasaurus in contrast to the distinct keeling in specimens referred to as Diplodocus. In “Morosaurus”, S 2-4 are nearly equal in overall size and ventral lengths, whereas, in the other specimens S 4 is proportionately larger compared with the adjoining S 2 - S 3. The holotype of A. ajax YPM 1860 is more similar to Camarasaurus (Morosaurus) in this aspect. Furthermore, Marsh (1877) stated that both type specimens of A. ajax and Camarasaurus (Morosaurus) grandis originated from the same locality. Thus, reexamination is urgent. The type needs to be compared and described properly to resolve these issues. The taxonomic status of A. ajax can be presently considered Notwithstanding the taxonomic status of Apatosaurus ajax, the description of the genus essentially rests on two specimens, the holotype skeleton of Apatosaurus louisae (Holland 1915) and the mounted skeleton of Brontosaurus excelsus (Como Bluff, YPM 1980 and YPM 4633). A. louisae is by far the most widely acclaimed example and is on exhibit at the Carnegie Museum of Natural History. The B. excelsus skeleton is mounted and exhibited at the Yale Peabody Museum. Despite the familiarity of these Apatosaurus specimens, various aspects of the skeleton remain poorly known, particularly the cervical vertebrae. Riggs (1903) and Upchurch et al (2004b) have described reasonably complete specimens, but in these specimens the cervical series are as incomplete and fragmentary as the Peabody and American Museum B. excelsus skeletons. In fact, the cervical vertebrae which form part of the type of A. louisae, were not found directly articulated to the dorsals and may have been from a different individual. Moreover, the posterior vertebrae C 13-15 are badly crushed and modeled plaster reconstructions are mounted on the skeleton and illustrated in Gilmore’s (1936) description. Proportions and lack of certain diplodocid details, e.g., a transverse central buttress (Berman and Rothschild 2005), gives more the impression of a camarasaurid than a diplodocid morphology. It should be pointed out that these cervical vertebrae were reconstructed during a time when ideas of Morrison sauropod relationships were vague and not widely accepted, so the reconstruction may be incorrect. It is not possible to judge the length of C 14 against C 15 and the relation to the first dorsal. Verification of an anterior rib process is also lacking. As a result, generic and species level diagnoses remain vague particularly in the cervical region. Another feature indicating that the cervicals may be incorrectly reconstructed and misleading is the noticeably short centrum length of C 14 in A. louisae. Comparisons with specimens preserving the required articulation show that the 14 th cervical vertebra is the longest in the series and is an Amphicoelias synapomorphy. If the cervicals are correctly reconstructed in A. louisae then it is suspect whether they belong to one individual or represent an aberrant form that displays an abnormal cervical skeleton. An aberrant individual is suggested by the odd fact that no other skeleton preserving similar associated cervicals has been reported belonging to A. louisae. Osborn & Mook (1921) observed little difference in the cervical vertebrae between Camarasaurus and Apatosaurus, which may have led to reconstructing the 34
Amphicoelias “brontodiplodocus” Galiano and Albersdörfer AMNH “Brontosaurus” skeleton with a camarasaur-like skull. They stated on page 291: “In form, the cervicals of Camarasaurus resemble very closely those of Apatosaurus but appear to be slightly more massive. The cervical ribs in Camarasaurus are much longer than those of Apatosaurus, and it also appears that the neck was relatively broader than in that genus.” Cervical rib length and proportions are a variable ontogenetic and gender related characters, which can be seen in A. “brontodiplodocus”. If this condition also applies to Camarasaurus, then the associated cervicals in Apatosaurus skeletons may be held in question. One observation should be clear. The post cervical skeleton of Apatosaurus represents one of the two morphs that occur frequently in the same sites together with Diplodocus morphs. The apatosaur morph displays a massive skeleton with thicker limbs, less pneumatic axial skeleton and shorter tail by contrast with the other morph or diplodocoid. The diplodocoid displays delicate skeleton, slender limb bones, highly pneumatic axial skeleton, and a proportionately longer tail. These morphs are identified as male and female respectively and this sexual dimorphism is an important autapomorphy in Amphicoelias. These morphs all share the same uniquely derived characters, which can best be interpreted as representing a single species displaying sexual dimorphism. In addition, to the well known post cranial similarities, the cranial morphological characters described and compared by McIntosh and Berman (1975) and Berman and McIntosh (1978) furthermore support convincingly the phyletic closeness of Apatosaurus and Diplodocus. The type skeleton Apatosaurus louisae (Holland 1915) was discovered in Dinosaur National Monument, Utah in the same quarry that produced the Barosaurus lentus (AMNH) and D. longus (USNM) specimens discussed above. The skeleton of Apatosaurus louisae was found together with other skeletons in overlapping positions. One of these other skeletons was identified as Diplodocus, and the other, a juvenile Apatosaurus. There is corroborative evidence of the same assortment of diplodocid morphotypes occurring directly together as they do in the Dana Quarry. Suuwassea emilieae (Harris and Dodson 2004) The type of Suuwassea emilieae, ANS 21122, is a partial skeleton (Harris and Dodson 2004, Harris, 2006a, 2006b, and 2007) collected from the lower part of the Morrison Formation in Carbon County, Montana, which warrants comparison with A. “brontodiplodocus”. Amphicoelias “brontodiplodocus” differs from Suuwassea emilieae, by lacking the following characters: no post parietal foramen, “optic” foramen not conjoined, neural spine bifurcation past C 9 and neural spines anteriorly positioned on cervical centra C 3-5. Of the four braincases comprising the Dana sample of 35 A. “brontodiplodocus”, a post parietal foramen is not present in the two adult braincases which have been prepared. In S. emailieae, the ball or convex joint in the whiptail caudal vertebra is not developed and the disproportionate large size of the scapula suggests that the specimen is an immature individual. Based on the hour-glass shaped humerus, and tall neural spines on the cervical vertebrae, the individual may have been male. Otherwise, all the other elements referred to Suuwassea emilieae compare favorably to Amphicoelias “brontodiplodocus” Therefore, the genus Suuwassea is referable to Amphicoelias, but the species A. emilieae may be kept in validity until further comparisons can be made. Eobrontosaurus yahnahpin (Filla and Redman 1994) The type specimen of Eobrontosaurus yahnahpin originates from the Bertha Quarry in the eastern part of the Como Bluff area in Wyoming. Comparison with the type of Eobrontosaurus yahnahpin from its description Filla and Redman (1994) and a cast of the hind leg in the exhibit collection at the Black Hills Institute in Hill City, SD, suggests that it is a small or young male individual of Amphicoelias. The ossified sternal ribs are also very similar in this specimen to ones preserved in DQ-EN. Both E. yahnahpin and specimens from the Dana locality display a clearly excessive rugose bone growth not seen in female examples. Therefore, a rugose sternal rib appears to be a diagnostic male feature. Sternal ribs in female examples are long and thin with smooth surfaces (Fig A) and (Marsh 1896, Figs. 12-15, “Brontosaurus excelsus”). Tornieria africana (Frass 1908) The Tendaguru species, Tornieria africana, is based on poorly documented isolated bones of uncertain association (Remes 2006) . Many of the described features point to both Apatosaurus and Diplodocus morphotypes, suggesting that it may represent a composite taxon. These characters include: robust distal ischium, distal scapula without expansion, flattened femur, short tibia and fibula, and broad humerus. In Tornieria africana, the illustrated (Remes 2006) caudal vertebrae are excavated ventrally, recalling adult Diplodocus and Barosaurus, which we also have seen is a variable character in the Dana sample of Amphicoelias “brontodiplodocus” The Tornieria africana bones appear to represent a composite of male and female morphotypes that need to be better characterized by more complete material. In Tornieria (Upchurch 1999) the preantorbital fenestrae are positioned immediately behind the last maxillary tooth, a similarity shared with Amphicoelias. Therefore, material referred to the genus Tornieria should be compared in light
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