The pneumatopore is above this ridge, 16 mm anterior to the acetabulum. The more ventral ridge extends to a tubercle on the anterior rim of the acetabulum, here called the preacetabular tubercle. iliotrochantericus (ITC Fig. 5), but also bears a pneumatopore ( Fig. 2A) and two ridges. The lateral surface of the preacetabular process ( Fig. 4A) was occupied mostly by the origin of M. The preacetabular process of the ilium tapers anteriorly in both lateral ( Fig. 2A) and dorsal views ( Fig. 2D). Accordingly, the bone bed is here interpreted as a channel lag deposit channel lags commonly host bone beds in the DPF ( Eberth 2015). This taphonomic variability is likely evidence of a time-averaged assemblage of reworked skeletal material. In contrast, the presence of teeth in hadrosaur and crocodylian mandibulae, combined with fine preservation of small theropod elements, suggests that those elements were buried rapidly without significant weathering or transport. Abrasion on UALVP 56200 suggests that it was either transported a long distance or subjected to rapid flow velocities when recovered, it was in contact with an even more weathered fragment of hadrosaur cancellous bone. Fossils in the bone bed are disarticulated and generally well preserved, but taphonomic signatures are conflicting. The fossil assemblage of BB151 is composed of a variety of micro- and macrofossils including ceratopsians, champsosaurs, crocodylians, hadrosaurs, and theropods. The bone bed occurs at the base of an intermittently sideritized, cross-bedded, medium-grained sandstone overlying a grey mudstone. UALVP 56200 was recovered from a dense multitaxic bone bed (BB151) in the lower part of the Upper Campanian (∼ 75 ma) DPF near Steveville, Alberta. Measurements were taken using digital calipers with an accuracy of 0.05 mm. The specimen was photographed using a Nikon D7200 with a 50 mm lens ( Figs. 2A– D, F), or with a Nikon D5000 with an 18–55 mm lens ( Figs. 2E, 3). The estimates presented are, therefore, conservative minimum estimates of ASP. The bone enclosing the large dorsal pneumatic spaces is broken, so the volume of this cavity was not estimated, but it would have increased the ASP considerably. Subsequently, a second estimate was generated based solely on sandstone-infilled spaces, which were easier to determine unequivocally. All internal regions of low density were manually segmented in Mimics 14.0, which automatically calculates mesh volume. Cavities infilled with sandstone were significantly less dense than surrounding bone, but because of the similar densities of the bone and ironstone matrix, determining the boundaries of ironstone-infilled cavities was difficult. However, UALVP 56200 was preserved in two types of matrix: soft, medium-grained sandstone and well-indurated siderite ironstone. Pterosaur material from the DPF, therefore, may represent as many as four different taxa.ĬT reconstruction of pneumatic spaces allowed estimation of volumetric air-space proportion (ASP). Despite the considerable geographic distance, it is conceivable and has been previously suggested ( Habib 2010) that, as volant animals, azhdarchids could disperse over such a large area. However, Sullivan and Fowler (2011) suggested that both wing phalanges IV-1 collected from the DPF were referable to Navajodactylus from the Kirtland Formation of New Mexico. In most cases, a lack of autapomorphic characters in the elements from the DPF prevents their assignment to these other taxa. A partial skeleton described by Currie and Jacobsen (1995) represents an intermediately sized individual (wingspan 6 m), although they point out that this individual was immature.
1995), although the azhdarchid identity of that genus is uncertain ( Carroll 2015). Godfrey and Currie (2005) suggested that the smallest azhdarchid material from the DPF is probably Montanazhdarcho ( Padian 1984 Padian et al. It has also been suggested that this element is a large, poorly preserved cervical vertebra ( Godfrey and Currie 2005 M Habib, personal communication, 2016). Others ( Padian and Smith 1992 Averianov 2014) have argued that TMP 1980.016.1367 is in fact a wing element and, therefore, represents a smaller individual, similar in size to Quetzalcoatlus northropi from Texas. If this bone is indeed a femur that individual would have had a wingspan of up to 13 m.
The largest of the azhdarchids is represented by a large limb bone (TMP 1980.016.1367) that Currie and Russell (1982) suggested was a femur. Godfrey and Currie (2005) suggested that, because of the widely disparate sizes of identifiable elements, up to three azhdarchid taxa may have coexisted.
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