Osteology of <i>Huabeisaurus allocotus</i> (Sauropoda: Titanosauriformes) from the Upper Cretaceous of China

<div><p>Background</p><p>The Late Cretaceous titanosauriform sauropod <i>Huabeisaurus allocotus</i> Pang and Cheng is known from teeth and much of the postcranial skeleton. Its completeness makes it an important taxon for integrating and interpreting anatomical observations from more fragmentary Cretaceous East Asian sauropods and for understanding titanosauriform evolution in general.</p><p>Methodology/Principal Findings</p><p>We present a detailed redescription of <i>Huabeisaurus allocotus</i> and a suite of anatomical comparisons with other titanosauriforms that demonstrate its validity via autapomorphies (e.g., division of some presacral vertebral laminae, reduced development of caudal ribs, the development of fossae relative to one another in caudal vertebral neural arches, high tibia-to-femur ratio). <i>Huabeisaurus</i> shares many features with other Cretaceous East Asian sauropods (e.g., pendant cervical ribs, anterior-middle caudal vertebrae with a nearly flat anterior centrum face and a concave posterior centrum face) that are absent in sauropods from other landmasses and strata, suggesting a close relationship among many of these forms within the clade Somphospondyli.</p><p>Conclusions/Significance</p><p>Restudy of <i>Huabeisaurus</i> provides further evidence for the existence of a clade of somphospondylans – Euhelopodidae – mainly found in the Cretaceous of East Asia. Euhelopodidae represents a fourth example of the evolution of narrow crowns within Sauropoda, along with diplodocoids, brachiosaurids, and advanced titanosaurs (lithostrotians). Despite being known from fewer species than Diplodocoidea, Brachiosauridae, or Lithostrotia, euhelopodids possessed a broader range of tooth shapes than any of these clades, suggesting that euhelopodids exemplified a comparably broad range of feeding strategies and perhaps diets.</p></div

Holotypic left tibia of <i>H. allocotus</i> (HBV-20001) from the Upper Cretaceous of Shanxi, China.

<p>In (A) lateral view during original preparation, (B) medial view during preparation, (C) lateral view in 2012, (D) medial view in 2012, (F) anterior view in 2012, (G) posterior view in 2012. Twisting arrow indicates that the tibia has been incorrectly restored (views C–D) by ‘twisting’ (breaking and re-gluing/plastering) since original preparation. <i>Abbreviations: ccr, cnemial crest.</i> Striped pattern indicates broken surface, dashed lines indicate broken bone margins.</p

Holotypic middle caudal vertebrae of <i>H. allocotus</i> (HBV-20001) from the Upper Cretaceous of Shanxi, China.

<p>In (A) anterior; (B) posterior, (C) left lateral, (D) right lateral, (E) dorsal, and (F) ventral views. Ninth, eleventh, twelfth, seventeenth, eighteenth, and nineteenth caudal vertebrae are depicted from left to right in each row. <i>Abbreviations: cf, chevron facet; pocdf; postzygapophyseal centrodiapophyseal fossa; posdf, postzygapophyseal spinodiapophyseal fossa, ri, ridge.</i> Striped pattern indicates broken surface; dashed lines indicate broken bone margins.</p

Holotypic left radius of <i>H. allocotus</i> (HBV-20001) from the Upper Cretaceous of Shanxi, China.

<p>In (A) proximal, (B) anterior, (C) lateral, and (D) posterior views. Silhouette between (C) and (D) shows schematic cross section of the diaphysis. (A) photographed in 2012; (B–D) photographed during original preparation. <i>Abbreviations: gl, glenoid; igl, infraglenoid lip; tu, tubercle.</i> Dashed lines indicate broken bone margins.</p

Measurements of the pelvic girdle elements of <i>Huabeisaurus allocotus</i> (HBV-20001) from the Upper Cretaceous of China.

<p>Measurements of the pelvic girdle elements of <i>Huabeisaurus allocotus</i> (HBV-20001) from the Upper Cretaceous of China.</p

Measurements of the sacrum of <i>Huabeisaurus allocotus</i> (HBV-20001).

<p>Measurements of the sacrum of <i>Huabeisaurus allocotus</i> (HBV-20001).</p

Holotypic dorsal vertebra of <i>H. allocotus</i> (HBV-20001) from the Upper Cretaceous of Shanxi, China.

<p>Photographs and line drawings of dorsal vertebra in (A) anterior, (B) posterior, and (C) right lateral views. (A–C) were taken during original preparation. <i>Abbreviations: ?acpl, ?anterior centroparapophyseal lamina; cam, camerate internal pneumaticity exposed on broken bone surface; cpol, centropostzygapophyseal lamina; cprl, centroprezygapophyseal lamina; hypa, accessory ventral articulation of hypantrum; pcdl, posterior centrodiapophyseal lamina; pl, pneumatic foramen (pleurocoel) in centrum; ?sprl, ?spinoprezygapophyseal lamina; tpol, ventral strut of intrapostzygapophyseal lamina.</i> Dashed lines indicate broken bone margins.</p

Holotypic left femur of <i>H. allocotus</i> (HBV-20001) from the Upper Cretaceous of Shanxi, China.

<p>Photographed during original preparation in (A) posterior, (B) medial, (C) anterior, and (D) distal views. Silhouette between (B) and (C) shows schematic cross section of the diaphysis. <i>Abbreviations: fic, fibular condyle; ftr, fourth trochanter; tic, tibial condyle.</i> Striped pattern indicates broken surface, dashed lines indicate broken bone margins.</p

Measurements of the left humerus (HBV-20002) from the Upper Cretaceous of China previously referred to as the paratype of <i>Huabeisaurus allocotus</i>.

<p>Measurements of the left humerus (HBV-20002) from the Upper Cretaceous of China previously referred to as the paratype of <i>Huabeisaurus allocotus</i>.</p

Isolated right humerus (HBV-20002) from the Upper Cretaceous of Shanxi, China.

<p>Photographed during original preparation in (A) anterior, (B) medial, (C) posterior, and (D) distal views. This bone was formerly regarded as the paratype of <i>H. allocotus.</i> Silhouette between (A) and (B) shows schematic cross section of the diaphysis. <i>Abbreviations: rac, radial condyle; ri, ridge.</i> Striped pattern indicates broken surface, dashed lines indicate broken bone margins.</p