Abstract
Therizinosaurian theropods evolved many highly specialized osteological features in association with their bulky proportions, which were unusual in the context of the generally gracile Theropoda. Here we report a new therizinosaur, Lingyuanosaurus sihedangensis gen. et sp. nov., based on a specimen recovered from the Lower Cretaceous Jehol Group of Lingyuan, Liaoning Province, China, which displays a combination of plesiomorphic and derived features. Most notably, the specimen is characterized by posterior dorsal vertebrae with a complex and unusual laminar structure; an ilium with a highly dorsoventrally expanded preacetabular process showing only slight lateral flaring of the ventral margin, a strongly anterodorsally inclined iliac blade, a small postacetabular process with a strongly concave dorsal margin, and a relatively robust pubic peduncle with a posteroventrally facing distal articular surface; a straight and robust femur with a small lesser trochanter; and a tibia that is longer than the femur. Phylogenetic analysis places Lingyuanosaurus in an intermediate position within Therizinosauria, i.e., between the early-branching therizinosaurs such as Falcarius, Jianchangosaurus, and Beipiaosaurus and the late-branching ones such as Alxasaurus and Therizinosaurus. This new therizinosaur sheds additional light on the evolution of major therizinosaurian characteristics, including particularly the distinctive pelvic girdle and hindlimb morphology seen in this group.
Highlights
Therizinosauria is a highly specialized theropod clade displaying a number of distinctive features suggestive of a herbivorous diet, including a rostral beak, numerous small leaf-shaped cheek teeth, an elongated neck and a broad pelvis
Despite the incompleteness of this specimen, IVPP V 23589 is clearly a therizinosaurian dinosaur as indicated by numerous therizinosaurian synapomorphies[2]: dorsal vertebrae with a complex laminar structure; laterally flattened manual unguals with dorsally positioned collateral grooves; and a highly modified ilium with a deep preacetabular process, a reduced postacetabular process, a preacetabular process whose ventral margin is dorsally displaced relative to the acetabulum, and a dorsoventrally elongated pubic peduncle
Lingyuanosaurus is similar to late-branching therizinosaurs in having the following apomorphic features: groove ascending proximal to entepicondyle on anterolateral margin of humeral shaft absent; ventral margin of preacetabular process of ilium gently deflected laterally; articular surface of pubic peduncle caudoventrally directed; long axis of iliac blade inclined above horizontal at an angle exceeding 35° (Fig. 10); femoral head dorsomedially oriented; greater trochanter significantly expanded in craniocaudal width relative to femoral head; proximal surface of femur depressed between greater trochanter and femoral head
Summary
Therizinosauria is a highly specialized theropod clade displaying a number of distinctive features suggestive of a herbivorous diet, including a rostral beak, numerous small leaf-shaped cheek teeth, an elongated neck and a broad pelvis. Therizinosaurs have been recovered mainly from the Cretaceous of Asia and North America, some putative material has been reported from the Cretaceous of Europe and Africa. We report a new basal therizinosaur based on a specimen recovered from the Lower Cretaceous Jehol Group of Sihedang, Lingyuan, Liaoning, and discuss its implications for the early evolution of the group. We identify the three maniraptoran manual digits as II-III-IV, following the numbering applied to the wing digits of living theropods in most ornithological literature and some recent paleontological studies[6,7]
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