A collection of primitive titanosauriform
sauropods from the Jones Ranch locality, Early Cretaceous Twin
Mountains Formation (~112 Ma), central Texas, represents one of
the richest accumulations of sauropod bones in North America.
Autapomorphic characters of the taxon include cranial and
mid-caudal neural arches with distinct intraprezygapophyseal
laminae (tprl), accessory vertebral laminae on cranial dorsal
neural arches, and dorsal neural spines that lack a postspinal
lamina.
Non-vertebral skeletal elements referred to the
genus Pleurocoelus from the Arundel Formation of Maryland
and Virginia possess some diagnostic morphological
characteristics and can be compared with the Jones Ranch
sauropod. The latter differs from Pleurocoelus in the
shape of the caudoventral margin of the maxilla, the shape of
the distal scapular blade, and the shape of the proximal condyle
of the tibia. The Jones Ranch sauropod is also morphologically
distinct from all other sauropods described and named from the
Early Cretaceous of North America.
Cladistic analysis places this sauropod within
Titanosauriformes. The Texas sauropod does not possess
synapomorphies of Somphospondyli, and derived characters that
have been used to define the Titanosauria are also absent,
affirming its placement as a basal titanosauriform. The new
taxon from Texas is known from more material than any other
North American Early Cretaceous sauropod. Description of the
taxon increases the diversity of sauropods in North America
during the Early Cretaceous and provides more complete,
associated material that can be compared to new discoveries from
this time period.
Peter J. Rose.
Department of Geological Sciences, Southern Methodist
University, Dallas, Texas, U.S.A.
Current address: Department of Geology and Geophysics,
University of Minnesota, Minneapolis, Minnesota, U.S.A.
