[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Falcarius, new therizinosaur from Utah

Whew! It's even mentioned on the title page of Nature -- even though the genome sequence of *Dictyostelium* is published in the same issue!

Comments and quotes (refs and mentions of figures removed):

Incredibly long tail. 40 vertebrae or something. At least in the reconstruction -- the text (Methods) says "vertebral numbers estimated on changing proportions of the vertebrae and comparisons with other maniraptoran theropods".

The alveoli for the first dentary teeth have twice the cross-sectional area of the others. Gnawing teeth? In any case the condition is compared to the premaxillary gnawing teeth of *Incisivosaurus*/*Protarchaeopteryx*.

Pneumatic fossae in the middle 3 (of 5) sacral vertebrae.

"Medial to distal caudals are more than four times as long as high. All caudal vertebrae seem to be apneumatic with loss of caudal ribs and neural spines distal to caudals 11â13, in contrast to the condition in derived oviraptorosaurs and derived therizinosauroids."

Functionally tridactyl foot.

"A phylogenetic analysis provides strong support for the hypothesis that *Falcarius* is the basalmost therizinosauroid known. *Falcarius* possesses several maniraptoran synapomorphies not previously documented in basal therizinosaurs, including hypapophyses on the presacral vertebral column, bowed ulna, presence of a semilunate comprised of fused distal carpals one and two, ischium less than two-thirds pubis length, and distally positioned obturator process of the ischium."

Simplified cladogram (57 taxa, 231 characters):

              |  `--+--*Falcarius*
              |     `--see below
                 |  `--rest of Troodontidae

"See below", the clade that should be called Therizinosauroidea, is an unresolved polytomy of *Segnosaurus*, *Erlikosaurus*, *Alxasaurus*, *Nothronychus* and *Beipiaosaurus*.

"The Early Jurassic Chinese jaw from the Lufeng Series in southern China described tentatively as the basal therizinosauroid *Eshanosaurus* is more derived in having a lateral shelf and down-turned symphysis, which are absent in Falcarius. Its therizinosauroid identification have been considered problematic by some authors. *Falcarius* casts further doubt on the affinities of [*]Eshanosaurus[*] by increasing its stratigraphic and phylogenetic inconsistency. Given the discovery of North American members of the therizinosauroid clade, together with the poor record of Middle Cretaceous dinosaurs, it seems that the generally accepted hypothesis of an Asian origin and radiation for Therizinosauroidea requires additional testing."

"Collections from the Crystal Geyser Quarry made so far preserve a minimum of ten individuals based on prepared femora, but the quarry size indicates that perhaps hundreds of disarticulated individuals remain interred, representing multiple growth stages as well as robust and gracile morphotypes. The locality spans about 8,000 m and the bone-bearing stratum is, on average, 1 m thick, with bone densities in some areas exceeding 100 elements per cubic metre. There is no evidence of another small theropod taxon, so all of the therizinosauroid materials are here referred to *Falcarius*. In addition to the therizinosauroid elements, the quarry contains rare remains of an unidentified ankylosaur. About 99% of all identified bones from the type locality (about 2,000 identifiable bones) represent *Falcarius*."

Some bones are "associated", so perhaps articulated. Most aren't, however.

"Five unambiguous synapomorphies support Therizinosauroidea: teeth serrated (reversal); ventral surface of dentary descends strongly posteriorly; ventral edge of anterior ala of ilium hooked anteriorly; distal humerus with large medial condyle, centred on distal end; and preacetabular portion of ilium laterally flaring. The basal position of *Falcarius* is supported by the absence of the following characters: labial face of dentary with lateral ridge and inset tooth row; interdental plates on dentary; obturator process of ischium does not contact pubis; metatarsal I without proximal articulating surface. Therizinosauroidea + Oviraptorosauria characterized by basipterygoid processes abbreviated or absent; suborbital fenestra reduced in size or absent; basipterygoid processes hollow; symphyseal region of dentary strongly recurved; maxillary and dentary teeth lanceolate and subsymmetrical."

Many typos, especially in the cladogram.