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

Sauropod clavicles, interclavicles, gastralia, and sternal ribs

From: Ben Creisler

A new advance online paper:

Emanuel Tschopp & Octávio Mateus (2012)
Clavicles, interclavicles, gastralia, and sternal ribs in sauropod
dinosaurs: new reports from Diplodocidae and their morphological,
functional and evolutionary implications.
Journal of Anatomy (advance online publication)
DOI: 10.1111/joa.12012

Ossified gastralia, clavicles and sternal ribs are known in a variety
of reptilians, including dinosaurs. In sauropods, however, the
identity of these bones is controversial. The peculiar shapes of these
bones complicate their identification, which led to various differing
interpretations in the past. Here we describe different elements from
the chest region of diplodocids, found near Shell, Wyoming, USA. Five
morphotypes are easily distinguishable: (A) elongated, relatively
stout, curved elements with a spatulate and a bifurcate end resemble
much the previously reported sauropod clavicles, but might actually
represent interclavicles; (B) short, L-shaped elements, mostly
preserved as a symmetrical pair, probably are the real clavicles, as
indicated by new findings in diplodocids; (C) slender, rod-like bones
with rugose ends are highly similar to elements identified as sauropod
sternal ribs; (D) curved bones with wide, probably medial ends
constitute the fourth morphotype, herein interpreted as gastralia; and
(E) irregularly shaped elements, often with extended rugosities, are
included into the fifth morphotype, tentatively identified as sternal
ribs and/or intercostal elements. To our knowledge, the bones
previously interpreted as sauropod clavicles were always found as
single bones, which sheds doubt on the validity of their
identification. Various lines of evidence presented herein suggest
they might actually be interclavicles – which are single elements.
This would be the first definitive evidence of interclavicles in
dinosauromorphs. Previously supposed interclavicles in the early
sauropodomorph Massospondylus or the theropods Oviraptor and
Velociraptor were later reinterpreted as clavicles or furculae.
Independent from their identification, the existence of the reported
bones has both phylogenetic and functional significance. Their
presence in non-neosauropod Eusauropoda and Flagellicaudata and
probable absence in rebbachisaurs and Titanosauriformes shows a clear
character polarity. This implicates that the ossification of these
bones can be considered plesiomorphic for Sauropoda. The proposed
presence of interclavicles in sauropods may give further support to a
recent study, which finds a homology of the avian furcula with the
interclavicle to be equally parsimonious to the traditional theory
that furcula were formed by the fusion of the clavicles. Functional
implications are the stabilizing of the chest region, which coincides
with the development of elongated cervical and caudal vertebral
columns or the use of the tail as defensive weapon. The loss of
ossified chest bones coincides with more widely spaced limbs, and the
evolution of a wide-gauge locomotor style.