Titanosauriform sauropod early evolution

[Ben Creisler <bcreisler@gmail.com>]

From: Ben Creisler
bcreisler@gmail.com


A new paper:

Michael D. D'Emic (2012)
The early evolution of titanosauriform sauropod dinosaurs.
Zoological Journal of the Linnean Society166(3): 624–671
DOI: 10.1111/j.1096-3642.2012.00853.x
http://onlinelibrary.wiley.com/doi/10.1111/j.1096-3642.2012.00853.x/abstract


Titanosauriformes was a globally distributed, long-lived clade of
dinosaurs that contains both the largest and smallest known sauropods.
These common and diverse megaherbivores evolved a suite of cranial and
locomotory specializations perhaps related to their near-ubiquity in
Mesozoic ecosystems. In an effort to understand the phylogenetic
relationships of their early (Late Jurassic–Early Cretaceous) members,
this paper presents a lower-level cladistic analysis of basal
titanosauriforms in which 25 ingroup and three outgroup taxa were
scored for 119 characters. Analysis of these characters resulted in
the recovery of three main clades: Brachiosauridae, a cosmopolitan mix
of Late Jurassic and Early Cretaceous sauropods, Euhelopodidae, a
clade of mid-Cretaceous East Asian sauropods, and Titanosauria, a
large Cretaceous clade made up of mostly Gondwanan genera. Several
putative brachiosaurids were instead found to represent
non-titanosauriforms or more derived taxa, and no support for a
Laurasia-wide clade of titanosauriforms was found. This analysis
establishes robust synapomorphies for many titanosauriform subclades.
A re-evaluation of the phylogenetic affinities of fragmentary taxa
based on these synapomorphies found no body fossil evidence for
titanosaurs before the middle Cretaceous (Aptian), in contrast to
previous reports of Middle and Late Jurassic forms. Purported
titanosaur track-ways from the Middle Jurassic either indicate a
substantial ghost lineage for the group or – more likely – represent
non-titanosaurs. Titanosauriform palaeobiogeographical history is the
result of several factors including differential extinction and
dispersal. This study provides a foundation for future study of basal
titanosauriform phylogeny and the origins of Titanosauria.