Re: Herrerasaurus - what was it?

[David Marjanovic <david.marjanovic@gmx.at>]

>  Analogous problems exist for Guaibasaurus (basal theropod, basal
>  saurischian, or basal saur... Well, let's just say a new strong
>  alternative has come up)

No, let's spell it out. SVP meeting abstracts are embargoed till the 
time of their presentation, but no further. Here goes:

Martin Ezcurra & Fernando Novas (2009): Guaibasauridae, a new clade of 
Triassic basal sauropodomorphs, Journal of Vertebrate Paleontology, 
online-only supplement to 29(3), 92A

================================

The family Guaibasauridae was coined as a monospecific entity composed 
by *Guaibasaurus
candelariensis* from the Norian Caturrita Formation of Brazil. Since 
then, the phylogenetic
position of *Guaibasaurus* remained controversial, being alternatively 
interpreted as a basal
saurischian or a basal theropod. Nevertheless, a new cladistic analysis 
depicts Guaibasaurus
as closely related with *Panphagia*, *Agnosphitys*, *Saturnalia*, and 
two yet undescribed forms
from Argentina and India. We employ the term Guaibasauridae for the 
monophyletic clade
gathering these Late Triassic taxa, which lies at the base of 
Sauropodomorpha. In particular,
*Guaibasaurus* is for the first time included within Sauropodomorpha, 
supported by the
presence of proximal caudal vertebrae with the base of the neural spine 
anteroposteriorly
longer than half the length of the neural arch, ilium with strongly 
laterally curved blade
and elongated pubic peduncle, and ischial shaft triangular-shaped in 
cross-section.
Features supporting the monophyly of Guaibasauridae include: ilium with 
incipiently open
acetabulum, elongated postacetabular process, femur with proximal 
anterior trochanter at
level with femoral head, and tibial distal end with concave 
posterolateral corner. Contrarily
to recent interpretations, *Panphagia* is not depicted as the most basal 
sauropodomorph,
and characters supporting its original assignment are more widely 
distributed among basal
saurischians (distally curved anterior dentary teeth and sub-circular 
distal ischium) or missinterpreted [sic]
(symmetric proximal tibial condyles). Accordingly, Guaibasauridae is 
interpreted
as a large monophyletic [duh] clade of early dinosaurs, which radiated 
during late Carnian-Norian
times and attained a wide geographic distribution. Furthermore, no large 
monophyletic
clades were previously recognized among basal dinosaurs, and 
Guaibasauridae constitutes
the first evidence of a large clade which radiated apart from the branch 
leading towards
Jurassic and Cretaceous taxa, in this case the sauropod lineage.

===================================

The presentations themselves are secret without explicit permission by 
the authors, but in this case the abstract pretty much says it all, so 
you're not missing much.

The same holds for the following poster on the phylogenetic position of 
*Silesaurus*, which I remember as not particularly information-rich:

Grzegorz NiedÅwiedzki, RafaÅ Piechowski & Tomasz Sulej (2009): New data 
on the anatomy and phylogenetic position of *Silesaurus opolensis* from 
the late Carnian of Poland, Journal of Vertebrate Paleontology, 
online-only supplement to 29(3), 155A

===================================

*Silesaurus opolensis* is one of the best-known early dinosauriform 
archosaurs, represented
by several, partially articulated skeletons and hundreds of isolated 
bones collected from
the Keuper beds (Late Triassic: late Carnian) at the KrasiejÃw [site?] 
near Opole, Upper Silesia,
Poland. *Silesaurus* is peculiar in having herbivorous-like teeth as 
well as evidence for a beak
on the anterior end of the dentary. The phylogeny of basal dinosaurs and 
closely related
taxa has been examined by numerous cladistic analyses. However, areas of 
uncertainty
remain, such as the relationships of *Silesaurus*-like dinosauriforms to 
basal ornithischian
and sauropodomorph dinosaurs. Following the initial description of this 
taxon in 2003,
*Silesaurus* has been the subject of detailed anatomical study. We 
present new observations
on the anatomy of the skull, dentary, limbs and pelvis, shedding new 
light on the
phylogenetic position of this taxon. A new phylogenetic dataset was 
constructed to resolve
relationships amongst dinosauromorphs, *Silesaurus*-like dinosauriforms, 
basal saurischians
(including basal sauropodomorphs) and basal ornithischians. This dataset 
includes 25 species
and 125 characters (10 new); characters were compiled based upon a 
thorough reassessment
of previous phylogenetic datasets and direct examination of relevant 
specimens. Character
scorings were drawn from previous analyses as well as the recently 
published and ongoing
results of taxonomic reviews of the Late Triassic dinosauriform and 
basal dinosaur record.
Analysis of the new dataset suggests that *Silesaurus opolensis* is the 
basalmost known
ornithischian, forming the sister taxon of other early ornithischians, 
including *Pisanosaurus*,
*Lesothosaurus*, *Eocursor*, âfabrosauridsâ and Heterodontosauridae. The 
major ornithischian
character of *Silesaurus* is a beak at the tip of mandible. The 
symphysis does not show
permanent junction of dentaries and they clearly had significant 
mobility, although their tip
was apparently armed with horny cover. *Silesaurus* was also advanced in 
the construction of
its pelvis and sacrum relative to other early dinosauromorphs.

========================================

And while I am at it...

Sterling Nesbitt (2009): The antiquity of Archosauria and the origin of 
Late Triassic archosaur assemblages, Journal of Vertebrate Paleontology, 
online-only supplement to 29(3), 155A

========================================

Archosaurs have a rich history that originated in the Triassic and 
continues today with
two extant clades, the crocodylians and the avians. Nonetheless, the 
initial divergence
of Archosauria is poorly understood. Few archosaur fossils have been 
found prior to the
Ladinian Stage (late Middle Triassic), even though published archosaur 
phylogenies
predict most Triassic archosaur ghost lineages stretch into the Middle 
Triassic or earlier.
New discoveries of archosaurs from the Middle Triassic Manda Formation 
of Africa,
the Moenkopi Formation of North America, and the re-identification of 
existing material
from the Early Triassic of China help fill these ghost lineages. I 
conducted a thorough
phylogenetic analysis (80 archosauriform taxa, 412 characters) to assess 
the early evolution
of Archosauria. The analysis recovered a well resolved, robustly 
supported consensus tree
that includes a monophyletic Archosauria. âRauisuchiansâ are found to be 
paraphyletic, but
include a monophyletic poposauroid clade, rauisuchid clade, and 
crocodylomorph clade.
A monophyletic clade containing Silesaurus and similar forms is 
supported as the sistertaxon
to Dinosauria. Time-calibration of this phylogeny indicates that the 
origin and initial
diversification of Archosauria occurred prior to the Middle Triassic, 
just after the Permian-
Triassic extinction. A *Silesaurus*-like taxon from the Anisian Manda 
Formation indicates
that the Pterosauria, Dinosauromorpha, Dinosauriformes, and Dinosauria 
lineages were
present by the Anisian. Similarly, the âsail-backedâ poposauroid 
*Xilousuchus* from the late
Early Triassic of China indicates that Archosauria, the Ornithodira, 
Phytosauria, Aetosauria,
Ornithosuchidae, and Paracrocodylomorpha lineages were present by the 
end of the Early
Triassic. High rates of homoplasy, long ghost lineages, and high rates 
of character evolution
characterize the early history of Archosauria. These data imply that 
much of the early history
of Archosauria has not been recovered, and the typical archosaur 
assemblages in the Late
Triassic were possibly established by the Middle Triassic.

=============================================

I should perhaps point out that the Anisian is the first of the two 
stages of the Middle Triassic. -- In case you're wondering, 
Paracrocodylomorpha is a misnamed clade that _includes_ Crocodylomorpha 
and its closest relatives (compare Paraves).