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

Re: [darren.naish@port.ac.uk: 52nd SVPCA meeting]



----- Original Message ----- 
From: "Mike Taylor" <mike@indexdata.com>
Sent: Thursday, September 16, 2004 2:19 PM

> - -- Stem-group tetrapods
>
> Jamie Robinson showed some fantastic animated 3D
> computer reconstructions of the basal temnospondyl
> _Dendrerpeton_. The specimen (BMNH R436) has both
> stapes preserved, with the left lodged inside the cranial
> cavity and thus invisible to human eyes. It seems that
> _Dendrerpeton_ had an impedence-matching middle ear
> homologous with that of anurans.

Homologous... meaning that frogs (if not all lissamphibians) are
temnospondyls?

> - -- Lepidosaurs
>
> Susan Evans talked about the Lower Cretaceous lepidosaurs
> of Pietraroia, Italy. _Chometokadmon_, originally described
> as a lizard but later reinterpreted as a rhynchocephalian, is a
> lizard after all and clearly a scleroglossan, an anguimorph
> and perhaps a stem varanoid close to _Parviraptor_.
> Scattered osteoderms preserved in the region of the orbit
> and temporal region show that they were arranged in this
> area in a manner perhaps similar to that of extant
> _Lanthanotus_. Ardeosaurids (including a new species of
> _Eichstaettisaurus_ named after Steve Gould) and among
> the last Laurasian rhynchocephalians indicate that Pietraroia
> had a relictual lepidosaur fauna, probably because  like the
> rest of Europe at this time  it was a region of archipelagos
> and isolated islands.

This has been published:

Susan E. Evans, Pasquale Raia & Carmela Barbera: New lizards and
rhynchocephalians from the Lower Cretaceous of southern Italy, Acta
Palaeontologica Polonica 49(3), 393 -- 408 (2004)

Abstract:
"The Lower Cretaceous (Albian age) locality of Pietraroia, near Benevento in
southern Italy, has yielded a diverse assemblage of fossil vertebrates,
including at least one genus of rhynchocephalian (*Derasmosaurus*) and two
named lizards (*Costasaurus* and *Chometokadmon*), as well as the
exquisitely preserved small dinosaur, *Scipionyx*. Here we describe material
pertaining to a new species of the fossil lizard *Eichstaettisaurus* (*E.
gouldi* sp. nov.). *Eichstaettisaurus* was first recorded from the Upper
Jurassic (Tithonian age) Solnhofen Limestones of Germany, and more recently
from the basal Cretaceous (Berriasian) of Montsec, Spain. The new Italian
specimen provides a significant extension to the temporal range of
*Eichstaettisaurus* while supporting the hypothesis that the Pietraroia
assemblage may represent a relictual island fauna. The postcranial morphlogy
of the new eichstaettisaur suggests it was predominantly ground-living.
Further skull material of *E. gouldi* sp. nov. was identified within the
abdominal cavity of a second new lepidosaurian skeleton from the same
locality. This second partial skeleton is almost certainly rhynchocephalian,
based primarily on foot and pelvic structure, but it is not *Derasmosaurus*
and cannot be accommodated within any known genus due to the unusual
morphology of the tail vertebrae."

The rhynchocephalian remains unnamed.

> The eggshell of the new embryo does not appear to be calcareous
> as argued but indicates instead that pterosaur eggshells were leathery.

This most probably pulls them out of the Archosauria crown.

> Mike Benton discussed Âecosystem remodelling across the
> P-Tr boundary as documented in the record of the South
> Urals basin. A fundamental change and simplification in
> guild structure occurred across the boundary  small
> piscivores and insectivores, mediun and large carnivores
> and large herbivores were all lost, and these guilds remained
> empty for 25 million years after the extinction event.

What, throughout the Triassic? Isn't that a bit much?

> Andreas Christian applied analysis of compressive forces to
> sauropod necks  those of you familiar with this research
> will known thatÂs been applied to _Brachiosaurus_, the
> conclusion from Christian et al. being that _Brachiosaurus_
> had a vertical mast-like neck. Christian explained the
> technique, showed that it worked when applied to such
> living animals as giraffes and camels, and then applied it to
> other sauropods. The data from _Diplodocus_ indicates a
> horizontal neck but that from _Euhelopus_ indicates that it,
> too, had a mast-like vertical neck.

As expected :-)

> Rebbachisaurid distribution indicates that diplodocoids
> were ancestrally Gondwanan (though _Histriasaurus_ was
> not mentioned):

*Histriasaurus* _is_ Gondwanan. The Adriatic Plate is a small splinter of
Africa that broke loose and drifted northward not long ago.

> Darren Naish discussed _Yaverlandia_.

What is it? An abelisaurid like *Majungatholus*? :^)

> Tom Kemp advocated a fairly controversial point of view
> that many of us who work on morphology might not like
> hearing. Attempts to reconstruct the total phylogeny of
> placentals were never particularly convincing, nor did they
> produce well resolved trees, nor were any nodes supported
> by multiple characters. It is the many independent molecular
> studies that seem to have sorted things out. Kemp therefore
> argued that morphology alone can probably never get it
> right, and if we look at phylogenies for fossil taxa we see
> that some trees, and some nodes in trees, are incredibly
> weak, and maybe we should have next to no confidence in
> these phylogenies (non-mammalian therapsids were used as
> the case study). Robert Asher pointed out after this talk that
> maybe this point of view was somewhat negative: after all,
> morphological work had been able to recover at least some
> chunks of the clades recognised by molecular work (e.g.,
> morphology-based Archonta constitutes a chunk of
> molecular Euarchontoglires and morphology-based
> Paenungulata constitutes a chunk of molecular Afrotheria).

I'm not so pessimistic either, because:
- There has simply never been a eutherian analysis of decent size. Too few
taxa, far too few characters. Let them grow to the size of any current
theropod matrix, or better yet to what Mickey is preparing, and we'll see
what comes out.
- Morphological coding is subjective... so subjective that people commonly
overlook characters that don't support any of the hypotheses they are taking
into account. Now that the molecules say whales are artiodactyls and that
Afrotheria exists, morphologists are starting to find hints in these
directions -- before they never got those ideas.

> Robert Presley showed quite convincingly that the groove
> on the medial surface of the Mesozoic mammal mandible
> should not be called Meckelian sulcus or anything like this
> and for various reasons we should return to calling this
> structure Âinternal mandibular grooveÂ.

What could it be, if not something Meckelian? Don't *Gobiconodon* and
*Repenomamus* have an ossified Meckelian cartilage in part of that region?