Saturday, February 25, 2012

Advance online publication and getting dates correct

We all know the issues caused by journals releasing online versions of their papers earlier than the paper versions are published.  I normally don't mind because the content is identical (though see the "Gryphognathus" vs. "Gryphoceratops" situation for an exception), but one thing it does negatively affect is that it causes lots of nomina nuda due to the ICZN's backwards Article 9.8 that doesn't accept electronic publications as valid.  I suppose technically every advance online publication naming a new taxon creates a short-lived nomen nudum, but I'm not pedantic enough to count them in most cases.  Where they matter more is when the electronic and paper versions are published in different years.  It's confused me more than once in the Database, where sometimes the online date is never corrected, sometimes the online date is never mentioned, and sometimes I happen to list both.  So to straighten it out once and for all, I've standardized my format to give all such taxa formal nomen nudum synonymies, in the comments I state what month and year the online and paper versions were published, and only list the final paper version in the references.  This should make it up on my next update, but until then, here are all the Mesozoic theropods affected, organized by journal. 

Acta Palaeontologica Polonica
- Cruxicheiros 2009 vs 2010

Cretaceous Research
- Albertonykus 2008 vs 2009
- Hollanda 2009 vs 2010
- Qiupalong 2010 vs 2011
- Bonapartenykus 2011 vs 2012
- Patagonykinae 2011 vs 2012

Historical Biology
- palmapenis 2011 vs 2012

Journal of South American Earth Sciences
- Alamitornis 2008 vs 2009

Journal of Systematic Paleontology
- Elsornis 2006 vs 2007
- Mystiornithiformes 2010 vs 2011
- Mystiornithidae 2010 vs 2011
- Mystiornis 2010 vs 2011

- Longirostravis 2003 vs 2004
- Skorpiovenator 2008 vs 2009
- Carcharodontosauria 2009 vs 2010
- Megaraptora 2009 vs 2010
- Neovenatoridae 2009 vs 2010

Proceedings of the Royal Society B
- Austroraptor 2008 vs 2009
- Beishanlong 2009 vs 2010
- Tianyuraptor 2009 vs 2010
- Xiongguanlong 2009 vs 2010
- Zhongjianornis 2009 vs 2010

Tuesday, February 14, 2012

"Syntarsus" "mexicanum"

Thanks to Pixagono, Harris, Chure and Scheetz for their combined work in finding this new theropod name.  It turns out the proper reference is-

Hernandez, 2002. Los dinosaurios en Mexico. in Gonzalez Gonzalez and De Stefano Farias (eds.). Fosiles de Mexico: Coahuila, una Ventana a Traves del Tiempo. Gobierno del Estado de Coahuila, Saltillo. 143-153.

Unfortunately, the entire section mentioning the species is-

"Otro material del grupo de los dinosaurios saurisquios (Cintura tipo reptil) ha sido determinada como una nueva especie del genero Syntarsus, llamada familia Syntarsus mexicanum, de la familia Coelophysidae: se trata de pequenos dinosaurios carnivoros de cuerpo esbelto y de 3 metros de longitud en promedia."

Or translated-

"Other material of the saurischian dinosaur group (reptile pelvic type) has been determined as a new species of the genus Syntarsus, named Syntarsus mexicanum family[sic?], of the family Coelophysidae: they are small carnivorous dinosaurs with a slender body and are 3 meters long on average."

Thus it is a nomen nudum for not including a diagnosis (ICZN 13.1.1) (the slender body and 3 meter length seem to refer to the family, not the species) or a type specimen (ICZN 16.4.1).  Harris wondered if Hernandez had planned to have an official description out by the time the book was published, but given the explicit designation of this as a new species, I don't see any evidence for that.  To the contrary, I'm curious if the apparent typo "llamada familia" used in reference to the species doesn't mean "familiar name", as in "informal name", and Hernandez didn't intend to name a new species at all.  In any case, I stand by my previous conclusion "S." "mexicanum" probably refers to the coelophysid material described by Munter and Clark (2006).  This is because the latter material comes from the locality Hernandez mentions "mexicanum" as being from ("Esta localidad descubierta en 1982 por el doctor James M. Clark") and was found to be sister to Megapnosaurus (as Syntarsus) by Munter (1999- SVP abstract and thesis).  In fact, it probably refers to the dorsals, sacrum and pelvis IGM 6624 specifically, since Hernandez also states "tambien se han identificado elementos craneales del genero Ceratosaurus", and the cranial specimen IGM 6625 was thought by Munter to be either a neoceratosaur or maniraptoran.

Probable intended holotype of "Syntarsus" "mexicanum", vertebrae and pelvis IGM 6624 in lateral view after Munter and Clark, 2006).
The Database's entry will be-

"Syntarsus" "mexicanum" Hernandez, 2002
Toarcian, Early Jurassic
La Boca Formation, Mexico
- (IGM 6624) partial twelfth dorsal vertebra (13.1 mm), partial thirteenth dorsal vertebra (20 mm), partial synsacrum (61.5 mm- 16.2, 12.7, 9.6, 9.6, 13.4 mm), incomplete fused pelvis
?...(IGM 6625) posterior braincase, incomplete laterosphenoid, fragments
Diagnosis- (after Munter, 1999) ilia contact dorsally on midline (may be taphonomic).
Comments- Discovered in 1994, Munter (1999) found IGM 6624 to be sister to Megapnosaurus (as Syntarsus) based on the antitrochanter projecting into the acetabulum (though this is also present in Coelophysis and Liliensternus). It differs in having ilia contact sacral neural spines two and three. The skull fragments may not belong to the same individual or taxon and were thought to be a neoceratosair or maniraptoran by Munter due to their pneumatized paroccipital roots. However, this has since been found to exist in coelophysids such as "M." kayentakatae, making the possibility it belongs to the same individual more likely. Hernandez (2002) erected a new species Syntarsus mexicanum from the locality, which is probably based on IGM 6624 since no other coelophysoid specimens have been reported from there and Munter emphasized similarity to what he called Syntarsus. However, it is a nomen nudum for not including a diagnosis (ICZN 13.1.1) or a type specimen (ICZN 16.4.1). Hernandez also mentioned cranial elements of Ceratosaurus, which are probably IGM 6625 based on Munter's comparison to neoceratosaurs. Munter and Clark later (2006) described the specimens and included IGM 6624 in Carrano et al.'s (2002) matrix where it emerged sister to Coelophysis+Megapnosaurus (excluded due to lacking fused sacral neural spines), and Rauhut's (2003) matrix where it was in the clade of Coelophysis+Megapnosaurus (the latter a chimaera of rhodesiensis and kayentakatae). They considered IGM 6625 provisionally theropod. The only potential apomorphy noted in the material has been the ilia which meet at the midline, but this may be taphonomic. Munter and Clark note that the dorsally oriented acetabulum suggests distortion, but the rugose medial ilial surface suggesting contact with the other ilium and general lack of distortion in other fossils from the locality suggests it was natural. As "mexicanum" has not been shown to be closer to Megapnosaurus than to Coelophysis, it is here retained under the name "Syntarsus" "mexicanum".
References- Clark, Montellano, Hopson, Hernandez and Reynoso, 1998. The Jurassic vertebrates of Huizachal canyon, Tamaulipas. Avances en Investigacion, Paleontologia de Vertebrados. Universidad Autonoma del Estado de Hidalgo Publicacion Especial 1. 1-3.
Munter, 1999. Two theropod dinosaur specimens from Huizachal Canyon, Mexico. Journal of Vertebrate Paleontology. 19(3), 65A.
Munter, 1999. Two theropod dinosaur specimens from Huizachal Canyon, Mexico. Masters thesis. George Washington University.
Hernandez, 2002. Los dinosaurios en Mexico. in Gonzalez Gonzalez and De Stefano Farias (eds.). Fosiles de Mexico: Coahuila, una Ventana a Traves del Tiempo. Gobierno del Estado de Coahuila, Saltillo. 143-153.
Munter and Clark, 2006. Theropod dinosaurs from the Early Jurassic of Huizachal Canyon, Mexico. In Carrano, Gaudin, Blob, Wible (eds.). Amniote paleobiology: Perspectives on the evolution of mammals, birds, and reptiles. University of Chicago Press, Chicago. 53-75.

Thursday, February 9, 2012

Peters is wrong (surprise) about Herrerasaurus and a new idea about Austroraptor

It's like shooting fish in a barrel, I know, but I felt the need to correct Peters' most recent Photoshop manipulation disaster, since in encroaches on Theropoda.  Peters has a blog which mostly concerns itself with taxa outside my area of expertise, but in this case he tackles Herrerasaurus.  Taking a photo of skull PVSJ 407, he reinterprets it as having a narrow premaxilla subnarial process and elongate antorbital fossa extending to the premaillary-maxillary fenestra (making the latter a promaxillary fenestra I suppose).  Yet that skull's actually featured on Digimorph, where we can use the CT scan to test Peters' idea without the skull in hand.

Picture from Peters' blog, of Herrerasaurus skull PVSJ 407 (taken from Alcober and Martinez 2010 I think) with his interpretation of snout elements on top.  Note his antorbital fossa in dark green.
As you can see, Peters thinks the premaxilla-maxillary suture is a crack in the maxilla.

Herrerasaurus skull PVSJ 407 ct scan taken from Franzosa (2001 online).
Here's the CT scan of the skull, and notice two things.  First is that now that we only have topography to work with, Peters' antorbital fossa disappears.  The maxilla simply isn't depressed there.  Second is that the anterior edge of his supposed maxilla is actually a crack that runs through the premaxilla.  How can we tell it's definitely a crack?  It continues downward through a tooth!  I've highlighted a portion of it in the comparison pic below.

Comparison of two pictures above, with part of crack Peters interprets as a suture highlighted in red.
Just more evidence not to trust Peters' morphological interpretations or his phylogenies based on them.

But that doesn't mean professionals always interpret things correctly.  Austroraptor is a supposed unenlagiine paravian which preserves one pneumatic opening in its maxillary antorbital fossa.  Novas et al. (2009) and everyone else has interpreted it as a maxillary fenestra, which would mean Austroraptor would have lost its promaxillary fenestra like derived troodontids. However, it seems more likely to me to be a promaxillary fenestra.  First note that it is of similar shape, size and position as the promaxillary fenestrae of basal paravians such as Archaeopteryx, Sinusonasus and Velociraptor- small, lenticular, along anterodorsal border of antorbital fossa.  Maxillary fenestrae are usually placed more posteriorly, away from the anterior antorbital fossa edge and close to the antorbital fenestra.  The exception is derived troodontids, but their maxillary fenestrae are highly elongate and placed along the ventral edge of the antorbital fossa.  Second, remember that Austroraptor is odd in having a posteriorly extensive postantral wall (labeled pan in the figure below).  As a bit of explanation, the antorbital fossa surface we usually see on the maxilla is the outside wall of the maxillary antrum.  There's an inside wall running alongside it that sometimes peeks out a bit and is responsible for taxa like Scipionyx that look like they have a maxillary fossa, since the inside wall can back the maxillary fenestra.  This inside wall is called the postantral wall where it sticks out behind the lateral wall.  But another way to think of it is that the lateral wall is missing its back end, and what would be in the back end of that lateral wall if it were there?  A maxillary fenestra.  So I hypothesize Austroraptor reduced the ossification of its posterior antorbital fossa wall, merging the maxillary fenestra with the antorbital fenestra, but keeping an ancestral promaxillary fenestra morphology.  I think this hypothesis is more parsimonious than losing the promaxillary fenestra, moving the maxillary fenestra into the same position as the promaxillary fenestra, then elongating the postantral wall.

Austroraptor maxilla (center, from Novas et al., 2009) compared to dromaeosaurid maxilla (left, from Norell et al., 2006) and mostly troodontid maxillae (right, from Senter et al., 2010).  Promaxillary fenestrae circled in blue, maxillary fenestra circled in green.  For Austroraptor, I've circled the part of the postantral wall in dotted green where I think the maxillary fenestra ancestrally was before the lateral wall was reduced.

I've often said I think that Peters is right insofar as most published cladistic analyses of reptiles suck, in both taxon and character count.  Yet his own analysis is worse because it's based on imaginary morphologies.  The same is true of his constant refrain to test others' interpretations, since scientists do sometimes get things wrong.  But this must be done intelligently.

References- Franzosa, 2001 online. Herrerasaurus ischigualastensis (On-line), Digital Morphology.

Norell, Clark, Turner, Makovicky, Barsbold and Rowe, 2006. A new dromaeosaurid theropod from Ukhaa Tolgod (Omnogov, Mongolia). American Museum Novitates. 3545, 51 pp.

Novas, Pol, Canale, Porfiri and Calvo, 2009. A bizarre Cretaceous theropod dinosaur from Patagonia and the evolution of Gondwanan dromaeosaurids. Proceedings of the Royal Society B. 276(1659), 1101-1107.

Alcober and Martinez, 2010. A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina. ZooKeys. 63, 55-81.

Senter, Kirkland, Bird and Bartlett, 2010. A new troodontid theropod dinosaur from the Lower Cretaceous of Utah. PLoS ONE. 5(12), e14329.

Thursday, February 2, 2012

Are Sauropod Skulls Actually Rare?

Hone recently mentioned this old piece of paleontological "common knowledge", but I wonder how true it really is.

For one, we're no longer back in the days of The Dinosauria where only ten skulls could be illustrated by McIntosh.  There have to be a few times that now at least, plus tons known from braincases and/or jaw elements.

Two, just how poorly known are skulls of other dinosaurs?  There are only four or so stegosaur taxa with known skulls, two therizinosaurs, and three alvarezsauroids, for instance.

Three, how much does it reflect the number of sauropods named from axial material as opposed to the percentage of sauropod skulls found per postcranium?  Maybe the elaborate vertebrae of sauropods make them more prone to being named from postcrania, whereas e.g. ornithopod or ceratopsian postcrania are often considered indeterminate.  I suspect if you counted all of the partial cerapod postcrania left undescribed or uncollected, their skulls would seem much more rare.

The first two questions could actually be answered statistically, once my sauropodomorph database were 'complete'.  You would need to try to include only valid taxa (nice and subjective), then find some way to represent cranial completeness (maybe on a scale of 20, where each kind of preserved skull element counts as 1, and having 20 is equivalent to a complete skull), then find the average cranial completeness number for various groups.  The third question would be more difficult, since not only would just trawling museum collections be tedious, it would leave the 'how many aren't collected' part unknown.  And just as I bet there's a bias in not collecting cerapod postcranial bits due to supposed indeterminacy, there's also a bias in not collecting sauropod fossils due to their size.