New in _Paleobiology_

["Jaime A. Headden" <qilongia@yahoo.com>]

  Evans, D. C. 2006. Nasal cavity homologies and cranial crest
   function in lambeosaurine dinosaurs. _Paleobiology_
   32(1):109-125.

Abstract:
  "A neurological method for assessment of nasal cavity homologies
   in extant archosaurs is extended to lambeosaurine hadrosaurids
   (Dinosauria: Ornithischia) to test functional hypotheses
   associated with their hypertrophied nasal passages and highly
   derived cranial crests. The olfactory system and associated
   cranial nerve pathways that have consistent relationships to
   soft tissue divisions of the nasal cavity are reconstructed in
   lambeosaurines on the basis of new paleoneurological data and a
   comparative phylogenetic approach. The new model of the
   lambeosaurine olfactory system and nasal cavity shows that a
   significant portion of nasal cavity proper was located outside
   the crest cavities and that the primary olfactory region was
   located rostromedial to the orbits.
  "All available data indicate that the evolutionary hypertrophy
   of the nasal cavity occurred predominantly within the
   non-olfactory nasal vestibule, and that crest development was
   not causally associated with olfaction. The high level of
   interspecific and ontogenetic variation in crest shape and
   nasal vestibule development in lambeosaurine dinosaurs is most
   consistent with proposed behavioral functions, notably acoustic
   resonance for intraspecific communication. Despite significant
   modification to the nasal cavity within Archosauria and its
   extreme hypertrophy and supraorbital development in
   Lambeosaurinae, the neural olfactory system and the olfactory
   region of the nasal cavity proper retain their plesiomorphic
   positions and associations, suggesting that this system is
   highly conserved in vertebrate evolution."

  Using the olfactory endocasts and assessing braincase structure, including
the sphenoid system, Evans informs us that the olfactory system is not related
to the growth of the dorsal cranial crest. Indeed, from the conclusions:

  "The olfactory region of the nasal cavity proper consistently
   retains its plesiomorphic position in archosaurs, despite
   significant independent structuralmodification to the nasal
   cavity in crocodilians and birds and its extreme supraorbital
   development in Lambeosaurinae. The homologous olfactory conchae
   of birds (caudal concha) and crocodilians (concha; the
   postconcha is neomorphic [Witmer 1995b]) are structurally
   associated with the lacrimal bone (Witmer 1995b), as appears to
   be the case in lambeosaurines as judged from the inferred
   pathways of olfactory nerve bundles. Regardless of whether
   behavioral or other factors were primary in the extreme
   evolutionary modification of the nasal cavity and surrounding
   bones in lambeosaurine hadrosaurids, the olfactory system was
   not radically modified in lambeosaurine evolution, suggesting
   that this system is evolutionarily conservative among
   vertebrates."

Also in the same issue:

  Plotnick, R. E. & P. J. Wagner. 2006. Round up the usual
   suspects: Common genera in the fossil record and the nature of
   wastebasket taxa. _Paleobiology_ 32(1) 126-146.

Abstract:
  "Understanding the extent to which the reported fossil record
   reflects biological history, rather than preservational
   artifacts or other biasing factors, remains one of the central
   issues in the interpretation of the history of life on Earth.
   The development of large interactive paleontological databases,
   such as the Paleobiology Database (PBDB), allows detailed
   analyses of the patterns of occurrence, both regionally and
   globally, of taxa in the fossil record and makes possible
   testing hypotheses of the controls of the patterns. An analysis
   of data from the PBDB shows that most genera in the fossil
   record are rare, whereas a relatively small percentage of taxa
   account for a disproportionate share of the total occurrences.
   These ubiquitous taxa tend to be speciose and have long
   stratigraphic ranges. These patterns of occurrence might
   represent a true biological signal; it is also possible that
   they reflect taphonomic processes or are the result of
   taxonomic practice. In particular, common taxa may be taxonomic
   wastebaskets, i.e., residual and polyphyletic groups resulting
   from inadequate systematic attention and/or from taphonomic
   biases resulting in inadequate specimens being preferentially
   placed in particular genera. A conceptual model for the
   development of taxonomic wastebaskets suggests that these taxa
   should be speciose, widely distributed, common, and old (in
   terms of year of first description), and that they should be
   the nominate forms for higher taxa. Our analyses suggest that
   many of the common taxa in the PBDB are consistent with two or
   more of these expectations and are thus good candidates for
   being wastebaskets. These taxa are, however, only a small
   percentage of total genera. A more detailed examination of one
   group, early gastropods, indicates that possible wastebaskets
   still are present in a group that has received much recent
   systematic work. Given that likely wastebasket taxa are a small
   fraction of all genera, they probably have little effect on
   overall temporal patterns of generic richness. Their impact on
   other types of metrics, such as turnover rates or metrics of
   community diversity or biogeographic similarity, however, might
   be quite important."

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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