A classification of living and fossil genera of - Raffles Museum of ...

Ahyong et al. (2007) work seems to us the strongest
evidence to date on the relationships of the primitive crab
families, and we have followed their suggestion in
recognizing the Dromiacea, Raninoida, and
Cyclodorippoida, and not the Podotremata.
The Ng et al. (2008) catalogue also differs from the Martin
& Davis (2001) list in recognizing subfamilies (in part
following Davie’s (2002) extremely useful catalogue of
Australian crabs and Ng & Davie’s (2002) list of crabs
from Phuket and western Thailand), and by including all
known species. This addition makes it a very useful
compendium, and we have followed the Ng et al. (2008)
catalogue, rather than the Martin & Davis (2001)
classification, in our treatment of nearly all families and
subfamilies and their included genera.
The current list also differs from the Ng et al. (2008)
catalogue in the inclusion of fossil taxa. Although all
named fossil taxa are now included, not all recently
proposed arrangements within families based on fossil taxa
have been incorporated [see e.g. revisions of the
Xanthoidea by Karasawa & Schweitzer (2006) and of the
Carcineretidae by Schweitzer et al. (2007)]. On the whole,
we have attempted to place the fossil taxa within a
framework based on living taxa, with one exception. For
the Portunoidea we do not follow the primarily fossilbased
Karasawa et al. (2008) classification (with some
minor exceptions). However, a recent preliminary analysis
by Schubart & Reuschel (2009) suggests that an extensive
rearrangement of portunoid families will be required. And
indeed, following Schubart & Reuschel (2009), we are
now treating the families Pirimelidae and Thiidae as
members of the Portunoidea. As an example of a widely
divergent placement between classifications based on
extant taxa and those used by fossil workers, the family
Mathildellidae could be cited. Although treated as a family
of the Portunoidea by Karasawa et al. (2008) on mostly
fossil evidence, the Mathildellidae is retained here in the
Goneplacoidea following Ng et al. (2008).
In part because of consideration of fossil taxa, we also
have not used the suggested subfamilies of the family
Dynomenidae as employed by Guinot (2008). We felt that
the addition of these subfamilies would result in too large a
number of unplaced fossil genera. The pending list of
fossil decapods [Schweitzer et al., 2009 (in press)] also
does not use these suggested dynomenid subfamilies. For
the freshwater crabs, we have combined the genera
formerly in the family Parathelphusidae (e.g. in Ng et al.,
2008) with those in the Gecarcinucidae, resulting in a
single family (Gecarcinucidae) in the superfamily
Gecarcinucoidea, following the suggestion of Klaus et al.
(2009), who found no support for recognizing both
families. However, with regard to the suggestion by Klaus
et al. (2009) that the Old World freshwater crabs should
perhaps be combined in one superfamily, we defer from
doing so until more evidence surfaces (see also
Cumberlidge & Ng, 2009).
De Grave et al.: Living and fossil genera of decapod crustaceans
8
There is still debate among systematists as to the recognition,
limits and constituencies of some of the proposed
higher crab taxa, such as the Podotremata (noted above),
Eubrachyura, Heterotremata and Thoracotremata. The use
of superfamilies has also been questioned recently, at least
for “grapsoid” families (see Schubart et al., 2006). We
have maintained these superfamily groupings and higher
taxa (other than Podotremata) for now in keeping with our
decision to follow the classifications used by Martin &
Davis (2001) and Ng et al. (2008). For most of the higher
level taxa (families and their organization into superfamilies
and sections), see discussions in Martin & Davis
(2001), Davie (2002), McLaughlin et al. (2005), Ahyong et
al. (2007), and Ng et al. (2008).
We refer readers to the Ng et al. (2008) paper for a large
number of synonymies, assigned authors, dates of publications
and discussions of questionable taxa in the
Brachyura. Also discussed at various points by Ng et al.
(2008) are recent changes suggested by Števčić (2005),
who proposed a number of new taxa and proposed
increasing the number of recognized superfamilies to 48
[up from 25 in Martin & Davis (2001) and 37 in Ng et al.
(2008)]. One of our goals in assembling the current list is
to establish a general framework that can then be tested
using a combination of molecular, morphological, and
paleontological characters. Števčić’s proposed classification
gives us another alternative that we will be
testing in the years ahead, along with the arrangements
proposed by Martin & Davis (2001), Ng et al. (2008), and
others.
THE PLACEMENT OF FOSSIL TAXA
Our classification draws heavily on the work Schweitzer et
al. [Schweitzer et al., 2009 (in press)] for the placement of
fossil taxa, but it differs in some respects. We have relied
more heavily on classifications based on extant taxa and in
many cases have “shoe-horned” fossil taxa into this
classification. For those forms, primarily Cenozoic in age,
that exhibit very close morphological affinities with extant
forms, the placement of fossil taxa has been a
straightforward exercise. However, many ancient decapods
are morphologically quite dissimilar from known modern
animals, and therefore they pose special problems in
classification. Modern classifications of Decapoda are
largely based upon characters of the anatomy that only
rarely are preserved in the fossil record, such as the
maxillipeds and the reproductive structures. Therefore,
paleontologists find it necessary to employ morphological
features that are preserved on fossils and relate those
attributes to comparable features on extant forms. These
so-called proxy characters (Schweitzer, 2003), although
not without problems (see Ng et al., 2008), often provide a
bridge that permits fossil taxa to be placed within
classification schemes developed solely for extant forms
(Feldmann, 2003; Feldmann & Schweitzer, 2000).