[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: when is a Lazarus Taxon not a Lazarus Taxon?
Tom Holtz wrote:
That thing that makes a critter a Lazarus taxon is our limited knowledge of
its stratigraphic and distributional record, and not properties of the
organism per se.
Just to emphasize this, Lazarus taxa occur when ghost lineages are extended
forward in the fossil record (or even to the Present). Ghost lineages are
all too common; but it's only when a stratigraphically older taxon (hitherto
thought to be the youngest member of a group) is linked phylogenetically to
a significantly younger taxon that the latter is termed a "Lazarus taxon".
The choristodere _Lazarussuchus_ (Oligocene) was named with this in mind.
Further, if _Lazarussuchus_ is a basal choristodere (as some phylogenetic
analyses have found), it implies a very long ghost lineage indeed.
I can't think of any obvious Lazarus taxa among the non-avian dinosaurs.
Most of the newer discoveries have been very helpful at filling in ghost
lineages, not creating new ones. Then again, maybe I'm not looking hard
Some "Lazarus taxa" prove not to be Lazarus taxa after all, but are instead
cases of mistaken identity. In other words, the allegedly 'resurrected'
clade is indeed extinct and the new taxon belongs to another group
altogether; the new taxon just happens to have evolved a similar morphology
independently (i.e., through convergence) to an extinct clade. There is a
separate term for this kind of taxon: "Elvis taxon". Coined by Erwin and
Droser (1993) "in recognition of the many Elvis impersonators who have
appeared since the death of the King.
The therizinosaurs (segnosaurs) might constitute "Elvis taxa", given that
they were once linked to prosauropods. But as maniraptoran theropods, the
derived, heavy-bodied and presumably herbivorous therizinosaurs are
"prosauropod impersonators". (Of course, therizinosaurs are a lot more than
this; and in terms of the number of individual characters they have in
common, the two groups are not really all that similar.)
Thank you very much.
were to discover a _Dilophosaurus_ from the end of the Middle Jurassic
that would constitute a Lazarus taxon, as it seemingly went extinct and
then reappears in the fossil record stages later.
Hope this helps,
Thomas R. Holtz, Jr.
Senior Lecturer, Vertebrate Paleontology
Department of Geology Director, Earth, Life & Time Program
University of Maryland College Park Scholars
Building 237, Room 1117
College Park, MD 20742
Phone: 301-405-4084 Email: firstname.lastname@example.org
Fax (Geol): 301-314-9661 Fax (CPS-ELT): 301-405-0796
Get today's hot entertainment gossip