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Darwinopterus paper: misrepresentations and red flags
Misrepresentations and Red Flags:
Darwinopterus is a fantastic find with grand implications.
Nevertheless, the following statements were found in the new
Darwinopterus paper by Lü et al. 2009. The Misrepresentations
(Misreps) appear to play politics with the facts. The Red Flags are
characters that should have prompted more investigation on the part of
the Lü team.
“The 65 Myr long Late Triassic–Late Jurassic interval seems to have
been almost completely dominated by basal clades consisting of small
to medium sized seemingly piscivorous or insectivorous pterosaurs
(Wellnhofer 1975, 1978, 1991; Kellner 2003; Unwin 2003a,b, 2005).”
Misrep: Huanhepterus, Ctenochasma, Cycnorhamphus, Pterodactylus and
Germanodactylus are all Late Jurassic.
“Typical characters of these [basal] pterosaurs include: separate
nasal and antorbital openings in the skull, elongate cervical ribs,
short metacarpus (less than 80% humerus length) and a fifth toe
consisting of two elongate phalanges that supported a flight membrane
(cruropatagium) stretched between the hind limbs (Unwin & Bakhurina
Misrep: No membrane stretched between the hind limbs. Membranes
trailed each hind limb.
In any case, Figure 4 of the Darwinopterus paper shows the membranes
stretched between the tail and hind limbs.
“…as shown, for example, by the differing allometric relationships
evident in growth patterns for the skull, neck and post-cervical axial
skeleton (Bennett 1996).”
Misrep: Pterosaur embryos are matches for parents. Bennett’s juvenile/
adult “pairings” were not congeneric.
“The skull is unusually large, almost twice the length of the dorsal
sacral vertebral series (DSV). This value is substantially greater
than for any basal pterosaur and is high even for pterodactyloids
Red Flag. A basal pterodactyloid-grade pterosaur should be a close
match (incrementally different) to its predecessor in most regards,
including the skull. That’s the way evolution works. The alternate
view supports and demonstrates that.
“…the tail of Darwinopterus is identical to that of most basal clades,
consisting of more than 20 caudals which, apart from the first three
or four vertebrae, are long and rod-like and enclosed by a sheath of
bony filaments composed of highly elongated ossified extensions of the
zygapophyses and hypapophyses (figure 2e) (Wellnhofer 1975, 1978).”
Misrep: Pterodaustro likewise has an elongated tail. We can suspect
its predecessors also did. Just because preparators haven’t prepped
out more long tails, doesn’t mean they’re not there. A little digging
will reveal more. That the tail of Darwinopterus is more robust than
the tail of Scaphognathus is notable.
“The glenoid is located on the scapula rather than equally shared by
the scapula and coracoid as in pterodactyloids (Wellnhofer 1978).”
Misrep: Also shared by scapula and coracoid in basal pterosaurs too.
IF the glenoid is only on the scapula in Darwinopterus (hard to see) ,
that would be a derived character, not a transitional character.
“The metacarpus is less than 70 per cent the length of the humerus, a
universal feature of basal pterosaurs (figure 3c),”
Misrep: This is Nature at her trickiest. This species has an
atypically short metacarpus for reasons aside from phylogenetic
transition, as determined by its placement higher in the family tree.
This is a reversal.
“Darwinopterus corresponds to the condition in all long-tailed
pterosaurs where phalanges two and three are of similar dimensions and
exceed the length of the first and fourth phalanges (Wellnhofer 1975,
1978; Kellner 2003).”
Misrep: M4.2 not < m4.1 also in Elanodactylus, Ninchengopterus, two
Pterodactylus specimens, Wellnhofer (1970) No. 6, No. 12, No 23, all
ctenochasmatids. M4.2 < m4.1 among basal pterosaurs in three basal
Rhamphorhynchus specimens, Raeticodatylus and eight higher
“Finally, the fifth toe consists of two elongate phalanges (figure 2d;
electronic supplementary material, figure S3), as in all basal
pterosaurs, and the distal phalanx is sharply recurved, a condition
only met with in some rhamphorhynchids (Kellner 2003; Unwin 2003a,b).”
Misrep: Such a toe appears in a wide variety of pterodactyloid-grade
pterosaurs, unrecognized until now. Preparators understood that a big
fifth toe was not to be found in certain pterosaurs, so they didn’t
bother to even try to prep them out.
“These contrasting results emphasize two key aspects of Darwinopterus:
the complete absence of ‘intermediate’ character states that fall
between those states found either in basal pterosaurs or in
pterodactyloids (figure 3), and the almost perfect modularity
exhibited by the mosaic pattern of character state distributions found
in this pterosaur.”
Red Flag: Evolution, by definition, is a series of small intermediate
steps. The alternate view demonstrates small steps.
“Darwinopterus provides, to our knowledge, the first detailed insights
into the transition from basal pterosaurs to pterodactyloids and, when
combined with our rapidly increasing knowledge of the pterosaur fossil
record (Barrett et al. 2008), helps to pinpoint several key features
regarding the nature and timing of this event (figure 4c).”
Misrep: Well, it wouldn’t be the first time the alternate view was
ignored. Both Lü and Unwin heard and read the alternate view in Munich
in Sept. 2007. The paper provides few insights in that no predecessor
genus is identified and no successor genus is identified. The
alternative view has these predecessors and successors.
“Two distinct phases are recognized. In the first, elongation of the
skull, breaching of the bony bar separating the nasal and antorbital
opening, reconfiguration of the cranium leading to an increase in the
relative size and volume of the braincase and simplification of the
dentition, together with changes to the shape of the cervical
vertebrae and loss of the cervical ribs, culminated in the
monofenestrate skull and modified neck inherited by Darwinopterus and
all pterodactyloids figure 4b).
Misrep: Simplificaton of the dentition? You can’t get simpler than
Scaphognathus. And ctenochasmatids do not have simplified dentition.
> The ctenochasmatid problem was the key to my searching for a new
answer to the pterodactyloid evolution issue. You can’t start from
Darwinopterus and get Ctenochasma or Gnathosaurus. It’s more
parsimonious to start with basal pterosaurs that have elongated teeth
and a relatively wide rostrum, like Dorygnathus and Angustinaripterus,
which elongates the skull and reduces the naris. When done right, you
can see the gradual evolution of characters in all parts of the head,
neck and body, including the feet. There is no need to invoke large
scale “modular” evolution. Evolution works in increments, sometimes
modular increments, but increments nevertheless, and these are all
visible when the taxon list is enlarged.
“In the second phase of the transition, modifications were confined to
the post-cervical axial column, limb girdles and limbs. Key among
these were shortening of the tail, elongation of the metacarpus and
reduction of the fifth toe, changes that appear to have significantly
improved the locomotory abilities of pterodactyloids (Unwin 2005).”
Misrep: Lü et al. will find with further study that reduction of the
fifth toe occurs, not once, but in several pterodactyloid-grade
lineages. Shortening of the tail begins with the smaller Scaphognathus
On the timeline I note long ghost-lineage lines in the Jurassic.
Plenty of time for evolution to work its magic.
On the phylogenetic chart I notice several taxonomic bunch-ups at the
transition from basal to pterodactyloid-grade. In other words, several
taxa are jockeying for positions both on the predecessor and the
successor sides of Darwinopterus. This is the reason for the 500,000+
trees. A good phylogeny would have showed which genus was closest to
Darwinopterus on both sides, but this study fails to do so. Increased
taxon inclusion will help.