Masillastega and the Origin of Boobies (Steganopodes: Sulidae)

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

Mayr, G. 2002. A skull of a new pelecaniform bird from the Middle Eocene
of Messel, Grmany. _Acta Paleontologica Polonica_ 47 (3): 507-512.

Mayr describes the new *Masillastega rectirostris,* a pelecaniform that is
superficially suloid in appearance (as in cormorants, boobies, and
anhingas; see Cracraft, 1985 [_The Auk_ 102: 834-853]) and is represented
only by a skull. The form resembles the fossil *Limnofregata*, but instead
of marine environments, *Masillastega* is from the freshwater deposits of
Messel (= Masilla, in Roman times, hence Mayr's *Masillapodargus*
{"*Podargus* from Messell"}).

Masillastega  Mayr, 2002
  M. rectirostris  Mayr, 2002

"straight-nosed [or beaked] Masilla [Messel] webbed[-footed one]." [note:
the suffix _-stega_ derives from steganos, meaning webbed, and has
previously been used for web-footed birds, rather than as a reference to
the _-stega_ suffix common in basal tetrapods/anamniotes. I think
_-stegana_ should be the useful stem, but nonetheless, an interesting
mixture, though ill-fitting of Greek and Latin.]

holotype and only specimen: IPB 140a, b (slab and counterslab) from the
Messel shales near Darmstadt, Hessan, Germany; dated as lower Middle
Eocene, a skull and mandible preserved on the left sidem imbedded in
matrix. Gross skull length is 139mm, and the mandible is 135mm.

diagnosis and relationships:

Mayr diagnosis *M. rectirostris* by the straigt, conical beak, more than
2/3 the total skull length (similar to fregatines and some cormorants); a
hooked rostrum; extensive narial ossification, a feature found in
pelecaniforms and most tube-nosed birds (precellariiforms); broadening of
the dorsal surface of the mandible, roughly planar on the surface; the tip
of the mandible is very short and the symphysis brief, a feature that
increases mandibular flexibility without sacrificing intramandibular
stability; the beak is estensively vascular; deep rectus tympanicus.
Wordings for characters are all after Mayr, except where Latin is used/

  Pelecaniform relationships are primarily found in 2 (1-3) unambiguous
synapomorphies and 2 (3-5) that are not found in ciconiiforms, including
scopids [hammerkops] and (I presume) balaenicipitids [shoebills] by
association, despite molecular evidence that suggests pelecaniform
similarities. None of those are morphological, and Feduccia is probably
right in pointing out that the shoebill is an odd stork. Genetic studies
suggesting the latter are summarized in Livezey and Zusi, 2002
[_Netherlands Journal of Zoology_ 51(2): 179-205]. Characters are: 1) beak
long, with upper tip hooked; 2) narial openings strongly reduced; 3)
dorsal surface of mandibular rami mediolaterally very wide; 4) symphyseal
region of mandible very short; 5) presence of distinct temporal fossae.
Characters 1-3 refer to the Steganopodes (=webbed feet): Fregatidae,
Pelecanidae, Sulidae, Phalacrocoracidae, and Anhingidae. The latter three
comprise Suloidea, and the first two Fregatae and Pelecanae respectively.
The Steganopodes does not comprise the Phaethontidae, which are considered
the most basal pelecaniforms. Tentative referal to the Sulidae for *M.
rectirostris* is acheived by 1) upper beak and mandibular rami deep; 2)
bearing numerous impressions of blood vessels; and 3) presence of a deeply
excavated dorsal tympanic recess; Mayr views these to be derived in
neognaths and to occur all together in sulids only.

  Mayr distinguishes *M. rectirostris* from other pelecaniforms by the
shape of the long and dorsoventrally high beak (most sulids, though, have
much deeper beaks, and the shape is intermediate between sulids and
phalacrocoracids); from the Eocene *Limnofregata* and *Prophaethon* in the
strongly ossified narial openings; from *Eostega* in being smaller
(mandible length is 135mm compared to *Eostega* being 152mm) and having a
straight dorsal margin of the mandibular rami.

  Mayr provides *Masillastega* as probably the most basal sulid, predating
the oldest known sulid fossil, *Sula ronzoni*, from the Oligocene of
France; it was approximately the size of the shag, *Phalacrocorax aristotelis*.

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