Bromsgroveia and other archosaurians from Mid-Triassic of England (free pdf)

[Ben Creisler <bcreisler@gmail.com>]

From: Ben Creisler
bcreisler@gmail.com

Another new paper that I somehow missed and that I don't think has
been mentioned yet on the DML. The pdf is free.


Peter M. Galton (2012)
Notes on bones and teeth of Bromsgroveia and other archosaurian reptiles from
the lower Middle Triassic (Anisian) of the English Midlands.
Revue de Paléobiologie, Genève 31 (1): 171-204
http://www.ville-ge.ch/mhng/paleo/paleo-pdf/31-1/pal_31_1_11.pdf




The archosaurian bones and teeth from the lower Middle Triassic (Late
Anisian) of the English Midlands (Warwick, Leamington, Bromsgrove) are
illustrated. Based on the apomorphic characters of the holotype ilium,
and of the referred bones, an ischium and vertebrae (mid-cervical,
mid- and last dorsals, sacrum, caudal 1), Bromsgroveia walkeri Galton,
1985a is probably a ctenosauriscid poposauroid rauisuchian archosaur.
It has four sacral ribs: the iliac attachment area for rib 1 extends
to the end of the anterior process and superiorly to reach the dorsal
edge, as do the areas for ribs 2 and 3, whereas that for rib 4 is only
on the dorsomedially facing dorsal edge of the posterior process, the
shallow C-shaped end of which is subhorizontal with the gently convex
outer surface facing dorsally and slightly laterally.  A
non-poposauroid archosaur, Rauisuchoidea indet., is represented by the
posterior process of an ilium, which is much less derived than that of
Bromsgroveia, a distal ischium that is almost identical to that of
Postosuchus, and sacral vertebra 2 in which the postzygapophyses are
not fused to the adjacent prezygapophyses and the sacral rib is deep
and more ventrally directed. This rauisuchoid, rather than
Bromsgroveia, is probably more closely related to the maker of the
trackways of Chirotherium from the Early Anisian of the English
Midlands.

Seven tooth types are recognized: in types A to D most of the distal
edge is uniformly serrated, with the denticles set perpendicular to
the edge, and most of the length of the mesial edge is also serrated
in type A, but in types B to D the denticles on the mesial edge are
restricted to the apical third or so. In type B the denticles are as
in type A whereas in type C the denticles are longer mesiodistally and
obliquely inclined slightly apically, being coarser at mid-height but
becoming fner in passing along the distal edge. The crowns of types D
and E are more slender: in type D the mesial denticles end abruptly,
and the basal section of the crown is subcircular, and in type E
serrations are present on the apical two thirds of the edge mesially
but only for an eighth distally. In type F both edges of the large
sub-symmetrical spatulate shaped crown are convex and mostly serrated.
In type G the small sub-symmetrical crown is only very slightly
recurved and denticles end at the widest part of the mesiodistally
expanded crown, beyond which the crown narrows to a neck region. Three
of the tooth types (A, B, F), which are tentatively referred to
Rauisuchia indet. because they could be either Bromsgroveia or
Rauisuchoidea indet., represent a premaxillary or most anterior
dentary tooth (F) and maxillary (or corresponding dentary) teeth (A,
B). The remaining tooth types indicate the presence of additional
non-rauisuchian archosaurian taxa, three separate carnivorous
Archosauria indet. (C-E) and a small omnivorous Archosauria indet.
(G). This, and the bones of the ctenosauriscid Bromsgroveia and a
possible rauisuchoidean, indicates the presence of six archosaurs, a
greater faunal diversity for the Middle Triassic of England than
previously recognized.