Chatham Islands theropods

["bh480@scn.org" <bh480@scn.org>]

From: Ben Creisler bh480@scn.org

In case this advance online article has not been mentioned yet:

Palaeo (advance online publication)

Dinosaur sanctuary on the Chatham Islands, Southwest Pacific: First record
of theropods from the K-T boundary Takatika Grit 
Jeffrey D. Stilwell,  Christopher P. Consoli, Rupert Sutherland, Steven
Salisbury, Thomas H. Rich, Patricia A. Vickers-Rich, Philip J. Currie and
Graeme J. Wilson

Abstract 
Cretaceous-Tertiary (K-T) boundary (ca. 65 Ma) sections on a Southwest
Pacific island containing dinosaurs were unknown until March 2003 when
theropod bones were recovered from the Takatika Grit on the remote Chatham
Islands (latitude 44 S, longitude 176 W), along the Chatham Rise. Tectonic
and palaeontologic evidence support the eastward extension of a ca. 900 km
land bridge that connected the islands to what is now New Zealand prior to
the K-T boundary. The Chathams terrestrial fauna inhabited coastal,
temperate environments along a low-lying, narrow, crustal extension of the
New Zealand subcontinent, characterised by a tectonically dynamic, volcanic
landscape with eroding hills (horsts) adjacent to flood plains and deltas,
all sediments accumulating in grabens. This finger-like tract was blanketed
with a conifer and clubmoss (Lycopodiopsida) dominated forest. The Chatham
Islands region would have, along with New Zealand, provided a dinosaur
island sanctuary after separating from the Gondwana margin ca. 80 Ma. 

........

Discussion:
The Takatika Grit is particularly significant in allowing the
reconstruction of the palaeoenvironment and biota for the latest
Cretaceous, just prior to the K-T boundary, and into the early Cenozoic,
representing the dawn of a "brave new world" dominated by birds and
mammals. This was a time of intense, global change. Furthermore, the
Takatika Grit consists of three horizons containing bones, and these
increase in abundance up-section. Whether or not these mass bone
accumulations of reptiles represent individual mass mortality events
remains to be determined. The bone horizons of terrestrial and marine
reptiles, sharks, teleost fish, ammonites and nautiloids (Consoli and
Stilwell, 2005), bivalves, gastropods, sponges, and plant matter, including
exquisitely preserved cones are laterally persistent, unique in the
Southern Hemisphere for this time. 
Until 1979 when the first vertebra of a Late Cretaceous dinosaur was
recovered from New Zealand, several hypotheses were advanced to explain
their absence in the widespread Cretaceous terrestrial and marine sequences
on this small microcontinent. To date, sparse terrestrial and flying
reptile bones have been recovered from the slightly older to coeval
Mangahouanga Stream site, including a tail vertebra (Molnar, 1981), pedal
phalanx from a terrestrial bird or theropod (Scarlett and Molnar, 1984) and
manual phalange from a theropod (Molnar et al., 1998), a rib fragment of a
small sauropod (Molnar and Wiffen, 1994), and a rib and tail vertebrae of
an ankylosaur (Molnar and Wiffen, 1994). Discovery of dinosaurs on the
Chatham Islands demonstrates that these successful reptiles inhabited the
most isolated parts of the Southern Hemisphere, and dinosaurs were
definitely present at high-latitudes in the temperate to warm, low-lying
coastal habitats nearly 1000 km east of New Zealand, an isolated and
unique, K-T boundary environment. 


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