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Re: Cool Jurassic Marine fauna
> Â Are there any late surviving placodonts that made it
> into the the Jurassic?
No. Unfortunately, because I'd love to see a placodont come to life with CGI.
One recent paper restores placodonts as Triassic analogs of modern dugongs and
Diedrich, C.G. (2010). Palaeoecology of Placodus gigas (Reptilia) and other
placodontids â Middle Triassic macroalgae feeders in the Germanic Basin of
central Europe â and evidence for convergent evolution with Sirenia.
Palaeogeography, Palaeoclimatology, Palaeoecology 285: 287â306.
Abstract: "The classical descriptions of Middle Triassic marine Placodus gigas
Agassiz, 1833 (Reptilia) from the Germanic Basin of central Europe as being
shell-crushing durophagous placodontids are revised in this paper through
analyses in convergent anatomy. In particular, the jaw morphologies of three
placodontid genera, Paraplacodus, Placodus and Cyamodus, are compared to those
of dugongs (Mammalia) such as the central European Tertiary Halitherium
schinzii and the modern Dugong dugon of the Arabian Gulf. The anatomies of
Paraplacodus, Placodus and Cyamodus exhibit convergences to Halitherium and
Dugong. Whereas mammalian dugongs developed pachyostotic thoracic ribs to
enhance their body weight, the placodontid reptiles achieved a similar result
in different ways: Paraplacodus developed enlarged thoracic ribs; Placodus had
pachyostotic gastral ribs, and Cyamodus had a thoracic osteoderm shield. The
teeth of the placodontids are also convergent with
those of Halitherium and Dugong in their general function and jaw morphology.
Whereas Halitherium and the modern Dugong possess a horny oral pad and
counterpart, and a specialized rasp-like tongue with which to grind the
seagrass and its roots, placodontids had large teeth that covered thewhole of
their upper and lower jaws forming a similar crushing or grinding pad. Both of
the extinct groups must have fed on sea-plants, as does the modern Dugong,
although Halitherium possibly fed on both seagrass and macroalgae. A study of
the wear stages of many Placodus teeth, skulls and jaws has revealed a large
proportion of highly worn anterior teeth, indicating a usage similar to that of
the procumbent front teeth of modern Dugong which are used to scrape plant
roots fromthe seafloor. In contrast, highly worn (wear stage 3) teeth are rare
(0.5%) amongst all other upper palatal, maxillary, or lower-jaw dentary teeth,
suggesting a relatively soft diet. Placodus
must have used their broadly spaced anterior teeth, to dig macroalgae from
carbonate sands in shallow marine, sand bar environments; indirect evidence for
the existence of such environments is provided by the benthic communities of
the Germanic Basin and the northern Tethys. Sea-plants would have been only
crushed and swallowed by the placodontids and not chewed with jaw rotation, in
a similar feeding strategy to that used by modern Dugong feeding on seagrass."