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STONESFIELD, ECHOLOCATION & LIFE OF MAMMALS



A few things that might be of interest in view of recent 
discussions here.

STONESFIELD THEROPODS

It's funny that no one's been doing anything with megalosaurids 
for ages; all of a sudden all hell breaks lose. As discussed, Allain 
and Chure (2002) argue that more than one theropod taxon is 
present in the Stonesfield Slate as indicated by different femora 
and ilia in British collections. On this note I was a bit surprised 
that they didn't mention the suggestion that OUM J13506, the left 
maxilla described by Huxley (1869) and later incorporated by 
Phillips (1871) into his skull reconstruction, is not from 
_Megalosaurus_ but from a sinraptorid. This suggestion was 
made by Bakker et al. (1992) in the _Edmarka_ paper and is based 
on the abbreviated rostral ramus. A long megalosaurid-style 
rostral ramus is not missing from the specimen as the rostral 
margin, even with its rostromedial process, is intact.

Whether or not OUM J13506 is from a sinraptorid, it's clearly 
from a theropod with a very different maxilla to that seen in 
_Torvosaurus_, _Afrovenator_, _Poekilopleuron? 
valesdunensis_ and _Walkersaurus hesperis_. It thus is almost 
certainly not from a megalosaurid and thus also supports the 
presence of more than one big theropod at Stonesfield.

Bakker, R. T., Kralis, D., Siegwarth, J. & Filla, J. 1992. 
_Edmarka rex_, a new, gigantic theropod dinosaur from the 
middle Morrison Formation, Late Jurassic of the Como Bluff 
outcrop region. _Hunteria_ 2 (9), 1-24.

Huxley, T. H. 1869. On the upper jaw of _Megalosaurus_. 
_Quarterly Journal of the Geological Society, London_ 25, 311-
314.

ECHOLOCATING MOSASAURS

Jaime covered most of the points but I don't recall him 
mentioning the following. Echolocation requires directional 
hearing and hence, in water, isolation of the ear bones from the 
rest of the skull (otherwise all sounds are conducted through all 
bones too quickly for the brain to effectively register the time 
delay). Cetaceans have oil-filled sacs isolating their ear bones 
from the rest of the skull. Mosasaurs (and other marine reptiles) 
don't and presumably would have employed bone-conducted 
hearing. 

The possibility of echolocation and/or high-frequency hearing has 
been considered (in the literature) for all the Mesozoic marine 
reptile groups and all the evidence indicates that 
echolocation/HFH was not practised by these animals. Wade (see 
below) reported the possible presence of a melon-like structure in 
_Platypterygius_ but, while some ichthyosaurs possess a 
frontoparietal concavity dorsal to the frontoparietal foramen, this 
interpretation is probably not correct.

Wade, M. 1984. _Platypterygius australis_, an Australian 
Cretaceous ichthyosaur. Lethaia 17, 99-113.

- . 1990. A review of the Australian Cretaceous longipinnate 
_Platypterygius_ (Ichthyosauria, Ichthyopterygia). _Memoirs of 
the Queesland Museum_ 28, 115-137.

EUROTAMANDUA

Did anyone see episode II of _Life of Mammals_? This was about 
insectivores (in the lose, generic sense) and included xenarthrans 
and pangolins as well as lipotyphlans and bats. The reason I'm 
mentioning this? Attenborough claimed that anteaters (s.s.) and 
pangolins have gone pretty much unchanged for 40-odd million 
years and.. cue Messel -  he then showed fossils of 
_Eurotamandua_ and _Eomanis_. Storch was credited as a 
technical consultant so it seems that, despite Szalay and Shrenk 
(1998), _Eurotamandua_ is still a myrmecophagid even though 
it's been shown not to be. See...
http://www.cmnh.org/dinoarch/2002Oct/msg00511.html

-- 
Darren Naish
School of Earth & Environmental Sciences
University of Portsmouth UK, PO1 3QL

email: darren.naish@port.ac.uk
tel: 023 92846045