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Re: Two questions on the dino-fleas



Martin Baeker <martin.baeker@tu-bs.de> wrote:


> 1. It is stated that "feathered dinosaurs became well-known from this
> period" - but only two references are given, one relating to the
> cretaceous, the other being the paper where Epidexipteryx is
> described. However, Epidexipteryx seems a bit small to host a
> 2cm-flea. So what are the supposed hosts during the jurassic? Are
> there any known fuzzy dinos from that period? Pterosaurs perhaps? Or
> do these fleas hint at the existence of large feathered dinos we don't
> know about?


Using phylogenetic bracketing, we could infer that a large chunk of
the Theropoda included forms that had some form of filamentous
integumentary
covering.  For example, the 1.6-to-2 m long tyrannosauroid _Dilong_
had 'protofeathers' - albeit larger and more derived tyrannosauroids
may not have had an extensive (if any) covering of these structures.
Although _Dilong_ itself lived in the Early Cretaceous, there were
similar-sized (and larger) theropods from the Jurassic that
undoubtedly had some form of filamentous body covering.  These
theropods could have served as hosts for large stem-siphonapterans.


Also, if modern fleas are any guide, there isn't always a neat
correlation between the size of the flea and the size of the mammal
host.  The largest extant flea (_Hystrichopsylla schefferi) is around
8mm long as an adult (female).  It parasitizes a fairly modest sized
mammal, the mountain beaver (_Aplodontia rufa_), which measures up to
~ 50 cm long (and is unrelated to the true beavers).  Nevertheless,
the large size of the fossil stem-siphonapterans (14.0 - 20.6 mm in
females), as well as the robustness of their mouthparts, accords with
fairly large hosts, as speculated in the paper.
.

> 2. It is explained that fleas evolved from animals feeding on plants
> (possibly gymnosperms). At least nowadays, these are rather small
> animals. If this was true in the Jurassic as well, shouldn't we assume
> that the first blood-sucking fleas were also small, which would make
> it more likely that they evolved from forms living either on early
> mammals or other synapsids or perhaps on pterosaurs? Isn't this more
> plausible than to assume that fleas started on big animals?


The fleas (Siphonaptera) are thought to have evolved from the
siphonate scorpionflies of the Mesozoic.  These included some rather
'large' insects - up to 28 mm long (excluding mouthparts).  The
siphonate mouthparts could themselves be very long.  For example, the
siphonate scorpionfly _Jeholopsyche liaoningensis_ had a body length
of around 24 mm long, and mouthparts  6.8 mm long.  In general, these
winged, proboscid scorpionflies have been reconstructed as liquid
feeders, and regarded as important pollinators of gymnosperm plants in
the Mesozoic, up until the gymnosperm-angiosperm turnover in the
mid-Cretaceous.  This is covered in:

Ren et al. (2009) A probable pollination mode before angiosperms:
Eurasian, long proboscid scorpionflies. Science 326: 840-847.

In fact, the quote cited by Huang et al. (2012) in the 'dino-flea'
paper regarding the feeding habits of siphonate scorpionflies
(‘‘ovular secretions of extinct gymnosperms") actually comes from Ren
et al. (2009), not the reference given (Palmer, 2010).  This is a typo
in the paper.

In general, and to return to your question, I think it is reasonable
to assume that "fleas" (stem-siphonapterans) started on fairly big
animals.  Or at least larger than offered by contemporary mammals (or
mammaliaforms).  Admittedly this is an assumption based on extant
siphonapterans, and their forbears might have had quite different
ecologies.





Cheers

Tim