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Re: Deinocheirus 2nd try



James Aronis wrote-


> It's arms and claws are unlike those found in its relative,
> _Therizinosaurus_. Apparently the proportions of key bones in the
forelimbs are not
> the same. I belive the forearms are proportionately shorter than those in
> _Therizinosaurus_. The claws are also very different being more curved and
thicker
> relative to length.

Differences from Therizinosaurus include- taller coracoid; short blunt
posteroventral coracoid process; low deltopectoral crest; more proximally
located deltopectoral crest; straighter humeral shaft; longer first and
third metacarpals; less robust first metacarpal; manual phalanges much
stouter; smaller flexor tubercles on manual unguals; unguals appear more
curved and lateromedially thicker because they are much shorter; lateral
ungual grooves placed higher.

Deinocheirus vs. Therizinosaurus ratios compared to ornithomimids and
Alxasaurus

                             Deino       Theriz        Ornithom        Alxas
 radius/humerus     67             72             65-75            65
 ulna/humerus        73             82             71-80            72
 mcI/mcII              93             51             85-108          50
mcII/humerus        25             38             31-37            30
 II-1/mcII              61            49             36-46
 II-2/mcII              98            50             80-104
 muII/mcII             85          150             67-117         117?
 mcIII/mcII          107            67             91-100          77

Deinocheirus mirificus
Holotype- (ZPAL MgD-I/6) (~15 m) two ceratobranchials, three vertebral
fragments, seven partial dorsal ribs, gastralia fragments, nearly complete
scapulacoracoids (1.53 m), humeri (938 mm), radii (630 mm), ulnae (688 mm),
metacarpal I (214, 220 mm), phalanx I-1 (320 mm), manual ungual I,
metacarpal II (230 mm), phalanx II-1 (140 mm), phalanx II-2 (226, 229 mm),
manual ungual II (196 mm), metacarpal III (246, 245 mm), phalanx III-1 (110,
105 mm), phalanx III-2 (104, 100 mm), phalanx III-3 (186, 182 mm), manual
ungual III
Referred- (ZPAL MgD-I/64)

Therizinosaurus cheloniformes
Holotype- (GI 551-483) manual ungual I, manual ungual II (654 mm), manual
ungual III (381 mm)
Referred- (GI 100/15) (~8 m) tooth, scapula (670 mm), coracoid (360 mm),
humerus (760 mm), radius (550.4 mm), ulna (620.2 mm), semilunate carpal,
distal carpal, metacarpal I (145.5 mm), metacarpal II (286.8 mm), phalanx
II-1 (141.7 mm), phalanx II-2 (145.8 mm), manual ungual II (~520 mm),
metacarpal III (191.6 mm), dorsal ribs, gastralia
(GI 100/16) distal manual ungual I
(GI 100/17) proximal manual ungual III
(GI 100/45) femur, tibia (253 mm wide), astragalus, calcaneum, distal tarsal
IV, proximal metatarsal I, metatarsal II (200 mm), phalanx II-1 (85 mm),
phalanx II-2 (95 mm), metatarsal III (250 mm), phalanx III-2 (~64.9 mm),
proximal metatarsal IV, phalanx IV-1 (70 mm), phalanx IV-2 (30 mm), phalanx
IV-3 (33 mm), phalanx IV-4 (~65 mm)

> All this speculation is a
> result of not knowing what the skull was like.

Well, it was an ornithomimosaur, so I would expect the skull to be
comparatively small (~670 mm) and toothless.  Of course, it's anyone's guess
what ornithomimosaurs ate, but Hurum (2001) feels their beaks are closest to
larids (seagulls) in shape, suggesting they were omnivorous.  Deinocheirus
probably ate leaves hooked by its long arms, as well as smaller dinosaurs
that the raptorial claws helped kill.

> The forelimbs of theropods have seen a gradual decline in size throughout
> their evolution. What evolutionary pressure would have been exerted on
_Deinocheirus_
> to evolve huge arms and claws for killing, would largely have depended on
the type of
> prey it hunted.

Ooooh... Don't let Tom Holtz hear you say theropods had an evolutionary
trend to decrease forelimb size.  :-) Perhaps I'll save his time by pointing
out such a trend doesn't exist.  It was fabricated back when coelurosaurs
were thought to be the most basal theropods and tyrannosaurids the epitomy
of carnivorous evolution.  Let's compare the humerofemoral ratios of various
theropods moving from basal to derived.
Eoraptor- ~58
Herrerasaurus- 51
Coelophysoidea- 44-66 (based on Coelophysis, Syntarsus and Liliensternus)
Dilophosaurus- 50
Neoceratosauria- 43-52 (based on Ceratosaurus, Elaphrosaurus, Masiakasaurus
and Indosuchus; 28 in Carnotaurus)
basal Tetanurae, basal Carnosauria- 45-53 (based on Megalosaurus,
Chilantaisaurus, Suchomimus, Eustreptospondylus, Piatnitzkysaurus,
Afrovenator and Fukuiraptor)
Allosauroidea- 40-56 (based on Gasosaurus, "Szechuanosaurus campi" and
Allosaurus; 29 in Acrocanthosaurus)
basal Coelurosauria- 38-61 (based on Deltadromeus, Compsognathus,
Sinosauropteryx, Coelurus, Nqwebasaurus, Ornitholestes; 22-38 in
tyrannosaurids)
Ornithomimosauria- 63-80
non-avian Maniraptora- 45-93 (based on Alxasaurus, Protarchaeopteryx,
oviraptorosaurs, Avimimus, troodontids, deinonychosaurs and basal avialans;
26-37 in alvarezsaurids)
Doesn't seem like a trend to shorten the arms to me.  They stay around
40-60% of femoral length until some maniraptoriformes elongate them.  Only a
few sidelines (carnotaurines, carcharodontosaurids, tyrannosaurids,
alvarezsaurids) shorten the arms.
No evolutionary pressure was exerted to give Deinocheirus huge arms, they
were huge because the animal was huge.  The humeroscapular ratio was 80%
compared to 118% in Gallimimus and 108% in Ornithomimus, so the arms were
possibly shorter compared to body size than smaller ornithomimosaurs.

Mickey Mortimer