Why giraffes have such short necks

Why giraffes havesuch short necks

Michael P. TaylorMathew J. Wedel

Why giraffes havesuch short necks

… and howsauropodsgot it right

Michael P. TaylorMathew J. Wedel

3-meter barrier for all non-aquatic animals

Long-necked sauropod groupsUpchurch et al. (2004:fig. 13.18)

Long-necked sauropod groups

I suck ...

Upchurch et al. (2004:fig. 13.18)

Long-necked sauropod groups

Magic

I suck ...


Factors contributing to long necks1. No constraint on vertebral count

Paraceratherium (Osborn 1923:fig 1)

Factors contributing to long necks1. No constraint on vertebral count

Mamenchisaurus (modified from Ouyang and Ye 2003:fig. 13)

Paraceratherium (Osborn 1923:fig 1)

Factors contributing to long necks2. Heads that did not process food


Diplodocus


Unholy Diplodocus ☓ Elephas hybrid

Factors contributing to long necks3. Absolutely large bodies

C


Crap.

Crap.C

Factors contributing to long necks3A. Large quadrupedal bodies

C

Factors contributing to long necks3A. Large quadrupedal bodies

Crap.


Parrish (2006) showed that sauropod neck lengthscales with torso length to the power 1.35


Carpenter (2006) scaled Amphicoelias fragillimus as 2.2 times Diplodocus.But Parrish suggests neck is 2.2^1.35 = 2.9 times => a neck 22 m long

Factors contributing to long necks4. Air-sacs overcame dead-space


Like ostriches?


But what aboutsperm whales?

Paul 1998:fig. 11

Factors contributing to long necks5. Vertebral architecture

Diplodocus carnegii holotype CM 84, cervical 10 (Hatcher 1901:plate III)

Cervical vertebral innovations

1. Extreme pneumaticity2. Bifid neural spines3. Elongate cervical ribs

Cervical vertebral innovations1. Extreme pneumaticity

Ostrich


Diplodocus


Diplodocus modified from Paul 1998:fig. 1(a)F


Diplodocus cervical cross-sections

Paul 1997:fig. 4 Schwarz et al. 2007:fig. 7A2


Diplodocus


Redtailedhawk

Cervical vertebral innovations2. Bifid neural spines

Apatosaurus

Long-necked sauropod groupsUpchurch et al. (2004:fig. 13.18)

Long-necked sauropod groupsBifid neural spines evolvedat least five times

Never secondarily lost?

Otherwise found only inthe rhea (and only just)



Alexander (1985) thoughtthe trough was filled witha giant elastin ligament

Diplodocus


Apatosaurus


Diplodocus (Schwarz et al. 2007:fig. 7A2)

Cervical vertebral innovations3. Elongate cervical ribs

Turkeycervical 7


4.1 m

Turkeycervical 7 Mamenchisaurus


4.1 m

Mamenchisaurus

That lamegiraffe

Turkeycervical 7


Giraffatitan

Comparison with birds and crocs

Turkey cervical 7

Comparison with birds and crocsAlligator Majungasaurus Turkey

Majungasaurus from O'Connor 2007:figs. 8, 20

Comparison with birds and crocsAlligator Majungasaurus TurkeyGiraffatitan

Giraffatitan from Janensch 1950:fig. 46

Majungasaurus from O'Connor 2007:figs. 8, 20

Comparison with birds and crocsAlligator Majungasaurus TurkeyGiraffatitan Camarasaurus

Giraffatitan from Janensch 1950:fig. 46Camarasaurus from Osborn and Mook 1921:plate LXVIIMajungasaurus from O'Connor 2007:figs. 8, 20

Comparison with birds and crocs

Analogous but not homologous

Alligator Majungasaurus TurkeyGiraffatitan Camarasaurus

Giraffatitan from Janensch 1950:fig. 46Camarasaurus from Osborn and Mook 1921:plate LXVIIMajungasaurus from O'Connor 2007:figs. 8, 20

Why are epipophyses not elongate?

Euhelopus (Wiman 1929:plate III)


Deinonychus (Ostrom 1969:fig. 37)


Giraffatitan (Janensch 1950:fig. 43)


Need finer control for precise movements – requires shorter levers



Tendon is stronger in tension than bone



Muscles expand when they contract lengthways



Crap.

Conclusion

TaxonManyvertebrae

No dental battery

Large body, four legs

Air-sacs Pneumatic vertebrae

Elongate cervical ribs

Giraffe Birds ✓ ✓ ✓ ✓Non-avian Theropods ✓ ✓ ✓Pterosaurs ✓ ✓ ✓Sauropods ✓ ✓ ✓ ✓ ✓ ✓

Conclusion

TaxonManyvertebrae

No dental battery

Large body, four legs

Air-sacs Pneumatic vertebrae

Elongate cervical ribs

Giraffe X X X X X XBirds ✓ ✓ ✓ ✓Non-avian Theropods ✓ ✓ ✓Pterosaurs ✓ ✓ ✓Sauropods ✓ ✓ ✓ ✓ ✓ ✓

Acknowledgements

Everyone who allowed us access to specimensEveryone that we stole images fromWestern University for sending Matt to SVPCA

Sauroposeidon

Why giraffes have such short necks

Documents

Transcript of Why giraffes have such short necks