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Did Acanthostega lose an intertemporal?

Friday, February 10, 2017 12:18
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Or was it overlooked?
(See Fig. 1, blinks organge/green above the orbit.)

Figure 1. Acanthostega skull from Porro et al. 2015 showing lack and presence of the intertemporal. ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2017/02/acanthostega_intertemporals.gif?w=584&h=430?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2017/02/acanthostega_intertemporals.gif?w=584&h=430?w=584″ class=”size-full wp-image-25959″ src=”https://pterosaurheresies.files.wordpress.com/2017/02/acanthostega_intertemporals.gif?w=584&h=430″ alt=”Figure 1. Acanthostega skull from Porro et al. 2015 showing lack and presence of the intertemporal. ” width=”584″ height=”430″ />

Figure 1. Acanthostega skull from Porro et al. 2015 showing lack and presence of the intertemporal above the postorbital and between the postfrontal and supratemporal — or else it is fused to the parietal.

Ancestral osteolepiformes
like Osteolepis have an intertemporal. So do many (but not all) basal tetrapods. Porro et al 2015 did not indicate one (Fig. 1), but I have added a green one where I think one would be, dorsal to the postorbitals and lateral to the parietals. It blinks on an off in that animation. It might have been overlooked because the whole skull roof has shifted forward. Typically the intertemporal is located somewhat behind the orbit (Fig. 2), where the supratemporal is in figure 1.

Ventastega, a closely related taxon,
(Fig. 2, green added) indicates the presence of an intertemporal. Earlier an intertemporal was located in Ichthyostega where one was overlooked before.

Figure 2. Ventastega from Ahlberg et al. 2008, showing their interpretation of an intertemporal (green). ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2017/02/acanthostega1_588.jpg?w=584?w=274″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2017/02/acanthostega1_588.jpg?w=584?w=406″ class=”size-full wp-image-25960″ src=”https://pterosaurheresies.files.wordpress.com/2017/02/acanthostega1_588.jpg?w=584″ alt=”Figure 2. Ventastega from Ahlberg et al. 2008, showing their interpretation of an intertemporal (green).” srcset=”https://pterosaurheresies.files.wordpress.com/2017/02/acanthostega1_588.jpg 406w, https://pterosaurheresies.files.wordpress.com/2017/02/acanthostega1_588.jpg?w=137 137w, https://pterosaurheresies.files.wordpress.com/2017/02/acanthostega1_588.jpg?w=274 274w” sizes=”(max-width: 406px) 100vw, 406px” />

Figure 2. Ventastega from Ahlberg et al. 2008, showing their interpretation of an intertemporal (green) above a missing postorbital.

Side note
Most Acanthostega relatives do not have such an elevated mandible tip. This hook-jaw morphology is similar to the spawning phase of the male sockeye salmon, which does not have such a hooked jaw in its ocean phase.

References
Ahlberg PE, Clack JA, Luksevics E, Bom H and Zupins I 2008. Ventastega curonica and the origin of tetrapod morphology. Nature 453: 1199-1204.
Clack JA 2006. The emergence of early tetrapods. Palaeogeography Palaeoclimatology Palaeoecology. 232: 167–189.
Clack JA 2009. The fin to limb transition: new data, interpretations, and hypotheses from paleontology and developmental biology. Annual Review of Earth and Planetary Sciences. 37: 163–179.
Coates MI 2014. The Devonian tetrapod Acanthostega gunnari Jarvik: Postcranial anatomy, basal tetrapod interrelationships and patterns of skeletal evolution. Earth and Environmental Science Transactions of the Royal Society of Edinburgh.
Coates MI and Clack JA 1990. Polydactly in the earliest known tetrapod limbs. Nature 347: 66-69.
Jarvik E 1952. On the fish-like tail in the ichtyhyostegid stegocephalians. Meddelelser om Grønland 114: 1–90.
Porro LB, Rayfield EJ and Clack JA 2015. Descriptive Anatomy and Three-Dimensional Reconstruction of the Skull of the Early Tetrapod Acanthostega gunnari Jarvik, 1952. PLoS ONE 10(3): e0118882. doi:10.1371/journal.pone.0118882

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Source: https://pterosaurheresies.wordpress.com/2017/02/11/did-acanthostega-lose-an-intertemporal/

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