Episode 5.5 · 28 min

how fishes in Devonian shallows became the first animals with limbs and digits

How fishes in Devonian shallows became the first animals with limbs and digits reveals how a fin's internal bones could be reshaped into a weight-bearing limb, opening the evolutionary path to tetrapods-including us. The episode follows the warm, oxygen-poor shallows where lobe-finned fishes used lungs, sturdy fins and changing body structures to prop, paddle and push along the bottom. Evidence from Tiktaalik, found on Ellesmere Island after a geological-map search, shows a fish with a neck, broad ribs and fin joints resembling a shoulder, elbow and wrist, while still carrying scales, gills and fin rays. Tiktaalik was a close relative of the first limbed animals, not their ancestor, and the story is a branching experiment rather than a straight ladder from fish to humans.

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Visual credits

54 sources

Sources and credits for imagery used in this film, including material incorporated into explanatory animations.

Eusthenopteron, complete specimen of juvenile individual, Miguasha - Redpath Museum - McGill University - Montreal, Canada - DSC07998
Daderot
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Panderichthys skull
Ghedoghedo
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Tiktaalik roseae (fish to amphibian transitional fossil) (Fram Formation, Upper Devonian; Ellesmere Island, Arctic Canada) 1 (49755118288)
James St. John
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
research 2 2 image
Uchicago
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
research 2 2 image
Uchicago
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Neil Shubin in the 2008 Ellesmere field crew; orange jacket
Andrew Gillis
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Ted Daeschler in the 2008 Ellesmere field crew; yellow/black jacket
Andrew Gillis
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Farish Jenkins in the 2008 Ellesmere field crew; rightmost, tan jacket
Andrew Gillis
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Bird Fiord camp valley, date unverified
Ted Daeschler
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Bird Quarry excavation in 2004
Neil Shubin
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Qikiqtania left pectoral-fin CT, Stewart 2022 Figure 3
Stewart et al. 2022
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Stensio Bjerg exposure looking toward camp
Jenny Clack expedition archive; individual photographer unverified
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Acanthostega Deep Time
Neil Pezzoni
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Acanthostega forelimb photograph, Coates and Clack 1990 Fig 1a
Coates and Clack 1990
Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Acanthostega eight-digit forelimb restoration, Coates and Clack 1990 Fig 1c
Coates and Clack 1990
Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Acanthostega virtual humerus sections, Sanchez 2016 Figure 2
Sanchez et al. 2016
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Skeleton of Ichthyostega
OlegTarabanov
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Ichthyostega seven-digit hindlimb restoration, Coates and Clack 1990 Fig 1f
Coates and Clack 1990
Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Pierce et al 2012 Fig 1c lateral CT skeletal reconstruction, complete anatomy
Pierce, Clack and Hutchinson 2012
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Figure 3 pectoral fin of Elpistostege MHNM 06-2067 showing CT-segmented humerus radius ulna wrist-region elements digit-like distal radials and fin rays (cropped figure, PDF page 4)
Cloutier et al., Nature (2020)
Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
press releases image
Mikhail Shekhanov for the Ukhta Local Museum
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Tetrapod dentary
Mynewsdesk
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
geoheritage sites image
Iugs Geoheritage
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Zachełmie Quarry - since 2013
Iugs Geoheritage
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Zachelmie Muz PGI 1728.II.16 trail photograph and interpretive outline, Fig 2a; NOT a scan
Niedzwiedzki et al. 2010
Zachelmie isolated probable pes cast Muz PGI 1728.II.3 and interpretive outline, Fig 3a; separate from the trail
Niedzwiedzki et al. 2010
The Tetrapod Trackway, Valentia Island - geograph.org.uk - 5656679
Phil Champion
View original source ↗Source licence: CC BY-SA 2.0
Photograph or map of the actual Valentia Island Devonian tetrapod trackway showing the paired footprint rows on the rock surface, not only a locality map or reconstruction (cropped figure, PDF page 11)
Stössel, Williams and Higgs (2016)
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Figure 12 only: complete photograph of Dohilla trackway Do6 with its thin central tail drag groove and the 15 cm ruler. Exclude article text and caption. Physical PDF page 10. (cropped figure, PDF page 10)
Stossel, Williams and Higgs 2016
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Devonian marine sequence, Jebel Mech Irdane
Heiko Huneke
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Established callback: dunkleosteus specimen
Robosorne
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
MediaObjects image
Jennifer A. Clack, Nature (2002); exact photographer unverified
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Pederpes foot photograph and restoration, Clack 2002 Fig 3b,c; five pedal digits; NOT the hand
Clack 2002
Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Burnmouth coastal section, Clack et al 2019 Figure 1B
Clack et al. 2019
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Aytonerpeton microps
Jenny Clack
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Burnmouth Bed 383 charcoal SEMs, Clack 2019 Figure 23
Clack et al. 2019
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Blue Beach (26330852151)
Paul from Hacketts Cove, Canada
View original source ↗Source licence: CC BY 2.0
Blue Beach tetrapod fossil evidence showing several distinct limb-bone morphotypes, especially the comparative humeri or femora demonstrating diversity rather than a complete skeleton (cropped figure, PDF page 10)
Anderson et al., PLOS ONE (2015)
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Victoria locator, Long Figure 1b
Long et al. 2025
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Figure or page excerpt cropped from the source publication.
Prints 2
Mynewsdesk
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Long 2025 Figure 1c stratigraphic column with full trackway-site and fish-correlation labels
Long et al. 2025
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Reptile tracks
Mynewsdesk
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Long 2025 Fig 2d isolated print Ip actual photograph with I-V digits and shared scale bar
Long et al. 2025
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Long 2025 Fig 2c isolated print surface model; false colour represents surface relief, not pigment
Long et al. 2025
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Long 2025 Fig 2f five-digit trackway print photograph with claw impressions and scale
Long et al. 2025
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Long 2025 Fig 2e trackway print surface model with shared scale bar
Long et al. 2025
View original source ↗Source licence: CC BY 4.0
Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Long 2025 Fig 2g trackway B hooked claw marks with scale bar
Long et al. 2025
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
press releases image
Marcin Ambrozik
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Long et al 2025 Figure 3d Victorian isolated print photograph and surface model
Long et al. 2025
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Long et al 2025 Figure 3a Notalacerta photographic and relief comparison
Long et al. 2025
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Long et al 2025 Figure 3h Hylopus amphibian-grade comparison with rounded toe tips
Long et al. 2025
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Joggins-beach
Cornellier
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Xenopus laevis claws indicated
B kimmel
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.
Established callback: sacabambaspis specimen
Bloopityboop
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Incorporated into an explanatory animation; presentation may include cropping, labels and overlays.

Animation design references 2 sources

These works informed the design of explanatory animations. A reference listed here is not necessarily reproduced on screen.

Fins to hands
Neil Pezzoni
View original source ↗Source licence: CC BY 4.0
Scientific image
Thomas Stewart / Penn State
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Research references

Selected sources from the episode’s research and scientific figures.

Music

Meditation From The Star Orion
OctahedronMusic · Envato Elements

Footage and image usage

Credits and usage times retained from the published edition or its production credit record. Where present, times identify visual appearances, not documentary chapters. Source and licence corrections are listed in the visual credits above.

Iugs Geoheritage - 14:33-14:48
James St. John - 7:11-7:28
Mynewsdesk - 22:24-22:31, 26:10-26:20
Niedzwiedzki et al. 2010 - 14:52-15:09, 15:09-15:14, 15:58-16:07
Paul from Hacketts Cove, Canada - 21:16-21:24
Phil Champion - 15:14-15:22
Stössel, Williams and Higgs (2016) - 16:07-16:10
Original animations and figures created by this channel.
Anderson et al., PLOS ONE (2015) — 21:38-22:01
Andrew Gillis — 6:20-6:30
B kimmel — 25:29-26:27
Bloopityboop — 26:49-28:42
Clack 2002 — 20:53-20:57
Clack et al. 2019 — 21:00-21:16, 21:23-21:30
Cloutier et al., Nature (2020) — 9:40-10:55
Coates and Clack 1990 — 8:07-8:12, 9:09-9:14
Cornellier — 24:34-24:46
Daderot — 3:34-3:42
Ghedoghedo — 3:49-3:59
Heiko Huneke — 17:13-17:21
Iugs Geoheritage — 14:43-14:58, 14:58-15:02
James St. John — 5:00-5:22, 5:22-5:28, 5:28-5:48, 7:15-7:32
Jennifer A. Clack, Nature (2002); exact photographer unverified — 20:34-20:53
Jenny Clack — 21:16-21:23
Jenny Clack expedition archive; individual photographer unverified — 7:50-8:02
Long et al. 2025 — 22:48-22:59, 23:04-23:21, 23:59-24:21, 25:29-26:27
Marcin Ambrozik — 23:52-23:55
Mikhail Shekhanov for the Ukhta Local Museum — 12:27-12:43
Mynewsdesk — 12:27-12:43, 22:41-22:48, 22:59-23:04, 23:21-23:31, 23:31-23:52, 26:27-26:37
Neil Pezzoni — 8:02-8:07
Neil Shubin — 7:00-7:10
Niedzwiedzki et al. 2010 — 15:02-15:19, 15:19-15:24, 15:48-16:09, 16:09-16:17
OlegTarabanov — 8:54-9:09
Paul from Hacketts Cove, Canada — 21:30-21:38
Phil Champion — 15:24-15:32
Pierce, Clack and Hutchinson 2012 — 9:14-9:24
Robosorne — 18:01-18:18
Sanchez et al. 2016 — 8:29-8:48
Stewart et al. 2022 — 7:32-7:50
Stossel, Williams and Higgs 2016 — 15:44-15:48
Stössel, Williams and Higgs (2016) — 15:32-15:44, 16:17-16:20
Ted Daeschler — 7:00-7:10
Uchicago — 5:48-6:06

How this film was made

Created and editorially directed by Anders Lunde using a custom production system developed over six months. AI assists research, drafting, programming, and visual production; I review and edit the material and make the final editorial decisions. Narration uses text-to-speech. Visuals combine custom-built scientific animations, AI-generated reconstructions, and credited scientific imagery.

Generated reconstructions illustrate scientific interpretations. They are distinct from photographs, specimens, and measured data.

More about the creator and production →

Visual credits

Eusthenopteron, complete specimen of juvenile individual, Miguasha - Redpath Museum - McGill University - Montreal, Canada - DSC07998

Panderichthys skull

Tiktaalik roseae (fish to amphibian transitional fossil) (Fram Formation, Upper Devonian; Ellesmere Island, Arctic Canada) 1 (49755118288)

research 2 2 image

research 2 2 image

Neil Shubin in the 2008 Ellesmere field crew; orange jacket

Ted Daeschler in the 2008 Ellesmere field crew; yellow/black jacket

Farish Jenkins in the 2008 Ellesmere field crew; rightmost, tan jacket

Bird Fiord camp valley, date unverified

Bird Quarry excavation in 2004

Qikiqtania left pectoral-fin CT, Stewart 2022 Figure 3

Stensio Bjerg exposure looking toward camp

Acanthostega Deep Time

Acanthostega forelimb photograph, Coates and Clack 1990 Fig 1a

Acanthostega eight-digit forelimb restoration, Coates and Clack 1990 Fig 1c

Acanthostega virtual humerus sections, Sanchez 2016 Figure 2

Skeleton of Ichthyostega

Ichthyostega seven-digit hindlimb restoration, Coates and Clack 1990 Fig 1f

Pierce et al 2012 Fig 1c lateral CT skeletal reconstruction, complete anatomy

Figure 3 pectoral fin of Elpistostege MHNM 06-2067 showing CT-segmented humerus radius ulna wrist-region elements digit-like distal radials and fin rays (cropped figure, PDF page 4)

press releases image

Tetrapod dentary

geoheritage sites image

Zachełmie Quarry - since 2013

Zachelmie Muz PGI 1728.II.16 trail photograph and interpretive outline, Fig 2a; NOT a scan

Zachelmie isolated probable pes cast Muz PGI 1728.II.3 and interpretive outline, Fig 3a; separate from the trail

The Tetrapod Trackway, Valentia Island - geograph.org.uk - 5656679

Photograph or map of the actual Valentia Island Devonian tetrapod trackway showing the paired footprint rows on the rock surface, not only a locality map or reconstruction (cropped figure, PDF page 11)

Figure 12 only: complete photograph of Dohilla trackway Do6 with its thin central tail drag groove and the 15 cm ruler. Exclude article text and caption. Physical PDF page 10. (cropped figure, PDF page 10)

Devonian marine sequence, Jebel Mech Irdane

Established callback: dunkleosteus specimen

MediaObjects image

Pederpes foot photograph and restoration, Clack 2002 Fig 3b,c; five pedal digits; NOT the hand

Burnmouth coastal section, Clack et al 2019 Figure 1B

Aytonerpeton microps

Burnmouth Bed 383 charcoal SEMs, Clack 2019 Figure 23

Blue Beach (26330852151)

Blue Beach tetrapod fossil evidence showing several distinct limb-bone morphotypes, especially the comparative humeri or femora demonstrating diversity rather than a complete skeleton (cropped figure, PDF page 10)

Victoria locator, Long Figure 1b

Prints 2

Long 2025 Figure 1c stratigraphic column with full trackway-site and fish-correlation labels

Reptile tracks

Long 2025 Fig 2d isolated print Ip actual photograph with I-V digits and shared scale bar

Long 2025 Fig 2c isolated print surface model; false colour represents surface relief, not pigment

Long 2025 Fig 2f five-digit trackway print photograph with claw impressions and scale

Long 2025 Fig 2e trackway print surface model with shared scale bar

Long 2025 Fig 2g trackway B hooked claw marks with scale bar

press releases image

Long et al 2025 Figure 3d Victorian isolated print photograph and surface model

Long et al 2025 Figure 3a Notalacerta photographic and relief comparison

Long et al 2025 Figure 3h Hylopus amphibian-grade comparison with rounded toe tips

Joggins-beach

Xenopus laevis claws indicated

Established callback: sacabambaspis specimen

Fins to hands

Scientific image

Research references

Music

How this film was made