Castorocauda

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Castorocauda
Temporal range:
Ma
↓
Restoration of Castorocauda underwater with the grassy lakebed visible on the bottom third of the image
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Clade:
Therapsida
Clade:
Cynodontia
Clade: Mammaliaformes
Order: †Docodonta
Family: †
Docodontidae
Genus: †Castorocauda
Ji et al., 2006
Type species
†Castorocauda lutrasimilis
Ji et al., 2006

Castorocauda is an extinct, semi-aquatic, superficially

dinosaurs
.

Weighing an estimated 500–800 g (1.1–1.8 lb), Castorocauda is the largest known

temperate
environment – which possibly had an average temperature not exceeding 15 °C (59 °F) – alongside salamanders, pterosaurs, birdlike dinosaurs, and other mammaliaforms.

Discovery and etymology

The

Daohugou Beds of the Jiulongshan Formation in the Inner Mongolia region of China, which dates to about 159–164 million years ago (mya) in the Middle to Late Jurassic.[1][2] It comprises a partial skeleton including an incomplete skull but well-preserved lower jaws, most of the ribs, the limbs (save for the right hind leg), the pelvis and the tail. The remains are so well preserved that there are elements of its soft anatomy and hair.[1]

The

species name lutrasimilis derives from Latin lutra "otter" and similis "similar", because some aspects of its teeth and vertebrae are similar to modern otters.[1]

Description

Castorocauda was the largest of known docodonts.[3] The preserved length from head to tail is 425 mm (16.7 in), but in life it was much larger. Based on the dimensions of the platypus, the lower weight limit was estimated to be 518 g (1.1 lb) in life, and the upper 700 to 800 g (1.5 to 1.8 lb), making it the largest known Jurassic mammaliaform, surpassing the previous record of 500 g (1.1 lb) for Sinoconodon.[1]

It had specialized teeth that curve backwards to help it hold onto slippery fish, as seen in modern seals and also ancestral whales.

canine, 5 premolars and 6 molars.[1]

The forelimbs of Castorocauda are very similar to those of the modern platypus: the

hypertrophied (large) epicondyles (where the joint attaches); the radial and ulnar joints are widely separated; the ulna has a massive olecranon (where it attaches to the elbow); the wrist bones are block-like; and the finger bones are robust. Docodontans were likely burrowing creatures and had a sprawling gait, and Castorocauda may have also used its arms for rowing, similar to the platypus. There are traces of soft tissue between the toes, suggesting webbed hind feet.[1] It likely also had claws,[6] and the holotype shows a spur on the hind ankle, which, in male platypuses, is venomous.[1]

Castorocauda likely had 14

transverse processes (which jut out diagonally from the centrum) on the headward side and another on the tailward side, making the centrum appear somewhat like the letter H from the top-view looking down. This tail anatomy is similar to beavers and otters, which use their tails for paddling and propulsion.[1][5]

Fur was preserved on the holotype, and it is the earliest known

sensory perception.[7]

Taxonomy

Stem Mammaliaformes
Castorocauda with other mammaliaforms[9]

Castorocauda is a member of the

paraphyletic and thus invalid, and Castorocauda appears to have been most closely related to Dsungarodon,[8][6] which came from the Junggar Basin of China and probably ate plants and soft invertebrates.[11]

Castorocauda is part of a Middle Jurassic mammaliaform diversification event, wherein mammaliaforms

multituberculates, australosphenidans, metatherians and eutherians, among others – disproves this notion. This may have been caused by the breakup of Pangaea, which started in the Early to Middle Jurassic and diversified habitats and niches, or modern traits that had been slowly accumulating since mammaliaforms evolved until reaching a critical point which allowed for a massive expansion into different habitats.[9]

Paleoecology

Castorocauda is the earliest known aquatic mammaliaform,

piscivory).[1]

Map of the Middle Jurassic

The Daohugou Beds also include several

cool temperate and wet climate with distinct wet and dry seasons,[15][16] possibly with an annual temperature of below 15 °C (59 °F).[16]

See also

References

  1. ^
    S2CID 46067702
    .
  2. ^
    S2CID 84944844
    .
  3. ^ Rose 2006, p. 56
  4. ^ "Mammal evolution: ancient mammals that lived in the age of dinosaurs". BBC Science Focus Magazine. Retrieved 2023-03-26.
  5. ^
    S2CID 83027037
    .
  6. ^
    S2CID 206562565
    .
  7. ^
    S2CID 940501
    .
  8. ^
    S2CID 199637122
    .
  9. ^
    S2CID 527196
    .
  10. S2CID 35820076
    .
  11. ^ Pfretzschner, H.-U.; Martin, T.; Maisch, M. W.; Matzke, A. T. (2005). "A new docodont mammal from the Late Jurassic of the Junggar Basin in Northwest China" (PDF). Acta Palaeontologica Polonica. 50 (4): 799–808.
  12. S2CID 29846648
    .
  13. S2CID 4346751
    .
  14. S2CID 4466953
    .
  15. doi:10.1080/10020070612330087A (inactive 31 January 2024).{{cite journal}}: CS1 maint: DOI inactive as of January 2024 (link
    )
  16. ^
    S2CID 131558706
    .

Further reading

External links
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