Entelognathus

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Entelognathus primordialis
Temporal range: 424–419 
Ma
↓
Late Silurian
Holotype, Paleozoological Museum of China
Life reconstruction of Entelognathus primordialis
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: †Placodermi
Order: †incertae sedis
Genus: †Entelognathus
Zhu et al., 2013 [1]
Species:
†E. primordialis
Binomial name
†Entelognathus primordialis
Zhu et al., 2013

Entelognathus primordialis (“primordial complete jaw”) is an early

Ludlow epoch) of Qujing, Yunnan, 419 million years ago.[2][1]

A team led by Min Zhu of the Academy of Sciences' Institute of Vertebrate Paleontology and Paleoanthropology in Beijing discovered the intact, articulated fossil in rock formations at Xiaoxiang reservoir.

Specimen and taxonomy

Paratype specimen IVPP V32322 with scales and fin spines preserved

The holotype of E. primordialis is the uncrushed and mostly intact anterior half of an individual with the articulating head and trunk armor preserved in three dimensions. The holotype is about 11 centimetres (4.3 in) long, and the live animal is estimated to have been over 20 cm (8 in) long. In overall form, the animal resembles primitive

dentary.[1] Most known placoderms had simple beak-like jaws made of bone plates.[2] In 2023, newly described articulated specimen is shown, which have preserved large scales some of which are rhomboid, and fin spines on dorsal and anal fins (the latter of which was a trait that was previously only found in stem-group chondrichthyes).[3]

The researchers' cladistic diagram suggests that E. primordialis forms a

acanthodians, and chondrichthyes).[1]

Etymology

The generic name translates as "complete jaw", referring to how the animal had a complete set of dermal marginal jaw bones. The specific name translates as "primordial".

Evolutionary significance

Prior to the discovery of Entelognathus, scientists assumed that the last common ancestor of jawed vertebrates was a shark-like animal, with no distinct jawbones, and that modern jaws evolved in early bony fishes. This discovery shows that modern jaws evolved earlier. It is possible that Chondrichthyes started with distinct jaws and then dispensed with them. This has been called the earliest known animal with what looks like a face.[2][4]

Gallery

  • Diagram with other maxillate placoderms in lateral view
    Diagram with other maxillate placoderms in lateral view
  • Diagram with other maxillate placoderms in dorsal view
    Diagram with other maxillate placoderms in dorsal view
  • Pair (middle background) among fauna from the Kuanti Formation including Sparalepis tingi (foreground), numerous conodonts, and Megamastax (background)
    Pair (middle background) among fauna from the Kuanti Formation including Sparalepis tingi (foreground), numerous conodonts, and Megamastax (background)
  • Video of 3D reconstruction

See also

References

  1. ^
    S2CID 4462506
    .
  2. ^
    S2CID 87470088
    . Retrieved 26 September 2013.
  3. PMC 10665347
    .
  4. PMID 24067615
    .

External links
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