| 词条 | Entelognathus |
| 释义 |
| name = Entelognathus primordialis | fossil_range = Late Ludlow | image = Life restoration of Sparalepis tingi.tiff | image_width = | image_caption = Pair (middle background) among fauna from the Kuanti Formation | regnum = Animalia | phylum = Chordata | classis = Placodermi | ordo = incertae sedis | genus = Entelognathus | genus_authority = Zhu et al., 2013 | species = E. primordialis | binomial = Entelognathus primordialis | binomial_authority = Zhu et al., 2013 }}Entelognathus primordialis (“primordial complete jaw”) is a placoderm from the late Ludlow epoch of Qujing, Yunnan, 419 million years ago.[1][2] 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 taxonomyThe 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 {{convert|11|cm}} long, and the live animal is estimated to have been over {{convert|20|cm|0|abbr=on}} long. In overall form, the animal resembles primitive arthrodires, but the anatomy of the jaws strongly suggests the anatomies of bony fish and tetrapods. Specifically, this is the first stem gnathostome with dermal marginal jaw bones. These bones are the premaxilla, maxilla, and dentary.[3] Most known placoderms had simple beak-like jaws made of bone plates.[1] The researchers' cladistic diagram suggests that E. primordialis forms a polytomy with arthrodires, ptyctodonts, and all advanced gnathostomes (namely bony fish, tetrapods, acanthodians, and chondrichthyes).[3] EtymologyThe 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 significancePrior 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.[1][4] References1. ^1 2 {{cite web | publisher = Nature | url = http://www.nature.com/news/ancient-fish-face-shows-roots-of-modern-jaw-1.13823 | title = Ancient fish face shows roots of modern jaw |first= Eliot |last= Barford | date = 25 September 2013 |accessdate = 26 September 2013 |doi= 10.1038/nature.2013.13823 }} 2. ^{{cite journal|last1=Zhu|first1=Min|last2=Yu|first2=Xiaobo|last3=Ahlberg|first3=Per Erik|last4=Choo|first4=Brian|last5=Lu|first5=Jing|last6=Qiao|first6=Tuo|last7=Qu|first7=Qingming|last8=Zhao|first8=Wenjin|last9=Jia|first9=Liantao|last10=Blom|first10=Henning|last11=Zhu|first11=You’an|title=A Silurian placoderm with osteichthyan-like marginal jaw bones|journal=Nature|volume=502|issue=7470|year=2013|pages=188–193|issn=0028-0836|doi=10.1038/nature12617|pmid=24067611}} 3. ^1 {{cite journal |first1= Min |last1= Zhu |first2= Xiaobo |last2= Yu |first3= Per Erik |last3= Ahlberg |first4= Brian |last4= Choo |first5= Jing |last5= Lu |first6= Tuo |last6= Qiao |first7= Qingming |last7= Qu |first8= Wenjin |last8= Zhao |first9= Liantao |last9= Jia |first10= Henning |last10= Blom |first11= You'an |last11= Zhu |year=2013 |title=A Silurian placoderm with osteichthyan-like marginal jaw bones |journal=Nature |volume= 502 |pages= 188–193 |doi=10.1038/nature12617 |pmid=24067611}} 4. ^{{cite journal |title=News & Views: Palaeontology: A jaw-dropping fossil fish |first= Matt |last= Friedman |author2=Martin D. Brazeau |year=2013 |journal=Nature |volume= 502 |pages= 175–177 |doi= 10.1038/nature12690 }} External links
8 : Placoderm genera|Placoderms of Asia|Silurian fish of Asia|Placodermi incertae sedis|Prehistoric animals of China|Transitional fossils|Fossil taxa described in 2013|2013 in China |
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