Editing Crab (section)

==Evolution==
[[File:Eocarcinus reconstructon.jpg|thumb|Reconstruction of ''[[Eocarcinus]]'', the earliest known crab]]

The earliest unambiguous crab [[fossil]]s date from the [[Early Jurassic]], with the oldest being ''[[Eocarcinus]]'' from the early [[Pliensbachian]] of Britain, which likely represents a [[Stem-group|stem-group lineage]], as it lacks several key morphological features that define modern crabs.<ref>{{Cite journal|last=Scholtz|first=Gerhard|date=November 2020|title=Eocarcinus praecursor Withers, 1932 (Malacostraca, Decapoda, Meiura) is a stem group brachyuran|journal=Arthropod Structure & Development |language=en |volume=59 |pages=100991 |doi=10.1016/j.asd.2020.100991 |pmid=32891896 |doi-access=free|bibcode=2020ArtSD..5900991S }}</ref><ref>{{cite journal |author1=Carrie E. Schweitzer |author2=Rodney M. Feldmann |year=2010 |title=The oldest Brachyura (Decapoda: Homolodromioidea: Glaessneropsoidea) known to date (Jurassic) |journal=[[Journal of Crustacean Biology]] |volume=30 |issue=2 |pages=251–256 |doi=10.1651/09-3231.1|doi-access=free }}</ref> Most Jurassic crabs are only known from [[Dorsal (anatomy)|dorsal]] (top half of the body) [[carapace]]s, making it difficult to determine their relationships.<ref>{{Cite journal |last=Guinot |first=Danièle |date=2019-11-14 |title=New hypotheses concerning the earliest brachyurans (Crustacea, Decapoda, Brachyura)|journal=Geodiversitas|volume=41|issue=1|pages=747|doi=10.5252/geodiversitas2019v41a22|issn=1280-9659|doi-access=free}}</ref> Crabs [[Evolutionary radiation|radiated]] in the [[Late Jurassic]], corresponding with an increase in reef habitats, though they would decline at the end of the Jurassic as the result of the decline of reef ecosystems. Crabs increased in diversity through the Cretaceous and represented the dominant group of [[Decapoda|decapods]] by the end of the period.<ref>{{Cite journal|last1=Klompmaker|first1=A. A.|last2=Schweitzer|first2=C. E.|last3=Feldmann|first3=R. M.|last4=Kowalewski|first4=M.|date=2013-11-01|title=The influence of reefs on the rise of Mesozoic marine crustaceans|url=https://pubs.geoscienceworld.org/geology/article/41/11/1179-1182/131064|journal=Geology|language=en|volume=41|issue=11|pages=1179–1182|doi=10.1130/G34768.1|bibcode=2013Geo....41.1179K|issn=0091-7613}}</ref>

The crab [[infraorder]] Brachyura belongs to the group [[Reptantia]], which consists of the walking/crawling decapods ([[lobsters]] and crabs).  Brachyura is the [[sister clade]] to the infraorder [[Anomura]], which contains the hermit crabs and relatives.  The [[cladogram]] below shows Brachyura's placement within the larger [[order (biology)|order]] [[Decapoda]], from analysis by Wolfe ''et al.'', 2019.<ref name="Wolfe2019">{{cite journal |last1=Wolfe |first1=Joanna M. |last2=Breinholt |first2=Jesse W. |last3=Crandall |first3=Keith A. |last4=Lemmon |first4=Alan R. |last5=Lemmon |first5=Emily Moriarty |last6=Timm |first6=Laura E. |last7=Siddall |first7=Mark E. |last8=Bracken-Grissom |first8=Heather D. |title=A phylogenomic framework, evolutionary timeline and genomic resources for comparative studies of decapod crustaceans |journal=Proceedings of the Royal Society B | date=24 April 2019 |volume=286 |issue=1901 |doi=10.1098/rspb.2019.0079 |pmid=31014217 |pmc=6501934 |doi-access=free }}</ref>

{{Decapoda cladogram}}

Brachyura is separated into several sections, with the [[basal (phylogenetics)|basal]] [[Dromiacea]] diverging the earliest in the evolutionary history, around the [[Late Triassic]] or [[Early Jurassic]].  The group consisting of [[Raninoida]] and [[Cyclodorippoida]] split off next, during the [[Jurassic]] period.  The remaining [[clade]] [[Eubrachyura]] then divided during the [[Cretaceous]] period into [[Heterotremata]] and [[Thoracotremata]].
A summary of the high-level internal relationships within Brachyura can be shown in the [[cladogram]] below:
<ref name="Ling">{{cite journal |title=Evolutionary History of True Crabs (Crustacea: Decapoda: Brachyura) and the Origin of Freshwater Crabs |author1=Ling Ming Tsang |author2=Christoph D. Schubart |author3=Shane T. Ahyong |author4=Joelle C.Y. Lai |author5=Eugene Y.C. Au |author6=Tin-Yam Chan |author7=Peter K.L. Ng |author8=Ka Hou Chu |journal=[[Molecular Biology and Evolution]] |publisher=[[Oxford University Press ]]|volume=31 |issue=5 |year=2014 |pages=1173–1187 |doi=10.1093/molbev/msu068 |pmid=24520090 |doi-access=free}}</ref>
<ref name="Wolfe2019"/>
{{clade| style=font-size:85%; line-height:85%
|label1='''Brachyura'''
|1={{clade
 |1=[[Dromiacea]]
 |2={{clade
  |1={{clade
   |1=[[Raninoida]]
   |2=[[Cyclodorippoida]] }}
  |label2=[[Eubrachyura]]
  |2={{clade
   |1=[[Heterotremata]]
   |2=[[Thoracotremata]] }} }} }} }}

There is a no consensus on the relationships of the subsequent [[superfamily (taxonomy)|superfamilies]] and [[family (biology)|families]].  The proposed [[cladogram]] below is from analysis by Tsang ''et al'', 2014:<ref name="Ling"/>
{{clade| style=font-size:85%; line-height:85%
|label1='''Brachyura'''
|1={{clade
 |label1=[[Dromiacea]]
 |1={{clade
  |label1=[[Dromioidea]]
  |1={{clade
   |1=[[Dromiidae]] (may be paraphyletic)
   |2=[[Dynomenidae]] }}
  |label2=[[Homoloidea]]
  |2={{clade
   |1=[[Homolidae]] (paraphyletic)
   |2=[[Latreilliidae]] }} }}
 |2={{clade
  |1={{clade
   |label1=[[Raninoida]]
   |1=[[Raninidae]]
   |label2=[[Cyclodorippoida]]
   |2={{clade
    |1=[[Cyclodorippidae]]
    |2=[[Cymonomidae]] }} }}
  |label2=[[Eubrachyura]]
  |2={{clade
   |label1=[[Heterotremata]]
   |1={{clade
    |label1=Freshwater crabs
    |1={{clade
     |label1=[[Potamoidea]] |sublabel1=(Old World freshwater crabs)
     |1={{clade
      |1=[[Potamonautidae]]
      |2={{clade
       |1=[[Potamidae]]
       |2=[[Gecarcinucidae]] }} }}
     |label2=Pseudothelphusoidea |sublabel2=(New World freshwater crabs)
     |2=[[Pseudothelphusidae]] }}
    |2=&nbsp; |state2=none
    |3={{clade
     |1={{clade
      |1={{clade
       |1=[[Trichodactylidae]] (freshwater crabs)
       |2=[[Orithyiidae]] }}
      |2={{clade
       |1={{clade
        |1=[[Belliidae]]
        |2=[[Chasmocarcinidae]] }}
       |2=[[Retroplumidae]] }} }}
     |2={{clade
      |1={{clade
       |1={{clade
        |label1=[[Dorippoidea]]
        |1={{clade
         |1=[[Ethusidae]]
         |2=[[Dorippidae]] }}
        |2=[[Leucosiidae]] }}
       |2={{clade
        |label1=[[Majoidea]]
        |1={{clade
         |1=[[Inachidae]]
         |2={{clade
          |1=[[Epialtidae]] (paraphyletic)
          |2=[[Majidae]] / [[Mithracidae]] }} }}
        |2=[[Corystidae]] }} }}
      |2={{clade
       |1={{clade
        |1=[[Euryplacidae]]
        |2=[[Matutidae]] }}
       |2={{clade
        |1={{clade
         |1={{clade
          |1=[[Calappidae]]
          |2={{clade
           |1={{clade
            |1=[[Parthenopidae]]
            |2=[[Cancridae]] }}
           |2={{clade
            |1=[[Carpiliidae]]
            |2={{clade
             |1=[[Aethridae]]
             |2=''[[Pseudocarcinus]]'' of [[Menippidae]] }} }} }} }}
         |2={{clade
          |1=''[[Menippe (crab)|Menippe]]'' of [[Menippidae]]
          |2={{clade
           |1=[[Polybiidae]]
           |2=[[Portunidae]] }} }} }}
        |2={{clade
         |label1=[[Pilumnoidea]]
         |1={{clade
          |1=[[Tanaochelidae]]
          |2={{clade
           |1=[[Galenidae]]
           |2=[[Pilumnidae]] }} }}
         |2={{clade
          |1={{clade
           |1={{clade
            |1=[[Mathildellidae]]
            |2={{clade
             |1=[[Eriphiidae]]
             |2={{clade
              |1=[[Oziidae]]
              |2=[[Vultocinidae]] }} }} }}
           |2=[[Trapeziidae]] }}
          |2={{clade
           |1=[[Goneplacidae]]
           |2={{clade
            |1=[[Scalopidiidae]]
            |label2=[[Xanthoidea]]
            |2={{clade
             |1=[[Xanthidae]] (paraphyletic)
             |2=[[Panopeidae]] }} }} }} }} }} }} }} }} }} }}
   |label2=[[Thoracotremata]]
   |2={{clade
    |1={{clade
     |1=[[Pinnotheridae]]
     |2=[[Dotillidae]] }}
    |2={{clade
     |1=[[Percnidae]]
     |2={{clade
      |1={{clade
       |1=[[Xenograpsidae]]
       |2=[[Cryptochiridae]] }}
      |2={{clade
       |1={{clade
        |1=[[Ocypodidae]]
        |2={{clade
         |1=[[Glyptograpsidae]]
         |2=[[Grapsidae]] }} }}
       |2={{clade
        |1={{clade
         |1={{clade
          |1=[[Plagusiidae]]
          |2=[[Gecarcinidae]] }}
         |2=[[Sesarmidae]] }}
        |2={{clade
         |1=[[Mictyridae]]
         |2={{clade
          |1=[[Varunidae]]
          |2=[[Macrophthalmidae]]
}} }} }} }} }} }} }} }} }} }} }}