EVOLUTION - THE TRANSITIONAL FOSSILS
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paenungulate stem group

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​The paenungulates (clade Paenungulata, infraclass Eutheria) comprise the clade Tethytheria (the sea cows and the elephants) and the order Hyracoidea (the hyraxes).

The crown group of the Paenungulata is characterized by the following synapomorphies (Benton, 2015):
  1. Short (retracted) nasal bones
  2. Amastoidy: mastoid process (a smooth conical projection of bone located at the base of the back part of the temporal bone) concealed by expansion and overlap of squamosal (bone at the back of the skull, near the ears)
  3. Jugal (cheek bone) extends posteriorly as a prominent ventral crest to anterolateral border of the glenoid fossa (depression in the temporal bone that articulates with the lower jawbone)
  4. Carpals (bones of the wrist) dorsoventrally compressed and serially arranged.
These features represent evolutionary novelties that developed along the paenungulate stem line after the split from the Afroinsectiphilia. They will be recognizable only in very well-preserved fossils.  Additional synapomorphies that appeared along the more basal part of the stem line of the Paenungulata are listed in Box 10.5 of Benton (2015).

To date, only two species have been identified as members of the paenungulate stem group. They are depicted in the following phylogenetic time tree:
Picture
Figure 1. Time tree of the stem-Paenungulata
​The two known stem-group fossils are Ocepeia daouiensis and Abdounodus hamdii, both described from the Paleocene (Selandian) Bed IIa of the Ouled Abdoun phosphate series in quarries at Sidi Chennane, Morocco (Gheerbrant et al, 2014; Gheerbrant et al, 2016; Gheerbrant et al, 2018). They are illustrated below (click on image for a larger view):
​Figure 2. Images of stem-Paenungulata
​The available fossil data (see Figure 1 above) indicate that the paenungulate stem group developed from Middle Paleocene to Early Eocene time, representing a minimum stem-to-crown transition period of 3.2 million years.
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References

Benton, M. J. (2015). Vertebrate Palaeontology - Fourth edition. John Wiley & Sons, 468 pages.

Gheerbrant, E., Amaghzaz, M., Bouya, B., Goussard, F., & Letenneur, C. (2014). Ocepeia (Middle Paleocene of Morocco): the oldest skull of an afrotherian mammal. PLoS One, 9(2), e89739.

Gheerbrant, E., Filippo, A., & Schmitt, A. (2016). Convergence of Afrotherian and Laurasiatherian ungulate-like mammals: First morphological evidence from the Paleocene of Morocco. PLoS One, 11(7), e0157556.

Gheerbrant, E., Schmitt, A., & Kocsis, L. (2018). Early African fossils elucidate the origin of embrithopod mammals. Current Biology, 28(13), 2167-2173.

Image credits – stem-Paenungulata
  • Figure 2 (Skull of Ocepeia daouiensis, fossil): Open Access article Gheerbrant, E., Amaghzaz, M., Bouya, B., Goussard, F., & Letenneur, C. (2014). Ocepeia (Middle Paleocene of Morocco): the oldest skull of an afrotherian mammal. PLoS One, 9(2), e89739.
  • Figure 2 (Head of Ocepeia daouiensis, life restoration): Open Access article Gheerbrant, E., Amaghzaz, M., Bouya, B., Goussard, F., & Letenneur, C. (2014). Ocepeia (Middle Paleocene of Morocco): the oldest skull of an afrotherian mammal. PLoS One, 9(2), e89739.
  • Figure 2 (Abdounodus hamdii): Open Access article Gheerbrant, E., Filippo, A., & Schmitt, A. (2016). Convergence of Afrotherian and Laurasiatherian ungulate-like mammals: First morphological evidence from the Paleocene of Morocco. PLoS One, 11(7), e0157556.
  • Home
  • Introduction
  • Evolution of life
    • Overview
    • Origin of the Eukaryotes
    • Animals >
      • Vertebrate stem group >
        • Cyclostome stem group
        • Hagfish stem group
        • Lamprey stem group
        • Gnathostome stem group
        • Chondrichthyan stem group
        • Chimaera stem group
        • Shark stem group
        • Osteichthyan stem group
        • Actinopterygian stem group
        • Bichir and reedfish stem group
        • Sturgeon and paddlefish stem group
        • Neopterygian stem group
        • Teleostean stem group
        • Holostean stem group
        • Sarcopterygian stem group
        • Coelacanth stem group
        • Lungfish stem group
        • Tetrapod stem group >
          • Mammalian stem group
          • Monotreme stem group
          • Therian stem group
          • Marsupial stem group
          • Eutherian stem group
          • Bat stem group
          • Pangolin stem group
          • Carnivoran stem group
          • Odd-toed ungulate stem group
          • Rodent stem group
          • Lagomorph stem group
          • Paenungulate stem group
          • Hyrax stem group
    • Land plants
    • Glossary
  • Navigation
  • Data
  • About the author
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