​The hyraxes or dassie (Order Hyracoidea, Infraclass Eutheria) are small hoofed mammals native to Africa and extreme southwestern Asia that are currently known in six extant species (Encyclopaedia Britannica). These species all belong to the family  Procaviidae.

Barrow et al (2012) define a clade that comprises the extant species Procavia capensis and the fossil species Prohyrax hendeyi. The authors do not state whether this clade comprises the crown group of the hyracoids, but their phylogeny shows that P. hendeyi occupies a very crownward position. This suggests that the synapomorphies of the clade, listed below, can be considered as closely representative of the crown group:
  1. Lower premolar tooth P1 metaconid (mesiolingual cusp) is present but small relative to protoconid (anterolingual cusp).
  2. Lower premolar tooth P1 entoconid (posterolingual cusp) is present but smaller than hypoconid (posterolabial cusp).
  3. Position of metaconid relative to protoconid on lower premolar tooth P4: metaconid is situated distal to protoconid. 
  4. Paraconid (anterolabial cusp) presence/paracristid (ridge leading to cusp) length on lower molar teeth M1 and M2: long paracristid, no cuspidate paraconid.
  5. Upper premolar P1 hypocone (posterolingual cusp) is present but small.
  6. Upper premolar P2 hypocone is present but subequal in size to protocone (anterolingual cusp).
  7. Configuration of postpalatine region (posterior to the palate): postpalatine spine present.
  8. Bones contributing to anterior wall of orbit (eye socket): primarily jugal bone, which closely approximates, or touches, the lacrimal bone.
  9. Maxilla-frontal contact (between the upper jawbone and the frontal bone): little or no contact between frontal and maxilla on the rostrum (the forward part of the cranium that holds the teeth, palate, and nasal cavity).
  10. Basioccipital keel (an extension of the basioccipital bone, which is in the part of the skull that articulates with the spine) is present but poorly developed.
These synapomorphies represent evolutionary novelties that developed along the hyracoid stem line after the split from the Tethytheria clade. They pertain to very detailed aspects of teeth and the skull and will only be recognized in very well-preserved specimens.
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The most extensive phylogenetic analysis available for the hyracoid stem group is that presented by Puttick and Thomas (2015). This analysis is the basis for the following phylogenetic time tree:
​Figure 1. Time tree of the stem-Hyracoidea
​The oldest known member of the stem-Hyracoidea is Seggeurius amourensis, described from the Early Eocene (Ypresian) El Kohol Formation in the Southern Atlas of Algeria (Mahboubi, 1993; Heritage et al, 2021). Unfortunately, no public-domain image is available either of this species or of most of the other stem-group fossils represented in the above time tree. The few available ones are shown below (for a larger view, click on image):
​Figure 2. Images of stem-Hyracoidea
The oldest known member of the hyracoid crown group is Heterohyrax auricampensis, described from a Late Miocene (Tortonian) fissure fill breccia at Berk Aukas (Site I) in Namibia (Heritage et al, 2021). Again, no image is available in the public domain.

The available fossil data indicate that the hyracoid stem group developed from Early Eocene to Late Miocene time, representing a stem-to-crown transition of at least 36 million years (see Figure 1). As shown below, the rate of evolutionary change was highest during the Oligocene:
Figure 3.   Rate of appearance of stem-group hyraxes (predating the crown group and including only the species shown in Figure 1)

References

Barrow, E. C., Seiffert, E. R., & Simons, E. L. (2012). Cranial morphology of Thyrohyrax domorictus (Mammalia, Hyracoidea) from the early Oligocene of Egypt. Journal of Vertebrate Paleontology, 32(1), 166-179.

Heritage, S., Seiffert, E. R., & Borths, M. R. (2021). Recommended fossil calibrators for time-scaled molecular phylogenies of Afrotheria. Afrotherian Conservation 17 https://www. afrotheria. net/newsletter. php.

Mahboubi, M. (1993). Reassessment of lower Eocene Seggeurius amourensis: aspects of primitive dental morphology in the mammalian order Hyracoidea. Journal of Paleontology, 67(5), 889-893. 
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Puttick, M. N., & Thomas, G. H. (2015). Fossils and living taxa agree on patterns of body mass evolution: a case study with Afrotheria. Proceedings of the Royal Society B: Biological Sciences, 282(1821), 20152023.
Image credits – stem-Hyracoidea
  • Header (Rock hyrax, Procavia capensis, photographed in Israel): Greg Schechter from San Francisco, USA, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons
  • Figure 2 (Afrohyrax championi): Chiswick Chap, earlier version Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Figure 2 (Saghatherium antiquum): Regents of the University of California, under Creative Commons Attribution 3.0 (CC BY 3.0) license
  • Figure 2 (Titanohyrax andrewsi): Gertrude Mary Woodward (1861-1939), CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Figure 2 (Titanohyrax sp.): DiBgd, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons