This Fossil Friday features the giant hyrax Titanohyrax andrewsi from the Early Oligocene of Fayum in Egypt (Tabuce 2016), because today we look into the origins of the placental mammal order Hyracoidea. This order only includes the herbivorous Afro-Arabian hyraxes that look rather like marmots even though they are believed to be close relatives of elephants and manatees. Whereas the five living species of the single surviving family Procaviidae look very similar, fossil hyraxes especially in the Paleogene were much more diverse with five extinct families (Geniohyiidae, Namahyracidae, Pliohyracidae, Sagatheriidae, and Titanohyracidae), sometimes subsumed in a single paraphyletic family Pliohyracidae. These included forms from the size of a mouse to that of a rhino (Tabuce 2016), which occupied very different ecological niches (Rasmussen & Simons 2000). The strange genus Rukwalorax described by Stevens et al. (2009), based on a single tooth from the Late Oligocene of Tanzania, could represent another extinct family and the oldest small-bodied hyracoid from East Africa. The Paleogene fossil record of hyraxes is surprisingly rich and diverse (Rasmussen 1989, Fischer 1992: table 1, Tabuce et al. 2008, Barrow et al. 2010: fig. 16, Rasmussen & Gutiérrez 2010).
The possibly oldest fossil record of Hyracoidea is represented by an isolated molar tooth of Seggeurius spec. from the earliest Eocene of the Ouled-Abdoun basin in Morocco (Gheerbrant et al. 2003, Asher & Seiffert 2010: fig. 46.2, Seiffert 2010a), which is dated to 55.8 million years. The second oldest find is Seggeurius amourensis from the middle Ypresian (ca. 52 mya) El Kohol Formation of the southern Atlas in Algeria (Mahboubi et al. 1986, Court & Mahboubi 1993, Seiffert 2010a, Benoit et al. 2016). Some of the other oldest fossils of Hyracoidea were also found in the Early Eocene of Algeria at Gour Lazib (Sudre 1979, Court & Mahboubi 1993, Adaci et al. 2007, Tabuce et al. 2001, 2011, Seiffert 2010a), which have been dated to a late Ypresian / early Lutetian age (ca. 52-46 mya) and include the species Megalohyrax gevini, Microhyrax lavocati, and Titanohyrax mongereaui. Titanohyrax tantulus from the Early Eocene of Chambi in Tunisia (Hartenberger et al. 1985, Court & Hartenberger 1992, Hartenberger et al. 2001) is of about the same age (Barrow et al. 2010, Seiffert 2010a). Numerous other very old hyraxes have been found in Late Eocene (Early Priabonian) layers of the Fayum Depression in Egypt (Barrow et al. 2010), such as the 37 million-year-old Dimaitherium, and the Late Eocene (Lutetian and Bartonian) of Sperrgebiet in Namibia (Pickford et al. 2008, Pickford 2015).
Abrupt and Diverse
We can conclude that hyraxes appeared abruptly and with a surprising diversity about 56 million years ago in the very window of time when most other orders of placental mammals appeared for the first time as well. There are no fossils that show an assumed gradual development of hyraxes from Late Cretaceous stem eutherians via stem afrotherians etc. The diversity was most developed very early in the Middle to Late Eocene and is comparatively small today, which is about the opposite of what should be expected in a Darwinian scenario. Tabuce et al. (2011) therefore admitted: “To conclude, the diversity of hyracoids in the first part of the Maghrebian Eocene is remarkable and surprising at such an early age.” Words like “surprising” are code in the technical evolutionary literature for facts that disagree with Darwinian expectations and predictions, to avoid clearly stating the embarrassing fact of the matter.
Hyraxes were initially wrongly believed to be related to rodents. Since George Cuvier’s (1884: 120) time until relatively recently, hyraxes have often been considered to be more closely related to the odd-toed ungulates (Perissodactyla) in a group called Altungulata or Pantomesaxonia (e.g., Fischer 1986, 1992, Fischer & Tassy 1993, Prothero & Schoch 1989, McKenna & Bell 1997, Halliday et al. 2015), while other researchers instead have followed George Gaylord Simpson (1945) in considering them as close relatives of manatees and elephants in a group called Paenungulata (Sale 1960). Studies disagreed about the precise position of hyraxes, with most studies suggesting a basal position, while others suggested a closer relationship with either elephants (Sale 1960) or more rarely with sea cows (Seiffert 2010b, Benoit et al. 2016). Modern phylogenomic studies confirmed the monophyly of Paenungulata and placed them in the Afrotheria clade of African mammals (Asher et al. 2003, Nishihara et al. 2005, Seiffert 2003, 2007, Asher & Seiffert 2010, O’Leary et al. 2013, Cooper et al. 2014, Heritage et al. 2020). Among the very few anatomical features that might support Afrotheria (Tabuce et al. 2007, 2008) is the increased number of thoracolumbar vertebrae (Sánchez-Villagra et al. 2007) and the lack of a scrotum, but the latter similarity is somewhat incongruent as it is absent in the aardvarks, which are supposed to be nested within afrotherians. Recently, genetic evidence has been found that indeed suggests that the reduction of the testicular descent happened independently within Afrotheria (Sharma et al. 2018).
Not Based on Common Ancestry
Once again, anatomical similarity turns out not to be based on common ancestry. This is supported even more by the striking fact that there are three groups of mammals that independently produced a hyracoid-like morphology, so that they were initially misidentified as hyraxes:
- The Eocene early Hippomorpha (“horses”) like Hyracotherium.
- The fossil elephant shrew family Miohyracidae (see Bechly 2022).
- The family Archaeohyracidae of the South American ungulate clade Notungulata. A recent study by Avilla & Mothé (2021) suggested that notungulates are indeed related to afrotherian hyracoids, but this result was immediately disputed by Kramarz & MacPhee (2022), who found them nested within the unrelated Boreoeutheria instead. See why I got personally frustrated with phylogenetics as a wannabe science?
Of course, it is only we “nitpicking” intelligent design proponents who point out such incongruences, while Darwinists generally see no problem at all. The theory must be correct, therefore any conflicting evidence must be wrong and explained away, following the Procrustean solution of shoehorning the data until they fit.
Next Fossil Friday we will look into the early fossil history of another member of the Afrotheria, the order Sirenia, which includes manatees and dugongs.
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