What is Archaeotherium? Pig or hippopotamus? What is Onychonycteris? Shrew or bat?

One of our readers, Louise W. asks us:

Figure 1. Skeleton of Archaeotherium mortoni

Is the Archaeotherium related to the pig? It looks just like one. Wiki says it is in between a pig and hippos/whales. What is it? You can check it out here: [Web link removed as per feedback rule—Ed.] . Also by the way, according to Wiki, pig evolution evidence is slim. They did not say that, but I looked up pig evolution and found little evidence for it. Lastly, I also searched bat evolution and found that there is strong evidence for bat evolution they found a fossil [that is] more shrew-like [as] you can see here. [Web link removed as per feedback rule—Ed.] and they say these ‘Two specimens of Onychonycteris’ were found in the Green River Formation in 2003 and placed in a new family when the discovery was published in Nature, in February 2008. Onychonycteris occurs alongside Icaronycteris index, previously thought to be the most primitive known bat species. Onychonycteris was unique among bats in that it had claws on all five fingers, as opposed to two or three in all other known species, hence Onychonycteris meaning ‘clawed bat’. The specific epithet is a tribute to the fossil prospector and preparator who discovered it, Bonnie Finney’ Making it very clear it is primitive it goes more in depth about the echolocation and other matters. It does seem to support being closer to shrews.

Dr. Matthew Cserhati (CMI-US) responds:

Archaeotherium (figure 1) is an interesting animal. It belongs to a group of animals called enteledonts. These are an extinct type of pig-like omnivores (animals which eat both plants and animals). Therefore, Archaeotherium could possibly be a pre-Flood member of the pig kind, but it could also belong to its own created kind. The skull does not have tusks on it, so it cannot be a hippopotamus.

Figure 2. Artistic depiction of Onychonycteris finneyi

The species Onychonycteris finneyi (figure 2) is the most primitive form of bat, according to evolutionists. This is because initially, it seemingly lacked echolocation abilities and because of the shape of its wings, which to the discoverers suggested an undulating gliding-fluttering flight style. But based on the description in the 2008 Simmons et al. Nature article which first described this animal,1 this species does not resemble a shrew. Rather it looks just like any other bat species. Let us now look at several of these morphological characters.

First, O. finneyi (figure 3) was found in the Fossil Butte Member of the Green River Formation in Wyoming along with what was until then held to be the most primitive bat species, Icaronycteris index. The initial analysis of O. finneyi showed that it has a small cochlea (inner ear), suggesting that it does not have an echolocation apparatus. However, later research showed that O. finneyi had bones in the throat (the so-called stylohyal bones, figure 4B), which connect the larynx (the voice-box) to the tympanic bones (which aid in hearing).2 The authors suggest that O. finneyi used laryngeal (throat) echolocation.

Adapted from figure 1 of ref. 1Calcar-bone
Figure 3. Skeleton of O. finneyi. Label 1. Calcar bone

According to a review paper by Jones and Teeling, echolocation is missing in several extant bat groups, such as the family Pteropodidae (Old World fruit bats). These authors even claim that the complex echolocation apparatus evolved several times in bats.3 Echolocation is an irreducibly complex structure that is too complicated to evolve. Therefore, the lack of echolocation cannot be said to be a primitive trait. Even if O. finneyi really lacked echolocarion, this would not make it ‘primitive’.

O. finneyi also has relatively short and small wingtips, similar to extant mouse-tailed bats. These bats have an unusual undulating flight style, in which fluttering alternates with gliding.4 Simmons et al. say that “[T]his flight style may represent both a functional and an evolutionary intermediate between gliding and continuous flapping flight in the chiropteran lineage”.1 If this is so, then O. finneyi’s flight style is not ‘primitive’.

Simmons et al. also say that “[T]he morphology of wing elements in Onychonycteris is similar to that in other bats.”1 The first three digits of the wing end in large claws, but digits four and five end in smaller claws. In comparison I. index has claws on the first and second digits, bit digits three and four end in small bony masses. Most extant bats lack claws on digits 2–5. This would seem to indicate that modern bats would have lost claws over time, if O. finneyi really was the oldest bat. This is devolution, not evolution.

Figure 3 of ref. 2skull-O-finneyi
Figure 4. Skull of O. finneyi. Distal part of stylohyal bone connected to larynx (arrow 1). Proximal part of stylohyal bone connected to the tympanic bones (arrow 2).

But there are other traits because of which O. finneyi can be ranked as any other bat. Its pelvic (hip) region resembles that of other bats, and its hindlimbs are also rotated outwards as in other bats. Its hands and arms, rib cage and its sternum (breastbone) all make O. finneyi capable of powered flight. Simmons et al. claim that this way, bats first evolved flight, but as to how, they provide no clue. Bats have always had the anatomical hallmarks of powered flight.5

The calcar (otherwise known as calcaneum) is a short strip of cartilage, which stretches out the tail membrane (called the uropatagium) between the leg and the tail in bats. O. finneyi has a large calcar (see label 1 on figure 3), just like modern bats. This suggests that it used this membrane to catch prey and to help in manoeuvring. The teeth of this animal also resemble those of other bats, indicating that it ate insects, just like other bats.

In summary, the few ‘primitive’ traits of O. finneyi are found not to be primitive at all. Furthermore, several more morphological traits indicate that this species looked just like extant bats and had a similar diet. There is variety within kinds, bats have always been bats. Just because a new fossil bat has been discovered only increases the variety that exists in this kind. O. finneyi is not a transitional fossil between non-bats and bats. Such species don’t exist.

Published: 21 September 2019

References and notes

  1. Simmons, N.B., Seymour, K.L., Habersetzer, J., Gunnell, G.F., Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation. Nature 451(7180):818–21, 2008. Return to text.
  2. Veselka, N., McErlain, D.D., Holdsworth, D.W., Eger, J.L., Chhem, R.K., Mason, M.J., Brain, K.L., et al. A bony connection signals laryngeal echolocation in bats. Nature 463(7283):939-42, 2010. Return to text.
  3. Jones, G., Teeling, E.C., The evolution of echolocation in bats. Trends Ecol Evol. 21(3):149–56, 2006. Return to text.
  4. Norberg, U.M. and Rayner, J.M.V., Ecological morphology and flight in bats (Mammalia: Chiroptera): wing adaptations, flight performance, foraging strategy and echolocation. Phil. Trans. R. Soc. B 316:335–427, 1987. Return to text.
  5. Sears, K.E., Behringer, R.R., Rasweiler, J.J. 4th, Niswander, L.A., Development of bat flight: morphologic and molecular evolution of bat wing digits. Proc Natl Acad Sci U S A. 103(17):6581-6, 2006. Return to text.

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