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Splitting up the Tenrecidae

Thursday, December 1, 2016 11:56
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Everyone agrees
that the current list of genera within the clade Tenrecidae are a diverse lot. Asher and Hofreiter 2006 report, With the exception of a single genus of shrew (Suncus), insectivoran-grade mammals from Madagascar are members of the family TenrecidaeThis group of placental mammals consists of eight genera endemic to Madagascar and two from equatorial Africa and is remarkably diverse, occupying terrestrial, semi-arboreal, fossorial, and semiaquatic niches.” Finlay and Cooper 2015 sought to quantify that diversity. They report, “There are tenrecs which resemble shrews (Microgale tenrecs), moles (Oryzorictes tenrecs) and hedgehogs (Echinops and Setifer tenrecs). The small mammal species they resemble are absent from the island.”

Olson and Goodman 2003 report,
“Morphological studies have not support [genomic studies], however and the higher-level origins of both tenrecs and golden moles remain in dispute.” However, they limited their report to tenrecs, assuming a single origin.

According to Poux et al. 2008
Tenrecidae includes the following clades:

  1. Potamogalinae includes the genera Potamogale and Micropotamogale
  2. Tenrecinae includes the genera Tenrec, Echinops, Setifer and Hemicentetes;
  3. Oryzorictinae includes the genera Oryzorictes, Limnogale and Microgale;
  4. Geogalinae: includes Geogale. 

What makes a tenrec a tenrec?
Wikipedia provides no clue. And the academic literature has been similarly bereft. Instead all authors emphasize the diversity in this clade. The traditional and recent hypotheses of common ancestry are based on genomic studies that provide no clues to skeletal similarities and differences. As mentioned earlier, the anus and genitals revert to a single cloaca, as in golden moles and the scrotum reverts to an internal arrangement, distinct from many other mammals, but similar to odontocetes and hippos + mysticetes. The permanent dentition in tenrecs tends not to completely erupt until well after adult body size has been reached. Some tenrecids [which ones?] erupt their molars before shedding any deciduous teeth other than the third milk incisors.

Helping to define tenrecs, MacPhee 1987 reported,
“Shrew tenrecs are sometimes considered to be the most primitive members of Tenrecoidea. They outwardly resemble other unspecialized soricomorph insectivores (e.g., Crocidura) in possessing dense, rather velvety fur, abundant vibrissae, tiny eyes, short pentadactyl limbs slung under a long, fusiform body, and an elongated skull tapering into a narrow rostrum. Notably, like other tenrecs they retain ancient plesiomorphies that have been lost in virtually all other eutherian lineages (including true shrews), such as variable and rather low body temperature and cloacae in both sexes.”

Genomic analysis
by Asher and Hofreiter 2006 found Tenrecidae to be monophyletic. The proximal outgroup taxon was  Chrysospalax, a highly derived genus within the Chrysochloridae, or golden moles. In like fashion, Elephantulus, an elephant shrew, and Procavia, the hyrax, were successive outgroups as members of the Afrotheria, a diverse clade that only arises in genomic analyses and seems to provide a long list of oddly matched sister taxa.

Figure 1. Subset of the LRT highlighting tenrecs and former tenrecs

Figure 1. Subset of the LRT highlighting tenrecs and former tenrecs

By contrast
The large reptile tree (LRT, Fiig. 1) found the members of the former Tenrecidae so diverse that they nested in three different clades, apart from one another.

  1. Potamogale and Micropotamogale (both from Africa) nested with the shrew, Scutisorex within Glires.
  2. Echinops, Limnogale and Microgale (all from Madagascar) nested with the hedgehog, Erinaceus, despite lacking spines and also within Glires,
  3. Hemicentetes and Tenrec (both from Madagascar) nested with several fossil leptictids basal to odontocetes (toothed whales)  among extant taxa.

Those taxa nesting in Glires
have enlarged central incisors lacking in Hemicentetes and Tenrec, which have a longer, more pointed rostrum with relatively tiny incisors. Shifting aquatic Limnogale to nest with aquatic Potamogale adds 13 steps, so water habits are convergent.

Genomic sequencing lumps

  1. Limnogale and Microgale, as in the LRT.
  2. Micropotamogale and Potamogale, as in the LRT.
  3. Hemicentetes and Tenrec, as in the LRT.

Dissimilarities in DNA and trait-based tree topologies arise
with greater phylogenetic distance. The LRT permits one to include fossil taxa and to observe changes in traits that genomic codes can not do.

In the LRT
Hemicentetes and Tenrec are surrounded by fossil lepitictids. Asher and Hofreiter do not list odontocetes in their analysis, but these nest with Hemicentetes and Tenrec among living taxa in the LRT. Rose 1999 ran an analysis of postcranial traits that included Leptictidae and Tenrecidae. It nested Tenrecidae between Solenodon and shrews and Leptictidae between Tupaia and Zalambdalestes, distinct from the LRT which includes more characters, more body parts and more taxa. In the LRT Lepticitis and Lepticitidium nest with Andrewsarchus and Tenrec between them.

See what happens when you include more taxa? Topologies change.

Body masses of tenrecs
Finlay and Cooper 2015 report, “Body masses of tenrecs span three orders of magnitude (2.5 to >2,000 g): a greater range than all other families, and most orders, of living mammals.” The new phylogenetic set will not include the tiniest shrew tenrecs, but it will include the sperm whale weighing in at 57,000 kg.

If anyone has access to 
skeletal images of Geogale and/or Oryzorictes, please send them my way in order to add them to the LRT.

When you use molecules

  1. you don’t use traits. Therefore you lump and divide taxa based on combinations of DNA you can’t see or argue about.
  2. you don’t use fossils. Therefore you can’t tell which fossil taxa gave rise to which other fossil and extant taxa.
  3. you often recover very odd sister taxa that anti-evolutionists love to use in their PowerPoint lectures. That gives them power over audiences who want to see the evidence of evolution, which the LRT provides.

We have to own up to the shortcomings of DNA
while we still can. Great for criminals and baby daddies, bad for turtles and archosaurs. I think we need to get back to morph studies in mammal phylogeny. Molecules have given us very weird and unwieldy answers that don’t start small, extinct and simple and end large, extant and exotic, like the LRT does.

Granted if have not seen any specimens first hand, nor am I anywhere near a tenrec expert. Like Galileo, I am metaphorically tossing balls off the Tower of Pisa, coming to my own conclusions following repeatable observations. Because you can do that in Science. Others may argue methods and observations, but they will have to duplicate the list of taxa before they can do so with their own authority. This post provides an expanded taxon list and tentative insights for future studies.

Asher RJ and Hofreiter M 2006. Tenrec phylogeny and the noninvasive extraction of nuclear DNA. Systematic Biology 55(2):181-194. 
Asher RJ 2007. 
A web-database of mammalian morphology and a reanalysis of placental phylogeny. BMC Evol Biol. 7: 108-10 online
Asher  RJ and Helgen KM 2010. Nomenclature and placental mammal phylogeny. BMC Evolutionary Biology 10:102 online
Du Chaillu P 1860. Descriptions of mammals from equatorial Africa. Proceedings of the Boston Society of Natural History, 7, 358–369.
Eisenberg JF and Gould E 1970. The tenrecs: a study in mammalian behavior and evolution. Smithsonian Institution Press, Washington, DC. 138 pp. PDF online
Finlay S and Cooper N 2015. Morphological diversity in tenrecs (Afrosoricida, Tenrecidae): comparing tenrec skull diversity to their closest relatives. PeerJ 3:e927; DOI 10.7717/peerj.927
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
MacPhee RDE 1987. The shrew tenrecs of Madagascar: systematic revision and Holocene distribution of Microgale (Tenrecidae, Insectivora).
Martin WCL 1838. On a new genus of insectivorous mammalia. Proceedings of the Zoological Socieety, London, 6:17.
Mouchaty SK, Gullberg A, Janke A, Arnason U 2000. Phylogenetic position of the Tenrecs (Mammalia: Tenrecidae) of Madagascar based on analysis of the complete mitochondrial genome sequence of Echinops telfairi. Zoologica Scripta. 2000, 29 (4): 307-317. 10.1046/j.1463-6409.2000.00045.x.
Nicoll M 1985. The biology of the giant otter shrew *Potamogale velox*. National Geographic Society Research Reports, 21: 331-337.
O’Leary, MA et al. 2013. The placental mammal ancestor and the post-K-Pg radiation of  placentals. Science 339:662-667. abstract
Olson LR and Goodman SM 2003. Phylogeny and biogeography of tenrecs. Pp. 1235-1242 in Natural History of Madagascar, SM Goodman & JP Benstead (eds.), University of Chicago Press, Chicago.
Poux C, Madsen O, JGlos J, de Jong WW and Vences M 2008. Molecular phylogeny and divergence times of Malagasy tenrecs: Influence of data partitioning and taxon sampling on dating analyses. BMC Evolutionary Biology 8:102. Open Access
Rose KD 1999. Postcranial skeleton of Eocene Leptictidae (Mammalia), and its implications for behavior and relationships. Journal of Vertebrate Paleontology 19(2):355-372.
Suárez R, Villalón A, Künzle H and Mpodozis J 2009. Transposition and Intermingling of Gαi2 and Gαo Afferences into Single Vomeronasal Glomeruli in the Madagascan Lesser Tenrec Echinops telfairi. PLoS ONE 4(11): e8005. doi:10.1371/journal.pone.0008005

Tenrec bones website here (Microgale and Tenrec skulls and jaws)


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