Monday 20 July 2015

Barbatodon transylvanicus: A red-toothed Multituberculate Mammal from the Late Cretaceous of Haţeg Island.

Small, isolated islands often produce distinctive faunas, unlike anything seen on larger landmasses, and have been termed ‘cradles of evolution’ for this reason. Such island faunas are also known in the fossil record, particularly during the Cainozoic, with examples such as the Dwarf Hominids of Flores Island in Indonesia, Pygmy Elephants and Giant Hedgehogs from the Mediterranean and Pygmy Elephants from the Channel Islands of California. Further back in the fossil record distinct landmasses are harder to identify, but one well documented case is Haţeg Island in the modern Transylvanian Basin of southern Romania, where high sea-levels in the Late Cretaceous flooded much of southern Europe. Haţeg Island is estimated to have been about the same size as modern Hispaniola, and has produced a variety of unique Dinosaurs, including Dwarf Sauropods, and a Mammalian fauna dominated by the Kogaionid Multituberculates, an unusual group of Mammals found nowhere else during the Cretaceous, but being one of two Mammal groups in Europe which survived the End Cretaceous Extinction, flourishing briefly during the Palaeocene before becoming extinct as more modern Mammal Faunas invaded Europe from elsewhere (the other group being the equally extinct Adapisoriculidae, tree dwelling Placental Mammals). The lifestyle of Kogaionids, like many other Multituberculates, is somewhat obscure, as most species are known only from isolated teeth, but they are thought to have been similar to modern Rodents or Insectivores.

In a paper published in the journal PLoS One on 15 July 2015, Thierry Smith of the Directorate Earth and History of Life at the Royal Belgian Institute of Natural Sciences and Vlad Codrea of the Faculty of Biology and Geology at University Babeş-Bolyai describe a partial skull of the Kogaionid Multituberculate Barbatodon transylvanicus, previously known only from a single lower molar, from the Late Cretaceous of Haţeg Island.

The new specimen comprises a partial rostrum (snout), the left premaxillary, the left squamosal, both petrosals, and both associated dentaries, along with attached teeth, as well as a number of detached teeth. This allows conformation that Barbatodon transylvanicus is in fact a true species, and not a specimen of Kogaionon ungureanui, as has been previously suggested.

Barbatodon transylvanicus, Maastrichtian, Pui, Romania, specimen UBB P-Mt 1. Partial skull in (A) dorsal, (B) ventral, (C) left lateral, (D) right lateral views; Left squamosal and petrosal (E) and right petrosal (F) in dorsal view; Left premaxillary in (G) lateral view; Left dentary in (H) occlusal, (I) labial, (J) lingual views; Right dentary in (K) occlusal, (L) labial, (M) lingual views. Specimens covered with ammonium chloride. Smith & Codrea (2015).

The crowns of the teeth of Barbatodon transylvanicus are tinted red with iron oxide minerals. This is seen in modern Red-toothed Shrews (Soricinae and Myosoricinae) as well as a variety of Rodents, such as the Brown Rat, Rattus norvegicus, and North American Beaver, Castor canadensis, as well as in some non-Mammals, such as the Axolotl, Ambistoma spp., Piranhas, Characidae, Butterflyfish, Chaetodonidae, and even some Molluscs such as the Limpet, Patella, and the Chiton, Acanthopleura. In all cases the presence of iron minerals is thought to add strength and durability to the teeth, for example in Butterflyfish more iron minerals are associated with a higher Coral content in the diet.

Close-up on tooth rows of Barbatodon transylvanicus. (A) Left dentary with p4-m2 and (B) left maxillary with P1-M2 in occlusal views and covered with ammonium chloride. (C) Left maxillary with P1-M2 in occlusal view; (D) premaxillary with in I2-3 in lateral view; (E) anterior part of right maxillary with P1-2 and (F) right dentary with p4-m2 in lingual view in natural colour. Smith & Codrea (2015).

Iron minerals have previously been identified in the teeth of the Paleocene Asian Taeniolabidoid Multituberculates Lambdopsalis bulla and Sphenopsalis nobilis, suggesting that this may be an ancestral trait found throughout the group, as with Red-toothed Shrews. However in Rodents the trait is thought to have arisen separately on numerous occasions (different iron minerals are found in different Rodent groups), so without further data no such assumption can be made. Tooth enamel is seldom preserved without alteration, and this is the first known example of iron minerals being preserved within the enamel of teeth from any Mesozoic animal, making it unlikely that it will ever be established how widespread this trait was in the largely-Cretaceous Multituberculates.

Reconstruction of the skull and dentary of Barbatodon transylvanicus in (N) dorsal and (O) lateral views. Grey zones indicate missing parts. Smith & Codrea (2015).

See also…

Shrews (Soricidae) are small insectivorous or omnivorous Mammals found across much of the...

Biologists studying modern mammals divide them into...

During the later part of the Cretaceous global sea levels were extremely high, and much of Europe was flooded, leaving he remaining land masses as a string of...

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