Sunday, December 20, 2015

[PaleoMammalogy • 2015] Xenokeryx amidalae • Systematics and Evolution of the Miocene Three-Horned Palaeomerycid Ruminants (Mammalia, Cetartiodactyla)

Fig 10. Life reconstruction of the head of Xenokeryx amidalae gen. et sp. nov. Adult male based on the fossils from La Retama.
 Illustrations by Israel M. SánchezDOI: 10.1371/journal.pone.0143034


Palaeomerycids were strange three-horned Eurasian Miocene ruminants known through fossils from Spain to China. We here study their systematics, offering the first cladistic phylogeny of the best-known species of the group, and also reassess their phylogenetic position among ruminants, which is currently disputed. The beautifully preserved remains of a new palaeomerycid from middle Miocene deposits of Spain, Xenokeryx amidalae gen. et sp. nov., helps us to better understand palaeomerycid anatomy, especially that of the nuchal region in the skull, significantly improving our current knowledge on these enigmatic ruminants. Our results show two main lineages of palaeomerycids, one containing the genus Ampelomeryx diagnosed by a characteristic type of cranium / cranial appendages and some dental derived traits, and another one that clusters those forms more closely related to Triceromeryx than to Ampelomeryx, characterized by a more derived dentition and a set of apomorphic cranial features. Xenokeryx branches as a basal offshoot of this clade. Also, we find that Eurasian palaeomerycids are not closely related to North American dromomerycids, thus rejecting the currently more accepted view of palaeomerycids as the Eurasian part of the dromomerycid lineage. Instead of this, palaeomerycids are nested with the African Miocene pecoran Propalaeoryx and with giraffoids. On the other hand, dromomerycids are closely related to cervids. We define a clade Giraffomorpha that includes palaeomerycids and giraffids, and propose an emended diagnosis of the Palaeomerycidae based on cranial and postcranial characters, including several features of the cranium not described so far. We also define the Palaeomerycidae as the least inclusive clade of pecorans containing Triceromeryx and Ampelomeryx. Finally, we reassess the taxonomy of several palaeomerycid taxa.

Systematic Palaeontology

MAMMALIA Linnaeus, 1758
CETARTIODACTYLA Montgelard, Catzeflis and Douzery, 1997

RUMINANTIA Scopoli, 1777
PECORA sensu Webb and Taylor, 1980


Fig 11. Evolution of palaeomerycids. Summary scheme showing a calibrated phylogeny of palaeomerycids (based on the corresponding MPT) with special emphasis on the main morphological traits of each basal clade (Ampelomeryx-clade and Triceromeryx-clade represented by reconstructions of Ampelomeryx and Xenokeryx) including their biogeographic distribution.
 Illustrations by Israel M. Sánchez.  DOI: 10.1371/journal.pone.0143034

Genus Xenokeryx nov.

Etymology: Xenos, greek for strange, keryx referring to horn. Meaning ‘strange horn’.

Diagnosis: T-shaped upright occipital appendage with well-developed pedicle and downwards-oriented branch tips; very faint longitudinal crests in the posterior face of the occipital appendage; ulna distally fused to radius; short palmar extension of the facet for the semilunate in the radius; straight disto-lateral border of the distal trochlea in the astragalus, showing no notch; distal articulation facet of the first phalanx not extended into the flexor area.

Xenokeryx amidalae sp. nov.

Synonyms: Triceromeryx conquensis, nomen nudum (in ref. [69], p. 63, 88);
Triceromeryx conquensis, nomen nudum (in ref. [70], p. 117);
Triceromeryx sp. nov. (in ref. [41], p. 257)

Etymology: Referred to the fictional character Padme Amidala from Star Wars, due to the striking resemblance that the occipital appendage of Xenokeryx bears to one of the hairstyles that the aforementioned character shows in The Phantom Menace feature film.


We here present a new (albeit limited) phylogenetic analysis of the pecoran ruminants, with an emphasis on fossil forms and morphology, but also incorporating molecular data. A new palaeomerycid here described, Xenokeryx amidalae gen. et sp. nov. from the middle Miocene of Spain, helps to reinterpret and understand the morphological evolution and phylogenetic relationships of the group. Despite their apparent external similarities, Eurasian palaeomerycids are not related with North American dromomerycids. Instead, they belong in the clade that also contains the giraffes besides several extinct groups. We name this clade the Giraffomorpha. Among giraffomorphs, the early Miocene African pecoran Propalaeoryx is the closest sister group to palaeomerycids. On the other hand, dromomerycids are very closely related to cervids.

There are two main lineages of palaeomerycids. One of them, the Ampelomeryx-clade, is characterized by a well-developed Palaeomeryx-fold and several other dental derived characters (although they retain a relatively primitive dentition), sloped not pneumatized flat ossicones and flattish and variably sized occipital appendage. The other one, the Triceromeryx-clade, is characterized by its more derived dentition, upright cylindrical pneumatized ossicones, and a great diversity of occipital appendages.

This study focused mainly on the systematics of several extinct clades (palaeomerycids, dromomerycids and their respective allies). Future ruminant research will benefit from total-evidence phylogenetic methods (e.g. Bayesian tip-dating analysis used here) for combining fossil and living taxa, morphological and molecular datasets, and fossil ages. The inclusion of more living and fossil lineages in larger datasets will be decisive to further testing our findings and conclusions.

Israel M. Sánchez, Juan L. Cantalapiedra, María Ríos, Victoria Quiralte and Jorge Morales. 2015. Systematics and Evolution of the Miocene Three-Horned Palaeomerycid Ruminants (Mammalia, Cetartiodactyla). PLoS ONE. DOI: 10.1371/journal.pone.0143034

Xenokeryx amidalae: Strange 'Padme Amidala' ruminant discovered in Spain is extinct ancestor of giraffes via @IBTimesUK #StarWars

No comments:

Post a Comment