Rusingoryx atopocranion

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Rusingoryx atopocranion


Life restoration of R. atopocranion.

Temporal range: Late Pleistocene (Ionian at maximum, Tarantian at mimimum; ~285ka at maximum, ~46.811-32.475ka at minimum[1])

Scientific classification:

Life
Domain: Eukaryota
(unranked): Unikonta
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Bilateria
Clade: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Clade: Olfactores
Clade: Craniata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Clade: Teleostomi
Superclass: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Clade: Synapsida
Clade: Eupelycosauria
Clade: Sphenacodontia
Clade: Sphenacodontoidea
Order: Therapsida
Suborder: Cynodontia
Clade: Prozostrodontia
Clade: Mammaliaformes
Class: Mammalia
Legion: Cladotheria
Sublegion: Zatheria
Infralegion: Tribosphenida
Subclass: Theria
Clade: Eutheria
Infraclass: Placentalia
Subcohort: Exafroplacentalia
Magnorder: Boreoeutheria
Superorder: Laurasiatheria
Clade: Ungulata
Clade: Artiodactyla
Clade: Artiofabula
Clade: Cetruminantia
(unranked): Ruminantiamorpha
(unranked): Ruminantia
Infraorder: Pecora
Family: Bovidae
Subfamily: Alcelaphinae
Genus: †Rusingoryx
Species: †R. atopocranion

Rusingoryx is an extinct genus of alcelaphine bovid that lived in what are now the Wasiriya Beds in Rusinga Island, Kenya during the Late Pleistocene epoch, at least from around ~33,765-32,475 years ago or ~46,811-43,899 years ago and at most around ~285 thousand years ago[1].

Nasal dome:
An analysis on the skull of Rusingoryx revealed that it had a hollow nasal crest. According to it

"The floor of the nasal tract significantly departs from the hard palate, ascending parallel to the outer surface of the nasal dome and serving as a roof to the extraordinarily voluminous maxillopalatine paranasal sinuses. These sinuses comprise the largest proportion of cranial volume and extend to the midline, where they are separated by a median septum. Based on careful examination of computed tomography (CT) scans, the paranasal sinuses and the airway are not connected by ostia larger than 2 mm, rendering them dead airspace. The nasal tract is straight through the rostral portion of the cranium but deviates ventrally in the frontal region, forming an “S”-shaped curve".


Skulls, digital renderings, and CT sections of Rusingoryx. From O'Brien et al. (2016).

Such unusual features are not found in any other mammal. Instead, the authors noted that the closest analogues to Rusingoryx's nasal cavities were those of basal lambeosaurine dinosaurs (indeed, the evolution of such structures in both completely unrelated groups provides yet another case of convergent evolution)[2].

A function for the dome was searched for. It is unlikely that it was used for enhanced turbinate function, as the elevated nasal cavity floor does not allow for much room for turbinates. Nor does it seem to have been particularly useful for evaporative cooling (there is no evidence for the necessary airflow between the sinuses and nasal passages) or headbutting (narrow skull bones, enormous cranial cavities in lieu of buttressing, and posteriorly positioned horns). The most likely function of the nasal dome was found to be of phonic modification. Rusingoryx seems to have been able to produce low frequency sounds of 248-746Hz, judging from acoustic models from harmonic wave production (although since the soft tissue vocal tract length can't be reconstructed, these figures are conservatively high). Adding another 20 centimeters would allow the animal to make noises below 20Hz, in the ballpark of infrasound. Typically, the vocal ranges of mammals tend to be at ~1,100Hz, which would imply the vocalizations of Rusingoryx would have been undetectable by predators, thus helping in anti-predator activities (as well as in intraspecific signaling). Rusingoryx lived in vast semi-arid grasslands, which would have been ideal for low frequency vocalizations[2].

References:

[1] Taxonomic status and paleoecology of Rusingoryx atopocranion (Mammalia, Artiodactyla), an extinct Pleistocene bovid from Rusinga Island, Kenya (Faith et al., 2010).
[2] Unexpected Convergent Evolution of Nasal Domes between Pleistocene Bovids and Cretaceous Hadrosaur Dinosaurs (O'Brien et al., 2016).

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Ecomorphology and ecology of the grassland specialist, Rusingoryx atopocranion (Artiodactyla: Bovidae), from the late Pleistocene of western Kenya

Rusingoryx atopocranion is an extinct alcelaphin bovid from the late Pleistocene of Kenya, known for its distinctive hollow nasal crest. A bonebed of R. atopocranion from the Lake Victoria Basin provides a unique opportunity to examine the nearly complete postcranial ecomorphology of an extinct species, and yields data that are important to studying paleoenvironments and human-environment interaction. With a comparative sample of extant African bovids, we used discriminant function analyses to develop statistical ecomorphological models for 18 skeletal elements and element portions. Forelimb and hindlimb element models overwhelmingly predict that R. atopocranion was an open-adapted taxon. However, the phalanges of Rusingoryx are remarkably short relative to their breadth, a morphology outside the range of extant African bovids, which we interpret as an extreme open-habitat adaptation. It follows that even recently extinct fossil bovids can differ in important morphological ways relative to their extant counterparts, particularly if they have novel adaptations for past environments. This unusual phalanx morphology (in combination with other skeletal indications), mesowear, and dental enamel stable isotopes, demonstrate that Rusingoryx was a grassland specialist. Together, these data are consistent with independent geological and paleontological evidence for increased aridity and expanded grassland habitats across the Lake Victoria Basin.

www.cambridge.org/core/journals/quaternary-research/article/ecomorphology-and-ecology-of-the-grassland-specialist-rusingoryx-atopocranion-artiodactyla-bovidae-from-the-late-pleistocene-of-western-kenya/A970B276EF273765C584DD3E42FB36CE