Eoalulavis

Eoalulavis Temporal range: Early Cretaceous, 125 Ma PreЄ Є O S D C P T J K Pg N ↓
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Order:	Saurischia
Suborder:	Theropoda
Clade:	†Enantiornithes
Genus:	†Eoalulavis Sanz et al., 1996
Species:	†E. hoyasi
Binomial name
Eoalulavis hoyasi Sanz et al., 1996

Eoalulavis (from the Ancient Greek: Éōs, "dawn"; alula, "bastard wing"; avis, "bird") is a monotypic genus of enantiornithine bird that lived during the Barremian, in the Lower Cretaceous around 125 million years ago. The only known species is Eoalulavis hoyasi.^[1][2]

Discovery

Its remains came from the Konservat-Lagerstätte of Las Hoyas, Cuenca, Spain. The holotype (LH13500), housed in the collection of Museo de las Ciencias de Castilla-La Mancha, consists on both slab and counterslab preserving mainly the thoracic region, part of the neck and both almost complete forelimbs of an adult specimen.^[1] It also preserves remains of the body, primary, secondary feathers and a bastard wing which have been covered by layers of limonite as a result of the fossilization process.^[1] The preservation is consistent with the taphonomic processes associated with obruption, stagnation and the action of microbial mats in the locality^[3] that have yielded a wide variety of examples of soft-tissue preservation (e.g., connective tissues in fishes and theropods^[3] or insect wings^[4]). Most of the osteological features of the holotype became apparent only after its acid preparation and transference to a resin cast.^[2]

Paleobiology and Paleoecology

E. hoyasi was roughly the size of a little fringilid with a wingspan of nearly 20 cm.^[1] The presence of alula and a complete set of aerodynamic asymmetric feathers arranged forming a modern wing,^[5] indicate well develop flight capabilities, as in many other enantiornithine taxa.^[6] Its hindlimb morphology remain uncertain as no material of this kind referable to the genus has been found to date.

The holotype preserves concentrated remains of crustacean cuticles in the area of the abdomen, interpreted as its last meal.^[2] It provided the first direct evidence of feeding behaviour in Enantiornithes and in Mesozoic birds in general, though, since then, more examples of undigested food associated with enantiornithine specimens have been discovered reporting a wide variety of feeding habits.^[6] This fact has been interpreted as evidence of an ecological role in Eoalulavis similar to that of extant waders; living mainly in the shore seeking for little invertebrates in a similar way of modern turnstones.^[4]

The locality of Las Hoyas was in the Barremian a seasonal subtropical wetland ecologically dominated by fully aquatic organisms (e.g.: holostean fishes).^[4] The avifauna of the locality includes so far two more enantiornithine taxa: the sparrow-sized Iberomesornis romerali^[7] and the pigeon-sized Concornis lacustris.^[7] Eoalulavis hoyasi is believed to be the most linked to a semi-aquatic environment of the three.^[8]

Classification

The phylogenetic relationships within Enantiornithes are largely unsolved so far whilst several phylogenetic analyses have been performed in the last decades.^[9][10] However, some groups of enantiornithines seem to have fairly strong statictical support.^[9] In the last cladistic analysis^[9] Eoalulavis groups with the Chinese genus Liaoningornis forming a monophyletic group of derived enantiornithines. Nevertheless, this concrete grouping has not a high statistical support and the enantiornithine status of Liaoningornis remains currently controversial.^[11][12]

Eoalulavis hoyasi presents numerous synapomorphies that justifies the inclusion of the taxon within Enantiornithes and the less inclusive clade Euenantiornithes.^[13] These traits include a groove in the inter-osseous surface of radius or a conspicuous foramen in the dorsal surface of the strut-like coracoids.^[2]

It also has some unique characteristics like the spear shaped ossified portion of the sternum.^[1][2]

The morphology of the forelimb is remarkably primitive compared with that of other genera of enantiornithine birds.^[6] The alular and major digits both bear a large ungual phalanx and the minor one bears two phalanx. Also the alular digit extends until the distal end of the major metacarpal, which is considered a primitive trait within the clade Enantiornithes.^[6]

At the time of its discovery, was the earliest bird known to possess an alula, a batch of feathers on the alular digit that in modern birds can be separately moved to improve stability at low flight speeds. Later, more enantiornithine specimens were discovered with alula^[14][15] and this fact has consequently strengthen the hypothesis that this animals were able to develop a highly complex and active flight.^[2][6] The wide presence of this trait in both Enantiornithes and Ornithuromorpha, the clade which comprises modern birds along with their fossil counterparts, suggest that the arisen of the alula, and the flight capabilities that imply, occur early in the avian evolution, presumably in the base of Ornithothoraces.^[2][10]

References