The Birds from the Lower Cretaceous of Las Hoyas (Province of Cuenca, Spain)

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Sanz et al. — Las Hoyas Birds — 491
CHAPTER 9
The Birds from the Lower Cretaceous of Las Hoyas (Province of Cuenca, Spain)
José L. Sanz, Bernardino P. Pérez-Moreno, Luis M. Chiappe, and Angela D. Buscalioni
— Running head: Sanz et al.—Las Hoyas Birds —

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INTRODUCTION
Our knowledge of the early evolutionary history of birds has changed dramatically since
the early 1980s (Chiappe, 1995a). The increasing information about the Mesozoic diversification
of birds is generating insightful hypotheses on their phylogenetic structure and evolutionary
history. Since 1986, the Konservat-Lagerstätte of Las Hoyas (Province of Cuenca, Spain) has
provided exceptional evidence contributing to the flourishing revision on this paleobiological
issue. In this paper we describe the avian taxa from Las Hoyas: Iberomesornis romerali,
Concornis lacustris, and Eoalulavis hoyasi. We review how these taxa have been interpreted and
discussed according to recent phylogenetic hypotheses. We also discuss the contribution made by
the birds from Las Hoyas to our current understanding of the early phases of avian flight.
The first report on Iberomesornis romerali (referred to as “the Las Hoyas bird” in
literature prior to 1992) appeared in 1988 (Sanz et al., 1988). This preliminary paper stressed the
significance of this primitive bird in regard to early avian diversification. Iberomesornis, lacking
the skull, the cranial portion of the neck, and most of the hands (see Anatomy, below), presents
apomorphic characters (e.g., pygostyle, strutlike coracoid) with respect to Archaeopteryx and
plesiomorphic characters (e.g., primitive sacropelvic elements, unfused metatarsus) with respect
to neornithine birds. Therefore, Iberomesornis was proposed to be the closest known sister-group
of Ornithurae, a suggestion promptly accepted by several authors (Cracraft, 1988; Chiappe,
1991). This conclusion was presented in the II International Symposium of the Society of Avian
Paleontology and Evolution, held in Los Angeles, California (USA) in September, 1988. Four
years later, a formal denomination of the Las Hoyas bird, along with a further description and
discussion, was published in the Proceedings of the above mentioned Symposium (Sanz and
Bonaparte, 1992).
At the end of the 1980s, a new bird skeleton was discovered at Las Hoyas. This new
specimen was published by Sanz and Buscalioni (1992) with the name Concornis lacustris.
Concornis, roughly twice the size of Iberomesornis, is known by an almost complete skeleton
with some feather evidence, although it lacks the skull and neck. Sanz et al. (1995) fully
described the holotype (and only known) specimen and provided strong evidence in support of its
placement within Enantiornithes. One of the most striking features of Concornis is the presence
of a broad, notched sternum with a caudal carina, similar to that described for Cathayornis (Zhou,
1995a; see also Zhou and Hou, this volume).
In 1994, a third avian skeleton was found at Las Hoyas. This new bird specimen is better
preserved than the other two, and consists of much of the skeleton but lacks the skull. Wing
feathers are preserved in position. It was interpreted as a new enantiornithine taxon and named
Eoalulavis hoyasi (Sanz et al., 1996). Here, we place more emphasis on this last specimen, which
to date has been only preliminarily described.
GEOLOGICAL SETTING
The Las Hoyas fossil site is located in the southern part of the Serranía de Cuenca, in the
Castilla-La Mancha region of Spain (Fig. 9.1). The outcropping is stratigraphically placed within
the Calizas de la Huérguina Formation, and is located about 30 km east of the city of Cuenca. It
is Early Cretaceous (Late Barremian) in age, as dated by means of palinomorphs, ostracods, and
charophytes (Diéguez et al., 1995). The fossiliferous facies of Las Hoyas are rhythmically
laminated limestones derived from a wide lacustrine carbonate system. Several phases of

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deepening and shallowing occurred in this lake. The fossil-bearing limestones were deposited in
the deepening periods (Fregenal-Martínez and Meléndez, 1995).
— Place Figure 9.1 near here —
Most of the faunal assemblage and facies from Las Hoyas indicate that the basin was a
freshwater lacustrine environment. Yet, the vicinity of contemporaneous marine deposits (a few
tens of kilometers to the southeast) and the presence of coelacanth and pycnodontiform fishes
may suggest some sort of marine influence. Nevertheless, a strontium isotope analysis of the
bones of these fishes and carbon and oxygen analyses of the carbonate rocks from the Las Hoyas
basin are consistent with a freshwater lacustrine environment (Talbot et al., 1995). Thus, the
limestone isotopic analyses clearly indicate that the carbonates were precipitated in a
hydrologically closed basin. This type of restricted basin is consistent with the warm, seasonally
dry climate proposed for the Las Hoyas area during Early Cretaceous times (Gómez-Fernández
and Meléndez, 1991).
Las Hoyas is a Konservat-Lagerstätte that has yielded the fossil remains of a high
diversity of organisms (Sanz et al., 2000; in press). The floral assemblage includes charophytes,
bryophytes, filicales, cicadophytes, gnetales, conifers, and angiosperms. A large part of the floral
remains belongs to the enigmatic species Montsechia vidali (Diéguez et al., 1995). Most of the
invertebrates are arthropods: 16 forms of ostracods (Rodríguez-Lázaro, 1995); 2 decapods
(Martínez-Delclós and Nell, 1995a); and 31 different forms of insects, mainly belonging to
Odonata, Blattodea, Heteroptera, Orthoptera, Coleoptera, Diptera, Neuroptera, and
Ephemeroptera (Martínez-Delclós and Nell, 1995b). The ichthyofauna includes
Coelacanthiformes, Semionotiformes, Amiiformes, Pycnodontiformes, and primitive Teleosteii
(Pholidophoriformes and Gonorynchiformes) (Poyato-Ariza and Wenz, 1995). Amphibians are
represented by the salamanderlike Albanerpetontidae, salamanders, and frogs (Evans et al.,
1995). Lizards (Barbadillo and Evans, 1995) and turtles (Jiménez-Fuentes, 1995) were also
present in the Las Hoyas biota. The crocodilian fauna is peculiar, as it is represented by four
small-sized taxa belonging to Gobiosuchidae and Neosuchia (Buscalioni and Ortega, 1995;
Ortega et al., 2000). The dinosaur fauna includes fragmentary evidence of Sauropoda,
Ornithopoda, and Theropoda. Along with the birds, the most complete remains belong to the
ornithomimosaur Pelecanimimus polyodon (Pérez-Moreno et al., 1994; Sanz and Pérez-Moreno,
1995). Ichnofossils include invertebrate traces, a large amount of unstudied coprolites, probably
from fishes, and a trackway from a medium-sized crocodile (Fregenal-Martínez and Moratalla,
1995). The exceptional quality of preservation of the Las Hoyas Konservat-Lagerstätte is
illustrated by the preservation of soft tissues in several fossils. An outstanding example are the
flight feathers of the enantiornithine bird Eoalulavis hoyasi, which are preserved in situ, attached
to their respective bones (Sanz et al., 1996). Other examples include both isolated and adhered
feathers (such as in Concornis), as well as other epidermal remains (such as the ornithomimosaur
Pelecanimimus (Briggs et al., 1997) or the albanerpetontid Celtedens (McGowan and Evans,
1995).
SYSTEMATIC PALEONTOLOGY
Taxonomic Hierarchy
Aves Linnaeus, 1758
Ornithothoraces Chiappe, 1995

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Enantiornithes Walker, 1981
Iberomesornis romerali Sanz and Bonaparte, 1992
Holotype—LH-22; Las Hoyas Collection, Museo de Cuenca, Cuenca, Spain
(provisionally housed in the Unidad de Paleontología of the Universidad Autónoma de Madrid,
Spain). Nearly complete articulated specimen, lacking the skull, the cranial portion of the neck,
and most of the hands (Figs. 9.2 and 9.3).
— Place Figure 9.2 near here —
— Place Figure 9.3 near here —
Referred specimens—LH-8200; Las Hoyas Collection, Museo de Cuenca, Cuenca,
Spain (provisionally housed in the Unidad de Paleontología of the Universidad Autónoma de
Madrid, Spain). Left metatarsals I–IV and their respective articulated digits (Fig. 9.4). Poorly
preserved specimen comparable in size to that of the holotype. Sanz and Buscalioni (1994)
regarded it as cf. Iberomesornis sp.
— Place Figure 9.4 near here —
Horizon and Locality—Las Hoyas fossil site, province of Cuenca, Spain. Calizas de La
Huérguina Formation, Late Barremian (Lower Cretaceous) (Fregenal-Martínez and Meléndez,
1995). Diagnosis—Autapomorphic characters include cervicals with a lateral shelf linking
cranial and caudal zygapophyses; high vertebral arches of dorsal vertebrae, with relatively high
neural arches and laminar spines; a very large and laminar pygostyle; and the absence of a
cnemial crest on the tibiotarsus.
Euenantiornithes Chiappe, Chapter 20 in this volume
Concornis lacustris Sanz and Buscalioni, 1992
Holotype—LH-2814; Las Hoyas Collection, Museo de Cuenca, Cuenca, Spain
(provisionally housed in the Unidad de Paleontología of the Universidad Autónoma de Madrid,
Spain). Articulated specimen, including the right forelimb and thoracic girdle, sternum, some
dorsal, synsacral, and caudal vertebrae, pubis, ischium, and hindlimbs (Fig. 9.5).
— Place Figure 9.5 near here —
Horizon and Locality—See above.
Diagnosis—Autapomorphic characters include a ribbonlike ischium; a transverse
ginglymoid articulation of trochlea of metatarsal I; and a strongly excavated distal end of
metatarsal IV.
Eoalulavis hoyasi Sanz et al., 1996
Holotype—LH-13500 a/b; Las Hoyas Collection, Museo de Cuenca, Cuenca, Spain
(provisionally housed in the Unidad de Paleontología of the Universidad Autónoma de Madrid,
Spain). Articulated specimen, including feathers, the last five cervical and the first ten dorsal
vertebrae, the thoracic girdle, sternum and ribs, both wings, and remains of the pelvic girdle and
femora (Fig. 9.6–9.9). — Place Figure 9.6 near here —
— Place Figure 9.7 near here —
— Place Figure 9.8 near here —
— Place Figure 9.9 near here —
Horizon and Locality—See above.

Sanz et al. — Las Hoyas Birds — 495
Diagnosis— Autapomorphic characters include the presence of laminar, keellike, cervical
and dorsal centra; an undulating ventral surface of the furcula; a distal end of the humerus with a
thick, caudally projected ventral margin; the presence of several small tubercles on the distal,
caudal surface of the minor metacarpal; a depressed, spear-shaped sternum, with a footlike
caudal expansion and a faint carina; and a deep, rostral cleft in the sternum.
ANATOMY
1. Iberomesornis romerali Sanz and Bonaparte, 1992 (Figs. 9.2–9.4, 9.10, and 9.11).
New preparation of the holotype specimen has revealed new details of its anatomy. Thus,
we include here this new information that revises the comprehensive description of Sanz and
Bonaparte (1992). Sereno (2000) also discussed the newly prepared holotype specimen and
provided an account of its anatomy and systematic significance, but it has not been possible to
adequately address any issues raised in that paper.
Ontogenetic Stage
As is discussed in detail below, the holotype of Iberomesornis romerali is probably an
adult individual (contra Martin, 1995; Feduccia, 1996). This assessment is supported by the
fusion between the pubis and ischium and the absence of neurocentral sutures in the presacral
vertebral series.
Vertebral Column
The vertebral column is nearly complete, lacking only the cranial portion of the cervical
series. The fifth preserved vertebra, starting from the front, is probably the first dorsal. The two
foremost cervical elements are elongate and have a lateral shelf linking cranial and caudal
zygapophyses, while the two subsequent cervicals are shorter, lacking the lateral ridge. The first
two preserved cervicals lack a spinous process; this process is also very reduced in the third
preserved cervical but it appears to increase in height in the last cervical vertebra. Pneumatic
foramina (pleurocoels) are not visible in any of these vertebrae. Although exposed in lateral
view, the cervical centra were almost certainly not heterocoelous.
There are eleven thoracic vertebrae from which the first three have a transitional
morphology with the caudalmost cervicals. The cranial thoracic vertebrae, like the last cervical,
bear prominent ventral crests (Chiappe, 1996a). The thoracic centra are slightly longer than those
of the last cervicals, becoming progressively longer and lower caudal to the fourth dorsal. They
have small, lateral depressions and they appear to be platycoelous. The vertebral arch is relatively
high, with well-developed zygapophyses, and with cranial zygapophyses projecting beyond the
cranial articular surface. From the fifth thoracic, the costal fovea seems to be situated on the
vertebral arch. The spinous processes are laminar and relatively high.
The sacrum is composed of five elements (Fig. 9.10). Sanz and Bonaparte (1992)
considered the sacral series to be exposed in lateral view and proposed the presence of keellike
ventral processes. Nevertheless, the sacral vertebrae are most likely exposed in ventral view, and
no ventral processes are visible. This is consistent with the position of the iliac blades and the
disposition of the three cranialmost free caudal vertebrae.
— Place Figure 9.10 near here —
There are eight free caudal vertebrae and a large pygostyle (Fig. 9.11). The distalmost free
centra appear to be slightly procoelous. In the cranial part of the pygostyle, the first three

Sanz et al. — Las Hoyas Birds — 496
elements can be individualized, while in the caudal part, there is no differentiation between the
elements. Sanz and Bonaparte (1992) suggested that the pygostyle was comprised of vertebral
elements 10–15. Chiappe (1996a) emphasized the primitiveness of the caudal vertebral count of
Iberomesornis which, when pygostyle elements are added to the more proximal, free vertebrae,
approaches the number of elements present in Archaeopteryx. Cranially, the pygostyle seems to
have a ventral expansion, with an inverted-T cross-section, becoming distally laminar. As a
whole, the caudal series is subequal in length to the dorsal series.
There is no evidence of either uncinate processes or gastralia.
— Place Figure 9.11 near here —
Thoracic Girdle and Limb
Sternum—A fragment of the sternum is visible. Five stout sternal ribs are attached to it.
It is probable that a portion of the sternum is concealed by the ulna. The presence or absence of a
carina is uncertain.
Furcula—The furcula is almost completely preserved. The rami are robust, becoming
thinner towards the hypocleideum. The interclavicular angle is approximately 60º at the base of
the clavicular rami, and approximately 45º if it is measured at the shoulder end of the rami. The
hypocleideum is partially hidden by the radius, but it seems to be long.
Scapula—A fragment of the scapula is preserved. The scapular blade seems to be rather
straight, long, and narrow. It articulates with the coracoid at a right angle, although it is uncertain
whether this condition was also present at the level of the humeral articular facet (Chiappe,
1996a).
Coracoid—The avian, strutlike coracoids of Iberomesornis are not well preserved. The
left coracoid, exposed in ventral view, is nearly complete, but its shaft and head lack any
anatomical details. The sternal margin is broad and straight, and the lateral margin lacks the
typical enantiornithine convexity.
Humerus—The left humerus is exposed craniodorsally, and its shaft is fractured in two
points. It is distinctly shorter than the ulna. The deltopectoral crest is well developed and the
bicipital crest is low. There is no visible transverse ligamental groove. Neither condyles nor an
intercondylar depression are observed. Nevertheless, the outline of the ventral epicondyle seems
to be placed more distally than the dorsal epicondyle. The absence of visible distal condyles is
not necessarily related to the suggested juvenile condition of the specimen, but rather to the
preservation of this area.
Ulna and Radius—Both are nearly articulated with the humerus. The ulnar shaft is
almost twice the radial shaft in width. The former is curved caudally in its proximal area. The
ends of both the ulna and radius are badly preserved.
Manus—Some bones placed close to the midshaft of the radius could be the distal end of
the metacarpus and some phalanges, although no clear features can be observed.
Pelvic Girdle and Limb
Ilium—The interpretation of the pelvic girdle is still problematic, even after the new
preparation of the specimen. Both ilia are preserved in ventral view at both sides of the sacrum
(Fig. 9.10). These bones are so poorly preserved that nothing can be said about their morphology.
Pubis—The new preparation revealed that Sanz and Bonaparte (1992) confused the right
pubis with the proximal half of the femur. The pubis is slightly retroverted, with a robust shaft of

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suboval cross-section. It is not possible to verify whether there is a pubic foot, as the distal ends
of both pubes are missing. No suture is visible between the pubis and ischium, and it seems that
these pelvic elements are fused to each other. This condition again suggests that this specimen
was not a juvenile.
Ischium—Both ischia are exposed. The left one is displaced dorsally with respect to the
right one. Behind the left ischiadic shaft, a process of the right ischium can be observed (Fig.
9.10). The base of this process is visible in the proximal area of the left ischium as well. As
pointed out by Zhou (1995b), this projection may compare to the caudodorsal process of the
ischium of Enantiornithes (see Chiappe and Walker, this volume). Yet, it can be alternatively
interpreted as the iliac process of the ischium (contra Zhou, 1995b) that forms the caudal margin
of the acetabulum. If this latter interpretation is correct, the concave outline dorsal to this process
is the ventral margin of the acetabulum. Both interpretations are plausible, although its proximal
position supports its interpretation as part of the acetabulum. The ischiadic shaft lacks the
characteristic caudal process of Archaeopteryx (Wellnhofer, 1974).
Femur—The right femur is clearly visible in medial view. The left is badly preserved,
and its proximal half is virtually missing (Fig. 9.10). The femur is relatively long, but shorter
than the tibia. Distally, it bears a well-developed popliteal fossa.
Tibia—The right tibia is almost complete, exposed in medial view. The left tibia is
broken into two, displaced pieces. There is no visible cranial cnemial crest. A round proximal
articular surface is present.
Tarsus—Both astragali are in their original positions. They are not fused to the tibia. The
ascending process is broad and low. Two small, free distal tarsals are also visible.
Metatarsals—Left and right metatarsals II–IV are preserved, although the right set is
difficult to interpret due to its bad preservation. The left metatarsals are visible in dorsal view.
The first metatarsal is slightly displaced from its original position. Metatarsals II–IV are subequal
in length, although metatarsal III is somewhat longer. There is no evidence of either proximal or
distal fusion between metatarsals.
Foot—The phalangeal formula is 2-3-4-5-x. The pes is anisodactyl, with three main
digits (II–IV) directed dorsally, and a reversed hallux.
2. Concornis lacustris Sanz and Buscalioni, 1992 (Figs. 9.5, 9.12, and 9.13).
A detailed description of Concornis lacustris after the definitive preparation of the
holotype was given elsewhere (Sanz et al., 1995). Thus, only its most significant features are
mentioned here.
Ontogenetic Stage
The only known specimen of Concornis is an adult individual, possessing a well-ossified
sternum, tibiotarsus, and tarsometatarsus.
Vertebral Column
There are eight vertebrae preserved. The four preserved thoracic centra are amphicoelous,
compressed, and excavated laterally by a longitudinal depression, as occurs in other
enantiornithine birds (Chiappe and Calvo, 1994; Chiappe and Walker, this volume). The last two
synsacral vertebrae have elongated transverse processes. The first two caudals are amphicoelous,

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with caudally directed transverse processes (as are those of the synsacrum). A haemal arch is
preserved at the proximal border of the second caudal vertebra.
Several dorsal ribs are well preserved, but none of them shows evidence of uncinate
processes. This suggests that these processes, if present, did not ossify.
Thoracic Girdle and Limb
Sternum—The sternum has a rounded cranial margin. The carina is developed only in its
caudal half, with lateral crests diverging from its cranial end. The caudal portion of the sternum
is deeply notched, with a stout and distally expanded lateral process and a less robust medial one
(Fig. 9.12). On the lateral margin of the sternum, there is a short notch, delimited caudally by a
cranially directed process, which is interpreted as the articular area for the ribs.
— Place Figure 9.12 near here —
Furcula—The furcula is very robust and excavated laterally, with the cranial margin projected
externally. The interclavicular angle is 60º. The hypocleideum is long and tapers distally, with a
weak crest on its cranial face.
Scapula—The scapular blade is straight. The shoulder end has a medial, subrectangular
area interpreted as the articular facet for the furcula.
Coracoid—The strutlike coracoid is long, lacking lateral and procoracoid processes. It
has a typical enantiornithine morphology: a dorsal fossa, a sternal half with a convex lateral
margin and a concave medial one, and a supracoracoidal nerve foramen opening into a medial
groove and separated from the dorsal surface by a thick bar (see Chiappe and Calvo, 1994;
Chiappe and Walker, this volume). However, the sternal margin is only slightly concave, lacking
the remarkable concavity typical of several Enantiornithes.
Humerus—The humerus also presents the characteristic morphology of
euenantiornithine birds (Chiappe and Walker, this volume). The humerus has a distinct torsion
between proximal and distal ends, a cranially concave and caudally convex head, a strong
development and cranioventral projection of the bicipital area, and a craniocaudally compressed
distal end.
Ulna and Radius—The ulna is nearly twice the width of the radius. The latter is badly
preserved, so the presence of the longitudinal groove typical of other Euenantiornithes (Chiappe
and Calvo, 1994; Chiappe and Walker, this volume) cannot be confirmed. The ulna has a
proximal end with a convex and strongly caudodorsally projected dorsal cotyla, which is
separated from the concave ventral cotyla and the olecranon by a shallow depression. The
bicipital tubercle is distally placed to the proximal articular surface.
Hand—The manus is slightly shorter than the forearm. The robust and ventrally convex
major metacarpal is subequal in length to the minor one, and these two metacarpals appear to be
fused distally. The intermetacarpal space is narrow. The alular metacarpal must have been short,
although it is not preserved.
The alular digit has two phalanges: the proximal one is slender and elongate, the distal
one is a claw. The major digit has three phalanges, with the proximal one being the largest, and
the distal one being a claw. The minor digit has only one preserved phalanx.
Pelvic Girdle and Limb
Pubis—The pubis is slender, elongate, and suboval in cross-section and has a short distal
symphysis (Fig. 9.13). Based on its preservation, the pubis was probably oriented caudally.

Sanz et al. — Las Hoyas Birds — 499
— Place Figure 9.13 near here —
Ischium—The ischium is about 25% shorter than the pubis. It lacks a distal contact, and is
narrow in its distal two-thirds, having a ribbonlike appearance (Figs. 9.12 and 9.13). It has a
prominent obturator process and a dorsal process similar to those of other enantiornithines (see
Chiappe and Walker, this volume).
Femur—The femur is notably shorter than the tibiotarsus. It is robust and slightly curved,
with the cranial surface being convex. The femoral head lacks the depression for the insertion of
the round ligament (fovea lig. capitis). The medially inclined lateral margin of the proximal end
suggests the presence of a well-developed posterior trochanter. There is no patellar groove in the
distal end. The lateral margin of the lateral condyle projects caudally, as in other
euenantiornithines.
Tibiotarsus—The tibia is gracile, with the proximal tarsals fused entirely to its distal
end. The fibular crest is relatively short and well developed. The proximal articular surface of the
tibiotarsus is round, and there is a single cnemial crest—two characters that are also present in
most Enantiornithes (see Chiappe, 1996a; Chiappe and Walker, this volume). The cross-section
of the shaft is subcircular, unlike the craniocaudally compressed condition of Lectavis bretincola
(Chiappe, 1993). The medial condyle of the distal end of the tibiotarsus is transversely broad, the
same condition present in other enantiornithines.
Tarsometatarsus—The tarsometatarsus is shorter than the tibiotarsus. The third
metatarsal is the longest, with the fourth one being the most slender. Metatarsals II–IV are
straight and co-planar, although the shaft of metatarsal III is strongly convex in its central
portion, being projected somewhat forward from metatarsals II and IV. Metatarsals II–IV are
fused proximally and closely connected to each other, lacking the distal divergence of metatarsal
II that appears in some avisaurid enantiornithines (Chiappe, 1993). The proximal end lacks an
intercotylar eminence as well as the dorsal sloping present in several avisaurids (Varricchio and
Chiappe, 1995). The trochlea of metatarsal IV is the most reduced, and that of metatarsal II the
most developed. Metatarsal I articulates with the medial surface of metatarsal II. This metatarsal
is not J-shaped in mediolateral view as in other enantiornithines (Chiappe, 1992, 1993; Chiappe
and Calvo, 1994), but straight.
Pedal Phalanges—Digit I is robust and reverted, with a large claw. The unguals lack
well-developed flexor tubercles.
3. Eoalulavis hoyasi Sanz et al., 1996 (Figs. 9.6–9.9, 9.14, and 9.15).
The specimen is preserved as a slab and a counterslab. The slab (LH-13500a) exhibits the
specimen in dorsal view (Figs. 9.8 and 9.14), and contains 15 vertebrae (of which five are
cervicals), the two scapulae, the left coracoid and the proximal half of the right coracoid, the
distal portion of the furcula including the hypocleideum, several ribs, almost all of the left wing
skeleton and the right wing lacking only the hand, part of the left side of the pelvic girdle, the
proximal end of the left femur, and the synsacrum. The counterslab (LH-13500b) exhibits the
specimen in ventral view (Figs. 9.9 and 9.15), including seven vertebrae (five of which are
cervicals), both coracoids and the proximal end of the left scapula, the complete furcula, the
sternum, several ribs, and the left wing and the humerus and ulna-radius of the right wing.
From the ninth preserved vertebra, the caudal part of the specimen is preserved as a cast
(in plastic resin) of the diagenetic dissolution of the bones. Thus, the available data from this area
of the specimen is poor.

Sanz et al. — Las Hoyas Birds — 500
Ontogenetic Stage
The well-ossified skeleton of Eoalulavis, lacking the pattern of foramina in the periosteal
surface that appears in the humerus and other bones in the nestling from El Montsec (Sanz et al.,
1997), indicates that it pertains to an adult individual (note: Concornis and Iberomesornis also
lack this punctate periosteal texture).
— Place Figure 9.14 near here —
Vertebral Column
The last five cervicals are preserved, of which the cranialmost preserved cervical is longer
than the others. All of the cervicals have very compressed spinous processes. These are relatively
small in the first three vertebrae and somewhat taller in the fourth and fifth. The epipophyses are
small. In ventral view, the cervical centra are very compressed, forming a ventral keel. From the
second to the fifth preserved cervicals, this ventral keel projects into a cranial ventral crest. The
cervical centra are roughly amphiplatyan. There are robust cervical ribs, of about the same length
as the centrum. The fourth and fifth have a transitional morphology with the thoracic vertebrae.
Ten thoracic vertebrae are preserved in articulation between the last cervical and the
cranial margin of the ilium. In the second and the subsequent vertebrae, the spinous processes are
tall and compressed. In the second thoracic vertebra, the tip of the neural spine forms a
rectangular platform. This appears to be absent in the third thoracic vertebra (although it could be
broken off), but it appears again in the fourth and subsequent vertebrae. In the fourth thoracic
vertebra this platform is forked caudally, and in the fifth vertebra it is forked both caudally and
cranially. This cranial and caudal bifurcation appears to be present in all of the remaining
thoracic vertebrae, because a bifurcation is visible in all the preserved portions. In the platform of
the seventh thoracic vertebra, the caudal bifurcation is doubled, with one fork situated on top of
the other. The spinous process of the sixth thoracic vertebra is missing, so it is uncertain whether
this feature was present in this vertebra. This condition is also present in the eighth and ninth
dorsals, but the area is not preserved in the tenth vertebra.
— Place Figure 9.15 near here —
The centra of the seventh to tenth thoracic vertebrae are copied by the resin. These show
very clearly that the bodies are excavated laterally by a large fossa, a condition common to
several other enantiornithine birds (Chiappe, 1996a; Chiappe and Walker, this volume). The
transverse processes are short and virtually centered. Only the first and second vertebrae are
exposed ventrally; the hypapophyses of the third and fourth are seen through the right coracoid.
These centra bear a ventral keel that is larger than that of the cervicals. In the cranial half of the
centrum, this keel projects into a well-developed ventral process. In the second, third, and fourth
thoracic vertebrae, this process is deep and very robust. In the second thoracic vertebra, the
cranial articular surface is flat; yet, the condition for the caudal articular surface of this vertebra is
uncertain.
There are several preserved thoracic ribs, some of them nearly complete. In none of these
is there evidence of uncinate processes, which suggests their true absence as ossified elements.
No evidence of gastralia has been found.
Thoracic Girdle and Limb

Sanz et al. — Las Hoyas Birds — 501
Sternum—The morphology of the sternum is singular within dinosaurs (Fig. 9.16),
although a similarly shaped sternum has been recently found for the Early Cretaceous
Liaoningornis of China (Hou et al., 1996). The sternum is a depressed, spear-shaped element,
with a footlike caudal expansion. On its ventral surface there is a faint carina. The rostral third of
the sternum is cleft by a narrow indentation, presumably an area interlocking with the extremely
long hypocleideum of the furcula (see below). The margins of the sternum are smooth and well
defined, lacking either facets for the articulation of the ribs or the coracoids. Regardless of the
peculiar morphology of the element, its median carina and position with respect to the ribs
indicate that it constitutes the central portion of the sternum. Conceivably, the sternum had
cartilaginous extensions that formed the articular areas for both the ribs and coracoids (Sanz et
al., 1996). — Place Figure 9.16 near here —
Furcula—The furcula is very robust and V-shaped, with an angle of approximately 45°
between the two rami. It is compressed mediolaterally, and its ventral margin undulates in lateral
view, with two “hills” and three “valleys.” The latter are placed at the midpoint of each third of
the rami. The dorsal margin is thinner than the ventral margin, as in Concornis (Sanz et al., 1995)
and Neuquenornis (Chiappe and Calvo, 1994), although it is not possible to discern whether there
is a lateral excavation. The hypocleideum is hypertrophied and strongly compressed. It is roughly
77% of the ramal length. In ventral view, there is a strong buttress in the middle of the
hypocleideum, although it may be a pathological condition.
Scapula—The scapular blade is straight with a sharp distal end. The well-developed
acromion is roughly depressed and placed somewhat perpendicular to the scapular blade. The
humeral articular facet is concave and subtriangular in outline.
Coracoid—The coracoid is very long and thin. The ventral surface is convex. Dorsally,
there is a subtriangular fossa. The shoulder end of this fossa converges towards the foramen for
the supracoracoideus nerve, which opens medially into a longitudinal groove. The shoulder end
of the coracoid is very compressed, and it is oriented caudodorsally. In dorsal view, this end is
sigmoidal in shape, with a laterally convex humeral articular facet and a laterally concave
articular facet for the scapula. The glenoid is flat and becomes thinner dorsally to form a convex
surface for the scapula. In the middle of the two articular surfaces (glenoid and sternal) there is a
small depression in the medial margin. As in the El Brete enantiornithine birds, there is no
tubercle between the glenoidal and the scapular articular surfaces. The sternal third of the
coracoid becomes wider abruptly, with the lateral margin strongly convex, although this becomes
straight distally. In ventral view, the sternal margin is straight.
Humerus—The humerus is sigmoidal in shape, with a length of about 2.7 cm. It presents
an evident torsion between the two ends. The humeral head is concave cranially and strongly
convex caudally. The deltopectoral crest runs along the proximal third of the humerus. This crest
is cranially flat without a cranial torsion. Just distal to the head, there is a small transverse fossa.
Dorsodistally to this fossa, a rounded scar appears on a small elevation. The bicipital area is
prominent, and projected cranioventrally. On the cranial face of this area, distally displaced, there
is a small fossa for a muscular insertion. This fossa is also found in other enantiornithines
(Chiappe and Walker, this volume). Proximal to the bicipital area, a distinct ligamental furrow
can be observed. In caudal view, the ventral tubercle is well developed and projected caudally,
separated from the humeral head by the capital incision. The caudal end of the ventral tubercle
bears a distinct subtriangular depression. Unlike Enantiornis leali, the ventral tubercle is not

Sanz et al. — Las Hoyas Birds — 502
perforated proximodistally by a fossa (Chiappe, 1996b). There is no evidence of either pneumatic
foramen or fossa.
Distally, the humerus is craniocaudally compressed. The dorsal epicondyle is projected
dorsally and proximally, and it possesses a shallow depression over its dorsal face. In caudal
view, the ventral margin presents a thick ridge projected caudally, which defines the ventral
margin of a deep olecranon fossa. The ventral epicondyle is projected somewhat distally. On the
ventral margin of this epicondyle two small suboval fossae appear. The condyles are situated on
the humeral cranial surface. The ventral condyle is oriented transversely, and its distal surface is
planar. The dorsal condyle is subspherical, oriented transversely, and situated more proximally
than the ventral condyle.
Ulna and Radius—The antebrachium is longer than the humerus (ulnar length: 3.1 cm.).
It is straight, although the ulna is curved somewhat caudally in its proximal area. Thus, the
interosseous space is wider proximally than distally. The radial shaft is notably thinner than the
ulnar shaft, which is roughly twice the radial shaft in width.
The radius has a subcircular proximal end. Its bicipital tubercle is conspicuous. The radial
shaft has a longitudinal groove, similar to that of several Enantiornithes (Chiappe and Calvo,
1994; Chiappe and Walker, this volume).
The ulna has a weak olecranon. The ventral cotyla is somewhat planar. There is an
elongated and strong scar for the bicipital muscle.
Hand—The hand is clearly shorter than the ulna and humerus, with a length of about 1.8
cm (length of major digit, including the metacarpal). The ratio between the different elements of
the forelimb is 0.88:1:0.58 (humerus:ulna:major digit).
Only the left hand is preserved. In ventral view, there is a small bone in the wrist, situated
in the angle formed by the distal end of the ulna and the proximal end of the minor metacarpal. It
could be interpreted as a displaced carpal bone, probably the ulnare.
The alular metacarpal is not preserved. The straight major metacarpal is clearly more
robust and somewhat shorter than the minor metacarpal, and it becomes wider distally. The distal
ends of the major and minor metacarpals are not fused to each other; it is uncertain whether these
metacarpals are fused one to another proximally. The intermetacarpal space is very narrow, even
thinner than in Neuquenornis (Chiappe and Calvo, 1994). The minor metacarpal is curved
slightly caudally, and its proximal end is compressed craniocaudally, with the shaft becoming
rounded gradually. On the caudal face of the distal half of this metacarpal there are several small
tubercles.
The alular digit has two phalanges and it is slightly shorter than the major metacarpal.
The first phalanx is thin and relatively long, with the distal end having a ginglymoid articulation
and collateral foveae. The distal phalanx is an ungual, having a strong flexor tubercle. The major
digit has three phalanges. The proximal one is very robust, and it is the longest of the hand. It has
a subquadrangular section unlike the depressed, comparable element of extant birds. This
phalanx presents collateral foveae in the distal end. The second phalanx of the major digit is
smaller than the first one, with a ginglymoid distal articulation and collateral foveae. The last
phalanx is a small ungual. Only one phalanx of the minor digit has been preserved.
Pelvic Girdle and Limb
Ilium—Most of the left ilium is copied by the resin. It has a postacetabular wing that is
shorter and much lower than the preacetabular one. The postacetabular wing tapers caudally.

Sanz et al. — Las Hoyas Birds — 503
Femur—The proximal portion of the left femur has been copied by the resin. It possesses
a well-developed posterior trochanter, a condition typical of euenantiornithine birds (Chiappe
and Walker, this volume).
Feathers
There is visible evidence of feathers in both slabs of the specimen. Most of the isolated
feathers from the Las Hoyas fossil site are preserved as carbonized remains, which is the most
common way of feather preservation in the fossil record (Davis and Briggs, 1995). Nevertheless,
the feathers of Eoalulavis are usually covered, like most of its bones, by limonite and, in some
cases, by piroluxite. Most of the oxide is removed during the transference process and the acid
preparation, but, fortunately, some remains. In any case, the plastic resin copies the structure of
the feathers, so all the information is maintained after the preparation of the specimen.
Remiges are preserved in both wings and body feathers are visible around the humeri and
pectoral girdle. There are eight preserved primary remiges, although the proximal two-thirds of
the major metacarpal lacks any feather evidence. As in neornithine birds, some feathers are
attached to the phalanges (five of the preserved ones) and others to the major metacarpal (only
three of these are preserved). Eight secondary remiges are preserved. Seven of these are in the
proximal portion of the ulna and the eighth attaches to its distal end. Although only 16 primary
and secondary remiges have been preserved, their number was probably comparable to that of
extant flying birds.
The alular digit of the left wing presents at least one feather adhered to the first phalanx
(although it is possible that two existed). This feather is the most ancient evidence of an alula
known in the fossil record, and Eoalulavis is the most primitive bird preserving an alula. A
clearly defined rachis seems to be lacking from the alular feather, which is very long. Although
the existence of a rachis is not evident, the disposition of barbs appears to be symmetrical.
PHYLOGENETIC RELATIONSHIPS
Two alternative phylogenetic hypotheses have been proposed for Iberomesornis romerali,
the first bird from Las Hoyas. Sanz et al. (1988) placed the Las Hoyas bird in an intermediate
position between Archaeopteryx and Neornithes, a hypothesis highly corroborated by a number
of studies (e.g., Chiappe, 1991, 1995a, b, 1996a; Sereno and Rao, 1992; Chiappe and Calvo,
1994; Chatterjee, 1995; Sanz et al., 1995). Specifically, this hypothesis supported the sister-group
relationship between Iberomesornis and a clade formed by Enantiornithes and Ornithurae.
Chiappe (Chapter 20 in this volume) proposed a sister-group relationship between Iberomesornis
and Euenantiornithes, including Iberomesornis within Sereno’s (1998) new phylogenetic
definition of Enantiornithes (all taxa closer to Sinornis than to Neornithes). Enantiornithes
(including Iberomesornis and Euenantiornithes) and its sister-group, Ornithuromorpha
(Patagopteryx, Vorona, plus Ornithurae), constitutes Ornithothoraces (Fig. 9.17). This clade is
phylogenetically defined as the common ancestor of Iberomesornis and neornithine birds plus all
its descendants (Chiappe, 1996a). Recently, Sereno (2000) also included Iberomesornis within
his phylogenetically defined Enantiornithes. Several authors (e.g., Feduccia, 1995, 1996; Hou et
al., 1995; Kurochkin, 1995; Martin, 1995) had placed Iberomesornis within Enantiornithes but
followed Martin’s (1983) “Sauriurae,” endorsing a sister-group relationship between
Archaeopteryx and the latter clade. This notion is dramatically different from the one supported
by us because it implies that the closest ancestor shared by Iberomesornis and neornithine birds is

Sanz et al. — Las Hoyas Birds — 504
the ancestor of all birds. The non-monophyletic status of “Sauriurae” has been pointed out many
times (e.g., Olson, 1985; Chiappe, 1991, 1995a, b, 1996a; Sanz et al., 1996; Forster et al., 1996;
see Chiappe [1995b, Chapter 20 in this volume] for a detailed discussion of this view) and does
not need to be repeated here. Unfortunately, none of those placing Iberomesornis within
“Sauriurae” have structured their views under a rigorous cladistic framework; nor have they tried
to explain the enormous amount of convergence (i.e., the independent origin of a pygostyle, a
strutlike coracoid, a low interclavicular angle, and many other characters shared by
Iberomesornis, Euenantiornithes, and neornithine birds) implied in such a hypothesis.
— Place Figure 9.17 near here —
Several synapomorphies support placement of Iberomesornis within Ornithothoraces
(Chiappe and Calvo, 1994; Chiappe, 1995a, b, 1996a, Chapter 20 in this volume; Sanz et al.,
1995, 1996). Some of these are the presence of prominent ventral processes on the
cervicothoracic vertebrae, 11 thoracic vertebral elements, a pygostyle, the presence of a strutlike
coracoid and a sharp caudal end of the scapula, a humerus shorter than or nearly equivalent to the
ulna, and a radial shaft that is considerably thinner than that of the ulna. Although an
unquestionable ornithothoracine, Iberomesornis lacks (or fails to evidence) most
euenantiornithine synapomorphies, such as the convex lateral margin of the coracoid, the strong
lateral depressions on the centra of thoracic vertebrae, or metatarsal IV being significantly
smaller than metatarsals II and III, for example (see Appendix II in Chiappe and Calvo [1994] for
a list of the synapomorphies of this clade). Additional data may support placement of
Iberomesornis as the sister-taxon of Euenantiornitheswith this clade outside “Sauriurae” (see
Chiappe, Chapter 20 in this volume).
Of importance for establishing its phylogenetic relationships is the fact that some of the
authors placing Iberomesornis within Enantiornithes have regarded its holotype as a juvenile. For
example, Kurochkin (1995) points out that the unfused metatarsals, incomplete ossification of
the sacrum, absence of co-ossification between astragalus and tibia, and poor definition of the
articular surfaces of the humerus, femur, and tibia are suggestive of its immature status.
Nevertheless, these features can alternatively be regarded as a combination of its general poor
preservation and its more plesiomorphic condition (see Anatomy, above). The partial fusion of
the pelvic elements and the absence of neurocentral sutures in the presacral vertebral series (see
Brochu, 1996) do not support Kurochkin’s point of view.
In the original description of Concornis lacustris—the second bird from Las Hoyas—
Sanz and Buscalioni (1992) regarded this taxon as more derived than Iberomesornis. Specifically,
these authors placed Concornis as the most basal taxon of a node situated between Iberomesornis
and the neornithine birds. This preliminary description of Concornis used the available
information on several small slabs containing the specimen. After its complete preparation and
restudy, Concornis was placed within Enantiornithes (Sanz et al., 1993, 1995). This hypothesis
has been accepted by most authors (e.g., Hou et al., 1995; Kurochkin, 1995; Martin, 1995),
except for Elzanowski (1995), who regards both Concornis and Cathayornis as non-
enantiornithine birds, placing them in a more basal position within an expanded Carinatae. Like
Concornis, the recently described Eoalulavis hoyasi—Las Hoyas’ third bird—has also been
identified as an Enantiornithes (Sanz et al., 1996) (Fig. 9.17). A large number of synapomorphies
support placement of these two taxa within Enantiornithes, and in particular within
Euenantiornithes. These include the presence of strong lateral depressions and of centered costal
foveae (parapophyses) on the bodies of the dorsal vertebrae, a coracoid with convex lateral

Sanz et al. — Las Hoyas Birds — 505
margin and a supracoracoidal nerve foramen opening into a medial furrow, a laterally-excavated
furcula, a prominent and cranioventrally projected bicipital crest of the humerus, a convex
external cotyla of the ulna that is separated from the olecranon by a groove, and several others.
PALEOBIOLOGY
The birds from Las Hoyas have made a significant contribution to our current
understanding of the early evolutionary phases of avian flight. The fossil record indicates that
several evolutionary novelties essential for the acquisition of a modern flight apparatus can be
traced back to Early Cretaceous times (Chiappe, 1995a).
Three fundamental evolutionary transformations are noticeable in the birds from Las
Hoyas: a strutlike coracoid, a modern, V-shaped furcula, and a pygostyle. These features, and
presumably the functions correlated to them, are definitively absent in Archaeopteryx
(Wellnhofer, 1974, 1992, 1993; Ostrom, 1976; Hecht et al., 1985).
The elongated, strutlike coracoid of Iberomesornis, Concornis, and Eoalulavis is an
important modification from the relatively short coracoid of Archaeopteryx. While a triosseal
foramen has not been directly documented in any of the birds from Las Hoyas, the morphology of
the shoulder end of the coracoid, scapula, and furcula of Eoalulavis and Concornis strongly
supports its presence. This foramen, which in extant birds allows a pulley-system of M.
supracoracoideus (Raikow, 1985), the most important muscle in the upstroke phase of the
wingbeat cycle, was absent in Archaeopteryx. The actual function of this muscle in
Archaeopteryx is not well understood. Despite traditional views regarding this muscle as a wing
elevator (Norberg, 1989; Rayner, 1991), new data from nerve stimulation and electromyography
suggest that its main action is to rotate the humerus on its longitudinal axis (Poore et al., 1997a,
b). This action is considered essential for positioning the wing in place for the subsequent
downstroke (Poore et al., 1997a, b). The elongation of the coracoid may have increased the
efficiency of M. supracoracoideus as well as increased its area of origin on a larger
coracoclavicular membrane. The presence of a basically modern design in the birds from Las
Hoyas suggests that the mechanisms involved in the recovery stroke of these birds may have
been comparable to those of their modern counterparts.
The boomerang-shaped furcula of Archaeopteryx has been interpreted as an important
flight element (Olson and Feduccia, 1979). This may be the case, but very similar furculae are
present in cursorial, non-avian theropods (Barsbold et al., 1990; Bryant and Russell, 1993; Chure
and Madsen, 1996; Makovicky and Currie, 1996). Thus, it is conceivable that the derived (flight)
function of the furcula, or at least a more important role in this novel activity, was attained with
its transformation into a V-shaped element similar to that of Iberomesornis and the other birds
from Las Hoyas, a structure equivalent to that of extant birds. Then, as now, a V-shaped furcula
may have played a significant role in the aeration during flight of the lungs and air sacs (Bailey
and DeMont, 1991).
The presence of a pygostyle in Iberomesornis (the tail is not complete in the remaining
birds from Las Hoyas) implies the presence of a large, fleshy rectricial bulb (Parson’s nose).
Although no feather evidence has been found in Iberomesornis (contra Chatterjee, 1997), it is
reasonable to suppose that this structure was flanked by a number of tail feathers. Therefore, as
compared to Archaeopteryx, the flight capabilities of the Las Hoyas bird probably included
greater mobility of the rectrices, and thus a larger capacity for steering and braking. The long,

Sanz et al. — Las Hoyas Birds — 506
frond-shaped tail of Archaeopteryx can be better interpreted as a device increasing lift, with a
low contribution to flight maneuverability.
Our understanding of the evolution of bird flight has been greatly clarified by the concept
of “locomotor modules” (Gatesy and Dial, 1996; see also Gatesy, this volume). The anatomy of
the birds from Las Hoyas has been instrumental in clarifying the temporal pattern of locomotor
modular evolution (Fig. 9.18). Gatesy and Dial (1996) recognized three locomotor modules in
extant birds—pectoral, hindlimb and tail—derived from an ancestral theropod locomotor module
composed by the hindlimb and tail. The early evolution of flight can be viewed as a transition
involving three sequential stages (Gatesy and Dial, 1996): (1) formation of the pectoral module;
(2) decoupling of the hindlimb and tail; and (3) novel allegiance of the pectoral and tail modules
to form the flight apparatus. The similarities between Archaeopteryx and other non-avian
theropods indicate that their main locomotor module reatins the coupling of the tail and hindlimb
for running. The dimensions of the bony tail of Archaeopteryx and other skeletal features suggest
the presence of a significant caudofemoral musculature to retract the hindlimbs, the caudal
appendage counterbalancing the cranial part of the body (Gatesy, 1990; Gatesy and Dial, 1996).
This implies that its tail and hindlimb were still combined in a single unit. On the other hand, the
avian pectoral module is present in Archaeopteryx, although lacking the fine-tuning that appears
in Iberomesornis, Concornis, Eoalulavis, and other ornithothoracine birds as well as any
allegiance between this module and the tail module (Fig. 9.18). Thus, it is possible to conclude
that, from the conceptual point of view of the “locomotor module,” Archaeopteryx is not a flying
bird in the modern sense. — Place Figure 9.18 near here —
Although the impressive rate of new discoveries steadily changes our understanding of
early character evolution, the known Early Cretaceous avian record (e.g., Iberomesornis and the
other birds from Las Hoyas, Sinornis, Cathayornis) appears to indicate a correlation between the
evolution of the modern avian pectoral and tail modules. The evolution of derived wing
proportions and strutlike coracoids, along with the furcula, correlates with a shortened tail and
the presence of a pygostyle. Thus, the evidence of Iberomesornis (confirmed later by other taxa)
shows a simultaneous, more than a sequential, development of stages (2) and (3) above. Yet, this
scenario gets more complicated when considering that decoupling of tail and hindlimb modules
may not have been fully accomplished in Iberomesornis. The number of total caudal elements of
the Las Hoyas bird could be comparable to that of Archaeopteryx (20–23). Furthermore, the large
pygostyle and the presence of a primitive pelvis and synsacrum in Iberomesornis, which indicates
the absence of a hiatus in the epaxial musculature between the trunk and tail, suggest the
persistence of a significant amount of caudofemoral musculature, and consequently, a greater
participation of the tail during terrestrial locomotion.
The birds from Las Hoyas have also rendered crucial data on the early development of
non-skeletal structures correlated to the fine-tuning of avian flight. The presence of an alula in
Eoalulavis is of great significance in understanding the early steps towards the evolution of
enhanced flight capabilities (Sanz et al., 1996). This structure plays a fundamental role in modern
avian aerodynamics, allowing low-speed flights and high maneuverability (Graham, 1932;
Brown, 1963; Nachtigall and Kempf, 1971). Eoalulavis documents the oldest known alula. It also
represents the most primitive bird for which an alula is known. The alula appears to be absent in
the feathered specimens of Archaeopteryx. This suggests some sort of flight constraints, mainly

Sanz et al. — Las Hoyas Birds — 507
related to low-speed flight and maneuverability (Rayner, 1991). This interpretation is consistent
with the skeletal differences and inferred functional aptitudes pointed out above.
The discovery of the birds from Las Hoyas revealed that an advanced perching capacity,
then known only for early Tertiary birds (Feduccia, 1980), was an early avian specialization. The
pedal anatomy of Iberomesornis and Concornis hints at improved perching capabilities. These
birds have an anisodactyl foot with an opposing hallux that is proportionally longer than that of
Archaeopteryx. For example, in Iberomesornis, the hallux is almost as long as digit II, whereas in
Archaeopteryx the hallux is about half the length of digit II. More important is that the hallux of
the birds from Las Hoyas is lower than that of Archaeopteryx. As pointed out by Bock and Miller
(1959), among others (e.g., Ostrom, 1976; Sereno and Rao, 1992; Chiappe, 1995a), the size and
position of the hallux of Archaeopteryx would reduce its effectiveness as an opposable toe.
Conversely, the pedal morphology of the birds from Las Hoyas supports a significant
improvement in perching and grip effectiveness.
The birds from Las Hoyas have also provided important evidence on the feeding
specializations of early birds. Sanz et al. (1996) reported scattered organic particles preserved
within a limonitic mass in the thoracic cavity of Eoalulavis. These particles, interpreted as
stomach contents, appear to be exoskeletal elements of crustaceans. This evidence provides the
oldest direct manifestation of trophic habits in Mesozoic birds. The fact that Eoalulavis fed on
crustaceans hints at aquatic feeding habits for this particular bird, and it reinforces previous
interpretations of the Las Hoyas birds as residing in near-shore or aquatic habitats (Sanz and
Buscalioni, 1992).
In conclusion, the fossil birds from Las Hoyas have provided evidence indicating that
enhanced flight capabilities similar to those of neornithine birds were already present at the
outset of the Cretaceous. These aptitudes were probably present in basal ornithothoracines and
almost certainly in enantiornithine birds.
ACKNOWLEDGMENTS
This work was supported by Junta de Comunidades de Castilla-La Mancha, DGICYT
(Promoción General del Conocimiento, project number PB93-0284), the European Union
(Human Capital and Mobility Program, Network contract number ERBCHRXCT930164), and
grants from the Guggenheim Foundation and The Dinosaur Society to L. M. Chiappe.

Sanz et al. — Las Hoyas Birds — 508
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FIGURE 9.2. Iberomesornis romerali (LH-22), Las Hoyas, Upper Barremian
(Lower Cretaceous), Cuenca, Spain. Holotype.

FIGURE 9.3. Iberomesornis romerali (LH-22), ultraviolet induced uorescence
photograph.

FIGURE 9.4. Iberomesornis romerali
(LH-8200). Las Hoyas, Upper
Barremian (Lower Cretaceous),
Cuenca, Spain. Referred specimen;
part and counterpart of an isolated
foot.

FIGURE 9.5. Concornis lacustris (LH-2814), Las Hoyas, Upper Barremian
(Lower Cretaceous), Cuenca, Spain.

FIGURE 9.6. Eoalulavis hoyasi (LH-13500a), Las Hoyas,
Upper Barremian (Lower Cretaceous), Cuenca, Spain.
Specimen before preparation.

FIGURE 9.7. Eoalulavis hoyasi (LH-13500a). Ultraviolet
induced uorescence photograph of the specimen before
preparation.

FIGURE 9.8. Eoalulavis hoyasi (LH-13500a). Dorsal view of
the specimen after preparation.

FIGURE 9.9. Eoalulavis hoyasi (LH-13500b). Ventral view
of the specimen after preparation.

FIGURE 9.13. Concornis
lacustris (LH-2814). Detail of
the sacropelvic region.

FIGURE 9.16. Eoalulavis
hoyasi (LH-13500b). Detail
of the spear-shaped
sternum, in ventral
view.