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Forster et al. — Vorona — 621
CHAPTER 12
Vorona berivotrensis, a Primitive Bird from the Late Cretaceous of Madagascar
Catherine A. Forster, Luis M. Chiappe, David W. Krause, and Scott D. Sampson
— Running head: Forster et al.—Vorona —
Forster et al. — Vorona — 622
INTRODUCTION
Vorona berivotrensis was discovered in the Upper Cretaceous (Maastrichtian) Maevarano
Formation, Mahajanga Basin, northwestern Madagascar (Rogers et al., 2000) in the austral winter
of 1995 by a joint State University of New York at Stony Brook-Université d’Antananarivo
expedition. Three specimens assigned to Vorona and previously described by Forster et al.
(1996a) were recovered from a productive quarry (site MAD 93-18) near the village of Berivotra.
This quarry has also produced a partial skeleton of the primitive bird Rahonavis ostromi (Forster
et al., 1998), teeth of the large abelisaurid theropod Majungatholus atopus, a nearly complete
skeleton and partial skull of a juvenile titanosaurid sauropod dinosaur, as well as isolated
elements of an undescribed small abelisaurid, crocodilians, fish, frogs, snakes, turtles, and at
least three additional taxa of birds (Krause et al., 1997a, 1999; Forster et al., 1996a, b; Fig. 12.1).
Interestingly, the faunal composition at site MAD 93-18 is nearly identical to that of the Late
Cretaceous El Brete site (Lecho Formation), Salta Province, Argentina, where a quarry in fluvial
sandstone produced four taxa of birds, associated titanosaurid sauropod remains, teeth of a large
theropod, and scattered elements of a small theropod (Bonaparte and Powell, 1980; Chiappe,
1993).
— Place Figure 12.1 near here —
Vorona was the first pre-Holocene avian described from Madagascar. The record of
Mesozoic birds in Gondwana is very poor, and no Jurassic birds have yet been discovered
(Chiappe, 1995, 1996b; Fig. 12.2). For the Cretaceous there is a growing number of taxa known
from South America, particularly Argentina (e.g., Walker, 1981; Chiappe, 1991, 1993; Alvarenga
and Bonaparte, 1992; Chiappe and Calvo, 1994; Novas, 1996). However, there are only three
occurrences of skeletal remains of Cretaceous birds outside of South America: two from the
Antarctic Peninsula (Chatterjee, 1989; Noriega and Tambussi, 1995; see also Hope, this volume)
and one from eastern Australia (Molnar, 1986). Several footprints from a single locality in the
Cretaceous of Morocco (Ambroggi and Lapparent, 1954; see also Lockley and Rainforth, this
volume) are the only record of Mesozoic birds from a large part of Gondwana that includes
Africa, Madagascar, the Indian subcontinent, and mainland Antarctica. Vorona thus marks the
first Mesozoic record of avian skeletal remains from this large area of the world.
— Place Figure 12.2 near here —
The extant Malagasy avifauna is striking in its low diversity (only 256 species) and high
endemism (53% of species) (Langrand 1990), which are odd characteristics in view of the high
habitat diversity on the island and the high vagility of birds relative to most other vertebrates.
Whether or not Madagascar obtained some of its modern and recently extinct avifauna prior to
separation from other major landmasses has been the subject of some considerable speculation
and controversy (Andrews, 1894; Lamberton, 1934; Rand, 1936; Darlington, 1957; Battistini,
1965; Moreau, 1966; Dorst, 1972; Mahé, 1972; Sauer, 1972; Cracraft, 1973, 1974; Feduccia,
1980; Keith, 1980; Briggs, 1995; Quammen, 1996; Chatterjee, 1997). Keith (1980:106), for
instance, posed the question in the following manner: "Are any of the birds found on Madagascar
today descendants of those that remained behind after its separation, or did all of these become
extinct, leaving Madagascar to be populated by birds that later flew in from overseas?" He
concluded that "the fossil record is so poor that unless further discoveries are made we may never
have a proper answer to this question."
The published record of fossil birds from Madagascar is indeed poor. Outside of the
avifauna recovered from the Maevarano Formation, it is restricted to the Holocene (MacPhee et
al. 1985). This, in turn, is owing in no small measure to the overwhelming predominance of
marine strata throughout the Cenozoic (Besairie, 1972). Included among extinct forms are the
FIGURE 12.1. Map showing the general location of quarry site MAD93-18 (marked
Study Area) in the Upper Cretaceous (Maastrichtian) Maevarano Formation. Inset map
shows the location of the Mahajanga Basin (in black) in northwestern Madagascar. At
least four taxa of fossil birds, including Vorona berivotrensis (described here) and
Rahonavis ostromi (Forster et al., 1998), were recovered from this site. Exact locality
information is on file in the Department of Geology, Field Museum of Natural History,
Chicago.
FIGURE 12.2. Right femur of referred specimen FMNH PA 715: A) cranial, lateral,
caudal, and medial views (left to right); B) proximal view, femoral head to the left (top),
and distal view, cranial surface facing up (bottom). Abbreviation: tc, trochanteric crest.
Scale bars = 1 cm.FIGURE 12.2. Right femur of referred specimen FMNH PA 715: A)
cranial, lateral, caudal, and medial views (left to right); B) proximal view, femoral head to
the left (top), and distal view, cranial surface facing up (bottom). Abbreviation: tc,
trochanteric crest. Scale bars = 1 cm.
Forster et al. — Vorona — 623
giant, flightless elephant-birds (Aepyornithidae), which according to some workers (e.g.,
Rothschild, 1911; Lambrecht, 1929, 1933; Sauer and Rothe, 1972; Sauer, 1976) are represented
outside of Madagascar as well (Egypt, Algeria, India, Mongolia, Canary Islands, Turkey). Others
(e.g., Feduccia, 1980, 1996; Olson, 1985; Rasmussen et al., 1987), however, are skeptical about
these records. In any case, the biogeographic origins of the Malagasy avifauna remain enigmatic,
and have previously been interpreted largely through the relationships of modern taxa. The
affinities of most species are generally regarded to be with Africa, but a few species indicate
Asian or even Australasian connections (e.g., Rand, 1936; Dorst, 1972; Cracraft, 1973; Keith,
1980). As stressed by Walker (1978:208) with regard to the origin of the Malagasy mammalian
fauna, the “one major piece of evidence missing is... fossils of Cretaceous, Paleocene or Eocene
age.” The discovery of Vorona, Rahonavis, and other taxa in the Late Cretaceous of Madagascar
provides the first pre-Late Pleistocene fossil evidence with which to address questions
concerning the biogeographic origins of the extant and recently extinct Malagasy avifauna.
Institutional abbreviations: FMNH: Field Museum of Natural History, Chicago, IL; UA:
Université d’Antananarivo, Service de Paléontologie, Antananarivo, Madagascar.
GEOLOGICAL AND PALEOGEOGRAPHIC SETTING
The Maevarano Formation is the uppermost nonmarine unit of Cretaceous age in the
Mahajanga Basin and has recently been considered Maastrichtian in age (Rogers and Hartman,
1998; Rogers at al., 2000). The Maevarano Formation is divided into three distinct members:
Masarobe, Anembalemba, and Miadana (Rogers et al., 2000). The quarry at MAD 93-18, like
most of the fossil-bearing sites in the Maevarano Formation, occurs in the Anembalamba
Member. This member averages 10-15 m in thickness and is composed of two distinctive,
alternating sandstone facies (facies 1 and facies 2). Facies 1 consists of light gray to white, fine-
to coarse-grained poorly sorted sandstone with an abundant clay matrix which displays small- to
medium-scale tabular and trough cross stratification. Facies 2 consists of a massive, fine- to
coarse-grained, poorly sorted, clay-rich sandstone that is olive green in color (Rogers et al.,
2000). Specimens of Vorona described here were recovered from both the top of a facies 1 layer
and the overlying facies 2 layer.
The importance of Vorona to the Mesozoic avian record is enhanced by its
paleogeographic location in eastern Gondwana. As discerned from a wealth of geophysical data,
the Cretaceous represents the most active period in the breakup of Gondwana. The sequence and
pattern of breakup, however, is poorly tested paleontologically. The current geophysical model
for plate tectonic evolution of the western Indian Ocean holds that Madagascar has long been an
island (summarized in Storey, 1995; Krause and Hartman, 1996; Krause et al., 1997b, 1999).
With the Indian subcontinent attached to its eastern coast, Madagascar separated from Africa in
the Late Jurassic, approximately 160-150 Ma, considerably earlier than generally regarded in
previous biogeographic scenarios involving the island's avifauna (e.g., Sauer, 1972; Cracraft,
1973; Keith, 1980). Indo-Madagascar attained its current position relative to the east coast of
Africa in the Early Cretaceous, approximately 130-125 Ma, and, according to most geophysical
reconstructions, rifted from Antarcto-Australia at about the same time. Hay et al. (1999),
however, posited a lingering connection between Indo-Madagascar and western Antarctica across
the Kerguelan Plateau that lasted well in to the Late Cretaceous, possibly as late as 80 Ma.
Separation of Madagascar from the Indian subcontinent did not occur until late in the Late
Cretaceous, at approximately 88 Ma (Storey et al. 1995). Thus, it is only since the Late
Cretaceous that Africa has been the nearest major landmass to Madagascar and it appears more
likely that the Late Cretaceous terrestrial and freshwater vertebrate fauna of Madagascar was
Forster et al. — Vorona — 624
more similar to that of the Indian subcontinent and, more distantly, with Antarctica, Australia,
and South America, than with Africa (Krause et al., 1997b, 1999; Sampson et al., 1998).
SYSTEMATIC PALEONTOLOGY
Taxonomic Hierarchy
Aves Linnaeus, 1758
Ornithothoraces Chiappe and Calvo, 1994
Vorona Forster et al., 1996a
Vorona berivotrensis Forster et al., 1996a
Holotype—UA 8651, a distal left tibiotarsus found in articulation with a complete
tarsometatarsus.
Referred specimens—FMNH PA 715, associated right tibiotarsus, fibula, and femur;
FMNH PA 717, left femur.
Locality and Horizon—Upper Cretaceous (Maastrichtian) Maevarano Fm., Mahajanga
Basin, near the village of Berivotra, northwestern Madagascar. Specimens were collected from
quarry site MAD 93-18. Locality coordinates are on file at FMNH and UA.
Diagnosis—Possesses short, blunt cnemial crest on tibiotarsus; irregular low ridge on
medial surface of proximal tibiotarsus; narrow but deep notch on proximodorsal tarsometatarsus
between metatarsals II and III; expanded vascular groove proximal to distal foramen on
tarsometatarsus.
ANATOMY
The three specimens assigned to Vorona together comprise nearly complete left and right
hindlimbs. The tibiotarsus and tarsometatarsus of UA 8651 were found in direct articulation in
the lower facies 1 level. The tibiotarsus, fibula, and femur of FMNH PA 715 were loosely
articulated in the overlying facies 2 level; the fibula was lying next to and paralleling the tibia,
and the proximal portion of the femur was lying next to the proximal tibiotarsus. The shaft and
distal portion of the femur was recovered a few centimeters south of the rest of the specimen.
At the time of its original description (Forster et al., 1996a), only a small portion of the
proximal right femur (FMNH PA 715) could be assigned with confidence to Vorona (Fig. 12.3).
Since then, additional preparation revealed contacts between this femoral fragment and the shaft
and distal right femur of a then unidentified avian. This discovery has allowed us to reconstruct
the now nearly complete right femur, and to assign another specimen from the quarry, a nearly
complete left femur (FMNH PA 717), to Vorona. Additionally, a more proximal segment of the
holotype tibiotarsus (UA 8651) was recovered during preparation of quarry material.
Measurements of all limb elements are given in Table 12.1.
— Place Figure 12.3 near here —
— Place Table 12.1 near here —
Pelvic Limb
Femur—The neck of the femur is short, robust, and weakly constricted (Figs. 12.2, 12.3).
The outline of the femoral head is nearly round in proximomedial view. The flattened
proximomedial surface of the femoral head bears a broad, shallow depression for the attachment
of the capital ligament. A fossa for the capital ligament is also present in Enantiornithes and
Ornithurae, but is absent in non-avian maniraptorans, Unenlagia (Novas and Puerta, 1997),
Archaeopteryx, and Mononykus (Perle et al., 1994). There is a distinct trochanteric crest
projecting slightly above the level of the femoral head. The lateral surface of the proximal femur
FIGURE 12.3. Left femur of referred specimen FMNH PA 717 in (left to right) cranial,
lateral, caudal, and medial views. Abbreviations: fcl, fossa for capital ligament; il,
intermuscular line; t, tubercle on lateral supracondylar ridge. Scale bar = 1 cm.
Forster et al. — Vorona — 621
TABLE 12.1
Measurements in millimeters of specimens of Vorona berivotrensis.
UA 8651 FMNH FMNH
PA 715 PA 717
femur
total length 93.7 --- 94.1
craniocaudal width trochanteric crest 10.9 --- ---
greatest diameter at mid-shaft 8.4 --- 8.1
mediolateral width distal condyles 15.3 --- 15.5
fibula
length of preserved portion --- 76.0 ---
craniocaudal length proximal end --- 9.3 ---
mediolateral width proximal end --- 3.9 ---
tibiotarsus
total length --- 165.8 ---
height astragalar ascending process 33.3 32.5 ---
mediolateral width proximal end --- 11.8 ---
craniocaudal length proximal end --- 16.0 ---
mediolateral diameter at mid-shaft 5.9 6.1 ---
craniocaudal diameter at mid-shaft 7.1 7.0 ---
mediolateral width distal condyles 12.3 12.4 ---
craniocaudal width distal condyles 11.8 12.0 ---
tarsometatarsus
total length 60.9 --- ---
mediolateral width proximal end 12.9 --- ---
dorsoplantar width proximal end 8.0 --- ---
mediolateral width at mid-shaft 9.0 --- ---
dorsoplantar depth at mid-shaft 4.2 --- ---
mediolateral width across trochleae 13.7 --- ---
MT II: total length 3.8 --- ---
mediolateral width trochlea 4.2 --- ---
dorsoplantar depth trochlea 4.7 --- ---
MT III: total length 61.0 --- ---
mediolateral width trochlea 5.6 --- ---
dorsoplantar depth trochlea 6.3 --- ---
MT IV: total length 58.4 --- ---
mediolateral width trochlea 3.9 --- ---
dorsoplantar depth trochlea 5.7 --- ---
MT V: total length 16.4 --- ---
length of tarsometatarsus/tibiotarsus
(UA 8651/FMNH PA 715) .37
Forster et al. — Vorona — 625
is slightly depressed but, unlike the condition seen in Enantiornithes, Archaeopteryx, and some
non-avian maniraptorans, it bears no evidence of a posterior trochanter.
The shaft of the femur is cranially bowed, and lacks a fourth trochanter. An
intermuscular line courses from the trochanteric crest down to the medial side of the distal femur,
crossing the cranial aspect of the femoral shaft. A caudal intermuscular line runs from the medial
condyle proximally across approximately three-fourths of the femur. A third intermuscular line
runs the length of the entire caudolateral edge of the shaft.
The distal femur is flat cranially and lacks a patellar groove. A well-developed patellar
groove is a synapomorphy of ornithurine birds (Chiappe, 1996a). On the caudal aspect, the
triangular popliteal fossa is bounded distally by an intercondylar bridge. This condition is
comparable to that of Enantiornithes, Patagopteryx, and Ornithurae. The lateral margin of the
popliteal fossa is developed into a supracondylar ridge that projects caudally beyond the level of
the medial margin, as in Enantiornithes (Chiappe and Calvo, 1994; Sanz et al., 1995; Chiappe,
1996a). Approximately 0.5 cm above the lateral condyle this ridge swells into a tubercle. This
tubercle does not occur in any known enantiornithine bird. The lateral supracondylar ridge,
along with the lateral condyle, defines the medial boundary of a weak fibular trochlea. This
trochlea, and the tibiofibular crest of the lateral condyle, appears less developed than in
neornithines.
Tibiotarsus—The tibiotarsus is long, slender, and straight (Figs. 12.4, 12.5). The shaft is
piriform in cross-section, with an evenly rounded medial surface that narrows to the lateral
margin. The tibiotarsus has a very blunt, broad, and robust cnemial crest. This single cnemial
crest is homologous to the lateral cnemial crest of neornithines (Chiappe, 1996a). A single
cnemial crest is also present in non-avian maniraptorans, Archaeopteryx, Alvarezsauridae, and
Patagopteryx, while two distinct crests are typical of Ornithurae (Chiappe, 1996a).
Iberomesornis (Sanz and Bonaparte, 1992) is specialized in having no distinct cnemial crest,
whereas Enantiornithes (Walker, 1981) have a faint, craniomedially placed crest. The proximal
articular surface of the tibiotarsus slopes slightly caudolaterally. Except for the rather bulbous,
subcircular lateral articular facet, the tilted proximal articular surface is nearly planar. The lateral
and medial articular facets are well developed and separated caudally by a broad notch; the
medial articular facet projects slightly more caudally than the lateral one. Running down the
medial surface of the proximal one-fifth of the tibiotarsus is a low, irregular ridge not found on
any other known Mesozoic bird. For most of its length, this ridge defines the cranial boundary of
an elongate rugose area, almost certainly an area of muscle attachment. The lateral surface of the
proximal one-fourth of the tibiotarsus bears a prominent fibular crest, which projects more
laterally at its distal end. A small vascular foramen pierces the shaft caudal to the distal fibular
crest, as in neornithines.
— Place Figure 12.4 near here —
The calcaneum and astragalus are firmly co-ossified, but are only partially fused to the
distal tibia. A well-defined line of contact on the caudal, medial, and lateral aspects of the tibia
delimit the edges of the proximal tarsals. Although patterns of fusion clearly have an ontogenetic
component, there nevertheless appears to be a phylogenetic signal present in the co-ossification
of the proximal tarsals, as well as their incorporation into the tibia (e.g., McGowan, 1984, 1985).
The two proximal tarsals are apparently fused to each other in some non-avian maniraptorans.
For example, in juvenile specimens of the troodontid Saurornithoides there is no sign of a
separate calcaneum, implying that fusion may have occurred early in ontogeny (Currie and Peng,
1993). These elements are also fused in the troodontid Sinornithoides (Russell and Dong, 1993).
The calcaneum and astragalus are co-ossified in all known birds except Archaeopteryx
FIGURE 12.4. Referred specimen FMNH PA 715: A) right tibiotarsus
in (left to right, on left) cranial, lateral, caudal, and medial views; and
partial right fibula in (left to right, on right) lateral and medial views; B)
articulated fibula and tibiotarsus in proximal view, cranial end facing
up; C) tibiotarsus in distal view, caudal end facing up. Abbreviations:
ap, ascending process of the astragalus; cc, cnemial crest; fc, fibular
crest; ir, irregular ridge; s, suture between tibia and proximal tarsals.
Scale bars = 1 cm.Scale bars = 1 cm.
Forster et al. — Vorona — 626
(Wellnhofer, 1992), Iberomesornis, and Alvarezsaurus (Bonaparte, 1991; Novas, 1997). In non-
avian maniraptorans, Archaeopteryx, Alvarezsauridae, and Iberomesornis, the proximal tarsals
are not co-ossified to the tibia. However, the proximal tarsals are completely fused to the tibia in
Enantiornithes, Patagopteryx, and Ornithurae (Chiappe, 1996a).
— Place Figure 12.5 near here —
The astragalus, including the ascending process, is one-fifth the length of the tibia in
Vorona, a proportion similar to that in other birds and non-avian maniraptorans. The tall,
triangular, ascending process is laterally placed and nearly fused to the tibia, although a faint
suture can still be seen around its perimeter on the cranial aspect.
Martin et al. (1980) disputed the homology of the ascending process of non-avian
theropods with that of Archaeopteryx on the basis of the lateral position of the ascending process
of the latter, and its interpretation as a non-homologous structure called the pretibial bone.
Additional embryological and paleontological data have shown the proposal of Martin et al.
(1980) to be incorrect. McGowan (1985) demonstrated that the pretibial bone is indeed a
modification of the astragalar ascending process, and pointed out the occurrence of a lateralized
ascending process in several non-avian theropods (e.g., Allosaurus), as well as in ratites and
tinamous. Additionally, the morphology and position of the ascending process of Vorona, along
with that of other recently found basal birds (e.g., Mononykus, Rahonavis), strongly supports the
hypothesis that the ascending process of non-avian theropods and birds are homologous (contra
Tarsitano and Hecht, 1980; Martin et al., 1980; Martin, 1983).
The medial condyle on the distal tibiotarsus is twice the width of the lateral one in cranial
view. This condition resembles that of Patagopteryx and Enantiornithes, but contrasts with that
of Ornithurae, where the condyles are subequal in width in cranial view. A narrow, deep
intercondylar sulcus separates the condyles on their cranial aspect. This sulcus opens proximally
into a small, deep fossa; the fossa and most of the sulcus is overhung by the median edges of
both condyles. This condition also occurs in Enantiornithes and Patagopteryx. The lateral
margin of the distal tibiotarsus (calcaneum) lacks any trace of a fibular articulation.
Fibula—The proximal end of the gracile fibula is transversely compressed with a slightly
concave medial face and a convex lateral face (Fig. 12.4A, B). Although medially concave, it
does not possess the prominent medial fossa typical of non-avian maniraptorans and other
theropods (e.g., Gallimimus, Deinonychus, Allosaurus). Distally, the fibula narrows rapidly to a
slender splint. Twenty-eight millimeters down the fibula (approximately two-thirds of the way
down the fibular crest), and just proximal to the fibular spine, is a small, laterally directed
tubercle for the insertion of M. iliofibularis. The lateral orientation of this tubercle, shared with
Mononykus and Patagopteryx, has been interpreted as an intermediate condition between the
craniolateral position of the tubercle in non-avian maniraptorans, and the caudally or
caudolaterally oriented tubercle of Ornithurae (Chiappe, 1996a).
Although incomplete distally, the fibula clearly did not reach the distal end of the
tibiotarsus as it does in Archaeopteryx, Alvarezsaurus, and non-avian maniraptorans. This
derived condition is confirmed by the lack of a fibular facet on the lateral (calcaneal) condyle of
the distal tibiotarsus.
Tarsometatarsus—The tarsometatarsus is approximately one-third the length of the
tibiotarsus (Fig. 12.6). Metatarsals (MT) II, III, IV, and V are preserved, and MT II, III, and IV
are completely fused except along the midshaft of MT III and IV distal to the proximolateral
foramen. This part of the tarsometatarsus is only partially fused. A lesser degree of fusion is
seen in the middle portion of their shafts: MT II and III are fused along their entire length
whereas a small gap between MT III and IV is present proximally. MT II-IV are completely co-
FIGURE 12.5. Left tibiotarsus of holotype UA 8651: A) cranial,
lateral, caudal, and medial views (left to right); B) cross section
at proximal broken end, lateral margin to the left (top); cross
section at break below fibular crest, lateral margin to left
(middle); distal view, caudal margin at top (bottom).
Abbreviations: fc, fibular crest; if, intercondylar fossa; vf,
vascular foramen. Scale bars = 1 cm.
Forster et al. — Vorona — 627
ossified in adults of Patagopteryx and Ornithurae, but exhibit a wide range of co-ossification
within other Mesozoic birds and non-avian maniraptorans (Chiappe, 1996a). The metatarsals are
fused only proximally in Enantiornithes (e.g., Concornis, Yungavolucris, Soroavisaurus), some
specimens of Archaeopteryx (e.g., London specimen, Solnhofen specimen), and some non-avian
theropods (e.g., Ceratosaurus, Elmisaurus, Avimimus). One enantiornithine, Avisaurus gloriae,
shows MT III and IV fused distally (Varricchio and Chiappe, 1995).
— Place Figure 12.6 near here —
The proximal portions of MT II-IV are coplanar, a primitive condition shared by non-
avian maniraptorans and basal birds such as Archaeopteryx, Rahonavis, Alvarezsauridae,
Iberomesornis, Enantiornithes, and Patagopteryx (Chiappe, 1996a). In proximal view, the
articular surface of the tarsometatarsus is kidney-shaped (concave dorsally), and the plantar
margin of the articular area is slightly elevated above the dorsal one. No free distal tarsals are
present despite the fact that the distal tibiotarsus and tarsometatarsus of UA 8651 were found in
articulation. We hypothesize that the distal tarsals are fused to the metatarsus and contribute to
the proximal articular surface. Metatarsal II is dorsoplantarly expanded and projects dorsally
with respect to MT III and IV. A deep, very narrow notch is present on the dorsal margin
between MT III and IV. Like most primitive birds (e.g., Archaeopteryx, Alvarezsauridae, most
Enantiornithes), the tarsometatarsus of Vorona lacks a hypotarsus and an intercondylar eminence.
The medial cotyla is transversely expanded and larger than the lateral one. It extends over the
expanded proximal surface of MT II and the small, restricted proximal surface of MT III. The
lateral cotyla is not well preserved but appears to have been circular and restricted to the
proximal surface of MT IV.
Metatarsal V is a very narrow, splintlike element that is sutured to the lateroplantar
margin of the proximal end of MT IV. Metatarsal V is slightly less than one-third the length of
MT IV. Metatarsal IV is not reduced to a noticeable degree relative to MT II and III, unlike the
condition seen in Enantiornithes (Chiappe, 1993). Aside from the grooves separating each
individual metatarsal, the shaft of the tarsometatarsus has a nearly flat dorsal surface. Plantarly,
however, it is strongly concave with a deep longitudinal fossa along most of the shaft. This
plantar fossa has MT III as its roof and is bounded by MT II and IV. A similar plantar fossa is
present in Patagopteryx and some Enantiornithes (e.g., Soroavisaurus), as well as in some non-
avian maniraptorans (e.g., Elmisaurus). The shaft of MT II is dorsoplantarly expanded and its
proximal plantar surface bears a blunt edge reminiscent of the ridge seen in Soroavisaurus. In
medial view, MT II is plantarly bowed, although less so than in Soroavisaurus (Chiappe, 1993).
There is no proximal, dorsolaterally placed tubercle on MT II (an Enantiornithes synapomorphy,
Chiappe, 1993). On the proximal end of MT III is a small, dorsally projecting tubercle. This
tubercle is situated at the level of a very weak muscular scar on the dorsolateral margin of the
proximal end of MT II. Most likely, these two features indicate the attachment area for M.
tibialis cranialis. Between the proximal ends of MT III and IV is a small, elongate
proximolateral foramen. This foramen also occurs in other primitive birds (e.g., Patagopteryx),
and in at least one non-avian maniraptoran (Elmisaurus).
Metatarsal II is slightly shorter than MT IV, which, in turn, is shorter than MT III.
Metatarsal III is more slender than MT II and, especially, IV proximally, but expands distally to
exceed the others in width. The dorsal surface of the distal one-third of MT III is laterally
excavated by a broad vascular groove. This groove ends in a broad distal foramen, which opens
distally between the trochleae of MT III and IV rather than onto the plantar surface. This distal
foramen is dorsally roofed by a bony bridge formed by projections of these two trochleae that fail
to fuse together. An elongate, shallow facet for the articulation of MT I is present on the medial
FIGURE 12.6. Left tarsometatarsus of holotype UA 8651: A) dorsal, lateral, palmar, and
medial views (left to right); B) proximal view, palmar margin up (top); cross section at
mid-shaft, dorsal margin up (middle); distal view, dorsal margin up. Abbreviations: df,
distal foramen; n, notch between MT III and IV; pf, proximolateral foramen; pfo, palmar
fossa; roman numerals refer to metatarsal number. Scale bar = 1 cm.
Forster et al. — Vorona — 628
surface of MT II just proximal to its trochlea. The distal location of MT I in Vorona is consistent
with the capability for perching.
The equally spaced trochleae are coplanar. The trochleae of MT II and III are square in
distal view and bear well formed ginglymi. The trochlea of MT II is significantly smaller than
that of MT III, the reverse of the condition in Enantiornithes. Proximal to each of these
trochleae, on the dorsal surface, there are small, circular fossae. Metatarsal III bears the largest
trochlea and lacks the medial plantar projection of avisaurid enantiornithines. The trochlea of
MT IV is subrectangular in distal view, with its main axis dorsoplantarly oriented. This trochlea
is non-ginglymoid, and its lateral face has a well-developed collateral fossa. No phalanges are
preserved.
PHYLOGENETIC RELATIONSHIPS
Although represented by incomplete specimens, the avian nature of Vorona berivotrensis
was clearly outlined by Forster et al. (1996a). In this initial article, a preliminary phylogenetic
placement was established for Vorona by scoring its preserved characters into the data matrix of
Sanz et al. (1995; Appendix 2) with minor modifications and additions. This analysis placed
Vorona in a trichotomy with Enantiornithes, and a clade that consists of Patagopteryx deferrariisi
plus Ornithurae (Forster et al., 1996a).
Due to the incompleteness of the known specimens, the position of Vorona within
primitive birds has proved difficult to refine. A reanalysis of Vorona among primitive birds is
presented elsewhere in this volume (Chiappe, Chapter 20 in this volume), in a new phylogenetic
analysis based on many more characters and taxa than that of Sanz et al. (1995). Importantly,
femoral characters for Vorona not available for the initial analysis were included in the
reanalysis. In this new analysis, Vorona forms a trichotomy with Patagopteryx and Ornithurae.
Although the relationship of Vorona to other basal avians is still not fully resolved, its
separation from the Enantiornithes is supported by several derived characters shared between
Vorona, Patagopteryx, and Ornithurae. These characters include the presence of a fossa for the
capital ligament in the head of the femur, the near complete fusion of metatarsals II-IV, and the
complete enclosure of the vascular distal foramen by metatarsal III and IV. The superficial
resemblance of Vorona and certain Enantiornithes (e.g., Soroavisaurus australis, Chiappe, 1993)
is shown to be plesiomorphic since these characters (e.g., bulbous medial condyle of tibiotarsus,
excavated plantar surface of the tarsometatarsus) are also present in the far more primitive bird
Confuciusornis sanctus (see Chiappe, Chapter 20 in this volume).
The hypothesis that Vorona lies outside Enantiornithes as a basal member of the
Ornithuromorpha (see Chiappe, Chapter 20 in this volume) reminds us that the phylogenetic
diversity of Mesozoic Gondwanan avifaunas is likely far greater than that sampled thus far. Of
particular note is the consistent phylogenetic proximity of Vorona and Patagopteryx, another
non-enantiornithine basal bird from Gondwana, in both cladistic analyses (Forster et al., 1996a;
Chiappe, Chapter 20 in this volume). Nevertheless, characters supporting a sister-taxon
relationship between Vorona and Patagopteryx have not been found yet, although future findings
may support such a relationship. Clearly, whatever the outcome, more complete material of
Vorona is necessary for a full understanding of its phylogenetic relationships.
PALEOBIOGEOGRAPHY
The discovery of Vorona demonstrates conclusively that birds were present on
Madagascar during the Late Cretaceous. This occurrence represents a significant geographic
range extension for Gondwanan birds since the only previous Late Cretaceous records of avian
Forster et al. — Vorona — 629
skeletal material are known from the western part of Gondwana (Argentina and the Antarctic
Peninsula) and from eastern Australia. The virtual absence of Mesozoic birds from other
landmasses surrounding the western Indian Ocean, coupled with our incomplete knowledge of
morphology for Vorona (and thus its unresolved phylogenetic placement) precludes the
derivation of a strong biogeographic signal from this new record.
The current biogeographic significance of Vorona, however, derives, in large part, from
what it is not. It is not a sister-taxon to, or a basal representative of, any of the modern or
recently extinct groups of Malagasy birds (including the Aepyornithidae), all of which belong
within Neornithes. The occurrence of Vorona, as well as that of the other four non-neornithine
birds from quarry MAD93-18, hardly constitute strong and persuasive evidence that the ancestors
of modern and recently extinct groups were not present on Madagascar in the Late Cretaceous. It
is, nevertheless, the only fossil evidence currently available that bears directly on the question.
Speculation that ancestors of these groups might have been isolated on Madagascar prior to the
island’s separation from Africa is not supported by any fossil evidence.
ACKNOWLEDGMENTS
None of this work could have been accomplished without the effort and endurance of the
1995 Madagascar field crew: R. Asher, G. Buckley, Prosper, L. Rahantarisoa, L.
Randriamiarimanana, A. Rabarison, F. Ravoavy, and C. Wall. We also thank B.
Rakotosamimanana, B. Andriamihaja, the staff of the Institute for the Conservation of Tropical
Environments, P. Wright, and S. Goodman for crucial logistical help in Madagascar. We
especially thank R. Fox for an early review of this work, and L. M. Witmer for a later review.
The specimens were prepared by V. Heisey and photographed by M. Stewart; L. Betti-Nash
drafted all the figures. We also thank the Field Museum of Natural History, Chicago, for
additional preparation and specimen assistance. This work was supported by National Science
Foundation grants EAR-9418816 and EAR-9706302 and The Dinosaur Society.
Forster et al. — Vorona — 630
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