New fossil anhingids (Late Miocene of southwestern Amazon) (1 Viewer)

[Fred Ruhe]

Edson Guilherme., Carlos D'Apolito, Fellipe Muniz, Silvia Oliveira Lomba, Leonardo Aldrin, Annie Schmaltz Hsiou , 2023

New fossil anhingids from the upper Acre River (Late Miocene of southwestern Amazon)

The Anatomical Record

First published: 01 October 2023
https://doi.org/10.1002/ar.25329

Abstract: https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.25329

Four extant species of anhingids are found worldwide, all belonging to a single genus (Anhinga). However, the fossil record reveals a much greater diversity of this group in the past. The oldest known anhingids date back to the upper Oligocene period in Australia, but during the Miocene epoch in South America, they achieved their most remarkable diversity. This study describes newly discovered anhingid fossils from the Late Miocene period in South America. These fossils were extracted from the Acre conglomerate member, part of the Upper Miocene deposits in the southwestern Amazon region. The described fossils consist of two fragments of pelvic girdles, two femora, and two vertebrae belonging to a giant anhingid (Macranhinga sp.), as well as a vertebra from Anhinga minuta, the smallest of all darters. The examination of these fossils suggests the presence of potentially three distinct anhingid taxa within the same locality. The environment in which the conglomerate deposits were formed was ecologically complex. It is likely that these three species coexisted within the same ecosystem but avoided direct competition for food and reproductive sites by not fully exploiting their fundamental niche.

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Fred

 

[Fred Ruhe]

Systematic paleontology

Suliformes Sharpe 1891
Anhingidae Reichenbach 1849

Macranhinga Noriega 1992

Macranhinga sp.

Referred material: UFAC 6990—pelvic girdle fragment and synsacrum

Identification (only for the referred material): The specimen UFAC 6990 is here assigned to the Family Anhingidae, differentiated from the Phalacrocoracidae based on the following characters (sensu Rinderknecht & Noriega, 2002; Diederle, 2015b): facies articularis cranialis of the first synsacral vertebra oval in shape; gradual reduction of the height of the crista iliaca dorsalis preacetabular in the craniocaudal direction. Among the Anhingidae, this pelvic girdle was assigned to the genus Macranhinga based on the presence of the following characters (modified from Diederle &
Agnolin, 2017). More elongated preacetabular portions of the ilium than in Anhinga anhinga; crista iliaca dorsalis preacetabular high; zygapophysis cranialis and corpus vertebrae of the preacetabular vertebrae more robust than in Anhinga anhinga; cotyloid cavity 50% larger than in Anhinga anhinga.

UFAC 5086—Anterior portion of synsacrum (Figure 1f,h).
Identification (only for the referred material): This small anterior portion of synsacrum is assigned to Macranhinga based on the presence of the following characters (sensu Diederle & Agnolin, 2017): zygapophysis cranialis and corpus vertebrae of the preacetabular vertebrae more robust than in A. anhinga; processus spinosus high.

Fred
Figure 1: Pelvic girdle and the synsacrum of Macranhinga sp. (UFAC 6990) from Patos locality (=LACM 4611). (a) Dorsal; (b) lateral; (c) cranial, and (d) ventral views. In (a), detail showing the cranial position of the vertex craniolateralis ilii. (e, f, h) Lateral view of the pelvic girdle and the synsacrum of UFAC 6990 and preacetabular portion of UFAC 5086 compared to the homologous region of A. anhinga (R-382) in (g). The black arrows indicate the region where the processus haemalis should be present in the fossils.
All scale bars = 1 cm.

 

[Fred Ruhe]

Macranhinga sp. indet. 1 (gracile)

Referred material: UFAC 6991—Left femur

Identification (only for the referred material): It differs from the femur of Phalacrocorax by having (a) a less robustly developed trochlea fibularis and (b) the region of the attachment for m. flexor hallucis longus is shallow and not a deep depression lateral and proximal to the condylus lateralis (see fig. 10 in Boles, 2010). This femur is assigned to Macranhinga by the following characters (modified from Diederle & Agnolin, 2017): total length 20% greater than that of extant and fossil Anhinga spp. with a known femur, and 13% smaller than that of the smallest Macranhinga with a known femur (e.g., M. paranensis) (for comparison see tab. 1 in Mayr et al., 2020); minimum shaft width of diaphysis with intermediate robustness between that of Anhinga spp. and Macranhinga spp. (Diederle, 2015b); distal end wide
and caudally pronounced; proximal surface of the fossa poplitea between the distal portions of the linea intermuscularis caudalis and the tuberculum m. gastrocnemialis lateralis wide and shallow; insertion for m. psoas well defined, narrow, and elongated in an anteroposterior direction (Figure 2j).

Fred


Figure 2: Left femur UFAC 6991 (a), (c) and UFAC 6993 (e), (g) attributed to Macranhinga compared to the A. anhinga counterpart (R 554 (b), (d) and R 382 (f), (h). (a), (b), (e), and (f) Dorsal views; (c), (d), (g), and (h) ventral views. (i) and (j) Muscular insertions in the femora of Macranhinga sp. indet. 1 and 2 (UFAC 6991 and 6993) and M. ranzii (UFAC 3640) compared to A. anhinga (R-554). (i) Insertion of m. flexor ischiofemoralis in A. anhinga (left) and in UFAC 6993 (right); (j) insertion of m. psoas in (left
to right): M. ranzii UFAC 3640, UFAC 6991, UFAC 6993, and R-554.
All scale bars = 1 cm.

 

[Fred Ruhe]

Macranhinga sp. indet. 2 (robust)

Referred material: UFAC 6993—Left femur (Figure 2e,g,i,j)

Identification (only for the referred material): differs from the homologous femur of Phalacrocorax by presenting (a) a slight expansion of crista trochantericus and (b) facies articularis antitrochantericus slightly bordered on its cranial side (sensu Boles, 2010). This femur is assigned to Macranhinga based on the presence of the following characters (modified from Diederle & Agnolin, 2017): femur length longer than extant Anhinga (Figure 2e,f); robust diaphysis; deep insertion of m. obturatorius medialis; remarkably wide insertion of m. iliotrochantericus caudalis; insertions of m. flexor ischiofemoralis proximodistally elongated (Figure 3i); insertion for m. psoas well defined, broad, and elongated in an anteroposterior direction (Figure 2,j previous page).

Fred

 

[Fred Ruhe]

Macranhinga sp.

Referred material: UFAC 6989—4th cervical vertebra (Figure 3a,c).

Identification: Considering the genetic proximity between darters (Anhingidae) and cormorants (Phalacrocoracidae) (Smith, 2010), this vertebra is attributed to the Anhingidae due to the following differences compared to its closest relatives (sensu Diederle et al., 2012): corpus vertebrae longer than wide; sulcus caroticus more concave and with more marked lateral crests. We assign the vertebra UFAC 6989 to the genus Macranhinga by the presence of the following diagnostic characters (modified from Diederle, 2015b): deep and well-defined sulcus caroticus; foramen of the sulcus caroticus oriented more laterally than in A. anhinga (Figure 2a,b); facies articularis cranialis wider than in A. anhinga (Figure 3a,b); vertebral body length about 25.3% larger than A. anhinga and 14.8% smaller than that of M. paranensis.

Fred


Figure 3: Fourth cervical vertebra of Macranhinga sp.— UFAC 6989 compared to the A. anhinga homologue (R-554). (a) and (b) Ventral view; (c) and (d) dorsal view; (e) and (f) fifteenth cervical vertebra of Macranhinga sp. (UFAC 6992) in comparison with the A. anhinga homologue (R-554, below). (e) Lateral view; (f) caudal view. Lp, lateral projections; VF, ventral foramina.
All scale bars = 1 cm.

 

[Fred Ruhe]

Macranhinga sp.

Referred material: UFAC 6992—Fifteenth cervical vertebra (Figure 3e,f, previous page)

Identification: Differs from Phalacrocoracidae by the following characteristics (modified from Diederle et al., 2012): processus ventralis occupies the entire corpus vertebrae and projects caudally; tuberositas ligamenti collateralis proportionally less concave. We assign UFAC 6992 to the genus Macranhinga by the following diagnostic characters (modified from Diederle & Agnolin, 2017): corpus vertebrae robust; tuberositas ligamenti collateralis deeper and broader the same morphometric dimensions as the M. paranensis counterpart (see tab. 22 in Diederle, 2015b, p. 129) but is 26.2% smaller than that of M. ranzii (see tab. 3 in Alvarenga & Guilherme, 2003) and 22.8% larger than its A. anhinga homologue (Figure 3e,f; Table 3). Although this vertebra presents diagnostic characters that allow us to assign it to the genus Macranhinga, the previously mentioned differences do not allow us to assign it to either of the two species of this genus for which the fifteenth cervical vertebra is known (e.g., M. paranensis and
M. ranzii). Similarly, to the fourth cervical vertebra discussed above, this vertebra may belong to M. fraileyi (sensu Cenizo & Agnolin, 2010) or to another species of a genus not yet described.

Fred

 

[Fred Ruhe]

Anhinga Brisson 1760

Anhinga minuta Alvarenga & Guilherme, 2003.

Referred material: UFAC 7296—19th cervical vertebra (Figure 4).

Identification (only for the referred material): 12.1% lower than that of the homologues in A. anhinga; the vertebral foramen is narrower and more rounded than in A. anhinga (Figure 4a); the ventral edge of the facies articularis cranialis is conspicuous in all its extensions (Figure 4c).

Fred


Figure 4: Nineteenth cervical vertebrae of Anhinga minuta compared to the homologue of A. anhinga (R-554, below). (a) Cranial view; (b) lateral view and (c) ventral view.
All scale bars = 1 cm.