Astronotus sp.

Carrillo-Briceño, Jorge D., Mora-Rojas, Laura, Hendricks, Kimberly, Vanegas, Andrés & Aguilera, Orangel, 2023, New clues on the palaeodiversity of the middle Miocene freshwater ichthyofauna from the Tatacoa Desert, Colombia, Geodiversitas 45 (10), pp. 327-351 : 334

cf. Astronotus sp.

( Fig. 2 H1-H4).

MATERIAL EXAMINED. — Isolated dentary bone ( VPPLT-668A )

LOCALITY. — La Victoria Fm. Tatacoita (see Fig. 1 B; Appendix 1).

DESCRIPTION

VPPLT-668A is a short and high left dentary bone, 22 mm in length and missing the posterior part of the mandibular sensory canal and the coronoid process ( Fig. 2 H1-H4). The dorsal margin is well preserved, but all teeth are missing. There are approximately six circular tooth implantation rows, with the first three from the outer border best defined ( Fig. 2 H3). Enlarged bases characterize the outer tooth row, reaching up to twice the diameter of those bases of the other inner rows. The external face of the dentary has three well-developed foramina on the bony mandibular canal. The largest one is oval in shape ( Fig. 2 H1) and corresponds with the foramen “f.5” referred by Casciotta & Arratia (1993). In the ventral section of the dentary, abundant small foramina can be observed.

REMARKS

Our comparison (based on osteological collections and literature review) suggests that VPPLT-668A is clearly different from other medium/large sizes South American cichlids such as Acaronia Myers, 1940 , Aequidens Eigenmann & Bray, 1894 , Caquetaia Fowler, 1945 , Cichla Bloch & Schneider, 1801 , Cichlasoma Swainson, 1839 , Crenicichla Heckel, 1840 , Geophagus Heckel, 1840 , Retroculus Eigenmann & Bray, 1894 , Satanoperca Günther, 1862 , Symphysodon Heckel, 1840 , and Uaru Heckel, 1840 . The dentary shape and the pattern and size of the tooth implantation rows in VPPLT-668A resemble the jaw morphology of Astronotus (see Fig. 2 I1-I2). These are features that are “apparently” observed only in this genus; although this should be confirmed in the future with more detailed studies on cranial elements of the South American cichlids. Our osteological comparisons with specimens of Astronotus were restricted to Astronotus ocellatus (Agassiz, 1831) . The genus Astronotus is represented by three extant species, Astronotus ocellatus , Astronotus crassipinnis ( Heckel, 1840) , and Astronotus mikoljii ( Pérez-Lozano et al. 2022) . The natural distribution of Astronotus includes the Amazon, Orinoco, upper Paraná, and French Guiana basins ( Pérez-Lozano et al. 2022), with habitat preference of quiet shallow waters ( van der Sleen & Albert 2018). Due to the state of preservation of VPPLT-668A, and the absence of more specimens with other diagnostic characters, we are unable to classify this fossil beyond cf. Astronotus sp. The presence of cf. Astronotus in the middle Miocene of the Honda Group represents the first fossil record for the genus.

Neotropical cichlids, with at least 44 genera, constitute the third most speciose group of freshwater fishes in South America ( van der Sleen & Albert 2018). Despite the high species richness, few studies based on comparative descriptions of cranial elements (e.g., dentaries, maxillary, and premaxillary bones) have been carried out (e.g., Casciotta & Arratia 1993). One of the problems added to the study of isolated fossil cichlid dentaries is that the morphology of dentary bone is similar among Neotropical cichlids ( Casciotta & Arratia 1993). Nevertheless, morphological features can allow some tentative assignments as long as the comparisons are supported by diversity in comparative osteological material.

Figures

FIG. 2. — Stingrays (A1-G2) and cichlids (H1-L2) from the Honda Group: A1, A2, cf. Potamotrygon sp. tooth (VPPLT 10000); B1-F, isolated dermal bucklers; B1, B2, VPPLT-1415; C, E, VPPLT-1245; D, VPPLT-1126; F, VPPLT-1239; G1, G2, isolated caudal spines (VPPLT-42) of Potamotrygonidae indet.; H1-H4, left dentary of cf. Astronotus sp. (VPPLT-668A); I1, I2, left dentary of the extant Astronotus ocellatus (Agassiz, 1831) (ANSP s/n); J1-J3, left dentary of cf. Cichla sp. (VPPLT-668B); K1-K3, left dentary of the extant Cichla Bloch & Schneider, 1801 (PIMUZ A/I 4897); L1, L2, indet. cichlid anal spine (VPPLT-1164). Views: L1, anterior; B, C-G1, H3, I2, J3, K3, dorsal; A1, labial; A2, lingual-lateral; H1, I1, J2, K1-K2, left lateral; L2, lateral; B2, profile; H4, J1, right lateral; G2, H2, ventral. Scale bars: A, 0.5 mm; B, 1 cm; C, E, I1, J, K2, 5 mm; D, H, 7 mm; F, K1, L, 6 mm; G, K3, 4 mm; I2, 3 mm.

FIG. 1. — Geographical position (A) of the Honda Group’s stratigraphic section (B) at La Venta site placed in the Upper Magdalena River Valley, Colombia. For details on the localities’ geographic coordinates and stratigraphic position, please see Appendix 2.