CLUPEIDAE Cuvier, 1817

Alvarado-Ortega, Jesús, Cuevas-García, Martha, Melgarejo-Damián, Pilar, Cantalice, Kleyton Magno, Alaniz-Galvan, Abril, Solano-Templos, Gisel & Than-Marchese, Bruno Andrés, 2015, Paleocene fishes from Palenque, Chiapas, southeastern Mexico, Palaeontologia Electronica 10 (14), pp. 1-22 : 8-9

Family CLUPEIDAE Cuvier, 1817

Genus and species indeterminate

Referred Material. IGM 4548 (Figure 4), complete specimen from the the División del Norte quarry (i.e., Locality-IGM 3869); standard length 38.5 mm. Remarks and comparison. The family Clupeidae belongs in the order Clupeiformes , a taxon that along with the order Ellimmichthyiformes constitute the teleostean cohort Clupeomorpha. Because the comprehensive analysis on extant and extinct Clupeomorpha developed by Grande (1985) has proven to be robust and predictive throughout nearly 30 years (see Alvarado-Ortega, 2014), it has been taken as a reference in the study of the División del Norte clupeomorph. From such evaluation, it was possible to recognize various diagnostic characteristics that support the inclusion of IGM 4548 within the family Clupeidae (Figure 4).

On the one hand, IGM 4548 shows the single indisputable synapomorphy of the Clupeomorpha clade, the presence of a series of abdominal scutes. This specimen also shows the presence of recessus lateralis, an intracranial space in the otic region of the skull where the supraorbital, infraorbital, preopercular, and temporal sensory canals open and which is diagnostic of the order Clupeiformes . Additionally, IGM 4548 exhibits at least two of the diagnostic features of the suborder Clupeoidei ( Grande, 1985, p. 258-259), the loss of the lateral line and the fusion of the first uroneural with the first preural centrum.

Grande (1985, figure 9) suggested that the suborder Clupeoidei is divided into three main groups or superfamilies, Clupeoidea , Engrauloidea, and Pristigasteroidea. Clupeoidea differs from the other two superfamilies and most species in the Clupeomorph basal groups (e.g., Ellimmich- FIGURE 5. Specimen IGM 4549, Phareodus sp. from the Paleocene marine strata of División del Norte quarry, Municipality of Palenque, Chiapas, Mexico. Scale bar equals 20 mm. Abbreviations: alj, articulation of lower jaw; op, opercle; pfr 1, first pectoral fin ray; psp, parasphenoid; arrows in the tail enclose the caudal principal fin rays.

thyiformes) in that it tends to develop larger abdominal areas, associated with an increase in the number of pleural ribs/number of preural vertebrae ratio (PR /PV). IGM 4548, displays 18 ribs and 37 or 38 vertebrae, i.e., it presents a PR /PV ratio of 0.48 or 0.47. And, although it overlaps with the ranges of Ellimmichthyiformes (0.37-0.56) and two suborders of Clupeiformes, Engrauloidea (0.27- 0.51) and Clupeoidea (0.49-0.74), it helps to differenciate IGM 4548 from some other clupeomorph groups with either lower or higher PR /PV ratios such as Pristigasteroidea (0.28-0.44), Denticipitoidei (0.37-0.40), Alosinae (0.50-0.63), Clupeinae (0.52-0.63), Chirocentridae (0.59), and Dusumeeriinae (0.58-0.74). Moreover, IGM 4548 shows two large rodlike poscleithra, a diagnostic character that supports its inclusion within the family Clupeidae , superfamily Clupeoidea .

Currently, GST is developing an extensive work on the description and affinities of the Paleocene clupeids of Palenque. However, two important notions can derive from the present work, 1) the fossil record of the family Clupeidae has extended further in time; prior to this paper, the oldest evidence of this family dated back to the Eocene ( Gaudant, 1991), and 2) since a number of interrelationships of the clupeid fishes is still uncertain ( Grande, 1985), the study of these Mexican fishes might provide new data to contribute to the creation of new and more comprehensive phylogenetic hypotheses of this family.